Synthesis of (PS-KBr) Composites and Studying the Effect of KBr Addition on the Electrical and Optical Properties of Polystyrene Moneer Ali Lilo Moneerlilo@Yahoo.Com Collag Of Sincies - Abstract Al-Muthanna University Phasics Department The aim of this study, preparation of (PS-KBr) composites and study the D.C electrical and optical properties of different concentrations of salt at different temperatures. The samples of (PS-KBr) composites were prepared by using casting method. The effect of the concentration of potassium bromide and temperature on the electrical conductivity of polystyrene was studied. Also, The effect of the concentration of potassium bromide on optical properties has been investigated. The results show that the electrical conductivity of polystyrene was increased with increasing concentration of potassium bromide and temperature. Also, the activation energy was decreased with increasing the concentration of potassium bromide. The optical constants change with increase of potassium bromide concentration. Key words: composites, polystyrene, potassium bromide, optical properties, electrical conductivity (PS-KBr) الخلاصة الهدف من هذه الدراسة تحضير متراكبات المستمرة لتراكيز مختلفة من الملح وبدرجات حرارة مختلفة.حضرت ودراسة الخواص البصرية النماذج لمتراكبات والكهرباي ية (PS-KBr) باستخدام طريقة الصب. للبولي ستايرين. درس تاثير تركيز بروميد البوتاسيوم ودرجة الحرارة على التوصيلية الكهرباي ية كذلك درس تاثير تركيز بروميد البوتاسيوم على الخواص البصرية. بينت النتاي ج ان التوصيلية الكهرباي ية للبولي ستايرين ازدادت مع زيادة تركيز بروميد البوتاسيوم ودرجة الحرارة. كذلك طاقة التنشيط قلت مع زيادة تركيز بروميد البوتاسيوم. الثوابت البصرية تتغير مع زيادة تركيز بروميد البوتاسيوم. كلمات دالة : متراكبات بولي ستايرين بروميد البوتاسيوم الخواص البصرية التوصيلية الكهرباي ية. 1-Introduction Polymers are considered to be good hosting matrices for composite materials because they can easily be tailored to yield a variety of bulk physical properties. Moreover, organic polymers generally have long-term stability and good processability. Polymers have relatively poor mechanical, thermal, and electrical properties as compared to metals and ceramics. Many types of polymers such as homopolymers, co-polymers, blended polymers and modified polymers are not sufficient enough to compensate various properties, which we have demanded. Alternative approaches to improve their properties are to reinforce polymers with inclusion of fiber, whisker, platelets, or particles. The choice of the polymers is usually guided mainly by their mechanical, thermal, electrical, optical and magnetic behaviors. However, other properties such as hydrophobic/hydrophilic balance, chemical stability, bio-compatibility, opto-electronic properties and chemical functionalities (i.e., solvation, wettability, templating effect, etc.) have to be considered in the choice of the polymers. The polymers in many cases can also allow easier shaping and better processing of the composite materials(in-yup and Jong-Beom, ١٦٦١
2010). Recently, effects of chiral media on electromagnetic waves have attracted a great deal of attentions. Related studies indicated that the left-hand and right-hand electromagnetic wave which has different velocity could be transmitted in the chiral medium. When the chiral medium was introduced in the coupling area of waveguide, it will have a special polarization response. With this response, it may be applied to the construction of depolarizers, polarimeters, diplexers, frequency meters, sensors, switches, etc(xue-, et al., 2006). Polymeric composite materials are widely used in weight sensitive applications due to their high strength-to weight and stiffness-toweight ratios compared with metallic materials. The weight and fuel savings offered by composite materials makes them attractive not only to the military, but also to the civilian aircraft, space, solar vehicles, and automobile industries(fahad,et al., 2009). 