Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 2014
Study of the Effect of Potassium Bromide on
Optical Properties of PVA
Angham. Ganem, Hadi, Nedhal Mohammed , Samah kareem , Ahmed Hashim
Babylon university, College of Education , physical department
Abstract
In this work, samples of pure polyvinyl alcohol and polyvinyl alcohol (PVA) doped with (KBr)
were prepared using casting method. The effect of addition of potassium bromide concentrations on
optical properties of polyvinyl alcohol have been studied in the wavelength range (200-800)nm. The
absorption coefficient ,energy gap, refractive index, extinction coefficient and real and imaginary
dielectric constants have been determined. The results show that the optical constants change with
increase of potassium bromide concentration.
‫الخالصة‬
.‫( النقي والمشوب ببروميد البوتاسيوم بطريقة الصب‬PVA) ‫في هذا البحث تم تحضير نماذج من البولي فاينيل الكحول‬
)800-200( ‫ضمن مدى األطوال الموجية‬. ‫تركيز بروميد البوتاسيوم على الخواص البصرية لبولي فاينيل الكحول‬
‫ودرس تأثير اضافة ا‬
‫ أظهرت النتائج‬.‫ تم حساب معامل األمتصاص فجو الطاةة معامل األنسسار معامل الخمود وثوابت العزل الحقيقي والخيالي‬.‫نانومتر‬
.‫ان الثوابت البصرية للمتراكبات تتغير مع زياد ترسيز بروميد البوتاسيوم‬
1.Introduction
A polymer of a particular group is characterized by the molecular weight of the
monomer unit. In recent years, polymers with different optical properties have been
attracted much attentions due to their applications in the sensors [McQuade et al,
2000], light-emitting diodes [Grazulevicius et al, 2003, Akcelrud, 2003, . Kim et al, 2000
], and others [Lo. and Burn, 2007, Cravino, Sariciftci, 2002]. The optical properties of
these materials can be easily tuned by controlling contents of the different
concentrations. Though a great deal of excellent work has been reported on such
materials [Luo et al, 2007, Liu et al, 2007, Zhen et al, 2007], it is still meaningful to
extend the research of these polymers. Polyvinyl alcohol offers a combination of
excellent film forming and binder characteristics, along with insolubility in cold water
and organic solvents. This combination of characteristics is useful in a variety of
applications. Moreover, it contains a carbon backbone with hydroxyl groups attached
to methane carbons. These hydroxyl groups can be a source of hydrogen bonding,
hence the assistance in the formation of polymer blends [Bhattacharya et al, 2007].
The purpose of this paper are reporting some of our results about the effect on
optical constants of pure polyvinyl alcohol as well as of doped polyvinyl alcohol
films.
2.Experimental Part
The polymer was dissolved in distill water by using magnetic stirrer in mixing
process to get homogeneous solution at 900C , then the solution was cooled at room
temperature. The weight percentages of KBr are (2, 4 and 6 ) wt.% were added and
mixed for 10 minute to get more homogenous solution , after which solution was
transferred to clean glass petri dish of (5.5cm) in diameter placed on plate form. The
dried film was then removed easily by using tweezers clamp. The polymer systems
were evaluated spectra photo metrically by using UV/160/Shimadzu
spectrophotometer.
Absorptance (A) is defined as the ratio between absorbed light intensity .
(IA) by material and the incident intensity of light (Io).
A = IA / Io
…….. (1)
885
Transmittance (T) is given by reference to the intensity of the rays transmitting from
the film(I) to the intensity of the incident rays on it (Io) (T=I/ Io), and can be calculated
by [Jordan,2005]:
T = exp [-2.303A] …………. (2)
And Reflectance (R) can be obtained from absorption and transmission spectra in
accordance with the law of conservation of energy by the relation [Jordan, 2005]:
R+T+A=1
……….…… (3)
Absorption coefficient (α) is defined as the ability of a material to absorb the light of a
given wavelength
α=2.303A/t
………. (4)
The relation between the absorption coefficient, α, and the incident photon energy, hν,
can be written as[4] :
(αhν)n =A(hν −Eg) ……(5)
Where A: is the absorption of the material t: the sample thickness in cm. The
Refractive index (n), the index of refraction of a material is the ratio of the velocity of
the light in vacuum to
that of the specimen:
R= ((n-1) 2+k2)/ ( (n+1)2+k2) …. (6)
When the ( k = 0)
R= (n-1) 2/ (n+1) 2
………… (7)
n= (1+R2)/ (1-R2 )
……… (8)
The extinction coefficient (k) was calculated using the following equation:
K=αλ/4π
………… (9)
Dielectric constant is defined as the response of the material toward the incident
electromagnetic field. The dielectric constant of compound (e) is divided into two
parts real (e1), and imaginary (e2) .The real and imaginary parts of dielectric constant
(e1and e2) can be calculated by using equations [Nahida, 2011]:
ε= ε1 – iε 2
………... (10)
2 2
ε1=n -k (real part)
…..... (11)
ε2=2nk (imaginary part) ….… (12)
3.Results & Discussion
3.1 The absorbance of composites
Fig. (1) shows the relationship between absorbance of (PVA-KBr) composite
with wave length, from the figure it was appeared that the absorbance tends to
decrease with the wavelength increasing, this behavear related to the absorption of
the polymer composite lies in high energies.
