Phase Transitions and Incommensurability in Crystalline Model Bilayers

Crystalline layer structure compounds containing aligned aliphatic chains show essentially the same phase transition behaviour as lipid bilayers in liquid systems. This is demonstrated on two representatives of the (CnH2n + 1NH3)2MCl4 family (n = 10, M = Cd and n = 3, M = Mn) and on one compound of the CnH2n + NH3Cl family (n = 10). Transitions from completely ordered closely packed structures to disordered states with “melted” chains, transitions from intercalated to nonintercalated structures, as well as modulated (“ripple”) phases can be observed in these model bilayers. A phenomenological description of these transitions is given in the framework of the Landau theory.