A magnetoelectric synergistic loss type super-hydrophobic wave-absorbing coating and its preparation method

Abstract

The present application discloses a super-hydrophobic absorbing coating with magneto-electric synergistic loss and a preparation method thereof, belonging to the technical field of electromagnetic wave absorbing coatings. Low surface energy fluorinated silicon dioxide SiO2-F is grown on the surface of a lightweight iron MOF derivative D-MOF by an in-situ growth method, and the surface-modified hydrophobic absorbing filler is uniformly dispersed in a hydrophobic polyethersulfone PES and a (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP to obtain a lightweight super-hydrophobic absorbing coating with a magneto-electric synergistic loss mechanism. The coating has a maximum reflection loss of up to 24.9 dB, an effective absorption bandwidth of 5.2 GHz, and a water contact angle of 151.2°.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorbing coatings, and in particular to a magneto-electric cooperative loss type super-hydrophobic absorbing coating and a preparation method thereof. Background Art

[0002] Electromagnetic wave absorbing coatings are widely used in fields such as electromagnetic pollution prevention and control, multi-frequency electromagnetic compatibility, and equipment stealth technology, playing a vital role in national economic development and military defense construction. However, with the rapid advancement of wireless communication technology and the development of information-based and intelligent warfare methods, the requirements for electromagnetic wave absorbing coatings are becoming increasingly stringent. These coatings must not only be thin, light, wide, and strong, but also possess good environmental adaptability, such as excellent corrosion resistance, high temperature resistance, and self-cleaning properties.

[0003] Currently, commonly used electromagnetic wave absorbing coatings are composed of ferrite, carbonyl iron powder, and magnetic alloy powder as absorbing fillers, epoxy resin or acrylic resin as a binder, and additives and diluents to form a uniform dispersion, which is then applied to a metal substrate. Although magnetic metal powders and alloy powders have strong absorbing capabilities, their high density, susceptibility to oxidation, and corrosion resistance limit their application in absorbing coatings. In addition, conventional absorbers and adhesives lack hydrophobic and self-cleaning properties, requiring manual cleaning, which is not only time-consuming and labor-intensive, but also accelerates the aging of the absorbing coating. Therefore, some researchers have obtained hydrophobic absorbing fillers through absorber particle size control and surface modification, and hydrophobic absorbing coatings using hydrophobic resins.

[0004] For example, patent CN 118240428 A discloses a corrosion-resistant super-hydrophobic absorbing coating and a preparation method thereof, which is to spray an epoxy absorbing bottom layer and a fluorocarbon super-hydrophobic surface layer on a substrate in sequence. The present invention exhibits excellent super-hydrophobic properties through the synergistic effect of the epoxy absorbing bottom layer and the fluorocarbon super-hydrophobic surface layer. The excellent super-hydrophobic properties enable the absorbing coating to have excellent corrosion resistance and self-cleaning properties. It solves the problems existing in the existing absorbing coating technology, such as easy corrosion under salt spray environment, unsatisfactory corrosion resistance, limited absorbing performance, and no self-cleaning function. The absorbing coating of the present invention adopts a double-layer structure design of epoxy absorbing bottom layer and fluorocarbon super-hydrophobic surface layer. While the epoxy absorbing bottom layer exerts excellent absorbing performance through the multi-stage core-shell structure absorber, it can also improve the binding force of the fluorocarbon super-hydrophobic surface layer. On the one hand, the fluorocarbon super-hydrophobic surface layer exerts a protective effect through super-hydrophobic properties, thereby improving the corrosion resistance and self-cleaning properties of the absorbing coating. A mixture of titanium dioxide-coated magnetic absorber and epoxy resin is used as the absorbing base layer, and micro-nano graded titanium dioxide powder double-treated with fluorosilane is dispersed in fluorocarbon resin as the super-hydrophobic surface layer. This method requires the use of the absorbing base layer and the hydrophobic surface layer in combination to achieve the absorbing and hydrophobic effects. On the one hand, it increases the application cost and construction process, and on the other hand, it increases the equipment load.

