Novel Liquid Crystal Nanocomposities with High Optical Birefringence

Holographically formed Polymer Dispersed Liquid Crystals (H-PDLC) have broad applications in video displays, switchable focus lenses, electro-optic filters, etc. The proper electro-optical performance of these devices requires Liquid Crystal materials with high diffraction efficiency; i.e. with high optical/dielectric anisotropy, low threshold voltage, and fast switching. One can achieve increase of dielectric anisotropy by using chemical synthesis or mixing LC materials. However, in the most cases, this causes increase in the threshold voltage and switching times. Therefore obtaining materials with high dielectric anisotropy and keeping threshold voltage and switching times low is a challenging task. We achieved promising results by making binary mixtures of certain type polar nematic LC with gold nanoparticles. We could increase the dielectric anisotropy, i.e. birefringence, of the materials by almost 100{\%}, while keeping the threshold voltage and switching times low. We propose that this is the result of cluster formation in the mixtures where presence of nanoparticles disrupts anti-parallel packaging of polar LC molecules in dimmers leaving more parallel LC molecules. This increases the order parameter of LC accordingly increasing dielectric anisotropy. Note that SEM images and microphotographs of the samples confirm our proposition.