A study on thermo-optic effect of beta poly(vinylidene fluoride) thin films prepared by solution casting method

摘要

The Poly(vinylidene) fluoride (PVDF) thin films with a high content of beta-phase were prepared by controlling heat-treatment temperature using casting from the poled solvents. The crystallite microstructure of thin films was depicted by the techniques of X-ray diffraction and FTIR. The results showed that heat treatment was favorable for inducing the beta- and gamma-phase formation of PVDF. The beta phase films were obtained with heat treatment at temperatures ranging from 60 degrees C to 120 degrees C and annealing at 120 degrees C after casting from DMF. The thermo-optical effect of beta phase PVDF films was investigated using a spectroscopic ellipsometer. At temperatures ranging from 20 degrees C to 100 degrees C, the refractive index of PVDF was negatively correlated with the temperature between 350 and 1500 nm. The value of the t.o. coefficient of PVDF films was calculated at all temperatures. The maximum value of the t.o. coefficient was about 3.3 x 10(-4)/degrees C at the ascending stage of temperature and 3.0 x 10(-4)/degrees C at the descending stage of temperature. Therefore, it is possible to use the thermo-optic effect of the beta phase PVDF for long wavelength infrared imaging.