Polar Switching of Dipolar Molecules Confined in Submicron- and Micron-sized Pores in Polymer Films

p-Nitroanisole (pNA) confined in submicron- and micron-sized pores in polyimide films shows enhanced dipolar polarization and polar switching characteristics in the liquid state, as revealed by hysteresis in the polarization (P)-electric field (E) curves. They reflect interface-induced orientational polarization of confined pNA molecules, i.e. inversion of molecular orientation depending on the direction of the external electric field. Such an enhanced orientational polarization is not observed for the bulk pNA nor pristine polyimide films, and interactions between the confined pNA molecules and the surface of the pores are indispensable for the polar switching phenomena.