A review of droplet dynamics on complex surfaces: mechanisms, regulation, and applications

The dynamic behavior of liquid droplets on complex solid surfaces represents a critical frontier at the intersection of surface science, fluid mechanics, and materials engineering. This review systematically examines the regulation of droplet dynamics, emphasizing the individual and synergistic effects of surface wettability and surface roughness. It highlights innovative investigations into the coupling between external fields and complex surfaces, as well as the integration of multi-scale experimental and simulation methodologies. Surface wettability governs droplet spreading and directional transport through precise modulation of interfacial energy, with the static contact angle and wettability gradients dictating the initial shape and self-driven motion tendencies. In contrast, surface topography influences motion resistance by mediating transitions between Wenzel and Cassie-Baxter regimes, where hierarchical micro-nano structures or roughness gradients further optimize dynamic performance. Their synergistic coupling, quantified by the dimensionless parameter χ which integrates the surface roughness ratio and intrinsic Young’s contact angle, determines the ease of droplet motion:low χ favors Cassie states with low resistance, while high χ promotes pinned Wenzel states. Recent advances in high-resolution experiments and multi-scale simulations have enhanced mechanistic understanding: however, challenges persist, including the lack of predictive frameworks for multi-factor coupling and insufficient validation between experimental and computational data. Future progress in cross-scale in-situ characterization and high-fidelity modeling will facilitate precise droplet manipulation, thereby advancing applications in anti-icing, microfluidics, and programmable liquid transport.