Control of Ice Propagation by Using Polyelectrolyte Multilayer Coatings

Reducing Ice Adhesion to Polyelectrolyte Surfaces by Counterion-Mediated Nonfrozen Hydration Water

Hydrophilic anti-icing coatings can be energy-effective passive solutions for combating ice accretion and reducing ice adhesion. However, their underlying mechanisms of action remain inferential and are ill-defined from a molecular perspective. Here, we systematically investigate the influence of the counterion identity on the shear ice adhesion strength to cationic polymer coatings having quaternary alkyl ammonium moieties as chargeable groups. Temperature-dependent molecular information on the hydrated polymer films is obtained using total internal reflection (TIR) Raman spectroscopy, complemented with differential scanning calorimetry (DSC) and ellipsometry. Ice adhesion measurements show a pronounced counterion-specific behavior with a sharp increase in adhesion at temperatures that depend on the anion identity, following the order Cl- < F- < SCN- < Br- < I-. Linked to the freezing of hydration water, the specific ordering results from differences in ion pairing and the amount of water present within the polymer film. Moreover, similar effects can be promoted by varying the cross-linking density in the coating while keeping the anion identity fixed. These findings shed new light on low ice adhesion mechanisms and may inspire novel approaches for improved anti-icing coatings.

Reversible Stacking and Delamination-Regulation of MXene via Controlled Freezing

MXene's configuration, whether it is aggregated or dispersed in a monolayer, determines the specific application areas and even greatly influences the intrinsic properties of MXene. However, how to desirably control MXene's configuration is challenging. Here, a simple, additive-free, chemical reaction-free, and scalable strategy to optionally and reversibly regulate MXene's ordered stacking and delamination of MXene aggregates (AM) is reported. Just by controlled freezing of MXene aqueous dispersions, the aggregation percentage, delamination percentage, and interlayer spacing of AM can be finely tuned. Experimental results reveal that the freezing-induced aggregation and delamination effects can be explained by the squeezing action of growing ice grains on the MXene excluded/concentrated between ice grains and the expanding action caused by the ice formation between AM lamellae, respectively. The dominance between them depends on the freezing parameter-influenced ice nucleation sites, numbers, and ice grain sizes. This work not only contributes to the preparation, storage, and practical applications of MXene, but also opens a new and green avenue for controlling materials' assembly structures.

Preparation methods and research progress of super-hydrophobic anti-icing surface

The problem of surface icing poses a serious threat to people's economy and safety, especially in the fields of aerospace, wind power generation and circuit transmission. Super-hydrophobic has excellent anti-icing performance, so it has been widely studied. As the most promising anti-icing technology, superhydrophobic anti-icing surface should not only be simple to prepare, but also have excellent comprehensive performance, which can meet the anti-icing task under harsh working conditions and long-term durability. This paper summarizes the basic performance requirements of superhydrophobic surface for anti-icing operation, and then summarizes the preparation methods and existing problems of superhydrophobic surface in recent years. Finally, the future development trend of superhydrophobic anti-icing surface is prospected and discussed, hoping to provide certain technical guidance for the subsequent research of high-performance superhydrophobic anti-icing surface.

Calixarene-based cryoprotectants for ice recrystallization inhibition and cell cryopreservation

The development of new cryoprotectants for cryopreservation of cells has attracted considerable interest. Herein, five calixarene-based CPAs (SC4A, S-S-C4A, S-SO2-C4A, SBAC4A, and CAC4A) were developed, and their IRI activity, DIS property and cryoprotective effect were studied. SBAC4A with a sulphobetaine zwitterion and SC4A with sulfo group modification possessed better cryoprotective effects than the other calixarene-based CPAs, especially for SBAC4A with the enhanced cell viabilities of 16.16 ± 1.78%, 12.60 ± 1.15% and 14.90 ± 1.66% against MCF-7, hucMSCs and A549 cells, respectively. This result provides a supramolecular principle for developing novel CPAs with consideration of the factors of hydrogen bonding, the macromolecular crowding principle and the three-dimensional (3D) structure.

