PSZ 19:16 (Pind. 1/97)
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS
JUDUL :
POLYETHYLENE OXIDE-MCM-41 AND POLYANILINE-MCM-41
NANOCOMPOSITES: PHYSICOCHEMICAL AND CONDUCTING
PROPERTIES.
SESI PENGAJIAN :
Saya :
2004/ 2005
NORIZAH BINTI ABDUL RAHMAN
(HURUF BESAR)
mengaku membenarkan tesis ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat
kegunaan seperti berikut :
1.
Hakmilik tesis adalah dibawah nama penulis melainkan penulisan sebagai projek bersama dan dibiayai
oleh UTM, hakmiliknya adalah kepunyaan UTM.
Naskah salinan di dalam bentuk kertas atau mikro hanya boleh dibuat dengan kebenaran bertulis daripada
penulis.
Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja.
Tesis hanya boleh diterbitkan dengan kebenaran penulis. Bayaran royalti adalah mengikut kadar yang
dipersetujui kelak.
*Saya membenarkan/tidak membenarkan perpustakaan membuat salinan tesis ini sebagai bahan
pertukaran antara institusi pengajian tinggi
** Sila tandakan (9)
2.
3.
4.
5.
6.
9
SULIT
(Mengandungi maklumat yang berdarjah keselamatan atau
kepentingan Malaysia seperti yang termaktub di dalam AKTA
RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan oleh
organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh
(TANDATANGAN PENULIS)
Alamat tetap : KG. TELOK BAKONG, SEROM,
SG. MATI, 84410
MUAR, JOHOR
Tarikh :
22 SEPTEMBER 2005
(TANDATANGAN PENYELIA)
PROF. MADYA. DR. SALASIAH ENDUD
(NAMA PENYELIA)
Tarikh :
22 SEPTEMBER 2005
Catatan : * Potong yang tidak berkenaan
** Jika Tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/
organisasi berkenaan dengan menyatakan sekali tempih tesis ini perlu dikelaskan sebagai
SULIT atau TERHAD
“I/we* hereby declare that I/we* have read this thesis and in my/our* opinion this
thesis is sufficient in term of scope and quality for the award of degree of
Master of Science (Chemistry)”
Signature
:
Name of Supervisor I : Assoc. Prof. Dr. Salasiah Endud
Date
:
Signature
:
22 September 2005
Name of Supervisor II: Dr. Hadi Nur
Date
* Delete as necessary.
: 22 September 2005
BAHAGIAN A - Pengesahan Kerjasama*
Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui
kerjasama antara dengan _____
Disahkan oleh:
Tandatangan :
Nama
:
Jawatan
(Cop rasmi)
:
Tarikh :
* Jika penyediaan tesis/ projek melibakan kerjasama.
BAHAGIAN B - Untuk Kegunaan Pejabat Sekolah Pengajian Siswazah
Tesis ini telah diperiksa dan diakui oleh:
Nama dan Alamat
Pemeriksa Luar
Nama dan Alamat
Pemeriksa Dalam I
:
Prof. Madya Dr. Abdul Halim Abdullah
Chemistry Department
Faculty of Science
Universiti Putra Malaysia
43400 UPM, Serdang
Selangor Darul Ehsan
: Dr. Zaiton Binti Majid
Fakulti Sains UTM,
Skudai
Pemeriksa Dalam 11
:
Nama Penyelia lain
(jika ada)
:
Disahkan oleh Penolong Pendaftar di Sekolah Pengajian Siswazah:
Tandatangan :
Nama
: GANESAN A/L ANDIMUTHU
Tarikh :
POLYETHYLENE OXIDE-MCM-41 AND POLYANILINE-MCM-41
NANOCOMPOSITES: PHYSICOCHEMICAL AND
CONDUCTING PROPERTIES
NORIZAH BINTI ABDUL RAHMAN
A thesis submitted in fulfilment
of the requirements for the award of the degree of
Master of Science (Chemistry)
Faculty of Science
Universiti Teknologi Malaysia
AUGUST 2005
I declare that this thesis entitled “Polyethylene Oxide-MCM-41 and PolyanilineMCM-41 Nanocomposites: Physicochemical and Conducting Properties” is the
result of my own research work except as cited in references. The thesis has not
been accepted for any degree and is not concurrently submitted in candidature of any
other degree.
Signature
:
Name
: Norizah binti Abdul Rahman
Date
:
22 September 2005
Dedicated to my beloved mother, family and…especially for my fiancé
ACKNOWLEDGEMENTS
First of all, in humble way I wish to give all the Praise to Allah, the Almighty
God for with His mercy has given me the strength, blessing and time to complete this
work.
I am deeply indebted to Assoc. Prof. Dr. Salasiah Endud and Dr. Hadi Nur,
my supervisors, for their patience, supervision, encouragement and thoughtful
guidance towards the completion of this thesis.
I wish to express special
appreciation to Prof. Dr. Halimaton Hamdan and Zeolite and Porous Material Group
members (ZPMG) for their help, support, interest and valuable hints. I am also
profoundly grateful to Prof. Dr. Kuramoto Noriyuki at Yamagata University, Japan
for his generous hospitality during my stay for 4 months at his laboratory and Assoc.
Prof. Dr. Madzlan Aziz for the use of the Impedance Analyzer for the conductivity
study.
I am particularly grateful to Universiti Putra Malaysia, especially to Prof. Dr.
Anuar Kassim and his research group, Ibnu Sina Institute for Fundamental Science
Studies, Department of Chemistry, Faculty of Science, Universiti Teknologi
Malaysia and Majlis Amanah Rakyat (MARA) for all facilities, study leave and
financial support.
Last but not list, I would like to acknowledge to my beloved mother, Mrs.
Zaharah Abdullah and my family, whose patience and love enabled me to complete
this research. And especially grateful to someone who is very supportive and caring
to me, my fiancé Habil Akram Rosland, thank you so much.
ABSTRACT
One of the exciting developments in material science today is the design and
synthesis of polymer nanocomposites (PNC) containing electrically-conductive
polymer and mesoporous MCM-41 that possess novel properties not exhibited by the
individual organic and inorganic materials. T he physicochemical and conducting
properties of two types of PNC namely, PEO/Li-MCM-41 and PANI/MCM-41
prepared by melt and solution intercalation and in situ polymerisation methods have
been investigated in this thesis. The aim was to obtain a more detailed
understanding of how the combination of polymers with the mesoporous
MCM-41 is related to the conducting properties of the PNC. Before PEO and
PANI are combined with MCM-41, several modifications of MCM-41 have been
done including ion exchange of MCM-41 with lithium chloride, silylation of MCM41 with trimethylchlorosilane (TMCS) and functionalization of MCM-41 with
sulfonic acid. The PNC obtained was characterized by X-ray diffraction (XRD),
infrared (IR) spectroscopy, thermogravimetric analysis and chemical analysis,
followed by 27Al, 7Li and 13C/CP MAS NMR spectroscopy. It is confirmed that the
structure of MCM-41 remains intact after combining with the polymers. The results
from the conductivity study have proven that the PNC possesses electrical properties.
It is revealed that the conductivity of PANI/MCM-41 is very much higher than
PEO/Li-MCM-41 since PANI is a conducting polymer whereas PEO is a polymer
electrolyte. The combination of PEO and MCM-41 was expected to increase
the conductivity of PEO/Li-MCM-41 by intercalation of PEO inside the pores
of MCM-41. However, it is demonstrated that unmodified Li-MCM-41 exhibits
conductivity in the same order of magnitude as the PEO/Li-MCM-41. The NMR
results suggested that the interfacial interactions occurring between the PEO and
Li-Al-MCM-41 is insufficient to improve the conductivity of the PEO/Li-MCM-41
nanocomposite. On the other hand, PANI/MCM-41 nanocomposite shows an
increase in thermal stability of conductivity compared to PANI, although its
conductivity was lower in the presence of MCM-41.
ABSTRAK
Antara pembangunan yang menarik dalam bidang sains bahan masa kini ialah
rekabentuk dan sintesis nanokomposit polimer (PNC) yang mengandungi polimer
mengkonduksi elektrik dan bahan mesoliang MCM-41 yang mempunyai sifat khas
yang tidak dapat dimiliki bahan asal organik dan tak organik secara individu. Sifat
fizikokimia dan kekonduksian bagi dua jenis PNC seperti PEO/Li-MCM-41 dan
PANI/MCM-41 yang telah disintesis menggunakan teknik interkalasi leburan dan
larutan serta pempolimeran in situ telah dikaji dalam tesis ini. Matlamat kajian ini
adalah untuk memahami secara mendalam kombinasi antara polimer dan bahan
mesoliang MCM-41 dan hubungannya dengan sifat kekonduksian. Sebelum PEO
dan PANI digabungkan dengan MCM-41, beberapa modifikasi telah dilakukan
terhadap MCM-41 seperti penukaran ion dengan litium klorida, sililasi dengan
trimetilklorosilana (TMCS) dan pemfungsian dengan asid sulfonik. PNC telah
dicirikan dengan menggunakan pembelauan sinar-X (XRD), spektroskopi inframerah
(IR), analisis termogravimetri dan analisis kimia, diikuti dengan spektroskopi 27Al,
7
Li dan 13C/CP MAS NMR. Struktur MCM-41 telah dipastikan tidak mengalami
perubahan selepas bergabung dengan polimer tersebut. Kajian kekonduksian telah
menunjukkan bahawa PNC memiliki sifat kekonduksian elektrik. Kekonduksian
PANI/MCM-41 adalah jauh lebih tinggi berbanding PEO/MCM-41 disebabkan
PANI adalah polimer mengkonduksi manakala PEO adalah polimer elektrolit.
Kombinasi PEO dan MCM-41 secara interkalasi PEO di dalam liang MCM-41
dijangkakan dapat meningkatkan kekonduksian nanokomposit polimer PEO/LiMCM-41. Sebaliknya, dalam kajian ini Li-MCM-41 tanpa diubahsuai menunjukkan
kekonduksian yang sama seperti PEO/Li-MCM-41. Data NMR menunjukkan
interaksi permukaan berlaku di antara PEO dan Li-MCM-41 tetapi ianya tidak
mencukupi untuk meningkatkan kekonduksian PEO/Li-MCM-41. Selain daripada
itu, nanokomposit PANI/MCM-41 menunjukkan kestabilan terma kekonduksian
yang meningkat berbanding PANI, begitu pun, kekonduksiannya menjadi lebih
rendah dengan kehadiran MCM-41.
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
TABLE OF CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF SYMBOLS
xvi
LIST OF APPENDICES
xvii
GENERAL INTRODUCTION
1.1
Research Background
1
1.2
Research Objectives
2
1.3
Scope of Thesis
3
PEO/MCM-41 NANOCOMPOSITES
2.1
PEO/MCM-41 Nanocomposites
5
2.2
Synthesis of PEO/MCM-41 Nanocomposites
6
2.3
Mesoporous Silica Materials MCM-41
7
2.4
Polyethylene Oxide (PEO)
8
2.5
Experimental
9
2.5.1
Synthesis of Si-MCM-41 and Al-MCM-41
9
2.5.2
Transformation of Mesoporous
11
Si-MCM-41 to Nonporous Silica
2.5.3 Synthesis of PEO/Li-Si-MCM-41 and
11
PEO/Li-Al-MCM-41 Nanocomposites by
Melt Intercalation Technique
2.5.4 Synthesis of PEO/Li-Si-MCM-41
12
Nanocomposites by Solution Intercalation
Technique
2.5.5
Synthesis of PEO/Li-TMCS/Si-MCM-41
12
Nanocomposites by Solution Intercalation
Technique
2.6
Characterization Techniques
13
2.6.1
14
Fourier Transform Infrared Spectroscopy
(FTIR)
2.6.2 X-ray Diffraction (XRD)
15
2.6.3
16
Solid State MAS NMR Spectroscopy
2.6.4 Thermogravimetric Analysis (TGA)
17
2.6.5 Atomic Absorption Spectroscopy (AAS)
19
2.6.6 Nitrogen Physisorption Measurement
20
2.6.7 Field Emission Scanning Electron
21
Microscopy (FESEM)
2.7
2.6.8 Conductivity Measurement
22
Results and Discussion
25
2.7.1
25
PEO/Li-Si-MCM-41 and
PEO/Li-Al-MCM-41 Nanocomposites
Prepared Through Melt Intercalation
Technique.
2.7.1.1 Parent Materials Si-MCM-41 and
25
Al-MCM-41
2.7.1.2 Li-Si-MCM-41 and Li-Al-MCM-41
28
2.7.1.3 PEO/Li-Si-MCM-41 and
30
PEO/Li-Al-MCM-41 Nanocomposites
2.7.1.4 Interfacial Interaction of
32
PEO/Li-Al-MCM-41
Nanocomposites: 27Al, 7Li and
13
C/CP MAS NMR Study
2.7.1.5 Ionic Conductivity of
41
PEO/Li-MCM-41 Nanocomposites
2.7.2
i) Effect of PEO Loading
41
ii) Effect of Aluminium Loading
41
PEO/Li-Si-MCM-41 Nanocomposites
43
Prepared by Solution Intercalation
Technique
2.7.2.1 Conductivity of PEO/Li-Si-MCM-41
48
Nanocomposites
2.7.3 PEO/Li-TMCS/Si-MCM-41
48
Nanocomposites Prepared by Solution
Intercalation Technique
2.7.3.1 Surface Silylation of Si-MCM-41
50
with TMCS, TMCS/Si-MCM-41
2.7.3.2 PEO/Li-TMCS/Si-MCM-41
54
Nanocomposites
2.7.3.3 Conductivity of
59
PEO/Li-TMCS/Si-MCM-41
Nanocomposites
2.8
3
Conclusion
59
PANI/MCM-41 NANOCOMPOSITES
3.1
Introduction
61
3.2
Polyaniline (PANI)
62
3.3
Polyaniline Nanocomposites
62
3.4
Characterization Techniques
64
3.4.1
UV/Vis Spectroscopy
64
3.4.2
Four Point Probe for Conductivity
65
Measurement
3.5
Experimental
67
3.5.1
67
Synthesis of PANI.DS/Si-MCM-41
Nanocomposites
3.5.2
Synthesis of PANI/Si-MCM-41-SO3H
68
Nanocomposites
3.6
Results and Discussion
69
3.6.1
PANI.DS/Si-MCM-41 Nanocomposites
69
3.6.1.1 Conductivity of PANI.DS/
74
Si-MCM-41 Nanocomposites
3.6.2
PANI/Si-MCM-41-SO3H Nanocomposites
76
3.6.2.1 Functionalization of
76
Si-MCM-41 with Sulfonic Acid
3.6.2.2 Physical Properties of PANI.DS
78
and PANI/Si-MCM-41SO3H
Nanocomposites
3.6.2.3 Conductivity of PANI.DS and
83
PANI/Si-MCM-41SO3H
Nanocomposites
3.7
4
Conclusion
CONCLUDING REMARKS
REFERENCES
85
86
88
APPENDICES
Appendices A - B
96 - 97
LIST OF TABLES
TABLE NO.
2.1
TITLE
Molar composition of SiO2 and Al2O3 for synthesis of
PAGE
10
Al-MCM-41.
2.2
The main band stretching of Si-MCM-41.
14
2.3
IUPAC classification of pores.
21
2.4
Conductivity series of Li-Si-MCM-41 and Li-Al-MCM-41
42
and PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41
nanocomposites with SiO2/Al2O3 ratios 10, 60 and 100.
2.5
Conductivity of PEO/Li-Si-MCM-41 and
49
PEO/Li-Al-MCM-41 nanocomposites obtained by melt
intercalation technique and PEO/Li-Si-MCM-41
nanocomposites obtained by solution intercalation
technique.
2.6
Conductivity of melt intercalation of PEO/Li-Si-MCM-41
60
and PEO/Li-Al-MCM-41, solution intercalation of
PEO/Li-Si-MCM-41 and solution intercalation of PEO/LiTMCS/Si-MCM-41 nanocomposites.
3.1
Composition of PANI.DS/Si-MCM-41 nanocomposites.
67
3.2
Composition of PANI.DS and PANI/Si-MCM-41-SO3H.
68
LIST OF FIGURES
FIGURE NO.
2.1
TITLE
Two possible structures of polymer/MCM-41
PAGE
7
nanocomposites.
2.2
Structure of polyethylene oxide.
9
2.3
Derivation of Bragg’s Law for X-ray diffraction.
16
2.4
Schematic representation of a thermobalance.
18
2.5
Schematic arrangement of an atomic absorption
20
spectroscopy.
2.6
(a) Schematic representation of a polymer
24
electrolyte/blocking electrode cell. Rb = electrolyte
resistance; Cb=electrolyte Capacitance; Ce = electrode
capacitance. Typically Rb = 102-108 S/cm. (b) Simulated
complex impedance plot for circuit (a).
2.7
IR spectra of Si-MCM-41 and Al-MCM-41 with SiO2/Al2O3 = 10, 60 and
26
100.
2.8
XRD patterns of calcined Si-MCM-41 and Al-MCM-41
27
with SiO2/Al2O3 = 10, 60 and 100.
