Arraying needle-like TiO2 particles in a composite film by applying ac bias and its transmittance anisotropy

In an effort to improve energy-efficient windows, we experimented with a precursor slurry composite by using needle-like TiO2 particles as the filler in a urethane matrix. Applying dc bias to the slurry failed to array the needle-like particles in the composite and to deposit on the film surface because of electrophoretic movement. However, applying ac bias of ±5 V to the precursor slurry composite for 12 h resulted in the needle-like TiO2 particles being arrayed in the composite in a direction normal to the film surface. This resulted in an improvement in the energy efficiency of the material through an angular dependence of transmittance in the visible–near-infrared range.