Evolution of Superhydrophilic Aluminum Alloy Properties in Contact with Water during Cyclic Variation in Temperature.

Hydrophilic or superhydrophilic materials in some cases are considered to be potentially icephobic due to a low ice-adhesion strength to such materials. Here, the evolution of the properties of a superhydrophilic aluminum alloy with hierarchical roughness, fabricated by laser processing, was studied in contact with water during prolonged cyclic variation in temperature. It was shown that the chemical interaction of rough alumina with water molecules caused the substitution of the surface oxide by polymorphic crystalline gibbsite or bayerite phases while preserving hierarchical roughness. Due to such substitution, mechanical durability was notably compromised. Thus, in contrast to the superhydrophobic laser-processed samples, the superhydrophilic samples targeted on the exploitation in an open atmosphere as a material with anti-icing properties cannot be considered as the industrially attractive way to combat icing.

The mechanisms of anti-icing properties degradation for slippery liquid-infused porous surfaces under shear stresses.

HYPOTHESIS: Loss of anti-icing properties of slippery liquid-infused porous surfaces (SLIPS) in conditions of repetitive shear stresses is the intrinsic process related to peculiarities of SLIPS structure. EXPERIMENTS: The study of the evolution of the ice adhesion strength to superhydrophobic surfaces (SHS) and SLIPS during repetitive icing/de-icing cycles measured by a centrifugal method was supplemented with the estimation of change in capillary pressure inside the pores, and SEM analysis of the effect of multiple ice detachments on surface morphology. FINDINGS: Obtained data indicated that although for freshly prepared SLIPS, the ice shear adhesion strength at -25 °C was several times lower than for SHS, repetitive icing-deicing cycles resulted in dramatic SLIPS degradation. In contrast, SHS showed weak degradation at least during 50 cycles. Additional to the depletion of an impregnating oil layer, other mechanisms of SLIPS degradation were hypothesized and tested. It was shown that lower capillary pressure required to displace air by water from the surface texture for SLIPSs compared to SHSs resulted in deeper water/ice penetration inside the grooves. The accelerated destruction of the mechanical texture caused by the Rehbinder effect constitutes another mechanism of SLIPSs degradation.

Superhydrophobic copper in biological liquids: Antibacterial activity and microbiologically induced or inhibited corrosion.

The bactericidal activity of copper and copper alloys is well appreciated and was already exploited in medical practice in 19th century. However, despite of being an essential nutrient required by organisms to perform life functions, excess copper is extremely toxic and detrimental to health. Recent studies have shown that superhydrophobic surfaces have a significant antibacterial potential for reduction of nosocomial infections. At the same time, the prolonged contact with biological liquids may cause a degradation of the superhydrophobic copper surface and corrosion with increasing egress of toxic copper ions. These aspects are poorly studied so far. In this paper, we analyze the evolution of the properties of both the superhydrophobic copper surface and the suspension of Escherichia coli bacteria during their prolonged contact and study the impact of such contact on the bactericidal activity of the surface. It is shown that by controlling the corrosion resistance and the wettability of the superhydrophobic copper substrate, it becomes possible to sustain the bactericidal action of copper substrates for a long time, simultaneously avoiding the excessive corrosive degradation and release of copper ions in the environment.

Reinforced Superhydrophobic Coating on Silicone Rubber for Longstanding Anti-Icing Performance in Severe Conditions.

We present a simple method for fabricating the superhydrophobic coatings on composite silicone rubber used for electrical outdoor applications. The coating is characterized by contact angles as high as 170° and is mechanically durable in contact with the aqueous phase. We discuss the impact of mechanical durability of the surface texture on the anti-icing performance of the coating on the basis of the experimental data on freezing delay of sessile aqueous droplets. A set of complementary data obtained in laboratory and outdoor experiments on freezing delay time, variation of wettability and practical work of adhesion for supercooled aqueous sessile droplets, impacting behavior of droplets at low negative temperatures, as well as the results of snow and ice accumulation in outdoor experiments indicate the very prospective icephobic properties of the developed coating.