Name: fabrication of superhydrophobic metal surfaces for anti-icing applications
Uploaded: 2018-08-15T13:30:00
Description: Watch this Scientific Journal Video about Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications at JoVE.com

This research was supported by the projects: MAT2014-60615-R and MAT2017-82182-R funded by the&#160;State&#160;Research&#160;Agency (SRA) and&#160;European&#160;Regional&#160;Development Fund (ERDF).

Note: The protocol follows the scheme shown in Figure 2.
1. Sample Preparation
<ol>
	<li>Cutting and cleaning 
	<ol>
		<li>Using a metal shear, cut 250 mm x 250 mm x 0.5 mm sheets of aluminum into 25 mm x 45 mm x 0.5 mm pieces. 
		Note: Special care must be taken when using the metal shear, and special training may be necessary.</li>
		<li>Remove the protective film covering one side of the sample and wash this side using around 50 mL of cl...

<ol>
	<li>Fang, G., Amirfazli, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+anti-icing+behavior+of+superhydrophobic+surfaces.">Understanding the anti-icing behavior of superhydrophobic surfaces.</a> Surface Innovations. 2 (2), 94-102 (2014).</li><li>Wang, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Robust+superhydrophobic+coating+and+the+anti-icing+properties+of+its+lubricants-infused-composite+surface+under+condensing+condition.">Robust superhydrophobic coating and the anti-icing properties of its lubricants-infused-composite surface under condensing condition.</a> New Journal of Chemistry. 41 (4), 1846-1853 (2017).</li><li>Jung, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Are+superhydrophobic+surfaces+best+for+icephobicity?.">Are superhydrophobic surfaces best for icephobicity?.</a> Langmuir. 27 (6), 3059-3066 (2011).</li><li>Milionis, A., Loth, E., Bayer, I. 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S., Kumar, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superhydrophobic+coatings+for+aluminium+surfaces+synthesized+by+chemical+etching+process.">Superhydrophobic coatings for aluminium surfaces synthesized by chemical etching process.</a> International Journal of Smart and Nano Materials. 7 (4), 248-264 (2016).</li><li>Ruiz-Cabello, F. J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Testing+the+performance+of+superhydrophobic+aluminum+surfaces.">Testing the performance of superhydrophobic aluminum surfaces.</a> Journal of Colloid and Interface Science. 508, 129-136 (2017).</li><li>Mahadik, S. 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K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrophobicity+of+rare-earth+oxide+ceramics.">Hydrophobicity of rare-earth oxide ceramics.</a> Nature Materials. 12, 315 (2013).</li><li>Ruan, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+anti-icing+behavior+of+superhydrophobic+surfaces+on+aluminum+alloy+substrates.">Preparation and anti-icing behavior of superhydrophobic surfaces on aluminum alloy substrates.</a> Langmuir. 29 (27), 8482-8491 (2013).</li><li>Yin, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+investigation+of+ice+formation+on+surfaces+with+representative+wettability.">In situ investigation of ice formation on surfaces with representative wettability.</a> Applied Surface Science. 256 (22), 6764-6769 (2010).</li><li>Boinovich, L., Emelyanenko, A. M., Korolev, V. V., Pashinin, A. 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B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combination+of+functional+nanoengineering+and+nanosecond+laser+texturing+for+design+of+superhydrophobic+aluminum+alloy+with+exceptional+mechanical+and+chemical+properties.">Combination of functional nanoengineering and nanosecond laser texturing for design of superhydrophobic aluminum alloy with exceptional mechanical and chemical properties.</a> ACS Nano. 11 (10), 10113-10123 (2017).</li><li>Wan, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superhydrophobic+ceria+on+aluminum+and+its+corrosion+resistance.">Superhydrophobic ceria on aluminum and its corrosion resistance.</a> Surface and Interface Analysis. 48 (3), 173-178 (2016).</li><li>G&#243;mez-Lopera, J. F., Mart&#237;nez-Aroza, J., Rodr&#237;guez-Valverde, M. A., Cabrerizo-V&#237;lchez, M. A., Montes-Ru&#237;z-Cabello, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Entropic+image+segmentation+of+sessile+drops+over+patterned+acetate.">Entropic image segmentation of sessile drops over patterned acetate.</a> Mathematics and Computers in Simulation. 118, 239-247 (2015).</li><li>Gao, L., McCarthy, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Teflon+is+hydrophilic.+comments+on+definitions+of+hydrophobic,+shear+versus+tensile+hydrophobicity,+and+wettability+characterization.">Teflon is hydrophilic. comments on definitions of hydrophobic, shear versus tensile hydrophobicity, and wettability characterization.</a> Langmuir. 24 (17), 9183-9188 (2008).</li><li>Ruiz-Cabello, F. J. M., Rodriguez-Valverde, M. 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In this paper, we demonstrate strategies to produce water-repellent surfaces on aluminum substrates. In addition, we show methods to characterize their wetting properties, roughness, durability and anti-icing performance.
To prepare the SH surfaces, we used two strategies. The first strategy incorporated the proper roughness degree to achieve the intrinsic hierarchical structure of SH surfaces by acid etching. This process is particularly critical, which may require further work for other meta...

