Constraint and flow: Poiseuille shear response of a surfactant sponge phase

摘要

To minimize their free energy in aqueous solution, surfactant molecules self-assemble to form some basic morphologies a€“ globular micelles, highly extended theadlike micelles and membrane bilayers a€“ which themselves order to display a rich variety of mesophase symmetries and properties. In membrane systems one of the more striking distinctions is that between the free flowing L3 `sponge' phase and the adjacent highly birefringent viscous Le??? phase. Their different macroscopic properties reflect their mesophase membrane ordering a€“ highly anisotropic stacking in the Le??? phase, and an isotropic labyrinth of interconnecting passages in L3 sponges spanning solution space, but without long range order. Our group has spent a number of years investigating the shear flow responses of L3 phases as well as their accommodation to the constraint of a proximate surface a€“ in both these situations over appropriate ranges the higher symmetry of the stacked membrane phases is established. These phases exhibit a strong dynamical scaling due to their entropic stabilization by hydrodynamic fluctuations, and a narrowing of this fluctuation spectrum in the proximity of a solid surface must also to some extent frustrate these membranes dynamically as well as geometrically. In recent experiments, we have begun measurements of the Poiseuille surface shear response of sponge phases a situation in which one might expect effects from an interplay between these dynamic and geometric effects.