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Register a new userOn the surface tension of fluctuating quasi-spherical vesicles
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We calculate the stress tensor for a quasi-spherical vesicle and we thermally average it in order to obtain the actual, mechanical, surface tension $tau$ of the vesicle. Both closed and poked vesicles are considered. We recover our results for $tau$ by differentiating the free-energy with respect to the proper projected area. We show that $tau$ may become negative well before the transition to oblate shapes and that it may reach quite large negative values in the case of small vesicles. This implies that spherical vesicles may have an inner pressure lower than the outer one.
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Within the framework of the Helfrich elastic theory of membranes and of differential geometry we study the possible instabilities of spherical vesicles towards double bubbles. We find that not only temperature, but also magnetic fields can induce topological transformations between spherical vesicles and double bubbles and provide a phase diagram for the equilibrium shapes.
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