MXene-based photothermal self-healing composite protective coating, and preparation method and application thereof

Abstract

The application provides a MXene-based photothermal self-healing composite protective coating and a preparation method and application thereof, and belongs to the technical field of protective coatings. The protective coating of the MXene-based photothermal self-healing composite protective coating is obtained by mixing crosslinking acrylic resin and MXene; and the raw materials for preparing the crosslinking acrylic resin include acrylic monomers, methacrylate monomers, capsaicin derivatives and 3'-diallyl acryloxy butyl dithiodipropionate. The monomer mixture composed of multiple monomers can form the crosslinking acrylic resin with good anti-permeability, strong wear resistance and strong weather resistance, and the two-dimensional nanomaterial MXene with excellent mechanical properties and good thermal stability is used, and the protective coating obtained by mixing the two can form a dense coating after curing. When micro-cracks occur on the surface of the coating, the cracks can be automatically closed through the recombination of the dynamic bonds in the coating and the migration of the molecular chains.

Description

Technical Field

[0001] This invention relates to the field of protective coating technology, and in particular to an MXene-based photothermal self-healing composite protective coating, its preparation method, and its application. Background Technology

[0002] Concrete, as a core structural material in marine engineering and intertidal structures, faces constant and severe corrosion from the marine environment. Its surface is prone to micro-cracks due to alternating wet and dry conditions, salt spray corrosion, and mechanical wear. Traditional surface protection methods for concrete often involve applying protective coatings that cure to form a protective layer. However, these coatings only provide physical isolation and cannot repair the micro-cracks. If these micro-cracks are not repaired in time, they become channels for seawater, corrosive ions, and microorganisms to invade, accelerating the corrosion of internal steel reinforcement, reducing structural strength, causing coating peeling, and significantly decreasing structural durability. This severely impacts the service life of marine engineering facilities, increasing maintenance costs and safety risks.

[0003] To address the aforementioned issues, existing technologies employ polypropylene glycol diglycidyl ether as a soft segment in protective coatings to impart a shape memory effect to the polymer matrix. Furthermore, under photothermal conversion materials, the photothermally responsive self-healing coating can rapidly heat up to initiate the shape memory process of the coating matrix, promoting crack closure. However, the self-healing coating prepared by this method requires near-infrared light irradiation to repair itself and cannot achieve self-healing under natural light, which limits the practical application of the coating.

[0004] Therefore, developing a self-healing protective coating for concrete surfaces under natural light to enable the autonomous healing of microcracks has become a key technological requirement for improving the reliability of marine engineering concrete structures. Summary of the Invention

[0005] The purpose of this invention is to provide an MXene-based photothermal self-healing composite protective coating with self-healing function under natural light, its preparation method, and its application.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an MXene-based photothermal self-healing composite protective coating, which is obtained by curing a protective coating film; the protective coating is obtained by mixing cross-linked acrylic resin and MXene. The MXene accounts for 2-10% of the mass of the crosslinked acrylic resin; The crosslinked acrylic resin is obtained by polymerizing a mixture of raw materials comprising the following components: monomer mixture, initiator, chain transfer agent and solvent; The monomer mixture includes acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivatives; the molar ratio of the acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivatives is (20~50):(20~60):(20~60):(5~20):(0.5~2).

[0007] Preferably, the acrylate monomer includes one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, and octadecyl acrylate.

[0008] Preferably, the methacrylate monomer includes one or more of methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, and octadecyl methacrylate.

[0009] Preferably, the urea methacrylate monomer includes one or more of ethoxylated ethylurea methacrylate, ethylurea methacrylate ethoxylate, and ethylurea methacrylate.

[0010] Preferably, the preparation method of the 3,3'-diacryloyloxybutyl dithiodipropionate includes: mixing 3,3'-dithiodipropionic acid, 4-hydroxyphenyl acrylate, butyl acetate and a catalyst, and carrying out an esterification reaction to obtain 3,3'-diacryloyloxybutyl dithiodipropionate.

[0011] Preferably, the capsaicin derivative comprises capsaicin monomers containing a benzene ring, phenolic hydroxyl group, or amide group.

[0012] Preferably, the MXene is a single-layer V4C3-MXene.

[0013] Preferably, the initiator accounts for 0.5-3.4% of the monomer mixture by mass; the chain transfer agent accounts for 0.5-2.5% of the monomer mixture by mass; and the solvent accounts for 70-120% of the monomer mixture by mass.

[0014] This invention also provides a method for preparing the MXene-based photothermal self-healing composite protective coating described in the above technical solution, comprising the following steps: (1) Mix acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate, capsaicin derivatives and initiators to obtain a monomer mixture containing initiators; (2) Dissolve the chain transfer agent in a solvent to obtain a chain transfer agent solution; in an inert atmosphere, mix the monomer mixture containing the initiator obtained in step (1) with the chain transfer agent solution to carry out a crosslinking reaction to obtain a crosslinked acrylic resin; (3) The cross-linked acrylic resin obtained in step (2) is mixed with MXene to obtain a protective coating; (4) Apply the protective coating obtained in step (3) onto the substrate and carry out a curing reaction to obtain an MXene-based photothermal self-healing composite protective coating.

[0015] The present invention also provides the application of the MXene-based photothermal self-healing composite protective coating described in the above technical solution or the MXene-based photothermal self-healing composite protective coating prepared by the preparation method described in the above technical solution as a protective coating for marine concrete surfaces.

[0016] This invention provides an MXene-based photothermal self-healing composite protective coating, which is obtained by curing a protective coating film. The protective coating is obtained by mixing crosslinked acrylic resin and MXene. The mass content of MXene in the crosslinked acrylic resin is 2-10%. The crosslinked acrylic resin is obtained by polymerizing a mixture of raw materials including the following components: monomer mixture, initiator, chain transfer agent and solvent. The monomer mixture includes acrylate monomer, methacrylate monomer, urea methacrylate monomer, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivative. The molar ratio of the acrylate monomer, methacrylate monomer, urea methacrylate monomer, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivative is (20-50):(20-60):(20-60):(5-20):(0.5-2). The MXene-based photothermal self-healing composite protective coating provided by this invention uses a monomer mixture as the raw material for preparing the crosslinked acrylic resin. The main function of the acrylate monomer is to impart flexibility to the crosslinked acrylic resin, improve film-forming properties, and increase the hydrophobicity of the MXene-based photothermal self-healing composite protective coating. The main function of the methacrylate monomer is to modify the hardness and adhesion of the crosslinked acrylic resin, giving the protective coating good adhesion. Furthermore, the methacrylate monomer contains urea groups, which can form reversible hydrogen bonds between molecules. After the coating is damaged, the molecular chains can be reassembled through hydrogen bond recombination, providing a key to the self-healing performance. Supporting the self-healing properties, the urea monomer in methacrylate contains urea groups, providing crucial support for its self-healing performance. The addition of capsaicin derivatives and control of their dosage range enhances the self-healing properties of the MXene-based photothermal self-healing composite protective coating, preventing insufficient self-healing due to low capsaicin derivative content, which could lead to stress concentration points and reduced mechanical strength. It also prevents excessive capsaicin derivative dosage from reducing the toughness and transparency of the acrylic resin. The 3'-disacryloyloxybutyl dithiodipropionate contains dynamic covalent disulfide bonds, enabling the MXene-based photothermal self-healing composite protective coating to fracture and regenerate under mild conditions, thereby improving its self-healing ability. The MXene-based photothermal self-healing composite protective coating provided by this invention also includes MXene, a two-dimensional nanomaterial with excellent photothermal conversion capabilities, allowing the coating to rapidly heat up under photothermal conditions, initiating the shape memory process of the coating and promoting crack closure.This invention utilizes a monomer mixture composed of multiple monomers to form a cross-linked acrylic resin with excellent properties such as good impermeability, strong wear resistance, and strong weather resistance. Simultaneously, it employs MXene, a two-dimensional nanomaterial with excellent mechanical properties, good thermal stability, and photothermal conversion capabilities. The combination of these two components yields a durable protective coating. This coating cures to form a dense MXene-based photothermal self-healing composite protective coating. When microcracks appear on the coating surface, the cracks self-close through the recombination of dynamic bonds and molecular chain migration within the coating. Example results show that this invention provides a microcrack repair efficiency exceeding 90% within 24 hours, while also exhibiting excellent waterproof, impermeable, and corrosion-resistant properties, as well as hydrophobic properties. Attached Figure Description

