Pitch-Length Independent Threshold Voltage of Polymer/Cholesteric Liquid Crystal Nano-Composites

Polymer/cholesteric liquid crystal (ChLC) nano-composites consisting of mesogenic monomers and LCs have nano-sized LC domains dispersed in an anisotropic polymer matrix. They exhibit characteristics not observed in conventional ChLCs, such as sub-millisecond and “deformation-free” electro-optic tuning of the selective reflection band; however, their driving voltage is high compared to conventional ChLCs, and is an issue that needs to be solved for the practical use. Here, we investigate the helical pitch dependence of threshold voltage in polymer/ChLC nano-composites. Five samples with different helical pitches were prepared and their electro-optic characteristics were compared before and after photopolymerization. Although the threshold voltage of the unpolymerized samples were inversely proportional to its helical pitch, the threshold voltage of the polymerized samples showed no dependence on the helical pitch. These results are explained to be a consequence of the driving mechanism of the polymer/ChLC nano-composite, in which electro-optic switching is achieved as a consequence of the nano-confined LC molecules reorienting along the electric field, instead of the helical structure becoming unwound. The threshold voltage is independent of pitch length because the pore sizes are similar in all samples.