Preparation method of a photothermal superhydrophobic coating with high photothermal conversion performance

Abstract

The present invention discloses a preparation method of a photothermal superhydrophobic coating with high-efficiency photothermal conversion performance. A composite powder with high-efficiency photothermal performance is prepared by compounding PTFE powder, nano-TiN particles and hydroxylated multi-walled carbon nanotubes at 325 °C. After being dispersed, it is sprayed on a semi-cured epoxy resin coating, thereby preparing a photothermal superhydrophobic coating with high-efficiency photothermal conversion performance. The coating of the present invention simultaneously has high-efficiency photothermal conversion performance and superhydrophobic performance, combines passive anti-icing and active photothermal de-icing, and can be used for anti-icing / de-icing requirements in various scenarios.

Description

Technical Field

[0001] The present invention belongs to the field of photothermal superhydrophobic materials, and particularly relates to a preparation method of a photothermal superhydrophobic coating with high photothermal conversion performance. Background Art

[0002] Droplets will freeze at low temperatures, which has a great adverse impact on industries such as power transportation, aviation, transportation, and wind power generation. It is necessary to reduce the damage caused by icing. At present, many technologies have focused on anti-icing / de-icing, such as coating an anti-icing / de-icing coating on the surface of a substrate, specifically including superhydrophobic coatings and photothermal coatings. The former can make the substrate surface have passive anti-icing performance by utilizing the property that droplets are difficult to adhere to the superhydrophobic surface, and the latter can make the substrate have active de-icing performance under sunlight irradiation by utilizing the photothermal conversion performance of the photothermal material. The use environment of the above single-functional coatings is limited. The superhydrophobic coating only has anti-icing characteristics and cannot actively remove the covered ice layer at ultra-low temperatures and loses its function. The liquid adhesion on the surface of the photothermal coating is still very large, and dust coverage will weaken its photothermal conversion performance. Therefore, the combined photothermal superhydrophobic coating is expected to make up for the deficiencies of the single coating.

[0003] Patent CN117861975A discloses a superhydrophobic coating with photothermal performance and its preparation method. It uses fluorocarbon resin as the matrix resin and superhydrophobic tungsten carbide as the photothermal material. The preparation method is spraying, which is convenient to prepare, but its photothermal performance is limited. The equilibrium temperature under the illumination condition of 1kW·m 2 is only 85°C, and its active de-icing performance is limited.

[0004] Patent CN117659749A discloses a superhydrophobic anti-icing coating and its preparation method. It uses iron oxide as the photothermal material and requires etching treatment on the surface of the substrate, which is only applicable to specific substrate surfaces.

[0005] Patent CN117487434A discloses an anti-icing superhydrophobic coating based on multi-walled carbon nanotubes and its preparation method, which obtains excellent superhydrophobic performance and photothermal conversion performance. However, carbon nanotubes are expensive, and only using carbon nanotubes as the photothermal material will make the cost of the final coating high and it cannot be used on a large scale. Moreover, the infrared emissivity of carbon-based materials is too high (generally greater than 0.9), which will increase the heat loss during the photothermal process. Summary of the Invention

[0006] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a preparation method of a photothermal superhydrophobic coating with high photothermal conversion performance. The present invention uses polytetrafluoroethylene (PTFE) powder, titanium nitride (TiN) powder and hydroxylated multi-walled carbon nanotubes (MWCNTs) to prepare a photothermal superhydrophobic coating. This coating combines carbon-based photothermal materials and cermet-based photothermal materials, which can not only achieve a very high equilibrium temperature and heating rate under sunlight irradiation, but also achieve excellent superhydrophobic performance, thus realizing the combination of passive anti-icing performance and active photothermal de-icing performance. During the preparation process of the present invention, no toxic raw materials are involved, only a very small amount of MWCNTs is used, which controls the preparation cost, reduces the infrared emissivity and heat loss, and uses a spraying method for coating, which is conducive to large-scale laying.