[0017] Figure 1 This is a correlation diagram of the coating-self-healing behavior of the acrylic coatings prepared in Comparative Examples 3-6 of this invention after curing; Figure 2 The fluorescence distribution diagrams are shown for the acrylic coatings prepared in Comparative Examples 3-6 of this invention after curing. Figure 3 This is a bar chart showing the water contact angle of the acrylic coatings prepared in Comparative Examples 3-6 of this invention after curing. Figure 4 The curves showing the change in capillary water absorption rate of the acrylic coatings prepared in Comparative Examples 3-6 of this invention after curing and forming a coating over 96 hours are shown. Figure 5 The images show the SEM morphology and elemental distribution mapping of C, O, N, and S of the acrylic coatings prepared in Comparative Examples 3-6 of this invention after curing. Detailed Implementation

[0018] This invention provides an MXene-based photothermal self-healing composite protective coating, which is obtained by curing a protective coating film; the protective coating is obtained by mixing cross-linked acrylic resin and MXene. The MXene accounts for 2-10% of the mass of the crosslinked acrylic resin; The crosslinked acrylic resin is obtained by polymerizing a mixture of raw materials comprising the following components: monomer mixture, initiator, chain transfer agent and solvent; The monomer mixture includes acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivatives; the molar ratio of the acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivatives is (20~50):(20~60):(20~60):(5~20):(0.5~2).

[0019] The protective coating provided by this invention includes cross-linked acrylic resin.

[0020] Unless otherwise specified, the raw materials used in this invention are commercially available products commonly used in the field.

[0021] In this invention, the crosslinked acrylic resin is obtained by polymerizing a mixture of raw materials comprising the following components: a monomer mixture, an initiator, a chain transfer agent, and a solvent.

[0022] In this invention, the raw materials for preparing the crosslinked acrylic resin include a monomer mixture. The monomer mixture in this invention includes acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetyloxybutyl dithiodipropionate, and capsaicin derivatives.

[0023] In this invention, the acrylate monomers preferably include one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, and octadecyl acrylate. The main function of the acrylate monomers in this invention is to impart flexibility to the acrylic resin, improve film-forming properties, and increase hydrophobicity after the protective coating has formed. In embodiments of this invention, the ethyl acrylate may be sourced from Datang Chemical Reagent Co., Ltd.; the hydroxyethyl acrylate may be sourced from Sinopharm Chemical Reagent Co., Ltd.

[0024] In this invention, the methacrylate monomers preferably include one or more of methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, and octadecyl methacrylate. The main function of using methacrylate monomers in this invention is to modify the hardness and adhesion of the crosslinked acrylic resin material, so that the prepared protective coating has good adhesion after forming a coating. Furthermore, the methacrylate monomers containing urea groups can form reversible hydrogen bonds between their molecules. After the coating is damaged, the molecular chains can be reassembled through hydrogen bond recombination, providing key support for self-healing properties. In the embodiments of this invention, the methyl methacrylate can be sourced from Sinopharm Chemical Reagent Co., Ltd.; the butyl methacrylate can be sourced from Tianjin Damao Chemical Reagent Factory.

[0025] In this invention, the urea methacrylate monomer preferably includes one or more of ethoxylated ethylurea methacrylate, ethoxylated ethylurea methacrylate, and ethylurea methacrylate. The presence of urea groups in the urea methacrylate monomer provides crucial support for its self-healing properties.

[0026] In this invention, the preferred structural formula of the 3,3'-diacetyloxybutyl dithiodipropionate is as shown in formula (1): Equation (1) In this invention, the preferred method for preparing 3,3'-diacryloyloxybutyl dithiodipropionate includes: mixing 3,3'-dithiodipropionic acid, 4-hydroxyphenylacrylate, butyl acetate and a catalyst, and carrying out an esterification reaction to obtain 3,3'-diacryloyloxybutyl dithiodipropionate.

[0027] In this invention, the catalyst is preferably N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine.

[0028] In this invention, the preferred mass ratio of 3,3'-dithiodipropionic acid, 4-hydroxyphenyl acrylate, butyl acetate, N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine is (18~24):(32~39):(45~55):(18~24):(0.3~1), more preferably 21:35.63:50:20.63:0.5.

[0029] In this invention, the preferred method for mixing the 3,3'-dithiodipropionic acid, 4-hydroxyphenylacrylate, butyl acetate, and catalyst is as follows: 3,3'-dithiodipropionic acid, 4-hydroxyphenylacrylate, and butyl acetate are mixed and dissolved to obtain a mixed solution; then, the mixed solution is mixed with the catalyst. In this invention, the mixing and dissolution are preferably carried out under stirring.

[0030] In this invention, the temperature of the esterification reaction is preferably 25~45℃, more preferably 35℃; the time of the esterification reaction is preferably 24~72h, more preferably 36~48h. In this invention, the esterification reaction is preferably carried out under stirring.

[0031] In this invention, the white byproduct dicyclohexylurea generated after the esterification reaction is removed by filtration. The resulting filtrate does not require additional purification and can yield 3,3'-diacetyloxybutyl dithiodipropionate.

[0032] In this invention, the capsaicin derivative preferably comprises capsaicin monomers containing a benzene ring, phenolic hydroxyl group, or amide group, and more preferably is the capsaicin derivative N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide. The addition of capsaicin derivatives in this invention enhances the self-healing properties of the protective coating after it has formed.

[0033] In this invention, the preferred molar ratio of the acrylate monomer, methacrylate monomer, urea methacrylate monomer, 3,3'-diacetoxybutyl dithiodipropionate and capsaicin derivative is (20~50):(20~60):(20~60):(5~20):(0.5~2), more preferably (30~40):(30~50):(30~50):(5~15):(0.7~1.5). In this invention, the molar ratio of acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivatives is controlled within the aforementioned range. If the amount of acrylate monomers is less than 20%, the length and flexibility of the acrylic resin molecular chain cannot be well adjusted; if the amount of acrylate monomers is more than 50%, the acrylic resin material of this invention will be too soft, which is not conducive to film formation; if the amount of methacrylate monomers is less than 20%, the hardness of the resin cannot be well adjusted; if the amount of methacrylate monomers is more than 60%, the mechanical properties of the acrylic resin material will be affected. If the amount of capsaicin derivatives is less than 0.5%, the self-healing properties of the resin will be insufficient and stress concentration points may be generated, reducing mechanical strength; if the amount of capsaicin derivatives is more than 2%, the toughness and transparency of the acrylic resin will decrease.

