Icephobicity

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Icephobicity (from ice and Greek φόβος phobos "fear") is the ability of a solid surface to repel ice or prevent ice formation due to a certain topographical structure of the surface. [1] [2] [3] [4] [5] The word "icephobic" was used for the first time at least in 1950; [6] however, the progress in micropatterned surfaces resulted in growing interest towards icephobicity since the 2000s.

Contents

Icephobicity vs. hydrophobicity

The term "icephobicity" is similar to the term hydrophobicity and other "-phobicities" in physical chemistry (oleophobicity, lipophobicity, omniphobicity, amphiphobicity, etc.). The icephobicity is different from de-icing and anti-icing in that icephobic surfaces, unlike the anti-icing surfaces, do not require special treatment or chemical coatings to prevent ice formation. [7] [8] [9] [10] [11]

There is further parallelism between the hydrophobicity and icephobicity. The hydrophobicity is crucial for the "hydrophobic effect" and hydrophobic interactions. For two hydrophobic molecules (e.g., hydrocarbons) placed in water, there is an effective repulsive hydrophobic force, entropic in its origin, due to their interaction with the water medium. The hydrophobic effect is responsible for folding of proteins and other macro-molecules leading to their fractal shape. During ice crystal (snowflake) formation, the synchronization of branch growth occurs due to the interaction with the medium (oversaturated vapor) – is somewhat similar to the hydrophobic effect – the apparent repulsion of the hydrophobic particles due to their interaction with the medium (water). Consequently, despite the shapes of snowflakes being very diverse with "no two flakes similar to each other," most snow crystals are symmetric with each of the six branches almost identical to other five branches. Furthermore, both hydrophobicity and icephobicity can lead to quite complex phenomena, such as self-organized criticality-driven complexity as a result of hydrophobic interactions (during wetting of rough/heterogeneous surfaces or during polypeptide chain folding and looping) or ice crystallization (fractal snowflakes). [7]

Note that thermodynamically both the hydrophobic interactions and ice formation are driven by the minimization of the surface Gibbs energy, ΔG = ΔH − TΔS, where H, T, and S are the enthalpy, temperature, and entropy, respectively. This is because in the hydrophobic interactions large positive value of TΔS prevails over a small positive value of ΔH making spontaneous hydrophobic interaction energetically profitable. The so-called surface roughening transition governs the direction of ice crystal growth and occurs at the critical temperature, above which the entropic contribution into the Gibbs energy, TΔS, prevails over the enthalpic contribution, ΔH, thus making it more energetically profitable for the ice crystal to be rough rather than smooth. This suggests that thermodynamically both the icephobic and hydrophobic behaviors can be viewed as entropic effects. [7]

However, icephobicity is different from the hydrophobicity. Hydrophobicity is a property which is characterized by the water contact angle (CA) and interfacial energies of the solid-water, solid-vapor, and water-vapor interfaces and thus it is a thermodynamic property usually quantitatively defined as CA>90 degrees. Another difference is that the hydrophobicity is opposed to the hydrophilicity in a natural way. There is no such an opposition for the icephobicity, which should therefore be defined by setting a quantitative threshold. The icephobicity is much more similar to how the superhydrophobicity is defined. [7]

Quantitative characterization of icephobicity

In recent publications on the subject there are three approaches to the characterization of surface icephobicity. [7] First, the icephobicity implies low adhesion force between ice and the solid surface. In most cases, the critical shear stress is calculated, although the normal stress can be used as well. While no explicit quantitative definition for the icephobicty has been suggested so far, the researchers characterized icephobic surfaces as those having the shear strength (maximum stress) less in the region between 150 kPa and 500 kPa and even as low as 15.6 kPa,. [1] [7]

Second, the icephobicity implies the ability to prevent ice formation on the surface. Such ability is characterized by whether a droplet of supercooled water (below the normal freezing temperature of 0 C) freezes at the interface. The process of freezing can be characterized by time delay of heterogeneous ice nucleation. The mechanisms of droplet freezing are quite complex and can depend on the temperature level, on whether cooling down of the droplet is performed from the side of the solid substrate or from vapor and by other factors.

Third, the icephobic surfaces should repel incoming small droplets (e.g., of rain or fog) at the temperatures below the freezing point. [12]

These three definitions imply that icephobic surfaces should (i) prevent freezing of water condensing on the surface (ii) prevent freezing of incoming water (iii) if ice formed, it should have weak adhesion strength with the solid, so that it can be easily removed. Anti-icing properties may depend on such circumstances as whether the solid surface is colder than the air/vapor, how big is the temperature gradient, and whether a thin film of water tends to form on the solid surface due to capillary effects, disjoining pressure, etc. Mechanical properties of ice and the substrate also of great importance since ice shedding occurs as fracture, either in the Mode I (normal) or Mode II (shear) cracking, so that crack concentrators are major contributors to the reduced strength. [4] [7]

Related Research Articles

<span class="mw-page-title-main">Frost</span> Coating or deposit of ice

Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is similar to the formation of dew, except it occurs below the freezing point of water typically without crossing through a liquid state.

<span class="mw-page-title-main">Hydrophobe</span> Molecule or surface that has no attraction to water

In chemistry, hydrophobicity is the chemical property of a molecule that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.

In physics and chemistry, flash freezing is the process whereby objects are rapidly frozen. This is done by subjecting them to cryogenic temperatures, or it can be done through direct contact with liquid nitrogen at −196 °C (−320.8 °F). It is commonly used in the food industry.

<span class="mw-page-title-main">Cloud physics</span> Study of the physical processes in atmospheric clouds

Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of atmospheric clouds. These aerosols are found in the troposphere, stratosphere, and mesosphere, which collectively make up the greatest part of the homosphere. Clouds consist of microscopic droplets of liquid water, tiny crystals of ice, or both, along with microscopic particles of dust, smoke, or other matter, known as condensation nuclei. Cloud droplets initially form by the condensation of water vapor onto condensation nuclei when the supersaturation of air exceeds a critical value according to Köhler theory. Cloud condensation nuclei are necessary for cloud droplets formation because of the Kelvin effect, which describes the change in saturation vapor pressure due to a curved surface. At small radii, the amount of supersaturation needed for condensation to occur is so large, that it does not happen naturally. Raoult's law describes how the vapor pressure is dependent on the amount of solute in a solution. At high concentrations, when the cloud droplets are small, the supersaturation required is smaller than without the presence of a nucleus.

<span class="mw-page-title-main">Hydrophobic effect</span> Aggregation of non-polar molecules in aqueous solutions

The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in an aqueous solution and to be excluded by water. The word hydrophobic literally means "water-fearing", and it describes the segregation of water and nonpolar substances, which maximizes the entropy of water and minimizes the area of contact between water and nonpolar molecules. In terms of thermodynamics, the hydrophobic effect is the free energy change of water surrounding a solute. A positive free energy change of the surrounding solvent indicates hydrophobicity, whereas a negative free energy change implies hydrophilicity.

<span class="mw-page-title-main">Deicing</span> Process of removing ice, snow, or frost from a surface

Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prevent adhesion of ice to make mechanical removal easier.

<span class="mw-page-title-main">Rime ice</span> Granular whitish deposit of ice formed by freezing fog

Rime ice forms when supercooled water droplets freeze onto surfaces. In the atmosphere, there are three basic types of rime ice:

<span class="mw-page-title-main">Wetting</span> Ability of a liquid to maintain contact with a solid surface

Wetting is the ability of a liquid to displace gas to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. This happens in presence of a gaseous phase or another liquid phase not miscible with the first one. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. There are two types of wetting: non-reactive wetting and reactive wetting.

