Name: fabrication of superhydrophobic metal surfaces for anti-icing applications
Uploaded: 2018-08-15T13:30:00.000+00:00
Duration: 11 min 20 s
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 cleaning solution. Wash the samples gently with gloved hands. Avoid the use of abrasive scourers.</li>
		<li>Rinse the samples abundantly in a flow of distilled water. Subsequently, immerse each sample in 30 mL of 96% ethanol, sonicate it for 300 s, and repeat in 30 mL of ultrapure water for 300 s.</li>
		<li>Remove the samples from the water and dry them for 1 h at room temperature.</li>
	</ol>
	</li>
	<li>Acid etching
	<ol>
		<li>For the etching reaction, prepare a 4 M solution of HCl in ultrapure water13. Immerse each sample in 80 mL of this solution for 480 s. The reaction becomes more vigorous after approximately 360 s, when the native oxide surface layer is removed. 
		CAUTION: For safety, conduct this reaction in a hood. Wear gloves, lab coat and protective glasses.</li>
		<li>Next to the beaker containing the acid solution, prepare another beaker with ultrapure water to abruptly stop the reaction. Using polytetrafluoroethylene tweezers, remove the sample from the acid solution and immerse it in water. Rinse the sample in abundant ultrapure water.</li>
		<li>Dry the samples completely by blowing them with filtered and compressed air. Note that the sample after the etching reaction is superhydrophilic and drying it may be a difficult task. After the macroscopic removal of water by blowing, remove traces of water in an oven at 120 &#176;C for 600 s. 
		Note: This drying process in essential, especially for samples to be later silanized.</li>
	</ol>
	</li>
	<li>Hydrophobization 
	<ol>
		<li>Hydrophobization by FAS-17 silanization
		<ol>
			<li>Prior to the vapor-phase silanization, treat the samples with air-plasma for 600 s using a plasma cleaner operating at 100 W. This process activates the surface functional groups (-OH groups) that act as linker to the silane molecules.</li>
			<li>Subsequently, introduce the samples inside a glass Petri dish slightly tilted with the help of a pipette tip to slightly incline the surface. Deposit two 50 &#181;L drops of 1H,1H,2H,2H-Perfluorodecyl-triethoxysilane (FAS-17 ) on the Petri dish next to the sample13.</li>
			<li>Cover the Petri dish partially and place it in an air-evacuated desiccator overnight. Finally, ventilate the desiccator. Remove the samples, which are ready to use.</li>
		</ol>
		</li>
		<li>Hydrophobization by fluoropolymer (polytetrafluoroethylene) deposition
		<ol>
			<li>Spray the etched samples16 from about 10 cm with a solution of amorphous fluoropolymer in a fluorocarbon solvent in a ratio of 1/20 (v/v)16. A perfume diffuser filled with the solution may be used for this purpose. Leave to dry at room temperature for 600 s. Repeat the same process over a clean non-etched surface to make a smooth-hydrophobic aluminum surface (Ra = 0.25&#177;0.03 &#181;m).</li>
			<li>Apply a second coat and introduce the samples in a 110 &#176;C oven for 600 s to ensure total removal of the solvent and a crosslinking of the fluoropolymer coating. This process increases the durability, as indicated by the manufacturer.</li>
		</ol>
		</li>
		<li>Hydrophobization by ceria-stearic acid deposition
		<ol>
			<li>Clean the etched samples in acetone/ethanol/water, sonicate them for 300 s in water and dry them in a flow of compressed air.</li>
			<li>Immerse the samples31 in 50 mL of aqueous solution containing 2 g of cerium trichloride heptahydrate (CeCl3&#183;7H2O), and 3 mL of 30% hydrogen peroxide (H2O2). Incubate the sample immersed in the solution in a 40 &#176;C oven for 1 h.</li>
			<li>Remove it from the solution, rinse it in distilled water and dry it in a 100 &#176;C oven for 600 s.</li>
			<li>Immerse the sample in a 30 mM ethanol solution of stearic acid for 900 s, rinse it in ethanol and dry it in a 100 &#176;C oven for 600 s. 
			Note: Once dried and cooled down to room temperature, the samples are ready to use. The SH surfaces produced with the ceria-stearic coating acid are hereinafter referred as the Ce-SA coated surface.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Sample Characterization
<ol>
	<li>Wetting analysis 
	<ol>
		<li>Bouncing drop experiments
		<ol>
			<li>Evaluate the water repellency degree of the produced sample by bouncing drops experiments13. Quantify the number of bounces given by a drop that is released from a fixed syringe whose needle is located at (10.1 &#177; 0.2) mm above the surface. The drop volume is typically 4 &#181;L.</li>
			<li>Capture the sequence with a high-speed camera. In the high-speed video acquisition software, fix the acquisition rate to 4200 images per second and the exposure time to 235 &#181;s.</li>
			<li>Once the video is recorded, select the sequence from the moment when the drop is released until the drop is already in full contact with the sample (no more bounces are observed). Save the video file.</li>
			<li>For each image, detect the drop profile using software32. Subsequently, quantify the number of bounces with the naked eye when playing the video sequence. In case that it is not easily identified, count the number of maxima above the center of mass position of the static drop (more than 15-20%).</li>
