A polyimide / polydimethylsiloxane superhydrophobic composite coating and a preparation method thereof

Abstract

The application discloses a polyimide / polydimethylsiloxane super-hydrophobic composite coating and a preparation method thereof. The preparation method comprises the following steps: firstly, under the protection of nitrogen, diamine monomers and polydimethylsiloxane are dissolved in an organic solvent, then dianhydride monomers are added in batches, and stirring reaction is carried out to prepare a polyimide / polydimethylsiloxane prepolymer; an organic dispersion liquid of modified GO is added into the polyimide / polydimethylsiloxane prepolymer to prepare a composite bottom layer slurry; the composite bottom layer slurry is coated on the surface of a substrate, and after a programmed thermal imidization treatment, a composite bottom layer is prepared; an adhesive and a suspension of fluorinated modified SiO2 are coated on the surface of the composite bottom layer, and after room temperature solidification, the polyimide / polydimethylsiloxane super-hydrophobic composite coating is prepared. The composite coating has good long-acting corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of development of super-hydrophobic coatings and relates to a polyimide / polydimethylsiloxane super-hydrophobic composite coating and a preparation method thereof. Background Art

[0002] The superhydrophobic phenomenon in nature is ubiquitous, such as the self-cleaning effect of lotus leaves. Studies have found that the reason for the superhydrophobicity of lotus is that the surface of lotus leaves has a large number of micro-nanostructured "papillaries" and paraffin substances, which together constitute the superhydrophobic effect of lotus leaves. Inspired by the lotus leaf effect, many scientific researchers have prepared superhydrophobic anti-corrosion and antifouling coatings based on the characteristics of superhydrophobic surface construction. This coating has a significant repulsive effect on various liquids. By reducing the contact area, it can delay or prevent corrosive ions from passing through the coating to reach the surface of the substrate and cause electrochemical corrosion. In recent years, superhydrophobic coatings have important application prospects in the fields of self-cleaning, anti-icing, anti-corrosion, oil-water separation, and anti-bacterial adhesion. At present, there are two conditions for constructing superhydrophobic coatings: one is that the surface of the material has low surface energy substances, and the other is that the surface has a rough structure. For example, Liu et al. used a method combining etching process and high-temperature calcination to prepare a superhydrophobic surface on a copper sheet. They found that when the etching time was 20 hours and the calcination temperature was 340°C, the micro-nanostructure on the surface of the copper sheet was relatively rough. They then used stearic acid to hydrophobize it and finally obtained a superhydrophobic surface with a contact angle of 157.6°C.

[0003] At present, traditional composite coatings rely on their excellent physical barrier effect to have anti-corrosion properties, but there is a common problem of serious lack of long-term anti-corrosion performance. Moreover, this type of coating itself does not have self-cleaning and anti-fouling properties, and it is difficult to meet the anti-corrosion and anti-fouling requirements in complex environments. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a polyimide / polydimethylsiloxane super-hydrophobic composite coating and a preparation method thereof, thereby solving the technical problem of insufficient long-term anti-corrosion performance of the composite coating in the prior art.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating comprises the following steps:

[0007] S1: Under nitrogen protection, dissolving diamine monomer and polydimethylsiloxane in an organic solvent, then adding dianhydride monomer in batches, stirring and reacting to prepare a polyimide / polydimethylsiloxane prepolymer;

[0008] S2: adding an organic dispersion of modified GO to the polyimide / polydimethylsiloxane prepolymer to prepare a composite base layer slurry, coating the composite base layer slurry on the surface of a substrate, and subjecting the substrate to a thermal imidization treatment to obtain a composite base layer; the modifying agent for modifying the GO comprises at least one of POSS, a silane coupling agent, a chain alkylamine, and a chain alkyl isocyanate, wherein the number of carbon atoms on the chain alkylamine and the chain alkyl isocyanate is 7 to 18;

[0009] S3: coating the adhesive and the suspension of fluorinated modified SiO2 on the surface of the composite base layer, and curing at room temperature to obtain the polyimide / polydimethylsiloxane super-hydrophobic composite coating.

[0010] Preferably, the polydimethylsiloxane accounts for 10% to 30% of the total mass of the diamine monomer and the dianhydride monomer.

[0011] Preferably, the diamine monomer is a fluorine-containing diamine monomer and / or the dianhydride monomer is a fluorine-containing dianhydride monomer.

[0012] Preferably, in the modified GO, the mass ratio of the modifying agent to GO is 1 wt% to 6.5 wt%.

[0013] Preferably, in step S2, the mass fraction of the modified GO in the polyimide / polydimethylsiloxane prepolymer is 0.01 wt% to 1.50 wt%.

[0014] Preferably, the thickness of the composite bottom layer is 40-50 μm.

[0015] Preferably, the preparation process of the fluorinated modified SiO2 is: adding sodium methylsiliconate to a dispersion of SiO2 particles, stirring evenly, adding 1H,1H,2H,2H-perfluorodecyltriethoxysilane and tetraethoxysilane, stirring and reacting at room temperature to obtain the fluorinated modified SiO2; the SiO2 particles include at least one of a particle size of 7~500nm and 2~20μm; when the SiO2 particles have a particle size of 7~500nm and 2~20μm, the mass percentage of SiO2 particles with a particle size of 7~500nm is 70%~85%, and the mass percentage of SiO2 particles with a particle size of 2~20μm is 15%~30%.

[0016] Preferably, in the suspension of the adhesive and fluorinated modified SiO2, the fluorinated modified SiO2 accounts for 0.01 wt% to 1.50 wt% of the mass of the adhesive.

[0017] Preferably, in step S3, before applying the adhesive and the suspension of fluorinated modified SiO2 on the surface of the composite base layer, a PU intermediate layer is applied on the surface of the composite base layer, and then the adhesive and the suspension of fluorinated modified SiO2 are applied.

