WO2023015575A1 - Pdms healable super hydrophobic coating and preparation method therefor - Google Patents

Abstract

Provided are a PDMS healable super hydrophobic coating and a preparation method therefor, comprising pressing a powdered water-soluble salt into a PDMS rubber curing precursor, followed by heat curing, water soaking and fire baking in sequence to obtain the PDMS healable super hydrophobic coating. The PDMS healable super hydrophobic coating obtained by fire baking in the present invention has a micro-nano binary roughness surface structure thereof and has a higher mechanical strength than a single nanoscale rough structure, and may also effectively resist abrasion by external forces.

Description

A PDMS repairable superhydrophobic coating and preparation method thereof technical field

The invention belongs to hydrophobic material technology, in particular to a PDMS repairable super-hydrophobic coating and a preparation method thereof.

Background technique

The application field of superhydrophobic coating determines that the hydrophobic layer will be exposed to harsh natural environments for a long time, such as ice and snow cover in severe cold winter, water impact in rainstorm weather, wind and sun in dry climate, and various forms of scraping and squeezing. If the mechanical strength and material stability of the superhydrophobic coating cannot be effectively improved to increase its service life, it will seriously hinder the superhydrophobic coating from playing a role in practical applications. At the same time, the preparation of hydrophobic coatings involves the use of various chemical reagents such as fluorine-containing compounds and organic solvents, which is not only expensive, but also threatens the environment and life safety once it is lost. Improving the wear resistance of the coating and optimizing the preparation process are key issues that must be solved in the current superhydrophobic field.

technical problem

The present invention is based on 184 silicone rubber (the main component polydimethylsiloxane PDMS), using sodium chloride particles as a template and combining flame treatment methods to prepare a PDMS single-component superhydrophobic coating containing a micro-nano hierarchical structure. The coating has good transparency, stability and certain self-healing function; the micro-nano binary roughness surface structure has higher mechanical strength than a single nano-scale rough structure, which can effectively resist external wear and tear, and will effectively improve Abrasion resistance properties of superhydrophobic surface structures.

technical solution

The invention discloses a PDMS repairable super-hydrophobic coating, which is prepared by pressing a powdery water-soluble salt into a PDMS rubber curing precursor, and then sequentially undergoing heating and curing, soaking in water, and baking to obtain a PDMS repairable super-hydrophobic coating. Hydrophobic coating.

Further, the PDMS rubber curing precursor is coated on the substrate, and then the powdery water-soluble salt is spread on the surface of the PDMS rubber curing precursor, and then pressed into the PDMS rubber curing precursor; wherein the PDMS rubber curing precursor is coated, spread The specific operation of powdered water-soluble salt and pressing the powdered water-soluble salt is a conventional method, such as spinning the PDMS rubber curing precursor on the substrate, and then spreading the powdery water-soluble salt on the surface of the PDMS rubber curing precursor, It is then pressed into the PDMS rubber cured precursor with a plastic or glass plate. Preferably, the surface of the PDMS rubber curing precursor is covered with a powdery water-soluble salt.

In the present invention, the PDMS rubber curing precursor is an existing product, which is a mixture of PDMS rubber before curing, a viscous liquid, such as the basic components and curing agent for preparing 184 silicone rubber. The present invention uses the existing rubber to creatively press the powdery water-soluble salt into the PDMS rubber curing precursor, and then sequentially undergoes heating and curing, soaking in water to obtain PDMS rubber with holes, and fire-baking to obtain a PDMS repairable super-hydrophobic coating, which has The micro-nano dual roughness surface structure has higher mechanical strength than a single nano-scale rough structure, which can effectively resist external force wear.

In the present invention, the powdery water-soluble salt is sodium chloride powder, potassium chloride powder, magnesium chloride powder, calcium chloride powder, and the like. Preferably, the particle size of the powdered water-soluble salt is 10-50 μm, preferably 15-30 μm. Water soaking removes salts and has an effect on the microstructure of the rubber, preferably hot water soaking, most preferably boiling water.

