EVIDENCE OF A SPONGE-TO-LAMELLAR PHASE-TRANSITION UNDER SHEAR BY X-RAY-SCATTERING EXPERIMENTS IN A COUETTE CELL

The L-3 sponge phase under shear in a Couette cell is totally transfor med to a lamellar phase L-alpha above some critical shear rate (gamma) over dot (c). In situ x-ray scattering and simultaneous light microsc opy observations show that the first nuclei of the L-alpha phase appea r at a low critical shear rate (gamma) over dot (a) and that the orien tation of the lamellae in the L-alpha phase tilts over from a so-calle d ''a'' orientation to a ''c'' orientation at (gamma) over dot (c). In the regime with two phases (gamma) over dot (a) and (gamma) over dot (c), the phases are in an epitaxial relationship immediately after the shear is removed.