Superhydrophobic versus SLIPS: Temperature dependence and the stability of ice adhesion strength

Investigating Shear Stress of Ice Accumulated on Surfaces with Various Roughnesses: Effects of a Quasi-Water Layer

The investigation of the anti-icing/deicing is essential because the icing phenomenon deteriorates the natural environment and various projects. By conducting molecular dynamics simulation, this work analyzes the effect of the quasi-water layer on the ice shear stress over smooth and rough surfaces, along with the underlying physics of the quasi-water layer. The results indicate that the thickness of the quasi-water layer monotonically increases with temperature, resulting in a monotonic decrease in the ice shear stress on the smooth surface. Due to the joint effects of the smooth surface wettability and the quasi-water layer, the ice shear stress increases and then decreases to almost a constant value when the surface changes from a hydrophobic to a hydrophilic one. For rough surfaces with stripe nanostructures, when the width of the bump for one case equals the depression for the other case, the variations of shear stress with height for these two cases are almost the same. The rough surface is effective in reducing the ice shear stress compared to the smooth surface due to the thickening of the quasi-water layer. Each molecule in the quasi-water layer and its four nearest neighboring molecules gradually form a tetrahedral ice-like structure along the direction away from the surface. The radial distribution function also shows that the quasi-water layer resembles the liquid water rather than the ice structure. These findings shed light on developing anti-icing and deicing techniques.

Ice-Enabled Transfer of Graphene on Copper Substrates Enhanced by Electric Field and Cu2O

Graphene films grown by the chemical vapor deposition (CVD) method suffer from contamination and damage during transfer. Herein, an innovative ice-enabled transfer method under an applied electric field and in the presence of Cu2O (or Cu2O-Electric-field Ice Transfer, abbreviated as CEIT) is developed. Ice serves as a pollution-free transfer medium while water molecules under the electric field fully wet the graphene surface for a bolstered adhesion force between the ice and graphene. Cu2O is used to reduce the adhesion force between graphene and copper. The combined methodology in CEIT ensures complete separation and clean transfer of graphene, resulting in successfully transferred graphene to various substrates, including polydimethylsiloxane (PDMS), Teflon, and C4F8 without pollution. The graphene obtained via CEIT is utilized to fabricate field-effect transistors with electrical performances comparable to that of intrinsic graphene characterized by small Dirac points and high carrier mobility. The carrier mobility of the transferred graphene reaches 9090 cm2 V-1 s-1, demonstrating a superior carrier mobility over that from other dry transfer methods. In a nutshell, the proposed clean and efficient transfer method holds great potential for future applications of graphene.

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.

Nanofluid Droplet Impact on Rigid and Elastic Superhydrophobic Surfaces

Ice accumulation on cold surfaces is a common and serious phenomenon that exists in numerous industrial fields, such as power transmission, wind turbines, and aircraft. Despite recent efforts in mitigating ice accumulation on the cold surface, it remains a challenge to achieve robust anti-icing on the cold surface in terms of nanofluid droplet. Here, we report a rigid superhydrophobic Cu surface and an elastic polydimethylsiloxane (PDMS) superhydrophobic surface to enhance water-repellency performance, characterized by a significant reduction in contact time and a decrease in the spreading ratio. As for the rigid superhydrophobic Cu surface, the underlying mechanism is ascribed to the existence of stable air cushions between the micropillar array, which reduce the contact area and further suppress the heat conduction. As for the elastic PDMS superhydrophobic surface, the rapid detachment of the nanofluid droplet relies on superior surface elasticity, which can further suppress the nanofluid droplet splashing at a high impacting velocity. We believe that this work can provide a new view for the improvement of water-repellency for a wide range of applications.

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

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

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.