Reactive Multilayer Coating As Versatile Nanoarchitectonics for Customizing Various Bioinspired Liquid Wettabilities

In last few decades, multilayer coatings have achieved enormous attention owing to their unique ability to tune thickness, topography, and chemical composition for developing various functional materials. Such multilayer coatings were mostly and conventionally derived by following a simple layer-by-layer (LbL) deposition process through the strategic use of electrostatic interactions, hydrogen bonding, host-guest interactions, covalent bonding, etc. In the conventional design of multilayer coatings, the chemical composition and morphology of coatings are modulated during the process of multilayer constructions. In such an approach, the postmodulations of the porous multilayers with different and desired chemistries are challenging to achieve due to the lack of availability of readily and selectively reactive moieties. Recently, the design of readily and selectively reactive multilayer coatings (RMLCs) provided a facile basis for postmodulating the prepared coating with various desired chemistries. In fact, by taking advantage of the inherent ability of co-optimizing the topography and various chemistries in porous RMLCs, different durable bioinspired liquid wettabilities (i.e., superhydrophobicity, underwater superoleophobicity, underwater superoleophilicity, slippery property, etc.) were successfully derived. Such interfaces have enormous potential in various prospective applications. In this review, we intend to give an overview of the evolution of LbL multilayer coatings and their synthetic strategies and discuss the key advantages of porous RMLCs in terms of achieving and controlling wettability properties. Recent attempts toward various applications of such multilayer coatings that are strategically embedded with different desired liquid wettabilities will be emphasized.

Inhibition of Defect-Induced Ice Nucleation, Propagation, and Adhesion by Bioinspired Self-Healing Anti-Icing Coatings

Anti-icing coatings on outdoor infrastructures inevitably suffer from mechanical injuries in numerous icing scenarios such as hailstorms, sandstorms, impacts of foreign objects, and icing-deicing cycles. Herein, the mechanisms of surface-defect-induced icing are clarified. At the defects, water molecules exhibit stronger adsorption and the heat transfer rate increases, accelerating the condensation of water vapor as well as ice nucleation and propagation. Moreover, the ice-defect interlocking structure increases the ice adhesion strength. Thus, a self-healing (at -20 °C) antifreeze-protein (AFP)-inspired anti-icing coating is developed. The coating is based on a design that mimics the ice-binding and non-ice-binding sites in AFPs. It enables the coating to markedly inhibit ice nucleation (nucleation temperature < -29.4 °C), prevent ice propagation (propagation rate < 0.00048 cm²/s), and reduce ice adhesion on the surface (adhesion strength < 38.9 kPa). More importantly, the coating can also autonomously self-heal at -20 °C, as a result of multiple dynamic bonds in its structure, to inhibit defect-induced icing processes. The healed coating sustains high anti-icing and deicing performance even under various extreme conditions. This work reveals the in-depth mechanism of defect-induced ice formation as well as adhesion, and proposes a self-healing anti-icing coating for outdoor infrastructures.

Transparent, Photothermal, and Icephobic Surfaces via Layer-by-Layer Assembly

Icing and frosting on transparent surfaces compromise visibility on various optical equipment and transparent infrastructures. It remains challenging to fabricate energy-saving coatings for harvesting solar energy while maintaining high transparency. Here, transparent, photothermic, and icephobic composite surfaces composed of photothermal nanomaterials and polyelectrolytes via layer-by-layer assembly are designed and constructed. The positively-charged polypyrrole nanoparticles and negatively-charged poly(acrylic acid) are assembled as exemplary materials via electrostatic attractions. The optically transparent photothermal coatings are successfully fabricated and exhibited photothermal capabilities and light-transmittance performance. Among the various coatings applied, the seven-bilayer coating can increase the temperature by 35 °C under 1.9-sun illumination, maintaining high transmittance (>60%) of visible light. With sunlight illumination at subzero temperatures (> -35 °C), the coatings show pronounced capabilities to inhibit freezing, melt accumulated frost, and decrease ice adhesion. Precisely, the icephobic surfaces remain free of frost at -35 °C as long as sunlight illumination is present; the accumulated frost melts rapidly within 300 s. The ice adhesion strength decreases to ≈0 kPa as the melted water acts as a lubricant. Furthermore, the negatively-charged graphene oxide and positively-charged poly(diallyldimethylammonium chloride) show their material diversity applicable in the coating fabrication.

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.

Ion-Specific Effects on the Growth of Single Ice Crystals

Understanding the effects of soluble impurities or suspended particles on ice growth is of significant importance from Earth science to materials engineering. Ions are common impurities with ice in a wide range of fields, but their effects on ice growth remain largely elusive. Here, we studied the ion-specific effects on single ice crystal growth in various electrolyte and polyelectrolyte solutions and found F^- and NH₄⁺ show remarkable abilities of inducing single ice crystals to form hexagonal shapes and reducing the growth rates of ice crystals. Molecular dynamics simulations reveal the accumulation of F^- around the ice/solution interface that plays a key role in the shapes and growth rates of single ice crystals. The understanding of ion-specific effects on ice growth opens up more possibilities for improving related fields, e.g., freeze desalination and cryopreservation.

