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 ...

This method can help answer key questions in the coating fields about the convenience and suitability of using superhydrophobic surfaces as anti-icing agents in real applications. The main advantage of these techniques is that analysis with a surface both prevents icing and is durable enough to resist the wetting conditions when icing occurs. To begin the sample preparation, in a fume hood, place a 100 milliliter beaker containing 80 milliliters of four molar hydrochloric acid in a 500 milliliter beaker.Fill another 500 milliliter beaker with ultrapure water. Immerse an aluminum sample in the acid, using polytetrafluoroethylene tweezers and allow it to soak for eight minutes. Then, quench the etched sample in ultrapure water.Thoroughly rinse the sample before proceeding. Next, dry the sample under a steam of filtered compressed air until no water is visible on the surface. Lastly, dry the sample in an oven at 120 degrees Celsius for 10 minutes.To hydrophobize the sample by vapor-phase silanization, first plasma-treat the sample with air plasma at 100 watts for 10 minutes. Then, immediately place the sample in a plastic Petri dish and incline the sample slightly with a 20 to 200 microliter pipette tip. Apply two 50 microliter drops of the silane about one centimeter from the sample.Cover most of the dish with the lid. Promptly place the dish in a vacuum dessicator. Cover about 80%of the dish with the lid and evacuate it to begin silanization.Silanize the sample overnight or for at least eight hours. To hydrophobize a sample by fluoropolymer deposition, first spray the sample from 10 centimeters away with a one to 20 by volume solution of an amorphous fluoropolymer in a fluorocarbon solvent. Allow the coating to dry in air at room temperature for 10 minutes.Apply a second coat and dry the sample at 110 degrees Celsius for 10 minutes to evaporate the solvent and crosslink the fluoropolymer coating. Then, check that the surface is superhydrophobic. To hydrophobize an etched sample by ceria-stearic acid deposition, first clean and dry the sample.Then, immerse the sample in 50 milliliters of an aqueous solution containing two grams of cerium trichloride heptahydrate and three milliliters of 30%by weight hydrogen peroxide. Keep the immersed sample in an oven at 40 degrees Celsius for one hour. Then, rinse the sample in distilled water, dry it at 100 degrees Celsius for 10 minutes and allow it to cool to room temperature.Then, soak the sample in a 30 millimolar solution of stearic acid in ethanol for 15 minutes. Afterwards, rinse the sample in ethanol, dry it at 100 degrees Celsius for 10 minutes and let it cool. Place a sample on the bouncing drop experiment platform under a fixed insulin needle.Set the high-speed camera acquisition rate to 4200 images per second and the exposure time to 235 microseconds. Then, fill a one milliliter syringe with ultrapure water and connect it to the needle. Confirm that the needle and sample are in focus and then begin recording.Stop recording a few seconds after a drop falls on the sample. Trim the video to start from the moment of the drop being released from the needle and end at the static drop being in full contact with the sample with no further bouncing observed. Create the drop profiles with image analysis software and quantify the number of bounces by watching the video sequence.To perform a lateral abrasion test, first set a linear abrader with a mild to moderate tip to 20 cycles per minute with a stroke length of 38.1 millimeters. Configure the abrader for the minimum applied pressure. Mount the sample on the abrader and perform an abrasion cycle.Then, gently clean and dry the sample. Evaluate the wetting properties with a tilting plate experiment. Repeat the abrasion and evaluate the sample again after two, three and five total cycles.To perform an abrasive particle impact test, first fix a sample on a surface with a 45 degree incline. Mount a glass funnel 24 to 26 centimeters above the sample. Pour 30 milliliters of ASTM 2030 abrasive test sand into the funnel and wait for the sand to flow over the sample.Evaluate the wetting properties with a tilting plate experiment. Perform this test up to three times per sample. To perform a UV-ozone degradation test, treat the sample in a UV-ozone cleaner for 10 minutes at room temperature.Afterwards, rinse the sample in ultrapure water, dry it with compressed air and evaluate the wetting properties. Repeat this test up to three times. To begin the freezing delay test, place a large sample on an isolated platform In the center of a freezing chamber.Ensure that the chamber humidifier is filled with water. Then, use a pipette to gently deposit an array of 25 drops of water on the sample, if it is superhydrophobic. For other samples, deposit an array of 70 drops.Close the chamber and start the cooling system. Once the chamber reaches about five degrees Celsius, start the humidifier. The drops will begin to nucleate below zero degrees Celsius.Once nucleation begins, record the number of frozen drops at intervals of 0.5 degrees Celsius until all drops have frozen. Repeat the test until about 200 drops have been tested on the sample. To begin the tensile ice-adhesion test, Tie 0.25 millimeter nylon thread to a digital force gauge mounted on a motorized test stand above the freezing chamber.Then, cut a 28 millimeter long piece of PTFE pipe with a 10 millimeter inner diameter. Drill two one millimeter-wide holes across from each other, five millimeters from one end of the cylinder. Put a narrow bar through these holes.Then, set the cylinder upright on a sample and fill it with 1.2 milliliters of distilled water. Carefully place the sample and cylinder on a platform in the freezing chamber, keeping the cylinder pressed against the sample. Close the freezing chamber, turn on the cooling system and wait one hour for the water to freeze.Then, firmly fix the sample to the platform using a striker plate with a hole slightly wider than the cylinder. Connect the sample to the force gauge by feeding the nylon thread through the bar at the top of the cylinder. Close the chamber and wait for 10 minutes.Then, when recording the force, vertically displace the gauge from the sample at 10 millimeters per minute until the ice separates from the sample. For the shear adhesion test, freeze 1.2 milliliters of water against a sample in a PTFE cylinder in the same way. Clamp the sample vertically in the freezing chamber and fit a metal ring attached to the force gauge via nylon thread over the cylinder.Close the chamber and wait 10 minutes. Then, vertically displace the gauge at 10 millimeters per minute until the ice shears. No correlation was observed between roughness and wetting properties of the superhydrophobic surfaces.For example, while the PTFE sample had a similar roughness value to the fluoro alkoxysilane sample, its average number of bounces was closer to that of the ceria-stearic acid sample. All three sample types exhibited poor mechanical resistance, losing their water-repelling properties after two cycles. The fluoro alkoxysilane and the ceria-stearic acid samples were degraded by UV-Ozone exposure, but the PTFE sample was not.At high humidity, the superhydrophobic surfaces delayed freezing longer than the smooth hydrophobic surfaces did. However, at low relative humidity, the superhydrophobic surfaces delayed freezing less efficiently than smooth hydrophobic surfaces did. Consistent with previous findings, the superhydrophobic surfaces showed greater shear and tensile ice-adhesion than coated and uncoated smooth surfaces.This was attributed to the roughness of the superhydrophobic surfaces. A hierarchical texture is required to produce a metal superhydrophobic surface. Acid etching is a very successful strategy, but the conditions depend on the metal.Advance screening is required to insure an optimal degree of roughness. The etching reactions on the hydrophobization molecules might be the most critical steps for successfully producing superhydrophobic surface on aluminum. Following this procedure, other materials like lubricant-impregnated slippery surfaces can be fabricated to answer additional questions about which surfaces avoid icing more efficiently.By combining the analysis of two important aspects of anti-icing agents'suitability, this technique paves the way for researchers in the coatings field to explore certain surfaces and coatings as anti-icing agents that are resistant to air in environmental conditions. Don't forget that working on acid is extremely dangerous. should be taken like training and wear different devices for protection, like goggles, gloves and so.

