Hypothesis: A sustainable dynamic anti-icing surface with the potential for rapid rechargeability

Ice accumulation poses significant challenges across numerous industries. While dynamic anti-icing surfaces (DAIS) have shown potential in mitigating ice formation and adhesion, their practical use is often limited by the rapid diffusion of liquids and lack of reusability. Overcoming these limitations is crucial to addressing the environmental and economic issues related to ice management. In this study, we introduce a novel approach by incorporating β-cyclodextrin (β-CD) into polydimethylsiloxane (PDMS) silicone rubber, enabling the creation of a sustainable DAIS with the potential of rapid rechargeability. The multiple hydroxyl groups present on the outer surface of β-CD facilitate dipole-dipole interactions and hydrogen bonding, particularly with polar molecules like ethanol and isopropanol. This transforms the surface into a rechargeable system, capable of restoring its low ice adhesion functionality within just 10 min after liquid replenishment. When ice forms on the surface, the system dynamically responds to environmental changes via concentration gradients, controlling the release of liquids and altering surface characteristics. These retained liquids effectively lower the freezing point, melt the ice, and disrupt the ice structure, converting the solid-liquid interface into a liquid-liquid interface. The DAIS effectively alter the ice-substrate interaction and enhance performance at temperatures as low as -18 ℃. By optimizing the β-CD mass ratio and liquid treatments, especially with isopropanol, we achieved an ultra-low ice adhesion strength of 0.6 kPa, which remains stable even after 35 days. This study presents a significant advancement in the development of sustainable, rapidly rechargeable DAIS, offering immense potential for applications in various industries.

Multi-component liquid-infused systems: a new approach to functional coatings

Antifouling liquid-infused surfaces have generated interest in multiple fields due to their diverse applications in industry and medicine. In nearly all reports to date, the liquid component consists of only one chemical species. However, unlike traditional solid surfaces, the unique nature of liquid surfaces holds the potential for synergistic and even adaptive functionality simply by including additional elements in the liquid coating. In this work, we explore the concept of multi-component liquid-infused systems, in which the coating liquid consists of a primary liquid and a secondary component or components that provide additional functionality. For ease of understanding, we categorize recently reported multi-component liquid-infused surfaces according to the size of the secondary components: molecular scale, in which the secondary components are molecules; nanoscale, in which they are nanoparticles or their equivalent; and microscale, in which the additional components are micrometer size or above. We present examples at each scale, showing how introducing a secondary element into the liquid can result in synergistic effects, such as maintaining a pristine surface while actively modifying the surrounding environment, which are difficult to achieve in other surface treatments. The review highlights the diversity of fabrication methods and provides perspectives on future research directions. Introducing secondary components into the liquid matrix of liquid-infused surfaces is a promising strategy with significant potential to create a new class of multifunctional materials. Keywords: Active surfaces; Antimicrobial; Antifouling; Interfaces; Sensing surfaces.

Icephobic Durability of Molecular Brush-Structured PDMS Soft Coatings

The accumulation of ice can pose numerous inconveniences and potential hazards, profoundly affecting both human productivity and daily life. To combat the challenges posed by icing, extensive research efforts have been dedicated to the development of low-ice adhesion surfaces. In this study, we harness the power of molecular dynamics simulations to delve into the intricate dynamics of polymer chains and their role in determining the modulus of the material. We present a novel strategy to prepare ultralow-modulus poly(dimethylsiloxane) (PDMS) elastomers with a molecular brush configuration as icephobic materials. The process involves grafting monohydride-terminated PDMS (H-PDMS) as side chains onto backbone chain PDMS with pendant vinyl functional groups to yield a molecular brush structure. The segments of this polymer structure effectively restrict interchain entanglement, thereby rendering a lower modulus compared to traditional linear structures at an equivalent cross-linking density. The developed soft coating exhibits a remarkably ultralow ice adhesion strength of 13.1 ± 1.1 kPa. Even after enduring 50 cycles of icing and deicing, the ice adhesion strength of this coating steadfastly stayed below 16 kPa, showing no notable increase. Importantly, the molecular brush coating applied to glass demonstrated an impressive light transmittance of 92.1% within the visible light spectrum, surpassing the transmittance of bare glass, which was measured at 91.3%. This icephobic coating with exceptional light transmittance offers a wide range of applications and holds significant potential as a practical icephobic material.

On the Durability of Icephobic Coatings: A Review

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an attempt to pave the roadmap from the lab to engineering applications. An icephobic material is expected to lower the ice adhesion strength, delay freezing time or temperature, promote the bouncing of a supercooled drop at subzero temperatures and/or reduce the ice accretion rate. To better understand what is more important for specific icing conditions, the different types of ice that can be formed in nature are summarized. Similarly, the alternative methods to evaluate the durability are reviewed, as this is key to properly selecting the method and parameters to ensure the coating is durable enough for a given application. Finally, the different types of icephobic surfaces available to date are considered, highlighting the strategies to enhance their durability, as this is the factor limiting the commercial applicability of icephobic coatings.

Erosion-resistant materials demonstrate low interfacial toughness with ice and superior durability

The strong adhesion of ice to surfaces results in unwanted effects in various industrial activities. However, current strategies for passive ice-phobic purposes lack either scalability or durability, or both, in industrial applications. In this study, erosion-resistant materials, including ceramic-based (WC, SiC, and alumina) and metal-based (a quasicrystalline coating, QC), were studied for their ice-phobic properties via push-off tests with bulk-water ice from -5 to -20 °C. Although their ice adhesion strengths were high (>400 kPa), their interfacial toughness with ice was quite low (1.1 to 2.6 J m-2) and comparable to polymeric surfaces. The force per width required to remove ice on the QC surface was even lower than that of a silicone (Sylgard 184) surface for an ice length of 7.0 cm. The low interfacial toughness of the erosion-resistant materials with ice was also retained after 1000 cycles of linear abrasion under a pressure of 27.0 kPa. The findings of this work expand the material selection options for durable large-scale ice-phobic applications and could enlighten the use of erosion-resistant materials in harsh industrial environments requiring effective de-icing.

