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 crystallization. In the mean field approximation, the <Ia(3)over bar d> phase is stable between the lamellar and hexagonal phases close to the disordered liquid phase. When allowance is made for Brazovskii critical fluctuations, a direct phase transition between the disordered liquid and <Ia(3)over bar d> phases is shown to be possible, in agreement with experimental observations. (C) 1996 American Institute of Physics.