2 -Experimental part Polystyrene is dissolved in chloroform by using magnetic stirrer in mixing process to get homogeneous solution. The concentrations of potassium bromide are (0,2,4 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 resistivity was measured over range of temperature from (30 to 80) o C using Keithly electrometer type (616C).The volume electrical conductivity defined by(ahmed and Zihilif, 1992) : Where : 1 LV AI A = guard electrode effective area. V/I=R = volume resistance (Ohm). L = average thickness of sample (cm). In this model the electrodes have circular area A= D 2 π/4 where D= 0.5 cm 2. The activation energy was calculated using equation(ahmed and Zihilif, 1992): σ = σ o exp(-e a /k B T)..(2) σ = electrical conductivity at T temperature σ 0 = electrical conductivity at absolute zero of temperature K B = Boltzmann constant E a = Activation Energy The composites 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 (I o ). A = IA / I o.. (1) v......( 1) ١٦٦٢
The 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 et al., 2005 ): T = exp (-2.303A). (3) And Reflectance (R) can be obtained from absorption and transmission spectra in accordance with the law of conservation of energy by the relation (Jordan et al., 2005): R + T + A = 1 (4) Absorption coefficient (α) is defined as the ability of a material to absorb the light of a given wavelength α=2.303a/t. (5) Where A: is the absorption of the material t: the sample thickness in cm. According to the generally accepted non-direct transition model for amorphous semiconductors proposed by: h B( h E g ) r...(6) Where B is a constant related to the properties of the valance band and conduction band, hυ is the photon energy, E g is the optical energy band gap, r=2,or3 for indirect allowed and indirect forbidden transition 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 ). (7) When the ( k 0) R= (n-1) 2 / (n+1) 2 (8) n= (1+R 1/2 )/ (1-R 1/2 ) (9) The extinction coefficient (k) was calculated using the following equation: K=αλ/4π (10) Dielectric constant is defined as the response of the material toward the incident electromagnetic field. The dielectric constant of compound (ε) is divided into two parts real(ε 1 ), and imaginary (ε 2 ).The real and imaginary parts of dielectric constant can be calculated by using equations (Nahida and Marwa, 2011) ε 1 =n 2 -k 2 (real part)... (11) ε 2 =2nk (imaginary part) (12) ١٦٦٣
3 -Results and Discussion 3.1The Effect of concentration of chromium chloride on D.C electrical conductivity Fig. (1) shows the variation of D.C electrical conductivity of composite with different concentrations of salt, it is found that the electrical conductivity was increased with increasing of salt concentration, this related to increase the numbers of carries charges in composites(ping Zhou, et al., 2007). 1.2E-11 1.1E-11 Conductivity(S/cm) 1.0E-11 9.0E-12 8.0E-12 7.0E-12 6.0E-12 5.0E-12 0 1 2 3 4 5 6 Con. of KBr wt.% FIG.1 Variation of D.C electrical conductivity with KBr wt.% concentration of composite. 3.2 The variation of the D.C electrical conductivity with temperature Fig. (2) shows the variation of D.C electrical conductivity of composites with different temperature, it is found that the electrical conductivity was increased with increasing the temperature this due to increase the movement of polymer chain and ions of salt, also increase the carries charges with increase the temperature (Alam, et al., 2011). ١٦٦٤
2.E-11 2.E-11 Conductivity(S/cm) 1.E-11 1.E-11 9.E-12 7.E-12 5.E-12 3.E-12 1.E-12 50 55 60 65 70 75 80 85 T(c) FIG.2 Variation of D.C electrical conductivity with temperature for(ps-kbr ) composite 3.3 Activation Energy The activation energy was calculated by using Eq.2 as shown in Fig.3. Fig (4). shows the variation of activation energy of D.C electrical conductivity of composite with salt concentration. From this figure, the activation energy was decreased with increasing of salt concentration, this behavior attributed to decrease the distance between conduction band and valance band (Majdi and Fadhal, 1997). -24 ln(conductivity) -24.5-25 -25.5-26 -26.5-27 2.8 2.85 2.9 2.95 3 3.05 3.1 1000/T(k) -1 FIG.3 Variation of D.C electrical conductivity with resprocal absoute temperature for ( PS-KBr) composite. ١٦٦٥
