THEORY OF RECONSTRUCTIVE PHASE-TRANSITIONS IN LYOTROPIC COMPLEX FLUIDS

A phenomenological theory that describes the reconstructive transforma tions between ordered phases in lyotropic complex fluids is proposed. The symmetry-breaking order parameter of such transformations is assum ed to be the undulation of the interfaces between the molecular aggreg ate regions and the solvent. It is shown to coincide with the first ha rmonics of a Fourier series expressing the form of the interfaces. In this framework, direct and reversed mesophases are shown to be related by a symmetry operation denominated the fluid-reversal symmetry. This underlying symmetry of the system clarifies a number of features of t he phase diagrams of lyotropic complex fluids. The case of oriented in terfaces, which corresponds to a tilting of the amphiphilic molecules on the interfaces, is also considered.