Swelling behavior and local topology of anL3(sponge) phase

The swelling behavior of an ${\mathit{L}}_3$ (sponge) surfactant phase was studied by the small angle x-ray scattering technique; we show that it is well described by the recently computed swelling law for minimal surfaces. In addition, the self-diffusion coefficient ${\mathit{D}}_{\mathit{S}}$ of several probes within the bilayers of the ${\mathit{L}}_3$ phase was measured by the fluorescent recovery after fringe pattern photobleaching technique. The variation of ${\mathit{D}}_{\mathit{S}}$ with the surfactant volume fraction provides a clue for the topology of the surface over which the midsurface of the bilayers is draped. This allows us to determine the location of the neutral surface near the polar-apolar interface of the bilayers. © 1996 The American Physical Society.