Eur. Phys. J. E 4, 153-159

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

D. Vollmer¹ and J. Vollmer<sup>2, 3

1</sup>  Institut für Physikalische Chemie, Universität Mainz, Welder-Weg 11, 55099 Mainz, Germany
²  Fachbereich Physik, Universität GH Essen, 45117 Essen, Germany
³  MPI für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany

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(Received 26 April 2000 and Received in final form 13 June 2000)

Abstract
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 differential-scanning microcalorimetry. A comparison of theoretical estimates and experimental findings for specific-heat measurements on mixtures containing different types of surfactants (weak and strong) support a broad range of applicability of an interfacial modeling ("Helfrich free energy"), provided a more general expression for the spontaneous curvature of the interface is considered than suggested so far. The model provides then a quantitative interfacial description even for the strongly curved diffuse interface of micelles of weak surfactants.

PACS
82.70.-y - Disperse systems.
05.70.Fh - Phase transitions: general studies.
07.20.Fw - Calorimetry.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001