[0005] Patent CN 116855120 A discloses a homogeneous, flexible, super-hydrophobic absorbing coating, its preparation method, and application. The coating utilizes organic-inorganic hybridization to modify the absorbing material, followed by a synergistic compounding of the modified absorber with a matrix resin. This method modifies the filler through an inverse vulcanization reaction, grafting sulfur radicals onto the absorber surface. Simultaneously, monomer encapsulation reduces the dielectric properties of the material and improves impedance mismatch. This modified absorber can participate well in the blending reaction with the matrix resin, increasing its compatibility with the resin matrix. In addition to good flexibility, excellent mechanical properties, and electromagnetic wave absorption capacity, the coating also exhibits certain super-hydrophobicity, low surface energy, and self-cleaning properties, reducing the effects of water or contaminants on the coating. By modifying traditional absorbers, the problems of self-agglomeration and impedance mismatch are improved. The modified absorber powder can be well dispersed in the resin and visually observed to be very uniform after curing. This homogeneous, flexible, super-hydrophobic, and absorbing coating exhibits excellent flexibility and mechanical properties, along with good resilience, making it suitable for diverse applications such as curved surfaces and complex-shaped equipment. The coating's smooth surface and excellent hydrophobicity, coupled with its low surface energy, reduces liquid retention and readily self-cleans when exposed to contaminants, reducing the likelihood of contaminant adhesion. This allows the coating to maintain its absorbing properties, cleanliness, and stability under varying conditions, resulting in a longer service life. While the coating exhibits excellent absorbing properties, its water contact angle is only 97.05°, indicating it lacks super-hydrophobic properties. Furthermore, the introduction of sulfur in this method accelerates corrosion of the metal substrate, significantly reducing the coating's service life.

[0006] In recent years, metal-organic framework (MOF) materials have attracted widespread attention due to their advantages, including high porosity, low density, large specific surface area, designable composition, and structural diversity. MOFs can be rationally engineered to possess topological structures and porosities by varying their organic ligands, allowing for the adjustment of particle sizes and dimensionality. The composition and structure of derivatives can be tuned by controlling the pyrolysis temperature. The resulting derivatives retain a well-defined porous structure and ultra-high specific surface area, facilitating multi-level scattering of electromagnetic waves. Iron-based MOFs, upon pyrolysis, form composites of magnetic metal oxides and porous carbon. Their rich heterogeneous interface structure, synergistic with the magnetic medium, exhibits excellent impedance matching characteristics and diverse loss mechanisms. Furthermore, their light weight and excellent resistance to harsh environments make them ideal electromagnetic wave absorbers. However, single iron-based MOF derivatives lack hydrophobic properties as absorbing fillers, necessitating surface modification and hydrophobic modification. Summary of the Invention

[0007] Technical problem to be solved: The purpose of the present invention is to overcome the technical problems existing in the prior art such as weak loss capacity, large mass and poor resistance to pollution of absorbing coatings. The present application provides a magneto-electric synergistic loss type super-hydrophobic absorbing coating and a preparation method thereof.

[0008] Technical solution: To achieve the above objectives, this application is implemented through the following technical solutions:

[0009] A method for preparing a magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating comprises the following steps:

[0010] The first step is the preparation of iron-based MOF derivatives: the iron salt and the organic complex are dissolved in deionized water in a molar ratio of 1:1, mixed evenly, and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven for reaction. After the reaction is completed, the precipitate is collected by centrifugation and washed three times with deionized water and ethanol alternately. The washed precipitate is dried in a vacuum drying oven for 24-48 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with an inert gas and a heating rate of 5°C / min to obtain an iron MOF derivative, which is recorded as D-MOF.

[0011] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water to form a homogeneous solution A; the silica sol is mixed with anhydrous ethanol to form a solution B, and the solution B is added dropwise to the homogeneous solution A, stirred at room temperature for 16-20 hours to completely hydrolyze it to obtain a mixed solution, and then fluorosilane is added to the mixed solution for hydrolysis reaction for 8 hours. The precipitate is collected by centrifugation and washed with anhydrous ethanol. The precipitate is repeated for three times and then vacuum dried to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, recorded as D-MOF@SiO2-F;

[0012] The third step is the preparation of the absorbing coating: polyethersulfone PES and polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP are mixed in a mass ratio of 1:3-6 as an adhesive, and D-MOF@SiO2-F is used as an absorbing filler. The adhesive and the absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes to obtain a dispersion, and then the dispersion is sprayed on a metal substrate with a spraying thickness controlled at 1.2-1.5 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0013] Preferably, the iron salt in the first step is FeCl3·6H2O, Fe2(SO4)3·5H2O or Fe(NO3)3·9H2O, and the organic complex is fumaric acid, dimethylimidazole or terephthalic acid.

[0014] Preferably, the oven temperature in the first step is 80-110° C., and the reaction time is 3-6 h; the vacuum drying oven temperature in the first step is 50-80° C.