886
Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 2014
pure
4.5
1 wt.%
2 wt.%
4
3 wt.%
Absorbance
3.5
3
2.5
2
1.5
1
0.5
0
200
300
400
500
600
700
800
Wavelength(nm)
FIG.1
The variation of optical absorbance for (PVA-KBr) composite with wavelength
3.2The Absorption coefficient and energy gap of composites
Fig. (2) shows the optical absorption spectrum of composite for different impurities
quantities, it was found that the composite have a low absorption coefficient at a small
photon energy then increase at different rates dependence on the composite structure.
The pure sample had low absorption coefficient this may be as a result of low
crystalinity[Mwolfe et al, 1989].
pure
350
1 wt.%
α(cm)-1
300
2 wt.%
3 wt.%
250
200
150
100
50
0
0
1
2
3
4
5
6
7
Photon energy(eV)
FIG.2
The absorption coefficient for (PVA-KBr) composite with various photon energy
Fig. (3) and Fig(4) represented the direct transition , the energy gab values
dependence in general on the crystal structure of the composites and on the
arrangement and distribution way of atoms in the crystal lattice, also the decrease of
energy band gap due to decease the distance between the valance band and conduction
band with the increase the concentration of KBr [Abd El-Raheem, 2007] .
887
pure
1000
1 wt.%
(αhυ)1/2(cm -1.eV)1/2
900
2 wt.%
800
3 wt.%
700
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
Photon energy(eV)
FIG.3
The relationship between (αhυ)1/2(cm-1.eV)1/2 and photon energy of
PVA-KBr composites.
(αhυ)1/3(cm -1.eV)1/3
pure
100
90
1 wt.%
2 wt.%
3 wt.%
80
70
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
Photon energy(eV)
FIG.4
the relationship between (αhυ)1/3(cm-1.eV)1/3 and photon energy of
PVA-KBr composites.
3.3 Extinction Coefficient and Refractive Index
Fig.(5) represent the variation of the extinction coefficient(k) with the incident
photon energy, the variation is simple in the low energy region while it increased in
the high photon energy region, this behavior may be as a result to the variation of the
absorption coefficient which leads to spectral deviation in the location of the charge
polarization at the attenuation coefficient due to the loses in the energy of the electron
transition between the energy bands[Saurav et al, 2010]. The transmittance and
reflectance spectra of the films are shown in Figure 5. Fig(6 ) shows the variation of
refractive index(n) of the composites with photon energy, the values increase
exponentially with increasing photon energy. This increase indicates that the
electromagnetic radiation passing through the material is faster in the low photon
energy [Tintu et al, 2010].
888
n
Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 2014
pure
3
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
1 wt.%
2 wt.%
3 wt.%
0
1
2
3
4
5
6
7
photon energy(eV)
FIG.6
The relationship between refractive index for (PVA-KBr) composite with
photon energy
889
3.4dielectric constant
Fig.(7) and Fig.(8) represented the real and imaginary parts of the dielectric
constant, in the real part the variation was very clear spatially in the high impurities
concentration this may be due to the absence the resonance between the frequencies of
the incident photon energy (electromagnetic and the induced dipoles in the
composite), while in the imaginary part there was an absorption to the energy of the
incident photon energy, so the variation nearly constant until it reaches to the high
photon energy. The pure composite shows the smaller variation[Saurav et al, 2010].