In the present invention, the substrate is not limited, such as glass. During spin coating, the rotation speed is 2000-10000 rpm, and the time is 10-50 s; preferably, the rotation speed is 7000-9000 rpm, and the time is 10-20 s.

In the present invention, the heating and curing temperature is 130-160° C., and the time is 8-12 minutes. When the temperature is too low, the surface of the cured PDMS will spontaneously recover after soaking in water, and the proper roughness cannot be obtained; when the temperature is too high, the sodium chloride particles will be sintered in the coating and cannot be dissolved and removed, affecting Hydrophobicity and transmittance of the coating.

In the present invention, the fire roasting is alcohol lamp fire roasting, preferably, the distance between the top of the flame and the PDMS rubber with holes is 2-5mm, and the fire roasting time is 3-30s, preferably 10-20s. The microstructure of the sodium chloride template cannot achieve a superhydrophobic state, and it needs to be baked with an alcohol lamp. The baking time will affect the density of the nanostructure on the coating surface and affect the hydrophobicity; under the fire baking parameters of the present invention, the coating The number of nano-synapses on the surface gradually increased, and eventually covered the surface of the coating, so the coating reached the best super-hydrophobic state. In addition, the present invention adopts alcohol lamp fire to avoid the production of substances such as candle ash and carbon black.

Beneficial effect

The invention discloses the application of the above-mentioned PDMS repairable superhydrophobic coating in the preparation of hydrophobic materials, especially the application in the preparation of wear-resistant and self-repairing hydrophobic materials.

The present invention tests and analyzes the coated surface after wear and finds that the nano-scale roughness is relatively well preserved in some sunken areas, especially in the "pothole" structure, indicating that the micron-scale rough structure constructed by sodium chloride particles is of great importance to The nanostructure plays an effective protective role. Since polydimethylsiloxane itself is a low surface energy material, the hydrophobicity is effectively improved after replicating the micron-scale rough structure formed by the surface structure of the sodium chloride particle template, even without the nanostructure The coating can still maintain a stable hydrophobic state, so the coating can effectively resist the damage of linear force abrasion. In addition, after heat treatment at 300 °C, the surface of the sample is still in a superhydrophobic state. After soaking in the acid solution for 24 hours, the roughness of the sample surface hardly changed, maintaining excellent hydrophobic properties.

Description of drawings

Figure 1 is a flow chart of the preparation of PDMS repairable superhydrophobic coating.

Figure 2 shows the hydrophobicity of the PDMS repairable superhydrophobic coating: (a) contact angle; (b) rolling angle.

Figure 3 is the SEM image of the PDMS repairable superhydrophobic coating surface: (a) micro-pit structure; (b) nano-synapse structure.

Figure 4 is the effect of the size of sodium chloride on the morphology of the coating: a, a1, a2 SEM images of the surface of the large particle sodium chloride coating. b, b1, b2 SEM images of small particle sodium chloride coating surface.

Figure 5 shows the effect of flame treatment time on the coating morphology: (a) 5 s; (b) 10 s; (c) 15 s; (d) 20 s.

Figure 6 shows the change of coating transparency: (a) 3000 rpm; (b) 5000 rpm; (c) 7000 rpm; (d) 9000 rpm.

Figure 7 is the change curve of contact angle-rolling angle when PDMS coating is worn (sanding).

Figure 8 is the surface morphology of the PDMS coating after abrasion, sanded 50 times, a and b indicate two different places.

Figure 9 is the physical picture of the PDMS coating after high temperature treatment: (a) Hydrophobicity after treatment at 500°C for 100 min; (b) Hydrophobicity after scraping with a steel knife.

Figure 10 shows the acid-base immersion test results of the PDMS coating: (a) the change of contact angle; (b) the SEM image after immersion in the acid solution.

Figure 11 is the change curve of hydrophobicity during the wear repair cycle: (a) change of contact angle; (b) change of rolling angle.

Figure 12 is the SEM images before and after the repair of PDMS coating: (a~b) the surface structure of the damaged sample; (c~d) the morphology of the repaired sandpaper after wear.

Figure 13 is a physical picture of the PDMS repairable superhydrophobic coating repaired 10 times.