The ability of superhydrophobic (SH) surfaces to repel water is the reason that they are traditionally proposed as a solution to prevent icing1,2. However, there are concerns about the suitability of SH surfaces for anti-icing agents: 1) the high costs of production, 2) that superhydrophobicity does not always lead to ice-phobicity3, and 3) the questionable durability of the SH surfaces4. Superhydrophobic surfaces hold two properties related to their topography and chemical composition5: they are rough, with particular topographic features; and their surface energy is low (intrinsically hydrophobic).
The roughness on a hydrophobic surface serves to reduce the ratio between the real solid-liquid area and the apparent contact area. The water is not fully in contact with the solid due to the lotus effect6,7, when the drop rests or moves onto the surface asperities. In this scenario, the solid-liquid interface acts heterogeneously with two chemical domains: the solid surface itself and the tiny air-bubbles trapped between the solid and water8. The degree of water repellency is connected to the amount of trapped air because the air patches are smooth and its intrinsic contact angle is 180&#176;. Some studies report the incorporation of a hierarchical surface texture with micro and nano-asperities as the optimal strategy to provide better water-repellent properties (greater presence of air at the solid-liquid interface)9. For some metals, a low-cost strategy to create two-level roughness features is acid-etching10,11. This procedure is frequently used in industry. With certain acid concentrations and etching times, the metal surface reveals the proper hierarchical roughness. In general, the surface roughening is optimized by varying the acid concentration, etching time, or both12. The surface energy of metals is high and for this reason, the fabrication of water-repellent metal surfaces requires later hydrophobization.
Hydrophobization is generally achieved by hydrophobic film deposition using different methods: silanization10,13, dip-coating14, spin-coating15, spraying16 or plasma-deposition17. Silanization has been proposed18 as one of the most promising tool for improving the low durability of SH surfaces. Unlike other deposition techniques, the silanization process is based on a covalent bond between the Si-OH groups with the surface hydroxyl groups of the metal substrate10. A drawback of the silanization process is the need for previous activation of the metal substrate to create enough hydroxyl groups for a high degree of coverage and uniformity. Another strategy recently proposed to produce resistant superhydrophobic surfaces is the use of rare-earth coatings19,20. Ceria coatings have two properties that justify this use: they can be intrinsically hydrophobic21, and they are mechanically and chemically robust. In particular, one of the most important reasons why they are chosen as protective coatings is their corrosion-protection abilities20.
To produce long-lasting SH metal surfaces, two issues are considered: the surface texture must not be damaged, and the hydrophobic film/coating must be firmly anchored to the substrate. Surfaces are typically exposed to wear originated by lateral abrasion or particle impact4. If the asperities are damaged, the water-repellency may be substantially reduced. Under extreme environments, the hydrophobic coating may be partially removed from the surface or may be chemically degraded by UV exposure, humidity or corrosion. The design of durable SH surfaces coatings is an important challenge for coating and surface engineering.
For metals, one of the most demanding requirements is that the anti-icing ability is based on three interconnected aspects22 as illustrated in Figure 1: subcooled water repellency, freezing delay, and low ice-adhesion. Outdoor icing occurs when subcooled water, typically rain drops, comes into contact with a solid surface and is rapidly frozen by heterogeneous nucleation23. The formed ice (rime) is firmly attached to the surface. Thus, the first step to avoid icing is to reduce the solid-water contact time. If the surface is superhydrophobic, rain drops may be expelled from the surface before freezing. In addition, it has been proven that, under humid conditions, surfaces with a high contact angle delay freezing more efficiently than those ones with a low contact angle24. For these two reasons, SH surfaces are the most appropriate surfaces to mitigate icing. However, the lifetime of superhydrophobic surfaces may be a key point since icing conditions are typically aggressive25. Some studies have concluded that SH surfaces are not the best choice for decreasing ice adhesion26. Once the ice forms on the surface, it stays firmly attached due to surface asperities. The roughness increases the ice-surface contact area and the asperities act as interlocking agents26. The use of durable SH surfaces is recommended to avoid icing if there are no traces of ice already present on the surface.
In this work, we present several protocols to produce durable SH surfaces on metal substrates. We use aluminum (Al) as the substrate because it is widely used in industry, and the incorporation of anti-icing properties is particularly relevant for certain applications (ski resorts facilities, aeronautics, etc.). We prepare three types of surfaces: a textured Al surface coated with a fluoropolymer coating, a textured Al surface silanized with a fluorosilane, and a ceria-stearic acid bilayer on an Al substrate. Similar techniques17,27,28,29 provide 100-300 nm film thicknesses or even monolayer films. For each surface, we measured their wetting properties and conducted wear tests. Finally, we analyzed their anti-icing performance by using three tests aimed to probe independently the three properties shown in Figure 1.
Our protocol is based on the scheme shown in Figure 2. Once the SH Al surfaces are prepared, their wetting properties and topography are analyzed to determine their repellency properties and roughness features. The wetting properties are analyzed by bouncing drop experiments, which is a technique connected to the water tensile adhesion. Since the observation of drop bounces is required, this technique is only suitable for superhydrophobic surfaces13. For each surface treatment, we prepared at least four samples to conduct the anti-icing tests and another four samples to perform the durability tests. The damage caused after each durability test was analyzed by measuring the loss of wetting properties and roughness features. Similar durability tests to the proposed ones in this work were recently used for other metal surfaces27,30.
Concerning the anti-icing tests, the aim of this study is to determine whether the use of the produced SH Al surfaces are convenient as anti-icing agents. Hence, we analyzed, for comparison, the performance of two control samples: a) an untreated Al sample (smooth hydrophilic sample) and b) a hydrophobized but not textured sample (smooth hydrophobic sample). For the same purpose, the use of a textured but not hydrophobized surface might be of interest. Unfortunately, this surface is extremely wettable and anti-icing tests cannot be carried out for them.