[0015] Preferably, the inert gas in the first step is a protective gas, specifically nitrogen or argon, the pyrolysis temperature is 400-600° C., and the pyrolysis time is 30-60 min.

[0016] Preferably, the volume ratio of anhydrous ethanol to aqueous ammonia in the step of preparing the homogeneous solution A is (7-10):1, and the ratio of the mass g of the iron MOF derivative to the volume mL of the mixed solution of anhydrous ethanol and aqueous ammonia is 1:(40-60).

[0017] Preferably, the silica sol in the step of preparing solution B is one or more of tetraethoxysilane, triethoxysilane, dialkoxysilane, trialkoxysilane, and dimethyldialkoxysilane, and the volume ratio of the silica sol to anhydrous ethanol is 1:(1.3~4).

[0018] Preferably, the volume ratio of the homogeneous solution A to the solution B in the second step is (3-5):1.

[0019] Preferably, the fluorosilane in the second step is one or more of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and hexafluorobutylpropyltrimethoxysilane, and the volume ratio of the fluorosilane to the silica sol in the second step is 1:(8~12).

[0020] Preferably, the mass ratio of the adhesive to the absorbing filler in the third step is (3-7):(7-3), and the mass ratio of the total amount of the adhesive and the absorbing filler to anhydrous ethanol is 1:(8-12).

[0021] The present application also discloses a magneto-electric cooperative loss type super-hydrophobic wave-absorbing coating prepared by any of the above preparation methods.

[0022] The technical principle of the present invention is: D-MOF@SiO2-F electromagnetic wave absorbing filler with a core-shell structure is prepared by an in situ growth method. The MOF derivative in the core provides magnetoelectric synergistic loss function, and the low surface energy SiO2-F in the shell provides self-cleaning function; in addition, the rich low surface energy groups in the adhesive further enhance the hydrophobicity of the coating.

[0023] This application provides a magneto-electric cooperative loss super-hydrophobic wave-absorbing coating and a preparation method thereof, which has the following beneficial effects compared with the prior art:

[0024] 1. Iron-based metal-organic framework derivatives are used as electromagnetic wave absorbing fillers, which have the advantages of rich pores, low density, and large specific surface area. Fluorinated SiO2 is generated on the surface of the MOF derivative through a simple in situ growth method. This "D-MOF@SiO2-F" core-shell structure has rich heterogeneous interfaces. The large amount of carbon and magnetic metal oxides in the D-MOF provide strong magnetoelectric synergistic loss capacity, and the low surface energy of SiO2-F gives the filler excellent self-cleaning properties.

[0025] 2. During the co-curing process of D-MOF@SiO2-F with PES and PVDF-HFP copolymers, low-surface-energy groups are enriched, forming micro- / nanostructures with abundant papillary structures. The porous structure of D-MOF allows small molecules such as O2 and N2 in the air to enter its internal pore channels, forming a coating and effectively capturing surface air, forming a reliable anti-adhesion barrier. In addition, the stable air film prolongs the superhydrophobic life of the coating in harsh environments such as mechanical and chemical damage.

[0026] 3. PES and PVDF-HFP are used as binders in the coating. Hydrogen bonds are formed between the O atoms in PES and the F atoms in PVDF-HFP and the -OH groups on the substrate, providing strong adhesion for the coating. The D-MOF@SiO2-F nanorods are interlaced and stacked to form a multi-layered network structure. This organic / inorganic hybrid system gives the superhydrophobic film a certain structural stability, which can improve the mechanical strength and wear resistance of the coating.

[0027] 4. A lightweight super-hydrophobic absorbing coating with a magneto-electric synergistic loss mechanism was obtained. The maximum reflection loss of this coating can reach -24.9 dB, the effective absorption bandwidth is 5.2 GHz, and the water contact angle is 151.2°. DETAILED DESCRIPTION

[0028] In order to make the technical solutions, advantages and objectives of the present invention clearer and more specific, the present invention is described in detail below through specific embodiments. The embodiments are merely illustrative and do not limit the scope of protection of the patent of the present invention. Any non-essentially equivalent changes or adjustments made based on the above-mentioned invention content and spirit are within the scope of protection of the present invention.