<span class="mw-page-title-main">Nucleation</span> Initial step in the phase transition or molecular self-assembly of a substance

In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that determines how long an observer has to wait before the new phase or self-organized structure appears. For example, if a volume of water is cooled significantly below 0 °C, it will tend to freeze into ice, but volumes of water cooled only a few degrees below 0 °C often stay completely free of ice for long periods (supercooling). At these conditions, nucleation of ice is either slow or does not occur at all. However, at lower temperatures nucleation is fast, and ice crystals appear after little or no delay.

<span class="mw-page-title-main">Cassie's law</span>

Cassie's law, or the Cassie equation, describes the effective contact angle θc for a liquid on a chemically heterogeneous surface, i.e. the surface of a composite material consisting of different chemistries, that is, non-uniform throughout. Contact angles are important as they quantify a surface's wettability, the nature of solid-fluid intermolecular interactions. Cassie's law is reserved for when a liquid completely covers both smooth and rough heterogeneous surfaces.

<span class="mw-page-title-main">Ultrahydrophobicity</span> Material property of extreme resistance to wetting

In chemistry and materials science, ultrahydrophobic surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet striking these kinds of surfaces can fully rebound like an elastic ball. Interactions of bouncing drops can be further reduced using special superhydrophobic surfaces that promote symmetry breaking, pancake bouncing or waterbowl bouncing.

<span class="mw-page-title-main">Ice protection system</span> System to limit ice on aircraft surfaces

In aeronautics, ice protection systems keep atmospheric moisture from accumulating on aircraft surfaces, such as wings, propellers, rotor blades, engine intakes, and environmental control intakes. Ice buildup can change the shape of airfoils and flight control surfaces, degrading control and handling characteristics as well as performance. An anti-icing, de-icing, or ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it becomes dangerous.

Adsorption is the adhesion of ions or molecules onto the surface of another phase. Adsorption may occur via physisorption and chemisorption. Ions and molecules can adsorb to many types of surfaces including polymer surfaces. A polymer is a large molecule composed of repeating subunits bound together by covalent bonds. In dilute solution, polymers form globule structures. When a polymer adsorbs to a surface that it interacts favorably with, the globule is essentially squashed, and the polymer has a pancake structure.

The strength of metal oxide adhesion effectively determines the wetting of the metal-oxide interface. The strength of this adhesion is important, for instance, in production of light bulbs and fiber-matrix composites that depend on the optimization of wetting to create metal-ceramic interfaces. The strength of adhesion also determines the extent of dispersion on catalytically active metal. Metal oxide adhesion is important for applications such as complementary metal oxide semiconductor devices. These devices make possible the high packing densities of modern integrated circuits.

<span class="mw-page-title-main">Superhydrophobic coating</span> Water-repellant coating

A superhydrophobic coating is a thin surface layer that repels water. It is made from superhydrophobic materials, and typically cause an almost imperceptibly thin layer of air to form on top of a surface. Droplets hitting this kind of coating can fully rebound. Generally speaking, superhydrophobic coatings are made from composite materials where one component provides the roughness and the other provides low surface energy.

The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface.

A slippery liquid-infused porous surface (SLIPS), liquid-impregnated surface (LIS), or multi-phase surface consists of two distinct layers. The first is a highly textured or porous substrate with features spaced sufficiently close to stably contain the second layer which is an impregnating liquid that fills in the spaces between the features. The liquid must have a surface energy well-matched to the substrate in order to form a stable film. Slippery surfaces are finding applications in commercial products, anti-fouling surfaces, anti-icing and biofilm-resistant medical devices.

