Controlled and uniform molecular alignment can provide and enhance functionality in polymer films. We first report that masked photopolymerization with non-polarized light enables direct and precise control of molecular alignment without using a conventional molecular alignment layer. The photopolymerization of a mixture composed of an optically anisotropic acrylate monomer and an isotropic dimethacrylate crosslinker induces either unidirectional or complex molecular alignment, depending upon the shape of the photomask. Such molecular alignments are successfully achieved by shear stress arising from molecular diffusion, even when the photopolymerization is carried out at isotropic temperatures of both the monomer mixture and the obtained polymers.
Photoalignment control of hierarchical structures is
a key process
to enhance the properties of optical and mechanical materials. We
developed an in situ molecular alignment method, where photopolymerization
with the scanned slit light causes molecular flow, leading to two-dimensional
precise alignment of molecules over large areas; however, the alignment
control has been explored only on a molecular scale. In this study,
we demonstrate this photopolymerization-induced molecular flow, enabling
mesoscopic alignment of smectic layer structures composed of anisotropic
molecules. Side-chain liquid-crystalline polymers were obtained from
two different monomers with or without alkyl spacers by photopolymerization
with one-dimensionally scanned slit light. The polymer with an alkyl
spacer displayed mesogens aligned parallel to the scanning direction,
while the polymer with no alkyl spacer resulted in perpendicular alignment
of mesogens to the scanning direction, regulated by the alignment
of the polymer main chain along the light scanning direction. Moreover,
the polymerization with the scanned light aligned not only the mesogens
but also mesoscopic smectic layer structures over large areas, depending
on the structure and scanning pattern of light. We envision that such
a simple polymerization technique could become a powerful and versatile
alignment platform of anisotropic materials in a wide range of scales.
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