Healable Anti-Corrosive and Wear-Resistant Silicone-Oil-Impregnated Porous Oxide Layer of Aluminum Alloy by Plasma Electrolytic Oxidation

Lubricant (or oil)-impregnated porous surface has been considered as a promising surface treatment to realize multifunctionality. In this study, silicone oil was impregnated into a hard porous oxide layer created by the plasma electrolytic oxidation (PEO) of aluminum (Al) alloys. The monolayer of polydimethylsiloxane (PDMS) from silicone oil is formed on a porous oxide layer; thus, a water-repellent slippery oil-impregnated surface is realized on Al alloy, showing a low contact angle hysteresis of less than 5°. This water repellency significantly enhanced the corrosion resistance by more than four orders of magnitude compared to that of the PEO-treated Al alloy without silicone oil impregnation. The silicone oil within the porous oxide layer also provides a lubricating effect to improve wear resistance by reducing friction coefficients from ~0.6 to ~0.1. In addition, because the PDMS monolayer can be restored by frictional heat, the water-repellent surface is tolerant to physical damage to the oxide surface. Hence, the results of this fundamental study provide a new approach for the post-treatment of PEO for Al alloys.

Precision Covalent Organic Frameworks for Surface Nucleation Control

Unwanted accumulation of ice and lime scale crystals on surfaces is a long-standing challenge with major economic and sustainability implications. Passive inhibition of icing and scaling by liquid-repellent surfaces are often inadequate, susceptible to surface failure under harsh conditions, and unsuitable for long-term/real-life usages. Such surfaces often require a multiplicity of additional features such as optical transparency, robust impact resistance, and ability to prevent contamination from low surface energy liquids. Unfortunately, most promising advances have relied on using perfluoro compounds, which are bio-persistent and/or highly toxic. Here it is shown that organic, reticular mesoporous structures, covalent organic frameworks (COFs), may offer a solution. By exploiting simple and scalable synthesis of defect-free COFs and rational post-synthetic functionalization, nanocoatings with precision nanoporosity (morphology) are prepared that can inhibit nucleation at the molecular level without compromising the related contamination prevention and robustness. The results offer a simple strategy to exploit the nanoconfinement effect, which remarkably delays the nucleation of ice and scale formation on surfaces. Ice nucleation is suppressed down to -28 °C, scale formation is avoided for >2 weeks in supersaturated conditions, and jets of organic solvents impacting at Weber numbers >105 are resisted with surfaces that also offer optical transparency (>92%).

Interdependence of Surface Roughness on Icephobic Performance: A Review

Ice protection techniques have attracted significant interest, notably in aerospace and wind energy applications. However, the current solutions are mostly costly and inconvenient due to energy-intensive and environmental concerns. One of the appealing strategies is the use of passive icephobicity, in the form of coatings, which is induced by means of several material strategies, such as hydrophobicity, surface texturing, surface elasticity, and the physical infusion of ice-depressing liquids, etc. In this review, surface-roughness-related icephobicity is critically discussed to understand the challenges and the role of roughness, especially on superhydrophobic surfaces. Surface roughness as an intrinsic, independent surface property for anti-icing and de-icing performance is also debated, and their interdependence is explained using the related physical mechanisms and thermodynamics of ice nucleation. Furthermore, the role of surface roughness in the case of elastomeric or low-modulus polymeric coatings, which typically instigate an easy release of ice, is examined. In addition to material-centric approaches, the influence of surface roughness in de-icing evaluation is also explored, and a comparative assessment is conducted to understand the testing sensitivity to various surface characteristics. This review exemplifies that surface roughness plays a crucial role in incorporating and maintaining icephobic performance and is intrinsically interlinked with other surface-induced icephobicity strategies, including superhydrophobicity and elastomeric surfaces. Furthermore, the de-icing evaluation methods also appear to be roughness sensitive in a certain range, indicating a dominant role of mechanically interlocked ice.

Review on Hydrophobic Thin Films Prepared Using Magnetron Sputtering Deposition

Hydrophobic thin films have gained significant attention due to their broad applications in self-cleaning, anti-corrosion, anti-icing, medicine, oil-water separation, and other fields. The target hydrophobic materials can be deposited onto various surfaces thanks to the scalable and highly reproducible nature of magnetron sputtering, which is comprehensively overviewed in this review. While alternative preparation methods have been extensively analyzed, a systematic understanding of hydrophobic thin films fabricated using magnetron sputtering deposition is still absent. After outlining the fundamental mechanism of hydrophobicity, this review briefly summarizes three types of sputtering-deposited thin films that originate from oxides, polytetrafluoroethylene (PTFE), and diamond-like carbon (DLC), respectively, primarily focusing on the recent advances in their preparation, characteristics, and applications. Finally, the future applications, current challenges, and development of hydrophobic thin films are discussed, and a brief perspective on future research directions is provided.

