Surface relaxation of lyotropic lamellar phases

TL;DR

This paper investigates the unique relaxation dynamics of interfaces between lyotropic lamellar phases and liquids, revealing diffusive surface modes influenced by surface tension, compressibility, bending, and slip mechanisms.

Contribution

It introduces a detailed analysis of surface relaxation modes in lyotropic lamellar phases, highlighting differences from simple liquids and smectic-A liquid crystals.

Findings

Surface relaxation is governed by a diffusive mode with decay rate proportional to q^2.

Dissipation is dominated by slip mechanisms involving relative motion of phase components.

Penetration depth of surface modes is large, of order (dq^2)^{-1} for sterically stabilized phases.

Abstract

We study the relaxation modes of an interface between a lyotropic lamellar phase and a gas or a simple liquid. The response is found to be qualitatively different from those of both simple liquids and single-component smectic-A liquid crystals. At low rates it is governed by a non-inertial, diffusive mode whose decay rate increases quadratically with wavenumber, $|\omega|=Aq^2$. The coefficient $A$ depends on the restoring forces of surface tension, compressibility and bending, while the dissipation is dominated by the so-called slip mechanism, i.e, relative motion of the two components of the phase parallel to the lamellae. This surface mode has a large penetration depth which, for sterically stabilised phases, is of order $(dq^2)^{-1}$, where $d$ is the microscopic lamellar spacing.