2.9
XRD patterns of Si-MCM-41 (a) and Al-MCM-41 ion
29
exchanged with LiCl 1 M [(b) – (d) for SiO2/Al2O3 =
10, 60 and 100, respectively].
2.10
Concentration Li+ ions (ppm) in Li-Si-MCM-41 and Li-
30
Al-MCM-41 (SiO2/Al2O3 = 10, 60, and 100) after ion
exchange with LiCl solution (1 M).
2.11
IR spectra of PEO and (a) PEO/Li-Si-MCM-41 and (b)
– (d) PEO/Li-Al-MCM-41 nanocomposites with
SiO2/Al2O3 = 10, 60 and 100, respectively.
31
2.12
XRD patterns of (a) PEO/Li-Si-MCM-41 and (b) – (d) PEO/Li-Al-MCM-41
33
nanocomposites with SiO2/Al2O3 = 10, 60 and 100, respectively.
2.13
27
2.14
13
2.15
13
Al MAS NMR of PEO/Li-Al-MCM-41 with various
34
SiO2/Al2O3 ratios.
C/CP MAS NMR of PEO and PEO/Li-Al-MCM-41
36
with various SiO2/Al2O3 ratios.
C/CP MAS NMR (a) PEO/Li-Si-MCM-41 (b) PEO/Li-Si-MCM-41 with
37
non-porous structure.
2.16
7
Li MAS NMR of Li-Al-MCM-41 (SiO2/Al2O3 = 10) and
39
PEO/Li-Al-MCM-41 with various SiO2/Al2O3 ratios.
2.17
Proposed intermolecular interactions of polyethylene
40
oxide (PEO) segments with Li-Al-MCM-41 surface
groups. The dashed lines indicate possible hydrogenbond donating (MCM-41)/hydrogen-bond accepting and
Al-Li-O interaction sites. The degree of the electrostatic
interaction of (c) and (b) is larger than (a).
2.18
Mean of conductivity of PEO/Li-Si-MCM-41 and
42
PEO/Li-Al-MCM-41 with SiO2/Al2O3 =10, 60 and 100
divided with concentration of Li+ ions.
2.19
IR spectra of (a) PEO and (b) – (e) PEO/Li-Si-MCM-41
45
nanocomposites with various weight percentages of PEO
(0, 5, 10 and 40 wt%, respectively).
2.20
XRD patterns of PEO/Li-Si-MCM-41 nanocomposites
46
with various weight percentages of PEO [(a) – (f) for 0,
2, 5, 8, 10 and 40 wt%, respectively].
2.21
TGA thermograms of PEO/Li-Si-MCM-41
47
nanocomposites for (a) 10 and (b) 40 wt% PEO.
2.22
IR spectra of functionalized Si-MCM-41 with TMCS
51
(TMCS/Si-MCM-41) and Si-MCM-41.
2.23
XRD patterns of Si-MCM-41 and Si-MCM-41
52
functionalized with TMCS (TMCS/Si-MCM-41).
2.24
13
2.25
TGA thermograms of Si-MCM-41 and
C/CP MAS NMR spectrum of TMCS/Si-MCM-41.
TMCS/Si-MCM-41.
53
53
2.26
IR spectra of (a) pure PEO and (b) – (e) PEO/Li-
55
TMCS/Si-MCM-41 nanocomposites with various weight
percentages of PEO 0, 5, 10 and 40 wt%, respectively.
2.27
Surface morphology of (a) Si-MCM-41 and (b) PEO/Li-
56
TMCS/Si-MCM-41 with 40 wt% of PEO.
2.28
XRD patterns of PEO/Li-TMCS/Si-MCM-41
57
nanocomposites with various weight percentages of PEO
[(a) – (f) for 0, 2, 5, 8, 10 and 40 wt%, respectively].
2.29
TGA profiles of PEO/Li-TMCS/Si-MCM-41
58
nanocomposites with 0, 10 and 40 wt% PEO measured in
nitrogen.
3.1
Structure of oxidation state and acid base behaviour of
63
polyanilines.
3.2
Four point probe measurement technique.
66
3.3
IR spectra of PANI.DS and PANI.DS/Si-MCM-41
70
nanocomposites with Si-MCM-41/aniline.HCl ratios of
50, 77 and 100 wt%.
3.4
X-ray diffraction patterns of the PANI.DS/Si-MCM-41
71
nanocomposites with Si-MCM-41/aniline.HCl ratios of
50, 77 and 100 wt%.
3.5
UV/Vis absorption spectra of PANI.DS and
72
PANI.DS/MCM-41 nanocomposites with Si-MCM41/aniline.HCl ratios of 50, 77 and 100 wt%.
3.6
TGA thermograms of PANI.DS and PANI.DS/MCM-41
73
nanocomposites with Si-MCM-41/aniline.HCl ratios of
50, 77 and 100 wt%.
3.7
Conductivity of the PANI.DS/Si-MCM-41
75
nanocomposites at room temperature.
3.8
Conductivity of PANI.DS and PANI.DS/Si-MCM-41
75
nanocomposites with Si-MCM-41/aniline.HCl ratios of
50, 77 and 100 wt% at 100oC.
3.9
Conductivity of PANI.DS and PANI.DS/Si-MCM-41
nanocomposites with Si-MCM-41/aniline.HCl ratio of 50
76
wt% at 150oC.
3.10
IR spectrum of Si-MCM-41 functionalized sulfonic acid,
77
Si-MCM-41-SO3H.
3.11
13
C/CP MAS NMR spectra of Si-MCM-41 functionalized
77
sulfonic acid, Si-MCM-41-SO3H.
3.12
The proposed structure of Si-MCM-41 functionalized
79
sulfonic acid, Si-MCM-41-SO3H.
3.13
TGA profiles of Si-MCM-41 and Si-MCM-41-SO3H.
79
3.14
IR spectra of Si-MCM-41-SO3H, PS = PANI.DS, PMS =
80
PANI/Si-MCM-41-SO3H.
3.15
TGA thermograms of Si-MCM-41-SO3H, PS = PANI.DS
80
and PMS = PANI/Si-MCM-41-SO3H.
3.16
UV/Vis spectra of PANI.DS and PANI/Si-MCM-41-
81
SO3H nanocomposite.
3.17
13
C CP/MAS spectra of (a) Si-MCM-41-SO3H (b)
82
PANI/Si-MCM-41-SO3H.
3.18
The propose interaction between polyaniline and Si-
83
MCM-41-SO3H in PANI/Si-MCM-41-SO3H
nanocomposite.
3.19
The conductivity of PANI.DS and PANI/Si-MCM-41SO3H nanocomposite at 100, 150 and 200oC versus time.
84
LIST OF SYMBOLS
2θ
-
Bragg Angle
BET
-
Brunnauer, Emmett and Teller
Cu Kα
-
X-ray diffraction from Copper K energy levels
FTIR
-
Fourier Transform Infrared Spectroscopy
KBr
-
Potassium Bromide
LiCl
-
Lithium Chloride
MAS NMR
-
Magic-Angle-Spinning Nuclear Magnetic Resonance
MPTS
-
Mercaptopropyltrimethoxysilane
nm
-
Nanometer
PANI
-
Polyaniline
PANI.DS
-
Polyaniline Doped Dodecylsulfonic Acid
PANI.HCl
-
Polyaniline Doped Hydrochloric Acid
PEO
-
Polyethylene Oxide
PMS
-
PANI/Si-MCM-41SO3H Nanocomposites
PNC
-
Polymer Nanocomposites
PS
-
PANI.DS
SDS
-
Sodium Dodecylsulfate
SiO2/Al2O3
-
Silica to Alumina Ratio
TGA
-
Thermogravimetric Analysis
TMCS
-
Trimethylchlorosilane
UV/Vis
-
Ultraviolet/Visible
XRD
-
X-ray Diffraction
LIST OF APPENDICES
APPENDIX
A
TITLE
Estimation of PEO used in PEO/Li-Si-MCM-41 and
PAGE
96
PEO/Li-TMCS/Si-MCM-41 nanocomposites.
B
An example of the complex impedance plot for
measurement of conductivity of Li-Al-MCM-41 with
SiO2/Al2O3 = 60.
97
1
CHAPTER 1
GENERAL INTRODUCTION
1.1
Research Background
Composites are generally defined as materials which are made by physically
combining two or more existing materials to produce a multiphase system. The
phase of the composites formed might differ from the starting material, depending on
chemical interaction occurred [1]. There are many types of composites such as
conventional
microcomposites
and
nanocomposites.
Nanocomposites
are
composites in which the components are combined in at least one dimension either
the length, width or thickness in the size ranges 1-100 nm. Differing from the
conventional microcomposite, nanocomposite is combination of two phases in which
one of the materials has at least one dimension in the nanometer range (10-9 m) and
gives possibility to synthesize nanostructured materials showing improved chemical
and physical properties which are not exhibited as individual properties.
Recently, polymer-inorganic nanocomposite received wide attention in the
field of materials science both in industrial and academia [2,3]. The most interesting
is to synthesize intercalated polymers in inorganic materials such as layered silicates,
mesoporous materials and zeolites. Two major findings have stimulated the revival
of interest in these materials; first, the report from Toyota research group of a Nylon6/montmorillonite (MMT), for which very small amounts of layered silicate loading
resulted in pronounced improvements of thermal and mechanical properties [2]; and
second the observation from Vaia et al., that it is possible to melt-mix polymer with
2
layered silicates without use of organic solvent [3].
Today, efforts are being
conducted globally, using almost all types of polymer matrices.
In general, organic polymer and inorganic materials have contrasting
properties.
Organic polymers are hydrophobic, flexible, tough, and are easy to
process, but they can also relatively easily damaged either chemically or
mechanically. In contrast, the inorganic materials are mostly hydrophilic, typically
much harder and have good chemical stability but are also brittle and difficult to
process. Many properties including strength, conductivity and chemical stability are
dramatically improved after combining the polymer with inorganic materials [1,2,3].
These examples clearly illustrate some of the characteristic of polymer-inorganic
nanocomposites.
There are many approaches that have been used by researchers to synthesize
intercalated polymer-inorganic composites.
The most important aspect in the
preparation of these composites is to increase the interaction between polymer and
inorganic materials. Different techniques have been used to synthesize intercalated
polymer-inorganic composites such as melt intercalation technique, solution
intercalation technique and in situ polymerization [2]. Besides that, in order to
prepare homogeneous and intercalated composites of organic polymer and inorganic
materials, many researchers have attempted to change chemical properties of these
materials in order to increase similarity between them. For example, hydrophobicity
of inorganic materials has been increased in order to make organic polymers easier to
intercalate in the inorganic materials.
1.2
Research Objectives
In this thesis we wish to investigate the physicochemical properties of
electrically-conductive polymer-mesoporous MCM-41 nanocomposite.
MCM-41
was chosen as the inorganic host because of its extremely high surface area which is
more than 1000 m2/g and large pore size with the diameter between 15 and 100 Å.
3
Polyethylene oxide (PEO), an electrolyte polymer and polyaniline (PANI), a
conducting polymer have been used as source of polymers.
In this study, polymer-mesoporous material nanocomposite is synthesized by
means of intercalation techniques. It is important to note that there are two possible
structures of nanocomposites which consist of intercalated nanocomposites and
conventional nanocomposites. Polymer chain is intercalated in the pores of MCM41 in intercalated nanocomposites, meanwhile, the polymers are located on the
external surface of MCM-41 in conventional nanocomposites.
For a maximum
interfacial interaction between polymer and mesoporous MCM-41, conventional
nanocomposites should be minimized.
One expects that increase interfacial
interaction efficiency can increase the conductivity properties of the nanocomposite.
However before this objective can be achieved, basic knowledge about that structureproperty of the nanocomposite is required. Only with this knowledge, polymerMCM-41 can be designed in order to obtain products with the desired properties.
This defines the objective of the present investigations:
“The primary aim of this investigation is to obtain a more detailed
understanding of how the combination of polymers with mesoporous MCM-41
is related to the conducting properties.”
1.3
Scope of Thesis
This thesis deals with the study of structure-conducting properties of the
combination of polyethylene oxide (PEO) and polyaniline (PANI) with mesoporous
MCM-41 prepared by melt and solution intercalation techniques. These two types of
polymers have attracted world-wide academic and industrial attention during the last
decade. Typically, these materials show promising performances in the practical
applications of electrically-conductive polymer composites, i.e. for a solid polymer
fuel cell. Despite the extensive research in this field, various aspects are not clarified
yet. For instance, the interfacial interaction of polymer-mesoporous silica is much
debated as well as the various described preparation procedures. Chapter 2 concerns
4
with the extensive characterization and conducting properties of various kinds of
PEO/Li-MCM-41 nanocomposites prepared by melt and solution intercalation
techniques. X-ray diffraction (XRD), Fourier transform infrared spectroscopy
(FTIR), thermogravimetric analysis (TGA), solid state MAS NMR and conductivity
measurement were used to characterize these polymer nanocomposites (PNC) in an
attempt to correlate the structure and conductivity. In Chapter 3, PANI/MCM-41
nanocomposites have been prepared by in situ polymerization technique. Thermal
stability of conductivity of the polymer nanocomposites (PNC) was studied in order
to know the effect of MCM-41 in PANI/MCM-41 nanocomposites.
concluding remarks will be given in Chapter 4.
Finally,
5
CHAPTER 2
PEO/MCM-41 NANOCOMPOSITES
2.1
PEO/MCM-41 Nanocomposites
Solid polymer electrolyte (SPEs) has been widely investigated due to the
solvation power and complexing ability of polyethylene oxide (PEO) to alkali metal
ions. However, one of the major drawbacks of PEO-based polymer electrolytes is
their low ionic conductivity at ambient temperature [4]. To improve the performance
of PEO-based electrolytes, various modifications such as polyether–salt complexes
and addition of inorganic filler and layered silicate have been studied.
Among the modifications carried out, it has been recognized that composite
polymer electrolytes (CPEs), obtained by combining with inorganic particles such as
alumina, silica and ceramic exhibit sufficient mechanical strength, higher ionic
conductivity, and better lithium anode and electrolyte interfacial stability [5,6,7].
The large surface area of the inorganic fillers has prevented the local PEO chain
reorganization which leads to locking in degree of disorder and favours high ion
transport.
Beside that, combination between PEO and layered silicate such as
montmorillonite yields intercalation of PEO in the silicates layer, which has been
proven to improve the mechanical strength and thermal stability of the PEO. Based
on this criteria of inorganic material, mesoporous silica MCM-41 which has large
pore size (15-100 Å), high surface area (>1000 m2/g), pore volume 0.7 – 1.2 cm3 g-1
[8] and high thermal stability gives advantages to be inorganic material host to the
PEO. The large pore of MCM-41 will make intercalation of PEO much easier. Chu
et al. [9] prepared composite polymer complex film by adding up to 15 wt% of
6
mesoporous silica (SBA-15) as filler to PEO/LiClO4 and claimed that SBA-15 served
to improve ionic conductivity and mechanical properties in the composite polymer
electrolyte system [9].
In this research, polyethylene oxide (PEO), a polymer electrolyte has been
chosen as polymer source of PNC and mesoporous MCM-41 as inorganic host. Our
main target is to synthesize polymeric and inorganic nanocomposites or polymer
nanocomposites (PNC) with conducting properties based on mesoporous materials in
order to study the structure-properties-conducting relationship. Recently, it has been
shown that the conducting mechanism of PEO in functionalized mesoporous silica in
PEO-based polymer electrolyte requires mobility of ions [10].
Generally, polymers/MCM-41 nanocomposites are expected to have two
possible structures.
These are intercalated nanocomposites and conventional
microcomposites (Figure 2.1). In intercalated nanocomposite structure, a single or
more polymer chain is intercalated in the pores of MCM-41. So, the amount of
polymer that can be intercalated in the pores of MCM-41 depends on the pore
diameter.
Meanwhile, in conventional microcomposites, the polymers are unable to
intercalate in the pores of MCM-41, so that a phase separated composite is obtained.
Between the two structures, intercalated polymer-mesoporous silica nanocomposite
can be produced via in situ polymerization, melt intercalation and solution
intercalation [2].
2.2
Synthesis of PEO/MCM-41 Nanocomposites
In this research, the techniques used in the synthesis of PEO/MCM-41
nanocomposites are melt and solution intercalation techniques. Melt intercalation is
becoming attractive since it came to prominence in 1990s [11]. In this technique, the
mesoporous silicate, MCM-41 is directly dispersed into PEO matrix in the molten
state.
7
Intercalated
Nanocomposites
MCM-41
Conventional
microcomposites
Microphase separation
Polymer
Figure 2.1
Two possible structures of polymer/MCM-41 nanocomposites [2].
Under these conditions, the PEO can crawl into the pores of MCM-41 to form an
intercalated nanocomposite. The melt intercalation technique is more flexible and
environmentally benign compared to in situ polymerization or solution intercalation
due to the absence of organic solvent [12].
In solution intercalation technique, the PEO is swelled in an appropriate
organic solvent. When the polymer is fully swollen in the organic solvent, MCM-41
is added to the solution to form a mixture containing the PEO and MCM-41
[12,13,14]. Swelled polymers diffuse into the pores of MCM-41, and followed by
evaporation of the solvent resulting in a PEO-intercalated nanocomposite.
