The optical properties of ( PVA + PVP ) + PANI blends

Polyaniline polymer has been prepared by chemical oxidationpolymerization method in laboratory successfully. The PANI and(PVA+PVP) as a polymer blends in different percentage (30%, 50%,70%) from Polyaniline was prepared. The sample was studies asoptical properties by UV-vis spectrophotometer at (400-700) nm.The result of optical energy gap was 2.23 eV for pure (PVA+ PVP)and with additive was increasing with increasing PANI concentrationto become (2.49 for 30% to 2.52 for 70%) PANI. The goal of thisproject is prepare triple blend polymer and study the effect when addconductive polymer (Polyaniline) on the optical properties andcalculate optical constant as energy gap, refractive index, dielectricconstant and dielectric losses for (PVA+PVP) blends.


‫البوليميرية‬ ‫للخالئط‬ ‫البصرية‬ ‫الخواص‬ (PVA+PVP) + PANI
When dry it is a light flaky hygroscopic powder, readily absorbing up to 40% of its weight in atmospheric water. In solution, it has excellent wetting properties and readily forms films. This makes it good as a coating or an additive to coatings. A polyanline (PANI) has been known for more than a century in its "aniline black" from, an undesirable black deposit formed on the anode during electrolysis involving aniline. Among the conducting polymers, polyaniline is the most promising polymer due to its low cost, ease of preparation, chemical stability [2], controllable electrical conductivity as well as excellent environmental stability [3]. PANI is represented by the general following formula and structure, where B denotes a benzoidreduced unit and Q is aquinoid oxidized unit, both Q and B = C 6 H 4 [4]. PANI is a typical phenylenebase polymer having a chemically flexible-NH-group in the polymer chain flanked on either side by a phenylene ring, Fig. 1 show the Structure of the polyaniline chain [5,6].

Theoretical part
The optical properties of material can be defined as any property that involves the interaction between electromagnetic radiation or light with the matter, including absorption, polarization, reflection, and scattering effects [7]. The optical constants fully describe the optical behavior of materials; they are important and fundamental properties of mater. Knowledge of optical constant of a film from a given material is basic importance in determining the characteristics of light transmission in the film. Such Knowledge of the optical parameters of the material is of importance when designing devices through which electromagnetic radiation absorbed or transmitted.
The absorption coefficient of the material is a very strong function of the photon energy and band gap energy. Absorption coefficient represents the attenuation that occurs in incident photon energy on the material for unit thickness, and the main reason for this attenuation is attributed to the absorption processes. The absorption of light by molecules occurs only if the difference between two energy levels exactly equal to the energy of the incident photon [8].
where E 2 and E 1 are the energies of single molecules in the final (higher level) and initial (lower level) states, respectively. Optical constants included refractive index (n), extinction coefficient (k), and real (ɛ r ) and imaginary parts (ɛ i ) of dielectric constant. The refractive index (n) can be calculated from the following equation [9].
where R: is the reflectance and given by the equation The extinction coefficient (imaginary part of the refractive index), which is related to the exponential decay of the wave as it passes through the medium and can be determined by using equation

4
Whereλ: is the wave length of the incident radiation and the absorption coefficient, α, is given by α = 2.303 (5) where A: is the absorption and t is the sample thickness. The real and imaginary part of the dielectric constant (ɛ r and ɛ i ) can be calculated by using equations. ɛ r = n 2 -k 2 (6) ɛ i = 2nk (7) Taucput the empirical equation between the optical energy gap and energy of incident photon which is [10,11]: αhv = D(hv -E g ) r (8) Where D is a constant, hνis the energy of incident photon, which can be calculated using the equationhν (eV) = . And r is the order of the optical transition depending on the nature of electronic transition. The transition is called direct if the extremities of V.B. and C.B. lie at the same point in k-space, while the transition is called indirect if the transition is possible only with phonon assisted (∆k≠0). Thus the value of r may be 1 2, 2, 3 2 and 3 ⁄ ⁄ , corresponding to the allowed direct,allowed indirect, forbidden direct and forbidden indirect transition respectively.

Experimental part Raw material
We have used the following materials for synthesis the polyaniline. All chemical materials which used in this paper has high purity and which supplied from different companies such as Aniline hydrochloric (C 6 H 5 NH 2 .HCL) from Hopkin and Williams, Ammonium persulphate (NHO) 2 S 2 O 8 from BDH, (PVA-PVP) from Panreac, Hydrochloric Acid(HCL)from BDH, Acetone from BDH and Diemethyel for Amide (DMF) from (BDH).