[0029] Example 1: A method for preparing a magnetoelectric cooperative loss super-hydrophobic wave-absorbing coating, comprising the following steps:

[0030] The first step is the preparation of iron-based MOF derivatives: iron salt FeCl3·6H2O and organic complex fumaric acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven at 100°C for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The washed precipitate is dried in a vacuum drying oven at 60°C for 24 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 500°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0031] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol to ammonia water is 7:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:56 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 1:1.3, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, the volume ratio of homogeneous solution A to solution B is 3:1, and stirred at room temperature for 17 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0032] The third step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:3 as an adhesive, D-MOF@SiO2-F is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.2:0.8:10. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on a metal substrate with a spraying thickness of 1.35 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0033] Example 2: A method for preparing a magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating, comprising the following steps:

[0034] The first step is the preparation of iron-based MOF derivatives: iron salt FeCl3·6H2O and organic complex fumaric acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an 80°C oven to react for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The washed precipitate is dried in a vacuum drying oven at 60°C for 24 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 400°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0035] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol to ammonia water is 8:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:56 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 1:1.7, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, and the volume ratio of homogeneous solution A to solution B is 3:1. The mixture is stirred at room temperature for 16 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0036] The third step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:4 as an adhesive, D-MOF@SiO2-F is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.3:0.7:10. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on a metal substrate with a spraying thickness of 1.22 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0037] Example 3: A method for preparing a magnetoelectric cooperative loss super-hydrophobic wave-absorbing coating, comprising the following steps:

[0038] The first step is the preparation of iron-based MOF derivatives: iron salt Fe(NO3)3·9H2O and organic complex fumaric acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven at 100°C for 5 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The washed precipitate is dried in a vacuum drying oven at 70°C for 36 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 500°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0039] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol to ammonia water is 9:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:40 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 1:2, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, and the volume ratio of homogeneous solution A to solution B is 3.5:1. The mixture is stirred at room temperature for 18 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0040] The third step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:5 as an adhesive, D-MOF@SiO2-F is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.4:0.6:10. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on a metal substrate with a spraying thickness of 1.28 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0041] Example 4: A method for preparing a magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating, comprising the following steps:

[0042] The first step is the preparation of iron-based MOF derivatives: iron salt FeCl3·6H2O and organic complex fumaric acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven at 110°C for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The washed precipitate is dried in a vacuum drying oven at 70°C for 36 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 600°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0043] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol to ammonia water is 10:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:50 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 1:2.5, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, the volume ratio of homogeneous solution A to solution B is 4:1, and stirred at room temperature for 19 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0044] The third step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:6 as an adhesive, D-MOF@SiO2-F is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.7:0.3:10. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on a metal substrate with a spraying thickness of 1.39 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0045] Example 5: A method for preparing a magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating, comprising the following steps:

[0046] The first step is the preparation of iron-based MOF derivatives: iron salt FeCl3·6H2O and organic complex terephthalic acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in a 90°C oven to react for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The washed precipitate is dried in a vacuum drying oven at 70°C for 48 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 600°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0047] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol to ammonia water is 10:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:60 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 1:3, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, and the volume ratio of homogeneous solution A to solution B is 4.5:1. The mixture is stirred at room temperature for 20 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0048] The third step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:6 as an adhesive, D-MOF@SiO2-F is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.3:0.7:11. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on a metal substrate with a spraying thickness of 1.3 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0049] Example 6: A method for preparing a magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating, comprising the following steps:

[0050] The first step is the preparation of iron-based MOF derivatives: the iron salt Fe2(SO4)3·5H2O and the organic complex dimethylimidazole are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven at 100°C for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The washed precipitate is dried in a vacuum drying oven at 70°C for 48 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 500°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0051] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol to ammonia water is 10:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:60 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 1:4, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, and the volume ratio of homogeneous solution A to solution B is 5:1. The mixture is stirred at room temperature for 20 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0052] The third step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:6 as an adhesive, D-MOF@SiO2-F is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.3:0.7:12. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on a metal substrate with a spraying thickness of 1.21 mm. After drying and curing at 240°C, a magnetoelectric cooperative loss type superhydrophobic absorbing coating is formed.

[0053] Comparative Example 1: A method for preparing an absorbing coating, using 30% polyethersulfone (PES) and (polyvinylidene fluoride-hexafluoropropylene) copolymer (PVDF-HFP) as a binder and 70% Fe3O4 particles as an absorbing filler, ultrasonically dispersed for 30 minutes at a mass ratio of binder to absorber to anhydrous ethanol of 1:10, and then sprayed onto a metal substrate with a spraying thickness of 1.29 mm. After drying and curing at 240°C, a self-cleaning absorbing coating is formed.