Figure 14 shows the self-cleaning process of the PDMS repairable superhydrophobic coating, a to d represent the self-cleaning process.

Figure 15 shows the freezing process of water droplets on the surface of the PDMSPDMS repairable superhydrophobic coating, a to d represent the freezing process.

Figure 16 shows the change of hydrophobicity of PDMS repairable superhydrophobic coating during icing-deicing process.

Embodiments of the present invention

The raw materials involved in the present invention are all existing products. 184 silicone rubber (PDMS) is Dow Corning SYLGARD184, a two-component kit product composed of liquid components, including basic components and curing agents. When used, the basic components and curing agents are completely mixed at a ratio of 10:1.

Desktop homogenizer is KW-4A/5.

Sample test and characterization method: wettability test: use JCY-4 contact angle measuring instrument to characterize the wettability of the sample, including dynamic contact angle and static contact angle, the test environment is room temperature, the size of each drop of water to 4 μL.

Surface morphology test: The Sigma 300 scanning electron microscope of German Zeiss Company was used to observe the surface morphology of the sample, and the test acceleration voltage was 3 KV. The surface of the sample was sprayed with gold before testing. The current of each sample was sprayed with gold at 20 mA, and the gold sprayed time was 40 s.

Transmittance test: Shimadzu's UV-3600 ultraviolet-visible light photometer is used to test the transmittance of the sample, and the test wavelength range is 300-800 nm.

Thermal stability test: put the sample in a tube furnace and bake it at different temperatures for 100 minutes. Observe the changes in the macroscopic morphology and hydrophobicity of the sample after baking. The initial temperature is 100 °C. The temperature interval is 100°C, and the test temperature range is 100°C-500°C.

Chemical stability test: Prepare a solution with a pH value of 1-14, completely immerse the sample in the solution, record the contact angle of the sample every 24 hours, and observe the change of the microstructure of the sample to characterize the corrosion resistance of the sample to acid and alkali solutions .

Self-cleaning performance test: soil, lime and gravel are uniformly mixed according to the mass ratio of 1:1:1 as the pollution source for the test, the pollutants are spread on the surface of the sample, and then slowly inject water droplets with a syringe to make the water droplets take away the sample Contaminants on the surface.

Referring to Fig. 1, the present invention coats the PDMS rubber curing precursor on the substrate, then presses the powdery water-soluble salt into the PDMS rubber curing precursor, and then heats and cures, soaks in boiling water, and bakes in order to obtain PDMS repairable superhydrophobic coating.

The glass slides were ultrasonically treated with 5 ml of acetone, 10 ml of ethanol, and 30 ml of deionized water for 30 min, and finally dried with nitrogen gas for later use. Mix the basic components of 184 silicone rubber with the curing agent at a volume ratio of 10:1, and stir evenly to obtain a PDMS rubber curing precursor for future use. Take sodium chloride powder with a particle size of 15-30 μm for later use.

Embodiment one  Spin-coat (7000rpm, 15s) a layer of prepared PDMS rubber curing precursor on the glass substrate to obtain a colloidal coating, and then spread a layer of the above-mentioned sodium chloride powder on the surface of the colloidal coating until the surface is completely covered, and then put Put a piece of glass on, press the powder into the colloid, remove the upper layer of glass and heat-cure it in a tube furnace at 150°C for 10 minutes, take it out and immerse the sample in boiling water (100°C) for 3 minutes, take out the sample and dry it to get a hole PDMS rubber, the test found that the contact angle reached 129°.

The rubber surface of the sample was baked with an alcohol lamp (distance 3mm, fire 20s) and then cooled naturally to obtain a PDMS repairable superhydrophobic coating.

Figure 2 shows the hydrophobic performance test of the above-mentioned PDMS repairable superhydrophobic coating. The results show that the contact angle of the prepared PDMS superhydrophobic coating is as high as 163°, and the rolling angle is less than 2°, which has excellent superhydrophobic performance.