[0034] In this invention, the raw materials for preparing the crosslinked acrylic resin include an initiator. Preferably, the initiator comprises one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl peroxide, methyl ethyl ketone peroxide, ammonium persulfate, and potassium persulfate. The initiator added in this invention can decompose into active species, initiating monomer polymerization of the monomer mixture. In embodiments of this invention, the azobisisobutyronitrile can be sourced from Tianjin Damao Chemical Reagent Factory; the potassium persulfate can be sourced from Tianjin Hedong Hongyan Reagent Factory.

[0035] In this invention, the initiator preferably accounts for 0.5 to 3.4% of the monomer mixture by mass. As an embodiment of this invention, the initiator can account for 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or 3.4% of the monomer mixture by mass.

[0036] In this invention, the raw materials for preparing the crosslinked acrylic resin include a chain transfer agent. Preferably, the chain transfer agent comprises n-dodecyl mercaptan, tert-dodecyl mercaptan, or an aliphatic thiol. The main function of the chain transfer agent in the synthesis of the crosslinked acrylic resin is to induce free radical transfer of chain-growing free radicals, thereby regulating the molecular weight of the polymer. In embodiments of this invention, the n-dodecyl mercaptan can be sourced from Sinopharm Chemical Reagent Co., Ltd.

[0037] In this invention, the chain transfer agent preferably accounts for 0.5% to 2.5% of the monomer mixture by mass. As an embodiment of this invention, the chain transfer agent can account for 0.5%, 1.0%, 1.5%, 1.7%, 1.9%, 2.0%, or 2.5% of the monomer mixture by mass. By controlling the amount of chain transfer agent within the above range, this invention can control the termination of free radical polymerization while preventing excessive chain transfer agent from causing a decrease in polymer viscosity and excessively short molecular chains. In this invention, the raw materials for preparing the crosslinked acrylic resin include a solvent. Preferably, the solvent includes toluene, xylene, n-butanol, butyl acetate, ethyl acetate, cyclohexanone, methyl isobutyl ketone, or N,N-dimethylformamide.

[0038] In this invention, the solvent preferably accounts for 70-120% of the monomer mixture by mass. As an embodiment of this invention, the solvent accounts for 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, or 120% of the monomer mixture by mass.

[0039] The protective coating provided by this invention also includes MXene.

[0040] In this invention, the MXene is preferably V4C3-MXene, and the V4C3-MXene is preferably a single-layer V4C3-MXene.

[0041] This invention uses a single layer of V4C3-MXene, which has a large specific surface area and excellent mechanical properties.

[0042] In this invention, the preferred method for preparing the monolayer V4C3-MXene includes: After mixing V4AlC3 powder with an acid solution, an etching reaction was carried out, followed by solid-liquid separation to obtain multilayer V4C3-MXene material; The multilayer V4C3-MXene material was mixed with an alcohol solution and then subjected to ultrasonic treatment. After one centrifugation, a precipitate was obtained. The precipitate was washed with deionized water and then centrifuged a second time. The supernatant was collected to obtain a V4C3-MXene dispersion.

[0043] In this invention, V4AlC3 powder is preferably mixed with an acid solution, followed by an etching reaction, and then solid-liquid separation is performed to obtain multilayer V4C3-MXene material.

[0044] In this invention, the acid solution is preferably at least one of hydrofluoric acid, sulfuric acid, and hydrochloric acid; the mass concentration of the acid solution is preferably 30-50%, more preferably 40-45%. This invention enables the etching of MXene using an acid solution of the above concentration. By using an acid solution for etching, this invention can etch the Al atomic layers in the V4AlC3MAX phase, forming interstitial spaces, thereby forming an accordion-shaped multilayer V4C3T. x MXene structure.

[0045] In this invention, the concentration of V4AlC3 in the precursor solution obtained by mixing the V4AlC3 powder with the acid solution is preferably 0.03~0.06 g / mL, more preferably 0.045~0.055 g / mL. By controlling the concentration of the precursor solution, this invention can avoid excessive etching that could damage the V4AlC3 structure, and also avoid incomplete etching reactions where some Al atomic layers in the V4AlC3MAX phase are not effectively removed by etching, thus failing to form a multilayer structure.

[0046] In this invention, the etching reaction temperature is preferably 45~65℃, more preferably 50~60℃; the etching reaction time is preferably 24~120h, more preferably 48~96h; and the etching reaction is preferably carried out under stirring. This invention performs etching at the above-mentioned temperatures, avoiding excessively low or high temperatures that could lead to overly vigorous reactions and rapid solvent evaporation, which would be detrimental to the reaction. Furthermore, etching at the above-mentioned time ensures that some Al atomic layers in the V4AlC3MAX phase are effectively removed through etching, preventing over-etching and damage to the V4AlC3 structure due to excessive time. This allows for a complete etching reaction, resulting in a multilayer structure.

[0047] In this invention, the system obtained after the etching reaction is preferably cooled to room temperature, and then solid-liquid separation is performed.

[0048] In this invention, the solid-liquid separation method is preferably centrifugation.

[0049] The present invention preferably involves centrifuging, washing and freeze-drying the solid obtained from the solid-liquid separation to obtain a multilayer V4C3-MXene material.

[0050] In embodiments of the present invention, the washing reagent for centrifugal washing can be deionized water. The present invention does not specifically limit the number of centrifugal washes, as long as the pH value of the washing reagent after washing reaches neutral.

[0051] In this invention, the freeze-drying temperature is preferably -50℃ to -45℃; the freeze-drying time is preferably 36 to 60 hours, more preferably 48 to 50 hours.

[0052] After obtaining the multilayer V4C3-MXene material, the present invention preferably mixes the multilayer V4C3-MXene material with an alcohol solution and then performs ultrasonic treatment, followed by centrifugation once to obtain a precipitate; the precipitate is washed with deionized water, and after a second centrifugation, the supernatant is collected to obtain a single-layer V4C3-MXene dispersion.

[0053] In this invention, the alcohol solution is preferably at least one of ethanol, methanol, and propanol. The mass concentration of the alcohol solution is preferably greater than or equal to 99.5%. This invention uses an alcohol solution as the dispersion medium, which has good polarity compatibility and can effectively weaken the interlayer forces of MXene. It avoids insufficient interlayer stripping due to poor dispersion medium compatibility, resulting in a large number of undissociated multilayer MXenes and the inability to obtain the target single-layer MXene product; nor does it damage the intrinsic structure of the MXene sheets due to the corrosiveness or excessive polarity of the medium, affecting the subsequent application performance of the product.