<table>
	<tbody>
		<tr>
			<td>Hydrochloric acid, 37%</td>
			<td>SICAL, S.A.</td>
			<td>AC07411000</td>
			<td>used for acid etching</td>
		</tr>
		<tr>
			<td>1H,1H,2H,2H-Perfluorodecyltriethoxysilane, 97%</td>
			<td>Sigma-Aldrich</td>
			<td>658758</td>
			<td>used for silanization with FAS-17</td>
		</tr>
		<tr>
			<td>Dupont AF1600</td>
			<td>Dupont</td>
			<td>D10389631</td>
			<td>used for fluropolymer deposition</td>
		</tr>
		<tr>
			<td>FC-72</td>
			<td>3M, Fluorinet</td>
			<td>1100-2-93</td>
			<td>used for fluropolymer deposition (flurocarbon solvent)</td>
		</tr>
		<tr>
			<td>Cerium(III) chloride heptahydrate, 99.9%</td>
			<td>Sigma-Aldrich</td>
			<td>228931</td>
			<td>used for Ceria coating deposition</td>
		</tr>
		<tr>
			<td>Hydrogen peroxide solution, 30%</td>
			<td>Sigma-Aldrich</td>
			<td>H1009</td>
			<td>used for Ceria coating deposition</td>
		</tr>
		<tr>
			<td>Stearic acid, &#8805;98.5%</td>
			<td>Sigma-Aldrich</td>
			<td>S4751</td>
			<td>used for Ceria coating deposition</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>SICAL, S.A.</td>
			<td>16271</td>
			<td>used throughout</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>SICAL, S.A.</td>
			<td>1090</td>
			<td>used throughout</td>
		</tr>
		<tr>
			<td>Aluminum sheets 0.5mm</td>
			<td>MODULOR (Germany)</td>
			<td>125993</td>
			<td>substrates used throught</td>
		</tr>
		<tr>
			<td>Micro-90 concentrated cleaning solution</td>
			<td>Sigma-Aldrich</td>
			<td>Z281506</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra pure Milli-Q water</td>
			<td>Millipore</td>
			<td>discontinued</td>
			<td>used throughout</td>
		</tr>
		<tr>
			<td>Plasma Etcher/Asher/Cleaner EMITECH K1050X</td>
			<td>Aname</td>
			<td>K1500XDEV-001</td>
			<td>used throughout</td>
		</tr>
		<tr>
			<td>PCC software</td>
			<td>AMETEK</td>
			<td>discontinued</td>
			<td>sofware controlling the high speed camera Phantom MIRO 4</td>
		</tr>
		<tr>
			<td>High Speed Camera Phantom Miro 4</td>
			<td>AMETEK</td>
			<td>discontinued</td>
			<td>used for bouncing drop experiments</td>
		</tr>
		<tr>
			<td>Open Loop PL&#181; 2.32</td>
			<td>UPC-CD6 &#38; Sensofar Tech S.L.</td>
			<td>version 2.32</td>
			<td>Sofware controlling PL&#181; Confocal Imaging Profiler</td>
		</tr>
		<tr>
			<td>Pl&#181;-Confocal Imaging Profiler 2300</td>
			<td>Sensofar Tech S.L.</td>
			<td>discontinued</td>
			<td>used for roughness measurements</td>
		</tr>
		<tr>
			<td>TABER 5750 LINEAL ABRASER</td>
			<td>TABER</td>