Figure 3 is the surface topography of the coating prepared above. It can be seen that the microscopic topography of the sample surface presents an irregular micron-scale rough state, with a scale of about 20 μm, and there are “pitholes” of about 10 μm. Craters are formed by the dissolution of previously encapsulated sodium chloride particles. There are dense nanoscale folds and synapses on the surface of the coating, which is due to the thermal stress caused by the uneven heating of the surface during the baking process of the alcohol lamp, which makes the surface micro-deformed. Under the combined action of the two factors, a dense micro-nano rough structure is formed on the surface of the coating, endowing the coating with excellent super-hydrophobicity.

Comparative example A layer of prepared PDMS rubber curing precursor was spin-coated (7000rpm, 15s) on a glass substrate to obtain a colloidal coating, and then cured in a tube furnace at 150°C for 10 minutes to obtain a PDMS coating. The test found that the contact angle was 101 °.

The PDMS rubber with holes in Example 1 was heat-treated in a tube furnace at 280°C for 10 minutes to obtain a coating, and the test found that the contact angle was 131°.

Embodiment two Spin-coat (3000rpm, 20s) a layer of prepared PDMS rubber curing precursor on the glass substrate to obtain a colloidal coating, and then spread a layer of sodium chloride powder with a particle size of 15-30 μm on the surface of the colloidal coating until the surface is covered. Cover it completely, put a piece of glass on it, press the powder into the colloid, remove the upper layer of glass and heat-cure it in a tube furnace at 150°C for 10min, take it out and immerse the sample in boiling water (100°C) for 3min, take out the sample and blow it After drying, the PDMS rubber with holes was obtained; the surface of the sample was baked with an alcohol lamp (distance 3mm, baked for 20s) and then cooled naturally to obtain a PDMS repairable superhydrophobic coating.

Spin-coat (3000rpm, 20s) a layer of prepared PDMS rubber curing precursor on the glass substrate to obtain a colloidal coating, and then spread a layer of sodium chloride powder with a particle size of 100-200 μm on the surface of the colloidal coating until the surface is covered. Cover it completely, put a piece of glass on it, press the powder into the colloid, remove the upper layer of glass and heat-cure it in a tube furnace at 150°C for 10min, take it out and immerse the sample in boiling water (100°C) for 3min, take out the sample and blow it After drying, the PDMS rubber with holes was obtained; the surface of the sample was baked with an alcohol lamp (distance 3mm, baked for 20s) and then cooled naturally to obtain a PDMS repairable superhydrophobic coating.

The SEM of the coating surface obtained above is shown in Figure 4. a1 and a2 show that the macroscopic roughness of the coating caused by the large particle size salt is too large, the surface is extremely uneven, and the transmittance of the coating drops seriously, making it impossible to read clearly; b1, b2 uses small particle size salt, the roughness of the surface is significantly improved, and the transmittance is improved.

Embodiment three On the basis of Example 1, the firing time was adjusted to 5s, 10s, 15s, 30s, and the rest remained unchanged. layer surface, the coating thus achieves an optimal superhydrophobic state. After 30s, the surface of the coating appears black and loses light transmission performance.

Embodiment Four On the basis of Example 1, the rotation speed of spin coating was adjusted to 3000rpm, 5000rpm, 9000rpm, and the rest remained unchanged. It has optical properties similar to frosted glass. At the same time, sodium chloride particles are embedded in the coating. If it cannot be dissolved completely, the transmittance of the coating will be further reduced. The coating in Example 1 reaches a transmittance of 61%. ; 9000rpm and 7000rpm have similar light transmission performance, but the strength of the coating is insufficient and the microstructure of the sodium chloride template cannot be fully reproduced.

Embodiment five The sandpaper abrasion test shows that the superhydrophobic coating prepared by the present invention has better mechanical stability. The coating in Example 1 was polished for 50 cycles with 1200-grit sandpaper at 1 cm/s under a weight load of 100 g. After a total of 500 cm, the contact angle was still maintained at 145°, and the rolling angle was lower than 10°. After grinding, the contact angle of the coating will not be lower than 140°, and it still has hydrophobic ability, see Figure 7. Through the test and analysis of the worn coating surface (Figure 8), it can be seen that the nanostructures exposed on the micron-scale protrusions are severely damaged, basically worn smooth, and lose roughness, but some depressed areas, Especially in the "pit hole" structure, the nanoscale roughness is relatively well preserved, indicating that the micron-scale rough structure constructed by sodium chloride particles has played an effective role in protecting the nanostructure, because polydimethylsiloxane itself is low Surface energy materials, after copying the micron-scale rough structure formed by the surface structure of sodium chloride particle templates, the hydrophobicity has been effectively improved, so the coating can effectively resist the damage of linear force wear.

