LIQUID-CRYSTAL MONOMER ADDITIVES FOR IMPROVED POLYMER-DISPERSED LIQUID-CRYSTALS

The performance of polymer dispersed liquid crystal (PDLC) films was i mproved markedly by introduction of a monofunctional liquid crystal mo nomer component into the photopolymerizable solution from which the PD LC was formed by phase separation. Small amounts of an LC-monomer addi tive enhanced the LC phase separation and slowed the rate of polymeriz ation. Use of 1-10% of LC-monomer in the solution led to the formation of larger LC droplets in a less rigid polymer, resulting in PDLC film s with lower threshold and operating voltages and increased the contra st ratio. The effects of LC-monomer additives on PDLC properties were studied as a function of their structure and concentration, particular ly in a photopolymerizable solution of Norland NOA65 monomer system wi th BDH-E9. For example an optimized amount of LC-monomer, such as 4% p -butylphenyl p-acryloyloxybenzoate in a 1:1 solution of NOA65 and BDH- E9, gave 50% lower threshold and operating voltages, together with 9% higher on-state transmission than the PDLC films without the LC-monome r additive.