Synthesis and characterization of hexamethylenetetramine-based ionic liquid crystals

Abstract

A series of hexamethylenetetramine-based ionic liquid crystals (ILCs) containing cholesterol derivatives and different anions including Br−1, BF4−1, PF6−1, H2PO4−, CF3COO−, TsO−, and CSA-SO3- were synthesized, and the characterization, possible applications and self-assembly behavior were discussed. The ILCs were synthesized from bromine-containing precursor liquid crystal, which was made of cholesterol and 4-bromobutyryl chloride. The ILCs showed smectic A (SmA) mesophase. For these hexamethylenetetramine-containing ILCs, Tg, Ti and liquid-crystalline temperature range reduced slightly in sequence of Br−1, BF4−1, PF6−1, H2PO4−, CF3COO−, TsO−, and CSA-SO3- anions. But the d-spacing of the lamellar structure in SmA phase increased in this sequence of these anions. Because of microphase separation and ionic electrostatic attraction, the SmA layers and self-assembly were formed in these ILCs. The ionic conductivities of the ILCs significantly increased in SmA phase due to unique facilitated ion transport pathways of lamellar ionic channels.