Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 2014

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1 Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 214 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 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 (2-8)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. الخلاصة في هذا البحث تم تحضیر نماذج من البولي فاینیل الكحول (PVA) النقي والمشوب ودرس تا ثیر اضافة ببرومید البوتاسیوم بطریقة الصب. تر اكیز برومید البوتاسیوم على الخواص البصریة لبولي فاینیل الكحول.ضمن مدى الا طوال الموجیة (٢٠٠-٨٠٠) نانومتر. تم حساب معامل الا متصاص فجوة الطاقة معامل الا نكسار معامل الخمود وثوابت العزل الحقیقي والخیالي. أظهرت النتاي ج ان الثوابت البصریة للمت اركبات تتغیر مع زیادة تركیز برومید البوتاسیوم. 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, 2], light-emitting diodes [Grazulevicius et al, 23, Akcelrud, 23,. Kim et al, 2 ], and others [Lo. and Burn, 27, Cravino, Sariciftci, 22]. 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, 27, Liu et al, 27, Zhen et al, 27], 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, 27]. The purpose of this paper are reporting some of our results about the effect on optical constants of 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 9 C, then the solution was cooled at room temperature. The weight percentages of KBr are (2, 4 and 6 ) wt.% were added and mixed for 1 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/16/Shimadzu spectrophotometer. Absorptance (A) is defined as the ratio between absorbed light intensity. (IA) by material and the incident intensity of light (I o ). A = IA / I o.. (1) 885

2 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 (I o ) (T=I/ I o ), and can be calculated by [Jordan,25]: T = exp [-2.33A]. (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, 25]: 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=2.33a/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 +k 2 )/ ( (n+1) 2 +k 2 ). (6) When the ( k = ) R= (n-1) 2 / (n+1) 2 (7) n= (1+R 2 )/ (1-R 2 ) (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 (e 1 ), and imaginary (e 2 ).The real and imaginary parts of dielectric constant (e 1 and e 2 ) can be calculated by using equations [Nahida, 211]: ε= ε 1 iε 2... (1) ε 1 =n 2 -k 2 (real part)... (11) ε 2 =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

3 Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 214 Absorbance 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 sample had low absorption coefficient this may be as a result of low crystalinity[mwolfe et al, 1989]. α(cm) 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, 27]. 887

4 (αhυ) 1/2 (cm -1.eV) 1/ 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/ 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, 21]. 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, 21]. 888

5 Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 214 n photon energy(ev) FIG.6 The relationship between refractive index for (PVA-KBr) composite with photon energy 889

6 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 composite shows the smaller variation[saurav et al, 21]. ε photon energy(ev) FIG.7 The variation of real part of dielectric constant (PVA-KBr) composite with photon energy ε2 9.E-5 8.E-5 7.E-5 6.E-5 5.E-5 4.E-5 3.E-5 2.E-5 1.E-5.E+ photon energy(ev) FIG.8 The variation of imaginary part of dielectric constant(pva-kbr) composite with photon energy 89

7 Journal of Babylon University/Pure and Applied Sciences/ No.(2)/ Vol.(22): 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., 27, "Dopping Effect On Optical Constants of Polymethylmethacrylate (PMMA)", J. of Eng. & Technology,Vol.25, No.4. Akcelrud L., 23, " Electroluminescent Polymers". Prog. Polym. Sci., 28(6): p Abd El-Raheem M.M, 27, J. Phys. Condens. Matter. 19, Bhattacharya, P. Ray, 23, Studies on Surface Tension of Poly(Vinl Alcohol): Effect of Concentration, Temperature, and Addition of Chaotropic Agents Received 3 September 23; accepted 16 December. Cravino A., Sariciftci N.S.,22, " Double-cable Polymers for Fullerene Based Organic Optoelectronic Applications". J. Mater. Chem., 12: p Grazulevicius J. V., Strohriegl P. and Pielichowski J.23, "Carba-zole-containing Polymers", Synthesis, Properties and Applications. Prog. Polym. Sci., 28(9): p Jordan, J., Jacob, K. I., Tannenbaum, R., Sharaf, M. A.; Jasiuk, I. 25, Experimental trends in polymer nanocomposites - a review. Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing 393 (1-2), Kim D. Y., Cho H. N. and Kim C. Y.,2, " Blue Light Emitting Polymers". Prog. Polym. Sci., 25(8): p Lo S. C., Burn P. L., 27,"Development of Dendrimers: Macromolecules for Use in Organic Light-Emitting Diodes and Solar Cells". Chem. Rev., 17(4):p Luo J., Li X., Hou Q., et al., 27, "High-Efficiency White-Light Emission from asingle Copolymer: Fluorescent Blue, Green, and Red Chromophores on a Conjugated Polymer Backbone"., Adv Mater., 19(8):p Liu J., Shao S., Chen L., et al., "White Electroluminescence From a Single Polymer System: Improved Performance By Means of Enhanced Efficiency and Red- Shifted Luminescence of the Blue-Light-Emitting Species". Adv. Mater.,19(14):p McQuade D. T., Pullen A E, Swager T. M.,2, " Conjugated Polymer-based Chemical Sensors. Chem. Rev., 1(7): p Mwolfe, N. Holouyak and G. B. Stillman, 1989, "Physical properties Semiconductor", prentice Hall, New York. Nahida J.H.,Marwa R.E. 211.Study of Optical Constants, Eng.& Tech. J.29,4. 891

8 Saurav, R Tintu,K.Sulakshna,Vpn.Nampoori,Pradhakrishnan and Sheenu Thomas, 21, "Ge 28 Se 6 Sb 12 /PVA composite films for photonic application. Journal of Non- Oxide Glasses", Vol. 2, No 4,, p Tintu, Nampoori V P, Radhakrishnan P and Sheenu Thomas, 21, J. Appl Phys. 18, Zhen H. Y., Xu W., King W., et al.,26, " White-Light Emission from a Single Polymer with Singlet and Triplet Chromophores on the Backbone.", Macromol. Rapid Commun, 27(24): p