Reduction of ice adhesion on nanostructured and nanoscale slippery surfaces

Ice nucleation and accretion on structural surfaces are sources of major safety and operational concerns in many industries including aviation and renewable energy. Common methods for tackling these are active ones such as heating, ultrasound, and chemicals or passive ones such as surface coatings. In this study, we explored the ice adhesion properties of slippery coated substrates by measuring the shear forces required to remove a glaze ice block on the coated substrates. Among the studied nanostructured and nanoscale surfaces [i.e., a superhydrophobic coating, a fluoropolymer coating, and a polydimethylsiloxane (PDMS) chain coating], the slippery omniphobic covalently attached liquid (SOCAL) surface with its flexible polymer brushes and liquid-like structure significantly reduced the ice adhesion on both glass and silicon surfaces. Further studies of the SOCAL coating on roughened substrates also demonstrated its low ice adhesion. The reduction in ice adhesion is attributed to the flexible nature of the brush-like structures of PDMS chains, allowing ice to detach easily.

Icephobicity of Hierarchically Rough Aluminum Surfaces Sequentially Coated with Fluoroalkyl and PDMS Alkoxysilanes

Superhydrophobic surfaces fabricated by grafting 1H,1H,2H,2H-heptadecafluorodecyl trimethoxysilane (FD-TMS) and polydimethylsiloxane triethoxysilane (PDMS-TES) onto a nano-micro hierarchical aluminum (Al) surface are considered to possess substantial anti-icing functionality, with delayed freezing and low ice-adhesion strength (IAS). Verifying the impacts of PDMS and the synergism of PDMS and FD on the anti-icing performance is the goal of this study. Roughness, one of the prerequisites for superhydrophobicity, was obtained by etching Al substrates in aqueous HCl, followed by immersion in boiling water. FD-TMS and PDMS-TES were then coated on the rough Al substrates layer by layer; a congener coated with a single layer was also prepared for comparison. The FD-PDMS_1.92 (1.92 wt.%) coating, in which FD-TMS and PDMS-TES were used as primary and secondary coating materials, respectively, exhibited superior icephobicity, with the lowest IAS of 28 kPa under extremely condensing weather conditions (-20 °C and 70% relative humidity, RH) and the longest freezing delay time of 230 min (at -18 °C). These features are attributed to the incorporation of a dense coating layer with a low-surface-tension FD and the high mobility of PDMS, which lowered the contact area and interaction between the ice and substrate. The substrate coated with FD-PDMS_1.92 exhibited improved durability with an IAS of 63 kPa after 40 icing/melting cycles, which is far less than that achieved with the FD single-layer coating.

Reduced Ice Adhesion Using Amphiphilic Poly(Ionic Liquid)-Based Surfaces

Ice build-up on solid surfaces causes significant economic losses for a range of industries. One solution to this problem is the development of coatings with low ice adhesion strength. Amphiphilic poly(ionic liquid) (PIL)-based surfaces have been recently reported for antifogging/antifrosting applications. However, they have possible anti-icing properties through lowering the ice adhesion strength that have yet to be reported. Herein, we designed well-defined triblock copolymers composed of a polydimethylsiloxane component coupled with PIL segments of poly([2 (methacryloyloxy)ethyl] trimethylammonium chloride) (PMETAC), which were subsequently UV-cured with an oligo(ethylene glycol) dimethacrylate (OEGDMA) cross-linker. The structure-property relationships of the resultant semi-interpenetrating polymer networks (SIPNs) were investigated by varying the counterion (i.e., trimethylammonium bis(trifluoromethanesulfonyl)imide (TFSI^-)) and the content of the PIL segments and cross-linker. An ice adhesion strength as low as 13.3 ± 8.6 kPa was observed for the coating containing 12.5 wt % of PMETAC segment and 5 wt % of OEGDMA, which is one of the lowest values reported so far for the amphiphilic coatings. Characterization of the coatings in terms of surface features, wettability, and hydration states have enabled the elucidation of different deicing mechanisms. Self-lubrication due to the existence of nonfreezable bound water led to the obtained low ice adhesion strength. This work offers a new approach for the exploration of PIL-based icephobic coatings for practical applications.

Key Factors Affecting Durable Anti-Icing of Slippery Surfaces: Pore Size and Porosity

Slippery liquid-infused porous surfaces (SLIPSs) are widely used as an effective passive approach to reduce icing disasters. However, various porous structures make SLIPSs exhibit different droplet mobility and lubricant stability. Undoubtedly, the substrate surface has a great impact on the durable anti-icing of SLIPSs. Herein, surfaces with different pore sizes and porosities were prepared to study their effects on the performance of SLIPS. The results show that small pores and high porosity are beneficial for the preparation of durable anti-icing SLIPS. The small pore size (about 100 nm) has a strong capillary pressure on the lubricant, and the surface with high porosity (66%) possesses a large lubricant-liquid contact ratio. These two can greatly improve the lubricant stability of SLIPS and achieve rapid self-healing. The SLIPS prepared by a suitable porous surface shows excellent anti-icing performance in the simulated glaze ice and durable anti-icing ability in the long-term icing/deicing cycles. In detail, the prepared SLIPS experiences more than 140 icing/deicing cycles through four effective self-healing while maintaining extremely low ice adhesion (<20 kPa). This work proposes a certain improved SLIPS with small pores and high porosity to achieve excellent durable anti-icing performance, broadening the practical applications of SLIPS.

