3-Dimensional structural control of silica microparticles using photoresponsive materials
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3-Dimensional structural control of silica microparticles using photoresponsive materials Taiji Ikawa1, Tomoya Furukawa2, Hidenori Shibata2, Mamiko Narita1, Makoto Mouri1, Osamu Watanabe1 and Masahiro Tawata2 1
Toyota Central R&D Labs., Inc., Nagakute, Aichi, 480-1192, Japan Department of Electrical and Electronic Engineering, Faculty of Science and Technology, Meijo University, 1-501 Shiogamaqguchi, Tenpaku-ku, Nagoya, Aichi, 468-8502, Japan 2
ABSTRACT We demonstrate the three-dimensional arrangement of silica microparticles in bodycentered cubic lattice structure using both a relief pattern formed in the film of the azopolymer and silica micro particles dispersed in a nematic liquid crystal. In the method, firstly, the square lattice relief structures with the spacing of 2000 nm and the depth of 400 nm were formed on the azopolymer film by twice exposure to two beam interference patterns with coherent light of 488 nm in wavelength from Ar ion laser. Next, a nematic liquid crystal (5CB) containing 2000 nm diam. silica microparticles, with the surface modified with silane coupling reagent giving rise to homeotropic texture, was dropped on the relief structure on the azopolymer. The two dimensional square lattice structures of the micropaticles were formed spontaneously in an isotropic to nematic phase transition. Finally, the microparticles were three-dimensionally arranged by using optical tweezers. The microparticles were successfully stacked in a four-step pyramid structure with body centered tetragonal lattice structure. INTRODUCTION Colloidal crystals, a highly ordered array of microparticles, have been receiving a much attention because of their possibility for the application in optics as photonic crystals, structural color, optical filter and so on [1]. A variety of methods have been used to fabricate colloidal crystals. Most of the formed structure has been limited to hexagonal close-packed or cubic closepacked structures. Meanwhile, we have shown that colloidal microparticles can be arrayed on a photochemically formed relief pattern in a film of an acrylate polymer containing azo-dye (azopolymer), successfully forming two-dimensional photonic crystal slabs with tetragonal or hexagonal structures, in which deliverately introduced defects or waveguides [2]. On the other hand, Musevic et al. showed that colloidal particles confined to a few-micrometer-thick layer of a nematic liquid crystal form a two-dimensional crystal structure with quadrupolar or dipolar symmetry [3]. Using a liquid crystal as matrix, a structural control of the colloidal particles by external field will be available, which have potential applications as active optical devices. These arrangements are, however, limited to planar structure. We demonstrate here the two-dimensional and three-dimensional arrangements of silica microparticles using both a relief pattern formed in the film of the azopolymer and silica microparticles dispersed in a nematic liquid crystal. The microparticles were successfully stacked
in a four-step pyramid str
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