Convection and evaporation dynamics of multicomponent droplets on nanostructured superhydrophobic surfaces

Abstract

The evaporation of multicomponent droplets on a nanostructured surface is a complex process influenced by local concentration, flow dynamics, and three-phase contact line. The coupling mechanism between surface hydrophobicity, liquid velocity, and concentration fields during multicomponent droplet evaporation remains poorly understood despite its fundamental importance. This study reveals the complex dynamics of velocity–concentration coupling in an ethanol/water droplet on nanostructured superhydrophobic surfaces. Through simultaneous characterization of flow behaviors and local concentration distribution, we discovered a distinct hysteresis phenomenon where concentration changes exhibit a time delay relative to velocity field variations. The coupling effects are particularly pronounced near the contact line, where local ethanol concentration gradients drive unique flow patterns and significantly influence the overall evaporative behaviors. Additionally, we conducted a theoretical analysis of the depinning behavior of the multicomponent droplet on a nanostructured doubly reentrant surface by combining the simultaneous local concentration field with the velocity field in the vicinity of the contact line area. Furthermore, a predictive model for real-time local concentration in the contact line area is proposed. The developed model demonstrates high accuracy in estimating depinning concentration when the droplet maintains a Cassie state.