PDLC FILMS FOR CONTROL OF LIGHT TRANSMISSION

We have investigated the light switching properties of polymer dispers ed liquid crystal (PDLC) films, which can be characterized by the spec tral change in transmittance and reflectance due to switching by appli cation of a suitable electrical voltage. The PDLC samples were prepare d using the standard liquid crystal mixture E7 in a uv-curable matrix material. Using these samples, a transmission reduction of up to 30% w as achieved in the solar spectral range. A strong dependence of the li ght switching behaviour on the mass ratio of liquid crystal and matrix material as well as on the curing rate of the matrix material was fou nd, whereas the film thickness has only a small influence. Light scatt ering measurements allowed us to determine the average size of the sca ttering centres. in the samples investigated the liquid crystal drople ts have radii below 2 mu m. Additional measurements of the electric pr operties of the PDLC films showed that the capacity and the resistivit y of the PDLC films depend on both the applied Ac voltage and its freq uency. The power consumption of the above PDLC films is in the range o f 5 W m(-2), if powered with a line frequency of 50 Hz; at lower frequ encies (e.g. 20 Hz) the power consumption can be reduced to about 2.5 W m(-2) without lowering the change in transmittance significantly.