Role of Molecular Chains Arrangement and Surface Energy State in the Low Ice Adhesion on Poly(tetrafluoroethylene)

The relation between polymer molecular chains arrangement and ice adhesion was studied at the molecular scale, and the energy states of water molecules on the poly(tetrafluoroethylene) surface were analyzed to explain the energy essence of ice adhesion. The ice adhesion on crystalline poly(tetrafluoroethylene) displayed a clear anisotropy phenomenon. Further research proved that the energy states of water molecules along the vertical direction of the molecular chains fluctuated regularly, and the water molecules in gaps between molecular chains were in the energy troughs, leading to the formation of energy traps. Water molecules needed more energy from outside to escape the energy traps, causing additional resistance to the ice movement and obvious increase of ice adhesion. Therefore, ice adhesion was closely related to the distribution of energy traps in the direction of ice removing, which mainly depended on the possibility of molecular chains perpendicularly arranged in the direction of ice removing.

Micro-Nano-Nanowire Triple Structure-Held PDMS Superhydrophobic Surfaces for Robust Ultra-Long-Term Icephobic Performance

Anti-icing superhydrophobic surfaces have attracted tremendous interests due to their repellency to water and extremely low ice affinity, whereas the weak durability has been the bottleneck for further applications. Surface durability is especially important in long-term exposure to low-temperature and high-humidity environments. In this study, a robust micro-nano-nanowire triple structure-held PDMS superhydrophobic surface was fabricated via a hybrid process: ultrafast-laser-prepared periodic copper microstructures were chemically oxidized, followed by modification of PDMS. The hedgehog-like surface structure was composed of microcones, densely grown nanowires, and tightly combined PDMS. The capillary force difference in micro-nanostructures drove PDMS solutions to distribute evenly, bonding fragile nanowires to form stronger composite cones. PDMS replaced the commonly used fragile fluorosilanes and protected nanowires from breaking, which endowed the surfaces with higher robustness. The ductile PDMS-nanowire composites possessed higher resiliency than brittle nanowires under a load of 1 mN. The surface kept superhydrophobic and ice-resistant after 15 linear abrasion cycles under 1.2 kPa or 60 icing-deicing cycles under -20 °C or 500 tape peeling cycles. Under a higher pressure of 6.2 kPa, the contact angle (CA) was maintained above 150° until the abrasion distance exceeded 8 m. In addition, the surface exhibited a rare spontaneously optimized performance in the icing-deicing cycles. The ice adhesion strength of the surface reached its lowest value of 12.2 kPa in the 16th cycle. Evolution of surface roughness and morphology were combined to explain its unique U-shaped performance curves, which distinguished its unique degradation process from common surfaces. Thus, this triple-scale superhydrophobic surface showed a long-term anti-icing performance with high deicing robustness and low ice adhesion strength. The proposed nanostructure-facilitated uniform distribution strategy of PDMS is promising in future design of durable superhydrophobic anti-icing surfaces.

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.

Plasmonic CuxS Nanocages for Enhanced Solar Photothermal Cell Warming

Highly efficient plasmonic photothermal nanomaterials are benefitial to the successful resuscitation of cells. Copper sulfide (Cu_xS) is a type of plasmonic solar photothermal semiconductor material that expands the light collecting range by altering its localized surface plasmonic resonance (LSPR) to the near- to mid-infrared (IR) spectral region. Particularly, nanocages (or nanoshells) have hybridized plasmon resonances as the result of superpositioned nanospheres and nanocavities, which extend their receiving range for the solar spectrum and increase light-to-heat conversion rate. In this work, for the first time, we applied colloidal hollow Cu_xS nanocages to revive cryopreserved HeLa cells via photothermal warming, which showed improved cell warming rate and cell viability after cell resuscitation. Moreover, we tested the photothermal performance of Cu_xS nanocages with concentrated light illumination, which exhibited extraordinary photothermal performance due to localized and enhanced illumination. We further quantified each band's contribution during the cell warming process via evaluating the warming rate of cryopreserved cell solution with illumination by monochromatic UV, visible, and NIR lasers. We studied the biosafety and toxicity of Cu_xS nanocages by analyzing the generated copper ion residue during cell warming and cell incubation, respectively. Our study shows that Cu_xS nanocages have huge potential for cell warming and are promising for vast range of applications, such as nanomedicine, life science, biology, energy saving, etc.

Overview of the development of slippery surfaces: Lubricants from presence to absence

The superhydrophobic surfaces inspired by the lotus have excellent performances and are known for their low contact angle hysteresis and smooth surfaces. However, there are still some problems, such as the unstable structure, poor durability, high product cost and so on that need to be improved. Those issues can be avoided via liquid-infused surfaces(LIS), which are inspired by Nepenthes and consist of a mico-nano structured substrate and a smooth continuous atomic-grade lubricant. Compared with superhydrophobic surfaces, LIS not only achieves the same hydrophobic properties but also has smaller contact angle hysteresis, smoother surface, more stable structure and lower preparation cost. Although the existence of a lubricant layer improves the performance of the material, it also leaves a hidden danger, which is easy to lose and leads to the deterioration of the durability of the material. Therefore, the lubricant-free slipper materials have attracted more and more attention in recent years due to their low volatility, good durability and excellent lubrication performance. In this review, the types of LIS lubricants and their physicochemical properties were summarized at the beginning and then the applications of LIS in various fields were introduced. At the end of this paper, some solid lubricants and their applications were described, and the future development prospects of LIS lubricants also were expected.