		</ol>
		</li>
		<li>Tilting plate experiments 
		<ol>
			<li>Use this test only to quantify the damage caused by each specific wear test. Analyze the shear adhesion of water drops with tilting plate experiments (TPE)33 using a lab-designed tilting apparatus34.</li>
			<li>Use side-view image acquisition of a sessile drop deposited on the sample fixed to an inclinable platform. During the image acquisition (at constant acquisition rate of 16 fps), incline the platform with constant angular velocity (5&#176;/s). Therefore, capture a drop image every 0.31&#176;. 
			Note: Above a specific inclination angle, the drop moves (slides/rolls-off) on the surface and this state may serve to determine the advancing and receding contact angles (ACA and RCA, respectively) simultaneously. The minimum tilting angle that produces a global displacement of the contact line (uphill and downhill contact line points move simultaneously) is referred to as the sliding angle (SA). The SA is the value reported here from TPE.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Roughness measurements
	<ol>
		<li>Analyze the micro-roughness of the samples using a white light confocal microscope. Set a scanning area of 0.252 x 0.187 mm per single topography.</li>
		<li>Take at least 4 single topographies per sample. Use the objective of magnification 50X, capturing 200 vertical planes in vertical steps of 0.2 &#181;m. Determine the Ra factor (arithmetic roughness amplitude).</li>
	</ol>
	</li>
</ol>
3. Durability Tests
Note: Evaluate the damage induced by each wear agent separately. Do not conduct more than one wear test per sample.
<ol>
	<li>Lateral abrasion tests 
	Note: The lateral abrasion tests (see Figure 3a) are performed by means of a commercial linear abrasive. This test aims to evaluate the wear induced by tangential displacement of a standard abrasive tip against a surface. This device allows the use of a wide variety of abrasives, setting a wide range of application pressures, lateral speeds and total number of abrasive cycles35.
	<ol>
		<li>Use a standard rubber abrasive CS-10, provided by the manufacturer. Fix the velocity to 20 cycles/min. Control the applied pressure by using weights. Set the minimum pressure allowed by the instrument, which corresponds to a total weight of 350 g. 
		Note: Considering the tip width (6.70&#177;0.05 mm), and the weight used, the corresponding applied pressure for these settings is 97.3&#177;1.4 kPa. The total worn area is limited by the width of the tip and the total length for each abrasion cycle. Set it to 38.1 mm.</li>
		<li>For each sample, evaluate the wear induced after 1, 2, 3 and 5 cycles.
		<ol>
			<li>After each wear treatment, gently brush the surface (using the brush provided by the manufacturer), rinse in water, and blow on using compressed air. Evaluate the wetting properties using TPE, as described in section 2.1.2.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Abrasive particle impact test
	<ol>
		<li>Conduct the particle impact test by using the set-up shown in Figure 3b, which is inspired by the standard abrasion Test D968. Release 30 mL (around 55 g) of abrasive sand from a glass funnel. Locate its extreme bottom at (25&#177;1) cm from the surface.</li>
		<li>Use a funnel tap diameter of (12&#177;1) mm and a length of (97&#177;1) mm. Place the funnel vertically, while inclining the sample 45&#176;. After impacting on the sample, collect the sand in a container placed below.</li>
		<li>Once a wear cycle is conducted, rinse the surface with distilled water, dry it in a flow of compressed air and evaluate the wetting properties by TPE (section 2.1.2). Repeat this entire process up to 3 times for each sample.</li>
	</ol>
	</li>
	<li>UV-ozone surface degradation test
	<ol>
		<li>Conduct the UV-ozone degradation test using an ozone cleaner. Treat each sample at room temperature for 600 s and repeat the cycle once.</li>
		<li>Subsequently, rinse the surfaces in water and dry them with compressed air.</li>
		<li>Evaluate the wetting properties by TPE described in section 2.1.2 to determine whether the superhydrophobic properties remain after UV-exposure.</li>
	</ol>
	</li>
	<li>Water immersion test
	<ol>
		<li>Evaluate the wear induced by water contact after a lengthy immersion in water. Introduce the sample in a 100 mL beaker of ultrapure water for 24 h.</li>
		<li>Remove the samples from the water, dry them with compressed air and place them in a 120 &#176;C oven for 600 s to ensure a total removal of water from the surface. When the surface is fully dried, evaluate the wetting properties after water exposure using the protocol described in section 2.1.2.</li>
	</ol>
	</li>
</ol>
4. Anti-icing Efficiency Evaluation
Note: The anti-icing efficiency evaluation is based on the three aspects shown in Figure 1.
<ol>
	<li>Subcooled water dripping test 
	Note: The subcooled water repellency of the samples is tested by means of the set-up shown in Figure 4a. The sample is introduced inside a freezing chamber at &#8211;20 &#176;C, which is fixed on top of an inclined (30&#176;) platform. A mixture of ice and distilled water in equilibrium (at stabilized temperature of 0 &#176;C) is placed outside the freezing chamber.
