Renaissance of the Plastic Age
Polymers for Electronics & Photonics
T.P.Radhakrishnan
School of Chemistry, University of Hyderabad
Hyderabad 500 046, India
tprsc@uohyd.ernet.in
http://chemistry.uohyd.ernet.in/~tpr/
This file is available at http://chemistry.uohyd.ernet.in/~ch521/
Materials and civilisation
Stone age (Before 5000 BC)
Copper age (5000 - 3000 BC)
Bronze age (3000 - 800 BC)
Iron age (800 BC - 40 AD)
Plastic age ?
Types of materials
Metals / Alloys
*
Ceramics
Polymers
Semiconductors
Composites
Biomaterials
Molecular materials
*Courtsey: W. D. Callister, Fundamentals of Materials Science and Engineering
Design of Molecular Materials
Elements / Compounds
Chemical /
Physical routes
Materials
Elements / Compounds
Chemical routes
Molecules
Chemical / Physical routes
Crystals
Nanostructures
Thin films
/ LB films
Polymers
Natural polymers
Synthetic polymers
Polyethylene
Polytetrafluoroethylene
(Teflon)
Phenol-formaldehyde
(Bakelite)
Polyhexamethylene adipamide
(Nylon 6,6)
Polyethyleneterephthalate
(PET)
Polycarbonate
Discovery of conducting polymers
1862
Lethby (College of London Hospital)
Oxidation of aniline in sulfuric acid
1970’s
Shirakawa (Japan)
Acetylene gas
HC
Ti(OBu)4 & Et3Al
Toluene
–78oC
copper-coloured film
cis-polyacetylene
CH
Ti(OBu)4 & Et3Al
Hexadecane
150oC
silvery film
trans-polyacetylene
Polyacetylene (PA)
n
n
Electrical conductivity (s)
cis PA
trans PA
For comparison
10-10 – 10-9 S cm-1
10-5 – 10-4 S cm-1
: s (copper) ~ 106 S cm-1
: s (teflon) ~ 10-15 S cm-1
Doping leads to enhanced
conductivity
n
Semiconductor
s ~ 10-5 S cm-1
- e-
+ e-
-
+
n
Metal
s ~ 104 S cm-1
n
Discoverers - Nobel Prize 2000
A. Heeger, A. McDiarmid, H. Shirakawa
(this photograph taken at the International Conference on
Synthetic Metals, 2000, was kindly provided by Prof. Heeger)
Polyacetylene - electronic structure
-electronic energy levels and electron occupation
(a)
(a) ethylene
(b) allyl radical
(c) butadiene
(b)
(c)
(d)
(d) regular trans-PA
(e) dimerised trans-PA
(e)
How does a conducting polymer work ?
Oxidative doping of polyacetylene by iodine
[CH]nx+ + xI3-
[CH]n + (3x/2) I2
+
.
I3 -
Polaron
and its delocalisation
+
.
I3 -
+
I3-
.
Excitations
Bipolaron
+
.
oxidation
+
+
Neutral Soliton
isomerisation
.