[0007] The preparation method of the photothermal superhydrophobic coating with high photothermal conversion performance of the present invention includes the following steps:

[0008] Step 1: Take a certain mass of PTFE powder, TiN powder and hydroxylated MWCNTs and place them in a container, stir and mix evenly;

[0009] Step 2: Place the mixed powder obtained in Step 1 in a crucible, put it into a muffle furnace, and slowly heat the muffle furnace to 325 °C and keep it for 1 h to obtain a composite powder, denoted as TPM;

[0010] Step 3: Sieve the TPM composite powder using a micro sieve;

[0011] Step 4: Coat epoxy resin on the surface of the substrate and semi-cure it for standby; there is no material requirement for the selected substrate, the surface needs to be flat, and glass, wood, ceramics, and steel can all be used;

[0012] Step 5: Take a certain mass of TPM composite powder in 10 mL of n-hexane, add 0.5 g of PDMS and 0.05 g of the corresponding curing agent, and stir magnetically to obtain a TPM coating;

[0013] Step 6: Use a high-atomization spray gun with a diameter of 0.8 to spray the TPM coating onto the surface of the substrate prepared in Step 4, the air pressure is about 0.2 kPa, the spraying distance is about 10 cm, and spray until the black powder completely and evenly covers the surface of the substrate. The thickness of the coating functional layer is generally about 100 μm, there is no precise requirement, but it is necessary to completely cover the surface of the substrate without omission to ensure the normal and uniform superhydrophobic performance and photothermal performance;

[0014] Step 7: Place the sprayed substrate in a hydrophobic modifier solution for 2 h;

[0015] Step 8: Take out the modified coating and place it in an oven for drying and curing to obtain a photothermal superhydrophobic coating.

[0016] Further, the mass ratio of PTFE powder, TiN powder, and hydroxylated MWCNTs in Step 1 is 3 - 1:3 - 2:0.1 - 0.3, such as 3:3:0.1, 1:3:0.2, 1:2:0.3, 2:3:0.3, etc., and preferably 1:3:0.2.

[0017] Further, the particle size of PTFE powder is 500 nm - 1 μm, preferably 500 nm; the particle size of TiN powder is 50 - 100 nm, preferably 50 nm.

[0018] Further, during the heating process of the muffle furnace in Step 2, it needs to be slow, and the time for heating from 25°C to 325°C is greater than 150 min, preferably 200 min.

[0019] Further, the aperture of the micron sieve used in Step 3 is 200 - 500 mesh.

[0020] Further, in Step 4, 2 - 5 g of epoxy resin E51 and the corresponding mass of curing agent are dissolved in 5 ml of absolute ethanol and coated on the surface of the substrate. The coating method can be spraying, brushing, or spin - coating, and different methods can be selected according to the shape of the substrate. The substrates used are glass, wood, steel, or ceramic chips.

[0021] Further, in Step 5, 0.5 - 1 g of TPM composite powder is added to 10 mL of n - hexane.

[0022] Further, in Step 7, the hydrophobic modifier is any one of cetyltrimethoxysilane (HDTMS), KH560, or KH570, and the concentration of the hydrophobic modifier solution is 2 - 6 wt%.

[0023] Further, in Step 8, the curing temperature is 80 - 100°C and the curing time is 2 - 4 h.

[0024] The photothermal super - hydrophobic coating prepared by the present invention has an equilibrium temperature as high as 139.6°C, a static contact angle of 158°, and a rolling angle of about 3.5° under 1 sun illumination conditions.

[0025] The photothermal super - hydrophobic coating prepared by the present invention has efficient light - to - heat conversion performance and super - hydrophobicity, and has remarkable effects in anti - icing / de - icing.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The photothermal super - hydrophobic coating prepared by the present invention utilizes the mutual cooperation of different photothermal materials to obtain a higher equilibrium temperature. Under 1 kW·m 2 illumination conditions, the equilibrium temperature is as high as 139.6°C, which can greatly accelerate the process of photothermal de - icing.

