Thermodynamics and mechanics of bilayer membranes

Abstract

A mean-field lattice model is applied to chain molecules for the study of surfactant systems. As an example, ${\mathrm{C}}_{12}{E}_5$ surfactants, modeled as ${\mathrm{C}}_{12}\mathrm{O}({\mathrm{C}}_2\mathrm{O}{)}_5$ chains, are forced into cylindrical and spherical shaped vesicles in a monomer solvent. These aggregates are used to obtain the rigidity constants of the bilayers as a function of the hydrophilicity of the surfactant’s headgroup from both a thermodynamic and a mechanical route. Within the numerical accuracy, both routes are fully consistent. The magnitude and sign of the rigidity constants are interpreted to gain insight into features of the experimentally well-established phase diagram. It is concluded that the lattice model is a potentially valuable tool to help understand the generic phase behavior of surfactant systems.