Effect of Methyl Red Acidity and UV illumination on Absorption coefficient of Polyvinyl Alcohol Thin Films,Physica B,Volume 406, Issue 10, 1940-1943, 2011

The absorption coefficient spectra of poly(vinyl alcohol), PVA, mixed with methyl red (MR) thin films on glass substrates, prepared by the spin coating method has been investigated using scanning electron microscopy (SEM) and spectroscopic ellipsometry. SEM imaging indicates that the surface of the MR/PVA film is smooth, uniform, and no crack could be observed. Spectroscopic ellipsometry measurements of PVA and MR/PMMA thin films were carried out at three angles of incidence, over the wavelength range 400-800 nm. Optical models were used to obtain the absorption coefficients for the prepared samples. These models include Cauchy formula for the glass substrate and PVA film, Lorentz model with three oscillators for MR layer, and a Bruggeman effective medium approximation for MR/PVA films. Absorption coefficients were found to be in the range 5?103-5?104 cm-1 with a maximum being at about 475 nm. Changing the absorption coefficient as a function of increasing the pH of MR causes a shift of the absorption band toward higher wavelengths. Our results show that the absorption coefficient of the film decreases upon increasing the UV illumination time.