[0018] A polyimide / polydimethylsiloxane super-hydrophobic composite coating is prepared by the above method; the contact angle of the composite coating is 153-162°, and after a 90-day neutral salt spray test, the low-frequency impedance value of the composite coating is 9.81×10 9 Ω⋅cm 2。

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The present invention discloses a preparation method of a polyimide / polydimethylsiloxane super-hydrophobic composite coating. The method comprises the following steps: firstly synthesizing a polyimide / polydimethylsiloxane prepolymer by solution polycondensation, then adding modified GO to the prepolymer to obtain a composite bottom slurry, wherein the modifying agent of the modified GO comprises at least one of POSS, a silane coupling agent, a chain alkylamine and a chain alkyl isocyanate, wherein the number of carbon atoms on the chain alkyl group in the chain alkylamine and the chain alkyl isocyanate is 7 to 18; in the bottom solution, the polyimide has good hydrophobicity and good moldability, while the polydimethylsiloxane has a strong adhesion to the metal substrate. The method comprises the following steps: first, applying a suspension of adhesive and fluorinated modified SiO2 on the surface of the composite bottom layer, and then curing at room temperature to obtain the polyimide / polydimethylsiloxane super-hydrophobic composite coating. The adhesive and the suspension of fluorinated modified SiO2 are used as the top coating. The fluorinated modified SiO2 has good super-hydrophobicity, which can effectively reduce the contact area between the coating and the aqueous solution and enhance the corrosion ion blocking effect. At the same time, the super-hydrophobic layer of the top layer has quasi-isotropic characteristics and excellent mechanical properties, which makes the coating more durable. By constructing a modified GO / polyimide / polydimethylsiloxane composite bottom layer and a fluorinated modified SiO2 surface layer, a multilayer superhydrophobic coating was successfully constructed. The anti-corrosion and anti-fouling mechanism of the multilayer superhydrophobic coating is as follows: first, "series" layer-by-layer barrier, the bottom composite coating and the surface superhydrophobic coating constitute a series barrier, which increases the penetration path of corrosive ions and forms a "maze effect" to effectively enhance the corrosion resistance; secondly, the superhydrophobic surface is anti-corrosion and anti-fouling, and the micro / nanostructure of the superhydrophobic surface reduces the contact area with the corrosive medium by forming an "air cushion effect" on its surface, greatly enhancing the anti-corrosion performance, and the low surface energy characteristics of the top superhydrophobic coating reduce the adhesion of stains, playing an anti-fouling and self-cleaning role; finally, through the effective combination of surface interface technology and bionic strategies, a multilayer composite superhydrophobic coating is constructed to obtain a superhydrophobic coating with excellent mechanical properties.

[0021] Furthermore, the diamine monomer is a fluorine-containing diamine monomer and / or the dianhydride monomer is a fluorine-containing dianhydride monomer, which can effectively improve the hydrophobicity of the composite coating and enhance its long-term corrosion resistance.

[0022] Furthermore, in step S3, before coating the adhesive and the suspension of fluorinated modified SiO2 on the surface of the composite bottom layer, a PU intermediate layer is coated on the surface of the composite bottom layer, and then the adhesive and the suspension of fluorinated modified SiO2 are coated. Here, the PU intermediate layer serves as an intermediate transition bonding layer, which allows the super-hydrophobic layer of the top layer to be embedded in the intermediate layer, effectively improving the adhesion between the bottom layer and the top layer, and effectively improving the long-term anti-corrosion performance of the composite coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 IR spectrum of the fluorinated polyimide / polydimethylsiloxane composite coating prepared in Example 1 of the present invention;

[0025] Figure 2 The corrosion performance of the fluorinated polyimide / polydimethylsiloxane composite coating prepared in Example 1 of the present invention is shown in FIG. 1 , wherein the left figure is a Nyquist plot and the right figure is a Bode plot;

[0026] Figure 3 The corrosion performance of the polyimide (non-fluorinated) / polydimethylsiloxane composite coating prepared in Example 3 of the present invention is shown in FIG. 1 , wherein the left figure is a Nyquist plot and the right figure is a Bode plot;

[0027] Figure 4 The corrosion performance of the polyimide (non-fluorinated) / polydimethylsiloxane composite coating prepared in Example 5 of the present invention is shown in FIG. 1 , wherein the left figure is a Nyquist plot and the right figure is a Bode plot;

[0028] Figure 5 The corrosion resistance of the double-layer super-hydrophobic coating prepared in Example 1 of the present invention is shown in the figure on the left, where the Nyquist plot is shown and the Bode plot is shown on the right.

[0029] Figure 6 The microscopic morphologies (a-c) and contact angles (d) of the double-layer super-hydrophobic coating prepared in Example 1 of the present invention at different magnification ratios are shown. In Figure (d), CA on the right is the static contact angle, and SA is the rolling contact angle. DETAILED DESCRIPTION

[0030] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0032] All features, such as values, amounts, contents, and concentrations, described herein as numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0033] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0034] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0035] The present invention provides a method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating, comprising the following steps:

[0036] S1: Under nitrogen protection, diamine monomer and polydimethylsiloxane are dissolved in an organic solvent, and then dianhydride monomer is added in batches, stirred and reacted, and a polyimide / polydimethylsiloxane prepolymer with a solid content of 10% to 50% is prepared by solution condensation;

[0037] The polydimethylsiloxane accounts for 10% to 30% of the total mass of the diamine monomer and the dianhydride monomer.

[0038] The diamine monomers are 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 4,4'-(1,4-phenylenedioxy)dianiline, 4,4'-diaminodiphenylmethane, 1,4-phenylenediamine, N-phenyl-1,4-phenylenediamine, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]propane, 2,2-[4-(2- 4,4'-Bis(2-trifluoromethyl-4-aminophenoxy)phenyl]hexafluoropropane, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)benzophenone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)diphenyl sulfone, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)diphenyl sulfide, 4,4'-bis(2-trifluoromethyl-4-aminophenoxy)biphenyl, 1,3-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 1,4-bis(2-trifluoromethyl-4-aminophenoxy)benzene, 1,3-bis[3'-trifluoromethyl-4'(4''-aminophenoxy)phenyl]benzene, 1,3-bis(4-amino-2-trifluoromethylphenoxy)benzene, 4,4''-bis(aminophenoxy)-3,3'-trifluoromethylterphenyl, 4 , one or more of 4-bis[3'-trifluoromethyl-4'(4''-aminophenoxy)phenyl]biphenyl.

