High Speed Optical switching and Long Memory Life for (Liquid Crystalline Polymer/Liquid Crystal) Compopsite Films

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(1) Reversible and bistable electro-optical switching characteristics of induced smectic composite systems compound of a side chain nematic liquid crystalline polymer (nematic LCP) and its copolymer with weak polar methoxy terminal groups in the side chains and low molecular weight nematic liquid crystals (nematic LCs) with each strong polar cyano end have been investigated. The liquid crystalline copolymer (LCcoP) with weak polar methoxy terminal groups in the side chains was used to improve the response speed at room temperature for the bistable and reversible light switching of the binary composite system. Since LCcoP with 52.5 mol% substituted mesogenic side chains did not exhibit mesophase characteristics, this LCcoP was named as pseudo LCcoP in the present study. The (pseudo LCcoP/nematic LCs) composite system showed an induced smectic phase over a wide range of mixing concentration and temperatures. A reversible and bistable electro-optical switching with a short response time ( … More 〜100 ms) was realized for the induced smectic binary composite system upon the application of an appropriate electric field at room temperature. Also, the binary composite system showed a reversible and bistable electro-optical switching based on the sign reversal of the dielectric anisotropy upon the application of ac electric fields with high (〜kHz) and higher (〜100kHz) driving frequencies.(2) The influence of the mesogenic side chain fraction in side chain liquid crystalline copolymer (LCcoP) on electro-optical effects for (LCcoP/low molecular weight nematic liquid crystals : nematic LCs) composite system in a smectic state was studied in order to improve reversible and bistable electro-optical switching characteristics driven by as electro fields with two different frequencies. In the case of LCcoP fraction lower than 40wt% the magnitudes of glass transition temperature (Tg) and the mesophase temperature range for the binary composite systems were independent of the mesogenic side chain fraction in LCcoP, that is 〜220 K and 220-340K, respectively. In the case of the LCcoP fraction of 30wt% and also, its mesogenic side chain fraction of 52.5 and 32.5 mol%, the binary composite systems showed a homogeneous smectic phase at room temperature. On the other hand, the LCcoP with mesogenic chain side fraction of 16.5 mol% did not exhibit any mesomorphic characteristics at any temperature without any addition of LCs. Then, this LCcoP was named as the pseudo LCcoP in this study. However, the (pseudo LCcoP/nematic LCs) composite system showed a novel type of induced smectic phase over a wide range of both mixing concentration (35-85 wt% of the pseudo LCcoP) and temperature (220-320K). This composite system showed a fast switching speed form a transparency state to a light scattering state. Therefore, it was reasonably concluded that the application of LCcoP with the optimum substituent fraction of mesogenic side chain is useful to realize a high electro-optical switching speed (〜50 ms) as well as a stable memory effect (〜years) at room temperatures. Less