[0054] In this invention, the ultrasonic treatment is preferably a first ultrasonic treatment and a second ultrasonic treatment performed sequentially. In this invention, the ultrasonic power of the first ultrasonic treatment is preferably 100-300W, and the ultrasonic time of the first ultrasonic treatment is preferably 0.5-1 min, more preferably 1 min; the ultrasonic power of the second ultrasonic treatment is preferably 100-300W, and the ultrasonic time of the second ultrasonic treatment is preferably 0.5-1 min, more preferably 1 min. This invention obtains a uniformly dispersed MXene dispersion system through ultrasonic treatment. The segmented ultrasonic treatment method of this invention, performed in two stages, provides a reasonable balance between ultrasonic intensity and time. The time is not too short, thus sufficiently weakening the interlayer bonding force of the multilayer MXene for efficient exfoliation; the time is not too long, avoiding excessive ultrasonication that could cause lamellar breakage, increased edge defects, and consequently, product performance degradation.

[0055] In this invention, the preferred centrifugation speed is 3800-4000 r / min, more preferably 4000 r / min. By performing a single centrifugation at the above speed, this invention can fully precipitate the solids in the ultrasonically treated system. This invention does not specifically limit the exact time of the single centrifugation; it can be adjusted to ensure sufficient precipitation of the solids in the ultrasonically treated system.

[0056] The present invention does not have a special limitation on the number of times the deionized water is washed, as long as the alcohol solution in the precipitate is removed.

[0057] In this invention, the rotation speed of the secondary centrifugation is preferably 1400~1500 r / min, more preferably 1500 r / min. This invention does not specifically limit the exact time of the secondary centrifugation; it can be adjusted to prevent the solids in the suspension from settling further.

[0058] This invention employs a gradient centrifugation strategy involving primary and secondary centrifugation, which prevents the loss of the target monolayer MXene with the precipitate or the inclusion of impurities in the supernatant due to improper centrifugation parameters. It can effectively separate the unpeeled multilayer MXene precipitate through primary centrifugation, and enrich the upper monolayer MXene dispersion through low-speed secondary centrifugation, avoiding excessive centrifugation and sedimentation of the monolayer sheets, and ultimately improving the yield of monolayer V4C3-MXene.

[0059] In this invention, the MXene accounts for 2-10% of the mass of the crosslinked acrylic resin. As an embodiment of this invention, the MXene accounts for 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the mass of the crosslinked acrylic resin.

[0060] In this invention, the preferred structural formula of the resin in the MXene-based photothermal self-healing composite protective coating is shown in formula (2): In equation (2), the preferred values ​​are m = 25~28 mol%, n = 20~22 mol%, x = 25~28 mol%, y = 20~22 mol%, and z = 1~3 mol%.

[0061] This invention also provides a method for preparing the MXene-based photothermal self-healing composite protective coating described in the above technical solution, comprising the following steps: (1) Mix acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate, capsaicin derivatives and initiators to obtain a monomer mixture containing initiators; (2) Dissolve the chain transfer agent in a solvent to obtain a chain transfer agent solution; in an inert atmosphere, mix the monomer mixture containing the initiator obtained in step (1) with the chain transfer agent solution to carry out a crosslinking reaction to obtain a crosslinked acrylic resin; (3) The cross-linked acrylic resin obtained in step (2) is mixed with MXene to obtain a protective coating; (4) Apply the protective coating obtained in step (3) onto the substrate and carry out a curing reaction to obtain an MXene-based photothermal self-healing composite protective coating.

[0062] The present invention mixes acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetyloxybutyl dithiodipropionate, capsaicin derivatives and initiators to obtain a monomer mixture containing an initiator.

[0063] In this invention, the types and sources of the acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetyloxybutyl dithiodipropionate, capsaicin derivatives, and initiators are the same as those described in the above technical solutions, and will not be repeated here.

[0064] In this invention, the preferred method for mixing the acrylate monomer, methacrylate monomer, urea methacrylate monomer, 3,3'-diacetoxybutyl dithiodipropionate, capsaicin derivative, and initiator is as follows: The acrylate monomer, methacrylate monomer, urea methacrylate monomer, 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivative are mixed to obtain a monomer mixture; the monomer mixture is then mixed with an initiator to obtain a monomer mixture containing the initiator. This invention, by first obtaining the monomer mixture and then mixing it with the initiator, prevents reactions from occurring during the mixing process, thereby promoting a more uniform crosslinked acrylic resin obtained from the subsequent crosslinking reaction.

[0065] After obtaining the monomer mixture containing the initiator, the present invention mixes the monomer mixture containing the initiator with a chain transfer agent solution to carry out a crosslinking reaction to obtain a crosslinked acrylic resin.

[0066] In this invention, the preferred method for preparing the chain transfer agent solution is to dissolve the chain transfer agent in a solvent to obtain the chain transfer agent solution. In this invention, the chain transfer agent and solvent are the same as those described in the above-described technical solutions, and will not be repeated here.

[0067] In this invention, the method for mixing the monomer mixture containing the initiator with the chain transfer agent solution preferably includes: mixing the chain transfer agent solution with a portion of the monomer mixture containing the initiator in a three-necked flask, then introducing a protective gas into the three-necked flask to carry out a crosslinking reaction; then dividing the remaining monomer mixture containing the initiator into 1-10 equal portions, and adding one portion to the three-necked flask every 10-20 minutes. In this invention, the crosslinking reaction time is preferably 2-6 hours, more preferably 3-5 hours. The crosslinking reaction time in this invention refers to the total time from the introduction of the protective gas, when the temperature in the three-necked flask rises to the crosslinking reaction temperature, to the time after the remaining monomer mixture containing the initiator is added, maintaining the temperature at the crosslinking reaction temperature. This invention avoids agglomeration or explosion caused by excessively large single additions of the monomer mixture containing the initiator.

[0068] The present invention uses a three-necked flask equipped with a stirrer and a condenser. This type of three-necked flask is a commonly used device in this technical field, and does not require the use of complex equipment.

[0069] In this invention, the protective gas is preferably nitrogen. By using nitrogen as the protective gas, the oxygen in the three-necked flask can be discharged to form an inert atmosphere.

[0070] In this invention, the temperature of the crosslinking reaction is preferably 80~110℃, more preferably 85~100℃, and even more preferably 88~93℃.

[0071] After obtaining the crosslinked acrylic resin, the present invention mixes the crosslinked acrylic resin with MXene to obtain a protective coating.

[0072] In this invention, the MXene is preferably a monolayer V4C3-MXene, and the preparation method of the V4C3-MXene is the same as the preparation method of the preferred monolayer V4C3-MXene described in the above technical solution, and will not be repeated here.

[0073] In this invention, the MXene accounts for 2-10% of the mass of the crosslinked acrylic resin. As an embodiment of this invention, the MXene accounts for 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the mass of the crosslinked acrylic resin.

[0074] The present invention does not have any particular limitation on the method of mixing the crosslinked acrylic resin and MXene; it is sufficient to mix the two evenly.

[0075] After obtaining the protective coating, the present invention applies the protective coating to the substrate and carries out a curing reaction to obtain an MXene-based photothermal self-healing composite protective coating.

[0076] In this invention, the matrix is ​​preferably concrete. The composition of the concrete is not particularly limited, and any conventional concrete can be used. In this invention, the marine concrete preferably comprises: 10-20 parts cement, 20-30 parts sand, 30-40 parts aggregate, and 5-10 parts water.

