Interfacial Charge Transfer Modulated Static Friction Resistance of Water Drops

The sliding of liquid drops over solid surfaces is a common phenomenon in nature and crucial in a variety of technological applications. Frictional dissipation along the contact line and viscous dissipation has long been regarded to dominate drop sliding. However, the ubiquitous solid-liquid interface charge transfer has received little attention. In this study, we systematically investigated the interfacial charge transfer between water drops and polarized poly(vinylidene fluoride) (ferroelectric insulator) surfaces and the effects of surface charge on static friction resistances acting on water drops. It is found that static friction resistance, reflected by the corresponding critical sliding angle, has a fourth-order function dependence on the surface potential as revealed by experiments and theoretical modeling. Interfacial charge transfer could either strengthen or weaken the surface potential up to the charge density carried by the water drops and substrates, thus resulting in the change of static friction resistance during sequential drop sliding. These findings apply to generalized problems for water at solid surfaces with charged interfaces (water, solid, or both are charged) and highlight the pivotal role of charge transfer at liquid-solid interfaces in governing drop motion.