[0039] The dianhydride monomers are 4,4'-oxydiphthalic anhydride, 4,4'-(4,4'-isopropyldiphenoxy)bis(phthalic anhydride), pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, triphenyl ether dianhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 1,3- One or more of bis(3,4-dicarboxyphenoxy)phthalic dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, and 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride.

[0040] The diamine monomer is preferably a fluorine-containing diamine monomer and / or the dianhydride monomer is a fluorine-containing dianhydride monomer.

[0041] The organic solvent is a high boiling point organic solvent, which may be at least one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO) and diacetone alcohol.

[0042] S2: 0.1-10 mg of modified GO is added to 1.0 mL of an organic solvent, wherein the organic solvent is at least one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO) and diacetone alcohol, and then ultrasonically dispersed for 10-60 min to obtain an organic dispersion of modified GO, i.e., a functional filler pre-dispersion liquid. The organic dispersion of modified GO is then added to the polyimide / polydimethylsiloxane prepolymer and ultrasonically dispersed for 15-60 min to obtain a composite bottom layer slurry with a solid content of 8%-20%, i.e., a polyimide / polydimethylsiloxane prepolymer composite slurry containing modified GO. The composite bottom layer slurry is coated on the surface of the substrate. At room temperature, the sprayed sample is placed for 1-2 hours to achieve surface drying. After programmed thermal imidization treatment, a thickness of 1-150 μm, preferably 10-100 μm, is obtained. The composite base layer, i.e., a polyimide / polydimethylsiloxane composite coating, has a thickness of 40-50 μm, preferably 38-42 μm. The thermal imidization process comprises volatilizing a large amount of solvent at 80-135°C, preferably curing at 135°C for 3 hours, then completing the imidization at 200-300°C, performing preliminary imidization at 200°C for 2 hours, and completing more thorough imidization at 240-300°C depending on the imide system, curing for approximately 1 hour.

[0043] The modification reagent for modifying GO includes at least one of POSS, a silane coupling agent, a chain alkylamine, and a chain alkyl isocyanate, wherein the number of carbon atoms on the chain alkylamine and the chain alkyl isocyanate is 7 to 18;

[0044] The POSS is an oligomeric silsesquioxane, which may include any one of monoamino oligomeric silsesquioxane, bisamino oligomeric silsesquioxane and octaamino oligomeric silsesquioxane;

[0045] The silane coupling agent includes 1H,1H,2H,2H-perfluorodecyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, 3-aminopropylmethyltrimethoxysilane, 3-aminopropylmethyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, dodecyltrimethoxysilane and hexadecyltrimethoxysilane;

[0046] The chain alkane includes an alkylamine having 7 to 18 carbon atoms, preferably, dodecylamine or hexadecylamine.

[0047] In the modified GO, the modifier is chemically grafted to the GO surface in a covalent bond manner;

[0048] In the modified GO, the mass ratio of the modifying agent to GO is 1 wt% to 6.5 wt%. Preferably, the mass ratio of the modifying agent to GO is 2.5 wt% to 3.0 wt%.

[0049] The mass fraction of the modified GO in the polyimide / polydimethylsiloxane prepolymer is 0.01 wt % to 1.50 wt %, preferably 0.20 wt % to 0.80 wt %, and more preferably 0.25 wt % to 0.60 wt %.

[0050] The coating process here can be spraying or brushing. During the spraying process, the composite base layer slurry is ultrasonically dispersed and then sprayed onto the metal substrate or part surface under 0.2 MPa oil-free compressed air or compressed nitrogen. The number of spraying times is 10 to 30 times, preferably 15 to 20 times. The diameter of the spraying equipment can be 0.5 mm. The substrate can be a metal substrate, such as electrogalvanized steel sheet, 304 stainless steel sheet, cold-rolled sheet, galvanized steel sheet, aluminum alloy sheet, aluminum-magnesium alloy sheet, or metal parts of any shape.

[0051] In addition, when the composite base layer is coated on the surface of the substrate, the substrate is first pretreated, and the pretreatment includes degreasing, rust removal and ultrasonic cleaning.

[0052] The coating thickness was measured using a MINITEST 1100 coating thickness gauge.

[0053] Taking hexadecylamine as an example, the chain alkylamine-modified GO process described above can be as follows: 1.2 g of graphene oxide powder is evenly dispersed in 2.4 L of deionized water and sonicated for 4 h (250 W power). 6 mmol of hexadecylamine (HDA) and 360 mL of anhydrous ethanol are then sonicated in a conical flask for 30 min and slowly added to the graphene oxide suspension. The mixture is then stirred under reflux for 24 h. The GO is then washed three times by centrifugation with excess ethanol and then distilled water. After freeze-drying, the GO is dried in a vacuum oven at 40°C overnight to evaporate any residual solvent, yielding the chain alkylamine-modified GO.

[0054] S3: Applying a suspension of adhesive and fluorinated modified SiO2 on the surface of the composite base layer, and curing at room temperature for 24 hours to obtain the polyimide / polydimethylsiloxane superhydrophobic composite coating. In this step, the curing temperature and time depend on the properties of the adhesive.

[0055] Super-hydrophobic SiO2 powder, i.e., fluorinated SiO2, is prepared by hydrolysis and condensation. The specific preparation process is as follows: sodium methylsiliconate is added to a dispersion of SiO2 particles, stirred evenly, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane and tetraethoxysilane are added. The reaction is stirred at room temperature to obtain the fluorinated SiO2. The SiO2 particles include at least one of a particle size of 7 to 500 nm and a particle size of 2 to 20 μm. When the SiO2 particles have a particle size of 7 to 500 nm and a particle size of 2 to 20 μm, the mass percentage of the SiO2 particles with a particle size of 7 to 500 nm is 70% to 85%, and the mass percentage of the SiO2 particles with a particle size of 2 to 20 μm is 15% to 30%. The particles of 7 to 500 nm can also be a mixture of particles of multiple particle sizes.

