Electro-optically oriented Kerr and orientational phase study of normal mode polymer dispersed liquid crystals – Effect of dispersion of nanoparticles

Abstract

The electro-optically oriented polymer dispersed liquid crystals (PDLCs) have importance for their optical transmission, scattering and optical phase modulation characteristics. In the reported work, pristine and nanoparticles (NPs) dispersed normal mode PDLCs were prepared using polymerization induced phase separation method by taking mixture of liquid crystals (LCs), polymeric material and minute concentration of NPs. Experimentally, temperature dependent polarized optical microscopic textural behavior of NPs dispersed PDLC showed the reduction in the phase transition temperature from nematic to isotropic compared to normal mode pristine PDLC sample. The morphological results also show that droplet size is bigger in NPs dispersed PDLCs than pristine. The much lower voltage (approximately half to the pristine PDLC) is required to reorient the LCs inside the NPs dispersed PDLC containing bigger sizes’ droplets. Here, two step electro-optical curves are obtained in both type of PDLCs. Correspondingly, optical phase shifts in PDLCs are measured theoretically and increase in the Kerr phase is found with dispersion of NPs, however Kerr phase is lesser than orientational phases in both normal mode pristine and NPs dispersed PDLCs. Moreover, the induced birefringence is found increased proportionally to the square of the applied electric field and Kerr constant value is one order of magnitude higher for NPs dispersed PDLC than pristine.