[0077] This invention does not specifically limit the coating method; any conventional coating method capable of forming a uniformly thick coating film on the substrate surface is acceptable. In this invention, the film-forming method can be a spray coating method.

[0078] In this invention, the curing temperature is preferably 55~60℃, more preferably 60℃; the curing time is preferably 2~2.5h, more preferably 2h.

[0079] In this invention, the thickness of the MXene-based photothermal self-healing composite protective coating is preferably 60-80 μm, more preferably 80 μm. In this invention, the thickness of the photothermal self-healing coating refers to the thickness of the dry film.

[0080] The present invention also provides the application of the MXene-based photothermal self-healing composite protective coating described above as a protective coating for marine concrete surfaces.

[0081] The present invention does not impose any particular limitation on the method of applying the MXene-based photothermal self-healing composite protective coating as a protective coating for marine concrete surfaces; any conventional method of applying a photothermal self-healing coating may be used.

[0082] In this invention, the preferred method for applying the MXene-based photothermal self-healing composite protective coating as a protective coating for marine concrete surfaces is to coat the marine concrete surface with a protective coating and then cure it to obtain the MXene-based photothermal self-healing composite protective coating.

[0083] This invention does not specifically limit the coating method; any conventional coating method can be used. In embodiments of this invention, the coating method can be spraying. This invention does not specifically limit the coating thickness; it can be adjusted according to the required dry film thickness. In embodiments of this invention, the dry film thickness is preferably 60-80 μm.

[0084] In this invention, the curing temperature is preferably 55~60℃, more preferably 60℃; the curing time is preferably 2~2.5h, more preferably 2h.

[0085] This invention provides a protective coating that, after curing, forms a photothermal self-healing coating on marine concrete surfaces. The invention utilizes a monomer mixture composed of multiple monomers to form a cross-linked acrylic resin with excellent properties such as good impermeability, strong abrasion resistance, and strong weather resistance. Simultaneously, it uses MXene, a two-dimensional nanomaterial with excellent mechanical properties and good thermal stability. The combination of these two components results in a durable protective coating. Upon curing, this coating forms a dense layer. When microcracks appear on the coating surface, the cracks self-close through the recombination of dynamic bonds and molecular chain migration within the coating, thus achieving a self-healing coating. Therefore, it can be used as a protective coating for marine concrete surfaces.

[0086] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0087] The preparation method of 3,3'-diacetoxybutyl dithiodipropionate used in this embodiment of the invention is as follows: 21 g of 3,3'-dithiodipropionic acid, 35.63 g of 4-hydroxyphenylacrylate, and 50 g of butyl acetate were added to a 250 mL three-necked flask and magnetically stirred until completely dissolved. 20.63 g of N,N'-dicyclohexylcarbodiimide and 0.5 g of 4-dimethylaminopyridine were simultaneously and slowly added to the reaction system at a rate of 2 mL / min as esterification catalysts. The reaction was stirred at 35 °C for 48 h. After the esterification reaction was completed, the generated white byproduct dicyclohexylurea was removed by filtration. The resulting filtrate was directly used for subsequent polymerization without additional purification, finally yielding the product 3,3'-diacetoxybutyl dithiodipropionate.

[0088] The preparation method of N-(2,3,4-trihydroxy-5-acrylamide methylbenzyl)acrylamide used in this embodiment of the invention is as follows: 12.6 g of O-methylhydroquinone, 24.26 g of N-hydroxymethylacrylamide, and 100 g of anhydrous ethanol were added to a three-necked flask and magnetically stirred until completely dissolved. 10 g of 98% concentrated sulfuric acid was slowly added dropwise to the reaction system. After the reaction was completed, the mixture was cooled to room temperature and filtered. The obtained solid was washed thoroughly with deionized water until the pH reached 7 to obtain a crude product. The crude product was then recrystallized three times with anhydrous ethanol to obtain a pure product.

[0089] Example 1 An MXene-based photothermal self-healing composite protective coating is obtained by curing a protective coating film; the protective coating is obtained by mixing cross-linked acrylic resin and MXene. The MXene accounts for 5% of the mass of the crosslinked acrylic resin; The crosslinked acrylic resin is obtained by polymerizing a mixture of the following components: monomer mixture, initiator (azobisisobutyronitrile), chain transfer agent (n-dodecyl mercaptan), and solvent (butyl acetate). The monomer mixture comprises acrylate monomers (n-butyl acrylate), methacrylate monomers (methyl methacrylate), urea methacrylate monomers (ethylidene urea ethoxylate), 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivative (N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide); the molar ratio of n-butyl acrylate, methyl methacrylate, ethylidene urea ethoxylate, 3,3'-diacetoxybutyl dithiodipropionate, and N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide is 30:35:25:8:0.8. The initiator (azobisisobutyronitrile) accounts for 1.8% of the monomer mixture by mass. The chain transfer agent (n-dodecyl mercaptan) accounts for 1.2% of the monomer mixture by mass. The solvent (butyl acetate) accounts for 80% of the monomer mixture by mass. The preparation method of the protective coating: (1) Mix n-butyl acrylate, methyl methacrylate, ethylidene urea ethoxylate, 3,3'-diacryloyloxybutyl dithiodipropionate and N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide to obtain a monomer mixture; mix the monomer mixture with azobisisobutyronitrile to obtain a monomer mixture containing an initiator; (2) Add butyl acetate and n-dodecyl mercaptan chain transfer agent to a three-necked flask to obtain a chain transfer agent solution. Add 15% of the weight of the monomer mixture containing the initiator obtained in step (1) to the three-necked flask, stir evenly and purge nitrogen into the three-necked flask for 30 min. At the same time, control the reaction temperature of the reaction mixture at 95°C under nitrogen protection. Divide the remaining monomer mixture containing the initiator into 5 equal parts and add one part every 15 min. React continuously for 4 h under nitrogen protection to obtain a transparent and viscous acrylic resin product, which is cross-linked acrylic resin. (3) The preparation method of monolayer V4C3-MXene is as follows: 10g of V4AlC3 powder was weighed and slowly added to a 40% hydrofluoric acid solution at a rate of 1.0g / min to prepare a precursor solution with a V4AlC3 concentration of 0.05g / mL. The precursor solution was placed in a 55℃ constant temperature water bath and etched and stirred for 72h. After the reaction was completed, the solution was cooled to room temperature and centrifuged at 8000r / min. The precipitate was collected and repeatedly centrifuged and washed until pH=7. Then, it was freeze-dried at -50℃ for 48h to obtain multilayer V4C3-MXene. 5g of the dried multilayer V4C3-MXene was added to 100mL of 99.7% ethanol solution for dispersion. The solution was sonicated twice (1min each time, 300W power). First, the unremoved multilayer precipitate was removed by centrifugation at 4000r / min for 10min. Then, the supernatant was centrifuged at 1500r / min for 15min and the supernatant was collected to obtain a monolayer V4C3-MXene dispersion (concentration 0.02g / mL). A single-layer V4C3-MXene dispersion with a concentration of 0.02 g / mL was slowly added to the cross-linked acrylic resin at a ratio of 5% of the mass of MXene to the cross-linked acrylic resin obtained in step (2). The mixture was stirred and dispersed at 30°C and 500 r / min for 60 min, and then ultrasonically dispersed for 30 min (power 200 W) to obtain a uniform MXene composite coating slurry, which is the protective coating. (4) Apply the protective coating obtained in step (3) to the surface of the pretreated marine concrete test block by spraying and cure it in an oven at 60°C for 2 hours to obtain the MXene-based photothermal self-healing composite protective coating (coating dry film thickness 80μm). The pretreatment method is as follows: remove floating dust, oil stains and loose debris from the surface of the marine concrete test block, rinse with deionized water to remove surface salt; then sand the surface of the test block with 120-grit sandpaper until the fresh substrate is exposed, blow away the surface dust with a hair dryer; finally, place the test block in a 60℃ oven to dry for 2 hours, and then cool it to room temperature.

