Photoinduced Localization of Orientationally Ordered Polymer Networks at the Surface of a Liquid Crystal Host

Abstract

We demonstrated liquid crystalline template-directed and photoinduced localization of orientationally ordered polymer networks in a liquid crystal host. In the limit of a diffusion-controlled polymerization process, the location of these networks in a liquid crystal (LC) cell can be controlled by varying the wavelength-dependent absorption coefficient of the UV radiation used to initiate photopolymerization. Specific results are presented for a bulk polymer network (obtained when λ = 365 nm) and a micrometer-thick polymer surface layer (for λ = 322 nm), both of which are produced in similar LC cells, using the same 5 wt % initial concentration of a liquid crystalline diacrylate, and for both planar and homeotropic orientations of the liquid crystal director. The surface-localized networks have minimal impact on the desirable electrooptic properties of the host, such as low operating voltage and minimal scattering loss. We discuss predictive models for surface localization in the opposite limits of “infinite” and zero monomer diffusion constant.