Embodiment six The coating in Example 1 was heated at 500°C for 100 minutes, and tested again, and it still had superhydrophobicity. After five times of flat scraping with a steel blade, the remaining part still had superhydrophobicity, see Figure 9.

The coating in Example 1 was heated at 100°C, 200°C, and 300°C for 100 minutes, and tested again. It still has superhydrophobicity, and the water contact angle is not lower than 160°.

Embodiment seven Moisture in nature is often corrosive due to dissolved impurities. Therefore, the hydrophobicity of the coating after soaking in different acidic solutions for 24 hours is tested to evaluate the chemical stability of the coating. As shown in Figure 10(a), solutions with different pH values have different effects on the hydrophobicity of the coating. In an acidic environment, the coating can effectively maintain its own hydrophobicity. It can be seen from the SEM pictures of the coating after soaking in the acid solution for 24 h that the roughness of the coating surface hardly changes in the acid solution (Fig. 10(b)).

After soaking the porous PDMS rubber in an acid solution with a pH of 5 for 24 h, the test found that the contact angle decreased from 129° to 113°.

Embodiment eight Research has found that the PDMS prepared by the present invention can repair the nanostructure of the superhydrophobic coating after loss or damage, and only need to perform flame treatment again to "grow" the nanostructure and restore the original hydrophobicity of the coating. The experimental method is to place a weight of 500g on the coating on the surface of 1200-grit sandpaper, and grind 10 cm (1cm/s) each time. Every 10 times of grinding is a cycle T. After each wear cycle, the coating is flamed. After treatment, test the change of hydrophobicity after wear and repair, so as to analyze the self-healing performance of the coating. As shown in Figure 11, after wearing a total of 1000 cm under a 500g weight load, the contact angle of the coating dropped to a minimum of 140° and lost its superhydrophobicity. Return to below 3°. Observing the SEM images of the microstructure of the coating surface before and after repair (Figure 12), it can be seen that after 100 grinding tests, the nanostructure of the coating surface after repair has been well restored, which is almost the same as that of the undamaged coating , indicating that the coating has a high self-healing efficiency. After 10 repair cycles, the coating can still maintain high hydrophobicity (Figure 13), indicating that the microstructure on the coating surface can be continuously repaired to the original super-hydrophobic state, and this repair method is simple and efficient without harsh conditions, high repeatability, and is expected to be practically applied.

Embodiment nine Self-cleaning performance is one of the properties of super-hydrophobic coatings with high practical value in application. The self-cleaning performance of the samples was tested by coating the mixture of soil, gravel and lime on the surface of the coating and then dripping water droplets with a syringe. test. Due to the high hydrophobicity of the sample surface, the dust accumulated on the coating is quickly taken away by the rolling water droplets, and finally the dust on the surface of the sample is basically cleaned, and the surface of the sample can effectively clean the external pollution with the help of water droplets. It has better self-cleaning performance, see Figure 14.

Embodiment ten The water droplets falling on the superhydrophobic surface are generally spherical and have a small contact area. A large amount of air can be trapped between the micro-nano scale grooves on the superhydrophobic surface. The existence of these "air cushions" further hinders the heat between the water droplets and the substrate. Therefore, the superhydrophobic surface can effectively delay the freezing process. The frost resistance test was carried out on the samples. It can be seen from Figure 15 that the water drops completely freeze on the superhydrophobic surface after 800s. In 100s, the ice is completely frozen and the ice beads are firmly frozen on the glass surface, which is difficult to remove. In contrast, the water droplets on the super-hydrophobic surface will fall when lightly touched. The super-hydrophobic surface can not only delay the freezing process, but also effectively reduce the freezing process. Adhesion between layer and substrate. In contrast, the water droplets on the PDMS coating surface were completely frozen in only 250s.