[0090] Comparative Example 1 A composite protective coating, which differs from Example 1 in that no MXene is added and the preparation method does not include step (3), while the remaining composition and steps are the same as in Example 1.

[0091] Test Example 1 The performance of the MXene-based photothermal self-healing composite protective coating prepared in Example 1 and the composite protective coating prepared in Comparative Example 1 were tested respectively. The test methods and results are as follows: (1) Self-healing performance test: Microcracks with a width of 50 μm were prepared on the coating surface and cured for 24 h at 25℃ (natural light) and 50℃ (simulated photothermal) respectively. The crack closure was observed by scanning electron microscopy. The crack repair efficiency of the MXene-containing coating at 50℃ reached 94.2%, which was significantly higher than 78.5% of the comparative example 1.

[0092] (2) Photothermal performance test: The surface temperature of the coating rose to 62°C after 10 minutes of simulated sunlight irradiation, providing sufficient heat for dynamic bond recombination.

[0093] (3) Corrosion resistance test: The test block was immersed in a 3.5% NaCl solution for 30 days. The water absorption rate of the concrete test block with the self-healing coating of the protective coating prepared in Example 1 was only 1.8%, which was much lower than the 4.5% of the coating of the protective coating prepared in Comparative Example 1, and there were no obvious rust marks.

[0094] Example 2 An MXene-based photothermal self-healing composite protective coating is obtained by curing a protective coating film; the protective coating is obtained by mixing cross-linked acrylic resin and MXene. The MXene accounts for 2% of the mass of the crosslinked acrylic resin; The crosslinked acrylic resin is obtained by polymerizing a mixture of the following components: monomer mixture, initiator (azobisisobutyronitrile), chain transfer agent (tert-dodecyl mercaptan), and solvent (a mixture of ethyl acetate and n-butanol in a volume ratio of 2:1). The monomer mixture comprises acrylate monomers (hydroxyethyl acrylate), methacrylate monomers (ethyl methacrylate), urea methacrylate monomers (ethylene urea ethoxylate), 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivative (N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide); the molar ratio of hydroxyethyl acrylate, ethyl methacrylate, ethylene urea ethoxylate, 3,3'-diacetoxybutyl dithiodipropionate, and N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide is 20:25:30:10:0.5. The initiator (azobisisobutyronitrile) accounts for 1.2% of the monomer mixture by mass. The chain transfer agent (tert-dodecyl mercaptan) accounts for 0.8% of the monomer mixture by mass. The solvent (a mixture of ethyl acetate and n-butanol in a volume ratio of 2:1) accounts for 75% of the monomer mixture by mass. The preparation method of the protective coating: (1) Hydroxyethyl acrylate, ethyl methacrylate, ethyl urea methacrylate, 3,3'-diacryloyloxybutyl dithiodipropionate and N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide are mixed to obtain a monomer mixture; the monomer mixture is mixed with azobisisobutyronitrile to obtain a monomer mixture containing an initiator; (2) Add ethyl acetate and n-butanol mixed solvent and tert-dodecyl mercaptan chain transfer agent to a three-necked flask to obtain a chain transfer agent solution. Add 12% of the weight of the monomer mixture containing the initiator obtained in step (1) to the three-necked flask, stir evenly and purge nitrogen into the three-necked flask for 30 min. At the same time, control the reaction temperature of the reaction mixture at 85°C under nitrogen protection. Divide the remaining monomer mixture containing the initiator into 4 equal parts, add one part every 18 min, and react continuously for 5 h under nitrogen protection to obtain a transparent and viscous acrylic resin product, which is cross-linked acrylic resin. (3) The preparation method of monolayer V4C3-MXene is as follows: Weigh 8g of V4AlC3 powder and slowly add it to a 35% hydrochloric acid-sulfuric acid mixed acid solution (volume ratio 1:1) to prepare a precursor solution with a V4AlC3 concentration of 0.035g / mL. Place the solution in a 48℃ constant temperature water bath and etch and stir for 96h. After the reaction is complete, cool to room temperature, centrifuge at 7000r / min, collect the precipitate, and centrifuge and wash until pH=7. Freeze-dry at -45℃ for 50h to obtain multilayer V4C3-MXene. Take 3g of the dried multilayer V4C3-MXene and add it to 80mL of 99.5% methanol solution for dispersion. Sonicate twice (1min each time, power 280W). First, centrifuge at 3800r / min for 12min to remove unremoved precipitate. Then, take the supernatant and centrifuge at 1400r / min for 18min. Collect the supernatant to obtain a monolayer V4C3-MXene dispersion (concentration 0.01g / mL). V4C3-MXene dispersion with a concentration of 0.01 g / mL was slowly added to the cross-linked acrylic resin at a ratio of 2% of the mass of MXene to the cross-linked acrylic resin obtained in step (2). The mixture was stirred and dispersed at 28°C and 450 r / min for 70 min, and then ultrasonically dispersed for 35 min (power 180 W) to obtain a uniform MXene composite coating slurry, which is the protective coating. (4) The protective coating obtained in step (3) is applied to the surface of the pretreated marine concrete test block by spraying and cured in an oven at 55°C for 2.5 hours to obtain the MXene-based photothermal self-healing composite protective coating (coating dry film thickness 60μm).

[0095] Comparative Example 2 A composite protective coating differs from Example 2 in that the amount of MXene added is 1%, while the remaining composition and steps are the same as in Example 2.

[0096] Test Example 2 The performance of the MXene-based photothermal self-healing composite protective coating prepared in Example 2 and the composite protective coating prepared in Comparative Example 2 were tested respectively. The test methods and results are as follows: (1) Self-healing performance test: Microcracks with a width of 40 μm were prepared on the coating surface and cured for 24 h under natural light at 25 °C. The crack repair efficiency of the protective coating in Example 2 as the coating reached 82.3%; after curing for 24 h under light and heat at 50 °C, the repair efficiency increased to 91.1%, which was higher than the 76.8% of the coating in Comparative Example 2.

[0097] (2) Photothermal performance test: The surface temperature of the coating rises to 55°C after 10 minutes of simulated sunlight irradiation, providing sufficient heat for dynamic bond recombination.

[0098] (3) Corrosion resistance test: The test blocks were immersed in a 3.5% NaCl solution for 30 days. The water absorption rate of the concrete test blocks with the self-healing coating of the protective coating prepared in Example 2 was only 2.3%, which was much lower than the 4.8% of the coating of the protective coating prepared in Comparative Example 2. This shows that the self-healing coating formed by the protective coating prepared in the present invention effectively blocks the intrusion of corrosive ions.