Positive Soliton
oxidation
+
Examples of conducting polymers
H
H
Polyaniline
(PANI)
Polypyrrole
(PPy)
Polyethylene
dioxythiophene
(PEDOT)
O
N
N
Polythiophene
(PT)
n
N
O
S
Polyparaphenylene
vinylene
(PPV)
N
N
n
S
Polyparaphenylene
(PPP)
n
n
Alkoxy-substituted
polyparaphenylene
vinylene
(MEH-PPV)
O
n
n
O
n
Electrical conductivities
Copper
Platinum
Bismuth
Graphite
10+6
10+4
10+2
100
Germanium
Silicon
Polyethylene
10-2
10-4
10-6
10-8
10-10
10-12
Diamond
10-14
10-16
Quartz
10-18 S cm-1
Conducting
Polymers
Synthesis of PANI
Cathode
Anode
(ITO plate)
Aniline +
dil. HCl
Instead of electrochemical oxidation, chemical oxidation may be
carried out : Aniline + acid + oxidising agent ((NH4)2S2O8)
Voltage (~ 0.3 - 0.5 V) applied
Result of electropolymerisation
The green coating on the ITO electrode is due to
the formation of emeraldine salt form of PANI
Polyaniline (PANI)
Leucoemeraldine
H
N
H
N
H
N
H
N
Colorless
(Insulator)
Emeraldine base
H
N
H
N
N
N
Blue
(Insulator)
Emeraldine salt
Pernigraniline
H
N
N
H
N
N
H+
N
X-
N
N
N
Green
(Conductor)
Purple
(Insulator)
Oxidation
Applications of conducting polymers
Polyaniline (PANI)
Transparent conducting electrodes
Electromagnetic shield
Corrosion inhibitor
‘Smart windows’ (electrochromism)
Polypyrrole (Ppy)
Radar-invisible screen coating
(microwave absorption)
Sensor (active layer)
Polythiophene (PT)
Field-effect transistor
Anti-static coating
Hole injecting electrode in OLED
Polyphenylenevinylene (PPV)
Active layer in OLED
Polypyrrole - conductivity switching
Enzyme Biosensor Using PPy
Glucose oxidase
-D-glucose + ½O2 + H2O  D-gluconic acid + H2O2
H2O2 + 2HCl + Ppy  2H2O + Ppy2+.2Cl-
PANI-PSS
PSSn-(100 kDa)
RT = 8.3x10-2 Scm-1
PSSn-(70 kDa)
RT = 3.6x10-2 Scm-1
*
n
*
PSSn-
-
SO3
Sensors
Typical example : Ammonia sensing by PANI-PSSM film
1.35
1.30
Resistance
change with
time
R/Ro
1.25
1.20
1.15
1.10
Ammonia in
1.05
Ammonia out
1.00
0
1000
2000
Time(sec)
3000
4000
Resistance change at 150 sec. for
different concentrations of ammonia
2.0
(R/Ro)150
1.8
1.6
1.4
1.2
0
50
100
150
200
Concentration of ammonia (ppm)
250
Electroluminescence
-
Metal electrode
Electric field
+
Organic thin film
Transparent
electrode (ITO)
Light
Principle of EL
eLUMO
LUMO
h+
HOMO
Cathode
HOMO
Anode
Light
Polymers for Organic Light
Emitting Diodes (OLED)
O
n
PPV
n
O
MEH-PPV
Commercial materials like Mn2+ in ZnS require 100V DC
PPV : requires 5 - 10V DC
runs even with AC
brightness ~40,000 cd/m2 ie. ~100 times brighter than a TV screen
Organic LED driven by organic transistor
D
S
Ca/Ag
MEH/PPV
Silica
Gold
P3HT
Silica
n+-Silicon
Aluminium
G
Electrochromic devices
Polymer
Polythiophene
Polypyrrole
Polyaniline
Undoped
Red
Yellow-green
Yellow
Doped
Blue
Blue-black
Green/Blue
Li anode
Polymer electrolyte
V
Conducting polymer
ITO electrode
Viewing side
On application of voltage
Li anode
Polymer electrolyte
V
Conducting polymer
ITO electrode
Viewing side
Conjugated polymers for
nonlinear optics
NLO materials interact with light
(C
C
Light changes the material properties
C
C
C
Changes the properties of the light
C
C
Polydiacetylene
C
)n
Photonic Application of Conducting
Polymers - Kerr gate
Laser 1
No light
Crossed
Polariser
Polariser
NLO (c(3))
polymer
Laser 2
Laser 1
Polariser
Crossed
Polariser
Future Outlook
All organic transistor
Plastic solar cell based on MDMO-PPV/PCBM
(conducting polymer - fullerene composite)
on flexible ITO coated PET
Thank you