Bending free energy and spontaneous curvature for micelles and microemulsions with weak and strong surfactants

For mixtures of water, oil and non-ionic surfactant the temperature-induced phase separation of a droplet-phase microemulsion into a phase of smaller sized droplets coexisting with a water- or oil-rich phase is studied by dif ferential-scanning microcalorimetry. A comparison of theoretical estimates and experimental findings for specific-heat measurements on mixtures contai ning different types of surfactants (weak and strong) support, a broad rang e of applicability of an interfacial modeling ("Helfrich free energy"), pro vided a more general expression fur the spontaneous curvature of the interf ace is considered than suggested so far. The model provides then a quantita tive interfacial description even for the strongly curved diffuse interface of micelles of weak surfactants.