[0099] Comparative Example 3 An acrylic coating is obtained by polymerizing a mixture of the following components: a monomer mixture, an initiator (ammonium persulfate), a chain transfer agent (tert-dodecyl mercaptan), and a solvent (methyl isobutyl ketone). The monomer mixture comprises acrylate monomer (butyl acrylate), methacrylate monomer (methyl methacrylate), and urea methacrylate monomer (ethylidene urea ethoxylate); the molar ratio of butyl acrylate, methyl methacrylate, and ethylidene urea ethoxylate is 25:20:25. The initiator (ammonium persulfate) accounts for 2.5% of the monomer mixture by mass. The chain transfer agent (tert-dodecyl mercaptan) accounts for 1.5% of the monomer mixture by mass. The solvent (methyl isobutyl ketone) accounts for 80% of the monomer mixture by mass. The preparation method of the acrylic coating is as follows: (1) Mix butyl acrylate, methyl methacrylate and ethyl urea methacrylate to obtain a monomer mixture; mix the monomer mixture with ammonium persulfate to obtain a monomer mixture containing an initiator; (2) Add methyl isobutyl ketone and tert-dodecyl mercaptan chain transfer agent to a three-necked flask to obtain a chain transfer agent solution. Add 20% of the weight of the monomer mixture containing the initiator obtained in step (1) to the three-necked flask, stir evenly and purge nitrogen into the three-necked flask for 30 min. At the same time, control the reaction temperature of the reaction mixture at 110°C under nitrogen protection. Divide the remaining monomer mixture containing the initiator into 6 equal parts and add one part every 20 min. React continuously for 3 h under nitrogen protection to obtain a transparent and viscous acrylic resin product, which is an acrylic coating. (3) After spraying the acrylic coating obtained in step (2) to form a coating, cure it at 60°C for 2 hours to obtain the coating (abbreviated as AC).

[0100] Comparative Example 4 An acrylic coating is obtained by polymerizing a mixture of the following components: a monomer mixture, an initiator (ammonium persulfate), a chain transfer agent (tert-dodecyl mercaptan), and a solvent (methyl isobutyl ketone). The monomer mixture comprises acrylate monomer (butyl acrylate), methacrylate monomer (methyl methacrylate), urea methacrylate monomer (ethylidene urea ethoxylate), and 3,3'-diacetoxybutyl dithiodipropionate; the molar ratio of butyl acrylate, methyl methacrylate, ethylidene urea ethoxylate, and 3,3'-diacetoxybutyl dithiodipropionate is 25:20:25:20. The initiator (ammonium persulfate) accounts for 2.5% of the monomer mixture by mass. The chain transfer agent (tert-dodecyl mercaptan) accounts for 1.5% of the monomer mixture by mass. The solvent (methyl isobutyl ketone) accounts for 80% of the monomer mixture by mass. The preparation method of the acrylic coating is as follows: (1) Butyl acrylate, methyl methacrylate, ethyl urea ethoxy methacrylate and 3,3'-diacryloyloxybutyl dithiodipropionate are mixed to obtain a monomer mixture; the monomer mixture is mixed with ammonium persulfate to obtain a monomer mixture containing an initiator; (2) Add methyl isobutyl ketone and tert-dodecyl mercaptan chain transfer agent to a three-necked flask to obtain a chain transfer agent solution. Add 20% of the weight of the monomer mixture containing the initiator obtained in step (1) to the three-necked flask, stir evenly and purge nitrogen into the three-necked flask for 30 min. At the same time, control the reaction temperature of the reaction mixture at 110°C under nitrogen protection. Divide the remaining monomer mixture containing the initiator into 6 equal parts, add one part every 20 min, and react continuously for 3 h under nitrogen protection to obtain acrylic coating. (3) After spraying the acrylic coating obtained in step (2) to form a coating, cure it at 60°C for 2 hours to obtain the coating (abbreviated as AC-AM).

[0101] Comparative Example 5 An acrylic coating is obtained by polymerizing a mixture of the following components: a monomer mixture, an initiator (ammonium persulfate), a chain transfer agent (tert-dodecyl mercaptan), and a solvent (methyl isobutyl ketone). The monomer mixture comprises acrylate monomer (butyl acrylate), methacrylate monomer (methyl methacrylate), urea methacrylate monomer (ethylidene urea ethoxylate), and capsaicin derivative (N-(2,3,4-trihydroxy-5-acrylamide methylbenzyl)acrylamide); the molar ratio of butyl acrylate, methyl methacrylate, ethylidene urea ethoxylate, and N-(2,3,4-trihydroxy-5-acrylamide methylbenzyl)acrylamide is 25:20:25:1. The initiator (ammonium persulfate) accounts for 2.5% of the monomer mixture by mass. The chain transfer agent (tert-dodecyl mercaptan) accounts for 1.5% of the monomer mixture by mass. The solvent (methyl isobutyl ketone) accounts for 80% of the monomer mixture by mass. The preparation method of the acrylic coating is as follows: (1) Butyl acrylate, methyl methacrylate, ethyl urea methacrylate, and 3,N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide are mixed to obtain a monomer mixture; the monomer mixture is mixed with ammonium persulfate to obtain a monomer mixture containing an initiator; (2) Add methyl isobutyl ketone and tert-dodecyl mercaptan chain transfer agent to a three-necked flask to obtain a chain transfer agent solution. Add 20% of the weight of the monomer mixture containing the initiator obtained in step (1) to the three-necked flask, stir evenly and purge nitrogen into the three-necked flask for 30 min. At the same time, control the reaction temperature of the reaction mixture at 110°C under nitrogen protection. Divide the remaining monomer mixture containing the initiator into 6 equal parts and add one part every 20 min. React continuously for 3 h under nitrogen protection to obtain a transparent and viscous acrylic resin product, which is an acrylic coating. (3) After spraying the acrylic coating obtained in step (2) to form a coating, cure it at 60°C for 2 hours to obtain the coating (abbreviated as AC-DS).

[0102] Comparative Example 6 An acrylic coating is obtained by polymerizing a mixture of the following components: a monomer mixture, an initiator (ammonium persulfate), a chain transfer agent (tert-dodecyl mercaptan), and a solvent (methyl isobutyl ketone). The monomer mixture comprises acrylate monomer (butyl acrylate), methacrylate monomer (methyl methacrylate), urea methacrylate monomer (ethylidene urea ethoxylate), 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivative (N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide); the molar ratio of butyl acrylate, methyl methacrylate, ethylidene urea ethoxylate, 3,3'-diacetoxybutyl dithiodipropionate, and N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide is 25:20:25:20:1. The initiator (ammonium persulfate) accounts for 2.5% of the monomer mixture by mass. The chain transfer agent (tert-dodecyl mercaptan) accounts for 1.5% of the monomer mixture by mass. The solvent (methyl isobutyl ketone) accounts for 80% of the monomer mixture by mass. The preparation method of the acrylic coating is as follows: (1) Butyl acrylate, methyl methacrylate, ethyl urea ethoxy methacrylate, 3,3'-diacryloyloxybutyl dithiodipropionate and N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide are mixed to obtain a monomer mixture; the monomer mixture is mixed with ammonium persulfate to obtain a monomer mixture containing an initiator; (2) Add methyl isobutyl ketone and tert-dodecyl mercaptan chain transfer agent to a three-necked flask to obtain a chain transfer agent solution. Add 20% of the weight of the monomer mixture containing the initiator obtained in step (1) to the three-necked flask, stir evenly and purge nitrogen into the three-necked flask for 30 min. At the same time, control the reaction temperature of the reaction mixture at 110°C under nitrogen protection. Divide the remaining monomer mixture containing the initiator into 6 equal parts and add one part every 20 min. React continuously for 3 h under nitrogen protection to obtain a transparent and viscous acrylic resin product, which is an acrylic coating. (3) After the acrylic coating obtained in step (2) is sprayed to form a coating, it is cured at 60°C for 2 hours to obtain a coating (abbreviated as AC-AMDS); the solid content of the acrylic coating is calculated by conventional solid content calculation method to be 96.7% by weight.

