Defect-Density-Controlled Phase-Change Phenomena.

Juxtaposing hydrophilicity and hydrophobicity on the same surface, known as hybrid surface engineering, can enhance phase-change heat transfer. However, controlling hydrophilicity on hybrid surfaces in a scalable fashion is a challenge, limiting their application. Here, using widely available metal meshes with variable dimensions and by controlling the patterning pressure, we scalably fabricate hybrid surfaces having spot and gridlike patterns using stamping. Using fog harvesting in a controlled chamber, we show that optimized hybrid surfaces have a ∼37% higher fog harvesting rate when compared to homogeneous superhydrophobic surfaces. Furthermore, condensation frosting experiments reveal that, on grid-patterned hybrid surfaces, frost propagates at ∼160% higher velocity and provides ∼20% less frost coverage when compared to homogeneous superhydrophobic surfaces. During defrost, our hybrid surfaces retain more water when compared to superhydrophobic surfaces due to the presence of hydrophilic patterns and melt water pinning. We adapt our fabrication technique to roll-to-roll patterning, demonstrating wettability contrast on round metallic geometries via atmospheric water vapor condensation. This work provides guidelines for the rapid, substrate-independent, and scalable fabrication of hybrid wettability surfaces for a wide variety of applications.

Durability and Degradation Mechanisms of Antifrosting Surfaces.

Rapid implementation of renewable energy technologies has exacerbated the potential for economic loss and safety concerns caused by ice and frost accretion, which occurs on the surfaces of wind turbine blades, photovoltaic panels, and residential and electric vehicle air-source heat pumps. The past decade has seen advances in surface chemistry and micro- and nanostructures that can promote passive antifrosting and enhance defrosting. However, the durability of these surfaces remains the major obstacle preventing real-life applications, with degradation mechanisms remaining poorly understood. Here, we conducted durability tests on antifrosting surfaces, including superhydrophobic, hydrophobic, superhydrophilic, and slippery liquid-infused surfaces. For superhydrophobic surfaces, we demonstrate durability with progressive degradation for up to 1000 cycles of atmospheric frosting-defrosting and month-long outdoor exposure tests. We show that progressive degradation, as reflected by increased condensate retention and reduced droplet shedding, results from molecular-level degradation of the low-surface-energy self-assembled monolayer (SAM). The degradation of the SAM leads to local high-surface-energy defects, which further deteriorate the surface by promoting accumulation of atmospheric particulate matter during cyclic condensation, frosting, and melt drying. Furthermore, cyclic frosting and defrost tests demonstrate the durability and degradation mechanisms of other surfaces to show, for example, the loss of water affinity of superhydrophilic surfaces after 22 days due to atmospheric volatile organic compound (VOC) adsorption and significant lubricant drainage for lubricant-infused surfaces after 100 cycles. Our work reveals the degradation mechanism of functional surfaces during exposure to long-term frost-defrost cycling and elucidates guidelines for the development of future surfaces for real-life antifrosting/icing applications.