Light Induced Spatial Structures in the Liquid Crystalline Azopolymers

Abstract

We studied the 3D distribution of azobenzene fragments in the films of two comb-like liquid crystalline azopolymers before and after irradiation by actinic UV light using a null ellipsometry technique. The polymer with an alkyl chain C₆H₁₃ at the end of the azobenzene fragment forms structures with preferred homeotropic alignment of the fragments. Polarized UV light irradiation at normal beam incidence induces biaxial structures with a preference for out-of-plane alignment of azobenzene fragments. High UV doses induce highly ordered homeotropic alignment of the fragments. The second polymer with polar NO₂ group at the end of the azobenzene moiety shows preferential in-plane orientation. Excitation with polarized light provides a highly ordered in-plane alignment of the azobenzene fragments perpendicular to the UV light polarization.

Key Words:

• azopolymer
• light induced anisotropy
• ellipsometry