Study on photoinduced anisotropy of liquid crystal doped in polymer film containing coumarin group

Abstract

In this article, the photoinduced anisotropy of a liquid crystal molecule doped into a polymer with photosensitive group was studied. The polymer with coumarin photosensitive group as side chain can generate a polarization axis-selective photoreaction and obtain anisotropy after being exposed at a certain wavelength of linearly polarized ultraviolet light, which occurs as [2+2] cycloaddition and form anchoring force. The thin film underwent subsequent annealing in the liquid crystal temperature range and it leads to a large optical anisotropic change in the polymer film for the self-assembly of molecule. The ultraviolet dynamic spectrum was used to evaluate the absorbance of the film, and the photoinduced optical anisotropy ΔA and order parameter S were calculated. The result shows that when the exposure energy was increased to 1908 mJ/cm2, the value of the absorbance does not change with the increase in exposure energy. When annealing temperature changed from 120 °C to 240 °C, ΔA changed from 0.07 to 0.11 and S changed from 0.02 to 0.04.