Photoinduced In-Plane Motions of Azobenzene Mesogens Affected by the Flexibility of Underlying Amorphous Chains

Abstract

Photoinduced in-plane motions are explored for a series of surface-grafted diblock copolymers comprising of an amorphous chain block and a liquid crystalline (LC) azobenzene (Az) side chain polymer block. In this architecture, amorphous polymers with different glass transition temperature (Tg) and the LC Az polymer are stepwisely grafted on substrate surfaces by the surface initiated atom transfer radical polymerization. Amorphous polymers employed are poly(hexyl methacrylate) (PHMA), poly(butyl methacrylate) (PBMA), and poly(methyl methacrylate) (PMMA) with Tg of −20, +27, and +110 °C, respectively. The extent of photoinduced in-plane anisotropy of the LC Az layer by linearly polarized light irradiation at optimal temperatures are in the order of PHMA > PBMA > PMMA which coincides with that of lowering Tg. Thus, the photoinduced motions of the LC Az blocks are coupled with the dynamic nature of the underlying amorphous chain anchored to the substrate. The structural information obtained by the grazing incidence angle X-ray diffraction measurements further shows the important role of the amorphous polymer layer in the ordering and photoalignment of LC mesogens on the top.