[0056] The fluorinated modified SiO2 accounts for 0.01 wt% to 1.50 wt% of the mass of the adhesive, more preferably 0.30 wt% to 1.50 wt%, and more preferably 0.45 wt% to 1.20 wt%.

[0057] The preparation process of the adhesive and the suspension of fluorinated modified SiO2 is as follows:

[0058] The adhesive is dissolved in a low-boiling-point solvent, and a semi-solid modified SiO2 containing anhydrous ethanol is added under continuous magnetic stirring. After continued stirring, a suspension of the adhesive and the fluorinated modified SiO2 is obtained, i.e., a uniform superhydrophobic suspension;

[0059] Here, the low boiling point solvent is at least one of butyl acetate, ethyl acetate, acetone, furan, anhydrous ethanol, anhydrous methanol, etc.

[0060] The adhesive herein is at least one of polyolefins, epoxies and acrylates.

[0061] In step S3, before applying the adhesive and the suspension of fluorinated modified SiO2 on the surface of the composite bottom layer, a PU intermediate layer is applied on the surface of the composite bottom layer, and then the adhesive and the suspension of fluorinated modified SiO2 are applied.

[0062] A polyimide / polydimethylsiloxane super-hydrophobic composite coating is prepared by the above method; the composite coating has a contact angle of 153° to 162°, and still has good anti-corrosion performance after a 90-day neutral salt spray test, and its low-frequency impedance value is as high as 9.81 × 10 9 Ω⋅cm 2 , the composite coating still has superhydrophobic properties after more than 100 sandpaper abrasions and more than 80 tape glass mechanical tests.

[0063] The synthesized polyimide / polydimethylsiloxane super-hydrophobic composite coating has the intrinsic hydrophobicity of polyimide. This is because polydimethylsiloxane has hydrophobicity and strong corrosion resistance. Polyimide can be non-fluorine-containing or fluorine-containing. At the same time, fluorine-containing polyimide and polydimethylsiloxane are low-surface energy materials. The prepolymer has good interfacial compatibility and strong bonding force with components such as fillers and adhesives. Polydimethylsiloxane has excellent bonding strength with metal substrates and low water absorption. This polymer coating has excellent and long-lasting anti-corrosion and anti-fouling properties.

[0064] In addition, the polyimide / polydimethylsiloxane of the present invention has a molecular structure combining a polyimide hard segment and a polydimethylsiloxane soft segment, and has excellent mechanical properties, which are the key factors determining the service life and performance of the anti-corrosion and anti-fouling coating.

[0065] The polyimide / polydimethylsiloxane prepared in this invention combines the anti-corrosion and anti-fouling properties of polyimide / polydimethylsiloxane. The barrier effect of modified GO and the shielding effect of the polymer resin synergistically enhance the coating's corrosion resistance. A superhydrophobic coating is created by spraying a suspension prepared from a commercial adhesive and superhydrophobically modified SiO2 (F-SiO2) onto the composite coating surface, imparting antifouling and self-cleaning properties. This method boasts a simple process and is easily scalable.

[0066] The present invention discloses a preparation method and application of a polyimide / polydimethylsiloxane super-hydrophobic composite coating, belonging to the technical field of organic coatings. The preparation method comprises: synthesizing a polyimide / polydimethylsiloxane prepolymer; modifying a graphene oxide (GO) functional filler, wherein the modifying reagent comprises oligomeric silsesquioxane (POSS), a silane coupling agent, a long-chain alkane, etc.; pre-dispersing a certain amount of the functional filler according to the mass content of the functional filler and the polyimide / polydimethylsiloxane for 10 to 30 minutes, mixing it into the polyimide / polydimethylsiloxane prepolymer slurry, and continuing ultrasonic dispersion for 10 to 50 minutes to obtain a composite solution; spraying the obtained functionalized graphene oxide polyimide / polydimethylsiloxane prepolymer mixed solution onto a metal substrate or part surface through a spraying process, and then sequentially performing room temperature pre-curing and high-temperature programmed temperature control to prepare a composite coating. Furthermore, a super-hydrophobic layer is constructed on the surface of the obtained composite coating to obtain a double-layer or "sandwich" super-hydrophobic composite coating. That is, fluorinated silicone or long-chain alkane silicone is used to perform super-hydrophobic modification on micro-nano SiO2 of one particle size or different particle sizes to obtain super-hydrophobic nano-SiO2 powder; secondly, an olefin adhesive of a preset mass ratio is dissolved in a low-boiling point ester-based solvent, and the modified SiO2 semi-solid containing anhydrous ethanol is added to the adhesive-containing solution and stirred to obtain a super-hydrophobic suspension, and the same spraying process is further used to spray the super-hydrophobic SiO2 suspension on the surface of the composite coating to prepare a super-hydrophobic composite coating, and after curing, a hydrophobic coating with a double-layer or "sandwich" structure of polyimide / polydimethylsiloxane composite layer as the base layer is obtained.

[0067] The present invention uses a polyimide / polydimethylsiloxane composite coating as the bottom layer to prepare a double-layer or "sandwich" structure super-hydrophobic composite coating. The prepared bottom composite layer has strong adhesion to the substrate and the top super-hydrophobic layer and the composite layer, or introduces an intermediate transition layer to prepare a "sandwich" structure super-hydrophobic coating. The design strategy of this super-hydrophobic coating has the advantages of being easy to prepare over a large area and having practical engineering application prospects. The preparation process is not limited by the metal substrate and the shape of the part, the coating is highly operable, the components of the coating are simple, and it is easy to construct and apply.