Ice Adhesion Properties on Micropillared Superhydrophobic Surfaces

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

Effect of Water Adsorption on Lubricating Film Stability in Slippery Coatings

The absorption of water by slippery coatings is a ubiquitous phenomenon that arises due to small but finite water dissolution during the contact of aqueous media with lubricants. In this study, using the concept of surface forces, we have analyzed the influence of trace amounts of water in lubricants on the stability of slippery coatings for both coatings with hydrophilic porous bases, prone to form hydrogen bonds with water, and those with hydrophobic porous bases. To perform such analysis, we have considered for the first time the electrostatic problem of the distribution of the electric potential and electric field strength in stratified films that contain two thin dielectric layers imitating the lubricant and a hydrophobic layer sandwiched between the porous substrate and air or water. Based on the developed approach, the equations for the calculation of the excess free energy and the disjoining pressure, associated with water dissolution in the lubricant film, were derived. An analysis of the excess film energy and the contribution of the image interaction to the disjoining pressure isotherm indicates that the dissolved water can both stabilize and destabilize the oil film, depending on the ratio of the static and dynamic dielectric permittivities of the lubricant and the phases confining the film. The results of calculations and simple experiments carried out here indicate much better water contact stability of silicone films impregnating a hydrophobized porous substrate than films impregnating a hydrophilic porous substrate. The obtained results indicate the preference for using the hydrophobic bases for the fabrication of long-lived slippery coatings characterized by better preservation of slippery functional properties under conditions of lubricant depletion and prolonged contact with water.

Adhesion of impure ice on surfaces

The undesirable buildup of ice can compromise the operational safety of ships in the Arctic to high-flying airplanes, thereby having a detrimental impact on modern life in cold climates. The obstinately strong adhesion between ice and most functional surfaces makes ice removal an energetically expensive and dangerous affair. Hence, over the past few decades, substantial efforts have been directed toward the development of passive ice-shedding surfaces. Conventionally, such research on ice adhesion has almost always been based on ice solidified from pure water. However, in all practical situations, freezing water has dissolved contaminants; ice adhesion studies of which have remained elusive thus far. Here, we cast light on the fundamental role played by various impurities (salt, surfactant, and solvent) commonly found in natural water bodies on the adhesion of ice on common structural materials. We elucidate how varying freezing temperature & contaminant concentration can significantly alter the resultant ice adhesion strength making it either super-slippery or fiercely adherent. The entrapment of impurities in ice changes with the rate of freezing and ensuing adhesion strength increases as the cooling temperature decreases. We discuss the possible role played by the in situ generated solute enriched liquid layer and the nanometric water-like disordered ice layer sandwiched between ice and the substrate behind these observations. Our work provides useful insights into the elementary nature of impure water-to-ice transformation and contributes to the knowledge base of various natural phenomena and rational design of a broad spectrum of anti-icing technologies for transportation, infrastructure, and energy systems.

Multifunctional slippery photothermal coating

Slippery liquid-infused porous surface (SLIPS) has shown significant application values in various areas and has been commonly obtained by injecting the water-immiscible lubricant into a low-surface-energy modified micro/nano-structured surface. Constrained by the availability of desirable structured substrates or simple preparation schemes, the exploration of SLIPS with multifunctionality and universality that is facile to fabricate and robust in realistic applications remains challenging. Herein, we propose a one-step, fluoride-free and unconventional protocol based on a one-pot reaction of polysilazane (PSZ), silicone oils and multiwalled carbon nanotubes (MWCNT), which creates not only the favorable micro/nano-scale physical structures and surface chemistry for the excellent slippery property (sliding angle < 3°) and robust lubricant retention, but also the superior photothermal responsiveness for the potential multifunctional applications. It has been demonstrated that the proposed multifunctional slippery photothermal coating (MSPC) displayed outstanding potential in corrosion resistance, droplet manipulation and anti/de-icing. We envision that the proposed strategy could be realized in the real-life applications.

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.

The roles of undercooling degree and materials surface configuration in the growth mechanism of ice layer caused by micro-droplets

Effect mechanisms of the undercooling degree and the surface configuration on the ice growth characteristics were revealed under micro-droplets icing conditions. Preferential ice crystals appear firstly on the surfaces due to the randomness of icing, and obtain growth advantages to form protruding structures. Protruding structures block the incoming droplets from contacting the substrates, causing voids around the structures. The undercooling degree mainly affects the density and the growth rate of preferential ice crystals. With the increase of undercooling degree, the preferential ice crystals have higher density and growth rate, resulting in stronger growth advantage and higher porosity. The surface configuration affects the growth mode, and the ice layer grows with uniform mode, spreading mode and structure-induced mode on the aluminum, smooth Polytetrafluoroethylene (PTFE) and rough PTFE surface respectively, causing the needle-like, ridge-like and cluster-like ice crystals. The rough structures effectively improve the porosity of the ice layer, which is beneficial for optimizing the icephobic property of the materials. This paper provides important theoretical guidance for the design of subsequent icephobic materials.

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.

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.

Microporous metallic scaffolds supported liquid infused icephobic construction

HYPOTHESIS

Ice accretion on component surfaces often causes severe impacts or accidents. Liquid-infused surfaces (LIS) have drawn much attention as icephobic materials for ice mitigation in recent years due to their outstanding icephobicity. However, the durability of LIS constructions remains a big challenge, including mechanical vulnerability and rapid depletion of lubricants. The practical applications of LIS materials are significantly restrained, and the full potential of LIS for ice prevention has yet to be demonstrated.

EXPERIMENTS

A universal approach was proposed to introduce microporous metallic scaffolds in the LIS construction to increase the applicability and durability, and to prompt the potential of LIS for ice mitigation. Microporous Ni scaffolds were chosen to integrate with polydimethylsiloxane modified by silicone oil addition.

FINDINGS

The new LIS construction demonstrated significantly improved durability in icing/de-icing cyclic test, and it also offered a solution for the rapid oil depletion by restraining the deformation of the matrix material. Low ice adhesion strength could be maintained via a micro-crack initiation mechanism. The results indicated that the multi-phase LIS construction consisting of microporous Ni scaffolds effectively addressed the shackles of the icephobicity deterioration of LIS materials, confirming a new design strategy for the R&D of icephobic surfaces.

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.

Passive Anti-Icing Performances of the Same Superhydrophobic Surfaces under Static Freezing, Dynamic Supercooled-Droplet Impinging, and Icing Wind Tunnel Tests

Overcoming ice accretion on external aircraft wing surfaces plays a crucial role in aviation, and developing environmentally friendly passive anti-icing surfaces is considered to be a promising strategy. Superhydrophobic surfaces (SHSs) have attracted increasing attention due to their potential advantages of keeping the airframe dry without causing additional aerodynamic losses. However, the passive anti-icing performances of SHSs reported to date varied a lot under different icing test conditions. Therefore, a systematic investigation is necessary to elucidate the icing conditions where SHSs can remain effective and pave the way for SHSs toward practical anti-icing applications. Herein, we designed and fabricated a typical type of SHS featuring dual-scale hierarchical structures with arrayed micromountains (with both spacings and heights of tens of micrometers) covered by single-scale sandy-corrugation-like periodic structures (with both spacings and heights of only several micrometers) (termed SS1). Its anti-icing performances under three representative icing conditions, including static water freezing, dynamic supercooled-droplet impinging, and icing wind tunnel conditions, were comparatively investigated. The SS1 SHS maintained a lower static ice-adhesion strength (<60 kPa even after 50 deicing cycles at temperatures as low as -25 °C), which was attributed to a cumulative cracking effect facilitating the ice detachment. Within the laboratory dynamic icing tests, the SS1 SHSs with micromountain heights of 20-30 μm performed optimally in the antiadhesion of supercooled droplets (at an impinging velocity of 3.4 m/s and temperatures of -5 to -25 °C). In spite of the significant anti-icing performances of the SS1 SHSs in both static and dynamic laboratory tests, they could hardly sustain reliable passive anti-icing performances in harsher icing wind tunnel tests with supercooled droplets impinging their surfaces at velocities of up to 50 m/s at a temperature of -5 °C for 10 min. This study can inspire the development of improved SHSs for achieving satisfactory anti-icing performances in real-aviation conditions.

