Matrix physical structure effect on the electro-optic characteristics of thiol–ene based H-PDLC films

Abstract

The physical and mechanical properties of several thiol–ene based polymers and their mixtures with the liquid crystal, E7, were characterized to probe their relationship with the liquid crystal film electro-optic performance properties. Kinetic data suggests that high conversion is achieved for each thiol–ene combination. Pre-polymerization phase diagrams indicate that each thiol–ene/E7 mixture phase separates well below room temperature, and thus prior to polymerization at room temperature all are in a single phase. Holographic polymer dispersed liquid crystals (HPDLC) were fabricated for several thiol–ene and E7 mixtures, and electro-optical parameters characterized to probe the relationship between the thiol–ene network properties and the electro-optic performance of the HPDLCs. The photocured matrices exhibited glass transitions and tan δ peak maxima that ranged from temperatures below 0 °C to well above room temperature. There is a clear correlation between the physical nature of the matrix and the electro-optic switching parameters with H-PDLC films fabricated from trithiol-pentaerythritol triallylether, all of which exhibit glass transition temperatures below 0 °C, having the fastest switching times and lowest switching voltages at room temperature. Also, in each case higher liquid crystalline concentration resulted in lower switching voltages.