[0068] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0069] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0070] Example 1

[0071] (1) Preparation of GO

[0072] Pre-oxidation of graphite powder: In a 250-ml three-necked flask equipped with a mechanical stirrer, add 30 ml of concentrated sulfuric acid to a 250-ml three-necked flask in a 25°C water bath. While stirring, add 5 g of natural flake graphene, 3 g of potassium persulfate, and 8 g of phosphorus pentoxide. Slowly raise the temperature to 60°C for oxidation for 3 h, then cool to 25°C and continue oxidation for 5 h. At the end of the experiment, filter and wash the filtrate until it is neutral. Dry the product in a vacuum desiccator at 50°C for later use.

[0073] Under 25 ℃ water bath conditions, 360 ml concentrated sulfuric acid and 40 ml phosphoric acid were added to a 500 ml three-necked flask equipped with a mechanical stirrer. 3 g of pre-oxidized graphene was added under rapid stirring. After mixing evenly, 18 g of potassium permanganate powder was added within 2 h. The temperature of the reaction system was kept constant and then heated to 50 ℃ and maintained at this temperature for 1 2 h before cooling to 25 ℃. The reaction liquid was then poured into 400 ml of ice water under stirring, and 30% hydrogen peroxide solution was added dropwise to make the system bright yellow and no bubbles were generated. An equal volume of 10% dilute hydrochloric acid solution was added and the system was placed in a dialysis bag for dialysis until the dialysate was free of SO4. 2- The ions stop dialyzing and then centrifugation is performed to concentrate the ions. The concentrate is freeze-dried to obtain GO.

[0074] (2) Preparation of single NH2-POSS modified graphene oxide (POSS-GO):

[0075] 350 mg of graphene oxide, 5.0 g of NH2-POSS, 100 mg of dicyclohexylcarbodiimide, and 50 mL of tetrahydrofuran were accurately weighed and dissolved in a 250 mL single-necked flask. The mixture was ultrasonicated for 30 min. The dispersion was then refluxed for 48 h, followed by removal of the solvent by rotary evaporation and heat treatment at 120°C for 12 h to obtain the product, labeled POSS-GO. This product was dissolved in 50 mL of tetrahydrofuran and precipitated in 500 mL of methanol. This experiment was repeated three times to remove unreacted NH2-POSS. The final product was then filtered through a 0.22 μm organic filter membrane, dried under vacuum at 80°C, and stored for later use.

[0076] (3) Synthesis of fluorinated polyimide / polydimethylsiloxane prepolymer:

[0077] Under mechanical stirring and nitrogen protection, 3.885 g of 2,2-bis(4-aminophenyl)hexafluoropropane and 2.5 g of low molecular weight polydimethylsiloxane were dissolved in 55 g of DMAc. 5.18 g of 4, 4'-(hexafluoroisopropylidene)diphthalic anhydride was added in batches at a constant temperature of 40 °C. After stirring for 6 h, the temperature was raised to 80 °C and the reaction was terminated for 2 h to obtain a fluorinated polyimide / polydimethylsiloxane prepolymer (solid content of 20 wt%).

[0078] (4) Preparation of fluorinated polyimide / polydimethylsiloxane composite coating: 4.0 mg of POSS-GO functional filler was added to 4 mL of DMAc and ultrasonically dispersed for 10 min. Then, it was added to 10 g of fluorinated polyimide / polydimethylsiloxane prepolymer and further dispersed for 30 min to obtain a composite mixed solution. The composite solution was sprayed on the surface of the substrate and subjected to a program of thermal imidization at 135 (3 h), 200 (1 h), 280 (1 h), and 300 (1 h) to obtain a composite coating with a thickness of approximately 45 ± 5 μm.

[0079] (5) Preparation of a double-layer super-hydrophobic coating: A double-layer super-hydrophobic coating was prepared on the surface of the composite coating in step (4). Specifically, 1.2 g of POA adhesive and 1.0 g of F-SiO2 were dispersed in a mixed solution of butyl acetate and anhydrous ethanol. The mixture was ultrasonically dispersed for 15 min and magnetically stirred for 30 min before being sprayed onto the surface of the composite coating to prepare a double-layer super-hydrophobic coating. The super-hydrophobic layer had a thickness of approximately 55 μm. Finally, the final super-hydrophobic coating was obtained by curing at room temperature for 24 h.

[0080] The preparation process for F-SiO2 is as follows: At room temperature, 4 g of SiO2 nanoparticles of varying sizes (2.4 g of 15 nm SiO2, 0.8 g of 30 nm SiO2, and 0.8 g of 5 μm SiO2, with mass contents of 60%, 20%, and 20%, respectively) were weighed, mixed with 100 mL of anhydrous ethanol and 20 mL of deionized water. The mixture was stirred at 500 rpm for 10 minutes, then sonicated for 10 minutes. 3.0 g of sodium methylsiliconate was added and stirring continued for 10 minutes. Finally, 750 μL of 1H,1H,2H,2H-perfluorodecyltriethoxysilane and 180 μL of tetraethoxysilane were added to the mixture. The mixture was allowed to react at room temperature for 4 hours to ensure complete hydrolysis and condensation. After the reaction, the product was centrifuged at 10,000 rpm for 10 minutes, washed with anhydrous ethanol, and centrifuged three times. The resulting product was then placed in a vacuum chamber at 60°C for 12 hours. Finally, fluorinated SiO2 nanoparticles were obtained, denoted by F-SiO2.

[0081] Example 2

[0082] (1) Preparation of GO

[0083] Pre-oxidation of graphite powder: In a 250-ml three-necked flask equipped with a mechanical stirrer, add 30 ml of concentrated sulfuric acid to a 250-ml three-necked flask in a 25°C water bath. While stirring, add 5 g of natural flake graphene, 3 g of potassium persulfate, and 8 g of phosphorus pentoxide. Slowly raise the temperature to 60°C for oxidation for 3 h, then cool to 25°C and continue oxidation for 5 h. At the end of the experiment, filter and wash the filtrate until it is neutral. Dry the product in a vacuum desiccator at 50°C for later use.

