Inhibiting Condensation Freezing on Patterned Polyelectrolyte Coatings

Ice Adhesion Properties on Micropillared Superhydrophobic Surfaces

In this work, we investigate the freezing behavior and ice adhesion properties of sessile drops on micropillared superhydrophobic surfaces (SHSs) with various sizes, which are of practical importance for anti/deicing. First of all, it is demonstrated that the recalescence is related only to the supercooling degree of drops but not to the geometrical parameters of micropillars. The freezing time of sessile drops first increases and then decreases with the area fraction of the SHSs, which demonstrates the nonmonotonic dependence of the icing time on the area fraction. Moreover, the influence of the geometrical parameters of the micropillars on the ice adhesion is discussed. With the decrease of the substrate temperature, the wetting state of the adhesive ice can be transformed from the Cassie ice to the Wenzel ice. For the Cassie ice, the adhesive force is proportional to the area fraction of the SHSs. Interestingly, experimental results show that there exist two interfacial debonding modes of the Wenzel ice: translational debonding and rotational debonding. Furthermore, it is found that the rotational debonding mode contributes to a much lower adhesive force between the ice and the micropillared surface compared to that of the translational debonding mode. By analyzing the critical interfacial energy release rate of the two modes, we deduce the threshold between the two modes, which is quantified as the geometrical parameters of the micropillars. In addition, quantitative relations between the geometrical parameters and the adhesion strengths of the two modes are also obtained. We envision that this work would shed new light on the design optimization of anti/deicing materials.

Iodine-Oxidized Diene-Based Rubbers as Anti-icing and Deicing Polymer Coatings

In an effort to prevent or minimize icing hazards, techniques and materials for icing inhibition and deicing have always been highly favored throughout human history. This work discovers the integrated anti-icing and deicing effects of poly(styrene-b-butadiene-b-styrene) triblock rubber (SBS) after its easy oxidation in iodine vapor. Iodine oxidation happens on the block of polybutadiene, featured by the conversion of SBS from hydrophobic to amphiphilic and the improved capability of photothermal conversion. The oxidized SBS can serve as a polymer coating, which possesses intriguing abilities to delay the kinetics of icing on its surface and repel the ice under light illumination. According to characterizations of surface chemistry and mechanical performance, iodine oxidation is assumed to involve the processes of iodine coordination to unsaturated bonds, the formation of radical cations as a result of the redox reaction between iodine and unsaturated carbon-carbon bonds, improved light absorption owing to the formation of polyiodide anions, and intermolecular coupling of radical cations. The appearance of polar moieties/species within the oxidized SBS is attributed to the delayed ice nucleation. The significant photothermal capacity in visible and near-infrared windows enables the iodine-oxidized SBS coating to remove the adhered ice by melting under light illumination when the icing process is inevitable, even at an extremely low temperature (-25 °C).

Recent advances of bio-inspired anti-icing surfaces

The need for improved anti-icing surfaces is the demand of the time and closely related to many important aspects of our lives as surface icing threatens not only industrial production but also human safety. Freezing on a cold surface is usually a heterogeneous nucleation process induced by the substrate. Creating an anti-icing surface is mainly achieved by changing surface morphology and chemistry to regulate the interaction between the surface and the water/ice to inhibit freezing on the surface. In this paper, recent research progress in the creation of biomimetic anti-icing surfaces is reviewed. Firstly, basic strategies of bionic anti-icing are introduced, and then bionic anti-icing surface strategies are reviewed according to four aspects: the process of ice formation, including condensate self-removing, inhibiting ice nucleation, reducing ice adhesion, and melting accumulated ice on the surface. The remaining challenges and the direction of future development of biomimetic anti-icing surfaces are also discussed.

