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Polymer Journal (2014) 46, 8588& 2014 The Society of Polymer Science, Japan (SPSJ) All rights reserved 0032-3896/14 http://www.nature.com/pj
Web End =www.nature.com/pj
Nobuhiro Kawatsuki, Hiroshi Shoji, Yotaro Inada, Shuhei Noguchi and Mizuho Kondo
Polymer Journal (2014) 46, 8588; doi:http://dx.doi.org/10.1038/pj.2013.59
Web End =10.1038/pj.2013.59; published online 10 July 2013
Keywords: LC display; liquid crystalline polymer; photoalignment; photoinduced orientation; photopolymer
INTRODUCTION
Photoalignment is emerging as a promising alternative to mechanical rubbing and stretching for orienting molecular structures because it is free from dust and static electricity and is easily patterned.16
Photoalignment is based on the axis-selective photoreaction of photosensitive polymeric lms with linearly polarized (LP) light. It is utilized as an alignment layer for low-molecular-weight liquid crystals (LCs) in LC displays and to fabricate molecularly oriented functional lms.16
Several types of photoreactive materials have been used for photoalignment, including polymers composed of azobenzene,7,8
cinnamate ester,36,9 cinnamic acid10 and phenyl benzoate.11
Exposing these lms to LP light induces a small optical anisotropy due to the axis-selective photoreaction of the photosensitive moieties. If the photoreaction does not induce molecular reorientation, the photoinduced in-plane order parameter (S) is very small (o0.1).12 In contrast, a large optical anisotropy (S40.5) occurs when molecular reorientation is induced by the photoreaction7 or if thermal amplication occurs.6,10,11
We previously reported that photoreactive liquid crystalline polymers exhibit thermally enhanced photoinduced molecular reorientation of their poly(meth)acrylate photo-cross-linkable side groups.5,6 For these liquid crystalline polymers, a small photoinduced optical anisotropy based on axis-selective photo-cross-linking is amplied either parallel or perpendicular to the polarization (E) of the LP light due to the intrinsic reorientation of the LC phases of the material.5 Photo-cross-linkable liquid crystalline polymers composed of cinnamate ester derivative side groups (PMCB6M, Figure 1) can achieve thermally enhanced photoinduced in-plane molecular reorientation parallel to E. These liquid crystalline polymers may be applicable for birefringent lms,6,13 photoalignment layers for functional materials,14,15 and polarization holographic optical devices.16
NOTE
Inuence of molecular weight on the photoinduced reorientation of photo-cross-linkable liquid crystalline polymeric lms
During thermal amplication of PMCB6M lms, the axis-selective photo-cross-linked mesogenic side groups undergo in-plane self-organization, acting as anchors that reorient the non-photoreacted groups such that they are parallel. This process is dictated by the thermal mobility of the mesogenic groups. The intrinsic self-organization in the parallel and perpendicular directions controls...