A model for the dynamics of the sterically stabilized dilute lamellar phase is constructed and studied. The model consists of a stack of flexible fluid sheets, with excluded volume, separated by macroscopic layers of solvent. The dynamics of small fluctuations of the sheets about their mean positions is found to have two distinct short-wavelength regimes in which the frequency to depends on the wavenumber q in an unusual manner. One is a singlemembrane Zimm mode, Β’o--iq 3, while the other is a "red-blood-cell mode", to--iq 6. These modes give rise to fluctuation corrections for the viscosities of the system, going as Β’o -1/3 and to 2/3, respectively. In addition, it is shown that a sufficiently rapid shear flow with velocity and gradient in the plane of the layers causes a transition into a state where regions of reduced layer spacing co-exist with regions devoid of any layer material. The critical shear-rate for this transition should go as (layer spacing) -3. Possible experimental tests of these predictions are discussed.
The dilute lamellar phase [1] in surfactant solutions consists of a regularly spaced stack of flexible fluid membranes in a background solvent (oil or water) with viscosity r 1. The normal to the layers is the z axis, while directions in the plane of the layers are labelled Β±. Each membrane is a bilayer of surfactant, typically 20 ,~ thick, while the distance d between adjacent bilayers can be as large as several thousand angstroms [2]. In the limit where all other interactions are effectively eliminated, this phase owes its stability to an interplay between the flexibility of each fluid bilayer governed by a curvature elasticity ~Β’ and the steric repulsion between bilayers [3,4].
In this paper, I present a summary of recent results on the dynamical properties of the dilute lamellar phase. The first part of this work [5a]* 1, on the short-wavelength dynamics at equilibrium, was done in collaboration with