Influence of Thickness Variation on Optical Properties of (Poly Vinyl Alcohol : violet Methyl) Composite

Poly(vinyl alcohol) doped by (Violet methyl) films with different thicknesses were prepared by casting method . The effects of thicknesses on the optical Characterization of poly (vinyl alcohol) films have been studied. The films show indirect allowed interband transitions that influenced by the thicknesses , the optical energy gap has been increased with increasing the thickness and the localized tail widths have been decreased with increasing the thickness.


Introduction
Poly vinyl alcohol (PVA) has been used in many applications since its discovery in 1924 [1].
We have used PVA as a host polymer because PVA is semicrystalline polymer, good chare storage capacity, having high dielectric strength, flexible light Wight materials and can be produced at a low cost [2][3].Various composite materials had been recently synthesized by starting from different polymers and a wide variety of dopants like metals, inorganic salts, oxides and other particles.The incorporation of the dopants in polar organic polymers can induce pronounced changes in various Characteristics of polymers in order to modify and improve its Characteristics [4][5].
In the present work is to investigate the optical properties of Poly Vinyl Alcohol (PVA) doped with 4% of Violet methyl with different thicknesses by casting method.

Experimental details
Poly vinyl alcohol polymer (PVA) solution was prepared by incorporation deionized distilled water at solid PVA and then stirred by a magnetic stirrer to 60 ˚C at one hour, a solution of (Violet methyl) was prepared by incorporation deionized distilled water to (Violet methyl) and then stirred by amagnetic stirrer at room temperature for (½ h).Appropriate mixtures of PVA and (Violet methyl) solution were mixed for (4% ) concentration by a different of thicknesses at ( 5 µm , 10 µm , 20 µm and 40 µm).
The solution was poured on flat glass dish.Homogenous films were obtained after drying in oven for (2 h) at 50 ˚C.The film thicknesses was measured with a digital micrometer (China Hunan E&K Tools Company) and the average area was (3 x 3) cm 2 .Absorbance and transmittance measurement were carried out using UV/VIS spectrometers in the wave length range (190 -1100) nm.

Results and discussion
The optical transmission spectra as a function of wavelength at range (190-1100) nm is shown in Figure (1).We can observe from this figure that the transmittance decreases with increasing the thickness.Also may be attributed to creation of levels at the energy band by increasing thickness and this leads to the shift of peak to smaller energies.There are no absorption previous studies [6,7].μm .This may be explained by invoking of occurrence to local cross linking within the amorphous phase of polymer, such a way as to increase the degree to ordering in these parts [10], process Similar behavior had been noticed by Shawki et al. [11].Table (1) give the values of optical energy band gap and urbach energy.

Conclusions
The PVA doped violet Methyl with different thickness films.

Fig. ( 3 )
Fig. (3) Shows the reflectance as a function of wavelength

Fig. ( 5 )
Fig. (5): Optical Energy Band Gap of (PVA-violet Methyl) with different thickness films.The absorption is due to the electronic transitions between the valence-band-tail and the conduction-band states and depends exponentially on the photon energy according to the Urbach relation as follows[12]: