Designing durable icephobic surfaces

Robust All-Day Frostphobic Surfaces

The application of solar-thermal surfaces for antifrosting and defrosting has emerged as a passive and environmentally friendly approach to mitigate the negative consequences of frost formation, such as structural damage and reduced heat transfer efficiency. However, achieving robust all-day frostphobicity solely through interfacial modification and solar-thermal effects is challenging in practical applications: The thick frost that accumulates at night strongly scatters solar radiation, rendering the solar-thermal coatings ineffective during the daytime. Additionally, these nanostructured coatings are susceptible to wear and tear when exposed to the outdoors for extended periods of time. To address these challenges, we present an innovative frostphobic surface that incorporates V-grooved structures with superhydrophobic solar-thermal layers (VSSs). The out-of-plane gradient structures facilitate spatially regulated vapor diffusion, an enhanced photothermal effect, and robust water repellency. These features not only prevent frost from covering the entire surface overnight, enabling effective solar-thermal defrosting during the daytime, but also protect the surface from deterioration. The combined merits ensure robust all-day frostphobicity and exceptional durability, making the VSS surface promising for practical applications and extending the lifespan in extreme environments.

Polyurethane Nanocomposite Coatings Coupled with Titanium-Based Conversion Layers for Enhanced Anticorrosion, Icephobic Properties, and Surface Protection

This study examines the efficacy of icephobic polyurethane nanocomposite coatings in mitigating corrosion on an aluminum substrate. A titanium-based conversion coating is applied to modify the substrate, and the research focuses on optimizing the dual functionalities of icephobicity and anticorrosion within the polyurethane coatings while ensuring strong substrate adhesion. The coatings are formulated using fluoropolyol, isocyanate, and silica nanoparticles treated with polydimethylsiloxane. Surface properties are analyzed using contact angles, contact angle hysteresis measurements, and atomic force microscopy, and the coatings' icephobicity is evaluated through differential scanning calorimetry, freezing time delay, ice adhesion under impact and non-impact conditions, and ice accretion tests. The corrosion resistance and adhesive strength of the coatings are assessed using electrochemical impedance spectroscopy and cross-cut tests, respectively. Increasing the concentration of silica nanoparticles to 10 wt.% increases contact angles to 167°, although the 4 wt.% coating produces the lowest contact angle hysteresis (3° ± 0.5°) and ice nucleation temperature (-23 °C). The latter coating is then applied to a substrate pretreated with a titanium/cerium-based conversion coating. This prepared surface maintains an ice adhesion of about 15 kPa after 15 icing/de-icing cycles and provides approximately 90 days of surface protection (|Z|lf = 1.6 × 109 Ω·cm2). Notably, the impedance value exceeds that of untreated substrates, underscoring the effectiveness of the titanium/cerium-based conversion coating in enhancing both corrosion resistance and coating adhesion to the substrate.

Unraveling Ice-Solid Interface Rupture Dynamics: Insights from Molecular Dynamics Simulations

Unwanted icing on exposed surfaces poses significant risks, driving the quest for effective anti-icing mechanisms. While fracture mechanics concepts have been developed for designing coatings that weaken the ice-solid interface on soft surfaces, the factors that dictate ice adhesion strength and its counterpart, ice removal force, on hard surfaces remain poorly understood. In this study, we employ molecular dynamics simulations to investigate the interface rupture between ice and a hard solid substrate. The results indicate that the ice adhesion strength is contingent on the length of the ice cube. By examining the shearing behavior, we reveal a nanoscale critical force-bearing length. The shear force required to detach the ice scales proportionally with the length of the ice cube when it is smaller than the critical length. Once the ice cube length exceeds the critical length, the shear force stabilizes at a constant maximum value, revealing the existence of a maximum ice-removal force. The results align with the so-called strength versus toughness-controlled deicing regimes and are in agreement with cohesive zone modeling at the continuum length scale and recent experimental results. Our results extend this understanding to the nanoscale, confirming consistency between macro and micro scales. This consistency suggests that the toughness of the ice-solid interface is intrinsically governed by ice-surface interactions. By unraveling key intrinsic factors and their scale-dependent effects on the interface rupture of ice on surfaces, this study lays a solid theoretical foundation for the design and fabrication of next-generation anti-icing surfaces.

Low ice adhesion on soft surfaces: Elasticity or lubrication effects?

HYPOTHESIS

Soft materials are promising candidates for designing passive de-icing systems. It is unclear whether low adhesion on soft surfaces is due to elasticity or lubrication, and how these properties affect the ice detachment mechanism. This study presents a systematic analysis of ice adhesion on soft materials with different lubricant content to better understand the underpinning interaction.

EXPERIMENTS

The wetting and mechanical properties of soft polydimethylsiloxane with different lubricant content were thoroughly characterized by contact angle, AFM indentation, and rheology measurements. The collected information was used to understand the relationship with the ice adhesion results, obtained by using different ice block sizes.

FINDINGS

Three different de-icing mechanisms were identified: (i) single detachment occurs when small ice blocks are considered, and the ice completely detaches in a single event. In the case of larger ice blocks, the reattachment of the ice block is promoted by either: (ii) stick-slip or, (iii) interfacial slippage, depending on the lubricant content. It was confirmed that the ice adhesion strength not only depends on material properties but also on experimental conditions, such as the ice dimensions. Moreover, differently than on hard surfaces, where wetting primarily determines the icephobic performance, also elasticity and lubrication should be considered on soft surfaces.

Advanced Anti-Icing Strategies and Technologies by Macrostructured Photothermal Storage Superhydrophobic Surfaces

Water is the source of life and civilization, but water icing causes catastrophic damage to human life and diverse industrial processes. Currently, superhydrophobic surfaces (inspired by the lotus effect) aided anti-icing attracts intensive attention due to their energy-free property. Here, recent advances in anti-icing by design and functionalization of superhydrophobic surfaces are reviewed. The mechanisms and advantages of conventional, macrostructured, and photothermal superhydrophobic surfaces are introduced in turn. Conventional superhydrophobic surfaces, as well as macrostructured ones, easily lose the icephobic property under extreme conditions, while photothermal superhydrophobic surfaces strongly rely on solar illumination. To address the above issues, a potentially smart strategy is found by developing macrostructured photothermal storage superhydrophobic (MPSS) surfaces, which integrate the functions of macrostructured superhydrophobic materials, photothermal materials, and phase change materials (PCMs), and are expected to achieve all-day anti-icing in various fields. Finally, the latest achievements in developing MPSS surfaces, showcasing their immense potential, are highlighted. Besides, the perspectives on the future development of MPSS surfaces are provided and the problems that need to be solved in their practical applications are proposed.

