Friction and Adhesion of Microparticle Suspensions on Repellent Surfaces

Abstract

With the recent advancements in the development and application of repellent surfaces, both in air and under liquid medium, accurate characterization of repellence behavior is critical in understanding the mechanism behind many observed phenomena and to exploit them for novel applications. Conventionally, the repellence behavior of a surface is characterized by optical measurement of the dynamic contact angle of the target (to be repelled) liquid on the test surface. However, as already established in literature, optical measurements are prone to appreciable error, especially for repellent surfaces with high contact angle. Here, we present an alternative, more accurate force-based characterization method of both friction and adhesion forces of microparticle laden aqueous droplets over various repellent surfaces, where the force signature is captured by probing the surface with a droplet of the test liquid mounted at the tip of a flexible cantilever and then tracking the deflection of the tip of the cantilever as the probe droplet interacts with the surface. A systematic investigation of response of repellent surfaces towards droplets with different microparticle concentration revealed the dependency and sensitivity of measured adhesion and friction signature towards particle concentration. A comparison with theoretical estimate from optical goniometry highlights the deviation of the theoretical data from experimentally measured values and further substantiates the need of such a force-based approach for accurate characterization of repellence behavior.