	<ol>
		<li>Pump the cold water inside the chamber using a peristaltic pump and have it circulate inside the freezer before being dripped on the sample at a low rate of 1 drop every 3 seconds. Single drops have a volume of roughly 50 &#181;L.</li>
		<li>Once the dripping process is initiated, capture a lateral image of the sample every 10 s to determine whether ice accretion occurs.</li>
	</ol>
	</li>
	<li>Freezing delay test
	<ol>
		<li>Conduct the freezing delay test inside the same freezing chamber mentioned in the previous section.</li>
		<li>Determine the percentage of sessile drops deposited on the sample that freeze, for each temperature, during a cooling process from room temperature down to approximately -25 &#176;C. The set-up for this test is shown in Figure 4b.</li>
		<li>Level the sample (with zero tilt) and deposit sessile drops carefully to avoid roll-off. Due to the high mobility of drops on water-repellent surfaces, place a lower number of them on SH samples. Repeat the experiment for SH surfaces several times.</li>
		<li>Monitor the temperature and relative humidity by using a thermal-probe. Control the relative humidity (RH) with a commercial humidifier. The RH is roughly 95% when the humidifier is switched on, and it decreases down to approximately 40% when the humidifier is switched off.</li>
		<li>Use around 200 drops of 30 &#181;L per sample (drop freezing is a stochastic phenomenon, and the analysis requires the use of a large number of drops). 
		Note: Thus, for this test use larger samples than those used for the rest of the studies. In this case the size is 125 mm x 62.5 mm and adapt the protocol to either etch the sample or hydrophobize their surfaces to the new sample dimensions.</li>
		<li>Place the sample in the middle of the bottom part of the freezer on top of an isolating platform. Gently deposit an array of 70 drops per sample (25 for the superhydrophobic sample). Close the freezer and turn it on. 
		Note: The temperature decreases linearly in time from room temperature down to approximately -25 &#176;C. The rate of cooling depends on the relative humidity. At low relative humidity (humidifier unplugged), the entire process takes roughly 2 hours, while it takes less time (around 1 hour) if the humidifier is connected. Once the temperature is lower than 0 &#176;C, drops start to nucleate.</li>
		<li>Count the number of drops that are frozen for each temperature (in intervals of 0.5 &#176;C), until all the totality of the drops is frozen.</li>
	</ol>
	</li>
	<li>Ice adhesion test
	<ol>
		<li>Quantify the force that must be applied to detach (pull-off) a piece of ice with a controllable contact area that has been formed on each sample. Perform these tests using the set-up illustrated in Figure 4c.</li>
		<li>Cut a polytetrafluoroethylene pipe with internal diameter of 10 mm in cylinders of ~28 mm height using scissors. Press the cylinder against the sample. Fill it with 1.2 mL of distilled water. Introduce the filled cylinder in the freezing chamber and wait for 1 h. 
		Note: Once the water is totally frozen, the sample with the cylinder is firmly fixed to a platform using a striker plate.</li>
		<li>Tie the cylinder to a digital force gauge using a nylon thread. The way this cylinder is tied to the thread and the orientation of the cylinder with respect to the thread depends on which type (shear or the tensile) adhesion is under evaluation. Fix this gauge to a motorized test stand. Close the freezing chamber and wait for 600 s.</li>
		<li>Displace the gauge from the sample at a constant velocity of (10 &#177; 0.5) mm/min.
		<ol>
			<li>Adjust this velocity manually within the control panel of the motorized test stand. Click the icon of the program controlling the dynamometer readings. Press START to record the force.</li>
			<li>Immediately after, move the dynamometer upwards by keeping on pressing the vertical displacement bottom within the motorized stand control panel.</li>
		</ol>
		</li>
		<li>When the displacement of the dynamometer with respect to the sample produces an extension of the thread and a separation of the ice from the sample, click on STOP and save the generated data file. 
		Note: The gauge monitors the force in terms of time. Knowing the velocity in which the dynamometer is displaced (10 mm/min), determine the force in terms of displacement. This serves to determine the rupture force (maximum retaining force) and the adhesion strength per unit area.</li>
		<li>Evaluate the shear adhesion when the pull-off is carried out laterally. The force in this case is parallel applied to the contact area (see Figure 4b). For this purpose, fix the sample vertically and connect the cylinder base to the thread using a metal ring. Pull this ring by the gauge until the sample detaches from the surface by shear displacement. 
		Note: The tensile adhesion test evaluates the peak force and work need to detach a piece of ice from the surface when it is pulled vertically.</li>
		<li>In this case, drill two small holes on the cylinder wall that serve to connect the cylinder to the gauge. Then, pull it vertically until the ice is finally detached from the surface.</li>
	</ol>
	</li>
</ol>