"Honeycomb" Photothermal Lubricated Porous Foam with Low-Temperature, Weak-Light, Anti-Icing/Deicing, and Long-Lasting Lubrication Properties

The prevalence of icing in nature has become a significant threat to human work and life, prompting the development of more energy-efficient active/passive combination anti-icing/deicing technologies. In order to overcome the disadvantage of the poor durability of superhydrophobic surfaces, lubricated surfaces inspired by nepenthes have been preferred. In this study, a paraffin and silicone oil-infused photothermal foam (PSIPF) with excellent overall performance was prepared using polypyrrole (PPy) as a photothermal conversion material, a mixture of silicone oil and paraffin as a lubricating fluid, and melamine foam (MF) as a carrier. The surface adhesive strength is less than 20 kPa at -20 °C, the melting time is only 1018 s at an irradiance of 200 W/m2 and -20 °C (0.2 sun), and surface droplets do not freeze within 1 h at -10 °C. Furthermore, the surface exhibits excellent mechanical durability and stability, maintaining optimal lubrication properties following repeated cycles of icing/deicing, water rinsing, and immersion for 2 days in acid and alkaline conditions. This photothermal lubricated surface with excellent anti-icing/deicing properties at low temperatures and in weak-light environments provides a wider range of applications for equipment at high latitudes and high altitudes.

Enhanced Anti/De-Icing Performance on Rough Surfaces Based on The Synergistic Effect of Fluorinated Resin and Embedded Graphene

Icing negatively impacts various industrial sectors and daily life, often leading to severe safety problems and substantial economic losses. In this work, a fluorinated resin coating with embedded graphene nanoflakes is prepared using a spin-coating curing process. The results shows that the ice adhesion strength is reduced by ≈97.0% compared to the mirrored aluminum plate, and the icing time is delayed by a factor of 46.3 under simulated solar radiation power of 96 mW cm-2 (1 sun) at an ambient temperature of -15 °C. The superior anti/de-icing properties of the coating are mainly attributed to the synergistic effect of the fluorinated resin with a low surface energy, the rough structure of the sandblasted aluminum plate, which reduces the contact area, and the embedded graphene nanoflakes with a superior photothermal effect. Furthermore, the hydrogen bonding competition effect between the exposed-edge oxygen-containing functional groups of the embedded graphene nanoflakes and water molecules further improves the anti-icing properties. This work proposes a facile preparation method to prepare coatings with excellent anti/de-icing properties, offering significant potential for large-scale engineering applications.

Thermomechanically Resilient Polyionic Elastomers with Enhanced Anti-Icing Performances

Anti-icing gels inhibit ice formation and accretion; however, current iterations face prevalent drawbacks such as poor strength, weak substrate adhesion, and limited anti-icing properties. Herein, we propose a novel approach to address these challenges by developing a thermomechanical robust polyionic elastomer (PIE) with enhanced anti-icing properties. The PIE surface exhibits an icing delay time up to 5400 s and remains frost-free after exposure to -10 °C for 3.5 h, attributed to the inhibitory effect on ice formation by ions from ILs and the polyelectrolyte network. Moreover, the PIE exhibits remarkable anti-icing durability, with ice adhesion strengths below 35 kPa after undergoing 30 icing/deicing cycle tests at -20 °C. Following sandpaper abrasion (300 cycles), scratching, and heat treatment (100 °C, 16 h), the adhesion strength remains ca. 20 kPa, highlighting its resilience under various thermal and mechanical conditions. This exceptional durability is attributed to the low volatility of the IL and the robust ionic interactions within the PIE network. Furthermore, the PIE demonstrates favorable self-healing properties and strong substrate adhesion in both low-temperature and ambient environments, facilitated by the abundance of hydrogen bonds and electrostatic forces within PIE. This work presents an innovative approach to developing high-performance, durable, and robust anti-icing materials with potential implications across various fields.

One-step synthesis of functional slippery lubricated coating with substrate independence, anti-fouling property, fog collection, corrosion resistance, and icephobicity

Ranging from industrial facilities to residential infrastructure, functional surfaces encompassing functionalities such as anti-fouling, fog collection, anti-corrosion, and anti-icing play a critical role in the daily lives of humans, but creating these surfaces is elusive. Bionic dewetting and liquid-infused surfaces have inspired the exploitation of functional surfaces. However, practical applications of these existing surfaces remain challenging because of their inherent shortcomings. In this study, we propose a novel functional slippery lubricated coating (FSLC) based on a simple blend of polysilazane (PSZ), silicone oil, and nano silica. This simple, nonfluorine based, and low-cost protocol promotes not only hierarchical micro-nano structure but also favorable surface chemistry, which facilitates robust silicone oil adhesion and excellent slippery properties (sliding angle: ∼1.6°) on various solid materials without extra processing or redundant treatments. The highly integrated competence of FSLC, characterized by robustness, durability, strong adhesion to substrates, and the ability for large-area preparation, render them ideal for practical production and application. The proposed FSLC holds outstanding application potentials for anti-fouling, self-cleaning, fog collection, anti-corrosion, and anti-icing functionalities.

Enhancing Icephobic Coatings: Exploring the Potential of Dopamine-Modified Epoxy Resin Inspired by Mussel Catechol Groups

A nature-inspired approach was employed through the development of dopamine-modified epoxy coating for anti-icing applications. The strong affinity of dopamine's catechol groups for hydrogen bonding with water molecules at the ice/coating interface was utilized to induce an aqueous quasi-liquid layer (QLL) on the surface of the icephobic coatings, thereby reducing their ice adhesion strength. Epoxy resin modification was studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR). The surface and mechanical properties of the prepared coatings were studied by different characterization techniques. Low-temperature ATR-FTIR was employed to study the presence of QLL on the coating's surface. Moreover, the freezing delay time and temperature of water droplets on the coatings were evaluated along with push-off and centrifuge ice adhesion strength to evaluate their icephobic properties. The surface of dopamine-modified epoxy coating presented enhanced hydrophilicity and QLL formation, addressed as the main reason for its remarkable icephobicity. The results demonstrated the potential of dopamine-modified epoxy resin as an effective binder for icephobic coatings, offering notable ice nucleation delay time (1316 s) and temperature (-19.7 °C), reduced ice adhesion strength (less than 40 kPa), and an ice adhesion reduction factor of 7.2 compared to the unmodified coating.

Dual-Energy-Barrier Stable Superhydrophobic Structures for Long Icing Delay

Using superhydrophobic surfaces (SHSs) with the water-repellent Cassie-Baxter (CB) state is widely acknowledged as an effective approach for anti-icing performances. Nonetheless, the CB state is susceptible to diverse physical phenomena (e.g., vapor condensation, gas contraction, etc.) at low temperatures, resulting in the transition to the sticky Wenzel state and the loss of anti-icing capabilities. SHSs with various micronanostructures have been empirically examined for enhancing the CB stability; however, the energy barrier transits from the metastable CB state to the stable Wenzel state and thus the CB stability enhancement is currently not enough to guarantee a well and appliable anti-icing performance at low temperatures. Here, we proposed a dual-energy-barrier design strategy on superhydrophobic micronanostructures. Rather than the typical single energy barrier of the conventional CB-to-Wenzel transition, we introduced two CB states (i.e., CB I and CB II), where the state transition needed to go through CB I and CB II then to Wenzel state, thus significantly improving the entire CB stability. We applied ultrafast laser to fabricate this dual-energy-barrier micronanostructures, established a theoretical framework, and performed a series of experiments. The anti-icing performances were exhibited with long delay icing times (over 27,000 s) and low ice-adhesion strengths (0.9 kPa). The kinetic mechanism underpinning the enhanced CB anti-icing stability was elucidated and attributed to the preferential liquid pinning in the shallow closed structures, enabling the higher CB-Wenzel transition energy barrier to sustain the CB state. Comprehensive durability tests further corroborated the potentials of the designed dual-energy-barrier structures for anti-icing applications.

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.

De-icing performance evolution with increasing hydrophobicity by regulating surface topography

It is of great significance to grasp the role of surface topography in de-icing, which however remains unclear yet. Herein, four textured surfaces are developed by regulating surface topography while keeping surface chemistry and material constituents same. Specifically, nano-textures are maintained and micro-textures are gradually enlarged. The resultant ice adhesion strength is proportional to a topography parameter, i.e. areal fraction of the micro-textures, owing to the localized bonding strengthening, which is verified by ice detachment simulation using finite element method. Moreover, the decisive topography parameter is demonstrated to be determined by the interfacial strength distribution between ice and test surface. Such parameters vary from paper to paper due to different interfacial strength distributions corresponding to respective situations. Furthermore, since hydrophobic and de-icing performance may rely on different topography parameters, there is no certain relationship between hydrophobicity and de-icing.

Multifunctional Anti-Icing Gel Surface with Enhanced Durability

Materials with low ice adhesion and long-lasting anti-icing properties remain an ongoing challenge in ultralow temperature environments (≤-30 °C). This study presents a gel material consisting of a polymer matrix (copolymer of polyurethane and acrylamide) and an anti-icing agent, ethylene glycol (EG), designed for anti-icing applications at ultralow temperatures. The surface shows a prolonged droplet freezing delay of ca. 322 s at -30 °C and frost resistance properties. It also exhibits an ice adhesion strength of 1.1 kPa at -10 °C and 39.8 kPa at -50 °C, resulting from the interaction between EG and water molecules that hinders the crystallization of ice as well as the significant mismatch between elastic gel and ice. In addition, the gel surface exhibits favorable anti-icing durability, with an ice adhesion strength below 20.0 kPa after 25 icing/deicing cycles and mechanical scratch tests. The gel demonstrates remarkable thermal durability, achieved through the H-bonds between the EG and polymer matrix. The H-bonds further enhance the anti-icing performance, thereby remarkably decreasing EG depletion and improving anti-icing durability. Overall, these properties suggest the potential application of this gel material in harsh environments including polar regions.

Icephobic Gradient Polymer Coatings Deposited via iCVD: A Novel Approach for Icing Control and Mitigation

Materials against ice formation and accretion are highly desirable for different industrial applications and daily activities affected by icing. Although several concepts have been proposed, no material has so far shown wide-ranging icephobic features, enabling durability and manufacturing on large scales. Herein, we present gradient polymers made of 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4D4) and 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) deposited in one step via initiated chemical vapor deposition (iCVD) as an effective coating to mitigate ice accretion and reduce ice adhesion. The gradient structures easily overcome adhesion, stability, and durability issues of traditional fluorinated coatings. The coatings show promising icephobic performance by reducing ice adhesion, depressing the freezing point, delaying drop freezing, and inhibiting ice nucleation and frost propagation. Icephobicity correlates with surface energy discontinuities at the surface plane resulting from the random orientation of the fluorinated groups of PFDA, as confirmed by grazing-incidence X-ray diffraction measurements. The icephobicity could be further improved by tuning the surface crystallinity rather than surface wetting, as samples with random crystal orientation show the lowest ice adhesion despite high contact angle hysteresis. The iCVD-manufactured coatings show promising results, indicating the potential for ice control on larger scales and various applications.

Transparent PDMS Surfaces with Covalently Attached Lubricants for Enhanced Anti-adhesion Performance

Liquid-like surfaces featuring slippery, omniphobic, covalently attached liquids (SOCALs) reduce unwanted adhesion by providing a molecularly smooth and slippery surface arising from the high mobility of the liquid chains. Such SOCALs are commonly prepared on hard substrates, such as glass, wafers, or metal oxides, despite the importance of nonpolar elastomeric substrates, such as polydimethylsiloxane (PDMS) in anti-fouling or nonstick applications. Compared to polar elastomers, hydrophobic PDMS elastomer activation and covalent functionalization are significantly more challenging, as PDMS tends to display fast hydrophobic recovery upon activation as well as superficial cracking. Through the extraction of excess PDMS oligomers and fine-tuning of plasma activation parameters, homogeneously functionalized PDMS with fluorinated polysiloxane brushes could be obtained while at the same time reducing crack formation. Polymer brush mobility was increased through the addition of a smaller molecular silane linker to exhibit enhanced dewetting properties and reduced substrate swelling compared to functionalizations featuring hydrocarbon functionalities. Linear polymer brushes were verified by thermogravimetric analysis. The optical properties of PDMS remained unaffected by the activation in high-frequency plasma but were impacted by low-frequency plasma. Drastic decreases in solid adhesion of not just complex contaminants but even ice could be shown in horizontal push tests, demonstrating the potential of SOCAL-functionalized PDMS surfaces for improved nonstick applications.

A simple fabrication of liquid-like polydimethylsiloxane coating for resisting ice adhesion

The rapid realization of efficient anti-icing coatings on diverse substrates is of vital value for practical applications. However, current approaches for rapid preparations of anti-icing coatings are still deficient regarding their surface universality and accessibility. Here, we report a simple processing approach to rapidly form icephobic liquid-like polydimethylsiloxane (PDMS) brushes on various substrates, including metals, ceramics, glass, and plastics. A poly(dimethylsiloxane), trimethoxysilane is applied as a reactant under the catalysis of a minimal amount of acid formed by hydrolysis of dichlorodimethylsilane. With such an advantage, this approach is approved to be applicable of coating metal surfaces with less corrosion. The distinctive flexibility of the PDMS chains provides a liquid-like property to the coating showing low contact angle hysteresis and ice adhesion strength. Notably, the ice adhesion strength remains similar across a wide temperature window, from -70 to -10 °C, with a value of 18.4 kPa. The PDMS brushes demonstrate perfect capability for resisting acid and alkali corrosions, ultra-violet degradation, and even tens of icing/deicing cycles. Moreover, the liquid-like coating can also form at supercooling conditions, such as -20 °C, and shows an outstanding anti-icing/deicing performance, which meets the in situ coating reformation requirement under extreme conditions when it is damaged. This instantly forming anti-icing material will benefit from resisting instantaneous ice accretion on surfaces under extremely cold conditions.

Unraveling the role of vaporization momentum in self-jumping dynamics of freezing supercooled droplets at reduced pressures

Supercooling of water complicates phase change dynamics, the understanding of which remains limited yet vital to energy-related and aerospace processes. Here, we investigate the freezing and jumping dynamics of supercooled water droplets on superhydrophobic surfaces, induced by a remarkable vaporization momentum, in a low-pressure environment. The vaporization momentum arises from the vaporization at droplet's free surface, progressed and intensified by recalescence, subsequently inducing droplet compression and finally self-jumping. By incorporating liquid-gas-solid phase changes involving vaporization, freezing recalescence, and liquid-solid interactions, we resolve the vaporization momentum and droplet dynamics, revealing a size-scaled jumping velocity and a nucleation-governed jumping direction. A droplet-size-defined regime map is established, distinguishing the vaporization-momentum-dominated self-jumping from evaporative drying and overpressure-initiated levitation, all induced by depressurization and vaporization. Our findings illuminate the role of supercooling and low-pressure mediated phase change in shaping fluid transport dynamics, with implications for passive anti-icing, advanced cooling, and climate physics.

Superhydrophobic Antifrosting 7075 Aluminum Alloy Surface with Stable Cassie-Baxter State Fabricated through Direct Laser Interference Lithography and Hydrothermal Treatment

Frost formation and accumulation can have catastrophic effects on a wide range of industrial activities. Hence, a dual-scale surface with a stable Cassie-Baxter state is developed to mitigate the frosting problem by utilizing direct laser interference lithography assisted with hydrothermal treatment. The high Laplace pressure tolerance under the evaporation stimulus and prolonged Cassie-Baxter state maintenance under the condensation stimulus demonstrate the stable Cassie-Baxter state. The dual-scale surface exhibits a lengthy frost-delaying time of up to 5277 s at -7 °C due to the stable Cassie-Baxter state. The self-removal of frost is achieved by promoting the mobility of frost melts driven by the released interfacial energy. In addition, the dense flocculent frost layer is observed on the single-scale micro surface, whereas the sparse pearl-shaped frost layer with many voids is obtained on the dual-scale surface. This work will aid in understanding the frosting process on various-scale superhydrophobic surfaces and in the design of antifrosting surfaces.

Cold granular targets slow the bulk freezing of an impacting droplet

When making contact with an undercooled target, a drop freezes. The colder the target is, the more rapid the freezing is supposed to be. In this research, we explore the impact of droplets on cold granular material. As the undercooling degree increases, the bulk freezing of the droplet is delayed by at least an order of magnitude. The postponement of the overall solidification is accompanied by substantial changes in dynamics, including the spreading-retraction process, satellite drop generation, and cratering in the target. The solidification of the wetted pores in the granular target primarily causes these effects. The freezing process over the pore dimension occurs rapidly enough to match the characteristic timescales of impact dynamics at moderate undercooling degrees. As a result, the hydrophilic impact appears "hydrophobic," and the dimension of the solidified droplet shrinks. A monolayer of cold grains on a surface can reproduce these consequences. Our research presents a potential approach to regulate solidified morphology for subfreezing drop impacts. It additionally sheds light on the impact scenario of strong coupling between the dynamics and solidification.

Recent progress in understanding the anti-icing behavior of materials

Despite the significant progress in fundamental research in the physics of atmospheric icing or the revolutionary changes in modern materials and coatings achieved due to the recent development of nanotechnology and synthetic chemistry, the problem of reliable protection against atmospheric icing remains a hot topic of surface science. In this paper, we present a brief analysis of the mechanisms of anti-icing behavior that attracted the greatest interest of the scientific community and approaches which realize these mechanisms. We also note the strengths and weaknesses of such approaches and discuss future studies and prospects for the practical application of developed coatings.

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.

Impact of the Undersaturation Level on the Longevity of Superhydrophobic Surfaces in Stationary Liquids

Although the longevity of superhydrophobic surface (SHS) induced by diffusive gas transfer has been extensively studied, the scaling relation between SHS longevity and undersaturation level of the liquid is still an open question. In this study, we address this question by performing experiments where the plastron decay is visualized by a nonintrusive optical technique based on light reflection, the gas diffusion is introduced by using liquid with low dissolved gas concentrations, and the SHS longevity is measured based on the status of gas on the entire surface. We find that the SHS longevity (tf) follows a scaling relation: tf ∼ (1 - s)-2, where s is the ratio of the gas concentration in liquid to that in the plastron. This scaling relation implies that as the gas is dissolving into the liquid, mass flux J reduces with time as J ∼ t-0.5. Furthermore, we find that the diffusion length LD reduces as the undersaturation level increases, following the scaling relation of LD ∼ (1 - s)-1. Lastly, we show that an SHS with a greater texture depth has a longer longevity and a larger LD. Our results provide a better understanding of SHS longevity in undersaturated liquid.

Silicone elastomers and the Persson-Brener adhesion model

Many modern anti-icing and anti-fouling coatings rely on soft, low surface energy elastomeric materials such as polydimethylsiloxane for their functionality. While the low surface energy is desirable for reducing adhesion, very little work considers the larger contribution to adhesive failure caused by the viscoelastic nature of elastomers. Here we examine several different siloxane elastomers using a JKR adhesion test, which was operated over a range of different speeds and temperatures. Additionally, we characterize the dynamic mechanical modulus over a large range of frequencies for each material. We note that surface energies of the materials are all similar, but variation in adhesion strength is clear in the data. The variation at low speeds is related to elastomer architecture but the speed dependence itself is independent of architecture. Qualitative correlations are noted between the JKR adhesion measurements and the dynamic moduli. Finally, an attempt is made to directly compare moduli and adhesion through the recent Persson-Brener model. Approximations of the model are shown to be inaccurate. The full model is found to be accurate at low speeds, although it fails to precisely capture higher speed behaviour.

Innovative Solid Slippery Coating: Uniting Mechanical Durability, Optical Transparency, Anti-Icing, and Anti-Graffiti Traits

Slippery coatings, such as the slippery liquid-infused porous surface (SLIPS), have gained significant attention for their potential applications in anti-icing and anti-fouling. However, they lack durability when subjected to mechanical impact. In this study, we have developed a robust slippery coating by blending polyurethane acrylate (PUA) with methyltriethoxysilane (MTES) and perfluoropolyether (PFPE) in the solvent of butyl acetate. The resulting mixture is homogeneous and allows for uniform coating on various substrates using a drop coating process followed by drying at 160 °C for 3 h. The cured coating exhibits excellent water repellency (contact angle of ~108° and sliding angle of ~8°), high transparency (average visible transmittance of ~90%), exceptional adherence to the substrate (5B rating according to ASTMD 3359), and remarkable hardness (4H on the pencil hardness scale). Moreover, the coating is quite flexible and can be folded without affecting its wettability. The robustness of the coating is evident in its ability to maintain a sliding angle below 25° even when subjected to abrasion, water jetting, high temperature, and UV irradiation. Due to its excellent nonwetting properties, the coating can be employed in anti-icing, anti-graffiti, and anti-sticking applications. It effectively reduces ice adhesion on aluminum substrates from approximately 217 kPa to 12 kPa. Even after 20 cycles of icing and de-icing, there is only a slight increase in ice adhesion, stabilizing at 40 kPa. The coating can resist graffiti for up to 400 cycles of writing with an oily marker pen and erasing with a tissue. Additionally, the coating allows for easy removal of 3M tape thereon without leaving any residue.

A Highly Transparent Photo-Electro-Thermal Film with Broadband Selectivity for All-Day Anti-/De-Icing

A photo- and electro-thermal film can convert sunlight and electricity into heat to solve icing problems. Combination of them provides an efficient strategy for all-day anti-/de-icing. However, only opaque surfaces have been reported, due to the mutual exclusiveness between photon absorption and transmission. Herein, a highly transparent and scalable solution-processed photo-electro-thermal film is reported, which exhibits an ultra-broadband selective spectrum to separate the visible light from sunlight and a countertrend suppress of emission in longer wavelength. It absorbs ≈ 85% of invisible sunlight (ultraviolet and near-infrared) for light-heat conversion, meanwhile maintains luminous transmittance > 70%. The reflection of mid-infrared leads to low emissivity (0.41), which further preserves heat on the surface for anti-/de-icing purpose. This ultra-broadband selectivity enables temperature elevation > 40 °C under 1-sun illumination and the mutual support between photo-thermal and electro-thermal effects contributes to > 50% saving of electrical consumption under weak solar exposure (0.4-sun) for maintaining unfrozen surfaces at -35 °C environment. The reverberation from photo-electro-thermal and super-hydrophobic effects illustrates a lubricating removal of grown ice in short time (< 120 s). The self-cleaning ability and the durability under mechanical, electrical, optical, and thermal stresses render the film stable for long-term usage in all-day anti-/de-icing applications.

Freezing Characteristics of a Water Droplet on a Multiscale Superhydrophobic Surface

Superhydrophobic surfaces have the potential to retard ice formation owing to their super water-repellant nature arising from high static contact angle and low contact angle hysteresis. Most of the previous studies have focused on patterned surfaces with mono-scaled prismatic structures. In contrast, the freezing behavior on multiscaled rough superhydrophobic surfaces that are of practical significance is relatively little studied. This article presents, for the first time, the freezing dynamics of a water droplet interacting with multiscale fractal superhydrophobic surfaces which validates well with experimental measurements. It is shown that the dual effects of increased contact angle and poor interfacial conduction due to trapped air cavities within the roughness features of the superhydrophobic surface lead to increasing freezing time with increasing surface hydrophobicity, determined as a function of the fractal surface parameters. A comparison of the freezing dynamics of sessile droplets of identical contact angle on a smooth versus a rough superhydrophobic surface shows that interfacial asperity thermal resistance contributes to over 14% increase in the freeze time. It is further shown that by tailoring the multiscale characteristics, the freeze time may be increased by up to 7-fold compared to freezing on a smooth surface. The application of the numerical model to studying ice formation on several practical superhydrophobic surfaces of a range of metallic materials and fabrication methods is also discussed, which offers guidelines for the design of anti-icing surfaces in practice.

Disregarded Free Chains Affect Bacterial Adhesion on Cross-Linked Polydimethylsiloxane Surfaces

The surface properties exhibited by chemically cross-linked polydimethylsiloxanes (CPDMS) such as morphology, stiffness, and wettability have garnered great interest in the study of bacteria-material interactions. Nevertheless, the hidden factor of uncross-linked free PDMS chains that dissociate in CPDMS has often been overlooked when studying the biofilm formation on these polymeric elastomer surfaces. Here, we undertake a comparative characterization of the effects of free chains in CPDMS on bacterial adhesion to both flat and textured Sharklet CPDMS surfaces. Surprisingly, compared to unextracted surfaces, removing free chains from flat and textured CPDMS through solvent extraction results in a tremendous increase in bacterial colony-forming units for both Gram-negative and Gram-positive bacteria up to 2-3 orders in the initial adhesion stage of 2 h. These findings demonstrate that the solvent extraction of free chains from CPDMS is essential in studying the interactions between bacteria and silicone elastomer materials when focusing on a single variable.

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.

Predictive model of ice adhesion on non-elastomeric materials

HYPOTHESIS

When ice accumulates on a surface, it can adversely impact functionality and safety of a platform in infrastructure, transportation, and energy sectors. Despite several attempts to model the ice adhesion strength on ice-shedding materials, none have been able to justify variation in the ice adhesion strength measured by various laboratories on a simple bare substrate. This is primarily due to the fact that the effect of underlying substrate of an ice-shedding material has been entirely neglected.

EXPERIMENTS

Here, we establish a comprehensive predictive model for ice adhesion using the shear force method on a multi-layered material. The model considers both shear resistance of the material and shear stress transfer to the underlying substrate. We conducted experiments to validate the model predictions on the effect of coating and substrate properties on the ice adhesion.

FINDINGS

The model reveals the importance of the underlying substrate of a coating on ice adhesion. Most importantly, the correlation between the ice adhesion and the coating thickness are entirely different for elastomeric and non-elastomeric materials. This model justifies different measured ice adhesion across various laboratories on the same material and elucidates how one could achieve both low ice adhesion and high mechanical durability. Such predictive model and understanding provides a rich platform to guide the future material innovation with minimal adhesion to the ice.

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.

Self-healable and transparent PDMS-g-poly(fluorinated acrylate) coating with ultra-low ice adhesion strength for anti-icing applications

The high ice adhesion strength (τ) and low adhesion of lubricant-free slippery polymers have restricted their applications. We synthesized polysiloxane-g-fluorinated acrylate polymer with a branched structure, anchored groups and dynamic cross-linked network, features imparting increased chain segment slipperiness and self-healability. The coating showed a low τ (6 kPa), strong adhesion and prolonged life.

Infusing Silicone and Camellia Seed Oils into Micro-/Nanostructures for Developing Novel Anti-Icing/Frosting Surfaces for Food Freezing Applications

Undesired ice/frost formation and accretion often occur on food freezing facility surfaces, lowering freezing efficiency. In the current study, two slippery liquid-infused porous surfaces (SLIPS) were fabricated by spraying hexadecyltrimethoxysilane (HDTMS) and stearic acid (SA)-modified SiO₂ nanoparticles (NPs) suspensions, separately onto aluminum (Al) substrates coated with epoxy resin to obtain two superhydrophobic surfaces (SHS), and then infusing food-safe silicone and camellia seed oils into the SHS, respectively, achieving anti-frosting/icing performance. In comparison with bare Al, SLIPS not only exhibited excellent frost resistance and defrost properties but also showed ice adhesion strength much lower than that of SHS. In addition, pork and potato were frozen on SLIPS, showing an extremely low adhesion strength of <10 kPa, and after 10 icing/deicing cycles, the final ice adhesion strength of 29.07 kPa was still much lower than that of SHS (112.13 kPa). Therefore, the SLIPS showed great potential for developing into robust anti-icing/frosting materials for the freezing industry.

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.

Freezing-induced wetting transitions on superhydrophobic surfaces

Supercooled droplet freezing on surfaces occurs frequently in nature and industry, often adversely affecting the efficiency and reliability of technological processes. The ability of superhydrophobic surfaces to rapidly shed water and reduce ice adhesion make them promising candidates for resistance to icing. However, the effect of supercooled droplet freezing-with its inherent rapid local heating and explosive vaporization-on the evolution of droplet-substrate interactions, and the resulting implications for the design of icephobic surfaces, are little explored. Here we investigate the freezing of supercooled droplets resting on engineered textured surfaces. On the basis of investigations in which freezing is induced by evacuation of the atmosphere, we determine the surface properties required to promote ice self-expulsion and, simultaneously, identify two mechanisms through which repellency falters. We elucidate these outcomes by balancing (anti-)wetting surface forces with those triggered by recalescent freezing phenomena and demonstrate rationally designed textures to promote ice expulsion. Finally, we consider the complementary case of freezing at atmospheric pressure and subzero temperature, where we observe bottom-up ice suffusion within the surface texture. We then assemble a rational framework for the phenomenology of ice adhesion of supercooled droplets throughout freezing, informing ice-repellent surface design across the phase diagram.

Crack-Initiated Durable Low-Adhesion Trilayer Icephobic Surfaces with Microcone-Array Anchored Porous Sponges and Polydimethylsiloxane Cover

Reducing unfavorable ice accretion on surfaces exposed in cold environment requires effective passive anti-icing/deicing techniques. Icephobic surfaces are widely applied on various infrastructures due to their low ice adhesion strength and flexibility, whereas their poor mechanical durability, common liquid infusion, weak resistance to contamination, and low bonding strength to substrates are the major remaining challenges. According to the fracture mechanics of ice layer, initiating cracks at the ice-solid interfaces via the proper design of internal structures of icephobic materials is a promising way to icephobicity. Herein, a crack initiating icephobic surface with porous PDMS sponges sandwiched between a protective, dense PDMS layer and a textured metal microstructure was proposed and fabricated. The combination of high- and low- stiffness PDMS layers anchored by the structured metal surface give the sandwich-like structure excellent icephobicity with both high durability and low ice adhesion (5.3 kPa in the icing-deicing cycles). The porosity and the elastic modulus of the PDMS sponges and the periodicity of the metal surface structures can both be tailored to realize enhanced icephobicity. The sandwich-like icephobic surface remained insignificantly changed under solid particle impacting and the durability characterized via linear abrasion tests was elevated compared with PDMS coating on flat metal surfaces. Additionally, the trilayer icephobic surface possesses durability, low ice adhesion strength, and improved resistance to contamination and is applicable on various surfaces.

