Formation of a Giant Anisotropically Ordered Assembled Structure of Inorganic Nanosheets through an Optically Induced Stream.

Formation of a desirable submillimeter-scaled assembled structure of particles in the colloid is a difficult subject in colloidal chemistry. Herein, a submillimeter-scaled ordered assembled structure consisting of highly anisotropic two-dimensional plate-like particles, niobate nanosheets, was obtained through an optical manipulation technique that was assisted by a scattering-force-induced stream. A 532 nm continuous wave laser beam with a power of 400 mW was used to illuminate a liquid crystalline niobate nanosheet colloid from the bottom side of a sample cell, inducing the stream of oriented nanosheets toward the upper side of the sample cell. As a result, a 200 μm ordered assembled structure consisting of oriented nanosheets was formed. The assembled structure was also characterized by two-dimensional anisotropy, reflecting that the highly anisotropic morphologies of each nanosheet and the shape of that structure were dependent on the polarization of incident illumination. This study has revealed a new noncontact and on-demand way to obtain submillimeter-scaled ordered anisotropic colloidal assembled structures of nanosized particles such as nanosheets, contributing to fundamental materials science and expanding the utilities of nanosheets.