UV tuning of the electro‐optical and morphology properties in polymer‐dispersed liquid crystals

Abstract

Polymer‐dispersed liquid crystal (PDLC) films operating in reverse mode are transparent electro‐optical devices, which can be turned into an opaque state by application of a suitable electric field. The effect was investigated of different UV powers, used during the polymerization process, on the electro‐optical and morphology properties of PDLCs, working in reverse mode operation. Films were obtained by UV polymerization of mixtures of a low molecular weight nematic liquid crystal and a photopolymerizable liquid crystal monomer, homeotropically aligned by rough conductive surfaces. The electro‐optical and morphology properties of samples were related to the polymerization conditions. Samples polymerized by lower UV powers exhibited “polymer ball” morphology and an electro‐optical response due to the liquid crystal director reorientation, whereas samples obtained at higher UV powers showed a “Swiss cheese” morphology and an electro‐optical response due to dynamic scattering. In addition, we observed by conductivity and IR measurements that UV exposure induces a degradation of the nematic liquid crystal.

Acknowledgments

MIUR, the Italian Ministry for University, is acknowledged for financial support (grants # EX‐60% and PRIN 2005).