2.3
Mesoporous Silica Material MCM-41
Over the past 20 years, the literature on design, synthesis, characterization
and properties of zeolites and molecular sieves for adsorption, separation, sieving,
environmental pollution control and catalysis has been dramatically increased.
During this period, organization of inorganic and organic molecular species into
three dimensionally structured arrays for the synthesis of nanocomposite materials
has been developed by biochemists. On the other hand, scientists of molecular sieves
8
have taken this concept which resulted in the discovery of new mesoporous
molecular sieves M41S family [15].
In 1992, researchers at Mobil Corporation discovered the M41S family of
aluminosilicate/silicate mesoporous material with exceptionally large pore structures.
There are three different mesophases in this family that have been identified as
hexagonal (MCM-41), cubic (MCM-48) and lamellar (MCM-50). MCM-41 has
uniform pore channels with a broad spectrum of pore diameters between 15 and 100
Å. The pore of MCM-41 can be controlled by a sophisticated choice of surfactant
templates, adding auxiliary organic chemicals and changing various reaction
parameters such as temperature and composition. These mesoporous materials have
extremely high surface areas (>1000 m2/g). The large pore size and surface area of
MCM-41 made this material suitable as inorganic host for polymer electrolyte or
conducting polymer.
Pure silica material, Si-MCM-41 is electrically neutral and therefore does not
have ion exchange capacity. Combination of MCM-41 with a polymer electrolyte
such as PEO is expected to produce a polymer nanocomposite with conducting
properties.
2.4
Polyethylene Oxide (PEO)
Polymer electrolytes are receiving considerable attention as solid electrolyte
materials for advanced applications such as rechargeable lithium batteries and
electrochromic devices. Combination of PEO with LiClO4 and NaSCN was reported
to exhibit high ionic conductivity at elevated temperatures [16,17].
The donor
oxygen atoms in the back bone of PEO can solvate cations such as Li+ and Na+
(Figure 2.2). Physically, PEO is a semicrystalline polymer at room temperature. The
melting point of PEO is 65oC. The crystal structure of PEO is a 7/2 helix, i.e. seven
ethylene oxide repeat units with two turns in a period of 1.93 nm [17].
9
Lone pair electron
C H2
CH 2 O
n
Figure 2.2
Structure of polyethylene oxide.
The most important electrical property of PEO is that the mobility of ionic
species occurs mainly in the amorphous phase which requires a relatively high
temperature of operation (80–100oC). For this reason, although conventional PEObased solid polymer electrolytes have been most commonly studied, their low
conductivity at room temperature excluded practical application at ambient
temperature [17]. The ionic conductivities of these electrolytes are typically in the
range of 10-9–10-8 S/cm at room temperature and 10-5–10-4 S/cm at 100oC [18].
Several approaches have been done by researchers to enhance ionic conductivity at
room temperature, such as reducing crystallinity or lowering the transition
temperature and addition of plasticizer into polymer matrix forming a gel polymer
electrolyte. Recently, an approach involving incorporation of mesoporous materials
in polymer matrices to obtain the polymer nanocomposite has shown enhanced ionic
conductivity. Herein, polymer nanocomposites, PEO/Li-MCM-41 has been prepared
in order to study structure-properties-conductivity relationship.
2.5
Experimental
2.5.1 Synthesis of Si-MCM-41 and Al-MCM-41
The synthesis of mesoporous material Si-MCM-41 is based on the procedure
of Kim et al. [19]. As a typical procedure for the preparation of Si-MCM-41, 47 g of
1 M aqueous NaOH solution and 18.83 g of colloidal silica, Ludox (30 wt% SiO2,
Aldrich) were first mixed and stirred in a propylene bottle to form a clear solution of
sodium silicate. The sodium silicate solution was dropwise added to a propylene
10
bottle containing a mixture of 5.72 g cetyltrimethylammonium bromide, CTABr
(assay 99%, BDH AnalaR®), 0.32 g of 25 wt% aqueous NH3 solution (J.T. Baker)
and 12.06 g of distilled water, with vigorous stirring at room temperature. The
mixture was stirred and heated at 97oC for 2 hours for resulting gel mixture.
After stirring for one hour, the gel mixture was heated in the oven for 1 day at
97oC. The mixture was then cooled to room temperature. Subsequently, pH of the
reaction mixture was adjusted to 10.2 by dropwise addition of 30 wt% acid acetic
with vigorous stirring. The reaction mixture was heated again at 97oC for 1 day and
the pH adjusted to 10.2 and subsequent heating was repeated twice more. The
product was filtered, washed with distilled water and dried in the oven at 97oC.
Finally, the product was calcined at 550oC for 10 hours to remove the CTABr
template in the Si-MCM-41 pores. Al-MCM-41 with various silica and alumina
(SiO2/Al2O3) ratios of 10, 60 and 100 were synthesized using the same procedure as
described for Si-MCM-41 by using sodium aluminate, NaAlO2 (53 wt% Al2O3)
(Riedel-de Haën®) as the aluminium source. The molar compositions of the gels are
tabulated in Table 2.1.
Table 2.1: Molar composition of SiO2 and Al2O3 for synthesis of Al-MCM-41a
a
SiO2/Al2O3 of
SiO2/mole x 10-3
Al2O3/mole x 10-3
Al-MCM-41
(x)
(y)
10
94
9.40
60
94
7.99
100
94
0.94
∞
94
-
The molar composition of gel is
x SiO2: y NaAlO2: 1 CTABr: 1.5 Na2O: 0.15 (NH4) 2O: 250 H2O
11
2.5.2 Transformation of Mesoporous Si-MCM-41 to Nonporous Silica
The purpose of transforming mesoporous Si-MCM-41 to nonporous silica is
to investigate the effect of the porous structure of Si-MCM-41 in the synthesis of
PEO/Li-Al-MCM-41 nanocomposites.
The framework of Si-MCM-41 was
completely collapsed by calcining crystalline mesoporous Si-MCM-41 at high
temperature i.e. 800oC for 18 hours. To ensure the structure of the MCM-41 has
been collapsed, the XRD pattern of the calcined material was monitored.
The
o
absence of XRD peaks of MCM-41 around 1.5-10 2θ is an indicator that Si-MCM41 has become completely amorphous.
2.5.3 Synthesis of PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41
Nanocomposites by Melt Intercalation Technique
In order to modify the MCM-41 structure with lithium, the parent materials
Si-MCM-41 and Al-MCM-41 were ion exchanged with 1 M lithium chloride
solution (LiCl 1 M). Calcined sample of Si-MCM-41 or Al-MCM-41 (1 g) was
added in a propylene bottle. Aqueous solution of LiCl 1 M (assay 95%, Merck) (50
ml) was added into the bottle and stirred at 80oC. After an overnight stirring, the Li+exchanged MCM-41 (Li-Si-MCM-41 or Li-Al-MCM-41) was recovered by
filtration, washed with distilled water and dried at 100oC in the oven. The amount of
Li+ ions was determined by using atomic absorption spectroscopy (AAS) and the
structure of the MCM-41 samples were characterized by using FTIR and XRD.
In
the
synthesis
of
PEO/Li-Si-MCM-41
and
PEO/Li-Al-MCM-41
nanocomposites by melt intercalation technique, the polymer, polyethylene oxide,
(PEO) (BDH Chemical Ltd, Mw 300, 000 g/mol) and Li+-exchanged MCM-41 (LiAl-MCM-41 and Li-Si-MCM-41) powders were weighed separately in appropriate
proportions and then ground together in an agate mortar. The PEO content was fixed
at 10 wt% in each sample. When a pellet of the mixture was required, the powder
was spooned into a 13 mm diameter stainless steel die and pressed into pellets under
1 tonne pressure for approximately 1 min at room temperature. The final pellet
12
obtained was about 2 mm thick. All the samples were heated as required at 90oC in a
vacuum oven, and then cooled to room temperature in vacuum desiccators.
2.5.4 Synthesis
of
PEO/Li-Si-MCM-41
Nanocomposites
by
Solution
Intercalation Technique
Polymer nanocomposites PEO/Li-Si-MCM-41 were synthesized by solution
intercalation technique in which the polymer, PEO, lithium perchlorate, LiClO4
(assay 99%, Acros Organics) and Si-MCM-41 were weighed according to the
designated ratios. The PEO was swelled in an excess amount of acetonitrile (assay
99.9%, Merck) and the Si-MCM-41 added into the solution and stirred for 1 day.
Acetonitrile (assay 99.9%, Merck) was used as the solvent because it has low
electron pair donor power and does not compete with the ether oxygen in PEO for
interaction with Li+ ions. Finally, the solvent was removed by drying in a vacuum
oven at 50oC for 1 day. The samples were prepared in which the PEO (BDH
Chemical Ltd, Mw 300, 000 g/mol) contents are 0, 2, 5, 8, 10 and 40 wt%
respectively, and the amount of LiClO4 (assay 99%, Acros Organics) was fixed at
0.0125 g.
2.5.5 Synthesis of PEO/Li-TMCS/Si-MCM-41 Nanocomposites by Solution
Intercalation Technique
Nanocomposites of PEO/Li-TMCS/Si-MCM-41 were synthesized by using
the same method as described for PEO/Li-Si-MCM-41 except for replacing SiMCM-41 with TMCS/Si-MCM-41. In order for this method to be effective, the
hydrophobicity of MCM-41 needed to be increased through chemical modifications
such as silylation, esterification and chemical vapour deposition [20].
In this
research, silylation reaction has been chosen to treat the surface of Si-MCM-41.
Mesoporous
material
Si-MCM-41
was
modified
by
treatment
with
trimethylchlorosilane (TMCS) (98% assay, Acros Organics). The existence of alkyl
13
groups attached to MCM-41 structure has been proven able to increase
hydrophobicity of MCM-41 [21]. It is well recognized that surface silylation of
MCM-41 takes place through the reaction between TMCS and surface SiOH groups
as follows [20].
≡Si-OH + Cl-Si(CH3)
≡Si –O-Si(CH3) 3 + HCl
(2.1)
Surface silylation of Si-MCM-41 has been carried out based on established
procedures [20] except for the dehydration of Si-MCM-41 at 150oC in vacuum
condition overnight before the treatment with TMCS. Dehydration of Si-MCM-41 is
carried out in order to prevent water from competing with the ether oxygen in PEO
for the silanol groups during the silylation reaction. Dehydrated Si-MCM-41 was
stirred for 5 hours in a round bottom flask with TMCS in dry toluene (5 wt%) in
which the Si-MCM-41 to TMCS solution ratio 1 g: 50 ml. The mixture was then
extensively washed with ethanol to rinse away any residual chemicals. Finally, the
powder was dried in an oven at 90oC. The TMCS modified Si-MCM-41 (TMCS/SiMCM-41) was characterized using XRD, FTIR and
13
C/CP MAS NMR. In this
research, nanocomposites of PEO/Li-TMCS/Si-MCM-41 with 0, 2, 5, 8, 10 and 40
wt% PEO were prepared.
2.6
Characterization Techniques
Several characterization techniques have been utilized in order to elucidate
and provide structural information and physicochemical properties of the parent
material MCM-41 and the polymer nanocomposites.
The bulk structure
characterization utilizes X-ray diffraction (XRD), Fourier transform infrared
spectroscopy (FTIR), nitrogen physisorption measurement, field emission scanning
electron microscopy (FESEM), atomic absorption spectroscopy (AAS) and
thermogravimetric analysis (TGA) techniques while the local order characterization
includes 27Al, 7Li and 13C/CP MAS NMR spectroscopy.
14
2.6.1 Fourier Transform Infrared Spectroscopy (FTIR)
Infrared spectroscopy is based upon the absorption of radiation of a particular
wavelength, which corresponds to the frequency of specific vibration of a part of the
sample molecule. FTIR spectrometers operate on the principle of the Michelson
Interferometer followed by Fourier transformation of the interferogram obtained, and
have several advantages over conventional IR spectrometers.
Firstly, the entire region under test is analysed simultaneously, and the
spectrum can be measured in a few seconds or several minutes. As the output is
measured digitally, this means that very dilute samples can be studied, as many
spectra can be added together to improve the signal to noise ratio. Secondly, the
resolution is determined by the speed of the scanning mirror, and is not dependent
upon a slit and prism, meaning that higher resolution is obtained without a reduction
in sensitivity [22,23].
Infrared spectroscopy is a method for characterization of long range and
short-range bond order caused by lattice coupling, electrostatic and other effects.
Normally FTIR provides meaningful information in the mid-infrared region (1400400 cm-1) which attributed to the framework vibrations of zeolite which tetrahedral
linked of SiO4 or AlO4 [24].
Table 2.2 shows the main band stretching of
mesoporous material Si-MCM-41.
Table 2.2: The main band stretching of Si-MCM-41
Types of vibration
Wavenumber / cm-1
Asymmetric Si-O-Si stretching
1200-1000
Symmetric Si-O-Si stretching
800
Si-O-Si bending
460
Si-OH stretching
960
15
Experimental procedure:
The FTIR spectra were recorded on Shimadzu Fourier transform infrared
(FTIR) 8300 spectrometer. The method applied is known as KBr technique. The
sample was first finely ground. Powdered sample was diluted with spectral grade
potassium bromide with 1: 100 ratio and ground into a homogeneous powder. It was
then loaded into a 13 mm die and pressed at 10 tonne for 3 minutes to form a selfsupporting pellet.
The pellet was mounted on a brass sample holder and the
spectrum measured in the range 4000 to 400 cm-1 and 4 cm-1 resolution at ambient
temperature. In order to record the FTIR spectrum for pure PEO, a thin film of PEO
was prepared via casting technique and the spectrum recorded as described above.
2.6.2 X-ray Diffraction (XRD)
Powder XRD diffraction measurements can reveal several important
properties. The X-ray diffractogram signify whether the material is amorphous,
crystalline, or quasi-crystalline, yield an estimate of the average crystallite size dspacings and lattice parameters, allowing identification of the phases present.
Monochromatic X-rays of wavelength λ, incident upon the sample at an angle
θ, are diffracted by planes of atoms in the crystal separated by a distance d. The
diffracted beams interfere constructively only when Bragg’s Law is satisfied, giving
rise to peaks (or spots) in the measured diffraction pattern. By using X-rays of
known wavelength, λ and measuring the different angle θ, this allows the
determination of the d-spacing of various planes of a crystal (Figure 2.3).
The X-ray wavelength commonly employed is the characteristic K α
radiation, λ = 1.5418 Ǻ, emitted by copper. Thus the d-spacing can be calculated
from the angle of diffraction using the Bragg equation [25]:
16
nλ = 2d sin θ
(2.2)
d = interplanar spacing, θ = Bragg’s angle, λ = Wavelength
n = integer number (1,2,3..)
Experimental procedure:
The XRD analysis for the sample were carried out using an XRD Bruker D8
Advance diffractometer which uses an X-ray beam of wavelength, λ = 1.5406 Å at
40 kV and 10 mA current. Each sample was measured at 2θ angles in the range
between 1.5o and 10o. The step size is 0.05 degree per step with a step time of one
second per step.
θ
θ
d
θ
θ
Figure 2.3: Derivation of Bragg’s Law for X-ray diffraction [25].
2.6.3 Solid State MAS NMR Spectroscopy
Magic angle spinning NMR spectroscopy (MAS NMR) is one of the
techniques used to elucidate zeolite and other porous structure. This technique
eliminates the broadening of the NMR signals normally observed in solids. The line
broadening is due to various anisotropic interactions which all contain a (3 cos2 θ –
1) term. When cos θ = (1/3)1/2, i.e. θ = 54o44’, this term becomes zero. Spinning the
sample about an axis inclined at this so-called magic angle to the direction of the
magnetic field eliminates these sources of broadening, and thus improves the
resolution in chemical shift spectra [25,26,27].
17
In this research, 27Al, 7Li and 13C/CP MAS NMR spectroscopy were used in
order to clarify the interfacial interactions between PEO and Li-Al-MCM-41.
27
Al
MAS NMR have been applied to observe types of coordination of Al in Al-MCM-41
whether in octahedral coordination [Al(H2O)6]3+, which is frequently trapped as a
cation in the pores and gives a peak at about 0 ppm (with [Al(H2O)6]3+ (aq.) used as
the reference) or tetrahedral coordination which is Al in the framework of Al-MCM41. The peak of tetrahedral Al occurs in the range 50-60 ppm [26]. The 7Li MAS
NMR and 13C/CP MAS NMR were used to study the environment of C atom and Li+
ions after the synthesis of PEO/Li-Al-MCM-41 nanocomposites. In
13
C/CP MAS
NMR, cross-polarization techniques have been used to increase the signal to noise
(S/N) and to bypass the T1 relaxation processes of the dilute nuclei being observed.
There is no effect on the line width from this technique. The line widths were
reported as full width at half-height (FWHH).