Fluid manipulation via multifunctional lubricant infused slippery surfaces: principle, design and applications

Water-repellent interfaces with high performance have emerged as an indispensable platform for developing advanced materials and devices. Inspired by the pitcher plant, slippery liquid-infused porous surfaces (SLIPSs) with reliable hydrophobicity have proven to possess great potential for various applications in droplet and bubble manipulation, droplet energy harvesting, condensation, fog collection, anti-icing, and anti-biofouling due to their excellent properties such as persistent surface hydrophobicity, molecular smoothness, and fluidity. This review aims to introduce the development history of interaction between SLIPSs and fluids as well as the design principles, preparation methods, and various applications of some of the more typical SLIPSs. The fluid manipulation strategies of the slippery surfaces have been proposed including the wettability pattern, oriented micro-structure, and geometric gradient. At last, the application prospects of SLIPSs in various fields and the challenges in the design and fabrication of slippery surfaces are analyzed. We envision that this review can provide an overview of the fluid manipulating processes on slippery surfaces for researchers in both academic and industrial fields.

Hydro- and Icephobic Properties and Durability of Epoxy Gelcoat Modified with Double-Functionalized Polysiloxanes

Anti-icing coatings have provided a very good alternative to current, uneconomic, active deicing methods, and their use would bring a number of significant benefits to many industries, such as aviation and energy. Some of the most promising icephobic surfaces are those with hydrophobic properties. However, the relationship between hydrophobicity and low ice adhesion is not yet clearly defined. In this work, chemical modification of an epoxy gelcoat with chemical modifiers from the group of double organofunctionalized polysiloxanes (generally called multifunctionalized organosilicon compounds (MFSCs)) was applied. The anti-icing properties of manufactured coatings were determined by means of measurements of shear strength between the ice layer and the modified surface, conducted using a tensile machine. In the work, tests were also performed on the roughness, wettability, and durability of the properties in an aging chamber. It was found that the performed modifications of the coating's chemical composition by the addition of polysiloxanes enabled us to reduce ice adhesion by 51% and to increase the water contact angle by 14% in comparison to the neat gelcoat. A reduction in ice adhesion was also observed with the increasing water contact angle and with decreasing surface roughness. In addition, only one modification recorded an increase in ice adhesion after exposure in the aging chamber.

A Slippery Liquid-Infused Network-like Surface with Anti/De-icing Properties Constructed Based on the Phosphating Reaction

The excessive accumulation of ice seriously threatens various industrial facilities and production activities. Currently, slippery liquid-injected porous surfaces (SLIPS) have been developed as a new strategy for anti/de-icing; however, the lack of research on the adsorption and storage capacity for lubricating fluids has limited the development of SLIPS in the anti/de-icing field to some extent. In this work, a slippery liquid-infused phosphate network-like surface (SLIPNS) is prepared that adjusts the texture of the surface by varying the phosphating time to control the adsorption and storage of lubricating fluids. The as-obtained surface structure gives the SLIPNS excellent oil-storage/locked properties, can delay the freezing time of sessile droplets up to 436 s, which is almost 10 times that of an untreated aluminum sheet, and exhibits one-tenth the ice adhesion strength of untreated aluminum substrates (14.39 kPa). In addition, the SLIPNS shows effective durability and antifouling ability and has great potential in solving long-term anti/de-icing problems.

Construction of durable superhydrophobic and anti-icing coatings via incorporating boroxine cross-linked silicone elastomers with good self-healability

The fragility of the micro-nano structure makes superhydrophobic coatings highly susceptible to stress, resulting in a decrease in their superhydrophobic and anti-icing performance. In this work, we proposed a new insight to improve durability by incorporating a thin layer of self-healable elastomer with a dynamic network on the micro-nano structure. We constructed superhydrophobic coatings (EP/SiO₂/BFVSE) with a three-layered structure of the epoxy resin/silica nanoparticle/silicon elastomer. The silicon elastomer (BFVES) with a B-O dynamic cross-linked network and fluorinated moieties was synthesized by graft polymerization on vinyl silicon oil. The preparation route is facile and convenient for mass production. BFVES has rapid self-healing properties for scratches at room-temperature, underwater and at -18 °C. EP/SiO₂/BFVSE preserved apparently higher CAs after being immersed in pH = 1, pH = 13, and NaCl solutions for 96 h as compared with the EP/SiO₂ coating. In a water striking environment, the CA of EP/SiO₂/BFVSE was slightly decreased to 153°. SEM images further reveal that the recovery of superhydrophobicity and icephobicity is attributed to the self-healing behavior of the boroxine-containing silicon elastomer. The EP/SiO₂/BFVSE coating also possesses additional self-healing ability under chemical oxidation. The high durability of the self-healable superhydrophobic coating enables great application potential in aircraft, marine vessels, and outdoor facilities in harsh environments.

In Situ Activation of Superhydrophobic Surfaces with Triple Icephobicity at Low Temperatures

Superhydrophobic surfaces have been widely studied due to their potential applications in aerospace fields. However, superhydrophobic surfaces with excellent water-repellent, anti-icing, and icephobic performances at low temperatures have rarely been reported. Herein, superhydrophobic surfaces with heating capability were prepared by etching square micropillar arrays on the surface of multiwalled carbon nanotube (MWCNT)/poly(dimethylsiloxane) (PDMS) films. The fabricated superhydrophobic surface has triple icephobicity, which can be activated even at low temperatures. The triple icephobicity is triggered by an applied voltage to achieve excellent water-repellent and icephobic capabilities, even at -40 °C. Additionally, theoretical calculations reveal that a droplet on a superhydrophobic surface loses heat at a rate of 8.91 × 10^-5 J/s, which is 2 orders of magnitude slower than a flat surface (2.15 × 10^-3 J/s). Also, at -40 °C, the mechanical interlocking force formed between the superhydrophobic surface and ice can be released by the heating property of the superhydrophobic surface. This low-energy, multifunctional superhydrophobic surface opens up new possibilities for bionic smart multifunctional materials in icephobic applications.

