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

Abstract

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.

Mesomorphic Ceramic Film Fabricated via Blade Coating of a Lyotropic Nematic Liquid Crystal for High-Power Lasers

“…Shear alignment of nanoparticle suspensions is effective between flat substrates. − We recently demonstrated a new approach to preparing mesomorphic ceramic films from lyotropic nematic suspensions of functionalized TiO 2 nanorods . The lyotropic mesophase was manually sheared in a sandwich cell to achieve a monodomain of oriented rods that were subsequently calcined and partially sintered to produce a 2.3 μm thick, solid film over millimeter scale exhibiting optical transparency at 650 to 1700 nm, with a modest birefringence of 0.018.…”

Aqueous Coassembly of Small TiO2 Nanorods with Cellulose Nanocrystals into Transparent, Uniaxially Aligned Inorganic Thin Films for Waveplates

“…Compared to blade- coated films from ZnO particles, blade-coated films from TiO 2 particles reported here resulted in better transparency because of the smaller dimensions. Also, compared to our previous TiO 2 mesomorphic ceramics obtained by manual shear of TiO 2 nanorod suspensions, 8 birefringence was improved due to better alignment achieved by the addition of companion CNCs. Further, uniform alignment over centimeter scales was achieved by blade-coating the suspensions to a controlled thickness.…”

Investigating the Trade‐off between Optical and Mechanical Properties during Constrained Sintering of Mesomorphic Ceramic Films

“…Due to their optical anisotropy, mesomorphic ceramics are under consideration as alternative waveplate materials. [13][14][15][16][17] Unlike inorganic single crystals processed into conventional waveplates, our group has recently developed a mesomorphic ceramic film that can be fabricated over large areas by blade coating a lyotropic nematic sol followed by calcination of the resulting oriented nanoparticle assembly. [13] Birefringence of the calcined films is attributed mainly to form birefringence originating in the anisotropic packing of rods with interstitial pores rather than intrinsic birefringence of the nanocrystal.…”