Transmission variation using scattering/transparent switching layers

摘要

Abstract: Due to the fallibility of mechanical shading devices such as shutters or blinds, thin films with variable transmittance, which can be applied directly to a glazing surface, are being investigated for so-called `smart windows' or for applications together with transparent insulating materials. In the films discussed here, the transmittance is changed by varying the scattering properties, which depend on changes in the effective refractive index and/or size of microstructures. This may be achieved by orientation and relaxation of birefringent liquid crystal molecules within polymer-encapsulated droplets by applying an electric field, by reversible separation and mixing of two polymers with temperature variation, or by exploiting the Christiansen effect. In this paper, the effect of varying experimentally accessible parameters on the transmittance change is first explored theoretically by applying Mie and multiple scattering theories. These results are complemented by measurements of the spectral dependence of the transmittance and reflectance of the first two types of switching samples, i.e., polymer-dispersed liquid crystal (PDLC) films and thermotropic layers of polymer blends. Changes of almost 40% in the visual and solar direct-hemispherical transmittance were measured for the range of sample thicknesses investigated here. !11