Effect of surfactant and evaporation on the thin liquid film spreading in the presence of surface acoustic waves

A theoretical model of a liquid film flow in the presence of surface acoustic waves (SAWs) is established by involving the effects of an insoluble surfactant and evaporation on the spreading process of the partially wetting thin liquid film. A numerical simulation is performed to investigate the liquid film spreading dominated by the SAWs-induced drift of mass and the capillary stress. The simulated results show that SAWs drive liquid films to spread and move, and surfactants promote the further spreading and movement of liquid films, while liquid evaporation suppresses the spreading and movement. The inhibiting contribution of liquid evaporation to the liquid film dynamics is greater than the promoting contribution of the surfactant in this simulation. The mass loss of the liquid film caused by evaporation leads the spreading range to gradually retract. In addition, the spreading range has a positive correlation with the coefficient between the disjoining pressure and surfactant concentration and has a negative correlation with the Marangoni number. The spreading stability of liquid films is strengthened by the surfactant effect, while it is weakened by the evaporation effect.