The role of nanoparticle charge in crystallization kinetics and ice adhesion strength for dispersions of detonation nanodiamonds

According to the classical nucleation theory, the presence of solid particles in a liquid should facilitate its heterogeneous nucleation upon supercooling. Here, we have analysed the behaviour of aqueous dispersions of detonation diamond nanoparticles (DND) with different signs of the surface charge in supercooled conditions and the frozen state. The behaviours of the diamond nanoparticles with a typical size of 4.5 nm were compared with each other and with deionized water in ice nucleation and ice shear experiments. The presented experimental data and analysis allowed the description of the significant increase in the freezing delay times for positively charged nanoparticles and the sharp decrease for negatively charged ones in comparison to deionized water, based on the peculiarities of the water structure around the nanoparticles and in the vicinity of a superhydrophobic surface. In addition, this approach has allowed the successful explanation of the difference in the practical work of adhesion for deionized water and dispersions of DND with different particle charges.

Atomistic Description of Interdroplet Ice-Bridge Formation during Condensation Frosting

The propagation of frost in an assembly of supercooled dew droplets takes place by the formation of ice protrusions that bridge ice particles and still-liquid droplets. In this work, we develop a Kinetic Monte Carlo (KMC) model to study the formation kinetics of the ice protrusions. The KMC simulations reproduce well the experimental results reported in the literature. The elongation speed of the ice protrusions does not depend on the droplet size but increases when the interdroplet distance decreases, the temperature increases, or the substrate wettability increases. While 2D diffusion of the water molecules on the substrate surface is sufficient to explain the process kinetics, high 3D (vapor) water-molecule concentration can lead to the development of 3D lateral branches on the ice protrusions. A 1D analytical model based on the water-molecule concentration gradient between a droplet and a nearby ice particle reproduces well the simulation results and highlights the relation between the protrusion elongation kinetics and parameters like the interdroplet distance, the water diffusivity, and the concentration gradient. The bridge-formation time has a quadratic dependence on the droplet-ice distance. Comparing the simulations, the analytical model, and the experimental results of the literature, we conclude that the propagation of frost on a flat substrate in an assembly of supercooled dew droplets with interdroplet spacing larger than about 1 μm is limited by water-molecule diffusivity.

Interfacial mechanical properties of tetrahydrofuran hydrate-solid surfaces: Implications for hydrate management

Understanding the interfacial mechanical properties between hydrate and solids is vital to designing and fabricating surfaces for hydrate management. Herein, the role of the surface wettability, the type of solid substrate and temperature on the interfacial adhesion properties of tetrahydrofuran (THF) hydrate and ice were examined by force analysis based shearing measurements and molecular dynamics (MD) simulations. The results showed that the adhesion strength of THF hydrate and ice on silica varies with the compositions of coating, and the adhesion strength of ice is larger than that of THF hydrate for all investigated solid substrates. Particularly, in contrast to a linear relationship between 1 + cosθr and hydrate adhesion on organic silanes/thiols/polymer surfaces, the hydrate adhesion on the coated inorganic glass surfaces is enhanced as a function of 1 + cosθr, in which θr is the receding contact angle. MD simulations uncovered that the adhesion strength of ice on solid substrates is dominated by the quasi-liquid water layer, however, that of hydrate is governed not only by the quasi-liquid layer but also newly formed unconventional clathrate cages. This study provides new insights and perspectives into the hydrate adhesion on solid surfaces, which is of help to develop hydrate-phobic coatings for advanced hydrate management.

