Silica aerogel films via ambient pressure drying for broadband reflectors

Abstract

As an unusual two-dimensional porous nanomaterial, a silica aerogel film was composited with a chiral nematic liquid crystal (N*-LC) to broaden the bandwidth. Here, a thin film of silica aerogel has been synthesized via ambient drying of the wet gel film that was obtained by the sol–gel process of tetraethoxysilane (TEOS). The porosity of the silica aerogel film depends on the hydrolysis and condensation of TEOS, and the modification of the microstructure of the wet gel film. The silica aerogel film/chiral nematic liquid crystal composite films were prepared by compositing the N*-LC with two kinds of silica aerogel films with different porosities. It is found that the reflection bandwidth (Δλ) of the composite film increased upon increasing the porosity of the silica aerogel film. Meanwhile, combining the anchoring effect of the polymer network, Δλ of the composite films was changed from 178 nm to 270 nm and the center wavelength was redshifted by approximately 120 nm. As a result, a presumed mechanism has been proposed to explain the effect of silica aerogel films on the N*-LC.