Although the superhydrophobic surface can delay freezing, it cannot completely block the freezing phenomenon. It is easy to encounter freezing and snow accumulation in outdoor cold climates for a long time, and even experience repeated freezing and melting and refreezing, and the mass of ice cubes is too large. The phenomenon of spontaneous exfoliation, which will cause a certain degree of damage to the superhydrophobic surface nanostructure. In order to analyze the durability of the sample in a low-temperature environment, the sample was subjected to an ice bead peeling cycle test, as shown in Figure 16, after 50 cycles of repeated icing-deicing processes, the hydrophobicity of the sample was not greatly affected , indicating that the sample still has a good adaptability to the severe frost and snow environment.

Existing self-healing materials generally repair the chemical composition through the migration of low surface energy substances embedded in the coating, or complete the repair or even reconstruction of the micro-nano structure through the expansion and flow of materials near the damaged area; Due to the high requirements for the preparation of self-healing materials, the repair process depends on specific conditions, and the repair efficiency and performance are limited, further exploration and improvement are still needed. In the present invention, the PDMS repairable superhydrophobic coating is prepared by combining sodium chloride particles with flame treatment. The thermosetting temperature is 130°C-160°C, and the flame treatment time is controlled at 15-20s to produce sufficient nano-scale roughness. The coating has a high transmittance and can withstand a load of 100g weight on 1200-grit sandpaper for 500cm and 10 repair cycle tests. The thermal stability test shows that the coating can stably withstand high temperatures of 300°C. When the temperature reaches 500°C, the coating is still hydrophobic. The acid resistance test shows that the coating can resist the corrosion of acidic solutions. The coating has good self-cleaning ability and frost resistance, and can still maintain hydrophobicity after 50 cycles of icing-deicing tests.

Claims (10)

1. A kind of PDMS repairable superhydrophobic coating, it is characterized in that, the preparation method of described PDMS repairable superhydrophobic coating is, powdery water-soluble salt is pressed into the PDMS rubber curing precursor body, then successively through heating curing, water soaking , fire roasting, to get PDMS repairable super-hydrophobic coating.
2. According to the described PDMS repairable superhydrophobic coating of claim 1, it is characterized in that, powdery water-soluble salt is one or more in sodium chloride powder, potassium chloride powder, magnesium chloride powder, calcium chloride powder; Powder The particle size of the water-soluble salt is 10-50 μm.
3. The PDMS repairable superhydrophobic coating according to claim 1, characterized in that the heating and curing temperature is 130-160° C., and the time is 8-12 minutes.
4. According to the described PDMS repairable superhydrophobic coating of claim 1, it is characterized in that, the fire roasting is alcohol lamp fire roasting.
5. The preparation method of the PDMS repairable superhydrophobic coating described in claim 1 is characterized in that, the PDMS rubber curing precursor is coated on the substrate, and then the powdered water-soluble salt is spread on the PDMS rubber curing precursor surface, and then pressed into the PDMS rubber curing precursor, and then sequentially heat-cured, soaked in water to obtain PDMS rubber with holes, and then baked to obtain a PDMS repairable super-hydrophobic coating.
6. According to the preparation method of the described PDMS repairable superhydrophobic coating of claim 5, it is characterized in that the surface of the PDMS rubber curing precursor is covered with powdery water-soluble salt.
7. The preparation method of the PDMS repairable superhydrophobic coating according to claim 5, characterized in that the distance between the apex of the flame and the PDMS rubber with holes is 2-5mm, and the firing time is 3-30s.
8. According to the preparation method of the described PDMS repairable superhydrophobic coating of claim 5, it is characterized in that, the PDMS rubber curing precursor is spin-coated on the substrate.
9. The preparation method of the PDMS repairable superhydrophobic coating according to claim 8, characterized in that, during spin coating, the rotation speed is 2000-10000 rpm, and the time is 10-50 s.
10. The application of the PDMS repairable superhydrophobic coating described in claim 1 in the preparation of hydrophobic materials.