Photoalignmentability of silsesquioxane-containing citraconimide and its solvent-induced surface enrichment in PMMA matrix

ABSTRACT

Photo-reactive polymer of silsesquioxane-containing citraconimide (SQ-CI) was synthesised and evaluated as a photoalignment layer for polymerisable liquid crystals (PLC). A generation mechanism of the anisotropy by the linearly polarised ultraviolet light was discussed by comparing optical retardation of SQ-CI with theoretical calculations using density functional theory. In addition, the SQ-CI and poly(methyl methacrylate) were blended for a model of unification of photoalignment layer and protection layer in liquid crystal display. The orientation of PLC on the blend film was dominated by the solvent used for the sample preparation of PMMA/SQ-CI blend. We found that the SQ-CI was enriched at surface of the blend film prepared from the ?-butyrolactone solution, while not in the case of the film prepared from cyclopentanone solution. The surface enrichment in the film prepared from ?-butyrolactone solution does not follow the conventional mechanism which is that the lower surface free energy component segregates to the blend surface, because the surface free energy of SQ-CI is higher than that of PMMA. Based on the result of solvent-annealing effect and photoalignmentability, we concluded that the mechanism of surface enrichment was explained due to the difference of affinity between the polymer and the solvent.

Graphical Abstract

KEYWORDS:

• Photoalignment
• anisotropic polarisability
• polymerisable liquid crystals
• solvent-induced enrichment
• citraconimide

Disclosure statement

The authors reported no potential conflict of interest.