Transparent Organogel Films Showing Extremely Efficient and Durable Anti-Icing Performance

Accumulation of ice and snow on solid surfaces causes destructive problems in our daily life. Therefore, the development of functional coatings/surfaces that can effectively prevent ice/snow adhesion by natural forces, such as airflow, vibration, solar radiation, or gravity, is in high demand. In this study, transparent organogel films possessing negligible ice adhesion strength were successfully designed by a simple cross-linking of poly(dimethylsiloxane) (PDMS) in the presence of commercially available oils. Both the molecular weights (MWs) of the infusing oils and their contents in the PDMS matrices have proven to be key parameters for primarily determining the cross-linking density of PDMS matrices and syneresis/nonsyneresis behaviors of our samples, which closely reflected the final surface static/dynamic dewetting and anti-icing properties. By tuning only these two parameters, three different types of transparent organogel films, that is, nonsyneresis organogel (NSG), self-lubricating organogel (SLUG-I, infused with highly mobile oils), and SLUG-II (infused with viscous oils) films, were prepared. Among them, on the SLUG-I films, the lubricating oils were found to be continuously released from the PDMS matrices through syneresis for more than 1 year. Due to this unusual syneresis behavior, the ice adhesion strength became virtually zero, and this excellent anti-icing property also remained almost unchanged even after several cycles of icing/deicing testing. On the other hand, in the case of SLUG-II films, as the lubricated oil layers were too viscous, ice had trouble sliding off the surfaces by gravity. In contrast to these SLUG films, ice adhesion strength on NSG films was markedly decreased by increasing the amount of the infusing oils. In spite of NSG films having no distinct mobile oil layer, the ice adhesion strength reached its minimum of only about 5 kPa.

Efficient and economical approach for flexible photothermal icephobic copper mesh with robust superhydrophobicity and active deicing property

Facing various problems caused by icing in daily life, preparing photothermal deicing materials with wide applicability in high efficiency and low cost is not only a current research hotspot but also a great challenge. Herein, an economical spray-coating method is applied to prepare high-efficiency flexible photothermal icephobic copper mesh using micro silicon carbide (SiC) particles as photothermal conversion material and nano silica (SiO₂) particles as a surface superhydrophobic modifier. Owing to the excellent hierarchical micro-nanostructures, the SiC/SiO₂ coated copper mesh exhibits a water contact angle (CA) of 162 ± 2° and a sliding angle (SA) of 3 ± 2°. Interestingly, the coated copper mesh exhibits exceptional mechanical durability against water droplet and water flow impact, repeated bending-twisting and tape-peeling. Benefitting from the robust superhydrophobicity, the SiC/SiO₂ coating on the copper mesh can significantly delay the freezing time of the droplets and reduce the ice adhesion strength. Furthermore, the coated copper mesh well retains the good photothermal conversion and thermal conductivity properties of the micro SiC particles. Under NIR irradiation, the surface temperature of the coated copper mesh placed on the ice layer can increase by 35.3 °C in 220 s, so that it can rapidly melt the accumulated frost and ice layer on the inner wall of the refrigerator. The presented flexible photothermal icephobic copper mesh exhibits enormous potential when applied to remove ice from apparatus that is accessible, such as road, overhead transmission lines and power networks owing to its flexibility, economy, and high energy efficiency.

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.

Condensation Frosting on Micropillar Surfaces - Effect of Microscale Roughness on Ice Propagation

Microscale surface structures have been widely explored as a promising tool for antifreezing or frost avoidance on heat transfer surfaces. Despite studies of many surface feature designs, the mechanisms associated with condensation freezing and ice propagation on microstructured surfaces have yet to be thoroughly elucidated, espectially when it comes to quantitative understanding. In this work, condensation freezing on circular micropillar surfaces is investigated, with varying pillar spacing and height (layout/microscale roughness) but a constant pillar diameter. The pillar layout is found to have significant effects on both liquid nucleation and neighboring droplet interactions, as reflected by the condensation droplet distribution prior to soilidification and eventually the freezing front propagation area velocity. In general, nucleation is preferred on the pillar top rather than the bottom of the pillared surface unless there is a large distance between the pillars. Interactions between neighboring droplets solely on pillar tops (or bottom surfaces) can induce heterogeneity in the droplet distribution and slow freezing front propagation. Based on the roles the pillars play in nucleation, droplet coalescence, and ice bridging, four different condensation states are identified and related to the layout of the pillars, and the freezing front area propagation velocity is found to be different in each state. The findings provide a quantitative basis for designing antifreezing surfaces, applicable to a wide range of thermal systems.

