PDLC FILMS FOR CONTROL OF LIGHT TRANSMISSION

We have investigated the light switching properties of polymer dispersed liquid crystal (PDLC) films, which can be characterized by the spectral change in transmittance and reflectance due to switching by application of a suitable electrical voltage. The PDLC samples were prepared using the standard liquid crystal mixture E7 in a uv-curable matrix material. Using these samples, a transmission reduction of up to 30% was achieved in the solar spectral range. A strong dependence of the light switching behaviour on the mass ratio of liquid crystal and matrix material as well as on the curing rate of the matrix material was found, whereas the film thickness has only a small influence. Light scattering measurements allowed us to determine the average size of the scattering centres. in the samples investigated the liquid crystal droplets have radii below 2 mu m. Additional measurements of the electric properties of the PDLC films showed that the capacity and the resistivity of the PDLC films depend on both the applied Ac voltage and its frequency. The power consumption of the above PDLC films is in the range of 5 W m(-2), if powered with a line frequency of 50 Hz; at lower frequencies (e.g. 20 Hz) the power consumption can be reduced to about 2.5 W m(-2) without lowering the change in transmittance significantly.