Deformability of Multilamellar Vesicles*

Abstract. Although a free unilamellar vesicle has zero or almost zero genuine surface tension, the multilamellar vesicle (“onion”) exhibits a nonzero effective surface tension σeff. The expression for σeff used in the literature is σeff ∼ κB/d0, where B is the interaction modulus between the vesicle bilayers, d0 the repeating distance between the bilayers in the droplet, and κ their bending rigidity. In this paper we calculate the contributions to the effective surface tension of a lamellar droplet in the case when the layers interact with one another and when they are free. It is shown that the interaction contribution to the surface tension is small and σeff is determined mainly by κ, the radius of the droplet R0, and the number of the shape undulation modes lmax. A nonzero surface tension of the layers is also included in the calculation which is necessary when the vesicle membrane is stressed in the complex of other membranes