ma501803g_si_001.pdf (655.21 kB)
Pathways toward Photoinduced Alignment Switching in Liquid Crystalline Block Copolymer Films
journal contribution
posted on 2014-10-28, 00:00 authored by Masami Sano, Shiyuko Nakamura, Mitsuo Hara, Shusaku Nagano, Yuya Shinohara, Yoshiyuki Amemiya, Takahiro SekiThe pathways toward linearly polarized
light (LPL)-induced alignment
switching in a diblock copolymer film composed of liquid crystalline
(LC) azobenzene (Az) and amorphous poly(butyl methacrylate) (PBMA)
blocks were studied in detail using polarized UV–vis absorption
spectroscopy, grazing incidence small-angle X-ray scattering measurements,
and polarized optical microscopy and transmission electron microscopy
observations. The hierarchical structures of microphase-separated
cylinders of PBMA in a smectic LC Az layer matrix were prealigned
by LPL and then irradiated by orthogonal LPL, which resulted in alignment
switching to the orthogonal direction. In this process, the large
prealigned domains were divided into substantially smaller domains
at the submicrometer level, and then the structures were realigned
in the orthogonal direction in a strongly cooperative manner, most
likely through the domain rotation mechanism. The alignment change
consisted of three stages: (i) fluctuations in the smectic layer of
LC Az side chains in the initial state and breaking up of smaller
grains to the submicrometer level before the orientation change (induction
period), (ii) actual rotation of the divided domains driven by the
photoinduced reorientation of Az mesogens (action period), and (iii)
slower fusion and growth of smaller domains in the orthogonally realigned
direction (postgrowth period). New aspects of dynamic self-assembly
behavior in which different hierarchical structures are involved are
proposed.