Experimental procedure:
MAS NMR experiments were performed using Bruker Advance 400 MHz
9.4T spectrometer. The
31
C/CP MAS NMR spectra were recorded with a recycle
delay of 5.0 s, number of transient of 2000 and spinning rate of 7 kHz. The 7Li MAS
NMR spectra were recorded at 155.50 MHz using 1.0 µs radiofrequency pulses, a
recycle delay of 2.0 s, number of transient of 600, and spinning rate of 7.0 kHz. The
27
Al MAS NMR spectra were recorded at 104.26 MHz using 2.0 µs radiofrequency
pulses, a recycle delay of 2.0 s, and spinning rate of 12.5 kHz. Chemical shifts for
13
C, 27Al and 7Li were referred to TMS, Al(H2O)6+ and LiNO3, respectively.
2.6.4 Thermogravimetric Analysis (TGA)
Thermogravimetric (TG) is the branch of thermal analysis which examines
the mass change of a sample as a function of temperature in the scanning mode or as
a function of time in the isothermal mode. Not all thermal events bring about a
change in the mass of the sample (for example melting, crystallization or glass
18
transition), but there are some very important exceptions which include desorption,
absorption, sublimation, vaporization, oxidation, reduction and decomposition.
TG is used to characterize the decomposition and thermal stability of
materials under a variety of conditions and to examine the kinetics of the
physicochemical process occurring in the sample. The mass change characteristics
of a material are strongly dependent on the experimental condition employed.
Factors such as samples mass, volume and physical form, the shape and nature
sample holder, the nature and pressure of atmosphere in the sample chamber and the
scanning rate all have important influences on the characteristics of the recorded TG
curve. TG curves are recorded using a thermobalance. The principal elements of a
thermobalance are an electronic microbalance, a furnace, a temperature programmer
and an instrument for simultaneously recording the outputs from these devices. A
thermobalance is illustrated schematically in Figure 2.4 [28].
Experimental procedure:
Thermal stability of the samples was measured by using DTG-50 Shimadzu,
simultaneous DTA-TG instruments by using alumina crucible, under nitrogen flow
(35 ml/min) and heating rate 10oC/min and measured from room temperature to
1000oC.
Microbalance
Computer or
Chart Recorder
Furnace
Temperature
Programmer
Sample and
crucible
Figure 2.4
Schematic representation of a thermobalance [28].
19
2.6.5 Atomic Absorption Spectroscopy (AAS)
Atomic absorption spectroscopy relies on the fact that atom of any element
can be excited, and is therefore capable of absorption, at a wavelength characteristic
of the element. The spectrum of the element to be determined, is emitted from a
hollow cathode lamp, and passes though a flame containing the solution under test.
A portion of the resonance line corresponding to the concentration of this element is
absorbed, and the attenuation of this line is measured. The amount of an element
present in a sample can then be determined using the Beer-Lambert law:
I
A = log ° = ε.l.c
I
t
(2.3)
Where A is the absorbance, Io and It the incident and transmitted intensities, ε is the
spectral absorption coefficient, l is the length of the absorbing layer, and c the
concentration of the sample under test. Thus from a plot of A against c for a set of
standard samples, we can determine the concentration of our test sample [29].
In atomic absorption spectroscopy, the resonance radiation of the analyte
element is passed through the flame into which the sample is nebulized and
atomised. This radiation is adsorbed only by ground state atoms of the analyte
element. Thus absorbance is a specific measure of the analyte element. As most
atoms are in the ground state, the method is sensitive and relatively independent of
the temperature of the flame. Because most elements, especially the metals and
metalloids, form ground state atoms in flame, the method is applicable to a large
number of elements.
The schematic arrangement of an atomic absorption
spectrophotometer is shown in Figure 2.5. It consists of light source (hollow-cathode
lamp), burner (nebulizer-burner), monochromator, detector and readout system.
Source for atomic absorption spectrophotometers are ordinarily hollow cathode
lamps or gaseous discharge tubes and there are two types of burners.
20
Nebulizer-burner
Hollow-cathode lamp
Figure 2.5
Detector
Monochromator
Readout system
Schematic arrangement of an atomic absorption spectroscopy [29].
Experimental procedure:
The lithium loading of the of Li+-exchanged Al-MCM-41 samples were
determined by digesting 0.5018 g of the material in hydrofluoric acid (J. T. Baker)
overnight, followed by careful dilution with doubly deionised water.
The
hydrochloric acid was added dropwise to the beaker until all the samples diluted. All
solutions were prepared using PTFE volumetric flasks (100 ml), and pipettes, and
stored in PTFE flasks. The blank solution was also prepared using the same method
used for the samples under test except the sample. For Li+ ions, the absorption was
measured at 670.7 nm using a lithium lamp. Solutions of the samples under test were
analysed using a GBC-Avanta atomic absorption spectroscopy.
2.6.6 Nitrogen Physisorption Measurement
Nitrogen adsorption analyses can reveal valuable information on the surface
properties of the Al-MCM-41 samples such as the surface areas, thickness of the
framework walls, average pore sizes, pore type, pore shape and total pore volumes
[8].
The most common technique for measuring the surface area is by static
volumetric determination, whereby a known quantity of an inert gas (usually
nitrogen) is adsorbed onto the material under test, maintained at a constant
21
temperature (usually liquid nitrogen temperature 77 K) and the surface area
determined by application of the Brunauer-Emmet-Teller (BET) theory. The IUPAC
classification of pores is given in Table 2.3 [30].
Table 2.3: IUPAC classification of pores.
Pores diameter (Å) Types of pores
> 500
Macropores
20-500
Mesopores
<20
Micropores
Experimental Procedure:
In this research, the nitrogen adsorption isotherms were measured at 77 K
using a Micromeritics ASAP 2010. Prior to each measurement, powder sample of
Al-MCM-41 weighing between 0.1 to 0.2 gram was outgassed at 473K for at least 4
hours under a pressure of below 10-5 atm. Then, the sample was cooled to ambient
temperature and the pressure increased to 1 atm for the nitrogen adsorption process.
2.6.7 Field Emission Scanning Electron Microscopy (FESEM)
This form of imaging is based upon the low energy (<50 eV) secondary electrons
emitted from the surface of the specimen. The beam can be concentrated to a small
probe that may be deflected across the specimen using scanning coils. The secondary
electrons can be detected above the specimen, and an image showing the intensity of
secondary electrons emitted from different parts of the specimen is obtained.
Scanning electron microscopy (SEM) provides information on the surface
topography, texture, and morphology of the specimen. It offers a great depth of focus
which facilitates three-dimensional visualization of specimen surfaces.
22
The disadvantage of SEM when dealing with samples such as
aluminosilicates is that the specimen is easily charged when subjected to the higher
electron beam even after the specimens are coated with a conducting layer of metal
such as gold or carbon. In order to overcome this problem, low accelerating voltages
were used in FESEM and the samples are instead coated with titanium because of its
small particle size and better coating homogeneity.
Experimental Procedure:
The PNC samples were mounted on copper plates using an industrial glue
(Bostik) followed by drying in an oven for 1 h. The samples were coated with Ti on
Ti sputter prior to examination by a JEOL JSM-6330F field emission scanning
electron microscope operating at 15 kV.
2.6.8 Conductivity Measurement
A several number of polymeric materials are known to conduct electricity by
the migration of ions. These include both organic and inorganic-based polymers.
Majority of these materials consist of a salt dissolved in a polymer matrix, such as
LiClO4 in polyethylene oxide. Usually both cations and anions contribute to the
conductivity. The addition of nanosize inorganic materials enhances the conductivity
of pure polymer.
There are three main techniques for the characterization of
ionically conducting polymer [4];
i)
Direct current (d.c.) measurements
ii)
Alternating current (a.c.) measurements
iii)
Transport number measurement
Alternating current methods has been used in this research. Alternating
current methods represent the most popular approach to the determination of the
electrical properties of polymer electrolytes.
This is undoubtedly because very
23
simple cells incorporating inert blocking electrodes may be used to determine bulk
electrolyte properties. The data carry information not only about the long range
migration of ions but also about polarisation phenomena occurring within the cell,
e.g. the relaxation of trapped ions.
In a.c. experiment a sinusoidal voltage is applied to a cell and the sinusoidal
current passing trough the cell as a result of this perturbation is determined (Figure
2.6). Now in d.c. measurement at moderate potentials the current flowing, I, is
related to potential, V, by just one parameter, the resistance, R, where R = V/I and it
is this parameter which can in turn be related to the electrical properties of the cell.
However, in the case of an a.c. perturbation two parameters are required to relate the
current flowing the applied potential. One represents the opposition to the flow of
charge and is equal to the ratio of the voltage and current maxima, Vmax/Imax, and
analogous to the resistance in d.c. measurements. The other parameter, θ, is the
phase difference between the voltage and current.
The combination of these
parameters represents the impedance, Z, of the cell. The conductivity values (σ)
have been calculated from the equation below [17]:
σ = (1/Rb)(t/A)
(2.4)
Where t is the thickness and A is the area of the sample.
In this research, the simplest case of a cell consisting of polymer electrolyte
with only one mobile species sandwiched between two blocking electrodes (Figure
2.6) was considered. An a.c. voltage is applied to the cell and the frequency is
varied. The equivalent circuit representing the a.c. response of the cell is given in
Figure 2.6 (a).
The electrodes become alternatively positively and negatively
charged and the alternating field across the electrolyte cause the Li+ ions to migrate
back and forth in phase with the voltage. The migration of Li+ ions is represented by
the resistor Rb in the diagram.
24
Blocking electrodes
Electrolyte
Rb
Ce
Ce
Cb
(a)
Z"
Electrolyte
Electrode
Rb/2
Z’
Rb
(b)
Figure 2.6
(a) Schematic representation of a polymer electrolyte/blocking
electrode cell. Rb = electrolyte resistance; Cb = electrolyte Capacitance; Ce = electrode
capacitance. Typically Rb = 102-108 S/cm. (b) Simulated complex impedance plot for
circuit (a) [4].
25
Experimental procedure:
Ionic conductivity measurement was conducted on a.c. mode by Frequency
Response Analyser model 1250 (Solartron Group Ltd) within the frequency range
from 10 kHz to 1 Hz. About 0.2 g of sample was weighted, loaded into a 13 mm
diameter die and pressed at 1 tonne for 1 minute to form a self-supporting pellet.
The polymer nanocomposite, PEO/Li-MCM-41 pellet was sandwiched between two
copper electrodes and the impedance plot was recorded.
2.7
Results and Discussion
2.7.1 PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41 Nanocomposites Prepared
Through Melt Intercalation Technique
2.7.1.1 Parent Materials Si-MCM-41 and Al-MCM-41
Figure 2.7 shows the FTIR spectra of Si-MCM-41 and Al-MCM-41 with
SiO2/Al2O3 ratios of 10, 60 and 100. Major peaks of MCM-41 were observed in the
IR spectra of Si-MCM-41 and Al-MCM-41 which consist of asymmetrical Si-O-T
stretching vibration (1200-1000 cm-1), symmetrical Si-O-T stretching vibration (800
cm-1) (T = Si, Al), Si-O-Si bending (460 cm-1) and Si-OH stretching vibration (960
cm-1). These peaks indicate that Si-MCM-41 and Al-MCM-41 with SiO2/Al2O3 = 10,
60 and 100 were successfully synthesized. This is so owing to the increment of Si-O
and Al-O bond distances.
Figure 2.8 shows the XRD patterns of Si-MCM-41 and Al-MCM-41 with
SiO2/Al2O3 = 10, 60 and 100 after calcination. All the XRD patterns are similar to
those described by Beck et al. [15]. Generally, a sharp Bragg peak ascribed to the
(100) reflection of the hexagonal structure of the mesopores was observed at 2θ =
2.3o to 2.6o. The weak peaks ascribed to (110) and (200) reflections were observed
at 2θ, 4.0o and 4.7o, respectively. Those data indicate that the long range order of
MCM-41 was maintained after calcination. It has been observed that the intensity of
26
SiO2/Al2O3c= 10
Transmittance / a.u.
SiO2/Al2O3 = 60
SiO2/Al2O3 = 100
Si-MCM-41
1400
1200
1000
800
600
400
Wavenumber / cm-1
Figure 2.7
and 100.
IR spectra of Si-MCM-41 and Al-MCM-41 with SiO2/Al2O3 = 10, 60
27
Relative Intensity / a.u.
SiO2/Al2O3 = 10
SiO2/Al2O3 = 60
SiO2/Al2O3 = 100
Si-MCM-41
2
4
6
2θ /
Figure 2.8
8
o
XRD patterns of calcined Si-MCM-41 and Al-MCM-41 with
SiO2/Al2O3 = 10, 60 and 100.
10
28
the (100) peak increases with the decrease of SiO2/Al2O3 ratios. Thus, it is suggested
that in the presence of Al, the degree of ordering in Al-MCM-41 increases even at
relatively high levels of aluminium incorporation.
2.7.1.2 Li-Si-MCM-41 and Li-Al-MCM-41
Insertion of Li+ ions in MCM-41 structure is important in order to prepare
conducting polymer nanocomposite because the conductivity of PEO relies on the
mobility of Li+ ions in the polymer matrix. In this study, Li+ ions were inserted in
the structure of Al-MCM-41 by ion exchange technique.
XRD patterns of Li-Si-MCM-41 and Li-Al-MCM-41 after ion exchange with
1 M LiCl solution are shown in Figure 2.9. Generally, the Bragg peak (100) is
observed in all XRD patterns of the samples. However, this peak is broadened and
shifted slightly to the higher angle with the increase in SiO2/Al2O3 ratios. Three
smaller peaks indexed as (110), (200) and (210) are no longer observed in the XRD
patterns suggesting that the regularity of the mesoporous channels has decreased
after ion exchange.
Figure 2.10 shows the concentration of Li+ ions versus SiO2/Al2O3 ratios of
Al-MCM-41 determined by AAS. The graph shows that the amount of Li+ ions in
Li-Si-MCM-41 is very much lower than that of Li-Al-MCM-41. For the Li-AlMCM-41 samples with SiO2/Al2O3 ratios of 10, 60 and 100, the amount of Li+ ions
increases when the Al content is increased. This result is an indirect evidence for the
incorporation of Al in the framework of Al-MCM-41, the amount of which is defined
through the framework silicon to aluminium ratio (SiO2/Al2O3). The presence of
framework aluminium [AlO4-] in zeolites creates an excess negative charge and ions
such as Na+ and Ca2+ in their hydrated form balance this excess negative charge.
This means that through ion exchange the Li+ ions also can interact electrostatically
with the negatively charged framework aluminium.
29
Relative Intensity / a.u
(d)
(c)
(b)
(a)
2
4
6
8
2θ / o
Figure 2.9
XRD patterns of Si-MCM-41 (a) and Al-MCM-41 ion exchanged
with LiCl 1 M [(b) – (d) for SiO2/Al2O3 = 10, 60 and 100, respectively].
10
30
Concentration of Li ions / ppm
25
20
+
15
10
5
0
Si-MCM-41
100
60
10
SiO 2 /Al 2 O 3 Ratios
Figure 2.10
Concentration of Li+ ions (ppm) in Li-Si-MCM-41 and
Li-Al-MCM-41 (SiO2/Al2O3 = 10, 60, and 100) after ion exchange with LiCl
solution (1 M).
2.7.1.3 PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41 Nanocomposites
Figure 2.11 shows the FTIR spectra of PEO/Li-Si-MCM-41 and PEO/Li-AlMCM-41 nanocomposites (SiO2/Al2O3 = 10, 60 and 100). The spectra of all the
nanocomposites are similar to the parent Si-MCM-41 and Al-MCM-41. All the IR
peaks belonging to parent Si-MCM-41, Al-MCM-41 and PEO are also present in the
spectra for the nanocomposites. The peak at 1000 cm-1 became broader when the
SiO2/Al2O3 ratios decreased. This suggests also that MCM-41 with low SiO2/Al2O3
is more unstable compared to one with high SiO2/Al2O3, resulting in a slight decrease
in long range integrity of the MCM-41 structure. However, two weak peaks in 1500
to 1300 cm-1 region which belong to C-H vibrations of PEO are still observed in the
spectra of the nanocomposites indicating that the structure of PEO was not altered.
31
(d)
C-H
C-H
(c)
Transmittance / a.u.
C-H
C-H
(b)
C-H
C-H
(a)
C-H
C-H
PEO
C-H
4000.
3000
2000
1500
1000
500
Wavenumber / cm-1
Figure 2.11
IR spectra of PEO and (a) PEO/Li-Si-MCM-41 and (b) – (d) PEO/Li-
Al-MCM-41 nanocomposites with SiO2/Al2O3 = 10, 60 and 100, respectively.
32
Figure 2.12 shows the XRD patterns of PEO/Li-Si-MCM-41 and PEO/Li-AlMCM-41 nanocomposites (SiO2/Al2O3 = 10, 60 and 100). The main peak of MCM41 indexed as (100) was observed for all the samples. The absence of the (110) and
(200) peaks of MCM-41 after the addition of PEO suggested that the structure of
MCM-41 has partially collapsed during the synthesis probably due hydrolysis of the
siloxane bonds [31].
