Adhesion Behavior Driven by Temperature Difference between Impinging Droplets and Superhydrophobic Surfaces

Abstract

Condensation occurs within the microtexture gaps when droplets impact and contact superhydrophobic surfaces due to temperature differences. This condensation leads directly to droplet pinning on the surface. However, the mechanisms behind condensation-induced droplet pinning remain unclear. Additionally, the effects of temperature differences and the suppression by surface structures have not been systematically studied under a subcooling environment. This study examines the impact dynamics of room-temperature and supercooled droplets on three structured surfaces: dense nanoneedle microtextures, micropillar arrays with nanoneedles, and rough micropillar arrays. High-speed imaging and condensation kinetic modeling are employed to analyze and compare dynamic behaviors across different structures. Results indicate that the condensation dynamics primarily dictate the pinning threshold. When the temperature difference increases, the filling rate of the condensed liquid within microtexture gaps surpasses the droplet retraction time, triggering the Wenzel state transition and enhancing pinning effects. This process suppresses droplet rebound and leads to droplet freezing upon impact. The interplay between surface structure and temperature difference significantly affects the detachment performance. The nanoneedle surface demonstrates the strongest anti-icing capability, achieving droplet detachment under the largest temperature difference due to its superior antipinning characteristics. The micropillar-nanoneedle composite structure balances antipinning performance by reducing contact time; however, the increased contact area introduced by micropillars weakens its anti-icing efficiency compared to the nanoneedle surface. The rough micropillar array exhibits the weakest antipinning ability, with its rough microtexture prone to temperature-induced pinning effects. This study provides valuable insights for developing anti-icing surfaces applicable to aerospace, energy systems, and other extreme environments.