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N., Alexander, D., Mool, C. G., Eric, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Linear+abrasion+of+a+titanium+superhydrophobic+surface+prepared+by+ultrafast+laser+microtexturing.">Linear abrasion of a titanium superhydrophobic surface prepared by ultrafast laser microtexturing.</a> Journal of Micromechanics and Microengineering. 23 (11), 115012 (2013).</li><li>Li, X. -. W., 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=Low-cost+and+large-scale+fabrication+of+a+superhydrophobic+5052+aluminum+alloy+surface+with+enhanced+corrosion+resistance.">Low-cost and large-scale fabrication of a superhydrophobic 5052 aluminum alloy surface with enhanced corrosion resistance.</a> RSC Advances. 5 (38), 29639-29646 (2015).</li><li>Meuler, A. J., 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=Relationships+between+water+wettability+and+ice+adhesion.">Relationships between water wettability and ice adhesion.</a> ACS Applied Materials &amp; Interfaces. 2 (11), 3100-3110 (2010).</li><li>Boinovich, L. 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. A., Cabrerizo-Vilchez, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+method+for+evaluating+the+most+stable+contact+angle+using+tilting+plate+experiments.">A new method for evaluating the most stable contact angle using tilting plate experiments.</a> Soft Matter. 7 (21), 10457-10461 (2011).</li><li>Pierce, E., Carmona, F. J., 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+of+sliding+and+contact+angle+results+in+tilted+plate+experiments.">Understanding of sliding and contact angle results in tilted plate experiments.</a> Colloids Surfaces A. 323 (1-3), 73-82 (2008).</li><li>Ye, H., Zhu, L., Li, W., Liu, H., Chen, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+spray+deposition+of+a+water-based+superhydrophobic+coating+with+high+stability+for+flexible+applications.">Simple spray deposition of a water-based superhydrophobic coating with high stability for flexible applications.</a> Journal of Materials Chemistry. 5 (20), 9882-9890 (2017).</li><li>Rolland, J. P., Van Dam, R. M., Schorzman, D. A., Quake, S. R., DeSimone, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvent-resistant+photocurable+&amp;#34;liquid+Teflon&amp;#34;+for+microfluidic+device+fabrication.">Solvent-resistant photocurable &amp;#34;liquid Teflon&amp;#34; for microfluidic device fabrication.</a> Journal of the American Chemical Society. 126 (8), 2322-2323 (2004).</li></ol>