9
pure
8
1 wt.%
7
2 wt.%
3 wt.%
6
ε1
5
4
3
2
1
0
0
1
2
3
4
5
6
7
photon energy(eV)
FIG.7
The variation of real part of dielectric constant (PVA-KBr) composite
with photon energy
pure
9.E-05
1 wt.%
8.E-05
2 wt.%
3 wt.%
7.E-05
ε2
6.E-05
5.E-05
4.E-05
3.E-05
2.E-05
1.E-05
0.E+00
0
1
2
3
4
5
6
photon energy(eV)
FIG.8
The variation of imaginary part of dielectric constant(PVA-KBr)
composite with photon energy
890
7
Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 2014
4. Conclusion
The absorbance is very large in the UV, region. The absorption coefficient is
smaller and stable in the low photon energy and its increased with increase the
potassium bromide concentrations. The absorption coefficient and extinction
coefficient are increasing as a result of the scattering centers in the composites. The
values of the refractive index(n) of the composites increase exponentially with
increasing photon energy. Also, the absorption coefficient and extinction coefficient
are increased with increase the potassium bromide concentrations. .The energy band
gap is decreased with increase the potassium bromide concentrations. The real and
imaginary dielectric constants show the exponential increase with increasing the
incident photon energy and increase with increasing the potassium bromide
concentrations.
REFERENCES
Ahmad A.H., Awatif A.M. and Zeid Abdul-Majied N., 2007, "Dopping Effect On
Optical Constants of Polymethylmethacrylate (PMMA)", J. of Eng. &
Technology,Vol.25, No.4.
Akcelrud L., 2003, " Electroluminescent Polymers". Prog. Polym. Sci., 28(6): p.875962.
Abd El-Raheem M.M, 2007, J. Phys. Condens. Matter. 19, 216209.
Bhattacharya, P. Ray, 2003, “Studies on Surface Tension of Poly(Vinl Alcohol):
Effect of Concentration, Temperature, and Addition of Chaotropic Agents”
Received 30 September 2003; accepted 16 December.
Cravino A., Sariciftci N.S.,2002, " Double-cable Polymers for Fullerene Based
Organic Optoelectronic Applications". J. Mater. Chem., 12: p.1931―1943 .
Grazulevicius J. V., Strohriegl P. and Pielichowski J.2003, "Carba-zole-containing
Polymers", Synthesis, Properties and Applications. Prog. Polym. Sci., 28(9): p.
1297―1353.
Jordan, J., Jacob, K. I., Tannenbaum, R., Sharaf, M. A.; Jasiuk, I. 2005,
Experimental trends in polymer nanocomposites - a review. Materials Science
and Engineering A-Structural Materials Properties
Microstructure and
Processing 393 (1-2), 1-11.
Kim D. Y., Cho H. N. and Kim C. Y.,2000, " Blue Light Emitting Polymers". Prog.
Polym. Sci., 25(8): p.1089―1139.
Lo S. C., Burn P. L., 2007,"Development of Dendrimers: Macromolecules for Use in
Organic Light-Emitting Diodes and Solar Cells". Chem. Rev., 107(4):p.1097 –
1116.
Luo J., Li X., Hou Q., et al., 2007, "High-Efficiency White-Light Emission from
aSingle Copolymer: Fluorescent Blue, Green, and Red Chromophores on a
Conjugated Polymer Backbone"., Adv Mater., 19(8):p.1113-1117.
Liu J., Shao S., Chen L., et al., "White Electroluminescence From a Single Polymer
System: Improved Performance By Means of Enhanced Efficiency and RedShifted Luminescence of the Blue-Light-Emitting Species". Adv.
Mater.,19(14):p.1859―1863.
McQuade D. T., Pullen A E, Swager T. M.,2000, " Conjugated Polymer-based
Chemical Sensors. Chem. Rev., 100(7): p. 2537―2574.
Mwolfe, N. Holouyak and G. B. Stillman, 1989, "Physical properties Semiconductor",
prentice Hall, New York.
Nahida J.H.,Marwa R.E. 2011.Study of Optical Constants’, Eng.& Tech. J.29,4.
891
Saurav, R Tintu,K.Sulakshna,Vpn.Nampoori,Pradhakrishnan and Sheenu Thomas,
2010, "Ge28Se60Sb12 /PVA composite films for photonic application”. Journal of
Non- Oxide Glasses", Vol. 2, No 4, , p. 167-174.
Tintu , Nampoori V P , Radhakrishnan P and Sheenu Thomas, 2010, J. Appl Phys.
108, 073525.
Zhen H. Y., Xu W., King W., et al.,2006, " White-Light Emission from a Single
Polymer with Singlet and Triplet Chromophores on the Backbone.", Macromol.
Rapid Commun, 27(24): p.2095―2100.
892