Influence of film thickness on the reorientation structure of photoalignable liquid crystalline polymer films

摘要

Polarized UV absorption and near-edge X-ray absorption fine structure (NEXAFS) spectroscopies are used to investigate the influence of film thickness on the thermally stimulated photoinduced reorientation of a polymethacrylate film comprised of 4-methoxycinnnamoylbiphenyl (MCB) side groups connected with a decylene spacer (PMCB10M) in the bulk (> 10 nm), at the inner-surface (similar to 10 nm), and at the near-surface (< 2 nm). Irradiation with linearly polarized (LP) UV light and subsequent annealing generate a biaxial molecular reorientation in the bulk of thick PMCB10M films, while the out-of-plane orientation is restricted in films less than 55-nm thick. In contrast, the in-plane reorientation is dominant at the near-surface regardless of the film thickness. Consequently, the roles of the rigid mesogenic MCB moieties and the flexible long decylene spacer depend on the film thickness. (C) 2016 Elsevier Ltd. All rights reserved.