IDENTIFICATION OF FLOW MECHANISMS FOR A SOFT CRYSTAL

We study the behavior under flow of soft, spherical micelles forming a fee phase at high volume fraction. Due to the size (300 Angstrom) of the elementary objects, the structure can be investigated through Xray s and neutron scattering, at rest and under flow in a Couette cell. Us ing scattering in two perpendicular directions, different mechanisms o f flow are identified. At intermediate shear (around 100 s(-1)) the sy stem exhibits the so called layer sliding mechanism where two dimensio nal hexagonal compact planes of spheres align themselves with the Coue tte cell walls. At lower shear rate, the fee structure is locally pres erved, and the flow is mediated by defects between crystallites. At hi gh shear rate, we observe the melting of the structure and a liquid-li ke structure factor. Moreover, we were able to use the existence of th e layer sliding regime to generate a fee monocrystal by annealing the satcking faults between the decorrelated planes created by the layer s liding.