ELASTICITY AND HYDRODYNAMIC PROPERTIES OF DOPED SOLVENT DILUTE LAMELLAR PHASES

The equilibrium fluctuations and weakly out-of-equilibrium relaxation properties of much-less-than doped solvent much-greater-than dilute la mellar phase are investigated, both theoretically and experimentally, in the low-frequency, long-wavelength limit. The physical system of in terest is a three-component smectic A lyotropic liquid crystal where s urfactant bilayers infinite in extent are periodically stacked along o ne direction in space and separated by a colloidal solution. Two exper imentally relevant modes are found in the lowest frequency part of the fluctuation spectrum of such multicomponent systems. Both are associa ted to the relaxation of coupled layer displacement and colloid concen tration waves. In the limit of small coupling, one mode is close to th e well-known undulation/baroclinic mode of two-component lamellar phas es, while the other corresponds to the Brownian diffusive motion of th e colloid in an anisotropic medium. Elastic constants of the smectic l iquid crystal and diffusion parameters of the colloidal solution may b e deduced from a measurement of the anisotropic dispersion relation of these two modes, as illustrated by dynamic light scattering experimen ts on the ferrosmectic system.