Spreading of liquid droplets on permeable polymeric surfaces

The spreading of liquid droplets on viscous liquid and glassy polymer films has been studied with molecular dynamics simulations. Unlike spreading on solid surfaces the liquid droplet simultaneously spreads and permeates the film, a process that takes place at a large variety of interfaces from biomembranes to thin coatings. The degree of interpenetration and amount of damping from the film depends on the viscosity of the film and the relative interaction of the droplet and film. For low viscosity liquid films, the interpenetration of the droplet follows a t1/2 Fickian power law and the droplet spreads without a precursor foot. For very viscous films a precursor foot spreads ahead of the film, and the droplet does not penetrate the film. The kinetic, hydrodynamic, and combined kinetic/hydrodynamic models of droplet spreading have been generalized to include the absorption of the droplet by the film and are used to analyze the droplet spreading. © EPLA, 2009.