AFM imaging of extracellular ice nucleators

Ice nucleators are substances that can initiate nucleation of pure water at and above -10 °C. Some plant pathogens possess a gene which encodes for a protein that acts as an ice nucleator, activity of which is enhanced when it is combined with the sugar and lipid components from the cell membrane. This matter retains its ice nucleation activity even after it is detached from the cell wall, and is termed extracellular ice nucleator (ECIN). In this paper, surface morphology of ECINs was investigated using atomic force microscopy (AFM) in tapping mode. ECINs were immobilized onto polyelectrolyte multilayers using the layer by layer deposition method. Effect of layer build-up, method of ECIN production, and polyelectrolytes used for multilayer fabrication were investigated. Globular and rod-like structures were observed on the AFM images of the nano-thin ECIN layers. Activity of ECINs, tested in food solutions in earlier studies, was retained when applied as a nano-thin layer onto a silicon wafer surface. Protein aggregate sizes decreased when higher centrifugation speeds were applied, and ice nucleation activity also decreased. Nucleation occurred faster and at higher temperatures when substrates were immersed in solutions of higher ECIN concentration, whereas number of bilayers formed did not have a significant effect. Higher concentration ECIN dipping solutions also led to the formation of thicker and denser ECIN layers as observed via AFM imaging. PRACTICAL APPLICATION: This study demonstrates the properties of nano-thin ECIN layers, which can crystallize pure water into ice at higher temperatures and in shorter time. Accelerating ice nucleation can potentially be utilized to freeze liquids in shorter time hence using less energy, or improve frozen foods' stability against the risk of cold chain breakage.

Inhibiting Condensation Freezing on Patterned Polyelectrolyte Coatings

Condensation freezing inhibition is of great practical importance for anti-icing applications; however, no coatings with this performance have been reported. Here, we report the inhibition of condensation freezing on patterned polyelectrolyte coatings, including polyelectrolyte brush (PB), polyelectrolyte multilayer (PEM), and polyelectrolyte hydrogel (PH) surfaces, benefiting from their feature in regulating ice nucleation and propagation via changing counterions. On the reported surfaces, ice nucleation can be initiated exclusively at the domains with the polyelectrolytes; moreover, spontaneous ice propagation can be achieved atop the patterned polyelectrolyte surface. Consequently, condensed water surrounding the frozen drops on the patterned polyelectrolyte surface evaporates due to the instantaneously released latent heat in the course of ice propagation. Afterward, ice grows specifically on polyelectrolyte surfaces via desublimation as the saturated vapor pressure of ice is smaller than that of condensed water drops. As such, an ice-free region up to 96% of the entire surface area can be accomplished. We demonstrate that various polyelectrolyte coatings can be easily introduced on almost all surfaces, revealing great promise for anti-icing applications.

A New Measuring System for the Determination of the Ice Adhesion Strength on Smooth Surfaces

To gain knowledge about cause-effect relationships for the adhesion of ice on surfaces with different chemical groups, we wanted to study the effect of thin polymer layers on the ice adhesion strength. To minimize the effect of roughness, smooth substrates that have generally relatively low ice adhesion strengths were chosen. To be able to obtain highly reproducible values for the region of low ice adhesion and to measure small differences of ice adhesion at surfaces with different chemical compositions, a new measuring system for the determination of the ice adhesion strength which is based on a modified spin-coater was developed. We show its technical potential on the basis of first results on pure silicon wafers and selected hydrophilic polymer layers. Furthermore, we investigated the effect of the water quality on the ice adhesion strength. The obtained data are discussed in the context of physicochemical properties of the layers and of the chemical characteristics of the used polymers.