2.7.1.4 Interfacial Interaction of PEO/Li-Al-MCM-41 Nanocomposites:
7
27
Al,
13
Li and C/CP MAS NMR Study
The purpose of the 27Al, 7Li and 13C/CP MAS NMR study was to clarify the
interfacial interaction of PEO with Li-Al-MCM-41. The 27Al MAS NMR spectra of
PEO/Li-Al-MCM-41 nanocomposites with various SiO2/Al2O3 ratios are shown in
Figure 2.13. The spectra show a broad main peak centred at –56 ppm corresponding
to tetrahedrally coordinated Al species [-AlO4] [26]. It can also be seen that the
intensity of the broad peak increases with the decrease in the SiO2/Al2O3 ratios of AlMCM-41 due to the increase in Al content in Al-MCM-41. There is no peak
observed at 0 ppm in the spectrum which confirms that octahedrally coordinated Al
was not present in the Al-MCM-41 structure [26].
The presence of tetrahedral Al species [AlO4-] in Al-MCM-41 generates an
overall negative charge in the framework of Al-MCM-41 and this negative charge
can interact with Li+ ions by means of electrostatic interaction during the ion
exchange process. From this point of view, it is assumed that each Li+ ions is
associated with one AlO4- in the framework. As expected, among the samples, AlMCM-41 with SiO2/Al2O3 = 10 which has the largest amount of Al gave the highest
amount of Li+ ions. This result is consistent with the AAS data previously described
in Section 2.7.1.2 which shows that Li+ ions concentration increases linearly with the
Al content in Li-Al-MCM-41.
33
Relative Intensity / a.u.
(a)
(b)
(c)
(d)
2
10
20
30
40
50
2θ / o
Figure 2.12
XRD patterns of (a) PEO/Li-Si-MCM-41 and (b) – (d) PEO/Li-
Al-MCM-41 nanocomposites with SiO2/Al2O3 = 10, 60 and 100, respectively.
60
34
Al (tetrahedral)
framework Al
Al (octahedral)
extraframework Al
- 56 ppm.
Relative Intensity / a.u.
SiO2/Al2O3 = 100
SiO2/Al2O3 = 60
SiO2/Al2O3 = 10
100
80
60
40
20
0
-10
ppm
Figure 2.13
ratios.
27
Al MAS NMR of PEO/Li-Al-MCM-41 with various SiO2/Al2O3
35
Figure 2.14 shows the 13C/CP MAS NMR spectrum of PEO in comparison to
PEO/Li-Al-MCM-41 having various SiO2/Al2O3 ratios and containing 10 %wt of
PEO. The spectra of PEO/Li-Al-MCM-41 samples show a single signal at 64 ppm.
The line width of the signal for PEO/Li-Al-MCM-41 (1 ppm) is smaller than that of
‘free’ PEO (5 ppm). This phenomenon might be due to the immobilization of PEO
in the pores of Li-Al-MCM-41 resulting in more rigid structure than in ‘free’ PEO.
From this information, the type of PEO/Li-Al-MCM-41 nanocomposites which could
have been obtained is intercalated polymer nanocomposites in which single
(sometimes more than one) extended; polymer chains have been intercalated in the
pores of MCM-41.
A chemical shift of ca. 2 ppm is also observed on PEO/Li-Al-MCM-41 from
‘free’ PEO. The large low field chemical shift of the signal at ca. 69 ppm can be
explained by the interaction of the free electron pairs of oxygen atoms in PEO with a
charged molecule on the surface of Li-Al-MCM-41. There are two possibilities of
interactions; with Li+ ions and/or silanol groups. These observations provide strong
support for the conclusion that an interaction between PEO with Li-Al-MCM-41,
presumably in internal pores, occurs in the nanocomposite. This argument was
supported by the fact that the
13
C peak of template surfactant (hexadecyltrimethyl-
ammonium bromide), as structure directing agent, of MCM-41 which is located
inside the pore also showed a chemical shift to lower magnetic field in comparison to
that of free surfactant [32].
A polymer nanocomposite which has a non-porous silica structure was also
prepared in order to study the effect of pores and whether or not PEO was
successfully intercalated in MCM-41. Figure 2.15 shows the 13C/CP MAS spectrum
of the PNC with non-porous structure. The spectrum shows a single sharp peak at 67
ppm similar to that of PNC obtained using crystalline mesoporous Si-MCM-41.
Apart from the much noisier signals observed in the spectrum, there is no chemical
shift observed from the non-porous PEO/Li-Si-MCM-41 (Figure 2.15). Based on
this information, we conclude that 13C/CP MAS NMR spectra alone cannot confirm
the location of PEO in the MCM-41 pores. However, from nitrogen adsorption
measurement, there is a significant reduction in BET surface area of PNC materials
(318.47 m2/g) compared to Li-Al-MCM-41 (889.51 m2/g). This may be due to
36
Relative Intensity /
au
PEO
SiO2/Al2O3 = 10
SiO2/Al2O3 = 60
SiO2/Al2O3 = 100
80
Figure 2.14
13
75
70
65
ppm
60
55
50
45
C/CP MAS NMR of PEO and PEO/Li-Al-MCM-41 with various
SiO2/Al2O3 ratios.
37
Relative Intensity /
au
(a)
(b)
74
72
70
68
66
64
62
60
58
56
ppm
Figure 2.15
13
C/CP MAS NMR of (a) PEO/Li-Si-MCM-41 (b) PEO/Li-Si-MCM-
41 with non-porous structure.
38
filling of the MCM-41 mesopores by PEO chains and/or partially collapse of the
MCM-41 structure.
Figure 2.16 shows the 7Li spectra of PEO/Li-Al-MCM-41 compared to Li-AlMCM-41. Nucleus 7Li is a quadruple having spin I = 3/2, a relatively low quadruple
moment and a high natural abundance of 93%, which renders the registration of 7Li
NMR spectra relatively easy.
7
Li MAS NMR spectra of a series of PEO/Li-Al-
MCM-41 with different degree of Li exchange showed that a sharp singlet with line
width of about 1 ppm was observed.
As clearly shown in Figure 2.16, the line shapes of the 7Li MAS NMR
spectra of PEO/Li-Al-MCM-41 are asymmetrical, whereas a shoulder peak is
observed for Li-Al-MCM-41 indicating that Li+ ions coordinate inside and outside of
the pores [16,33].
However, no significant chemical shift was observed in the
spectrum suggesting only weak electrostatic interaction of PEO and Li+ ions were
present. The intensity of the peak increases when the SiO2/Al2O3 is decreased and
this trend further supports the AAS data which give similar results. In addition, as
shown in Figure 2.16, it is seen that the 7Li MAS NMR line width of PEO/Li-MCM41 is larger than that of Li-Al-MCM-41. This result suggests the broadening of the
line width is presumably caused by segmental motion of PEO chains [34].
It was commonly accepted that the main driving force for the adsorption of
PEO chain segments to MCM-41 surface silanol groups was attributed to the acidbase interactions of the free electron pairs of the oxygen atoms of the PEO chain
[hydrogen-bond accepting (HBA) groups] with the active hydrogen course dispersion
forces and specific interactions between siloxane bridges and the oxygen atoms the
silanol groups of the MCM-41 surface [hydrogen-bond donating (HBD) groups]. Of
course, dispersion forces and specific interactions between siloxane bridges and the
oxygen atoms of the PEO chains are also conceivable [16,34].
Based on all of the above consideration, as shown in Figure 2.17, an
interaction model is proposed. Since only weak interaction between Li+⇔PEO (a)
was observed, the interaction of SiOH⇔PEO (c) became dominant.
This is
supported by the fact that a strong Li+⇔AlO4- (b) interaction also occurs, since fully
39
SiO2/Al2O3 = 10
Relative Intensity / a.u.
SiO2/Al2O3 = 60
SiO2/Al2O3 = 100
Li-Al-MCM-41
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
ppm
Figure 2.16
7
Li MAS NMR of Li-Al-MCM-41 (SiO2/Al2O3 = 10) and
PEO/Li-Al-MCM-41 with various SiO2/Al2O3 ratios.
-2.0
40
O
(a)
O
H
O O
Si O
Si O
Figure 2.17
(c)
O
(b)
O
O
PEO
O
H
Li +
O
O Si O Si
Al O
Proposed intermolecular interactions of polyethylene oxide (PEO) segments with Li-Al-MCM-41 surface groups. The dashed
lines indicate possible hydrogen-bond donating (MCM-41)/hydrogen-bond accepting and Al-Li-O interaction sites. The degree of the
electrostatic interaction of (c) and (b) is larger than (a).
41
Li-exchanged was observed in 7Li spectra of Li-Al-MCM-41. Finally, the degree of
electrostatic interaction of SiOH⇔PEO and AlO4-⇔Li+ is larger than Li+⇔PEO.
2.7.1.5 Ionic Conductivity of PEO/Li-MCM-41 Nanocomposites
i)
Effect of PEO Loading
Ionic conductivity of PEO/Li-MCM-41 is derived from complex impedance
plot of circuit. The bulk resistance (Rb) is determined from the graph of Z’’ versus
Z’. Table 2.4 shows the conductivity of Li-Si-MCM-41 and Li-Al-MCM-41 after
ion exchange with lithium chloride (1 M) and PEO/Li-Si-MCM-41 and PEO-Li-AlMCM-41 nanocomposites with SiO2/Al2O3 ratios 10, 60 and 100. Both PEO/Li-SiMCM-41 and PEO/Li-Al-MCM-41 showed similar lower conductivity compared to
the corresponding Li-Si-MCM-41 and Li-Al-MCM-41 after the addition of PEO.
The NMR results described in Section 2.7.1.4 suggested that not only strong
interaction between Li+ ions and Al tetrahedral in Al-MCM-41 structure occur in
PEO/Li-Al-MCM-41 but also interaction between Li+ ions with the partially
negatively charged oxygen atoms in the back bone of PEO. The fact that there is no
variation in the conductivity among the samples confirm that strong interactions of
Li+ ions limit the mobility of Li+ ions resulting in low conductivity of the
nanocomposites.
ii)
Effect of Aluminium Loading
The
conductivity
of
PEO/Li-Si-MCM-41
and
PEO/Li-Al-MCM-41
nanocomposites with different SiO2/Al2O3 ratios seems to show no significant
enhancements.
However, when the conductivity of PEO/Li-Si-MCM-41 and
PEO/Li-Al-MCM-41 nanocomposites is divided by the amount of Li+ ions (ppm), a
linear relationship was observed between conductivity and the SiO2/Al2O3 ratios. As
42
Table 2.4: Conductivity series of Li-Si-MCM-41 and Li-Al-MCM-41 and
PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41 nanocomposites with SiO2/Al2O3
ratios 10, 60 and 100.
Type of nanocomposites
Li-Si-MCM-41 and
Li-Al-MCM-41
Log Conductivity per [Li+] / S cm-1 ppm-1 (x 10-8)
PEO/Li-Si-MCM-41 and
PEO/Li-Al-MCM-41
SiO2/Al2O3 ratio
Log conductivity / S cm-1 a
∞b
1.5 x 10-7 ± 3.0 x 10-9
100
1.6 x 10-7 ± 1.1 x 10-8
60
2.4 x 10-7 ± 1.4 x 10-7
10
1.9 x 10-7 ± 3.5 x 10-8
∞b
1.6 x 10-7 ± 3.6 x 10-9
100
1.8 x 10-7 ± 2.0 x 10-8
60
1.4 x 10-7 ± 3.3 x 10-8
10
1.5 x 10-7 ± 2.5 x 10-8
4.50
3.50
2.50
1.50
5.00
10
60
100
Si-MCM-41
SiO2/Al2O3 Ratios
Figure 2.18
Mean of conductivity of PEO/Li-Si-MCM-41 and
PEO/Li-Al-MCM-41 with SiO2/Al2O3 =10, 60 and 100 divided with
concentration of Li+ ions.
43
depicted in Figure 2.18, it reveals that the lower the SiO2/Al2O3 ratio, the lower the
conductivity because the negatively charged aluminium reduces the mobility of Li+
ions following strong interaction between Li+ and [AlO4-] ions.
It is therefore
desirable to use an alternative route which utilizes pure silica mesoporous MCM-41.
The following section describes the preparation and characterisation of PEO/Li-SiMCM-41 nanocomposites from PEO and Si-MCM-41 by solution intercalation
technique.
2.7.2 PEO/Li-Si-MCM-41 Nanocomposites Prepared by Solution Intercalation
Technique
In solution intercalation technique, Li+ ions, PEO and MCM-41 were mixed
together and the resulting mixture stirred in acetonitrile overnight at room
temperature. By performing this modification at room temperature, the damage to
the MCM-41 structure is minimized.
Figure 2.19 shows the IR spectra of PEO and PEO/Li-Si-MCM-41
nanocomposites with various weight percentages of PEO (0, 5, 10 and 40 wt%). The
most significant change observed in the IR spectra in Figure 2.19 is the stretching
and deformation vibrations of the methylene groups (CH2 stretching). Pure PEO
exhibits a large, broad band of asymmetric CH2 stretching between 3000 and 2750
cm-1 and two narrow bands of lower intensity in the range 2750-2700 cm-1. In the
spectra of PEO/Li-Si-MCM-41 nanocomposites (Figure 2.19 b-d) this band is split
into two well defined bands in the region between 2900 and 2850 cm-1 at low
contents of PEO up to 10 wt%. Similar changes have been reported previously for
PEO composites with montmorillonite (MMT) [35]. The intensity of this band
increased with the increase of PEO content in the nanocomposites and the band
broadened at 40 wt% PEO (Figure 2.19 e).
Vibrations at 1100 and 1450 cm-1 belong to C-O stretching and CH2 bending
for PEO, respectively.
In PEO/Li-Si-MCM-41 nanocomposites, the C-O peak
overlaps with the asymmetric Si-O-Si stretching band. The peak corresponding to
44
CH2 wagging mode at 1343 cm-1 was not observed in the nanocomposites containing
from 2 to 10 wt% PEO owing to the low amounts of PEO. The unchanged lattice
vibrations in the region of 3000-800 cm-1 of the FTIR spectra shown in Figure 2.19
supports the idea that the product obtained after melt intercalation is still pure PEO
and Si-MCM-41. One implies that there is no interaction between PEO and SiMCM-41 in the polymer nanocomposites.
Figure 2.20 shows the XRD patterns of PEO/Li-Si-MCM-41 nanocomposites
with various weight percentages of PEO (0, 2, 5, 8, 10 and 40 wt%). Generally, in
each of the XRD patterns, three Si-MCM-41 peaks indexed as (100), (110) and (200)
occur for all the samples. The (100) peak in the XRD pattern of Si-MCM-41 is sharp
but slightly lower compared to Si-MCM-41 before the addition of PEO.
This
indicates that long range order structure of Si-MCM-41 was maintained after mixing
with PEO.
The XRD patterns of PEO/Li-Si-MCM-41 nanocomposites are all
similar. At 40 wt% PEO in the nanocomposites, there is a slight shifting of the main
(100) peak of Si-MCM-41 towards higher 2θ angle which evidenced the intercalation
or penetration of PEO within the channel of mesoporous Si-MCM-41; in agreement
with that reported by Chu et al. [16].
TGA thermograms of the PEO/Li-Si-MCM-41 nanocomposites with 10 and
40 wt% PEO measured in nitrogen from room temperature to 1000°C have two
weight loss steps (Figure 2.21). The first weight loss (ambient to 100) is due to
release of physisorbed water from the nanocomposites. It was expected that the
amount of water in the polymer nanocomposites would be different after
intercalation because of the different PEO contents.
According to the thermal
analysis, the amount of water in the parent Si-MCM-41 is relatively higher than in
the nanocomposites because of hydrophilicity of Si-MCM-41 [16]. On the other
hand, the percentage weight loss of water in PEO/Li-Si-MCM-41 nanocomposite
with 40 wt% PEO is lower compared to PEO/Li-Si-MCM-41 nanocomposite with 10
wt% PEO.
The steep slope representing the second weight loss in PEO/Li-Si-MCM-41
nanocomposite with 40 wt% PEO is due to degradation of PEO which must be
higher in this sample. Comparison of the second weight loss with that of the 10 wt%
45
(e)
C-H
C-H2 bending
C-H2 wagging
Transmittance / a.u.
(d)
C-H
C-H2 bending
(c)
C-H
C-H2 bending
(b)
(a)
C-H2 bending
C-O-C
stretching
C-H2 wagging
4000
3000
2000
1500
1000
Wavenumber / cm-1
Figure 2.19
IR spectra of (a) PEO and (b) – (e) PEO/Li-Si-MCM-41
nanocomposites with various weight percentages of PEO (0, 5, 10 and 40 wt%,
respectively).
400
46
Relative Intensity / a.u.
(f)
(e)
(d)
(c)
(b)
(a)
2
10
20
30
40
50
2θ / o
Figure 2.20
XRD patterns of PEO/Li-Si-MCM-41 nanocomposites with various
weight percentages of PEO [(a) – (f) for 0, 2, 5, 8, 10 and 40 wt%, respectively].
47
PEO loading material show that this commences some 50oC lower in the former.
This implies that the material that has been formed at higher loading of 40 wt% has a
much lower thermal stability than that formed at lower loading.
Comparison of the TGA results for the materials with different PEO loading
in Figure 2.21 shows that as the loading increases, the temperature at which the
decomposition of the PEO commences decreases, implying the presence of loosely
physisorbed polymer chains which are more loosely physisorbed bound at the higher
loading. The weight loss percentage in the TGA profile is directly related to the
amount of PEO present. Thus, if we compare the relative peak height of the PEO,
we can see an increase in the amount of the more weakly bond with increasing
loading.