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Research

JoVE Journal

Engineering

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Fabrication of VB2/Air Cells for Electrochemical Testing

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for synthesizing nanoscopic VB2 is presented as well as step-by-step procedure for applying a zirconium oxide coating to the VB2 particles for stabilization upon discharge. The process for disassembling existing zinc/air cells is shown, in addition construction of the new working electrode to replace the conventional zinc/air cell anode with a the nanoscopic VB2 anode. Finally, discharge of the completed VB2/air battery is reported. We show that using the zinc/air cell as a test bed is useful to provide a consistent configuration to study the performance of the high-energy high capacity nanoscopic VB2 anode.

Fabrication of VB2/Air Cells for Electrochemical Testing

A protocol is presented to study multi-electron metal/air battery systems by using previous technology developed for the zinc/air cell. Electrochemical testing is then performed on fabricated batteries to evaluate performance.

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Preparation of Large-area Vertical 2D Crystal Hetero-structures Through the Sulfurization of Transition Metal Films for Device Fabrication

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition metal dichalcogenides (TMDs) MoS2 and WS2 can be prepared on sapphire substrates. By controlling the metal film thicknesses, good layer number controllability, down to a single layer of TMDs, can be obtained using this growth technique. Based on the results obtained from the Mo film sulfurized under the sulfur deficient condition, there are two mechanisms of (a) planar MoS2 growth and (b) Mo oxide segregation observed during the sulfurization procedure. When the background sulfur is sufficient, planar TMD growth is the dominant growth mechanism, which will result in a uniform MoS2 film after the sulfurization procedure. If the background sulfur is deficient, Mo oxide segregation will be the dominant growth mechanism at the initial stage of the sulfurization procedure. In this case, the sample with Mo oxide clusters covered with few-layer MoS2 will be obtained. After sequential Mo deposition/sulfurization and W deposition/sulfurization procedures, vertical WS2/MoS2 hetero-structures are established using this growth technique. Raman peaks corresponding to WS2 and MoS2, respectively, and the identical layer number of the hetero-structure with the summation of individual 2D materials have confirmed the successful establishment of the vertical 2D crystal hetero-structure. After transferring the WS2/MoS2 film onto a SiO2/Si substrate with pre-patterned source/drain electrodes, a bottom-gate transistor is fabricated. Compared with the transistor with only MoS2 channels, the higher drain currents of the device with the WS2/MoS2 hetero-structure have exhibited that with the introduction of 2D crystal hetero-structures, superior device performance can be obtained. The results have revealed the potential of this growth technique for the practical application of 2D crystals.

Through the sulfurization of pre-deposited transition metals, large-area and vertical 2D crystal hetero-structures can be fabricated. The film transferring and device fabrication procedures are also demonstrated in this report.

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition ...

Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 &#956;m). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl ...

Fused Filament Fabrication (FFF) of Metal-Ceramic Components

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.

Fused Filament Fabrication FFF of Metal-Ceramic Components

This study shows multi-material additive manufacturing (AM) using fused filament fabrication (FFF) of stainless steel and zirconia.

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with ...