[0084] Under 25 ℃ water bath conditions, 360 ml concentrated sulfuric acid and 40 ml phosphoric acid were added to a 500 ml three-necked flask equipped with a mechanical stirrer. 3 g of pre-oxidized graphene was added under rapid stirring. After mixing evenly, 18 g of potassium permanganate powder was added within 2 h. The temperature of the reaction system was kept constant and then heated to 50 ℃ and maintained at this temperature for 1 2 h before cooling to 25 ℃. The reaction liquid was then poured into 400 ml of ice water under stirring, and 30% hydrogen peroxide solution was added dropwise to make the system bright yellow and no bubbles were generated. An equal volume of 10% dilute hydrochloric acid solution was added and the system was placed in a dialysis bag for dialysis until the dialysate was free of SO4. 2- The ions stop dialyzing and then centrifugation is performed to concentrate the ions. The concentrate is freeze-dried to obtain GO.

[0085] (2) γ-Methacryloxypropyltrimethoxysilane (KH570) modified graphene oxide: 500 mg of GO and 50 g of anhydrous ethanol were added to a 250 mL single-necked flask and ultrasonicated for 30 min to obtain a dispersion. Subsequently, 3 g of KH570 was added to the dispersion and refluxed for 24 h. The experiment was terminated. The product was washed three times with deionized water and anhydrous ethanol alternately and dried at 80°C for 24 h to obtain KH570-modified graphene oxide, which was labeled KH570-GO.

[0086] (3) Synthesis of polyimide (non-fluorinated) / polydimethylsiloxane prepolymer: Under mechanical stirring and nitrogen protection, 1.64 g of 4,4'-diaminodiphenyl ether and 1.8 g of low molecular weight polydimethylsiloxane were dissolved in 50 g of DMAc. 5.32 g of 4,4'-(4,4'-isopropyldiphenyloxy)bis(phthalic anhydride) was added in batches at a constant temperature of 40°C. After stirring for 5 h, the temperature was raised to 70°C and the reaction was continued for 2 h to terminate the experiment. The polyimide / polydimethylsiloxane prepolymer (solid content of 20 wt.%) was obtained. Prepolymers with different polydimethylsiloxane contents were prepared using the same method.

[0087] (4) Preparation of polyimide (non-fluorinated) / polydimethylsiloxane composite coating: 4.0 mg of KH570-GO functional filler was added to 4 mL of DMAc and ultrasonically dispersed for 10 min. Then, it was added to 10 g of polyimide / polydimethylsiloxane prepolymer and further dispersed for 30 min to obtain a composite mixed solution. The composite solution was sprayed on the surface of the substrate and subjected to a program of thermal imidization at 135 (3 h), 200 (1 h), 280 (1 h), and 300 (1 h) to obtain a composite coating with a thickness of approximately 45 ± 5 μm.

[0088] (5) Preparation of a double-layer super-hydrophobic coating: A double-layer super-hydrophobic coating was prepared on the surface of the composite coating prepared in step (4). Specifically, 1.2 g of POA adhesive and 1.0 g of F-SiO2 were dispersed in a mixed solution of butyl acetate and anhydrous ethanol. The mixture was ultrasonically dispersed for 15 min and magnetically stirred for 30 min before being sprayed onto the surface of the composite coating to prepare a double-layer super-hydrophobic coating. The super-hydrophobic layer had a thickness of approximately 55 μm. Finally, the final super-hydrophobic coating was obtained after curing at room temperature for 24 h.

[0089] The preparation process of F-SiO2 is referred to Example 1.

[0090] Example 3

[0091] The difference from Example 1 is that PU is sprayed onto the surface of the composite coating prepared in step (4) as an intermediate transition layer, and then a mixed suspension of POA adhesive and F-SiO2 is sprayed onto the surface of the intermediate transition layer. After curing at room temperature for 24 hours, a "sandwich" structure super-hydrophobic coating is obtained. The thickness of the prepared intermediate transition layer is 10±5 μm, and the thickness of the super-hydrophobic layer (i.e., the mixed layer of POA adhesive and F-SiO2) is 40±5 μm.

[0092] Example 4

[0093] The difference from Example 2 is that PU is sprayed on the surface of the composite coating prepared in step (4) as an intermediate transition layer, and then a mixed suspension of POA adhesive and F-SiO2 is sprayed on the surface of the intermediate transition layer. After curing at room temperature for 24 hours, a "sandwich" structure super-hydrophobic coating is obtained. The thickness of the prepared intermediate transition layer is 10±5 μm, and the thickness of the super-hydrophobic layer (i.e., the mixed layer of POA adhesive and F-SiO2) is 40±5 μm.

[0094] Example 5

[0095] Preparation of a fluorinated polyimide / polydimethylsiloxane composite coating: 4.0 mg of KH570-GO functional filler was added to 4 mL of DMAc and ultrasonically dispersed for 10 minutes. This was then added to 10 g of a fluorinated polyimide / polydimethylsiloxane prepolymer and dispersed for a further 30 minutes to obtain a composite mixed solution. This composite solution was sprayed onto the substrate surface and subjected to a thermal imidization process at 135°C (3 h), 200°C (1 h), 280°C (1 h), and 300°C (1 h) to obtain a composite coating with a thickness of approximately 45 ± 5 μm.

