Morphology control of liquid crystalline composite gels based on molecular self-assembling kinetics

Liquid crystalline composite gels consisting of a low molecular weight gelator and a low molecular weight liquid crystal were prepared by two types of gelation method: (1) a continuous cooling method and (2) an isothermal gelating method, which provide different molecular self-assembling kinetics of the low molecular weight gelator in gelation processes. Optical microscopic and atomic force microscopic studies revealed that numerous fine strands of the one-dimensionally assembled low molecular weight gelators were formed in the composite gels in the case of the continuous cooling method as well as that of the isothermal gelating method. However, the thinner strands were more homogeneously dispersed in the composite gel prepared via the isothermal gelation at an appropriate temperature than those of the continuous cooling method. This difference on the dispersion state of the strands was shown, by polarizing optical microscopic observation, to have a significant influence on the molecular alignment state of the low-molecular-weight liquid crystal in the liquid crystalline composite gel. The electro-optical response, the light scattering-transmitting switching, of the liquid crystalline composite gel to an applied electric field was drastically dependent on the morphology of the gelators. High-contrast light switching was achieved for the composite prepared by the isothermal gelation. The response time of the electro-optical switching was less than 100μs under 30 V_rms.