Chromium-based compound-silane composite super-hydrophobic coating based on molecular anchoring and preparation method of chromium-based compound-silane composite super-hydrophobic coating

Abstract

The invention provides a chromium-based compound-silane composite super-hydrophobic coating based on molecular anchoring and a preparation method thereof.The preparation method comprises the following steps that a mixed solution serves as anodic oxidation liquid, an aluminum alloy sheet serves as an anode, an inert electrode serves as a cathode, anodic oxidation treatment is carried out, and the chromium-based compound-silane composite super-hydrophobic coating is obtained; the preparation method comprises the following steps: treating an aluminum alloy sheet, forming a porous aluminum oxide layer on the surface of the aluminum alloy sheet after the treatment is completed, depositing a micro-nano structure layer on the aluminum oxide layer by using an active hydroxyl solution, spin-coating a silane solution on the micro-nano structure layer, and drying to obtain the composite super-hydrophobic coating. According to the chromium-based compound-silane composite super-hydrophobic coating based on molecular anchoring, a molecular anchoring technology is introduced, covalent bonds are formed between coatings through anchoring groups such as hydroxyl and carboxyl, and the interface bonding strength between the coatings is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and in particular relates to a chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring and a preparation method thereof. Background Art

[0002] As a lightweight structural material, aluminum alloy has been widely used in the fields of aerospace, transportation, and construction engineering due to its comprehensive advantages such as low density, high specific strength, excellent processing performance, and controllable cost. However, in the actual service environment, the surface of aluminum alloy is prone to electrochemical corrosion due to the attachment of corrosive ions such as Cl - etc., resulting in the degradation of material properties. By constructing a superhydrophobic protective coating through material surface treatment technology, the wetting and adsorption behavior of corrosive media on the material surface can be effectively reduced, and the material is endowed with dual protective properties of self-cleaning and corrosion resistance.

[0003] There are various existing methods for preparing superhydrophobic coatings, mainly including laser etching method, chemical etching method, electrochemical deposition method, sol-gel method, etc. However, there are the following defects: 1. The mechanical durability of the coating is insufficient, and it is prone to local peeling under external stress, resulting in the loss of hydrophobic performance; 2. The chemical stability of the coating is poor, and it is difficult to maintain corrosion resistance for a long time. 3. The preparation process is complex and the cost is relatively high. Summary of the Invention

[0004] In view of this, the present invention aims to overcome the defects in the prior art and proposes a chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring and a preparation method thereof.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] The present invention provides a preparation method of a chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring, including the following steps: using a mixed solution as an anodizing solution, using an aluminum alloy sheet as an anode, using an inert electrode as a cathode, performing anodizing treatment, and after the treatment is completed, a porous alumina layer is formed on the surface of the aluminum alloy sheet, using an active hydroxyl solution to deposit a micro-nano structure layer on the alumina layer, spin-coating a silane solution on the micro-nano structure layer, and after drying, obtaining the composite superhydrophobic coating;

[0007] The active hydroxyl solution contains a chromium-containing compound with a concentration of 0.1-0.3 mol / L. The inert electrode is a graphite electrode or a platinum electrode.

[0008] Further, the mixed solution contains oxalic acid and citric acid with a molar ratio of 2-3:1.5-2.

[0009] Further, the chromium-containing compound is at least one of chromium chloride, chromium nitrate, or chromium sulfate.

[0010] Further, the silane solution is an ethanol solution containing silane molecules, and the volume concentration of the silane molecules is 5-60%.

[0011] Preferably, the silane solution is an ethanol solution containing silane molecules, and the volume concentration of the silane molecules is 5-30%.

[0012] Further, the number of carbon atoms of the silane molecules is 8-18; the silane molecules contain methoxy groups and / or ethoxy groups.

[0013] Further, the current density in the anodization treatment step is 80-100 mA·cm-2, and the time is 15-25 minutes.

[0014] Further, the deposition step is specifically to continuously treat for 20-30 minutes under the condition of a constant temperature water bath at 65-75°C.

[0015] Further, the rotation speed in the spin coating step is 1500-2500 r·min-1, and the time is 20-30 seconds.

[0016] Further, the temperature in the drying step is 100-150°C, and the time is 30-90 min.

[0017] The present invention also provides a molecular-anchored chromium-based compound-silane composite superhydrophobic coating prepared by using the above preparation method.

