DOI: 10.1051/jp2:1994203
J. Phys. II France 4 (1994) 1333-1362

Phase transitions and shapes of two component membranes and vesicles II : weak segregation limit

Takashi Taniguchi¹, Kyozi Kawasaki¹, David Andelman^{2, 3} and Toshihiro Kawakatsu<sup>1

1</sup>  Department of Physics, Kyushu University 33, Fukuoka 812, Japan
²  School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat Aviv 69978, Tel Aviv, Israel
³  Laboratoire P.S.I., Section Physique et Chimie, Institut Curie, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France

(Received 29 December 1993, received in final form 28 April 1994, accepted 4 May 1994)

Abstract
We investigate equilibrium shapes of vesicles composed of a mixture of partially miscible amphiphiles embedded in two- and three-dimensional space. The amphiphilic molecules can diffuse within the membrane and undergo an intramembrane phase separation below a critical temperature. We assume a simple phenomenological coupling between the local relative composition of the amphiphiles and the local curvature of the membrane shape. A linear stability analysis in the vicinity of the critical temperature indicates that a shape instability is induced by the coupling. Using a single mode approximation, we obtained phase diagrams for : (i) two-dimensional vesicles and (ii) three-dimensional axisymmetric vesicles. The equilibrium shape deformations are shown to depend on the phenomenological parameters of our model yielding highly non-trivial vesicle shapes which deviate from spherical-like objects.

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