			<td>5750</td>
			<td>used for lateral abrasion tests</td>
		</tr>
		<tr>
			<td>Abbrasive sand: ASTM 20-30 SAND C778</td>
			<td>U.S. SILICA COMPANY (USA)</td>
			<td>1-800-635-7263</td>
			<td>used for abrasive partcile impact tests</td>
		</tr>
		<tr>
			<td>Ozone cleaner: PSDP-UV4T, Digital UV Ozone System</td>
			<td>Novascam</td>
			<td>discontinued</td>
			<td>UV-ozone degradation test</td>
		</tr>
		<tr>
			<td>Peristalitic Pump GILSON 312, France</td>
			<td>GILSON (France)</td>
			<td>discontinued</td>
			<td>used for water dripping test</td>
		</tr>
		<tr>
			<td>Nylon thread</td>
			<td>Dracon fishing line, Izorline internacional, inc. (USA)</td>
			<td>discontinued</td>
			<td>used for ice adhesion tests</td>
		</tr>
		<tr>
			<td>Digital force gauge (ZTA-200N, ZTA Series</td>
			<td>IMADA (USA)</td>
			<td>370199</td>
			<td>used for ice adhesion tests</td>
		</tr>
		<tr>
			<td>Motorized test stand I, MH2-500N-FA</td>
			<td>IMADA (USA)</td>
			<td>366942</td>
			<td>used for ice adhesion tests</td>
		</tr>
		<tr>
			<td>Force Recorder Professional</td>
			<td>IMADA (USA)</td>
			<td>version 1.0.2</td>
			<td>software provided by IMADA to register the force</td>
		</tr>
		<tr>
			<td>HYGROCLIP XD - STANDARD PROBE</td>
			<td>Rotronic</td>
			<td>discontinued</td>
			<td>Temperature and humidity probe</td>
		</tr>
		<tr>
			<td>HW3 Lite software</td>
			<td>Rotronic</td>
			<td>version 2.1.2</td>
			<td>Sofware controlling the HYGROCLIP Probe</td>
		</tr>
	</tbody>
</table>

fabrication of superhydrophobic metal surfaces for anti-icing applications

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film.
The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.

The wetting and roughness properties of the SH surfaces that were used in this study are shown in Figure 5. The average number of bounces measured for each sample is displayed in Figure 5a and the average roughness is shown in Figure 5b. There is no correlation between the roughness and wetting properties. The number of bounces measured for the polytetrafluoroethylene coated sample agrees with the Ce...

Watch this Scientific Journal Video about Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications at JoVE.com

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

We illustrate several methodologies to produce superhydrophobic metal surfaces and to explore their durability and anti-icing properties.

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in ...

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