[0018] Figure 1 It is a schematic diagram of a molecular-anchored chromium-based compound-silane composite superhydrophobic coating. This system mainly consists of four functional layers: 1. The first layer is a low surface energy modification layer (silane modification layer). There are a large number of low surface energy molecules in the layer. These molecules form a dense monolayer through the directional arrangement of the terminal alkyl chains, endowing the material with superhydrophobic properties; 2. The second layer is a chemical deposition layer (micro-nano structure layer), which contains a large number of surface-active hydroxyl groups. These hydroxyl groups can serve as sites to anchor the upper layer of hydrophobic molecules, and the two are tightly connected through a bonding effect; 3. The third layer is an alumina layer. The rough and porous micro-nano structure provides space for the growth of the second layer. This structure also improves the surface roughness and enhances the hydrophobic performance of the coating; 4. The fourth layer is an aluminum alloy substrate, which provides mechanical support for the overall structure.

[0019] The present invention first adjusts the surface morphology of aluminum alloy through anodic oxidation, providing a more favorable attachment basis for the subsequent deposition of chromium and chromium compounds, increasing the specific surface area, and enabling more uniform and firm deposition. Then, the chromium hydroxyl bond is grafted with silane to closely link the silane with the interface, significantly improving the bonding strength between the coating and the substrate, and effectively improving the adhesion and durability of the coating. At the same time, it is necessary for the silane molecule to have a long alkyl chain, such as octadecyltrimethoxysilane, hexadecyltrimethoxysilane, etc. The long alkyl chain can reduce the surface energy and improve the hydrophobicity. Moreover, the silane molecule usually contains hydrolyzable groups, such as methoxy, ethoxy, etc. These groups can undergo dehydration condensation reactions with the hydroxyl groups on the substrate surface after hydrolysis to achieve the firm bonding of silane on the substrate surface. Among them, the deposition of chromium not only changes the surface thermal conductivity, endows the coating with anti-icing characteristics, but also can achieve the hydrophobic function through grafting with silane, integrating multiple functions into one, and enabling the coating to have a wider application scenario and better comprehensive performance.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring described in the present invention introduces the molecular anchoring technology, and uses anchoring groups such as hydroxyl and carboxyl to form covalent bonds between the coatings, significantly enhancing the interfacial bonding strength between the coatings. Through the superhydrophobic coating system strengthened by molecular anchoring, it not only maintains the hydrophobic characteristics of low-surface-energy substances, but also constructs a stable "molecular bridge" interface through chemical bonding, providing a new path for solving the coating failure problem, and having important engineering value for improving the environmental adaptability of aluminum alloy components.

[0022] The chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring described in the present invention constructs a superhydrophobic coating with both mechanical durability and chemical stability on the aluminum alloy surface through chemical bonding, and can achieve the synergistic effect among functions such as corrosion resistance, anti-icing and self-cleaning on the aluminum alloy surface, providing a solution for metal surface protection. Brief Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring described in the embodiment of the present invention.

[0024] Description of the Reference Numerals:

[0025] 1. Silane modification layer; 2. Micro-nano structure layer; 3. Alumina layer; 4. Aluminum alloy substrate. Detailed Embodiments

[0026] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0027] The present invention will be described in detail below with reference to the examples.

[0028] Example 1

[0029] A preparation method of a chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring includes the following steps:

[0030] First, prepare a mixed aqueous solution of 0.3 mol·L-1 oxalic acid and 0.2 mol·L-1 citric acid, and inject it into the electrolytic cell. Using a constant current anodic oxidation process, with an aluminum alloy sheet as the anode and a platinum electrode as the cathode, anodic oxidation treatment is carried out at a current density of 100 mA·cm-2 to obtain a uniform porous alumina layer. Subsequently, prepare a solution containing 0.2 mol·L-1 chromium chloride, and continuously treat it under a constant temperature water bath condition of 70±2 °C for 25 min to achieve the construction of micro-nano structures on the material surface. Then, adopt the spin-coating process, spin-coat an ethanol solution of 5% (volume concentration) hexadecyltrimethoxysilane at a rotation speed of 2000 r·min-1 for 30 s to form a functional liquid film with uniform thickness. Finally, place it in a drying oven and perform a constant temperature drying treatment at 150 °C for 1 h. After drying, a superhydrophobic film is obtained, with its hardness increased by 25% and the contact angle being 164°.