Weight Loss / %
100
(b)
80
60
(a)
40
20
0
200
400
600
800
1000
Temperature / oC
Figure 2.21
TGA thermograms of PEO/Li-Si-MCM-41 nanocomposites for (a)
10 and (b) 40 wt% PEO.
48
2.7.2.1 Conductivity of PEO/Li-Si-MCM-41 Nanocomposites
Table 2.5 shows the conductivity of PEO-Li-Si-MCM-41 and PEO-Li-AlMCM-41 nanocomposites obtained by melt intercalation technique and PEO-Li-SiMCM-41 nanocomposites obtained by solution intercalation technique.
The
conductivity of the PNC prepared using the different methods are similar in the range
of 10-7 S/cm. This means that there is no significant improvement achieved by using
both synthesis approaches to conducting polymer nanocomposites.
conductivity
of PEO/Li-Si-MCM-41
nanocomposites
The low
obtained by solution
intercalation technique is probably hampered by the poor miscibility of PEO with SiMCM-41 since PEO is hydrophobic and Si-MCM-41 is hydrophilic. Li+ ions are
likely to prefer to be attached to the walls of Si-MCM-41 because of its
hydrophilicity.
Since the mobility of Li+ ions is closely associated with the
segmental motion of PEO chain, the miscibility of PEO and Si-MCM-41 is very
crucial. In order to yield a nanocomposite with improved miscibility and more
enhanced conductivity, a hydrophobic Si-MCM-41 is required. One of the strategies
is
to
functionalize
the
hydrophilic
silanol
group
of
Si-MCM-41
with
trimethylchlorosilane (TMCS).
2.7.3 PEO/Li-TMCS/Si-MCM-41 Nanocomposites Prepared by Solution
Intercalation Technique
PEO/Li-TMCS/Si-MCM-41 nanocomposites were prepared by using the
same technique as PEO/Li-Si-MCM-41 nanocomposites which is solution
intercalation technique. Si-MCM-41 was functionalized with TMCS in order to
increase the hydrophobicity of Si-MCM-41 and to improve miscibility between PEO
and Si-MCM-41.
PEO/Li-TMCS/Si-MCM-41 nanocomposites were synthesized
with 0, 2, 5, 8 and 40 wt% of PEO content.
49
Table 2.5: Conductivity of PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41 nanocomposites obtained by melt intercalation technique and PEO/Li-
Si-MCM-41 nanocomposites obtained by solution intercalation technique.
Type of nanocomposites
PEO/Li-Si-MCM-41 and
PEO/Li-Al-MCM-41
PEO/Li-Si-MCM-41
a
b
The conductivity is measured in triplicate.
Purely siliceous MCM-41 (Si-MCM-41).
PEO content / wt%
SiO2/Al2O3 ratio
Log conductivity / S cm-1 a
10
∞b
1.6 x 10-7 ± 3.3 x 10-9
10
100
1.8 x 10-7 ± 2.0 x 10-8
10
60
1.4 x 10-7 ± 3.2 x 10-8
10
10
1.5 x 10-7 ± 2.5 x 10-8
0
∞b
1.5 x 10-7 ± 1.6 x 10-8
2
∞b
1.5 x 10-7 ± 1.2 x 10-8
5
∞b
1.5 x 10-7 ± 8.0 x 10-9
8
∞b
1.5 x 10-7 ± 7.0 x 10-9
10
∞b
1.5 x 10-7 ± 10.0 x 10-9
40
∞b
1.5 x 10-7 ± 3.0 x 10-8
50
2.7.3.1 Surface Silylation of Si-MCM-41 with TMCS, TMCS/Si-MCM-41
Figure 2.22 shows the IR spectra of functionalized Si-MCM-41 with TMCS
(TMCS/Si-MCM-41) and Si-MCM-41.
The IR spectrum of TMCS/Si-MCM-41
shows the main vibrations peaks corresponding to Si-MCM-41 at 1200-1000 cm-1,
980 cm-1, 810 cm-1 and 460 cm-1. A broad peak at around 810 cm-1 is attributed to the
symmetrical Si-O-Si stretching vibration while the peak at 980 cm-1 is assigned to
symmetric stretching vibration of Si-OH groups. Three weak peaks at region 2850 to
2970 cm-1 of TMCS/Si-MCM-41 are attributed to the attached C-H groups from
TMCS on the silanol groups on Si-MCM-41 surface. This suggests that the SiMCM-41 is successfully modified with TMCS.
Figure 2.23 shows that XRD pattern of TMCS/Si-MCM-41 which is similar
to parent Si-MCM-41 suggesting that structure of Si-MCM-41 remains intact after
functionalization with TMCS. However, a decrease in intensity of the (100), (110)
and (200) peaks was observed in the XRD patterns of TMCS/Si-MCM-41 indicating
a significant reduction in the long order structure of Si-MCM-41 after modification.
Figure 2.24 shows the
13
C/CP MAS NMR spectrum of TMCS/Si-MCM-41
which contains single and sharp peak centred at 2 ppm. This peak represents the C
atoms of the methyl groups in TMCS, demonstrating that TMCS groups are adhered
to the surface of Si-MCM-41. The main sharp signal might be due to the similar
environments of the C atoms in the methyl groups of TMCS. This interpretation is
further supported by the FTIR investigation which suggests also the presence of
TMCS in the TMCS/Si-MCM-41 sample.
Figure 2.25 shows the TGA thermograms of TMCS/Si-MCM-41 and calcined
Si-MCM-41. The thermograms show a one step thermal degradation pattern of SiMCM-41 and TMCS/Si-MCM-41. The initial degradation at around 30oC for SiMCM-41 is due to the removal of water. The higher percentage of weight loss of
TMCS/Si-MCM-41 as compared to Si-MCM-41 is due to the removal of both water
and TMCS. The weight losses of Si-MCM-41 and TMCS/Si-MCM-41 are ca. 10
wt% and ca. 20 wt% respectively. Hence, the amount of TMCS in Si-MCM-41 after
silylation with TMCS is modification is ca. 10 wt%.
51
TMCS/Si-MCM-41
Transmittance / a.u.
C-H
vibration
Si-MCM-41
4000
3000
2000
1500
1000
Wavenumber / cm-1
Figure 2.22
IR spectra of functionalized Si-MCM-41 with TMCS
(TMCS/Si-MCM-41) and Si-MCM-41.
400
Relative Intensity / a.u.
52
Si-MCM-41
TMCS/Si-MCM-41
2
10
20
2θ /
Figure 2.23
30
o
XRD patterns of Si-MCM-41 and Si-MCM-41 functionalized with
TMCS (TMCS/Si-MCM-41).
40
53
50
Figure 2.24
13
0
ppm
C/CP MAS NMR spectrum of TMCS/Si-MCM-41.
100
Si-MC M-41
TMCS/Si-MC M-41
Weight Loss / %
80
60
40
20
0
100
200
300
400
500
o
Temperature / C
Figure 2.25
TGA thermograms of Si-MCM-41 and TMCS/Si-MCM-41
54
2.7.3.2 PEO/Li-TMCS/Si-MCM-41 Nanocomposites
The IR spectra of PEO and PEO/Li-TMCS/Si-MCM-41 nanocomposites with
PEO content of 0, 5, 10 and 40 wt%, are shown in Figure 2.26.
In PEO/Li-
TMCS/Si-MCM-41 nanocomposites, peaks at 1500 to 400 cm-1 are similar to that of
the parent Si-MCM-41. Two peaks in the region from 1500 to 1300 cm-1 which
compared to CH2 wagging and bending modes of PEO were observed only when the
PEO content is 40 wt%. These peaks are not observed in the spectra of the
nanocomposites containing 0 to 10 wt% PEO due to low amounts of PEO in the
samples. The most significant observation is the appearance of a new peak at 1660
cm-1 corresponding to C-O stretching of 40 wt% PEO loading [36]. This peak was
not observed in the spectra of PEO-Li-Si-MCM-41 and PEO-Li-Al-MCM-41
nanocomposites which have been prepared by melt intercalation technique and the
PEO-Li-Si-MCM-41 nanocomposites obtained by solution intercalation technique.
Since the internal surface area of MCM-41 amounts to approximately 900
2 -1
m g which is related to more than 90% of the total surface area, homogeneously
dispersed PEO can be situated at the internal surface and therefore has to be
incorporated inside the mesopores. Theoretically, the surface area of MCM-41 is
sufficiently large to accommodate a homogeneous dispersion of PEO at loadings as
high as 10 wt% PEO (Appendix B). In view of the fact that the proposed amount of
PEO is 40 wt%, one should expect that the excess amount of PEO could be dispersed
on the external surface of MCM-41. This argument is supported by the SEM (Fig.
2.27) which shows that the surface morphology of MCM-41 with 40 wt% of PEO is
rougher than that of purely siliceous MCM-41 and the MCM-41 and PEO phases
separated due to excess PEO.
It is suggested that interfacial interactions between PEO chains and the SiMCM-41 walls in PEO/Li-TMCS/Si-MCM-41 nanocomposites occur. However, at
lower than 40 wt% PEO, the C-O peak was also not observed due to very weak or no
interaction between PEO and TMCS/Si-MCM-41.
55
(e)
C-H2 bending
C-H2 wagging
C-H
Si-O-Si
stretching
C-H2 twisting
(d)
C-H
Transmittance / a.u.
C-H2 twisting
Si-O-Si stretching
(c)
C-H
C-H2 twisting
C-H2 twisting
C-H
Si-O-Si stretching
(b)
Si-O-Si stretching
(a)
C-H2 bending
C-H2 wagging
4000
3000
2000
1500
C-O-C
stretching
1000
400
Wavenumber / cm-1
Figure 2.26
IR spectra of (a) pure PEO and (b) – (e) PEO/Li-TMCS/Si-MCM-41
nanocomposites with various weight percentages of PEO 0, 5, 10 and 40 wt%,
respectively.
56
(a)
(b)
Figure 2.27
Surface morphology of (a) Si-MCM-41 and (b) PEO/Li-TMCS/
Si-MCM-41 with 40 wt% of PEO.
Figure 2.28 shows the XRD patterns of PEO/Li-TMCS/Si-MCM-41
nanocomposites containing 0, 2, 5, 8, 10 and 40 wt% PEO. XRD patterns of PEO/LiTMCS/Si-MCM-41 nanocomposites are similar to that of the parent Si-MCM-41.
The (100) peak is sharp and intense, indicating the long range integrity of Si-MCM41 structure is maintained. A slight shift of the (100) peak of Si-MCM-41 towards
higher 2θ angles was observed when the PEO content was increased to 40 wt%. This
observation is in agreement with that reported previously which indicated with a
higher PEO content, intercalation or penetration of PEO was found to occur inside
the MCM-41 channels [16].
57
(f)
Relative Intensity / a.u.
(e)
(d)
(c)
(b)
(a)
2
10
20
30
40
50
2θ / o
Figure 2.28
XRD patterns of PEO/Li-TMCS/Si-MCM-41 nanocomposites with
various weight percentages of PEO [(a) – (f) for 0, 2, 5, 8, 10 and 40 wt%,
respectively].
58
Figure 2.29 shows the TGA profiles of PEO/Li-TMCS/Si-MCM-41
nanocomposites containing 0, 10 and 40 wt% PEO measured in nitrogen. At 0 wt%
PEO, the nanocomposite shows a single weight loss pattern. Below 100oC, the sharp
weight loss occurs due to loss of TMCS and moisture. The very gradual degradation
rate observed at temperatures over the range 100oC-300oC for the nanocomposites
with 10 wt% PEO is likely due to degradation of PEO. The PEO/Li-TMCS/SiMCM-41 nanocomposite with 40 wt% PEO shows two stages of thermal degradation
which can be explained as follows: The first, degradation below 200oC is due to
removal of both physisorbed water and TMCS. Increased hydrophobicity of SiMCM-41 after silylation with TMCS and the presence 40 wt% PEO prevented
adsorption of moisture in the PNC. The second, rather sharp weight loss from
200oC-400oC is due to decomposition of PEO.
100
Weight Loss / %
80
0 wt%
10 wt%
60
40 wt%
40
20
0
200
400
600
800
1000
o
Temperature / C
Figure 2.29
TGA profiles of PEO/Li-TMCS/Si-MCM-41 nanocomposites with 0,
10 and 40 wt% PEO measured in nitrogen.
59
2.7.3.3 Conductivity of PEO/Li-TMCS/Si-MCM-41 Nanocomposites
Table 2.6 shows the conductivity of PNC obtained by the different synthesis
routes; i.e. melt intercalation of Li-Si-MCM-41 and Li-Al-MCM-41, solution
intercalation of Si-MCM-41 and TMCS/Si-MCM-41. The results reveal that the
conductivity of the PNC obtained from all three different approaches as described in
Sections 2.5.3, 2.5.4 and 2.5.5, is in the same order of magnitude (10-7 S/cm). It is
interesting to note that Li-Si-MCM-41 and Li-Al-MCM-41 which do not contain
PEO exhibit conductivity similar to the PNC. This indicates that the conductivity of
the PEO-modified Li-Si-MCM-41 and Li-Al-MCM-41 are not improved by the
presence of the polymer electrolyte, PEO.
2.8
Conclusion
The PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41 were successfully
synthesized by melt and solution intercalation techniques. Before addition of
PEO, the Si-MCM-41 was also functionalized by TMCS in order to enhance
the hydrophobicity of Si-MCM-41. It is expected that the hydrophobic SiMCM-41 will increase the interfacial interaction of Si-MCM-41 with PEO,
and hence the conductivity. However, it is demonstrated that unmodified LiMCM-41 exhibit conductivity similar to PEO/Li-Al-MCM-41 and PEO/Li-Si-MCM41 prepared by melt and solution intercalation techniques. The 27Al, 7Li and 13C/CP
MAS NMR have been used to investigate the interfacial interactions between the
PEO and Li-Al-MCM-41. The results show that conductivity of Li-Si-MCM-41 and
Li-Al-MCM-41 are not enhanced in the presence of PEO. This result is supported by
the fact that the degree of the electrostatic interaction of Li+ ions with Al in the
framework of Al-MCM-41, as analyzed by solid-state NMR, is relatively high. This
interaction causes the retardation of the mobility of Li+ ions in the PNC. It is
concluded that the interaction occur in the nanocomposites is insufficient to improve
conductivity of the nanocomposites.
60
Table 2.6: Conductivity of melt intercalation of PEO/Li-Si-MCM-41 and PEO/Li-Al-MCM-41, solution intercalation of
PEO/Li-Si-MCM-41 and solution intercalation of PEO/Li-TMCS/Si-MCM-41 nanocomposites.
Type of nanocomposites
PEO/Li-Si-MCM-41 and
PEO/Li-Al-MCM-41
PEO/Li-Si-MCM-41
PEO/Li-TMCS/Si-MCM-41
a
b
The conductivity is measured in triplicate.
Purely siliceous MCM-41 (Si-MCM-41).
PEO content / wt%
SiO2/Al2O3 ratio
Log conductivity / S cm-1 a
10
∞b
1.6 x 10-7 ± 3.3 x 10-9
10
100
1.8 x 10-7 ± 2.0 x 10-8
10
60
1.4 x 10-7 ± 3.3 x 10-8
10
10
1.5 x 10-7 ± 2.5 x 10-8
0
∞b
1.5 x 10-7 ± 1.6 x 10-8
2
∞b
1.5 x 10-7 ± 1.2 x 10-8
5
∞b
1.5 x 10-7 ± 7.9 x 10-9
8
∞b
1.5 x 10-7 ± 7.5 x 10-9
10
∞b
1.5 x 10-7 ± 10.0 x 10-9
40
∞b
1.5 x 10-7 ± 3.0 x 10-8
0
∞b
1.6 x 10-7 ± 1.1 x 10-8
2
∞b
1.7 x 10-7 ± 2.8 x 10-9
5
∞b
1.5 x 10-7 ± 8.1 x 10-9
8
∞b
1.4 x 10-7 ± 1.8 x 10-9
10
∞b
1.5 x 10-7 ± 5.4 x 10-9
40
∞b
2.1 x 10-7 ± 3.1 x 10-8
61
CHAPTER 3
PANI/MCM-41 NANOCOMPOSITES
3.1
Introduction
In Chapter 2, Li+-PEO polymer electrolyte has been combined with Si-MCM41 and Al-MCM-41 to produce conducting polymer nanocomposites (PNC). It was
found that the nanocomposites, exhibit low conductivity. One of the reasons is the
Li+-PEO system has low conductivity because the Li+ ions in the system have low
ionic mobility. Therefore, it was decided to pursue with another polymer system
with high electrical conductivity. One of the promising candidates is a conducting
polymer such as polyaniline (PANI).
The conducting polymers (CPs) have intrinsic conductivity which generally
comprised simply of C, H and simple heteroatom such as N and S with π-conjugated
bond [37]. In 1967, conducting polymers such as pyrrole, thiophene and furan were
characterized and the electrical conductivity of these polymers were noted [37,38].
