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      From superhydrophobicity to icephobicity: forces and interaction analysis

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      Scientific Reports
      Nature Publishing Group

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          Abstract

          The term “icephobicity” has emerged in the literature recently. An extensive discussion took place on whether the icephobicity is related to the superhydrophobicity, and the consensus is that there is no direct correlation. Besides the parallel between the icephobicity and superhydrophobicity for water/ice repellency, there are similarities on other levels including the hydrophobic effect/hydrophobic interactions, mechanisms of protein folding and ice crystal formation. In this paper, we report how ice adhesion is different from water using force balance analysis, and why superhydrophobic surfaces are not necessary icephobic. We also present experimental data on anti-icing of various surfaces and suggest a definition of icephobicity, which is broad enough to cover a variety of situations relevant to de-icing including low adhesion strength and delayed ice crystallization and bouncing.

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          Most cited references9

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          Liquid-infused nanostructured surfaces with extreme anti-ice and anti-frost performance.

          Ice-repellent coatings can have significant impact on global energy savings and improving safety in many infrastructures, transportation, and cooling systems. Recent efforts for developing ice-phobic surfaces have been mostly devoted to utilizing lotus-leaf-inspired superhydrophobic surfaces, yet these surfaces fail in high-humidity conditions due to water condensation and frost formation and even lead to increased ice adhesion due to a large surface area. We report a radically different type of ice-repellent material based on slippery, liquid-infused porous surfaces (SLIPS), where a stable, ultrasmooth, low-hysteresis lubricant overlayer is maintained by infusing a water-immiscible liquid into a nanostructured surface chemically functionalized to have a high affinity to the infiltrated liquid and lock it in place. We develop a direct fabrication method of SLIPS on industrially relevant metals, particularly aluminum, one of the most widely used lightweight structural materials. We demonstrate that SLIPS-coated Al surfaces not only suppress ice/frost accretion by effectively removing condensed moisture but also exhibit at least an order of magnitude lower ice adhesion than state-of-the-art materials. On the basis of a theoretical analysis followed by extensive icing/deicing experiments, we discuss special advantages of SLIPS as ice-repellent surfaces: highly reduced sliding droplet sizes resulting from the extremely low contact angle hysteresis. We show that our surfaces remain essentially frost-free in which any conventional materials accumulate ice. These results indicate that SLIPS is a promising candidate for developing robust anti-icing materials for broad applications, such as refrigeration, aviation, roofs, wires, outdoor signs, railings, and wind turbines.
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            Relationships between water wettability and ice adhesion.

            Ice formation and accretion may hinder the operation of many systems critical to national infrastructure, including airplanes, power lines, windmills, ships, and telecommunications equipment. Yet despite the pervasiveness of the icing problem, the fundamentals of ice adhesion have received relatively little attention in the scientific literature and it is not widely understood which attributes must be tuned to systematically design "icephobic" surfaces that are resistant to icing. Here we probe the relationships between advancing/receding water contact angles and the strength of ice adhesion to bare steel and twenty-one different test coatings (∼200-300 nm thick) applied to the nominally smooth steel discs. Contact angles are measured using a commercially available goniometer, whereas the average strengths of ice adhesion are evaluated with a custom-built laboratory-scale adhesion apparatus. The coatings investigated comprise commercially available polymers and fluorinated polyhedral oligomeric silsesquioxane (fluorodecyl POSS), a low-surface-energy additive known to enhance liquid repellency. Ice adhesion strength correlates strongly with the practical work of adhesion required to remove a liquid water drop from each test surface (i.e., with the quantity [1 + cos θ(rec)]), and the average strength of ice adhesion was reduced by as much as a factor of 4.2 when bare steel discs were coated with fluorodecyl POSS-containing materials. We argue that any further appreciable reduction in ice adhesion strength will require textured surfaces, as no known materials exhibit receding water contact angles on smooth/flat surfaces that are significantly above those reported here (i.e., the values of [1 + cos θ(rec)] reported here have essentially reached a minimum for known materials).
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              Superhydrophobic surfaces: are they really ice-repellent?

              This work investigates the anti-ice performance of various superhydrophobic surfaces under different conditions. The adhesion strength of glaze ice (similar to that deposited during "freezing rain") is used as a measure of ice-releasing properties. The results show that the ice-repellent properties of the materials deteriorate during icing/deicing cycles, as surface asperities appear to be gradually damaged. It is also shown that the anti-icing efficiency of superhydrophobic surfaces is significantly lower in a humid atmosphere, as water condensation both on top of and between surface asperities takes place, leading to significantly larger values of ice adhesion strength. This work thus shows that superhydrophobic surfaces are not always ice-repellent and their use as anti-ice materials may therefore be limited.
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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                12 July 2013
                2013
                : 3
                : 2194
                Affiliations
                [1 ]College of Engineering & Applied Science, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53211, United States
                Author notes
                Article
                srep02194
                10.1038/srep02194
                3709168
                23846773
                96152033-80f4-4356-97b0-f385364005fe
                Copyright © 2013, Macmillan Publishers Limited. All rights reserved

                This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/

                History
                : 25 January 2013
                : 26 June 2013
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