Electrically switchable reflection gratings in polymer dispersed liquid crystals

摘要

Electrically switchable volume reflection holograms were written by inhomogeneous illumination of a prepolymer syrup containing a nematic liquid crystal and a multifunctional acrylate monomer. Switchable holograms are diffractive optics structures and the diffraction efficiency can be controlled by the application of an electric field. Reflection gratings with grating spacing spacing varying between 0.16-0.27 mu m were made during the phase separation of liquid crystals from the fast curing prepolymer syrup. The reflection efficiency of the holograms were electrically modulated with the applied field of approx 10-15V/ mu m. Real time study of the grating formation revealed that the maximum efficiency is reached in approx 15 seconds. The shrinkage of the host polymer during grating formation resulted in the blue shift of the reflection notch. The response time of the grating in an electric field is approx 50 mu s. Low voltage scanning electron microscope studies showed the presence of discrete nematic droplet domains of sizes 30-60 nm in liquid crystal rich region.