0.35 0.3 0.25 Ea(eV) 0.2 0.15 0.1 0 1 2 3 4 5 6 Con. of KBr wt.% FIG.4 Variation activation energy for D.C electrical conductivity with KBr wt.% concentration for (PS-KBr) composite 3.4 The absorbance of (PS-KBr) composites Fig.(5) shows the of the absorbance of the composites with wavelength at different weight percentages of salt. The absorbance of composites increases with increasing the concentration of potassium bromide, this behavior due to the absorbance of salt more than the absorbance of polymer (Ahmad et al., 2007). 4.5 4 3.5 Absorbance 3 2.5 2 1.5 1 0.5 0 200 300 400 500 600 700 800 Wavelength(nm) FIG.5 The variation of optical absorbance for (PS-KBr) composite with wavelength ١٦٦٦
3.5 The Absorption coefficient and energy gap of composite The variation of the absorption coefficient of the composites with photon energy is shown in Fig.(6). The absorption, which corresponds to electron excitation from the valence band to conduction band, can be used to determine the nature and value of the optical band gap, E g which calculated by using Eq. 6. (Ahmad et al., 2007). α(cm) -1 300 250 200 150 100 50 0 Photon energy(ev) FIG.6 The absorption coefficient for (PS-KBr) composite with various photon energy (αhυ) 1/2 (cm -1.eV) 1/2 800 700 600 500 400 300 200 100 0 Photon energy(ev) FIG.7 The relationship between (αhυ) 1/2 (cm-1.ev) 1/2 and photon energy of PS-KBr composites. Figs. (7 and 8) show the energy band gap of indirect transition composites. From these figures the energy band gap is decrease with increasing the potassium bromide concentration, this attributed to decrease the distant between the conduction band and valance band with the increase the potassium bromide weight percentages (Muhsien, et al., 2010). ١٦٦٧
(αhυ) 1/3 (cm -1.eV) 1/3 90 80 70 60 50 40 30 20 10 0 Photon energy(ev) FIG.8 the relationship between (αhυ) 1/3 (cm -1.eV) 1/3 and photon energy of PS-KBr composites. 3.6 Refractive Index and Extinction Coefficient Figure(9) shows the variation of the refractive index of composites with photon energy. The value of refractive index is increased with increasing the concentration of salt which is a result of increasing the number of atomic refractions due to the increase of the linear polarizability in agreement with Lorentz - Lorentz formula(tariq, 2010). n 3 2.8 2.6 2.4 2.2 2 1.8 1.6 1.4 1.2 1 photon energy(ev) FIG.9 The relationship between refractive index for (PS-KBr) composite with photon energy ١٦٦٨
The variation of the extinction coefficient (K) of composites with the photon energy is shown in figure(5). The figure shows that the extinction coefficient increases with increasing of potassium bromide weight percentages; this may be attributed to absorption coefficient which increases with increase of concentration of potassium bromide (Tariq, 2010). 1.E-05 1.E-06 k 1.E-07 1.E-08 photon energy FIG.10 The extinction coefficient for (PS-KBr) composite with various photon energy 3.7 dielectric constants The variation of real and imaginary parts of dielectric constants (ε 1 =n 2 -k 2 and ε 2 =2nk) ((Muhsien, et al., 2010) with energy photon of composites are shown in figures(11 and 12). These figures show that the real and imaginary parts of dielectric constants are increasing with increase the concentration of potassium bromide, this related to increase the refractive index and extinction coefficient with increase the weight percentages of potassium bromide[(muhsien, et al., 2010; Hamed et al., 2012]. ١٦٦٩
9 8 7 6 5 ε1 4 3 2 1 0 photon energy(ev) FIG.11 The variation of real part of dielectric constant (PS-KBr) composite with photon energy 7.E-05 6.E-05 5.E-05 ε2 4.E-05 3.E-05 2.E-05 1.E-05 0.E+00 photon energy(ev) 4 - FIG.12 The variation of imaginary part of dielectric constant(ps-kbr) composite with photon energy Conclusions The electrical conductivity of polystyrene was increased with increasing the concentration of salt and temperature, The activation energy was decreased with increasing the weight percentages of potassium bromide The absorbance of (PS-KBr) is large in the UV, region and it is increased with increasing the concentration of potassium bromide. The optical constants are increased with increasing the potassium bromide concentration and the energy band gap is decreased with increasing of potassium bromide concentration. ١٦٧٠
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