How Slippery Surfaces Retain Their Function: Lubricant Film Dynamics Upon Droplet Contact.

Slippery surfaces, prepared by coating functionalized solids with thin viscous lubricant films, offer excellent liquid repellency and are promising for applications ranging from water harvesting to anti-biofouling. Upon liquid contact, the lubricant film deforms, critically influencing phenomena such as droplet coalescence, mobility, and lubricant depletion, yet its dynamics remain unclear. In this study, using principles of fluid dynamics, optics, and capillarity, the spatio-temporal evolution of lubricant films on smooth solid surfaces upon contact with sessile liquids is presented, and their equilibrium configurations are numerically determined. It is found that beneath sessile liquids, the lubricant films exhibit three distinct dynamic stages, while beyond liquids, their maxima propagate according to a defined scaling law. By controlling the key system parameters, partial lift-off of liquid bridges is also demonstrated, a previously unreported phenomenon driven by a capillary rise-like mechanism. Finally, the equilibrium configuration is revealed in which the film thickness at the droplet center stabilizes at tens of nanometers, independent of the initial film thickness. These findings provide fundamental insights into the coupled wetting and transport processes that govern the stability and performance of lubricant-infused slippery surfaces.