Adhesion of impure ice on surfaces.

The undesirable buildup of ice can compromise the operational safety of ships in the Arctic to high-flying airplanes, thereby having a detrimental impact on modern life in cold climates. The obstinately strong adhesion between ice and most functional surfaces makes ice removal an energetically expensive and dangerous affair. Hence, over the past few decades, substantial efforts have been directed toward the development of passive ice-shedding surfaces. Conventionally, such research on ice adhesion has almost always been based on ice solidified from pure water. However, in all practical situations, freezing water has dissolved contaminants; ice adhesion studies of which have remained elusive thus far. Here, we cast light on the fundamental role played by various impurities (salt, surfactant, and solvent) commonly found in natural water bodies on the adhesion of ice on common structural materials. We elucidate how varying freezing temperature & contaminant concentration can significantly alter the resultant ice adhesion strength making it either super-slippery or fiercely adherent. The entrapment of impurities in ice changes with the rate of freezing and ensuing adhesion strength increases as the cooling temperature decreases. We discuss the possible role played by the in situ generated solute enriched liquid layer and the nanometric water-like disordered ice layer sandwiched between ice and the substrate behind these observations. Our work provides useful insights into the elementary nature of impure water-to-ice transformation and contributes to the knowledge base of various natural phenomena and rational design of a broad spectrum of anti-icing technologies for transportation, infrastructure, and energy systems.

A Family of Frost-Resistant and Icephobic Coatings.

Anti-icing and icephobic materials play a crucial role in demanding applications ranging from energy to transportation systems operating in frigid climates. Despite remarkable advancements in the development of such surface coatings, the use of anti/de-icing chemicals remains one of the go-to solutions for ice management. However, they are notoriously prone to removal by shear forces and dissolution. Herein, the design rationale for developing a family of cryoprotectant and phase-change material (PCM)-based compositions in the form of mixtures, non-aqueous emulsions-creams, and gels that can substantially overcome such challenges is reported. This is achieved through the sustenance of an in-situ-generated surface hydration layer that protects the underlying substrate from a variety of foulants, varying from ice to disease-causing bacteria. Each formulation utilizes unique chemistry to curtail the embodied cryoprotectant loss and can be easily applied as an all-in-one sprayable/paintable coating capable of significantly outperforming untreated industrial materials in terms of their ability to delay condensation-frosting and shed ice simultaneously. Concomitantly, an array of formulation-specific functionalities is observed in the family, which includes optical transparency, mechanical durability, high shear-flow stability, and self-healing characteristics.

Delaying Ice and Frost Formation Using Phase-Switching Liquids.

Preventing water droplets from transitioning to ice is advantageous for numerous applications. It is demonstrated that the use of certain phase-change materials, which are in liquid state under ambient conditions and have melting point higher than the freezing point of water, referred herein as phase-switching liquids (PSLs), can impede condensation-frosting lasting up to 300 and 15 times longer in bulk and surface infused state, respectively, compared to conventional surfaces under identical environmental conditions. The freezing delay is primarily a consequence of the release of trapped latent heat due to condensation, but is also affected by the solidified PSL surface morphology and its miscibility in water. Regardless of surface chemistry, PSL-infused textured surfaces exhibit low droplet adhesion when operated below the corresponding melting point of the solidified PSLs, engendering ice and frost repellency even on hydrophilic substrates. Additionally, solidified PSL surfaces display varying degrees of optical transparency, can repel a variety of liquids, and self-heal upon physical damage.