Highly Stable Amphiphilic Organogel with Exceptional Anti-icing Performance

Various organogel materials with either a liquid or solid surface layer have recently been designed and prepared. In this work, amphiphilic organogels (AmOG) are innovatively developed from copolymer P(PDMS-r-PEG-r-GMA) and 2,2'-diaminodiphenyldisulfide via epoxy group addition reaction and then infiltrated with amphiphilic lubricants instead of traditional hydrophilic or hydrophobic lubricants. Because of synergistic effects of hydrophilic and hydrophobic segments of amphiphilic lubricants, the AmOG surfaces showed high stability and excellent anti-icing performance. The delay in the freezing point of water was 1000 s on AmOG surfaces, which is 40 times longer as compared to the untreated hydrophilic glass surface. More importantly, low ice adhesion strength (15.1 kPa) was observed on AmOG which remained about 40 kPa even after 20 icing-deicing cycles. The novel amphiphilic organogels provide a new idea to prepare long-term anti-icing materials for practical applications.

Tuning the Properties of Charged Polymers at the Solid/Liquid Interface with Ions

In conventional theories, where ions are treated as point charges, the properties of charged polymers can be tuned using ions via the ionic strength. However, this article will show that the properties of charged polymers at the solid/liquid interface, including charged polymer brushes and polyelectrolyte multilayers, can be tuned by ions beyond ionic strength effects. Ion specificity, multivalency, ionic hydrogen bonding, and ionic hydrophobicity/hydrophilicity are used to tune a range of properties of charged polymers at the solid/liquid interface such as hydration, conformation, stiffness, surface wettability, lubricity, adhesion, and protein adsorption. The ionic effects demonstrated here greatly broaden our understanding of the use of ions to tune the interfacial properties of charged polymers. It is anticipated that these ionic effects can be further expanded by incorporating new types of important ion-charged polymer interactions and can also be extended to neutral polymer systems.

Icephobic Durability of Branched PDMS Slippage Coatings Co-Cross-Linked by Functionalized POSS

Ice accretion poses a severe impact on diverse aspects of human life. Although great efforts have been dedicated to prevent or alleviate ice adhesion to the surface of substrates by developing various icephobic coatings, it is still needed to improve the integrated performance. Herein, we present a novel strategy to prepare poly(dimethylsiloxane) (PDMS) slippage coatings by combining a soft architecture-driven branched PDMS with partial short PDMS-functionalized polyhedral oligomeric silsesquioxane (POSS) as a co-cross-linker, in which silicone oil with certain viscosity was added as a lubricant. The chemical structure, surface morphology, and icephobic durability of the prepared coatings were investigated with concerns for the potential anti-icing uses. The PDMS slippage coating shed light on extraordinary icephobic durability with the ice shear strength at approximately 11.2 kPa and maintained low values below 14 kPa even after 50 icing/deicing cycles. Due to the elaborate control of the cross-link density, the side chains of the branched PDMS provided a rich storage space for entrapped silicone oil for the formation of the interfacial slippage. Moreover, the introduction of the functionalized POSS brought about significantly improved mechanical resistance in abrasion and elastic modulus. It is suggested that the branched PDMS slippage coating is a promising candidate in practical anti-icing applications.

Metal-catechol complexes mediate ice nucleation

The capability of mediating ice nucleation is pertinent to a broad range of fields. Herein, inspired by metal-catechol coordination found in adhesive proteins in which catechol moieties can construct strong complexes with a diverse array of metal ions, we develop a platform for mediating ice nucleation based on metal-catechol complexes and demonstrate that ice nucleation can be successively mediated by varying the characteristics and valence of the metal in metal-catechol complexes.

Tuning Ice Nucleation and Propagation with Counterions on Multilayer Hydrogels

Ice formation on solid surfaces includes heterogeneous ice nucleation and ice propagation processes. However, no study has been focused on tuning of both ice nucleation and ice propagation via a simple anti-icing coating method. In this work, we have prepared multilayer hydrogels based on simple layer-by-layer (LBL) deposition approach and discover the ion-specific effect on both ice nucleation and ice propagation. A large ice nucleation temperature window of 11 °C is controlled via changing different counterions; meanwhile, the differences in ice propagation time can be tuned up to 4 orders of magnitude. Through synergistically controlling of ice nucleation and propagation delay times, we can tune the freezing delay time of water droplets on multilayer hydrogel surfaces up to 3 orders of magnitude via changing various counterions. Considering the application requirements, these multilayer hydrogels are stable under different conditions and can be coated on various materials without destroying the existing surface. This new insight can inspire the design of anti-icing surfaces based on regulating both ice nucleation and ice propagation.

Control of ice nucleation: freezing and antifreeze strategies

Water freezing remains a perennial topic of great relevance to many important aspects of our lives; from the climate to human society and from economics to medicine, frozen water profoundly influences our living environment and life activities.