Spreading of soluble surfactant solutions over a thin aqueous layer on isothermal solid substrate

摘要

The spreading of a drop of soluble surfactant over thin aqueous layer in the presence of isothermal heating is considered. Use of lubrication theory yields a coupled pair of partial differential equations for the film thickness, surface and bulk surfactant concentrations. The numerical results by the PDECOL procedure show that droplet patterns are obtained under the isothermal conditions of underlying substrate. The effects of variation of Marangoni parameter and air-liquid Biot number are examined. Decreasing Marangoni parameter leads to flatter drop peak and longer time to rupture. Decreasing the air-liquid Biot number flattens the film thickness and surfactant concentration profile of the drop. In all situations the surfactant is found to rigidify the air-liquid interface, while the thermal capillary acts to destabilize the film.