Recent advances in bioinspired superhydrophobic ice-proof surfaces: challenges and prospects

Bionic superhydrophobic ice-proof surfaces inspired by natural biology show great potential in daily life. They have attracted wide research interest due to their promising and wide applications in offshore equipment, transportation, power transmission, communication, energy, etc. The flourishing development of superhydrophobic ice-proof surfaces has been witnessed due to the availability of various fabrication methods. These surfaces can effectively inhibit the accumulation of ice, thereby ensuring the safety of human life and property. This review highlights the latest advances in bio-inspired superhydrophobic ice-proof materials. Firstly, several familiar cold-resistant creatures with well-organized texture structures are listed briefly, which provide an excellent template for the design of bioinspired ice-proof surfaces. Next, the advantages and disadvantages of the current techniques for the preparation of superhydrophobic ice-proof surfaces are also analyzed in depth. Subsequently, the theoretical knowledge on icing formation and three passive ice-proof strategies are introduced in detail. Afterward, the recent progress in improving the durability of ice-proof surfaces is emphasized. Finally, the remaining challenges and promising breakthroughs in this field are briefly discussed.

Gels as emerging anti-icing materials: a mini review

Gel materials have drawn great attention recently in the anti-icing research community due to their remarkable potential for reducing ice adhesion, inhibiting ice nucleation, and restricting ice propagation. Although the current anti-icing gels are in their infancy and far from practical applications due to poor durability, their outstanding prospect of icephobicity has already shed light on a new group of emerging anti-icing materials. There is a need for a timely review to consolidate the new trends and foster the development towards dedicated applications. Starting from the stage of icing, we first survey the relevant anti-icing strategies. The latest anti-icing gels are then categorized by their liquid phases into organogels, hydrogels, and ionogels. At the same time, the current research focuses, anti-icing mechanisms and shortcomings affiliated with each category are carefully analysed. Based upon the reported state-of-the-art anti-icing research and our own experience in polymer-based anti-icing materials, suggestions for the future development of the anti-icing gels are presented, including pathways to enhance durability, the need to build up the missing fundamentals, and the possibility to enable stimuli-responsive properties. The primary aim of this review is to motivate researchers in both the anti-icing and gel research communities to perform a synchronized effort to rapidly advance the understanding and making of gel-based next generation anti-icing materials.

Dynamic Anti-Icing Surfaces (DAIS)

Remarkable progress has been made in surface icephobicity in the recent years. The mainstream standpoint of the reported antiicing surfaces yet only considers the ice-substrate interface and its adjacent regions being of static nature. In reality, the local structures and the overall properties of ice-substrate interfaces evolve with time, temperature and various external stimuli. Understanding the dynamic properties of the icing interface is crucial for shedding new light on the design of new anti-icing surfaces to meet challenges of harsh conditions including extremely low temperature and/or long working time. This article surveys the state-of-the-art anti-icing surfaces and dissects their dynamic changes of the chemical/physical states at icing interface. According to the focused critical ice-substrate contacting locations, namely the most important ice-substrate interface and the adjacent regions in the substrate and in the ice, the available anti-icing surfaces are for the first time re-assessed by taking the dynamic evolution into account. Subsequently, the recent works in the preparation of dynamic anti-icing surfaces (DAIS) that consider time-evolving properties, with their potentials in practical applications, and the challenges confronted are summarized and discussed, aiming for providing a thorough review of the promising concept of DAIS for guiding the future icephobic materials designs.

Improving Anti-Icing and De-Icing Performances via Thermal-Regulation with Macroporous Xerogel

The accumulation of ice in winter has brought many problems in industrial production and everyday life, and how to prevent icing or remove ice rapidly has aroused great attention from researchers in recent years. In this work, we demonstrated a strategy of using a superhydrophobic photothermal and thermal isolation macroporous xerogel (PMX) to delay icing and remove ice efficiently under faint sunlight irradiation. An oriented macroporous xerogel was prepared by an ice templating method, and multi-walled carbon nanotubes acting as the photothermal genesis component under sunlight irradiation were introduced into the xerogel. After fluorination, the PMX presented a robust water repellency and delayed icing. More importantly, numerous macropores in the PMX matrix acted as the thermal barrier that can restrict heat transmission to surroundings at maximum, which guarantees efficient anti-icing and de-icing in low temperature. Water on the PMX surface can never freeze at -30 °C under 0.25 kW/m² ("0.25 sun") sunlight irradiation. The outdoor experiment also has confirmed the availability of PMX in a natural winter environment. The PMX integrated with thermogenesis and thermo-isolation functions provides a new route for highly efficient anti-icing and de-icing.