Self-cleaning surfaces are a class of materials with the inherent ability to remove any debris or bacteria from their surfaces in a variety of ways. The self-cleaning functionality of these surfaces are commonly inspired by natural phenomena observed in lotus leaves, gecko feet, and water striders to name a few. The majority of self-cleaning surfaces can be placed into three categories:

  1. superhydrophobic
  2. superhydrophilic
  3. photocatalytic.
<span class="mw-page-title-main">Liquid marbles</span>

Liquid marbles are non-stick droplets wrapped by micro- or nano-metrically scaled hydrophobic, colloidal particles ; representing a platform for a diversity of chemical and biological applications. Liquid marbles are also found naturally; aphids convert honeydew droplets into marbles. A variety of non-organic and organic liquids may be converted into liquid marbles. Liquid marbles demonstrate elastic properties and do not coalesce when bounced or pressed lightly. Liquid marbles demonstrate a potential as micro-reactors, micro-containers for growing micro-organisms and cells, micro-fluidics devices, and have even been used in unconventional computing. Liquid marbles remain stable on solid and liquid surfaces. Statics and dynamics of rolling and bouncing of liquid marbles were reported. Liquid marbles coated with poly-disperse and mono-disperse particles have been reported. Liquid marbles are not hermetically coated by solid particles but connected to the gaseous phase. Kinetics of the evaporation of liquid marbles has been investigated.

<span class="mw-page-title-main">Droplet cluster</span> Self-assembled levitating monolayer of microdroplets

Droplet cluster is a self-assembled levitating monolayer of microdroplets usually arranged into a hexagonally ordered structure over a locally heated thin layer of water. The droplet cluster is typologically similar to colloidal crystals. The phenomenon was observed for the first time in 2004, and it has been extensively studied after that.

References

  1. 1 2 Meuler, A. J. et al. Relationships between Water Wettability and Ice Adhesion. ACS Appl. Mater. Interfaces 2010, 11, 3100–3110
  2. ↑ Zheng, L. et al. Exceptional Superhydrophobicity and Low Velocity Impact Icephobicity of Acetone-Functionalized Carbon Nanotube Films. Langmuir, 2011, 27, 9936–9943
  3. ↑ Jung, S.; Dorrestijn, M.; Raps, D.; Das, A.; Megaridis, C. M.; and Poulikakos, D. Are Superhydrophobic Surfaces Best for Icephobicity?. Langmuir, 2011, 27, 3059–3066
  4. 1 2 Nosonovsky, M.; Hejazi, V. I (2012). "Why superhydrophobic surfaces are not always icephobic". ACS Nano. 6 (10): 8488–8913. doi:10.1021/nn302138r. PMID   23009385.
  5. ↑ Menini, R.; Ghalmi, Z.; Farzaneh, M. Highly Resistant Icephobic Coatings on Aluminum Alloys. Cold Reg. Sci. Technol. 2011, 65, 65-69
  6. ↑ Chemical Industries, 1950, v. 67, p. 559
  7. 1 2 3 4 5 6 7 Hejazi, V.; Sobolev, K.; Nosonovsky, M. I (2013). "From superhydrophobicity to icephobicity: forces and interaction analysis". Scientific Reports. 3: 2194. doi:10.1038/srep02194. PMC   3709168 . PMID   23846773.
  8. ↑ Kulinich, S. A.; Farhadi, S.; Nose, K.; and Du, X. W. Superhydrophobic Surfaces: Are They Really Ice-Repellent?. Langmuir, 2011, 27, 25-29
  9. ↑ Bahadur, V.; Mishchenko, L.; Hatton, B., Taylor, J. A.; Aizenberg, J.; and Krupenkin, T. Predictive Model for Ice Formation on Superhydrophobic Surfaces. Langmuir, 2011, 27 , 14143–14150
  10. ↑ Cao, L. -L.; Jones, A. K.; Sikka, V. K.; Wu, J.; and Gao, D. Anti-Icing Superhydrophobic Coatings. Langmuir, 2009, 25, 12444-12448
  11. ↑ Chen, Dayong; Gelenter, Martin D.; Hong, Mei; Cohen, Robert E.; McKinley, Gareth H. (2017). "Icephobic Surfaces Induced by Interfacial Nonfrozen Water". ACS Applied Materials & Interfaces. 9 (4): 4202–4214. doi:10.1021/acsami.6b13773. PMC   6911363 . PMID   28054770.
  12. ↑ Zheng et al., Langmuir 27:9936 (2011)
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