Smart low interfacial toughness coatings for on-demand de-icing without melting

Ice accretion causes problems in vital industries and has been addressed over the past decades with either passive or active de-icing systems. This work presents a smart, hybrid (passive and active) de-icing system through the combination of a low interfacial toughness coating, printed circuit board heaters, and an ice-detecting microwave sensor. The coating's interfacial toughness with ice is found to be temperature dependent and can be modulated using the embedded heaters. Accordingly, de-icing is realized without melting the interface. The synergistic combination of the low interfacial toughness coating and periodic heaters results in a greater de-icing power density than a full-coverage heater system. The hybrid de-icing system also shows durability towards repeated icing/de-icing, mechanical abrasion, outdoor exposure, and chemical contamination. A non-contact planar microwave resonator sensor is additionally designed and implemented to precisely detect the presence or absence of water or ice on the surface while operating beneath the coating, further enhancing the system's energy efficiency. Scalability of the smart coating is demonstrated using large (up to 1 m) iced interfaces. Overall, the smart hybrid system designed here offers a paradigm shift in de-icing that can efficiently render a surface ice-free without the need for energetically expensive interface melting.

Microscale investigation on interfacial slippage and detachment of ice from soft materials

Surface icing is detrimental to applications ranging from transportation to biological systems. Soft elastomeric coatings can engender remarkably low ice adhesion strength, but mechanisms at the microscale and resulting ice extraction outcomes need to be understood. Here we investigate dynamic ice-elastomer interfacial events and show that the ice adhesion strength can actually vary by orders of magnitude due to the shear velocity. We study the detailed deformation fields of the elastomer using confocal traction force microscopy and elucidate the underlying mechanism. The elastomer initially undergoes elastic deformation having a shear velocity dependent threshold, followed by partial relaxation at the onset of slip, where velocity dependent "stick-slip" micropulsations are observed. The results of the work provide important information for the design of soft surfaces with respect to removal of ice, and utility to fields exemplified by adhesion, contact mechanics, and biofouling.

Effects of Freezing Temperature and Salinity on the Adhesion Shear Strength of Amphibious Aircraft Tires under Static Icing

This research investigates the effects of freezing temperature and salinity on the adhesion shear strength of amphibious aircraft tires under static icing. It found that the lower the freezing temperature, the greater the ice adhesion shear strength, and the higher the salinity of the water sample, the lower the ice adhesion shear strength. This is related to the thickness of the brine layer at the ice-tire substrate interface; the temperature decreased, the brine layer became thinner, and, accordingly, the adhesion shear strength increased. This paper analyzes the problem of brine precipitation during seawater freezing and its influencing mechanism on the ice adhesion shear strength. In addition, it also found that the lower the temperature, the greater the growth rate of the ice adhesion shear strength. When the salinity in different ranges changed, its influence on the adhesion shear strength was different. When the salinity of the water sample is close to 0%, a small change in the salinity will cause a large change in the ice adhesion shear strength. When the salinity is large, the change of salinity has a weaker influence on the ice adhesion shear strength. This research provides a strong reference for the design and study of amphibious aircraft tires.

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

HYPOTHESIS

Loss of anti-icing properties of slippery liquid-infused porous surfaces (SLIPS) in conditions of repetitive shear stresses is the intrinsic process related to peculiarities of SLIPS structure.

EXPERIMENTS

The study of the evolution of the ice adhesion strength to superhydrophobic surfaces (SHS) and SLIPS during repetitive icing/de-icing cycles measured by a centrifugal method was supplemented with the estimation of change in capillary pressure inside the pores, and SEM analysis of the effect of multiple ice detachments on surface morphology.

FINDINGS

Obtained data indicated that although for freshly prepared SLIPS, the ice shear adhesion strength at -25 °C was several times lower than for SHS, repetitive icing-deicing cycles resulted in dramatic SLIPS degradation. In contrast, SHS showed weak degradation at least during 50 cycles. Additional to the depletion of an impregnating oil layer, other mechanisms of SLIPS degradation were hypothesized and tested. It was shown that lower capillary pressure required to displace air by water from the surface texture for SLIPSs compared to SHSs resulted in deeper water/ice penetration inside the grooves. The accelerated destruction of the mechanical texture caused by the Rehbinder effect constitutes another mechanism of SLIPSs degradation.