Polyaniline (PANI) is one of the materials studied intensively due to its unique
properties such as high electrical conductivity and good environmental stability in
doped and neutral states.
62
3.2
Polyaniline (PANI)
Basically polyanilines have four structures; pernigraniline base (PN),
emeraldine base (EB), leucomeraldine base (LEB) and emeraldine salt (ES) as shown
in Figure 3.1 [39]. However, only emeraldine salt shows electrical conductivity.
Electrical properties of PANI can be reversibly controlled by charge-transfer doping
and protonation. Polyaniline is environmentally stable and inert. It has a wide range
of potential technological applications including storage batteries, electrochromic
devices, light emitting diodes, corrosion inhibitor and a variety of sensor including
chemical [40]. It is currently used in cell phones and calculators, and other LCD
technology. However, as with other conducting polymer, it is not readily processable
in non toxic solvents due to its low solubility and the fact that the materials are
normally not melt processable. A number of attempts for enhancement of PANI
processability such as substitution of an aromatic ring of PANI with -CH3, -OCH3,
-SO3 or dodecylsulfate (DS) leads to higher solubility in organic solvents and even
water.
PANI has been combined with inorganic materials such as mica-type silica
[40], montmorillonite [41], zeolites and mesoporous molecular sieves, MCM-41
[42,43,44,45]. These PANI/inorganic nanocomposites have also been proven to
possess a variety of unique properties such as mechanical, electrical and structure
properties because of the synergistic effect owing to the intimate mixing between
inorganic and organic components at a molecular level.
3.3
Polyaniline Nanocomposites
Bein and co-workers [46,47] demonstrated the encapsulation of PANI doped
HCl (PANI.HCl) in mesoporous Si-MCM-41.
The PANI.HCl/Si-MCM-41
nanocomposite was reported to have relatively lower conductivity compared to
PANI.HCl. It has been demonstrated that the PANI doped DS (PANI.DS) has higher
conductivity than the PANI.HCl [48].
63
NH
N
N
NH
Pernigraniline base
NH
+
NH2
Cl
NH
+
NH2
Cl
Emeraldine salt
NH
NH
NH
NH
N
N
Emeraldine base
N
NH
Leucomeraldine base
Figure 3.1
[39].
Structure of oxidation state and acid base behaviour of polyanilines
64
In the first approach of this research, it is highly desirable to encapsulate
PANI.DS in Si-MCM-41 in order to obtain PNC with high conductivity. In order to
encapsulate the polymer inside the pores of Si-MCM-41, the miscibility between
hydrophilic Si-MCM-41 and hydrophobic PANI is very crucial. Si-MCM-41 was
chemically modified by functionalization with mercaptopropyltrimethoxysilane
(MPTS) to create sulfonic acid which will increase interactions between PANI and
Si-MCM-41.
3.4
Characterization Techniques
Materials have been characterized by using Fourier transform infrared
(FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), MAS NMR
and UV/Vis spectroscopy.
Conductivity of polyaniline and its composites was
measured by a four point probe method. The experimental procedures of FTIR,
XRD, TGA and NMR have been described in Chapter 2.
3.4.1 UV/Vis Spectroscopy
UV/Vis spectroscopy is designed for measuring the emission or the
absorption of radiant energy from substances.
Basic components of a UV/Vis
spectrophotometer must contain collimating mirror, lamp, prism, slit, photo detector,
amplifier and meter [29]. All spectrometers include some way of discriminating
between different radiation frequencies by dispersion of the radiation with a prism or
grating into a spectrum of wavelengths. In the visible region every colour is observe
violet to red in a continuous rainbow. The dispersed radiation is swept past a slit
until the desired emission line or band of colour falls on the slit opening and reach
the sample. The slit, often adjustable to allow any bandwidth to be chosen, blocks
off all but a narrow band of radiation.
65
The sample absorbs portion of the light; the reminder is transmitted through
the sample and strikes a detector where it is changed into an extremely small
electrical signal. The signal is then sent to an amplifier. By greatly increasing the
strength of the minute signal from the detector, the amplifier eliminates the need for
delicate parts, permitting a rugged meter to indicate amount of light passing through
the sample.
By making a series of such measurements and using different
wavelengths of light, the analyst can construct a curve showing the exact location
and degree of the absorption of the sample over a wide range of wavelength the
unmistakable “finger print” of the sample.
Experimental procedure:
The UV/Vis spectra of PANI.DS and PANI/Si-MCM-41-SO3H composite
were recorded using UV/VIS/NIR Spectrometer Jasco V-570.
PANI and its
composites were dissolved in methanol in 0.5 cm quartz cell. The measuring mode
of UV/Vis measurement is absorption and the wavelength range is from 200 to 1500
nm.
3.4.2 Four Point Probe for Conductivity Measurement
Conductivity measurement for the conducting polymer, polyaniline in this
research is based on the four point probe method. The four-point probe technique
was originally developed by Wenner in 1916 to measure the earth’s resistivity [49].
In geophysics it is referred to as Wenner’s method. In 1954 Valdes adopted the
technique for semiconductor wafer resistivity measurements. The technique has also
been applied to characterize electrolytes and to analyze gases.
The four point probe technique has become the most common methods for
measuring resistivity. The classic arrangement is to have four needle-like electrodes
in a linear arrangement with a current injected into the material via the outer two
electrodes. The resultant electric potential distribution is measured via the two inner
electrodes.
By using separate electrodes for the current injection and for the
66
determination of the electric potential, the contact resistance between the metal
electrodes and the material will not show up in the measured results [50]. Because
the contact resistance can be large and can strongly depend on the condition and
materials of the electrodes, it is easier to interpret the data measured by the four-point
probe technique than results gathered by two-point probe techniques. The technique
has also been applied to characterize electrolytes and to analyze gases. Today the
four point probe technique is widely used in the semiconductor industry to monitor
the production process.
Electrical measurements are done on test structures to
provide information on the various process steps.
For example, resistivity
measurements on doped semiconductor structures provide information on the active
charge carrier concentration and the mobility and are used as feedback to the doping
process. Figure 3.2 shows four point probe measurement technique.
Experimental procedure:
Thin film of acid doped PANI and its composites were prepared by using
solvent casting technique. Conductivity measurement of the thin film was measured
by Loresta HP (Mitsubishi Chemical) by standard four point probe technique at room
temperature, 100oC, 150oC and 200oC and measurement has been done every 15
minutes for 1 hour in order to study the thermal stability of conductivity of PANI/SiMCM-41 nanocomposites.
Graph of conductivity versus time at constant
temperature was plotted to see the trend in conductivity.
Thermal stability of
conductivity study has not been done for PEO/MCM-41 nanocomposites because of
the low conductivity of the nanocomposites.
Figure 3.2
Four point probe measurement technique.
67
3.5
Experimental
3.5.1 Synthesis of PANI.DS/Si-MCM-41 Nanocomposites
A typical synthesis for PANI.DS/Si-MCM-41 is as follows. Powder sample
of Si-MCM-41 was dried in an oven at 120oC overnight. Aniline hydrochloric acid
salt (aniline.HCl) (assay 99.5%, Kanto chemicals) dissolved in 1 N HCl (50 ml) was
mixed with Si-MCM-41 and stirred for 3 hours (mixture A). In another roundbottom flask, sodium dodecylsulfate (SDS) (assay 95%, Kanto chemical) was
dissolved in 125 ml 1 N HCl and heated at 90oC for 45 minutes (mixture B). After 3
hours, mixture A was heated at 90oC for 4-5 minutes to increase the temperature and
was added to the heated mixture B and stirred for 10 minutes and then cooled to 0oC
for 30 minutes under stirring. After 30 minutes, ammonium peroxydisulfate (APS)
(assay 97%, Kanto chemical) was dissolved in 50 ml 1 N HCl and introduced to the
mixture dropwise for 1-2 hours under stirring for 24 hours at 0oC. Methanol (50 ml)
was then added to the mixture and stirred for 30 minutes and then filtered under
vacuum. Thin films of PANI.DS/Si-MCM-41 nanocomposites have been prepared
by casting technique on a silica glass. The compositions of the materials used in the
composites are shown in Table 3.1.
Table 3.1: Composition of PANI.DS/Si-MCM-41 nanocomposites.
Samples code
Aniline.HCl
/ mmol g-1
SDS /
mmol g-1
APS
/ mmol g-1
Si-MCM-41 :
aniline.HCl /
wt %
PANI.DS
20/2.592
20/5.768
24/5.477
0
PANI.DS/Si-MCM-41-S50
20/2.592
20/5.768
24/5.477
50
PANI.DS/Si-MCM-41-S77
40/5.184
40/11.535
48/10.954
77
PANI.DS/Si-MCM-41-S100
20/2.592
20/5.768
24/5.477
100
68
3.5.2 Synthesis of PANI/Si-MCM-41-SO3H Nanocomposites
PANI/Si-MCM-41-SO3H was synthesized according to the procedure
described for PANI.DS/Si-MCM-41 but without the SDS.
The molar ratio of
aniline.HCl to APS is 1: 2. A sample of 1.5 g of Si-MCM-41-SO3H was dried in an
oven at 120oC for 24 hours.
Aniline.HCl (assay 99.5%, Kanto chemical) was
dissolved in 1 N HCl (37.2 ml) was slowly added to the dried Si-MCM-41-SO3H
under stirring and the suspension was stirred for 3 hours. The mixture was then
heated at 90oC for 45 minutes and subsequently cooled to 0oC for 30 minutes under
stirring. After 30 minutes, APS (assay 97%, Kanto chemical) was added dropwise to
the solution during a 1-2 hours period and then left stirring for 24 hours. Then, 100
ml methanol was added into the PANI/Si-MCM-41-SO3H and stirred for 30 minutes
and filtered in vacuum. The composition of PANI.DS and PANI/Si-MCM-41-SO3H
nanocomposites are shown in Table 3.2.
Table 3.2: Composition of PANI.DS and PANI/Si-MCM-41-SO3H
Aniline.HCl
/ mmolg-1
APS / mmolg-1
Si-MCM-41SO3H / g
PANI.DS
20/2.5918
24/5.4768
-
PANI/Si-MCM-41-SO3H
15/1.94385
18/4.3257
1.5
Samples code
In the synthesis of PANI/Si-MCM-41-SO3H, Si-MCM-41 was first modified
with mercaptopropyltrimethoxysilane (MPTS) (assay 98%, Kanto chemical) based
on the procedure reported previously [51], except for the dehydration of Si-MCM-41
at 393 K. About 3.5 g of calcined Si-MCM-41 was evacuated overnight at 393 K,
and then added to a solution of 7.4 g of MPTS (assay 98%, Kanto chemical) in 300
ml toluene (assay 98%, Kanto chemical).
Toluene was dried over zeolite 4A
molecular sieve before use. After 4 hours of refluxing, the powder was collected and
subjected to the soxhlet extraction for purification. The MPTS (assay 98%, Kanto
chemical) modified materials were oxidized with H2O2 in a methanol–water mixture.
Typically, 2.04 g of aqueous solution 35% H2O2 dissolved in three parts of methanol
69
was used per gram of the material. After 24 hours, the suspension was filtered, and
washed with distilled water and ethanol. The wet material was resuspended (1 wt%)
in sulphuric acid (H2SO4; 0.1 M) for another 4 hours. Finally, the materials were
extensively rinsed with H2O, dried at 333 K, and stored in desiccators. These acidactivated materials are denoted with the suffix –SO3H.
13
C/CP MAS NMR of the
sample was recorded to prove that the procedure left no –SH or –S-S groups on the
surface; the only signals are those of heterogenized -(CH2) 3SO3H.
3.6
Results and Discussion
3.6.1 PANI.DS/Si-MCM-41 Nanocomposites
Figure 3.3 shows the FTIR spectra of PANI.DS and PANI.DS/Si-MCM-41
nanocomposites with Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt%. The
appearance of peaks around 1560, 1467, 1296, and 1237 cm-1 suggested that all the
polyaniline compounds have the emeraldine salt structure. The 1237 and 1296 cm-1
peaks characteristic of the conducting polaron structure C-N+ of doped PANI
associated with the oxidation or protonation states of PANI, confirms the interactions
of PANI.DS and Si-MCM-41 [52,53]. Bands near 1467 and 1560 cm-1 are assigned
to C=C stretching of benzenoid and quinoid rings in doped PANI, respectively [54].
According to M.G. Han et al. [55] the peak at 1120 cm-1 can be assigned to in-planebending vibration of C-H (mode of N=Q=N, where Q=N+H-B and B-N+H-B, Q =
quinoid and B = benzenoid) which occurs during protonation. The peaks near 3000
cm-1 are derived from C-H stretching vibration of DS alkyl groups. The major peak
around 1200 cm-1 was assigned to the Si-O-Si asymmetric vibration of Si-MCM-41.
As predicted, the intensity of this peak increases with the increase of Si-MCM-41 in
the nanocomposites. In addition, no change was observed in the peaks derived from
PANI.DS after the addition of Si-MCM-41.
Figure 3.4 shows the X-ray diffraction patterns of the nanocomposites with
various Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt% in the range 1.5° to
60° 2θ. All the patterns were similar to each other indicating that the samples were
70
100 wt%
77 wt%
Transmittance / a.u.
50 wt%
PANi.DS
C-H(op)
C-N
C-N+
N-H
4000
C-N stretching +C-C
or
C-N+ stretching +C-C
C-H
2000
1000
Wavenumber / cm-1
Figure 3.3
IR spectra of PANI.DS and PANI.DS/Si-MCM-41 nanocomposites
with Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt%.
400
Relative Intensity / a.u.
71
100 wt%
77 wt%
50 wt%
2
12
22
32
42
52
2θ / o
Figure 3.4
X-ray diffraction patterns of the PANI.DS/Si-MCM-41
nanocomposites with Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt%.
isomorphous, but the relative intensities of the peaks were different. The broad peak
between at 20° and 26° is considered to depend on PANI.DS, and these peaks are
identical with that of the PANI.DS [56]. The intensity of the broad peak decreased
with the increase in composition ratio of Si-MCM-41. On the other hand, the
intensity of the peak around 2θ = 2° assigned to the (100) reflection of Si-MCM-41
increases with the increase wt% of Si-MCM-41 relative to PANI. In these cases, no
reflection peaks indexed to the (110) and (200) planes of Si-MCM-41, were detected
due to overlap with the broad peak of PANI. These results clearly indicate that these
samples comprise of PANI and Si-MCM-41 components. In addition, based on the
relative intensity of the (100) peak of Si-MCM-41, the amount of PANI was found to
increase with increasing amount of aniline.HCl monomer in the sample.
UV/Vis absorption spectra of PANI.DS and PANI.DS/MCM-41 composites
dispersed in ethanol were shown in Figure 3.5.
These samples show three
characteristic absorptions at 320-400, 400-450 and 740-1000 nm wavelength. The
first two bands have two local maxima at 400 and 450 nm, respectively. The first
72
absorption band is assigned to π-π* electron transition within benzenoid segments.
The second and third absorption bands, which have the local maxima around 420 and
785 nm, should be related to doping level and formation of polaron, respectively
[57,58,59]. In addition, the peak intensity over 1400 nm corresponding to π-π*
transition of benzenoid segments, which is related to the number of the repeating unit
of monomer in PANI, decreased after addition of Si-MCM-41.
However, the
absorption profile of each composite indicated that the doping level of PANI in these
nanocomposites was relatively higher than that of common conductive PANI doped
with HCl, because the spectra show a free carrier tail extending into the near-infrared
region typical for the –(OSO3-)PANI+. Thus, these composites are suggested to have
relatively long conjugated PANI emeraldine salt structure doped with DS.
Absorbance / a.u.
PANi.DS
50 wt%
77 wt%
100 wt%
300 400
600
800
1000
1200
1400
Wavelength / nm
Figure 3.5
UV/Vis absorption spectra of PANI.DS and PANI.DS/MCM-41
nanocomposites with Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt%.
73
Figure 3.6 shows the TGA profiles of PANI.DS and PANI.DS/MCM-41
nanocomposites with various Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt%,
measured between 25 and 600°C. As the result, these composites indicated similar
thermal degradation behaviour to common conductive PANI derivative in which
three weight loss steps were observed [54]. Thus, the first weight loss of 1-2%
observed up to 110°C should be due to loss of residual water from the polymer. The
second stage observed within the temperature range of 110-300°C should be related
to removal of DS dopant molecules from the polymer structure. The weight loss
observed between 450 and 600°C after the removal of the dopant molecules should
correspond to the degradation of the polymer chain [60,61,62]. In addition, the
nanocomposite with 50 wt% of Si-MCM-41/aniline.HCl ratio showed relatively
large weight loss behaviour over 200°C compared to those of nanocomposites with
77 and 100 wt% of Si-MCM-41/aniline.HCl ratios where the TGA profiles of the
latter are similar within the present measurement range. The results should be
considered to depend on the nanocomposite ratio of organic to inorganic
components. The thermograms also show that the higher the amount of the organic
components in the nanocomposites, the higher is the weight loss observed.
Weight loss / %
100
80
60
40
100 wt%
77 wt%
20
50 wt%
PANi.DS
0
200
400
600
800
Temperature / oC
Figure 3.6
TGA thermograms of PANI.DS and PANI.DS/MCM-41
nanocomposites with Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt%.