[0096] In order to explore the performance of the composite coating prepared by the present invention, the following characterization tests were performed:

[0097] According to GB / T6458.86 standard, the anti-corrosion, anti-fouling and self-cleaning performance of the composite coating prepared by the present invention was tested and analyzed. Specifically, at 5.0 wt % NaCl solution, and the anti-corrosion performance of the coating was tested by electrochemical impedance spectroscopy at different intervals. The test frequency range was 10 -2 ~10 5 Hz, 10 mV amplitude sinusoidal disturbance. Z / Simp-Win software was used to fit and analyze the equivalent circuit. The antifouling performance of the coating was tested by applying different stains to the surface of the coating, then rinsing it with water droplets while the coating was slightly tilted at a certain angle. The test results are as follows:

[0098] in, Figure 1This is the infrared spectrum of the fluorinated polyimide / polydimethylsiloxane composite coating prepared in Example 1 of the present invention. As can be seen from the figure, the infrared spectrum at 2965 cm -1 The absorption peak at 1250 cm is attributed to the asymmetric stretching vibration of -CH3. -1 、795 cm -1 The peaks at 1000 cm are attributed to the bending vibration and stretching vibration of Si-CH3. -1 to 1100 cm -1 The strong peak at 1778 cm corresponds to the stretching vibration of Si-O-Si bond. -1 The absorption peaks at 1720 cm-1 are characteristic peaks of asymmetric and symmetric carbonyl stretching vibrations in the imine ring. FT-IR results indicate that the FPI-PDMS / POSS-GO composite coating was successfully prepared.

[0099] Figure 2 The corrosion performance of the fluorinated polyimide / polydimethylsiloxane composite coating prepared in Example 1 of the present invention is shown in the figure. As can be seen from the figure, the |Z| of the fluorinated polyimide / polydimethylsiloxane composite coating before the salt spray corrosion test is conducted. 0.01 HZ The value is 1.21 × 10 11 Ω∙cm 2 .

[0100] Figure 3 The corrosion performance of the polyimide (non-fluorine-containing) / polydimethylsiloxane composite coating prepared in Example 2 of the present invention is shown in the figure. The |Z| 0.01 HZ The value is 1.18 × 10 11 Ω∙cm 2 .

[0101] Figure 4 The corrosion performance of the fluorinated polyimide / polydimethylsiloxane composite coating prepared in Example 5 of the present invention is shown in the figure. As can be seen from the figure, the |Z| of the fluorinated polyimide / polydimethylsiloxane composite coating before the salt spray corrosion test is conducted. 0.01 HZ The value is 1.27 × 10 11 Ω∙cm 2 .

[0102] Figure 5 The corrosion resistance of the double-layer super-hydrophobic coating prepared in Example 1 of the present invention is shown in the figure. The |Z| 0.01 HZ The value is 1.37 × 10 11 Ω∙cm 2 .

[0103] Figure 6The microscopic morphology and contact angle of the double-layer super-hydrophobic coating prepared in Example 1 of the present invention are shown in FIG. Figure 6 (a) (b) (c) are the microscopic morphologies of the super-hydrophobic coating. It can be seen from the figures that the surface of the super-hydrophobic coating is rough; Figure 6 The static contact angle shown in (d) reaches 162.2° and the dynamic contact angle is 4.6°, indicating good hydrophobic function.

[0104] Example 6

[0105] A method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating comprises the following steps:

[0106] S1: Under nitrogen protection, diamine monomer and polydimethylsiloxane are dissolved in an organic solvent, and then dianhydride monomer is added in batches, stirred and reacted, and a polyimide / polydimethylsiloxane prepolymer with a solid content of 10% is synthesized by solution condensation; the polydimethylsiloxane accounts for 10% of the total mass of the diamine monomer and the dianhydride monomer.

[0107] S2: 0.1 mg of modified GO was added to 1.0 mL of organic solvent and then ultrasonically dispersed for 10 minutes to obtain an organic dispersion of modified GO, i.e., a functional filler pre-dispersion. The organic dispersion of modified GO was then added to the polyimide / polydimethylsiloxane prepolymer and ultrasonically dispersed for 15 minutes to obtain a composite base layer slurry with a solid content of 8%, i.e., a polyimide / polydimethylsiloxane prepolymer composite slurry containing modified GO. The composite base layer slurry was coated on the surface of the substrate. At room temperature, the sprayed sample was left for 1 hour to dry on the surface. After a programmed thermal imidization treatment, a composite base layer with a thickness of 1 μm was obtained, i.e., a polyimide / polydimethylsiloxane composite coating. The thermal imidization process involves evaporating a large amount of solvent at 80°C and then completing the imidization at 200°C.

[0108] In the modified GO, the mass ratio of the modifying agent to GO is 1 wt %, and the mass fraction of the modified GO in the polyimide / polydimethylsiloxane prepolymer is 0.01 wt %.

[0109] S3: Coating a PU intermediate layer on the surface of the composite bottom layer, and then coating the surface of the PU intermediate layer with a suspension of adhesive and fluorinated modified SiO2, and curing at room temperature for 24 hours to obtain the polyimide / polydimethylsiloxane super-hydrophobic composite coating. In this step, the curing temperature and time depend on the properties of the adhesive. The fluorinated modified SiO2 accounts for 0.01wt% of the adhesive mass.

[0110] Example 7

[0111] A method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating comprises the following steps:

[0112] S1: Under nitrogen protection, diamine monomer and polydimethylsiloxane are dissolved in an organic solvent, and then dianhydride monomer is added in batches, stirred and reacted, and a polyimide / polydimethylsiloxane prepolymer with a solid content of 50% is synthesized by solution condensation; the polydimethylsiloxane accounts for 30% of the total mass of the diamine monomer and dianhydride monomer.

[0113] S2: 10 mg of modified GO was added to 1.0 mL of organic solvent and ultrasonically dispersed for 60 minutes to obtain an organic dispersion of modified GO, i.e., a functional filler pre-dispersion. The modified GO organic dispersion was then added to the polyimide / polydimethylsiloxane prepolymer and ultrasonically dispersed for 60 minutes to obtain a composite base layer slurry with a solid content of 20%, i.e., a polyimide / polydimethylsiloxane prepolymer composite slurry containing modified GO. The composite base layer slurry was coated on the surface of the substrate. The sprayed sample was left to stand for 2 hours at room temperature to allow the surface to dry. After a programmed thermal imidization treatment, a composite base layer with a thickness of 150 μm, i.e., a polyimide / polydimethylsiloxane composite coating, was obtained. The thermal imidization process involves evaporating a large amount of solvent at 135°C and then completing the imidization at 300°C.

