Dynamiclight scattering study of membrane interactions in colloidal smectics

Abstract

Dynamic light scattering measurements on oriented samples of dilute lyotropic smectics have been performed. The hydrodynamics of a two-component smectic A is reviewed and applied to describe the fluctuation spectrum in our multi-component samples. The layer compressibility modulus (at constant chemical potential) $\bar B$ is extracted from the anisotropic dispersion relation of the so-called slip mode, which arises from the coupling between concentration and layer displacement fluctuations. The samples, diluted with three different solvents, afford repeat distances of 50–800 Å; the behavior of $\bar B$ suggests either undulation or electrostatic repulsions between membranes, depending on the swelling solvent.