Effect of Doping SiO2 Nanoparticles and Phenylmethyl Silicone Oil on the Large-Scale Deicing Property of PDMS Coatings

Recently, low interfacial toughness (LIT) materials have been developed to solve large-scale deicing problems. According to the theory of interfacial fracture, ice detachment is dominated by strength-controlled or toughness-controlled regimes, which are characterized by adhesive strength or constant shear force. Here, a new strategy is introduced to regulate the interfacial toughness of poly(dimethylsiloxane) (PDMS) coatings using silicon dioxide nanoparticles (SiO₂ NPs) and phenylmethyl silicone oil (PMSO). By systematically adjusting the doping proportion of SiO₂ NPs and PMSO, it is found that a lower interfacial toughness can be achieved with a lower constant shear force. The synergistic effect of the two dopants on the adhesive strength and interfacial toughness is analyzed. Meanwhile, finite element method (FEM) analysis of ice detachment is conducted to show the cracking process intuitively and explicate the mechanism of lowering the interfacial toughness of PDMS by doping SiO₂ NPs and PMSO. It can be concluded that the cohesive zone material (CZM) model is effective for simulating the deicing process of PDMS coatings and provides a comprehensive understanding of the modulation of interfacial toughness.

Robust Anti-Icing Surfaces Based on Dual Functionality─Microstructurally-Induced Ice Shedding with Superimposed Nanostructurally-Enhanced Water Shedding

Research into anti-icing surfaces often conflates the two separate problems of ice accumulation: water adhesion and ice adhesion. The body feathers of perpetually ice-free penguins are very good natural examples of anti-icing surfaces, which use two different mitigation strategies for the two disparate problems. Herein, we mimic the form of the feather's wire-like structure, which is decorated with superimposed nanogrooves by laser micromachining fine woven wire cloths. Post-processing techniques also allow us to isolate the role of surface chemistry by creating both hydrophilic and hydrophobic versions of the synthetic anti-icing surfaces. Our results show that water-shedding and ice-shedding characteristics are indeed derived from different physical functions of the hierarchical structure. The microstructure of the woven wire cloth leads to facile interfacial cracking and therefore extremely low ice adhesion strengths; the superimposed laser-induced periodic surface structures with hydrophobic surface chemistry lead to water shedding. Our work shows that by first taking a fracture mechanics approach to designing the ice-shedding function, a robust anti-icing surface can be engineered by separately designing the water-shedding functions.

Fracture-controlled surfaces as extremely durable ice-shedding materials

Icing imposes a significant burden on those living in cold climates, with negative impacts on infrastructure, transportation, and energy systems. Over the past few decades, a wide range of materials with ice-shedding characteristics have been developed, including surfaces that are non-wetting/hydrophobic, liquid-infused, stress-localized, and those with low interfacial toughness. Although many of these materials have demonstrated low ice adhesion in a laboratory setting, none have achieved widespread practical adoption. This is primarily a result of the fact that they tend to have very low durability, limiting their applicability. Thus, the primary challenge in developing ice-shedding materials is finding materials with both low ice adhesion AND good durability. Here, we introduce the concept of a so-called "fracture-controlled surface." Through coordinated mechanical and chemical heterogeneity in the material structure, we affect the interfacial crack nucleation and growth on these surfaces. Through this controlled process, fracture-controlled surfaces exhibit both low ice adhesion and very high mechanical durability. Measurements of the durability of these surfaces indicate performance that is three orders of magnitude greater than other state-of-the-art ice-shedding materials. Physically, via mechanical heterogeneity of the material, we pre-specified the crack nucleation coordinates at the interface and guided the crack growth in an interfacial plane, with no kinking in other directions. This helps to maximize the energy that goes towards crack nucleation and growth. A detailed mathematical model is developed to predict adhesion of external solid objects on these materials. The model suggests that an elastic matching criterion is required to achieve minimal adhesion of solid objects on these materials. Fracture-controlled surfaces provide a rich material platform to guide future innovation of materials with minimal adhesion while having very high durability.

Thermo-responsive Fluorinated Organogels Showing Anti-fouling and Long-Lasting/Repeatable Icephobic Properties

Accumulations of ice on modern infrastructures often cause severe consequences. As such, there is significant interest in developing functional coatings/surfaces that can prevent this. One such approach has been demonstrated with slippery liquid-infused porous surfaces (SLIPS) and organogels where the ice adhesion strength is reduced to the critical point (less than 10 kPa) where it can be removed by natural forces such as gravity, wind, vibrations, and so forth. However, both designs are limited by lubricant depletion. If lubricant release and reabsorption (syneresis) of organogels can be arbitrarily controlled by the surrounding temperature, the loss due to unfavorable evaporation and drainage of infused lubricants can be minimized and its durability can be extended. This study demonstrates the tunable thermo-responsive syneresis of transparent fluorinated organogels (F-ORGs) prepared from a commercial silicone elastomer and a lubricant mixture of fluorinated silicone oil and either poly(dimethylsiloxane) or poly(methylphenylsiloxane). By carefully tuning the ratio of the two lubricants in the mixture, the corresponding F-ORGs demonstrated arbitrarily tunable critical syneresis temperatures from -15 to 40 °C, below which the lubricant is released on the surface and above which the lubricant is re-absorbed. The resulting surfaces showed not only exceptionally long-lasting/repeatable low ice adhesion strengths (≤10 kPa over 50 icing/de-icing cycles) but also significant improvements in their repellency toward a variety of organic liquids. Compared to non-fluorinated organogels, F-ORGs could offer improved protection against outdoor pollutants to further enhance their practicality.

Bioinspired Freeze-Tolerant Soft Materials: Design, Properties, and Applications

In nature, many biological organisms have developed the exceptional antifreezing ability to survive in extremely cold environments. Inspired by the freeze resistance of these organisms, researchers have devoted extensive efforts to develop advanced freeze-tolerant soft materials and explore their potential applications in diverse areas such as electronic skin, soft robotics, flexible energy, and biological science. Herein, a comprehensive overview on the recent advancement of freeze-tolerant soft materials and their emerging applications from the perspective of bioinspiration and advanced material engineering is provided. First, the mechanisms underlying the freeze tolerance of cold-enduring biological organisms are introduced. Then, engineering strategies for developing antifreezing soft materials are summarized. Thereafter, recent advances in freeze-tolerant soft materials for different technological applications such as smart sensors and actuators, energy harvesting and storage, and cryogenic medical applications are presented. Finally, future challenges and opportunities for the rapid development of bioinspired freeze-tolerant soft materials are discussed.