Primož
Peterlin1, Saša Svetina1,2 and
Boštjan Žekš1,2
1Institute of Biophysics, Medical Faculty, University of
Ljubljana, Lipičeva 2, 1000 Ljubljana, and 2Jožef
Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
External AC electric field deforms flaccid phospholipid vesicles in aqueous solution into approximate rotational ellipsoids, with the rotational axis aligned to the direction of the applied field. At low frequencies, the deformation is prolate. As the frequency is increased, a transition into oblate deformation is observed. A theoretical explanation for this phenomenon was sought. The shape of vesicle is determined by minimising its total free energy, consisting of membrane bending energy and the work done by the force of electric field during vesicle deformation. The latter contribution is calculated by first solving the Laplace equation for electric potential in case of a spherical shell, immersed in a medium with different electric properties. From the potential, Maxwell stress tensor is calculated. Evaluated on the membrane-water boundaries in the direction perpendicular to it, scalarly multiplied by the local membrane displacement and integrated over the vesicle surface, it yields the sought term. Described theoretical model provides both qualitative and quantitative agreement with the experiment, and can in turn be used for determining electrical parameters of the observed system.