Highly oriented mesostructured thin films: shear-induced deposition of optically anisotropic coatings of tungsten oxide/surfactant composites

A new method has been demonstrated to synthesize highly oriented mesostructured coatings of tungsten oxide/surfactant composites on amorphous substrates by a shear-flow-induced deposition mechanism. The applied flow field provides convective transport of film precursors and orients the domains of the mesostructure, resulting in its macroscopic alignment. Two-dimensional X-ray diffraction, scanning electron microscopy, and transmission electron microscopy suggest a hexagonal-close-packed channel structure with periodicity along the c-axis generated by a sequence of tungsten oxide polyanions. The mesostructure has been indexed with a hexagonal unit cell with lattice constants a = b = 46.45 angstrom, c = 12.93 angstrom, α = β = 90°, and γ = 120°. The channels have no preferred rotational orientation about the c-axis and are oriented in the direction of the applied flow field with an order parameter of 0.95. The high degree of orientation renders the films optically anisotropic and results in preferential scattering of light perpendicular to the flow direction. Also, the anisotropies of the real and imaginary parts of the refractive index tensor are measured as 0.005 and 0.002, respectively.