Frost accretion on material surfaces has led to severe impact and even disasters in diverse fields involving aviation, transportation, energy, agriculture, forestry, and food processing. Recent decades have witnessed the booming in material and surface science, in which superhydrophobic and slippery surfaces have been manifested great potential in anti-frosting and defrosting. These two classes of surfaces, inspired by natural creatures featuring with unique physic-chemical properties, are able to impart energy-saving and eco-friendly control over frost formation, propagation and removal across multiple length and time scales. Despite considerable progress, three challenges are still facing us: 1) In the stage of condensation prior to frost occurrence, current designs for superhydrophobic surfaces suffer from uncontrolled condensation dynamics and thus the limited anti-frosting performance when exposed to humid sub-zero environments; 2) During frost propagation stage after the frost occurrence, ice bridging modes on surfaces with different wettabilities in three-dimensional space remain elusive; 3) After the frost accretion, study on efficient defrosting that solely depends on surface coating property is missing. On these bases, this thesis adopts experimental evidence, theoretical analysis and simulation methods to explore and figure out the rationally designed superhydrophobic and slippery surfaces in achieving suppression in frost occurrence by controlling condensation dynamics, mitigation in frost propagation via defining ice bridging modes, and reduction in frost adhesion through using slippery coating.

We first proposed a nanowire cluster (NC) design that imparts the spatiotemporal control of the condensation frosting dynamics. The NC surface can be fabricated by a simple template-assisted electrochemical deposition and naturally form a densely packed nanowire cluster isolated by V-shape groove. We found that, during condensation frosting, such NC structure can simultaneously form a vertical vapor gradient in the groove and a horizontal wetting discreteness. In particularly, at a groove vertex of θ=30° and interfacial contact fraction of φ=0.31, the condensates tended to form on the edge of the of cluster with a stable Cassie-Baster state and be timely removed via coalescence-induce self-jumping. While the remaining droplets exhibited minimized average size and enlarged inter-droplet space, which remarkably reduced the chance of the ice bridging and frost propagation, with 3 and 4 times of enhancement in frost-free duration compared with the conventional superhydrophobic surfaces.

We further revealed the effect of surface wettability on ice bridging modes during frost propagation, breaking the traditional conception that solely considers a single mode. Through microscopic photography from top view, we found the difference in morphological change of a freezing of droplets upon touched by the ice bridge on superhydrophobic and hydrophobic surfaces, where ice tip formed on the side of the droplet on superhydrophobic surface while forming on the top of the droplet on hydrophobic surface. We attributed such distinctions to the different ice bridging modes, i.e., in-air mode on a superhydrophobic surface and along-surface mode on a hydrophobic surface, which was verified via macroscopic photography from side view. Using COMSOL simulations, we found the water vapor concentration difference in the radial direction between droplets on the superhydrophobic surface was the largest, which was beneficial for in-air mode of ice bridging, whereas the along-surface direction concentration difference on hydrophobic surface was the largest and thus generating the along-surface mode. Such a finding provides solutions for design of surface with desired wettability pattern to regulate frost propagation.

We finally investigated the defrosting efficiency of a smooth surface with both hydrophilic and ultra-slippery coating. Especially, we studied the effects of surface hydrophilicity and slipperiness on the growth and movement dynamics of condensates, the propagation and growth of frost layer, and the movement of meltwater. We found that, the hydrophilicity enabled the formation of the well-connected basal frost layer with a large surface coverage, which boosted the substrate-to-frost heat transfer and thus the frost melting efficiency. The exceptional slipperiness facilitated both the microscale and macroscale water mobility, which led to facile frost shedding. Finally, this surface can achieve almost 100% defrosting, with the defrosting efficiency 13 and 19 times higher than the counterparts with only hydrophilicity or slipperiness. A further comparison revealed that the hydrophilic and slippery surface in our work demonstrated a superior defrosting performance over previous works.