Shape deformation of a vesicle under an axisymmetric non-uniform alternating electric field.

We suggest that non-uniform electric fields that are commonly used to study vesicle dielectrophoresis can be employed in hitherto relatively unexplored areas of vesicle deformation (for electromechanical characterization) and electroporation. Conventionally, the tension generated in vesicles is commonly modeled to be entropic or enthalpic in origin. A comparison of the configuration of a vesicle in the enthalpic and entropic regimes as well as the cross over between the two regimes during vesicle deformation has eluded understanding. A lucid demonstration of this concept is provided by the study of vesicle deformation under axisymmetric quadrupole electric field and the shapes of the vesicles obtained using the entropic and the enthalpic approaches, show significant differences. A strong dependence of the final vesicle shapes on the ratio of electrical conductivities of the fluids inside and outside the vesicle as well as on the frequency of the applied quadrupole electric field is observed. A comparison with experimental data from the literature is also made. Moreover, an excess area dependent transition between the entropic and enthalpic regimes is observed. The method could be used to estimate electromechanical properties of the vesicle.