Patterning Configuration of Surface Hydrophilicity by Graphene Nanosheet towards the Inhibition of Ice Nucleation and Growth

Freezing of liquid water occurs in many natural phenomena and affects countless human activities. The freezing process mainly involves ice nucleation and continuous growth, which are determined by the energy and structure fluctuation in supercooled water. Herein, considering the surface hydrophilicity and crystal structure differences between metal and graphene, we proposed a kind of surface configuration design, which was realized by graphene nanosheets being alternately anchored on a metal substrate. Ice nucleation and growth were investigated by molecular dynamics simulations. The surface configuration could induce ice nucleation to occur preferentially on the metal substrate where the surface hydrophilicity was higher than the lateral graphene nanosheet. However, ice nucleation could be delayed to a certain extent under the hindering effect of the interfacial water layer formed by the high surface hydrophilicity of the metal substrate. Furthermore, the graphene nanosheets restricted lateral expansion of the ice nucleus at the clearance, leading to the formation of a curved surface of the ice nucleus as it grew. As a result, ice growth was suppressed effectively due to the Gibbs–Thomson effect, and the growth rate decreased by 71.08% compared to the pure metal surface. Meanwhile, boundary misorientation between ice crystals was an important issue, which also prejudiced the growth of the ice crystal. The present results reveal the microscopic details of ice nucleation and growth inhibition of the special surface configuration and provide guidelines for the rational design of an anti-icing surface.

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.

Design of Icephobic Surfaces by Lowering Ice Adhesion Strength: A Mini Review

Ice accretion can lead to severe consequences in daily life and sometimes catastrophic events. To mitigate the hazard of icing, passive icephobic surfaces have drawn widespread attentions because of their abilities in repelling incoming water droplets, suppressing ice nucleation and/or lowering ice adhesion strength. As time elapses and temperature lowers sufficiently, ice accretion becomes inevitable, and a realistic roadmap to surface icephobicity for various outdoor anti-icing applications is to live with ice but with the lowest ice adhesion strength. In this review, surfaces with icephobicity are critically categorized into smooth surfaces, textured surfaces, slippery surfaces and sub-surface textured surfaces, and discussed in terms of theoretical limit, current status and perspectives. Particular attention is paid to multiple passive anti-icing strategies combined approaches as proposed on the basis of icephobic surfaces. Correlating the current strategies with one another will promote understanding of the key parameters in lowering ice adhesion strength. Finally, we provide remarks on the rational design of state-of-the-art icephobic surfaces with low ice adhesion strength.

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.

Designing Self-Sustainable Icephobic Layer by Introducing a Lubricating Un-Freezable Water Hydrogel from Sodium Polyacrylate on the Polyolefin Surface

A convenient, environment-friendly, and cost-effective method to keep anti-icing for a long time was highly desirable. Slippery lubricant layers were regarded to be effective and promising for anti-icing on different surfaces, but the drought-out of lubricants and the possible detriments to the environment were inevitable. By combining super-high molecular weight sodium polyacrylate (H-PAAS) with polyolefin through a one-pot method, a self-sustainable lubricating layer with extremely low ice adhesion of un-freezable water hydrogel was achieved at subzero conditions. The lubricant hydrogel layer could auto-spread and cover the surface of polyolefin after encountering supercooled water, frost, or ice. Due to the reduction of storage modulus in the interface, the ice adhesion of the specimen surfaces was far below 20 kPa, varying from 5.13 kPa to 18.95 kPa. Furthermore, the surfaces could preserve the fairly low adhesion after icing/de-icing cycles for over 15 times and thus exhibited sustainable durability. More importantly, this method could be introducing to various polymers and is of great promise for practical applications.

The challenge of lubricant-replenishment on lubricant-impregnated surfaces

Lubricant-impregnated surfaces are two-component surface coatings. One component, a fluid called the lubricant, is stabilized at a surface by the second component, the scaffold. The scaffold can either be a rough solid or a polymeric network. Drops immiscible with the lubricant, hardly pin on these surfaces. Lubricant-impregnated surfaces have been proposed as candidates for various applications, such as self-cleaning, anti-fouling, and anti-icing. The proposed applications rely on the presence of enough lubricant within the scaffold. Therefore, the quality and functionality of a surface coating are, to a large degree, given by the extent to which it prevents lubricant-depletion. This review summarizes the current findings on lubricant-depletion, lubricant-replenishment, and the resulting understanding of both processes. A multitude of different mechanisms can cause the depletion of lubricant. Lubricant can be taken along by single drops or be sheared off by liquid flowing across. Nano-interstices and scaffolds showing good chemical compatibility with the lubricant can greatly delay lubricant depletion. Often, depletion of lubricant cannot be avoided under dynamic conditions, which warrants lubricant-replenishment strategies. The strategies to replenish lubricant are presented and range from spraying or stimuli-responsive release to built-in reservoirs.

Hydrophobic and Anti-Icing Behavior of UV-Laser-Treated Polyester Resin-Based Gelcoats

Ice accumulation on wind turbine blades due to the impact of supercooled water droplets can be reduced by the application of surfaces with anti-icing properties. Hydrophobic surfaces are considered as a promising solution because of their water repellent behavior. In recent years, short-pulsed laser technologies have been developed as an efficient technique to modify the surface properties of materials. However, the anti-icing properties of such surfaces have not yet been validated. In this work, a hybrid modification of polyester resin-based gelcoats was adopted. Laser patterning (LP) was used to produce periodic surface structures on modified unsaturated polyester resin (UPR) substrates. One of the innovations of this research is the utilization of novel purpose-made chemical modifiers for gelcoats. The implementation of linear polymethylhydrosiloxane (PMHS) as a building block is a key improvement in terms of durability and functionality of the coating, since there is an option of introducing not only groups bonding in the polyester into one molecule, but also groups that increase hydrophobicity. The other novelty is a successfully conducted experiment combining such chemical modification with laser texturization of the surface. The influence of the laser energy, pattern shape, and spatial periods on the topographical characteristics and hydrophobicity as well as the anti-icing properties of the produced surfaces were investigated. To characterize the surface topography of the produced structures, scanning electron microscopy (SEM) and profilometer were utilized. Measurements of the wettability parameters (static contact angle and contact angle hysteresis) on the treated surfaces allowed the identification of the influence of wetting behavior and laser parameters on the investigated materials. Anti-icing properties were characterized by ice adhesion (IA) and freezing delay time (FDT) tests. It was found that hybrid modification of unsaturated polyester resin by chemical modifiers and laser treatment increased the hydrophobic and anti-icing properties of polyester gelcoats.

