Dynamic light scattering study of dilute lamellar phases.

2014 Dynamic light scattering measurements on oriented samples of dilute lyotropic smectics have been performed. The hydrodynamics of two-component smectics A is applied to describe the fluctuation spectrum in our multicomponent samples. The experimentally relevant hydrodynamic mode is the undulation/baroclinic mode, which arises from the coupling between concentration and layer displacement fluctuations. Two elastic constants, the layer compressibility modulus (at constant chemical potential) B and the bending modulus K, are extracted from its anisotropic dispersion relation. Membrane flexibility (K) and intermembrane interactions (B) have been studied along a dilution line, with smectic repeating distances in the range 4-35 nm. The results support the view of flexible membranes (flexibility of the order of kB T) interacting by means of Helfrich’s steric interaction. J. Phys. France 50 (1989) 3147-3165 15 OCTOBRE 1989, Classification Physics Abstracts 61.30 62.90 82.70D