DOI: 10.1051/jp2:1993157
J. Phys. II France 3 (1993) 631-645

Thermally induced budding of phospholipid vesicles - a discontinuous process

J. Käs¹, E. Sackmann¹, R. Podgornik², S. Svetina^{2, 3} and B. Zeks<sup>2, 3

1</sup>  Physik Department (Biophysik E22), Technische Universität München, James-Franck Strasse, D-8046 Garching, Germany
²  Department of Theoretical Physics (F-1), J. Stefan Institute, Jamova 39, 61111 Ljubljana, Slovenia
³  Institute of Biophysics, Medical Faculty, University of Ljubljana, Lipiceva 2, 61105 Ljubljana, Slovenia

(Received 6 July 1992, revised 10 February 1993, accepted 11 February 1993)

Abstract
The process of thermally induced budding is studied for DMPC vesicles. With increasing temperature a pear shaped vesicle changes discontinuously into a pair of spherical vesicles connected by a narrow neck. In the course of the cooling process a thermal hysteresis in a stepwise manner is observed. The size of the daughter vesicle diminishes by repeated widening and narrowing of the neck until it finally remains open and the vesicle attains the pear shape again. These experimental findings are difficult to rationalize within the bare bilayer couple model of phospholipid vesicles. To model the discontinuous behavior in the heating process the expansion of the elastic energy of the bilayer up to the third order in the area difference of the two monolayers is empirically introduced. The van der Waals forces between moter and daughter vesicles are shown to be responsible for the repeated widening and narrowing of the neck in the cooling process.

PACS
82.70 - 87.20 - 68.00

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