Tracking Time-Dependent Surface Reactions via Rolling Drop Dynamics

Super liquid-repellent surfaces have increasingly been employed for various applications during recent decades. Many of these applications entail time-dependent processes occurring over extended exposure times. For example, surface fouling, corrosion, or surface degradation which can result in surface performance loss over time. Changes to conventional wetting parameters, including static contact angles, advancing/receding contact angles, and sliding/roll-off angles before and after exposure, do not always accurately reflect performance loss due to the heterogeneous nature of time-dependent interfacial phenomena. Accordingly, conventional wetting analysis provides discontinuous data that strongly depends on the tested spots on the surface. We suggest a different method for studying gradual surface reactions via monitoring the dynamics of continuously rolling drops on slightly tilted super liquid-repellant surfaces. By studying rolling drops of various liquids on silanized super liquid repellent nanoparticle coatings, we find that alterations in rolling dynamics with time is significantly more sensitive than conventional wetting analysis to small changes at the surface. By observing the deceleration of drops over time, we can quantify how retention forces change at the solid-liquid interface. This provides continuous in-situ surface force data over time. Thus, we can use these dynamics to study time-dependent phenomena occurring on liquid-repellant surfaces exposed to etching and potentially other interfacial reactions.