Bandgap tuning induced by polymer deformation in PSCLCs with positive dielectric anisotropies (Conference Presentation)

Abstract

Recently, we demonstrated large magnitude tuning (1500nm) of reflection band in polymer stabilized cholesteric liquid crystals (PSCLCs) formulated with negative dielectric anisotropy (negative ) liquid crystals with low polymer content (~5% by wt.). Evidence suggests an ionic charge (cation) trapping mechanism by the polymer network which subjects the material system to pitch expansion near the positive electrode and pitch compression near the negative electrode resulting in a nonlinear pitch variation throughout the cell thickness when under the influence of a direct current (DC) field. Thus far this effect has only observed PDLC systems with near zero and negative dielectric anisotropies. In general, the field interaction in systems with negative  stabilize the cholesteric structure as the field strength increases while those systems with positive become are dominated by higher fields becoming homeotropic. Here we explore a PSCLC system with a positive  that suppresses the Freedericksz transition to homeotropic at low field strengths allowing for a unique combination of switching and tuning of the reflection band. This kind of electro-optical control of the reflection band in PSCLCs may have potential use as optical filters, display technologies, telecommunications and tunable lasers.