Mesomorphic Ceramic Films Synthesized via Lyotropic Self-Assembly of Metal Oxide Nanorods Complete with Sintering

Mesomorphic ceramics are broadly defined as solid systems with morphologies intermediate between isotropic materials and single crystals. To illustrate this materials concept, a class of mesomorphic ceramics with nematic-like superstructures has been synthesized via lyotropic liquid crystals of titanium dioxide, TiO2, in an isotropic solvent for a demonstration of uniaxially oriented solid films. A lyotropic dispersion of ligand-capped anatase nanorods at 60 wt % in chlorobenzene was calcined and sintered with prior manual shear to form an optically anisotropic, 2.3 ± 0.3 μm-thick solid film. In the course of sintering, nanorods fuse into low-aspect ratio grains that form nematic domains. Shear-induced alignment of nanorods followed by thermal treatment creates uniaxial orientation across millimeters, which exhibits high optical transparency and a nearly constant birefringence of 0.018 ± 0.002 from 650 to 1700 nm. Distinct from liquid-crystal templating, this new approach yields superstructures of nanoparticles with relative ease and at lower costs. The present study opens a pathway toward robust, ceramic-based solid films for diverse application.