[0028] 2. Compared with general photothermal coatings, the present invention has excellent superhydrophobic performance, which can combine the active photothermal de-icing performance with the passive superhydrophobic anti-icing performance, greatly delaying the freezing of droplets on the coating surface and endowing the coating with the ability to quickly remove the droplets by means of light irradiation after droplet freezing.

[0029] 3. In the photothermal superhydrophobic coating prepared by the present invention, the MWCNTs used are in close contact with TiN particles under the connection of PTFE, endowing the composite coating with better thermal conductivity. On the one hand, it can enable the coating to obtain a faster heating rate under light irradiation, and on the other hand, it can enable the coating to transfer heat from the irradiated coating to the blocked coating faster, thus realizing more comprehensive photothermal de-icing.

[0030] 4. The method for preparing the coating in the present invention does not involve the use of highly polluting chemical raw materials, and is safe and green.

[0031] 5. The present invention uses a spraying method to prepare the coating, which has low cost and is convenient for large-scale laying. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the SEM image of the TPM composite powder in Example 1;

[0033] Figure 2 It is the SEM image of the TPM photothermal superhydrophobic coating in Example 1;

[0034] Figure 3 It is the 3D surface topography map and wetting performance test map of the TPM photothermal superhydrophobic coating in Example 1;

[0035] Figure 4 It is the infrared emissivity test photo of the TPM photothermal superhydrophobic coating in Example 1;

[0036] Figure 5 It is the heating curve of the TPM photothermal superhydrophobic coating in Example 1 under the illumination condition of 1 kW·m 2 ;

[0037] Figure 6 It is the infrared photo during the heating process of the TPM photothermal superhydrophobic coating in Example 1 under the illumination condition of 1 kW·m 2 ;

[0038] Figure 7 It is the temperature curve of the TPM photothermal superhydrophobic coating in Example 1 continuously irradiated for 1 h under the illumination condition of 1 kW·m 2 ;

[0039] Figure 8 It is the process diagram of droplet freezing on the surface of the TPM photothermal superhydrophobic coating in Example 1 and its comparison with the surface of the glass slide;

[0040] Figure 9 are the photos of the melting process of the frozen droplets of the TPM photothermal superhydrophobic coating in Example 1 under no light and 1 kW·m 2 light illumination conditions;

[0041] Figure 10 are the photos of the self-cleaning performance process of the TPM photothermal superhydrophobic coating in Example 1;

[0042] Figure 11 are the WCA test chart of the coating in Comparative Example 1 and the heating curve of the coating under 1 kW·m 2 light illumination conditions;

[0043] Figure 12 are the WCA comparisons of various coatings in Example 1, 2 and Comparative Examples 2, 3. Detailed implementation manners

[0044] The technical solution of the present invention will be further analyzed and described below through specific examples.

[0045] Example 1:

[0046] 1. Take 1 g of PTFE, 3 g of TiN and 0.2 g of hydroxylated MWCNTs in a crucible, and slowly heat it to 325 °C in a muffle furnace for 1 h over 200 min;

[0047] 2. After cooling, take out the above composite powder and sieve it through a 300-mesh micro sieve to obtain the TPM composite powder;

[0048] 3. Take 0.5 g of the TPM composite powder in 10 ml of n-hexane, add 0.5 g of PDMS and 0.05 g of the corresponding curing agent, and stir at room temperature for 1 h to obtain the photothermal superhydrophobic coating;

[0049] 4. Take 5 g of epoxy resin E51 and 5 g of 5618 curing agent in 5 ml of absolute ethanol to obtain the EP coating, spin-coat it onto a glass slide with the spin-coating parameters of 1000 r / min and a spin-coating time of 10 s, and place the glass slide at room temperature for 20 min to obtain a semi-cured EP coating;

[0050] 5. Use a high-atomization spray gun with a caliber of 0.8, select a pressure of 0.2 MPa and a spraying distance of 10 cm, and evenly spray the photothermal superhydrophobic coating onto the semi-cured EP coating;

[0051] 6. Take 2 g of HDTMS and configure it into a 4 wt% HDTMS solution in absolute ethanol, and immerse the coating obtained in step 5 in the HDTMS solution for 2 h;

[0052] 7. Place the soaked coating in an 80 °C oven for 2 h to complete drying and curing, and finally obtain the TPM photothermal superhydrophobic coating, denoted as TPM@glass.

