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.
