Electro-Marangoni Effect in Thin Liquid Films

Abstract

The present paper reports a new drainage model accounting for the electro-Marangoni effect in thin liquid films stabilized by ionic surfactants. It was shown that the liquid outflow during the film drainage drifts charges from the diffuse part of the electrical double layer toward the film rim and thus generates a streaming potential along the film plane. This creates reverse fluxes near the film surfaces due to the requirement for zero electric current in the film. In a previous paper on this model (Tsekov et al. Langmuir, 2010, 26, 4703), the immobile surfaces were assumed. Here, the film surfaces were considered mobile, and surface velocity is controlled by an electro-Marangoni number. It was also shown that the motion of the charges makes the film surfaces more mobile, and they flow in reverse direction to the overall liquid outflow. The theory was validated by experimental data on drainage of planar foam films stabilized by cationic (tetrapentyl ammonium bromide) and anionic (sodium dodecyl sulfate) surfactants. A good agreement between the theoretical prediction and experimental data was found.