Dynamic light scattering from a highly swollen nonionic lamellar liquid crystal

We have conducted a dynamic light-scattering study of the homeotropically aligned highly swollen lamellar phase (layer separation d∼180 nm) of a nonionic binary system, dodecylpentaglycol (C12E5) and water, where the steric and entropic repulsion is the dominant intermembrane force stabilizing the lamellar order. We have identified a hydrodynamic mode in the two momentum-transfer limits available to light scattering. Based on previous models, we have found an explicit expression for the dispersion relation of this ‘‘baroclinic’’ or ‘‘slip’’ mode for systems with large layer spacing, which successfully explains our experimental results. When d is large, the bilayer curvature elasticity and the viscous coupling between water and the bilayers become more important to the understanding of the baroclinic mode. We found the curvature elastic constant ${\mathit{k}}_{\mathit{c}}$≃${\mathit{k}}_{\mathit{B}}$T, consistent with generally accepted values for flexible membranes.