LANDAU-BRAZOVSKII THEORY FOR THE IA3D STRUCTURE

The stability of the so-called ''gyroid'' phase, of <Ia(3)over bar d> symmetry, observed for lyotropic liquid crystals and block copolymers is accounted for using the Landau-Brazovskii theory of weak crystalliz ation. In the mean field approximation, the <Ia(3)over bar d> phase is stable between the lamellar and hexagonal phases close to the disorde red liquid phase. When allowance is made for Brazovskii critical fluct uations, a direct phase transition between the disordered liquid and < Ia(3)over bar d> phases is shown to be possible, in agreement with exp erimental observations. (C) 1996 American Institute of Physics.