Hybrid Modification of Unsaturated Polyester Resins to Obtain Hydro- and Icephobic Properties

Ice accumulation is a key and unsolved problem for many composite structures with polymer matrices, e.g., wind turbines and airplanes. One of the solutions to avoid icing is to use anti-icing coatings. In recent years, the influence of hydrophobicity of a surface on its icephobic properties has been studied. This solution is based on the idea that a material with poor wettability maximally reduces the contact time between a cooled drop of water and the surface, consequently prevents the formation of ice, and decreases its adhesion to the surface. In this work, a hybrid modification of a gelcoat based on unsaturated polyester resin with nanosilica and chemical modifiers from the group of triple functionalized polyhedral oligomeric silsesquioxanes (POSS) and double organofunctionalized polysiloxanes (generally called multi-functionalized organosilicon compounds (MFSC)) was applied. The work describes how the change of modifier concentration and its structural structure finally influences the ice phobic properties. The modifiers used in their structure groups lowered the free surface energy and crosslinking groups with the applied resin, lowering the phenomena of migration and removing the modifier from the surface layer of gelcoat. The main studies from the icephobicity point of view were the measurements of ice adhesion forces between modified materials and ice. The tests were based on the measurements of the shear strength between the ice layer and the modified surface and were conducted using a tensile machine. Hydrophobic properties of the obtained nanocomposites were determined by measurement of the contact angle and contact angle hysteresis. As the results of the work, it was found that the modification of gelcoat with nanosilica and multi-functionalized silicone compounds results in the improvement of icephobic properties when compared to unmodified gelcoat while no direct influence of wettability properties was found. Ice adhesion decreased by more than 30%.

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.

Facile One-Step Method to Fabricate a Slippery Lubricant-Infused Surface (LIS) with Self-Replenishment Properties for Anti-Icing Applications

In this work, a slippery lubricant-infused surface (LIS) was prepared by simple one-step mixing of polydimethylsiloxane (PDMS) resin and dimethyl silicone oil (PMX-200) directly. Silicone oil showed good compatibility with PDMS resin, and the added amount of silicone oil had no significant effect on the surface morphology of LIS. According to the results of surface observations, once the silicone oil film anchored on the LIS was removed, the silicone oil inside the PDMS polymer automatically diffused to the surface and formed a new silicone oil film again in a short time. Furthermore, with the increase of silicone oil content, the oil self-replenishment speed and amount of the LIS were enhanced, which also promoted a decrease of the surface water sliding angle and the improvement of the lubrication ability of the LIS. In the icing/deicing cycle tests, the slippery LIS still maintained very low ice adhesion strength after 24 cycles, showing excellent anti-icing performance.

Liquid-Infused Surfaces: A Review of Theory, Design, and Applications

Due to inspiration from the Nepenthes pitcher plant, a frontier of devices has emerged with unmatched capabilities. Liquid-infused surfaces (LISs), particularly known for their liquid-repelling behavior under low tilting angles (<5°), have demonstrated a plethora of applications in medical, marine, energy, industrial, and environmental materials. This review presents recent developments of LIS technology and its prospective to define the future direction of this technology in solving tomorrow's real-life challenges. First, an introduction to the different models explaining the physical phenomena of these surfaces, their wettability, and viscous-dependent frictional forces is discussed. Then, an outline of different emerging strategies required to fabricate a stable liquid-infused interface is presented, including different substrates, lubricants, surface chemistries, and design parameters which can be tuned depending on the application. Furthermore, applications of LIS coatings in the areas of anticorrosion, antifouling, anti-icing, self-healing, droplet manipulation, and biomedical devices will be presented followed by the limitations and future direction of this technology.

An ultra-durable icephobic coating by a molecular pulley

Slide-ring crosslinked polydimethylsiloxane (PDMS) is designed and prepared for anti-icing/deicing applications. Compared with the covalent crosslinks, the slidable crosslinks enhance the mobility of polymer networks and endow the materials with low elastic modulus. The PDMS matrix guarantees the hydrophobicity of as-prepared coatings. These properties synergistically lead to ultra-low ice adhesion strength (13.0 ± 1.3 kPa) and excellent mechanical durability. The ice adhesion strength on the coating maintains a value of ∼12 kPa during 20 icing/deicing cycles, and increases gradually to a value of ∼22 kPa after 800 cycles of abrasions. The novel design strategy provides one-step forward to anti-icing/deicing solutions for targeted applications.

Physics of pre-wetted, lubricated and impregnated surfaces: a review

Wetting phenomena occurring on pre-wetted flat and rough solid surfaces are reviewed. The wetting of lubricated flat surfaces is strongly correlated with the tribological properties of a solid/lubricant pair. The phenomena taking place on micro- and nano-rough oil-impregnated surfaces have attracted the attention of the scientific community due to their numerous promising applications as omniphobic, self-healing, anti-icing and anti-bacterial interfaces. On the other hand, these phenomena are rich in their physical content. The effects observed on natural and artificial, bioinspired oil-impregnated surfaces are discussed, including electrowetting of oil-impregnated surfaces, enabling low-voltage reversible control of the droplet shape. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology'.