We have nothing to disclose.

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, &amp;ge;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&amp;micro; 2.32</td><td>UPC-CD6 &amp;amp; Sensofar Tech S.L.</td><td>version 2.32</td><td>Sofware controlling PL&amp;micro; Confocal Imaging Profiler</td></tr><tr><td>Pl&amp;micro;-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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8.4K Views.  University of Granada. We illustrate several methodologies to produce superhydrophobic metal surfaces and to explore their durability and anti-icing properties.

Video: Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

Chemistry

TiO2-coated Hollow Glass Microspheres with Superhydrophobic and High IR-reflective Properties Synthesized by a Soft-chemistry Method

This manuscript proposes a soft-chemistry method to develop superhydrophobic and highly IR-reflective hollow glass microspheres (HGM). The anatase TiO2 and a superhydrophobic agent were coated on the HGM surface in one step. TBT and PFOTES were selected as the Ti source and the superhydrophobic agent, respectively. They were both coated on the HGM, and after the hydrothermal process, the TBT turned to anatase TiO2. In this way, a PFOTES/TiO2-coated HGM (MCHGM) was prepared. For comparison, PFOTES single-coated HGM (F-SCHGM) and TiO2 single-coated HGM (Ti-SCHGM) were synthesized as well. The PFOTES and TiO2 coatings on the HGM surface were demonstrated through X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive detector (EDS) characterizations. The MCHGM showed a higher contact angle (153&#176;) but a lower sliding angle (16&#176;) than F-SCHGM, with a contact angle of 141.2&#176; and a sliding angle of 67&#176;. In addition, both Ti-SCHGM and MCHGM displayed similar IR reflectivity values, which were about 5.8% higher than the original HGM and F-SCHGM. Also, the PFOTES coating barely changed the thermal conductivity. Therefore, F-SCHGM, with a thermal conductivity of 0.0479 W/(m&#183;K), was quite like the original HGM, which was 0.0475 W/(m&#183;K). MCHGM and Ti-SCHGM were also similar. Their thermal conductivity values were 0.0543 W/(m&#183;K) and 0.0543 W/(m&#183;K), respectively. The TiO2 coating slightly increased the thermal conductivity, but with the increase in reflectivity, the overall heat-insulation property was enhanced. Finally, since the IR-reflecting property is provided by the HGM coating, if the coating is fouled, the reflectivity decreases. Therefore, with the superhydrophobic coating, the surface is protected from fouling, and its lifetime is also prolonged.

TiO2-coated Hollow Glass Microspheres with Superhydrophobic and High IR-reflective Properties Synthesized by a Soft-chemistry Method

This manuscript proposes a soft-chemistry method to synthesize superhydrophobic, TiO2-coated hollow glass microspheres (HGM) with high IR-reflective properties.

This manuscript proposes a soft-chemistry method to develop superhydrophobic and highly IR-reflective hollow glass microspheres (HGM). The anatase TiO2 ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 &#176;C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Slippery surfaces provide a new way to solve the adhesion problem. This protocol describes how to fabricate slippery surfaces at high temperatures. The results demonstrate that the slippery surfaces showed anti-wetting for liquids and a remarkable anti-adhesion effect on soft tissues at high temperatures.

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial applications. Here we describe how electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester (e.g., polycaprolactone and poly(lactide-co-glycolide)), as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate) affords a superhydrophobic biomaterial. The fabrication techniques of electrospinning or electrospraying provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively. The use of a low surface energy copolymer dopant that blends with the polyester and can be stably electrospun or electrosprayed affords these superhydrophobic materials. Important parameters such as fiber size, copolymer dopant composition and/or concentration, and their effects on wettability are discussed. This combination of polymer chemistry and process engineering affords a versatile approach to develop application-specific materials using scalable techniques, which are likely generalizable to a wider class of polymers for a variety of applications.

