STABILITY OF ULTRATHIN LIQUID FILM EVOLUTION WITH SURFACTANT

For an ultrathin liquid film thickness less than 100 nm, instability often accompanies ultrathin liquid film flow driven by surfactant on solid substrate. In present paper, the process of film evolution under the effect of disjoining pressure was simulated with three evolution equations for the film thickness, surfactant interfacial and bulk concentration, which are derived in lubrication approximation. The effects of characteristic parameters on the stability of evolution process are analyzed, and the coincidence between the stability prediction based on linear theory and the simulation results with nonlinear characteristic equation derived with regular modules method is compared. Results show that van der Waals forces promote the instability characteristic while Born repulsion depress it; the secondary instability occurs on the depression section of the film under the condition of small capillary number, which results in a dewetting structure formation ultimately; the increasing of initial value of the film thickness and surfactant bulk concentration enhances the stability of film evolution, however, the increasing of interfacial concentration and the adsorption coefficient leads to an opposite effect instead.