Effects of prepolymer structure in holographic polymer dispersed liquid crystal

Three different types of polyols—poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and poly(tetramethylene glycol)—with different molecular weights ( M n ) were incorporated into the prepolymer structure, and the effects were examined with regard to the morphology and performance of holographic polymer dispersed liquid crystal. Among them, PEG showing the lowest glass transition temperature ( T g ) exhibited the lowest threshold voltage ( V th ), lowest operating voltage ( V op ), and lowest diffraction efficiency with slow grating formation owing to its high viscosity of prepolymer mixture. The T g decreased with increasing M n because of the decreased crosslink density and hydrogen bonding, which reduced the anchoring strength, V th and V op . PPG400 gave V th and V op of approximately 7 and 24 V, respectively, with a contrast ratio of approximately 12.