Two- and three-dimensional superhydrophobic polymeric materials are prepared by electrospinning or electrospraying biodegradable polymers blended with a lower surface energy polymer of similar composition.

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial ...

Bioengineering

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (&#952;o &#60; 90&#176;) renders them even more wetting (&#952;r &#60; &#952;o &#60; 90&#176;), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica &#952;o &#8776; 40&#176; for the water/air system, and &#952;o &#8776; 20&#176; for the hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are &#952;r &#62; 90&#176;. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (&#952;r &#8776; 150&#176;&#8211;160&#176;) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within &#60;1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

This work presents microfabrication protocols for achieving cavities and pillars with reentrant and doubly reentrant profiles on SiO2/Si wafers using photolithography and dry etching. Resulting microtextured surfaces demonstrate remarkable liquid repellence, characterized by robust long-term entrapment of air under wetting liquids, despite the intrinsic wettability of silica.

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping ...

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus allowing only pure water vapor to pass through. To achieve this feat, commercial DCMD membranes are derived from or coated with water-repellent perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, the use of perfluorocarbons is limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Unveiled here is a new class of membranes referred to as gas-entrapping membranes (GEMs) that can robustly entrap air upon immersion in water. GEMs achieve this function by their microstructure rather than their chemical make-up. This work demonstrates a proof-of-concept for GEMs using intrinsically wetting SiO2/Si/SiO2 wafers as the model system; the contact angle of water on SiO2 is &#952;o &#8776; 40&#176;. Silica-GEMs had 300 &#956;m-long cylindrical pores whose diameters at the (2 &#956;m-long) inlet and outlet regions were significantly smaller; this geometrically discontinuous structure, with 90&#176; turns at the inlets and outlets, is known as the &#34;reentrant microtexture&#34;. The microfabrication protocol for silica-GEMs entails designing, photolithography, chrome sputtering, and isotropic and anisotropic etching. Despite the water loving nature of silica, water does not intrude silica-GEMs on submersion. In fact, they robustly entrap air underwater and keep it intact even after six weeks (&#62;106 seconds). On the other hand, silica membranes with simple cylindrical pores spontaneously imbibe water (&#60; 1 s). These findings highlight the potential of the GEMs architecture for separation processes. While the choice of SiO2/Si/SiO2 wafers for GEMs is limited to demonstrating the proof-of-concept, it is expected that the protocols and concepts presented here will advance the rational design of scalable GEMs using inexpensive common materials for desalination and beyond.

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Presented here is a stepwise protocol for realizing gas-entrapping membranes (GEMs) from SiO2/Si wafers using integrated circuit microfabrication technology. When silica-GEMs are immersed in water, the intrusion of water is prevented, despite the water-loving composition of silica.

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and ...

Fabrication of Gradient Nanopattern by Thermal Nanoimprinting Technique and Screening of the Response of Human Endothelial Colony-forming Cells

Nanotopography can be found in various extracellular matrices (ECMs) around the body and is known to have important regulatory actions upon cellular reactions. However, it is difficult to determine the relation between the size of a nanostructure and the responses of cells owing to the lack of proper screening tools. Here, we show the development of reproducible and cost-effective gradient nanopattern plates for the manipulation of cellular responses. Using anodic aluminum oxide (AAO) as a master mold, gradient nanopattern plates with nanopillars of increasing diameter ranges [120-200&#8239;nm (GP 120/200), 200-280&#8239;nm (GP 200/280), and 280-360&#8239;nm (GP 280/360)] were fabricated by a thermal imprinting technique. These gradient nanopattern plates were designed to mimic the various sizes of nanotopography in the ECM and were used to screen the responses of human endothelial colony-forming cells (hECFCs). In this protocol, we describe the step-by-step procedure of fabricating gradient nanopattern plates for cell engineering, techniques of cultivating hECFCs from human peripheral blood, and culturing hECFCs on nanopattern plates.

Here, we present a protocol for the fabrication of gradient nanopattern plates via thermal nanoimprinting and the method of screening responses of human endothelial progenitor cells to the nanostructures. By using the described technology, it is possible to produce a scaffold that can manipulate cell behavior by physical stimuli.

Nanotopography can be found in various extracellular matrices (ECMs) around the body and is known to have important regulatory actions upon cellular ...

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

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