[0031] Comparative Example 1

[0032] A preparation method of a chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring includes the following steps:

[0033] First, prepare a mixed aqueous solution of 0.3 mol·L-1 oxalic acid and 0.2 mol·L-1 citric acid, and inject it into the electrolytic cell. Using a constant current anodic oxidation process, with an aluminum alloy sheet as the anode and a platinum electrode as the cathode, anodic oxidation treatment is carried out at a current density of 100 mA·cm-2 to obtain a uniform porous alumina layer. Subsequently, prepare a solution containing 0.2 mol·L-1 nickel chloride, and continuously treat it under a constant temperature water bath condition of 70±2 °C for 25 min to achieve the construction of micro-nano structures on the material surface. Then, adopt the spin-coating process, spin-coat an ethanol solution of 5% (volume concentration) hexadecyltrimethoxysilane at a rotation speed of 2000 r·min-1 for 30 s to form a functional liquid film with uniform thickness. Finally, place it in a drying oven and perform a constant temperature drying treatment at 150 °C for 1 h. After drying, a superhydrophobic film is obtained.

[0034] Comparative Example 2

[0035] A preparation method of a molecular-anchored silane composite superhydrophobic coating, comprising the following steps:

[0036] First, prepare a mixed aqueous solution of 0.3 mol·L-1 oxalic acid and 0.2 mol·L-1 citric acid, and inject it into the electrolytic cell. Using the constant current anodic oxidation process, with an aluminum alloy sheet as the anode and a platinum electrode as the cathode, perform anodic oxidation treatment at a current density of 100 mA·cm-2 to obtain a uniform porous alumina layer. Then, adopt the spin-coating process, spin-coat an ethanol solution of 5% (volume concentration) hexadecyltrimethoxysilane at a rotation speed of 2000 r·min-1 for 30 s to form a functional liquid film with a uniform thickness. Finally, place it in an oven and perform constant-temperature drying treatment at 150 °C for 1 h to obtain a superhydrophobic film after drying.

[0037] Comparative Example 3

[0038] A preparation method of a molecular-anchored chromium-based compound-silane composite superhydrophobic coating, comprising the following steps:

[0039] First, prepare a mixed aqueous solution of 0.3 mol·L-1 oxalic acid and 0.2 mol·L-1 citric acid, and inject it into the electrolytic cell. Using the constant current anodic oxidation process, with an aluminum alloy sheet as the anode and a platinum electrode as the cathode, perform anodic oxidation treatment at a current density of 100 mA·cm-2 to obtain a uniform porous alumina layer. Subsequently, prepare a solution containing 0.2 mol·L-1 chromium chloride, and continuously treat it under the condition of a constant temperature water bath at 70 ± 2 °C for 25 min to achieve the construction of micro-nano structures on the material surface. Then, adopt the spin-coating process, spin-coat an ethanol solution of 5% (volume concentration) vinylsilane at a rotation speed of 2000 r·min-1 for 30 s to form a functional liquid film with a uniform thickness. Finally, place it in an oven and perform constant-temperature drying treatment at 150 °C for 1 h to obtain a superhydrophobic film after drying.

[0040] Comparative Example 4

[0041] A preparation method of a molecular-anchored chromium-based compound composite superhydrophobic coating, comprising the following steps:

[0042] First, prepare a mixed aqueous solution of 0.3 mol·L-1 oxalic acid and 0.2 mol·L-1 citric acid, and inject it into the electrolytic cell. Using the constant current anodic oxidation process, with an aluminum alloy sheet as the anode and a platinum electrode as the cathode, perform anodic oxidation treatment at a current density of 100 mA·cm-2 to obtain a uniform porous alumina layer. Subsequently, prepare a solution containing 0.2 mol·L-1 chromium chloride, and continuously treat it under the condition of a constant temperature water bath at 70 ± 2 °C for 25 min to achieve the construction of micro-nano structures on the material surface. Finally, place it in an oven and perform constant-temperature drying treatment at 150 °C for 1 h to obtain a superhydrophobic film after drying.