[0103] Test Example 3 The coating-self-healing behavior correlation diagrams of the acrylic coatings prepared in Comparative Examples 3-6 are shown below. Figure 1 As shown. In Figure 1 In the figure, the temperature parameter represents the environmental temperature conditions under which the coating undergoes a self-healing reaction, and the time parameter represents the time it takes for the coating to heal completely from damage at the corresponding temperature. At 25℃, the scratches on each coating showed almost no repair; at 50℃, AC showed no significant change, AC-AM scratches narrowed, AC-DS scratches were almost closed, and AC-AMDS scratches healed significantly; at 75℃, AC only showed edge passivation, AC-AM / AC-DS showed enhanced repair, and AC-AMDS scratches completely disappeared (the surface returned to continuity). Meanwhile, under aquatic conditions, after immersion in 25℃ water for one day, the outline of AC-AM scratches faded, and AC-AMDS showed the best repair effect, demonstrating the promoting effect of water molecules on the dynamic rearrangement of hydrogen bonds.

[0104] Figure 2 The images show the fluorescence distribution of the acrylic coatings prepared in Comparative Examples 3-6. Figure 2 As can be seen, the coatings exhibit significantly different fluorescence responses before and after water immersion. The figure shows the green fluorescence phenomenon of the coatings under 365nm ultraviolet light irradiation.

[0105] Figure 3This is a bar chart showing the water contact angles of the acrylic coatings prepared in Comparative Examples 3-6. The contact angle values ​​represent the degree of hydrophobicity of the coating surface (higher values ​​indicate stronger hydrophobicity). Figure 3 As can be seen, the AC-AMDS coating has a contact angle of 92.1°, which is significantly higher than other formulations, proving that it has better surface hydrophobicity and can reduce the adhesion of water on the coating surface.

[0106] Figure 4 The capillary water absorption rate of the acrylic coatings prepared for comparative examples 3-6 changes over 96 hours. Figure 4 In the comparison, Blank serves as the blank group. Water absorption rate represents the coating's ability to absorb and retain moisture (the lower the value, the better the water resistance). From... Figure 4 As can be seen from the figure, the water absorption rate of the AC-AMDS coating increases the most gradually, and the final value is much lower than that of the Blank group. Combined with the contact angle data in the left figure, this verifies that the coating of this formulation has better waterproof and seepage-proof performance.

[0107] Figure 5 SEM images and elemental mapping diagrams of C, O, N, and S for the acrylic coatings prepared in comparative examples 3-6 are shown. Figure 5 It can be seen that before self-healing, the scratch areas of each coating showed morphological fracture and interrupted element distribution; after self-healing, the AC coating had clear scratch outlines, but the C / O element distribution was still discontinuous; the AC-AM coating had shallower scratches, and the C / O / N element distribution tended to be uniform; the AC-DS coating had basically filled the scratches, and the S element was continuously distributed in the original scratch area; and the AC-AMDS coating had the C / O / N / S element distribution consistent with the undamaged area.

[0108] The results above demonstrate that the MXene-based photothermal self-healing composite protective coating provided by this invention exhibits highly efficient self-healing capabilities at room temperature, while also possessing excellent waterproof and impermeable properties and hydrophobicity, making it particularly suitable for protecting marine engineering concrete. Furthermore, the preparation of this protective coating is simple, uses readily available raw materials, and is cost-effective, indicating significant development potential.

[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An MXene-based photothermal self-healing composite protective coating, characterized in that, The MXene-based photothermal self-healing composite protective coating is obtained by curing a protective coating film; the protective coating is obtained by mixing cross-linked acrylic resin and MXene. The MXene accounts for 2-10% of the mass of the crosslinked acrylic resin; The crosslinked acrylic resin is obtained by polymerizing a mixture of raw materials comprising the following components: monomer mixture, initiator, chain transfer agent and solvent; The monomer mixture comprises acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivatives; the molar ratio of the acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate, and capsaicin derivatives is (20~50):(20~60):(20~60):(5~20):(0.5~2). The capsaicin derivative is N-(2,3,4-trihydroxy-5-acrylamide methyl benzyl)acrylamide.

2. The MXene-based photothermal self-healing composite protective coating according to claim 1, characterized in that, The acrylate monomers include one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, and octadecyl acrylate.

3. The MXene-based photothermal self-healing composite protective coating according to claim 1, characterized in that, The methacrylate monomers include one or more of methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, and octadecyl methacrylate.

4. The MXene-based photothermal self-healing composite protective coating according to claim 1, characterized in that, The urea methacrylate monomer includes one or more of ethoxylated ethyl urea methacrylate, ethyl urea methacrylate ethoxylate, and ethyl urea methacrylate.

5. The MXene-based photothermal self-healing composite protective coating according to claim 1, characterized in that, The MXene is a single-layer V4C3-MXene.

6. The MXene-based photothermal self-healing composite protective coating according to claim 1, characterized in that, The initiator accounts for 0.5-3.4% of the monomer mixture by mass; the chain transfer agent accounts for 0.5-2.5% of the monomer mixture by mass; and the solvent accounts for 70-120% of the monomer mixture by mass.

7. A method for preparing the MXene-based photothermal self-healing composite protective coating according to any one of claims 1 to 6, comprising the following steps: (1) Mix acrylate monomers, methacrylate monomers, urea methacrylate monomers, 3,3'-diacetoxybutyl dithiodipropionate, capsaicin derivatives and initiators to obtain a monomer mixture containing initiators; (2) Dissolve the chain transfer agent in a solvent to obtain a chain transfer agent solution; in an inert atmosphere, mix the monomer mixture containing the initiator obtained in step (1) with the chain transfer agent solution to carry out a crosslinking reaction to obtain a crosslinked acrylic resin; (3) The cross-linked acrylic resin obtained in step (2) is mixed with MXene to obtain a protective coating; (4) Apply the protective coating obtained in step (3) onto the substrate and carry out a curing reaction to obtain an MXene-based photothermal self-healing composite protective coating.

8. The application of the MXene-based photothermal self-healing composite protective coating according to any one of claims 1 to 6 or the MXene-based photothermal self-healing composite protective coating prepared by the preparation method according to claim 7 as a protective coating for marine concrete surfaces.

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