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.

Formation of Icephobic Surface with Micron-Scaled Hydrophobic Heterogeneity on Polyurethane Aerospace Coating

Development of an anti-icing surface on a desired industrial coating patch/object has been the persistent challenge to several industries, such as aviation and wind power. For this aim, performing surface modification to implement the icephobic property on existing commercial coatings is important for practical applications. This work accomplishes an icephobic coating overlying a PPG aerospace polyurethane coating. It manifests a clear capability to delay the formation of frost as well as to reduce the adhesion strength of ice. This icephobic coating is sustained by a unique hydrophobic heterogeneity in the micron-scale of segregation, which is realized through solution casting of a specific copolymer consisting of random rigid and soft segments, namely poly(methyl methacrylate) and poly(lauryl methacrylate-2-hydroxy-3-(1-amino dodecyl)propyl methacrylate), respectively. A wrinkled pattern developed over the coating is observed because of the diverse traits between these two segments. Besides, the OH/NH groups of the soft segment are crosslinked by a diisocyanate monomer upon drying and curing to strengthen the coating. More importantly, integration of a small dose of paraffin wax into the copolymer induces a spread of soft microdomains on the winkled pattern surface. It is hypothesized that these dual heterogeneous assemblies are responsible for the icephobicity since they instigate distinct interactions with condensed water droplets. Lastly, the thermoelectric cooling (Peltier effect) and the adhesion strength of ice on the typical coatings were assessed. This investigation also includes examination on the icephobic durability of coating, which is enhanced when a small amount of polyethylene oligomer is incorporated into the coating.

Mapping Depletion of Lubricant Films on Antibiofouling Wrinkled Slippery Surfaces

Slippery liquid infused porous surfaces (SLIPS) have recently gained a lot of attention because of their wide range of applications. We recently showed that SLIPS with most of their surface depleted of lubricant, as little lubricant as 0.02 ± 0.01 μL cm^-1, were effective against marine biofouling. Characterization of the depletion and configuration of the immobilized liquid layer on SLIPS is crucial to optimizing their performance. Previous attempts at mapping lubricant thickness have been diffraction limited or indirectly measured thickness. Here, we use atomic force microscopy meniscus force measurements to directly map lubricant thickness with nanoscale resolution on wrinkled surfaces made from Teflon and poly(4-vinylpyridine) (P4VP). Using this method, we show that SLIPS are easily depleted and are effectively heterogeneous surfaces, where the majority of the surface is a thick lubricating layer stabilized by capillary forces and part nanothin layer stabilized long-range intermolecular forces. We found that the depleted silicone oil thickness on the tops of nonwettable (Teflon) wrinkles is approx. 5 nm, close to but greater than the minimum measurable thickness of approx. 3 nm. The silicone oil thickness on the tops of wettable (P4VP) wrinkles is approx. 15 nm. Surfaces in this state still show antibiofouling properties and thus show that a thick lubricating layer is not necessary for all favorable properties of SLIPS.

Self-Assembly and Applications of Amphiphilic Hybrid POSS Copolymers

Understanding the mechanism of molecular self-assembly to form well-organized nanostructures is essential in the field of supramolecular chemistry. Particularly, amphiphilic copolymers incorporated with polyhedral oligomeric silsesquioxanes (POSSs) have been one of the most promising materials in material science, engineering, and biomedical fields. In this review, new ideas and research works which have been carried out over the last several years in this relatively new area with a main focus on their mechanism in self-assembly and applications are discussed. In addition, insights into the unique role of POSSs in synthesis, microphase separation, and confined size were encompassed. Finally, perspectives and challenges related to the further advancement of POSS-based amphiphilics are discussed, followed by the proposed design considerations to address the challenges that we may face in the future.

One-Step Fabrication of Bioinspired Lubricant-Regenerable Icephobic Slippery Liquid-Infused Porous Surfaces

Icephobic coating and surfaces are essential for protecting infrastructures such as transmission lines, transportation vehicles, and many others from severe damages of excessive icing. The slippery liquid-infused porous surfaces (SLIPS) are attracting escalating attention because of their low-ice adhesion strength. Despite all of the encouraging laboratory scale results, the SLIPS are still far from being applicable in real environments owing to the key unsolved problem, namely anti-icing durability. Inspired by the functionality of the amphibians' skin, lubricant regenerability was introduced to conventional SLIPS and realized by a facile and scalable fabrication route. A series of polydimethylsiloxane (PDMS)-based skinlike SLIPS were designed and fabricated by using a one-step method, the solvent evaporation-induced phase separation technique. The obtained skinlike SLIPS were able to regenerate surface lubricant constantly by internal residual stress because of phase separation and survive more than 15 cycles of wiping/regenerating tests. Thanks to the regenerability of the surface lubricant, the new SLIPS demonstrated durable icephobicity, showing a long-term low-ice adhesion strength below 70 kPa, which was only 43% of 160 kPa that for the pristine PDMS (Sylgard 184), even after 15 icing/deicing cycles. This work paves a new and facile way for achieving icephobic durability of SLIPS.

