Thermodynamics and mechanics of bilayer membranes

A mean-field lattice model is applied to chain molecules for the study of surfactant systems. As an example, C12E5 surfactants, modeled as C12O(C2O)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.