[0114] In the modified GO, the mass ratio of the modifying agent to GO is 6.5 wt %, and the mass fraction of the modified GO in the polyimide / polydimethylsiloxane prepolymer is 1.50 wt %.

[0115] S3: A PU intermediate layer is applied to the surface of the composite bottom layer, and then a suspension of an adhesive and fluorinated modified SiO2 is applied to the surface of the PU intermediate layer. After curing at room temperature for 24 hours, the polyimide / polydimethylsiloxane super-hydrophobic composite coating is obtained. In this step, the curing temperature and time depend on the properties of the adhesive. Wherein, the fluorinated modified SiO2 accounts for 1.50wt% of the adhesive mass.

[0116] Example 8

[0117] A method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating comprises the following steps:

[0118] S1: Under nitrogen protection, diamine monomer and polydimethylsiloxane are dissolved in an organic solvent, and then dianhydride monomer is added in batches, stirred and reacted, and a polyimide / polydimethylsiloxane prepolymer with a solid content of 30% is synthesized by solution condensation; the polydimethylsiloxane accounts for 20% of the total mass of the diamine monomer and dianhydride monomer.

[0119] S2: 5 mg of modified GO was added to 1.0 mL of organic solvent and ultrasonically dispersed for 30 minutes to obtain an organic dispersion of modified GO, i.e., a functional filler pre-dispersion. The organic dispersion of modified GO was then added to the polyimide / polydimethylsiloxane prepolymer and ultrasonically dispersed for 40 minutes to obtain a composite base layer slurry with a solid content of 15%, i.e., a polyimide / polydimethylsiloxane prepolymer composite slurry containing modified GO. The composite base layer slurry was coated on the surface of the substrate. The sprayed sample was allowed to stand for 1.5 hours at room temperature to achieve surface drying. After a programmed thermal imidization treatment, a composite base layer with a thickness of 80 μm, i.e., a polyimide / polydimethylsiloxane composite coating, was obtained. The thermal imidization process involves evaporating a large amount of solvent at 100°C and then completing the imidization at 250°C.

[0120] In the modified GO, the mass ratio of the modifying agent to GO is 3 wt %, and the mass fraction of the modified GO in the polyimide / polydimethylsiloxane prepolymer is 1.0 wt %.

[0121] S3: A PU intermediate layer is applied to the surface of the composite bottom layer, and then a suspension of an adhesive and fluorinated modified SiO2 is applied to the surface of the PU intermediate layer. After curing at room temperature for 24 hours, the polyimide / polydimethylsiloxane super-hydrophobic composite coating is obtained. In this step, the curing temperature and time depend on the properties of the adhesive. Wherein, the fluorinated modified SiO2 accounts for 1wt% of the adhesive mass.

[0122] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating, characterized in that: The following steps are involved: S1: Under nitrogen protection, dissolving a diamine monomer and polydimethylsiloxane in an organic solvent, then adding a dianhydride monomer in batches, stirring and reacting, to prepare a polyimide / polydimethylsiloxane prepolymer; the polydimethylsiloxane accounts for 10% to 30% of the total mass of the diamine monomer and the dianhydride monomer; S2: adding an organic dispersion of modified graphene oxide to the polyimide / polydimethylsiloxane prepolymer to prepare a composite bottom layer slurry, coating the composite bottom layer slurry on the surface of a substrate, and subjecting the composite bottom layer to a program thermal imidization treatment to prepare a composite bottom layer; the modifying agent of the modified graphene oxide is at least one of POSS, a chain alkylamine, and a chain alkyl isocyanate, wherein the number of carbon atoms on the chain alkylamine and the chain alkyl isocyanate is 7 to 18; the POSS comprises any one of monoamino oligomeric silsesquioxane, bisamino oligomeric silsesquioxane, and octaamino oligomeric silsesquioxane; the mass fraction of the modified graphene oxide in the polyimide / polydimethylsiloxane prepolymer is 0.01 wt% to 1.50 wt%; S3: Coating a PU intermediate layer on the surface of the composite bottom layer, and then coating a mixed suspension of an adhesive and fluorinated modified SiO2 on the surface of the PU intermediate layer. After curing at room temperature, the polyimide / polydimethylsiloxane superhydrophobic composite coating is obtained.

2. The method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating according to claim 1, wherein The diamine monomer is a fluorine-containing diamine monomer and / or the dianhydride monomer is a fluorine-containing dianhydride monomer.

3. The method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating according to claim 1, wherein The thickness of the composite bottom layer is 40-50 μm.

4. The method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating according to claim 1, wherein The preparation process of the fluorinated modified SiO2 is as follows: sodium methylsiliconate is added to a dispersion of SiO2 particles, and after stirring evenly, 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane and tetraethoxysilane are added, and the mixture is stirred and reacted at room temperature to obtain the fluorinated modified SiO2; the SiO2 particles include at least one of SiO2 particles with a particle size of 7 to 500 nm and SiO2 particles with a particle size of 2 to 20 μm; when the SiO2 particles are SiO2 particles with a particle size of 7 to 500 nm and SiO2 particles with a particle size of 2 to 20 μm, the mass percentage of SiO2 particles with a particle size of 7 to 500 nm is 70% to 85%, and the mass percentage of SiO2 particles with a particle size of 2 to 20 μm is 15% to 30%.

5. The method for preparing a polyimide / polydimethylsiloxane super-hydrophobic composite coating according to claim 1, wherein In the mixed suspension of the adhesive and fluorinated modified SiO2, the fluorinated modified SiO2 accounts for 0.01 wt% to 1.50 wt% of the mass of the adhesive.

6. A polyimide / polydimethylsiloxane super-hydrophobic composite coating, characterized in that: The composite coating is prepared by the method according to any one of claims 1 to 5; the contact angle of the composite coating is 153 to 162°, and after a 90-day neutral salt spray test, the low-frequency impedance value of the composite coating is 9.81 × 10 9 Ω•cm 2 .

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