[0054] Comparative Example 2: A method for preparing a radar absorbing coating, comprising the following steps:

[0055] The first step is the preparation of iron-based MOF derivatives: iron salt FeCl3·6H2O and fumaric acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven at 100°C for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The precipitate is dried in a vacuum drying oven at 60°C for 24 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 500°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0056] The second step is the preparation of the absorbing coating: polyethersulfone PES and (polyvinylidene fluoride-hexafluoropropylene) copolymer PVDF-HFP are mixed in a mass ratio of 1:3 as an adhesive, D-MOF is used as an absorbing filler, and the mass ratio of adhesive: absorbing filler: anhydrous ethanol is 0.3:0.7:10. The adhesive and absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then the dispersion is sprayed on the metal substrate with a spraying thickness of 1.38 mm. After drying and curing at 240°C, an absorbing coating is formed.

[0057] Comparative Example 3: A method for preparing a radar absorbing coating, comprising the following steps:

[0058] The first step is the preparation of iron-based MOF derivatives: iron salt FeCl3·6H2O and fumaric acid are dissolved in deionized water in a molar ratio of 1:1, mixed evenly and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven at 100°C for 4 hours. After the reaction is completed, the precipitate is collected by centrifugation and washed alternately with deionized water and ethanol three times. The precipitate is dried in a vacuum drying oven at 60°C for 24 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with nitrogen, a heating rate of 5°C / min, and a temperature of 500°C for 30 minutes to obtain an iron MOF derivative, which is recorded as D-MOF.

[0059] The second step is the preparation of D-MOF@SiO2-F core-shell structure materials: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water, wherein the volume ratio of anhydrous ethanol and ammonia water is 8:1, and the mass g of the iron MOF derivative and the volume mL ratio of the mixed solution of anhydrous ethanol and ammonia water is 1:56 to form a homogeneous solution A; according to the volume ratio of silica sol: anhydrous ethanol = 3:5, silica sol tetraethoxysilane is mixed with anhydrous ethanol to form a solution B; solution B is added dropwise to the homogeneous solution A, the volume ratio of homogeneous solution A to solution B is 3:1, and stirred at room temperature for 16 h to completely hydrolyze to obtain a mixed solution, and then 1H,1H,2H,2H-perfluorodecyltriethoxysilane (10% by volume of tetraethoxysilane) is added to the mixed solution for hydrolysis reaction 8 h, collecting the precipitate by centrifugation, washing the precipitate with anhydrous ethanol, repeating the centrifugation and anhydrous ethanol washing steps three times, and then vacuum drying the precipitate to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F;

[0060] The third step is the preparation of the absorbing coating: using 25% epoxy resin and 5% phenolic amine curing agent as adhesives, 70% D-MOF@SiO2-F as absorbing filler, the mass ratio of adhesive to absorbing filler and anhydrous ethanol is 1:10, and the mixture is stirred and dispersed for 30 minutes. The dispersion is then sprayed onto a metal substrate with a spraying thickness of 1.41 mm. The absorbing coating is formed after drying and curing at 240°C.

[0061] The performance test results of the embodiments and comparative examples of the present invention are as follows: .

[0062] The coatings of Examples 1, 3 and 6 all showed good absorbing effects and hydrophobic properties. Due to the low hydrothermal reaction temperature, Examples 2 and 5 failed to completely react to form iron MOF or the product crystal structure was incomplete, so they did not show absorbing properties, but the coatings had a certain hydrophobicity. The absorbing ability of the coating of Example 4 was poor because the content of the absorber in the coating was low, and it failed to produce strong absorption of electromagnetic waves, but it still showed a certain hydrophobicity. Comparative Example 1 only used conventional Fe3O4 particles as absorbing fillers, showing a certain absorbing ability, but no obvious hydrophobic effect. Comparative Example 2 did not coat the MOF derivative with fluorinated SiO2, and still showed good absorbing ability, but its hydrophobic effect was far worse than that of Examples 1 to 6. Comparative Example 3 used conventional epoxy resin and amine curing agent as adhesives, and its absorbing ability was good, but it did not show a hydrophobic effect. Comprehensive analysis of the examples and comparative examples shows that the coating with iron MOF derivatives as fillers has a better absorbing effect than the Fe3O4 particle absorbing coating, especially the iron MOF derivative has a wider absorption band. The hydrophobic PES and PVDF-HFP binders play a decisive role in the hydrophobic effect of the coating, and the micro-nano dual-scale fluorinated SiO2-coated iron MOF derivative core-shell material is beneficial to improving the hydrophobic properties of the coating.

