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 inplane 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.

Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications

“…The Kawatsuki group has synthesized a variety of LC polymers containing photo cross-linkable cinnamate side chains. − These polymer films upon irradiation with polarized UV light undergo axis-selective cross-linking which produces alignment of the mesogens in the polymer film. This light-driven orientation of the mesogens yields high value of birefringence for the polymer films.…”

A message passing neural network for predicting dipole moment dependent core electron excitation spectra

“…2.2.4 Output block. The non-zero initialization of ṽi by using eqn (3) and the modied message function by using eqn (4) make s i satisfy the required symmetry in eqn (2). The prediction of the site-specic spectrum is performed by converting s i at the site of interest by using a multilayer perceptron consisting of two fully connected layers.…”

“…Since the fine structures differ depending on the symmetry of the orbital against the momentum transfer during the core electron excitation, orientation-dependence of the spectra can be used to analyze the local atomic environments including the anisotropic nature of orbitals. This kind of analysis has been applied for analyzing the orientation of molecules such as polymer films, 1 liquid crystals 2 and organic solar cells 3,4 through analysis of orientation dependence of characteristic peaks corresponding to anisotropic orbitals. Meanwhile, quantitative analysis of fine structures has conventionally been performed by fingerprint matching of reference spectra obtained from standard samples with known structures, but it is difficult to apply to unknown structures.…”