Control of phase separation and morphology of thiol–ene based PDLCs by curing light intensity

Abstract

Polymer dispersed liquid crystals (PDLCs) based on nematic liquid crystal (LC) E7 and pre-polymeric composition NOA65 were formed via the photoinduced phase separation in a wide intensity range of the actinic UV light ( I = 0.5–40 mW cm −2). The phase separation process was monitored by measuring transmittance kinetics of the composite layers. Increase of curing light intensity accelerates the phase separation and drastically influences the final structure of PDLC samples. Reduction of light intensity below 2 mW cm −2 results in transition from the conventional PDLC morphology of fine monodispersed LC droplets (with a droplets’ diameter d ∼ 1 μm) to the more complex morphology combining fine droplets ( d ∼ 1 μm) with the large LC domains ( d ∼ 10 μm) of irregular shape. The dual-size morphology is explained by essential contribution of both liquid–liquid and liquid–gel demixing processes at low intensities of curing light. This morphology causes unusual electro-optic response characterized by non-monotonic dependence of optical transmittance on the applied voltage, low driving voltage and high initial transmittance. It extends range of potential applications of thiol–ene based PDLCs.