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1154 Langmuir 1995,11,1154-1161 The Vesicle-Micelle Transition in Mixed Lipid-Surfactant

Summary: 1154 Langmuir 1995,11,1154-1161
The Vesicle-Micelle Transition in Mixed Lipid-Surfactant
Systems: A Molecular Model
Deborah R. Fattal,' David Andelman,*?$and Avinoam Ben-Shaul*lt
Department of Physical Chemistry and The Fritz Haber Research Center,
The Hebrew University of Jerusalem, Jerusalem 91904,Israel, School of Physics and
Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University,
Ramat Aviv, Tel-Aviv 69978,Israel, and Section de Physique et Chimie, Institut Curie,
11 rue P. et M. Curie, 75231Paris Cedex 05,France
Received October 13,1994. In Final Form: January 26,1995@
of lipid molecules and short chainsurfactants. The freeenergyofboth aggregates(modeledas an infinite
planar bilayer and an infinite cylindrical aggregate)is represented as a sum of internal free energy and
mixingentropycontributions. Theinternal freeenergyistreated as a sumofchain(conformational),head
group,and surfacetensionterms. Calculatingthe free energyof each aggregationgeometryas a function
of lipidhurfactant compositionand using commontangent constructionwe obtainthe compositionsof the
bilayer and the micelle at the phase transition. By varying certain molecular parameters (such as the
"hard core"area of the surfactant head group or the length of the surfactant tail) we study the role of
molecular packing characteristics in determining the compositions at phase coexistence. We find, as
expected,thatuponincreasingthepreferenceofthe surfactantforthemicellargeometry(largerspontaneous


Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University
Ben-Shaul, Avinoam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry; Materials Science; Physics