Kinetic pathway of lamellar -> gyroid transition: Pretransition and transient states

The kinetic pathway of a lamellar --> gyroid transition has been investigat ed by means of a small angle x-ray scattering (SAXS) and a new computer sim ulation scheme developed by Saeki. Approaching temperature to a lamellar -- > gyroid transition temperature (T-LG) from the lamellar phase, SAXS profil es reveal that modulation fluctuations with local hexagonal arrangement dev elop in the lamellar state. The modulation fluctuation layer (MFL) structur e is an equilibrium structure and corresponds to the most unstable fluctuat ion modes of lamellar structure. The MFL transforms to a unique three dimen sional network lattice having R-(3c) over bar symmetry, which agrees with t he prediction of the computer simulation. This rhombohedral structure is a transient structure and transforms to the gyroid structure with elapse of t ime. (C) 2001 American Institute of Physics.