Lei Shi, Sang Hwa Kim and Liang-Chy Chien Chemical Physics Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242

This paper describes a method of fabrication a fast-switching flexoelectric liquid crystal device consisting of a cholesteric liquid crystal using a dual-frequency-addressable nematic liquid crystal and with a small amount of polymer network fixed on the substrate surfaces [1]. The photopolymerization of a polymer-precursor initiated by an UV lamp induces the intensity gradient across the cell and leads to the localization of the polymer network on the substrate surface. The polymer network adopts a uniform lying one-dimensional texture of the cholesteric host. The resulting grating-like cholesteric structure can be modulated by an external electrical field as well as a variation of the frequency at a constant voltage. The device enables the amplitude modulation with sub-milliseconds in response time, while the device responds to the phase modulation in a few ms with the applying of a higher voltage to unwind the cholesteric helix. Figure 1 shows the optical properties of a cholesteric flexoelectric device under a frequency modulation at constant voltage. A triangle wave form is applied to the display with the voltage reaches the transition of linear and quadratic responses, i.e., the amplitude and phase modulations. The quadratic response is suppressed by increasing the frequency of applied voltage. Figure 2 shows the short-pitch cholesteric templated growth of polymer network at the substrate surfaces in order to maintain the uniform optical state of cholesteric at zero voltage, whose helixes are lying parallel to the substrates.

[1] S.H. Kim, L. Komitov, L.C. Chien, Appl. Phys. Lett., 86,161118 (2005).