[0043] The superhydrophobic films obtained in Example 1 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0044] Table 1 Test Results

[0045]

[0046] As shown in Table 1, in Comparative Example 1, when the deposition solution was CrCl3 solution, the deposited layer exhibited a villous micro-nano structure. After this structure was modified with silane, there were more air cavities on the surface, which could reduce the contact area between water and the surface and increase the contact angle. At the same time, due to the chromium-rich compounds in the chromium deposition layer, such as CrOOH, Cr2O3, etc. Cr 3+ and O 2- are combined by strong ionic bonds and partial covalent bonds, enhancing the structural rigidity and the deposited layer has high hardness. When the solution was changed to NiCl2 solution, Ni2 + and O 2- are combined by ionic bonds with weak bond strength, and the hardness of the prepared coating is reduced. Due to the use of the molecular anchoring method with pre-implanted hydroxyl groups, the interfacial bonding strength is high, and the superhydrophobic contact angle can maintain 96.9% of the initial value after 30 days of immersion in brine.

[0047] In Comparative Example 2, due to the loss of the barrier effect of the deposited layer, the surface hardness is reduced. In addition, due to the absence of the villous micro-nano structure to optimize the surface roughness, the hydrophobic contact angle after modification also decreases. In Example 1 and Comparative Example 1, both used the molecular anchoring method with pre-implanted hydroxyl groups, and the interfacial bonding strength was high. After 30 days of immersion in brine, the superhydrophobic contact angles could maintain 96.9% and 92.3% of the initial values, showing a relatively high level. However, Comparative Example 2 did not use the molecular anchoring method, and the interfacial bonding force was weak. After 30 days of immersion in brine, the water contact angle of the hydrophobic coating only maintained 84.3% of the initial value, and the hydrophobic performance decreased significantly.

[0048] In Comparative Example 3, we replaced hexadecyltrimethoxysilane with vinylsilane. Vinylsilane has poor hydrophobicity and cannot effectively reduce the surface energy, and the water contact angle decreases significantly. Since the silane layer is thin, its contribution to the coating hardness is weak, so the hardness value changes little compared with Example 1, only slightly decreasing.

[0049] In Comparative Example 4, we did not use silane for modification, and the surface did not have hydrophobicity. Instead, due to the large amount of surface-active hydroxyl groups in the deposited layer, its surface showed hydrophilicity, and the liquid spread into a thin film on the surface. At this time, the measured contact angle reached the lowest. In terms of hardness, since the silane layer is thin and its contribution to the coating hardness is weak, the hardness value decreased slightly compared with Example 1.

[0050] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring, characterized in that: The method includes the following steps: using a mixed solution as the anodizing solution, using an aluminum alloy sheet as the anode, using an inert electrode as the cathode, and performing anodizing treatment. After the treatment, a porous alumina layer is formed on the surface of the aluminum alloy sheet. Then, an active hydroxyl solution is used to deposit a micro-nano structure layer on the alumina layer, and a silane solution is spin-coated on the micro-nano structure layer. After drying, the composite superhydrophobic coating is obtained. The active hydroxyl solution contains a chromium-containing compound with a concentration of 0.1 - 0.3 mol / L.

2. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, characterized in that: The mixed solution contains oxalic acid and citric acid with a molar ratio of 2 - 3:1.5 - 2.

3. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, wherein: The chromium-containing compound is at least one of chromium chloride, chromium nitrate, or chromium sulfate.

4. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, characterized in that: The silane solution is an ethanol solution containing silane molecules, and the volume concentration of the silane molecules is 5 - 60%.

5. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, wherein: The number of carbon atoms of the silane molecule is 8 - 18; the silane molecule contains methoxy groups and / or ethoxy groups.

6. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, wherein: The current density in the anodizing treatment step is 80 - 100 mA·cm-2, and the time is 15 - 25 minutes.

7. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, characterized in that: The deposition step is specifically to continuously treat for 20 - 30 minutes under the condition of a constant temperature water bath at 65 - 75 °C.

8. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, wherein: The rotation speed in the spin-coating step is 1500 - 2500 r·min-1, and the time is 20 - 30 seconds.

9. The preparation method of the chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring according to claim 1, characterized in that: The temperature in the drying step is 100 - 150 °C, and the time is 30 - 90 min.

10. A chromium-based compound-silane composite superhydrophobic coating based on molecular anchoring prepared by using the preparation method described in any one of claims 1 - 9.

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