Preparation of polyanline
Pure polyaniline was prepared at room temperature. A three-necked round bottomed flask equipped with a thermometer. Electromagnetic stirrer and condenser were used to polymerize polyaniline. The preparation of (PANI) is based on the oxidation of (0.2M) aniline hydrochloric with (0.25M) ammonium peroxydisulphate in aqueous medium. Both solutions are mixed in a round bottomed flask and gentle stirring to polymerize the mixture. The reaction is found to be exothermic. The mixture was left to rest to the next day. The precipitate (PANI) was collected on filter papers and washed with three 100 ml of(0.2 MHCL) and 150 ml of acetone.After that(PANI)was dried in air for one hour and then in vacuum oven at (80 o C) for 6 hours. The average yield was (2.3)g.

Preparation of (PVA+PVP) blend
The solutions of (PVA+PVP) were prepared separately. The casting solution was prepared by mixing the appropriate amount of each stock to a chive the desired blend composition, the final concentration of each casting solution was adjusted to the (30%, 50%, 70%) of PANI, the blend solution was cast onto a glass plate. The 1g of total (PVA+PVP) was dissolved in 10 ml of distal water, the solution was where heated at 60 0 C on the magnetic starrier for one hr to allow polymer to dissolve completely to yield clear solution. The PANI solution was prepared by weighted 0.1g of PANI and dissolved in 10 ml of (MDF, die methyelforimade) and stirring for 3 hr after allowing them to dissolve completely the three solutions were mixed together. A glass plate (10 cm) diameter washed with hot water and then cleaned with acetone was used as a substrate. To achieve perfect leveling and uniformly in the thickness of the film the glass plate was kept freely in the air for 24 hr and for another 2 hr in oven and the film was heating at constant temperature (50 0 C) to remove the traces of solvent finally, the film was remove from the glass plate and then was measured by UV-Vis, the absorbance A and transmittance T of the sample were measured in the wave length range (400-700nm) using UV-Vis spectrophotometer model (UV/160) manufactured by Shimadzu Co. (Japan). Fig. 2 shows the variation of transmittance of all samples as a function of wave length, when the λ changed from (400-700 nm). We note from the figure, the samples are transmitted in the visible range and value is greater than 70% from the transmittance.

Results and discussion
The change of transmittance with concentration was not systematic, because the thickness of sample is not the same for all the samples, due to the preparation method (casting method) and we not control on the thickness, but in general the transmitted decreasing with increasing of PANI concentration.    Fig. 4 shows the variation of (αhγ) 3 with photon energy (hγ) for indirect allowed transition to pure and blends samples and the optical energy gap are determined from this figure as listed in Table 1. From the table the PANI additive increases the optical band gap from (2.3eV to 2.52eV). The increasing in the optical band gap is probably due to the increasing the legalized state in optical energy gap due to increasing the PANI Concentration, that means the increasing in the optical band gap is probably due to modification of the polymer structure [10,12].   values compared with (PVA+PVP) matrix, in general, the reflective index increases by increasing the C-H bonds, which leads increasing in cross linking in polymer chain [13]. The dependence of the extinction coefficient k on wavelength was carried out using Eq.(4) and depicted in Fig.6. The extinction coefficient for doped sample is increasing for PVP+PVA, The explanation of this behavior of k can be describes to increase of absorption coefficient according to Eq.(4).   Fig. 7 shows the variation of ε r and ɛ i is as a function of light wavelength in the range (400-700nm)at different PANI percentage in blend samples, at room temperatures. The variation of ε r and ɛ i , with the increase of wave length of the incident radiation is due to the change of reflectance and absorbance. The increasing of dielectric constant is due to increasing of cross linking polymer chain which leads to increasing the scattering operation which means prevent the dipole aliment with the field (distribution of dipoles) which leads decreasing the dielectric constant with wave length. The behavior of ε r is similar to that of the refractive index because of the smaller value of k 2 compared with n 2 , while ɛ i mainly depends on the k value, which is related to the variation of absorption coefficient. In general at higher wave length (interfacial polarization) is caused by the alternating accumulation of charges at interfaces between different phases of the material [14,15]. Fig. 7: Dielectric constant, (a) dielectric loss (b)

Conclusions
In this work we have prepared a triple blend (PVA-PVP)+PANI polymers, PVA and PVP was the matrix and we add PNAI polymer in different concentrations. Optical properties for (PVA-PVP)+PANI blends have been investigated, the optical energy gap and optical constants such as the reflective index, the extinction coefficient and dielectric constants were determined from the optical transmission and absorption in the wave length range (400-700)nm, the measurements of those parameter are strongly depending on the light wave length. Our results indicate that the samples have allowed indirect transition. Also, it was found that the optical energy gap depends on the percentage of PNAI polymer in the blends sample, the refractive index and dielectric constants increased with the increase of the PANI additives.