THERMOTROPIC SMECTIC LIQUID-CRYSTALS OF IONIC AMPHIPHILIC COMPOUNDS - A GENERAL DISCUSSION

Starting from a reinvestigation of the long-chain Na n-alkanoates in the molten state, the mesomorphism of amphiphilic mols. comprising an alkyl chain and an ionic endgroup is discussed. Two different smectic mesophases of the "neat" type can occur for these compds.: smectic I, viscous and birefringent, with regular layer stacking; smectic II (often described in the lit. as a conventional liq.), fluid and optically isotropic, due to the small dimensions of the liq.-cryst. domains, and with fluctuations in the interlayer distances. Possible structural arrangements of the ionic end-groups in the smectic layers are presented, and the differences exptl. obsd. between short-chain and long-chain compds. explained in terms of a simple electrostatic model. The mesomorphic state is stable relative to the isotropic state up to temp. well above those at which thermal decompn. occurs.