Improvements in morphological and electro-optical properties of polymer-dispersed liquid crystal grating using a highly fluorine-substituted acrylate monomer

To improve the morphological and electro-optical properties of a polymer-dispersed liquid crystal (PDLC) grating, a type of highly fluorine-substituted acrylate monomer was added to the prepolymer mixture. The morphologies of the PDLC gratings were investigated using atom force microscopy and scanning electron microscopy. The grating had a very clear polymer/LC interface after addition of 3.9 wt% of fluorine-substituted monomer. The LC droplets in this case were much larger than the sample without fluorinated monomer. This phenomenon indicated that an almost complete phase separation had occurred. However, as the content of fluorine-substituted monomer increased, the morphologies of gratings became less defined and the volumes of LC droplets were smaller. The diffraction efficiency ( DE) decreased with increasing of fluoride content and the V-90 increased simultaneously, which may be ascribed to the blurry interface and the small LC droplets. The highest DE (90%) and lowest V-90 (70 V) were obtained simultaneously under the condition of 3.9 wt% fluoride added in the prepolymer. In addition, it was also found that the fluorine-substituted monomer may disorder the alignment of LCs in the grating.