[0063] The above description of the examples is intended to facilitate understanding and application of the invention by those skilled in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made and the general principles described herein can be applied to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating, characterized in that: The following steps are involved: The first step is the preparation of iron-based MOF derivatives: the iron salt and the organic complex are dissolved in deionized water in a molar ratio of 1:1, mixed evenly, and transferred to a high-pressure reactor. The high-pressure reactor is placed in an oven for reaction. After the reaction is completed, the precipitate is collected by centrifugation and washed three times with deionized water and ethanol alternately. The washed precipitate is dried in a vacuum drying oven for 24-48 hours to obtain iron MOF powder. Finally, the iron MOF powder is transferred to a crucible and pyrolyzed in a tubular furnace with an inert gas and a heating rate of 5°C / min to obtain an iron MOF derivative, which is recorded as D-MOF. The second step is the preparation of D-MOF@SiO2-F core-shell structure material: the iron MOF derivative obtained in the first step is ultrasonically dispersed in a mixed solution of anhydrous ethanol and ammonia water to form a homogeneous solution A; the silane compound is mixed with anhydrous ethanol to form a solution B, and the solution B is added dropwise to the homogeneous solution A, stirred at room temperature for 16 to 20 hours to completely hydrolyze it to obtain a mixed solution, and then fluorosilane is added to the mixed solution for hydrolysis reaction for 8 hours, the precipitate is collected by centrifugation, and the precipitate is washed with anhydrous ethanol. After repeating the centrifugation and anhydrous ethanol washing steps for 3 times, the precipitate is vacuum-dried to a constant weight to obtain a fluorinated SiO2-coated iron-based MOF derivative, which is recorded as D-MOF@SiO2-F; the silane compound in the preparation step of solution B is one or more of tetraethoxysilane, dialkoxysilane, and trialkoxysilane, and the volume ratio of the silane compound to anhydrous ethanol is 1:(1.3~4); The third step is the preparation of the absorbing coating: polyethersulfone PES and polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP are mixed in a mass ratio of 1:3-6 as an adhesive, and D-MOF@SiO2-F is used as an absorbing filler. The adhesive and the absorbing filler are ultrasonically dispersed in anhydrous ethanol for 30 minutes to obtain a dispersion, and then the dispersion is sprayed on a metal substrate with a spraying thickness controlled at 1.2-1.5mm. After drying and curing at 240°C, a magnetoelectric synergistic loss type superhydrophobic absorbing coating is formed.

2. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic absorbing coating according to claim 1, characterized in that: The iron salt in the first step is FeCl3·6H2O, Fe2(SO4)3·5H2O or Fe(NO3)3·9H2O, and the organic complex is fumaric acid, dimethylimidazole or terephthalic acid.

3. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic absorbing coating according to claim 1, characterized in that: The oven temperature in the first step is 80-110° C., and the reaction time is 3-6 h; the vacuum drying oven temperature in the first step is 50-80° C.

4. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic absorbing coating according to claim 1, characterized in that: The inert gas in the first step is a protective gas, specifically nitrogen or argon, the pyrolysis temperature is 400-600° C., and the pyrolysis time is 30-60 min.

5. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating according to claim 1, characterized in that: The volume ratio of anhydrous ethanol to aqueous ammonia in the preparation step of homogeneous solution A is (7-10):1, and the ratio of the mass of the iron MOF derivative to the volume of the mixed solution of anhydrous ethanol and aqueous ammonia is 1 g:(40-60) mL.

6. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating according to claim 1, characterized in that: The volume ratio of the homogeneous solution A to the solution B in the second step is (3-5):

1.

7. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic wave-absorbing coating according to claim 1, characterized in that: The fluorosilane in the second step is one or more of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and hexafluorobutylpropyltrimethoxysilane, and the volume ratio of the fluorosilane to the silane compound in the second step is 1:(8~12).

8. The method for preparing the magnetoelectric cooperative loss type super-hydrophobic absorbing coating according to claim 1, characterized in that: The mass ratio of the adhesive to the absorbing filler in the third step is (3-7):(7-3), and the mass ratio of the total amount of the adhesive and the absorbing filler to anhydrous ethanol is 1:(8-12).

9. A magneto-electric cooperative loss super-hydrophobic wave-absorbing coating prepared by the preparation method according to any one of claims 1 to 8.