Comparison of the Photoinduced Orientation Structure in the Bulk and at the Near-Surface of a Photoalignable Liquid Crystalline Polymer Film

Abstract

The thermally stimulated photoinduced in-plane and out-of-plane molecular reorientation behaviors of a polymethacrylate film comprised of 4-methoxycinnnamoylbiphenyl (MCB) side groups connected with a decylene spacer (PMCB10M) are compared in the bulk (>10 nm), at the inner-surface (∼10 nm), and at the near-surface (<2 nm) using polarized UV absorption and near-edge X-ray absorption fine structure (NEXAFS) spectroscopies. The biaxial reorientation characteristics in the bulk of the PMCB10 M films can be controlled by irradiating with linearly polarized (LP) UV light and subsequent annealing to generate self-organization of the MCB side groups. However, the homogeneous in-plane orientation at the near-surface, which can introduce homogeneous nematic low-molecular-weight liquid crystal mixture alignment, is observed regardless of the self-organization process. The differences in the orientation characteristics arise from long alkylene spacer and bulky mesogenic side groups.