Electrical Instabilities in Double Layers and Membranes

The effect of applied voltage V on local thickness fluctuations (LTF) in lipid bilayers is examined using the continuum model and accounting for non-locality of membrane elastic moduli. Ponderomotive forces, calculated from the linearized Poisson-Boltzmann equation, reduce LTF energy quadratically with V . Combined with a significant increase in the apex field gradient and perturbation of lipid packing at large LTF amplitudes, this creates a driving force for instability. The critical voltage, though less than Crowley's classical prediction, is still 2-3 times that experimentally observed. This, and the even larger voltages applied in recent molecular dynamics (MD) simulations, demonstrate the difficulty of fully understanding low-voltage breakdown. Some MD results are critically reviewed, including the paradox of negligible pre-breakdown membrane compression. Possible connections between MD results and the question of negative capacitance and related instabilities at electrified interfaces are outlined.