Optical properties and structural features of UV-C irradiated polyvinylidene chloride films

Abstract

Abstract The modifications caused in polyvinylidene chloride (PVDC) polymer films on exposure to ultra-violet light (UV-C light of wavelength 254 nm) in air for different exposure times varying from one hour up to six hours have been investigated by using ultraviolet - visible (UV-Vis) and Fourier transform infrared (FTIR) spectroscopic techniques, as well as powder X-ray diffraction (XRD) technique. XRD scans reveal that the degree of crystallinity (Xc) increased from 4.7% up to 28.6% on increasing the UV exposure time of PVDC from 1 hour up to 4 hours, and a further increase in the exposure time causes a decrease in the value of Xc. The FTIR scans reveal the formation of hydrogen bonded hydroxyl groups as well as conjugated alkene structures in the PVDC sample on exposure to UV-C radiation. For the study of modification in band structure of the UV irradiated PVDC films, the UV-Vis spectroscopy was used; it was found that the optical band gap decreases from 4.70 eV down to 3.92 eV, as obtained from the plot of √εi hν versus hν, using linear fit method and the penetration depth (δ) decreased from 0.0074 cm down to 0.0035 cm at 4.88eV, the energy corresponding to UV-C radiation. The calculation of percentage decrease in the value of δ with respect to wavelength and UV-C exposure time reveals that UV-C irradiated PVDC films are good radiation shields against both UV-A and UV-B EM radiation. The study of refractive index with respect to wavelength reveals that UV irradiation of PVDC films is an effective method to modify the refractive index of PVDC, thereby making the material suitable for use in different optical applications. The optical dielectric constant was studied systematically, which demonstrates that the energy storage properties of the PVDC films can be tuned and tailored by UV-C radiation. Details are discussed.