Dynamic Repellency of Water-Proof Surfaces

Abstract

Dynamic wettability is essential for various applications in biology and technology. Conventional optical-based contact angle methods, such as sessile-drop goniometry and tilting-plate techniques, suffer from difficulties in baseline determination and inconsistencies in surface topography. Moreover, they frequently neglect the critical influence of micro/nanostructures, thereby hindering the advancement of liquid-repellent surfaces. Here, we demonstrate a normal force-based method to accurately quantify dynamic wettability via a characteristic parameter, K, which is derived from force curves during the dynamic receding state of the contact line. This force-derivation method avoids optical distortion, accounts for droplet compression, and accurately classifies surfaces into Wenzel, Cassie, and combined states. We demonstrate that K arises from the interplay of normal force, surface energy, and adhesion work, being exclusively dependent on the liquid–solid interface. Validated across diverse artificial and natural substrates, it is crucial for applications in the self-cleaning industry and agricultural spray and related to impact dynamics, enabling the prediction of rebound ability with high resolution.