Biomimetic anti-freezing polymeric hydrogels: keeping soft-wet materials active in cold environments

As one of the most outstanding materials, the analysis of the structure and function of hydrogels has been extensively carried out to tailor and adapt them to various fields of application. The high water content, which is beneficial for plenty of applications in the biomedical setting, prevents the adoption of hydrogels in flexible electronics and sensors in real life applications, because hydrogels lose their excellent properties, including conductivity, transparency, flexibility, etc., upon freezing at sub-zero temperatures. Therefore, depressing the liquid-solid phase transition temperature is a powerful means to expand the application scope of hydrogels, and will benefit the chemical engineering and materials science communities. This review summarizes the recent research progress of anti-freezing hydrogels. At first, approaches for the generation of anti-freezing (hydro)gels are introduced and their anti-freezing mechanisms and performances are briefly discussed. These approaches are either based on addition of salts, alcohols (cryoprotectants and organohydrogels), and ionic liquids (ionogels), modification of the polymer network or a combination of several techniques. Then, a concise overview of applications leveraged by the widened temperature resistance is provided and future research areas and developments are envisaged.

Suppressing Condensation Frosting Using an Out-of-Plane Dry Zone

The vapor pressure above ice is lower than that above supercooled water at the same temperature. This inherent hygroscopic quality of ice has recently been exploited to suppress frost growth by patterning microscopic ice stripes along a surface. These vapor-attracting ice stripes prevented condensation frosting from occurring in the intermediate regions; however, the required presence of the sacrificial ice stripes made it impossible to achieve the ideal case of a completely dry surface. Here, we decouple the sacrificial ice from the antifrosting surface by holding an uncoated aluminum surface in parallel with a prefrosted surface. By replacing the overlapping in-plane dry zones with a uniform out-of-plane dry zone, we show that even an uncoated aluminum surface can stay almost completely dry in chilled and supersaturated conditions. Using a blend of experiments and numerical simulations, we show that the critical separation required to keep the surface dry is a function of the ambient supersaturation.

Bioinspired Tough Organohydrogel Dynamic Interfaces Enabled Subzero Temperature Antifrosting, Deicing, and Antiadhesion

Icing of water (moisture) at subzero temperatures with different length scales is harmful to a variety of applications spanning from large-scale aircraft to small camera lens. Existing strategies relying on controlling the surface structure and material are encumbered with shortcomings of short frost delay time, poor durability, and difficulty in large-scale production. Inspired from the mucus secretion of mollusks, we introduce organohydrogel dynamic interfaces that can perform dynamic and reversible exchange of the cryoprotectant and water at the interface, resulting in exceptional antifrosting, antiadhesion, and deicing properties with long-term durability. The replenishable coating shows superlubrication to the surface ice with a sliding angle up to 1.9 ± 0.4^o and a frost delay time up to 970 ± 31 min in the presence of water spray (99% relative humidity) at subzero temperatures. The strategy offers a reliable and scalable solution to prevent engineering surfaces, i.e., aircraft, pavement, bridge, and other public facilities, from icing/frosting and ice adhesion, even under extreme cold environments.

Freezing of Nanofluid Droplets on Superhydrophobic Surfaces

Droplet freezing on cold superhydrophobic surfaces has been studied extensively in recent years. However, previous works are mainly focused on studying water droplet freezing behavior; little work has been conducted to investigate the freezing dynamics of nanofluid droplets on superhydrophobic surfaces. In this work, freezing morphologies of water and nanofluid droplets on superhydrophobic surfaces with different roughnesses were compared and studied. The nanofluid droplets underwent a shape transition from spherical to flat plateau morphology, different from the frozen water droplets that exhibit a sharp cusp. The size of the flat plateau for the frozen nanofluid droplet increases with increasing nanoparticle concentration. The underlying mechanism of the morphology change during the freezing process was elucidated using COMSOL Multiphysics. Compared to the frozen water droplets, more air bubbles are trapped inside the frozen nanofluid droplets, which might be ascribed to the fast freezing speed of the nanofluid droplets. These results can provide important insights for many applications that require freezing of nanofluid droplets, such as material solidification, three-dimensional (3D) printing, as well as phase change enhancement.