Ionic Liquid Crystalline Systems Consisting of Polyammonium and Counter Carboxylate Ions

Novel ionic liquid crystals consisting of polyammonium and carboxylate ions were synthesized by ion complexation of polyethyleneimine and carboxylic acids (α,ω-dicarboxylic acids and hydroxyalkanoic acid). Their thermal properties and orientational behavior were examined by polarizing microscopic observation, differential scanning calorimetry, and variable temperature X-ray diffraction measurements. The ionic liquid crystals exhibited thermotropic liquid crystalline phases. The ionic liquid crystals (BP/ n dA) bearing counter dicarboxylate ions formed a cubic phase upon heating and cooling. On the other hand, the ionic liquid crystal bearing the counter hydroxyalkanoate ion exhibited enantiotropic smectic A and smectic B phases with focal conic fan textures. These ionic liquid crystalline phases were formed by ionic and hydrophobic interactions because they did not have an aromatic mesogenic group.