Mesophase of colloidally dispersed nanosheets prepared by exfoliation of layered titanate and niobate

Colloidal dispersion of oxide nanosheets was prepared by exfoliation of lepidocrocite-type layered titanate H1.07Ti1.73O4, and the obtained “nanosheet colloid” formed a liquid crystalline phase which was detected by birefringence of the colloid with naked-eye and optical microscope observations between crossed polarizers. The nanosheet colloids exhibited phase transition from isotropic to isotropic–liquid crystalline biphasic, and finally to full liquid crystalline, as the nanosheet concentration increased. The mesophase was characterized by the stability; liquid crystallinity appeared at low particle concentrations due to high aspect ratio (around 1 nm of thickness and ∼7 μm of lateral length) of the nanosheets. Mixing the titanate nanosheet colloid with hectorite clay yielded apparently homogeneous birefringent colloids, where a cationic cyanine dye was selectively adsorbed onto the clay nanosheets.