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. Vollmer2, 31 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
vollmerd@mail.uni-mainz.de
(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.
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
