Electrohydrodynamic stability of unsymmetrical aqueous films. Application to membrane–membrane interactions

Abstract

The stability of unsymmetrical aqueous films has been investigated. The asymmetry is due to the existence of two different viscous phases surrounding the aqueous film and two different viscoelastic surface layers dividing the three media. The external phases behave as a dielectric (linear potential drop) whereas electrical diffuse layers overlap each other in the aqueous film. The dynamic behaviour of the system under small fluctuations has been analysed. Electrical and van der Waals interactions are treated as body forces. The general dispersion equation is derived and displays coupling terms between the two modes of vibration (bending and squeezing) usually obtained for symmetric systems. Two different situations are studied: (i) an unsymmetrical surface-mechanic profile with identical electric properties and (ii) an unsymmetrical electric profile with identical surface-mechanic properties. Results in the limit of negligible viscosities are obtained for the long-wavelength approximation. The coupling terms due to the asymmetry are destabilizing in both cases (i) and (ii). Our theoretical predictions are applied to the vesicle–vesicle interaction. With such parameters marginal curves (locus of transitory regimes between aperiodically stable and unstable states) show a shift to shorter wavelengths.