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Liquid-crystalline physical gels have been obtained by the self-aggregation of a gluconamide derivative through intermolecular hydrogen bonding in liquid crystals. These liquidcrystalline gels are microphase-separated composites consisting of the solid fibrous aggregates of the gelling agent and the liquid-crystalline phase of mesogenic molecules. Thermoreversible three states, isotropic liquid, normal (isotropic) gel, and liquid-crystalline gel, have been achieved for the mixtures of liquid crystals and the gelling agent. As the concentration of the gelling agent increases, the sol-gel transition temperature and the enthalpy change of the transition from isotropic to anisotropic increase. The increase of the enthalpy change suggests that some mesogenic molecules are anchoring strongly to the surface of the fibrous gelling agents. Variable-temperature infrared spectra show that the association and the dissociation of intermolecular hydrogen bonding of the gelling agent occur in the process of the sol-gel transition. Liquid-crystalline gels are responsive to electric fields in a twisted nematic (TN) cell. These anisotropic gels would be applicable to new dynamically functional materials.

A new bisurea gelator derived from 2,6-diaminopyridine has been developed. It efficiently gelates common organic and liquid crystalline (LC) solvents by forming elongated self-assembled fibres in solvents. X-Ray crystallography and 1H NMR measurements reveal that two urea groups in pyridine-based bisurea compounds form different hydrogen bonding patterns. One of two urea units is involved in intramolecular hydrogen bonding with the pyridyl nitrogen, while the other urea unit forms bifurcated intermolecular hydrogen bonding. This hydrogen-bonded structure is key for the fibrous self-assembly along with the efficient gelation. In addition, LC gels based on the pyridine-based gelator exhibit good electrooptic properties. These results indicate that the pyridine-based bisurea compound is a good gelator not only effective in gelation but also useful as a component of functional soft materials.

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