Rational materials processes, allowing one to create arbitrary molecular ordering over large areas, are crucial for designing highly functional organic materials and devices for applications in electronics, photonics, mechanics, etc. Recently, such materials have been realized by one-dimensionally (1D) controlled ordering using the assistance of various external stimuli such as pressure, or electric, magnetic, and light fields. Amongst these, optical methods are the most attractive techniques, known as photo-alignment, enabling elaborate molecular ordering over two-dimensions (2D). Until now however, even by photo-alignment, it is a great challenge to optically inscribe complex, macroscopic 2D molecular ordering, and requires dye molecules to be doped in, that dis-color and de-stabilize the materials. Previously we had serendipitously found that photo-polymerization with light through a slit had ability to generate a uniform 1D molecular ordering at the edge of slit, without any dye molecules, or extra setup such as polarized light, or surface alignment layers. Observation of surface structure of a resultant polymer film revealed that surface was embossed after photo-polymerization in the irradiated region. This means that molecules diffuse towards there from an un-irradiated region, and thus implied that the molecular diffusion is one of driving forces for molecular ordering along the diffusion direction. However, there remain the issues of what is the molecular ordering mechanism, and how to increase the pattern capabilities of molecular ordering. Herein we show a new concept developed from the initial discovery, where spatial designs of a photomask enable one to spatially control the photo-polymerized regions generating molecular diffusion in 2D, that would be the single-step, optical, dye-free inscription of arbitrary 2D molecular ordering, over large areas. As an example, photo-polymerization with ultraviolet light through a pinhole mask, of photo-polymerizable liquid crystal monomers, resulted in a radial molecular orientation in the polymer film. Polarized optical microscopic and spectroscopic observations clearly revealed that molecular ordering by this is controlled by the spatial design of the photomask used.

Two-dimensional molecular ordering in liquid crystal polymer films directed by masked photo-polymerization

254th National Meeting (2017)

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