[0053] SEM images of the TPM composite powder prepared by this method at different magnifications are as Figure 1 shown. It can be seen that the smaller nano-TiN particles coat the larger PTFE particles, and carbon nanotubes can be seen interspersed among them in the high-magnification images. The SEM image of the TPM coating prepared by this method is as Figure 2 shown. It can be seen the rough structure on the coating surface, which is the source of the superhydrophobic property of the coating. Figure 3 shows the 3D morphology and wetting property test diagrams of the TPM coating. Its surface roughness reaches 14.757 μm, the WCA is about 158°, and the WSA is about 3.5°. Figure 4 shows the infrared emissivity test photo of the TPM coating. Its infrared emissivity is 0.82, which is less than that of general carbon-based photothermal materials, and this will reduce the heat loss of the coating during the light-induced heating process. Figure 5 shows the photothermal property test diagram of the TPM coating. The test condition is a light intensity of 1 kW·m 2 . After 10 min of light-induced heating, the temperature of the TPM coating stabilizes near 139.6 °C. As a control group, the surface temperature of the glass slide is only 67.5 °C. The TPM coating has excellent photothermal conversion performance, and the TPM coating quickly heats up to 90% (125.6 °C) of the equilibrium temperature within 185 s. Figure 6 shows the infrared photos of the TPM during the light-induced heating process. Figure 7 shows the 1-h light-induced heating process of the TPM. The temperature on the coating surface stabilizes near the equilibrium temperature (139.6 °C), demonstrating the good photothermal stability of the TPM coating. Figure 8 shows the passive anti-icing performance of the TPM coating. Place the TPM coating on a refrigeration platform that can be cooled to -20 °C, place a 10-μL droplet on the coating, and record the photos and time during the freezing process of the droplet. Use the glass slide as the control group. The droplet on the surface of the glass slide shows a diffused shape and starts to freeze at the 12th second and completely freezes at the 25th second. The droplet on the TPM coating surface shows a spherical shape, and its freezing time is the longest. It starts to freeze at the 205th second and completely freezes at the 264th second. Its start-freezing time and complete-freezing time are significantly extended by 1608% and 956% respectively compared with the glass slide. Figure 9 shows the photothermal de-icing performance of the TPM coating. The frozen droplet in the figure is formed by fully freezing a 10-μL droplet on the refrigeration platform. Under the condition of no light, the frost around the frozen droplet takes about 25 s to completely melt, and the frozen droplet completely melts at the 100th second. Under 0.5 kW·m 2Under light illumination, the frost around the frozen droplet takes 14 s to completely melt, and the frozen droplet completely melts at the 50th s. Figure 10 The superhydrophobic self-cleaning performance of the TPM coating is demonstrated, and the dust pollutants on the surface are easily carried away by the rolling droplets.

[0054] Example 2:

[0055] Referring to Example 1, the difference from Example 1 is that in the preparation process of this example, the dosages of PTFE, TiN, and hydroxylated MWCNTs are 2 g, 3 g, and 0.3 g respectively, and the remaining methods remain unchanged. As shown in the example, the WCA of the coating slightly decreases to about 155°, as Figure 12 shown.

[0056] Comparative Example 1:

[0057] Referring to Example 1, the difference from Example 1 is that in the preparation process of this comparative example, hydroxylated MWCNTs are not added during the preparation of the composite powder, and only 1 g of PTFE and 1 g of TiN are added, and the remaining methods remain unchanged as in Example 1. Tested according to the test method in Example 1, it is found that the obtained coating does not have superhydrophobic performance but still has photothermal performance, as Figure 11 shown. The WCA of the coating is only 115°, and under the light illumination of 1 kW·m 2 the equilibrium temperature of the coating is 122.6 °C.