1000
74
3.6.1.1 Conductivity of PANI.DS/Si-MCM-41 Nanocomposites
Figure 3.7 depicts the conductivities (S/cm) of the PANI.DS and
PANI.DS/Si-MCM-41 nanocomposites with various Si-MCM-41/aniline.HCl ratios
of 50, 77 and 100 wt% at room temperature. As expected based on the UV/Vis
spectra, the composites presented lower conductivity than PANI.DS at room
temperature, in which the conductivity of each composite decreases by two orders of
magnitude over the conductivity of the constituent components (PANI.DS 1.28 S/cm
and Si-MCM-41 1.59x10-7 S/cm).
The relationship between conductivity and curing time at 100°C of PANI.DS
and PANI.DS/Si-MCM-41 nanocomposites with various Si-MCM-41/aniline.HCl
ratios 50, 77 and 100 wt% was investigated every 15 minutes for 1 hour. This study
is important in determining the thermal stability of conductivity of the
nanocomposites. The conductivity of the cure sample compared to PANI.DS is
plotted against the duration of heating. Figure 3.8 shows the conductivity-curing
time curve. In all cases the conductivity substantially decreased particularly in the
first 15 minute interval and beyond the initial stage, the conductivity remains almost
the same.
In spite of prolonged heating up to 1 hour, the reduction rates of
conductivity of the nanocomposites are relatively low compared to PANI.DS. PANI
doped DS clearly shows a marked degradation upon heating at 100oC. The results
prompted us to investigate further the conductivity at a higher curing temperature.
The conductivity of the nanocomposites which have Si-MCM-41/aniline.HCl
ratio of 50 wt% compared to PANI.DS is investigated based on the thermal stability
of the sample at 150°C from the TGA results (see section 3.6.1). As shown in Figure
3.9, the conductivities in both samples are sequentially decreased. However, the
reduction rate of the conductivity of PANI.DS is four times larger compared to
PANI.DS/Si-MCM-41 nanocomposites (Si-MCM-41/aniline.HCl ratios 50 wt%).
Based on these results, the thermal stability of conductivity of PANI.DS is enhanced
with the addition of the Si-MCM-41.
75
Log Conductivity / S cm-1
101
100
10-1
0
20
40
60
80
100
Si-MCM-41 : aniline.HCl / wt%
Figure 3.7
Conductivity of the PANI.DS/Si-MCM-41 nanocomposites at room
temperature.
PANi.DS
50 wt%
77 wt%
100 wt%
Log Conductivity / S cm-1
100
10-1
0
20
40
60
Time / Min
Figure 3.8
Conductivity of PANI.DS and PANI.DS/Si-MCM-41 nanocomposites
with Si-MCM-41/aniline.HCl ratios of 50, 77 and 100 wt% at 100oC.
76
100
PANi.DS
Log Conductivity / S cm-1
50 wt%
10-1
10-2
10-3
0
20
40
60
Time / min
Figure 3.9
Conductivity of PANI.DS and PANI.DS/Si-MCM-41 nanocomposites
with Si-MCM-41/aniline.HCl ratio of 50 wt% at 150oC.
3.6.2 PANI/Si-MCM-41-SO3H Nanocomposites
3.6.2.1 Functionalization of Si-MCM-41 with Sulfonic Acid
The IR spectrum of functionalized sulfonic acid of Si-MCM-41 is shown in
Figure 3.10. The absorption in the region between 3500 and 2700 cm-1 in the IR
spectrum can be assigned to hydrogen bonded propyl and SO3H groups. Peaks of –
SO3H in regions 1360 to 1000 cm-1 region cannot be observed due to overlap with
peaks of Si-MCM-41. The absence of bands of –SH at 2600 to 2550 cm-1 [50] in the
spectrum confirmed that only SO3H is present in the structure of Si-MCM-41 after
modification. For further confirmation of the sulfonic acid attached in the structure
of the Si-MCM-41, the Si-MCM-41-SO3H has been analyzed by using 13C/CP MAS
NMR spectrum shown in Figure 3.11. The NMR spectrum shows the major signals
at 54, 14 and -2 ppm which give strong evidence for the prevalence of (CH2)3SO3H
surface groups. The signals at 54 ppm stand for C3 and 14 ppm for C2 and -2 ppm
for C1.
Transmittance / %
77
S-H vibration
Hydrogen bond
2000
4000
1000
400
Wavenumber / cm-1
Figure 3.10
IR spectrum of Si-MCM-41 functionalized sulfonic acid,
Si-MCM-41-SO3H.
C2
C1
C3
160 140 120 100 80
Figure 3.11
13
60
40
20
0
ppm
C/CP MAS NMR spectra of Si-MCM-41 functionalized sulfonic
acid, Si-MCM-41-SO3H.
78
The proposed structure of the sulfonic acid functionalized Si-MCM-41 is
shown in Figure 3.12. TGA profiles of Si-MCM-41 and Si-MCM-41-SO3H are
shown in Figure 3.13. Generally, the TGA thermograms show two major steps of
weight loss for Si-MCM-41-SO3H and one step of weight loss for Si-MCM-41. The
first weight loss for both samples is due to the removal of water, while the second
weight loss is due to the removal of sulfonic acid in Si-MCM-41-SO3H.
3.6.2.2 Physical Properties of PANI.DS and PANI/Si-MCM-41-SO3H
Nanocomposites
Figure 3.14 shows the FTIR spectra of Si-MCM-41-SO3H, PANI.DS (PS)
and PANI/Si-MCM-41-SO3H (PMS). The major peaks of MCM-41 are around
1200-1000 cm-1 (asymmetric Si-O-Si stretching), 960 cm-1 (Si-OH stretching), 800
cm-1 (symmetric Si-O-Si stretching) and 460 cm-1 (Si-O-Si bending) which can be
clearly observed also for Si-MCM-41-SO3H. This indicates that the structure of SiMCM-41 remains unaltered after modification. Generally, all the peaks of PS are
present in the PMS nanocomposites but the intensity of these peaks is low because
the sulfonic acid content is only about 10 wt%.
Peaks in the 2900-3000 cm-1 region are assigned to C-H stretching vibration
of alkyl groups. The reduction in intensity of these peaks is due to the lower number
of alkyl groups in PMS compared to DS in PS. The peak corresponding plane
bending vibration of C-H (mode of N=Q=N, Q=N+H-B, and B-N+H-B, Q = quinoid,
B = benzenoid) which occurs during protonation can be observed at 1120 cm-1
[63,64].
Further evidence of the presence of polymer was confirmed by TGA analysis
(Figure 3.15). The content of sulfonic acid and PANI estimated from the gravimetric
analysis were ca. 10 % and 60% (w/w) respectively. The decomposition rate of the
polymer when combined with MCM-41 is found to be very different from the
decomposition rate of the bulk polymer.
79
C3
C2 C1
CH2CH2CH2 SO3H
Si
O
Figure 3.12
O O
The proposed structure of Si-MCM-41 functionalized sulfonic acid,
Si-MCM-41-SO3H.
100
Si-MCM-41
90
Weight Loss / %
80
Si-MCM-41-SO3H
70
60
50
40
30
20
10
0
200
400
600
800
Temperature / OC
Figure 3.13
TGA profiles of Si-MCM-41 and Si-MCM-41-SO3H.
1000
80
Transmittance / a.u.
Si-MCM-41-SO3H
PS
PMS
4000
2000
1000
400
Wavenumber / cm-1
Figure 3.14
IR spectra of Si-MCM-41-SO3H, PS = PANI.DS and PMS =
PANI/Si-MCM-41-SO3H.
Weight Loss / %
100
Si-MCM-41-SO3H
80
60
40
PMS
20
PS
0
200
400
600
800
1000
Temperature / oC
Figure 3.15
TGA thermograms of Si-MCM-41-SO3H, PS = PANI.DS and PMS =
PANI/Si-MCM-41-SO3H.
81
The bulk PANI emeraldine salt (PANI.DS) decomposes between 200 and 700
o
C, but the polymer composite decomposes slowly nanocomposite (PMS) and Si-
MCM-41-SO3H.from 300 to 600oC (Figure 3.15). This result implies that PANI
interacted strongly with the surface Si-MCM-41-SO3H, enhancing the thermal
stability of polyaniline [43].
The UV-Vis spectra of PANI.DS and PANI/Si-MCM-41-SO3H composites
are shown in Figure 3.16. These samples show three characteristic absorptions at
300 – 420, 420 – 450 and 740 - 1000 nm wavelength. The first absorption band is
assigned to π-π* electron transition within benzenoid segments. The second and
third absorption bands should be related to doping level and formation of polaron,
respectively [57,58,59]. From Figure 3.16, it can be seen that the characteristic
peaks of PANI.DS all appear in PANI/Si-MCM-41-SO3H composite. Although
three distinctive peaks do not shift obviously, two peaks at 400 and 450 nm almost
coalesce together into a peak. This implies that the presence of Si-MCM-41 has
some effect on the conjugated structure of the conducting polyaniline.
895
PANi.DS
Absorption / a.u.
400
450
PANi/Si-MCM41-SO3H
400
600
800
1000
1200
1400
Wavelength / nm
Figure 3.16
UV/Vis spectra of PANI.DS and PANI/Si-MCM-41-SO3H
nanocomposite.
82
In addition, the peak intensity over 1400 nm corresponding to π-π* transition
of benzenoid segments, which is related to the number of the repeating unit of
monomer in PANI, was decreased after addition of Si-MCM-41. These results
suggest that the PANI/Si-MCM-41-SO3H has relatively short conjugated PANI
emeraldine salt structure due to the polymerization of PANI is occurred in the
constrained space of the channels of Si-MCM-41.
Figure 3.17 shows 13C CP/MAS spectra of (a) Si-MCM-41-SO3H (b) PANI/SiMCM-41-SO3H. Spectrum of PANI/Si-MCM-41-SO3H composite shows a broad
peak of PANI at around 120 ppm was appeared [65], and the signals at 54 ppm, 14
ppm and -2 ppm of -(CH2)3SO3H were shifted towards a higher magnetic field (see
Figure 3.17) compared to Si-MCM-41-SO3H. The high field chemical NMR shift of
these signals can be explained by the interaction of the free electron pairs of the
nitrogen atoms of the PANI with a charged molecule on the surface of Si-MCM-41SO3H with PANI.
C2
C3
C1
(b)
(a)
160 140 120 100 80
Figure 3.17
SO3H.
13
60
40
20
0
ppm
C CP/MAS spectra of (a) Si-MCM-41-SO3H (b) PANI/Si-MCM-41-
83
This argument was supported by the fact that, from thermogravimetric analysis, there
is a shift to a higher temperature of the decomposition of PANI in PANI/Si-MCM41-SO3H compared to PANI.DS (Figure 3.15). On the basis of these results, a model
of the interaction of polyaniline with Si-MCM-41-SO3H in PANI/Si-MCM-41-SO3H
composite is proposed (see Figure 3.18).
+
NH
SO3H
Si
Figure 3.18
δ
+
O CH3
NH
-
NH2
SO3H
H
O
Si
δ
O H
+
O CH3
Si
The propose interaction between polyaniline and Si-MCM-41-SO3H
in PANI/Si-MCM-41-SO3H nanocomposite.
3.6.2.3 Conductivity of PANI.DS and PANI/Si-MCM-41-SO3H
Nanocomposites
Figure 3.19 illustrates the effect of curing temperature on the conductivity
of PANI.DS and PANI/Si-MCM-41-SO3H composite at 100, 150 and 200oC. At
room temperature, the conductivity of the PANI.DS and PANI/Si-MCM-41-SO3H
composites are 1.28 and 0.22 S cm-1, respectively. These values are very much
lower than the conductivity reported for pure PANI after being doped with HCl (12 S
cm-1) [65].
As seen in Figure 3.19, the increase in curing temperature reduces the
conductivity of PANI.DS. However, at 100oC, the conductivity of the PANI.DS and
PANI/Si-MCM-41-SO3H composites are steadily maintained with the increase of
time from 15 minutes to 1 hour. The increase of temperature to 150oC causes a
84
larger reduction rate of conductivity of PANI.DS than PANI/Si-MCM-41-SO3H
composite. At 200oC, PANI.DS started to decompose which was shown in the TGA
thermogram in Figure 3.16. This explains why the reduction rate of conductivity is
the highest for PANI.DS. In contrast, the reduction rate of conductivity of PANI/SiMCM-41-SO3H is low after the temperature was increased to 200oC. However, the
conductivity of the PANI/Si-MCM-41-SO3H became so low that after 45 minutes, it
could no longer be measured through the four-point probe method.
The data
presented in Figure 3.19 is sufficient to establish the high thermal stability of
PANI/Si-MCM-41-SO3H composite and consequently the desirability and efficacy
of this polymer-mesoporous silica system in high temperature applications.
101
100oC (PANI.DS)
100oC (PANI/Si-MCM-41-SO3H)
150oC (PANI.DS)
150oC (PANI/Si-MCM-41-SO3H)
200oC (PANI.DS)
200oC (PANI/Si-MCM-41-SO3H)
Log Conductivity / S cm-1
100
10-1
10-2
10-3
10-4
10-5
10-6
0
Figure 3.19
20
40
Time / Minutes
60
The conductivity of PANI.DS and PANI/Si-MCM-41-SO3H
nanocomposite at 100, 150 and 200oC versus time.
85
3.7 Conclusion
PANI/Si-MCM-41-SO3H composites were successfully synthesized by in situ
polymerization technique in the presence of aniline.HCl monomers as starting
material. It reveals that the long order integrity of Si-MCM-41 remains intact after
encapsulation of PANI.
FTIR spectra of PANI in PANI/Si-MCM-41-SO3H
composites show that they are in the emeraldine salt form. Composites show lower
conductivity compared to PANI.DS, they show a higher thermal stability of
conductivity than that of PANI.DS, because there is the interaction of the free
electron pairs of the nitrogen atoms of the PANI with a charged molecule on the
surface of Si-MCM-41-SO3H with PANI. As a global guide for future actions, this
work opens new perspectives for the use of PANI/Si-MCM-41 composite as a
conducting material at high temperature.
86
CHAPTER IV
CONCLUDING REMARKS
I n this thesis, the physicochemical and conducting properties of two types
of polymer nanocomposites (PNC), i.e. PEO/Li-MCM-41 and PANI/MCM-41 have
been investigated. The aim was to obtain a more detailed understanding of
how the combination of polymers with the mesoporous MCM-41 is related to
the conducting properties.
The results from the study have proven that the PNC possesses conducting
properties. It is revealed that the conductivity of PANI/MCM-41 (ca. 0.1-1 S cm-1)
is very much higher than those of PEO/Li-MCM-41 (ca. 10-7 S cm-1) since PANI is a
conducting polymer whereas PEO is a polymer electrolyte.
The combination of PEO and MCM-41 in the nanocomposites is
obtained when PEO and Li-MCM-41 or Li-Al-MCM-41 was combined by
several methods, including melt and solution intercalation techniques. I t was
expected
that
this
combination
would
increase
the
conductivity
by
intercalation of PEO inside the pores of MCM-41. However, it is demonstrated
that unmodified Li-MCM-41 exhibit conductivity similar to the PNC. The 7Li, 27Al
and
13
C/CP MAS NMR spectra have been used to investigate the interfacial
interactions between the PEO and Li-Al-MCM-41.
The results show that the conductivity of Li-MCM-41 and Li-Al-MCM-41 is
not enhanced in the presence of PEO. This result is supported by the fact that the
degree of the electrostatic interaction of Li+ ions with Al in the framework of Al-
87
MCM-41, as analyzed by solid-state NMR, is relatively high.
This causes the
+
retardation of the mobility of Li ions in the PNC. It can be concluded that the
interactions that occur in the nanocomposites are insufficient to improve conductivity
of the PEO/Li-MCM-41 nanocomposites.
PANI/MCM-41 nanocomposite was obtained by in situ polymerization
method. Before the polymerization, MCM-41 was functionalized with sulfonic acid.
It is revealed that although conductivity measurement shows that conductivity of
PANI was reduced after addition of MCM-41, its thermal stability of conductivity
was significantly enhanced. As a global guide for future actions, this work opens
new perspectives for the use of PANI/MCM-41 nanocomposite as a conducting
material at high temperature.
88
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96
APPENDIX A
Estimation of PEO used in PEO/Li-Si-MCM-41 and PEO/Li-TMCS/Si-MCM-41
nanocomposites.
Density of PEO = 0.15 kg/l = 0.15 g/cm3
Pore volume of MCM-41 = 0.7 cm3 g-1 (Adapted from reference [8])
1 g MCM-41 = 0.7 cm3 pore volume
The estimated amount of PEO required to fill the pores of 1 g MCM-41 is
= 0.15 g cm-3 x 0.7 cm3
= 0.105 g
So, the loading amount of PEO is ~10 wt% of MCM-41.
97
APPENDIX B
An example of the complex impedance plot for measurement of conductivity
of Li-Al-MCM-41 with SiO2/Al2O3 = 60.
800000
700000
600000
500000
Z”
400000
300000
200000
100000
0
0
200000
400000
Z'
600000
800000