Relationship between mesogenic side chain fraction in liquid crystalline copolymer and bistable electro-optical switching for (liquid crystalline copolymer liquid crystals) composite systems

摘要

The influence of the mesogenic side chain fraction in a side chain liquid crystalline copolymer (LCcoP) on electro-optical effects for (LCcoP/low-molecular-weight nematic liquid crystals (nematic LCs)) composite systems in a smectic state was studied in order to improve reversible and bistable electrooptical switching characteristics driven by ac electric fields with two different frequencies. In the case of the LCcoP fraction lower than 40 wt %, the magnitudes of glass transition temperature (T-g) and the mesophase temperature range for the binary composite systems were independent of the mesogenic side chain fraction in LCcoP, that is, similar to 220 K and 220-340 K, respectively. In the case of the LCcoP fraction of 30 wt % 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 the mesogenic side chain fraction 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-LCcoPematic LCs) composite system showed a novel type of induced smectic phase over a wide range of both mixing concentration (35-85 wt % pseudo-LCcoP) and temperature (220-320 K). This composite system showed a fast switching speed from a transparency state to a lightscattering 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 (similar to 50 ms) as well as a stable memory effect (similar to years) at room temperature. [References: 34]