Liquid crystalline physical gels: electrooptic properties and microphase-separated structures

A nematic liquid crystal, 4-(trans-4-pentylcyclohexyl)benzonitrile, has been physically gelled by hydrogen-bonded network formation of low molecular weight additives, that is, three amide compounds. Electro-optic measurements in twisted nematic (TN) cells have been performed for the resultant gels that exhibit liquid-crystalline gel states at room temperature. Each of the anisotropic gels formed by the three gelling agents, exhibiting microphase-separated structures, shows different electro-optic responses. One of the gels responds to an electric field more than twice as fast as the single liquid crystal component. Network aggregates with different morphologies are observed for each of the gelling agents. More finely dispersed fibrous networks would contribute to the faster electro-optic response. Thermal transition behavior and composite structures of the anisotropic physical gels have been examined by polarizing optical microscope observation and differential scanning calorimetry.