MORPHOLOGY OF ANISOTROPIC POLYMER-DISPERSED LIQUID-CRYSTALS AND THE EFFECT OF MONOMER FUNCTIONALITY

The morphology of transmission gratings with varying Bragg spacings fo rmed using polymer-dispersed liquid crystals were examined using high- resolution scanning electron microscopy and image analysis techniques. The effect on the morphology of small changes in the overall function ality of the prepolymer syrup was observed. An increase in the amount of monofunctional compound resulted in small, nearly spherical domains (<100 nm in diameter) confined in well-defined lamellae for samples w ith a 0.49 mu m Bragg spacing. A decrease in concentration( an effecti ve increase in monomer functionality) at this Bragg spacing resulted i n larger domains (100-200 nm) with much greater distribution of sizes and shapes. The local volume fractions of discrete liquid crystalline (LC) domains was considerably larger in the latter case. An increase i n the Bragg spacing to 1.35 mu m also resulted in well-defined lamella e of LC domains, although much more coalescence into irregularly shape d individual domains was observed. Surprisingly, the local volume frac tion of LC increased in the larger Bragg spacing samples. The morpholo gy results are discussed qualitatively in terms of liquid-gel demixing where the inherent crosslink density and elasticity of the polymeric host must be considered in phase separation processes on the nanoscale . (C) 1997 John Wiley & Sons, Inc.