[0058] Comparative Example 2:

[0059] Referring to Example 1, the difference from Example 1 is that in the preparation process of this comparative example, the dosages of PTFE, TiN, and hydroxylated MWCNTs are 3 g, 2 g, and 0.2 g respectively, and the remaining methods remain unchanged as in Example 1. After testing, it is found that the WCA of the coating is about 144°, as Figure 12 shown.

[0060] Comparative Example 3:

[0061] Referring to Example 1, the difference from Example 1 is that in the preparation process of this comparative example, the dosages of PTFE, TiN, and hydroxylated MWCNTs are 1 g, 1 g, and 0.1 g respectively, and the remaining methods remain unchanged as in Example 1. After testing, it is found that the WCA of the coating is about 148°, as Figure 12 shown.

[0062] It can be seen from Example 1 and Comparative Example 1 that the incorporation of MWCNTs can not only greatly improve the photothermal conversion performance of the composite powder, but also greatly enhance the hydrophobic performance of the final coating; it can be seen from Example 1, Example 2 and Comparative Example 2 and Comparative Example 3 that the ratio of PTFE, TiN and MWCNTs affects the hydrophobic performance of the final coating, and an appropriate ratio can endow the coating with both excellent superhydrophobic performance and photothermal performance.

Claims

1. A method for preparing a photothermal super-hydrophobic coating with high-efficiency photothermal conversion performance, characterized in that The steps include: Step 1: Place a certain amount of PTFE powder, TiN powder and hydroxylated MWCNTs in a container and stir to mix them evenly; Step 2: Place the mixed powder obtained in step 1 in a crucible and place it in a muffle furnace, heat it to 325°C and maintain it for 1 hour to obtain a composite powder, which is recorded as TPM; Step 3: Sieve the TPM composite powder using a micron sieve; Step 4: Coat epoxy resin on the surface of the substrate and semi-curing it for later use; Step 5: Take the TPM composite powder in n-hexane, add PDMS and the corresponding curing agent, stir evenly with magnetic force to obtain TPM coating; Step 6: Use a 0.8-caliber high-atomization spray gun to spray the TPM coating onto the surface of the substrate prepared in step 4. The air pressure is about 0.2 kPa and the spraying distance is about 10 cm. Spray until the black powder completely and evenly covers the surface of the substrate. Step 7: Place the sprayed substrate in the hydrophobic modifier solution for 2 hours; Step 8: Take out the modified coating and place it in an oven for drying and curing to obtain a photothermal super-hydrophobic coating; In step 1, the mass ratio of PTFE powder, TiN powder and hydroxylated MWCNTs is 3-1:3-2:0.1-0.3; the particle size of the PTFE powder is 500nm-1μm, and the particle size of the TiN powder is 50-100nm; In step 2, the time for the muffle furnace to heat up from 25°C to 325°C is ≥150min.

2. The preparation method according to claim 1, characterized in that: The mass ratio of PTFE powder, TiN powder and hydroxylated MWCNTs is 3:3:0.1, 1:3:0.2, 1:2:0.3 or 2:3:0.

3.

3. The preparation method according to claim 2, characterized in that: The mass ratio of PTFE powder, TiN powder and hydroxylated MWCNTs is 1:3:0.

2.

4. The preparation method according to claim 1, characterized in that: In step 3, the pore size of the micron sieve is 200-500 mesh.

5. The preparation method according to claim 1, characterized in that: In step 5, 0.5-1 g of TPM composite powder is added to 10 mL of n-hexane, followed by adding 0.5 g of PDMS and 0.05 g of the corresponding curing agent, and magnetic stirring is performed to obtain a TPM coating.

6. The preparation method according to claim 1, characterized in that: In step 7, the hydrophobic modifier is any one of hexadecyltrimethoxysilane, KH560 or KH570, and the concentration of the hydrophobic modifier solution is 2-6 wt %.

7. The preparation method according to claim 1, characterized in that: In step 8, the curing temperature is 80-100° C. and the curing time is 2-4 hours.

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