Amphiphilic Copolymers Containing POSS and SBMA with N-Vinylcaprolactam and N-Vinylpyrrolidone for THF Hydrate Inhibition

Icelike gas hydrates deposited in the pipelines under low temperatures and high pressures could remarkably reduce the transport efficiency, and a low dosage of water-soluble polymers could act as kinetic hydrate inhibitors (KHIs) to prevent gas hydrate formation. It was believed that the hydrophobic moiety in the water-soluble polymers played a vital role in enhancing the KHI performance. In this work, amphiphilic copolymers containing hydrophobic polyhedral oligomeric silsesquioxane (POSS) and superhydrophilic sulfobetaine methacrylate (SBMA) as well as N-vinylcaprolactam (VCap) and N-vinylpyrrolidone (VP) were prepared, and an efficient effect of the obtained amphiphilic copolymers on tetrahydrofuran (THF) hydrate inhibition was found. When a certain amount of the amphiphilic copolymers was introduced, the THF hydrate as an analogue of structure II gas hydrates presented a prolonged induction time and gave rise to a looser state rather than a crystalline solid. Analyses of low-field nuclear magnetic resonance and differential scanning calorimetry verified that there were strong interactions between the copolymer and water molecules by incorporation of SBMA units, which could enhance the KHI properties of the prepared amphiphilic copolymers. Additionally, the hydrophobic POSS in the amphiphilic copolymers could possibly modulate the hydrophilic/hydrophobic balance, contributing to the synergistical ability of the copolymers for THF hydrate inhibition. It was suggested that the amphiphilic copolymers containing POSS and zwitterionic units with VCap or VP could have potential for the inhibition and antiaggregation of gas hydrates in the transportation pipelines.

Fabrication of superhydrophobic composite coating based on fluorosilicone resin and silica nanoparticles

Composite superhydrophobic coating built with film former and filler is attracting much attention for its facile and convenient fabrication, but significant limitations and disadvantages still remain. In this paper, a composite superhydrophobic coating is introduced which can be cured at room temperature and made by dispersing modified silica nanoparticles with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane in fluorosilicone resin. Silica content and dispersion time showed obvious influences on the morphology and topography of composite coating by reuniting dispersed nanoparticles to form peaks on the surface. Excessively large distances between these peaks would decrease water contact angle value. Increasing slope of peaks, appropriate distance between peaks and decreasing diameter size of peaks would diminish sliding angle value. Formation mechanism of the composite coating based on fluorosilicone resin and modified nanoparticles was explained using interpenetrating polymer model.

Enhancing the Mechanical Durability of Icephobic Surfaces by Introducing Autonomous Self-Healing Function

Ice accretion presents a severe risk for human safety. Although great efforts have been made for developing icephobic surfaces (the surface with an ice adhesion strength below 100 kPa), expanding the lifetime of state-of-the-art icephobic surfaces still remains a critical unsolved issue. Herein, a novel icephobic material is designed by integrating an interpenetrating polymer network (IPN) into an autonomous self-healing elastomer, which is applied in anti-icing for enhancing the mechanical durability. The molecular structure, surface morphology, mechanical properties, and durable icephobicity of the material were studied. The creep behaviors of the new icephobic material, which were absent in most relevant studies on self-healing materials, were also investigated in this work. Significantly, the material showed great potentials for anti-icing applications with an ultralow ice adhesion strength of 6.0 ± 0.9 kPa, outperforming many other icephobic surfaces. The material also exhibited an extraordinary durability, showing a very low long-term ice adhesion strength of ∼12.2 kPa after 50 icing/deicing cycles. Most importantly, the material was able to exhibit a self-healing property from mechanical damages in a sufficiently short time, which shed light on the longevity of icephobic surfaces in practical applications.

Unprecedented Influence of Carbon Dot@TiO2 Nanohybrid on Multifaceted Attributes of Waterborne Hyperbranched Polyester Nanocomposite

Herein, we wish to report fabrication of multifaceted environmentally friendly benign renewable resource-based waterborne hyperbranched polyester nanocomposites using three different doses of carbon dot@TiO2 nanohybrid through a facile in situ polymerization technique in the absence of solvent or additional catalyst. Carbon dot@TiO2 nanohybrid was prepared through a greener one-pot hydrothermal process from bio-based raw materials. The nanocomposites were characterized by different instrumental techniques. The thermosets of these nanocomposites are obtained by curing them with glycerol-based hyperbranched epoxy and fatty acid-based poly(amido amine). Enhancements of 6.67 folds tensile strength, 3.8 folds toughness, 1.7 folds Young's modulus, >2.5 units gloss, and 46 °C thermal stability were observed for the thermosets by the formation of nanocomposites. The nanocomposites also showed antifogging and anti-icing properties. More interestingly, they can also be used for efficient separation of crude oil and water from their mixture. Thus, these environmentally benign polymeric materials could find applications in different fields.

Bioinspired Surfaces with Superwettability for Anti-Icing and Ice-Phobic Application: Concept, Mechanism, and Design

Ice accumulation poses a series of severe issues in daily life. Inspired by the nature, superwettability surfaces have attracted great interests from fundamental research to anti-icing and ice-phobic applications. Here, recently published literature about the mechanism of ice prevention is reviewed, with a focus on the anti-icing and ice-phobic mechanisms, encompassing the behavior of condensate microdrops on the surface, wetting, ice nucleation, and freezing. Then, a detailed account of the innovative fabrication and fundamental research of anti-icing materials with special wettability is summarized with a focus on recent progresses including low-surface energy coatings and liquid-infused layered coatings. Finally, special attention is paid to a discussion about advantages and disadvantages of the technologies, as well as factors that affect the anti-icing and ice-phobic efficiency. Outlooks and the challenges for future development of the anti-icing and ice-phobic technology are presented and discussed.