Effect of Cell Gap on Electro-Optical Properties of Polymer Dispersed Liquid Crystal Lens for Smart Electronic Glasses

Polymer dispersed liquid crystal (PDLC) lenses with a cell gap of 11 mu m and 30 mu m were made from a uniformly dispersed mixture of 40% prepolymer (NOA 65, Norland optical adhesive 65) and 60% E7 liquid crystal. PDLC's mixture between two ITO coated glasses was polymerized by UV (ultraviolet) curing in the polymerization induced phase separation (PIPS) process. Decline of cell gap is a physical approach to improve the electrooptical properties, while cooling or doping of SiO2 nanoparticles is the microstructural approach to enhance the properties, because the electric field applied to the liquid crystal molecules in LC droplets is inversely proportional to the cell gap. A smaller cell gap significantly and effectively increases the electric field applied to PDLCD devices. The driving voltages and slope for the sample with a cell gap of 11 mu m and 30 mu m were drastically improved. The driving voltage and the slope of the linear region of PDLC lens with narrow cell gap of 11 mu m were drastically enhanced compared to those of the samples with 30 mu m cell gap and the cooled and doped samples. These improvements were due to the increase of the applied electric field. However, the response time and contrast ratio were deteriorated. It seems that this deterioration was caused by the sticking or fixing of liquid crystal molecules in LC (liquid crystal) droplets by the intensive electric field applied to the PDLC device.