Long-acting super-hydrophobic microcapsules, preparation method and application thereof

Abstract

The application discloses long-acting super-hydrophobic microcapsules, a preparation method and application thereof, and belongs to the technical field of super-hydrophobic materials. The long-acting super-hydrophobic microcapsules comprise a shell layer and a reactive core material wrapped in the shell layer; the outer surface of the shell layer is a rough surface formed by dispersed particle protrusions; the particle protrusions are formed by accumulation of a plurality of nanoparticles; a cross-linked polymer network is covered on the outer surface of the shell layer; the cross-linked polymer network is a polydimethylsiloxane functionalized SiO2 nanoparticle network; and the material of the shell layer is preferably polyurea formaldehyde, and the reactive core material is preferably hexamethylene diisocyanate. The long-acting super-hydrophobic microcapsules provided by the application exhibit excellent thermal stability, super-hydrophobicity, self-cleaning and wear resistance, not only prolonging the service life of the microcapsules, but also ensuring the stability and reliability of the microcapsules under complex environmental conditions, thus having great significance for solving the problem of hydrophobic function failure of the microcapsules caused by environmental factors.

Description

Technical Field

[0001] This application relates to a long-lasting superhydrophobic microcapsule, its preparation method, and its application, belonging to the field of superhydrophobic materials technology. Background Technology

[0002] Superhydrophobic materials, due to their unique wetting properties, have shown broad application prospects in various fields, including self-cleaning, antifogging, oil-water separation, anti-fogging, anti-icing, corrosion resistance, and new transportation equipment. Among these, superhydrophobic materials with antifogging properties have attracted considerable attention in self-cleaning applications. The superhydrophobicity of a material surface is mainly determined by its chemical composition and surface microstructure. On superhydrophobic surfaces, due to the high contact angle (>150°) and low adhesion, water droplets will roll off at slight tilt angles. For example, the excellent superhydrophobicity of rice leaves is attributed to their ultra-low surface energy nano / micro-scale structure. This structure is formed through the Cassie-Baxter wetting state. The air trapped within the rough protrusions maintains a stable liquid-gas interface with the water droplet, preventing water penetration and minimizing contact between the solid and the water. Unlike ordinary smooth surfaces (such as glass), rolling water droplets collect dust particles from superhydrophobic surfaces, exhibiting self-cleaning efficiency. Therefore, superhydrophobic properties of material surfaces can be achieved by introducing low surface energy materials or constructing surface micro / nano hierarchical structures. In practical applications, superhydrophobic properties are inevitably affected by external environmental factors such as chemical corrosion and mechanical wear. These factors may lead to the loss of low surface energy components or the destruction of micro-nano hierarchical structures, resulting in a decrease in superhydrophobic properties. Although existing hydrophobic microcapsules help protect the core material and prolong its release time, they do not clearly demonstrate their performance and advantages in terms of long-term effectiveness. However, long-term hydrophobic effectiveness is of great significance for the practical application of microcapsules, especially when facing environmental factors such as temperature changes, mechanical stress, or chemical erosion. Environmental factors may cause damage or rupture of the microcapsule wall, thereby causing leakage of the hydrophobic core material and leading to microcapsule failure.

[0003] Currently, superhydrophobic materials synthesized on a large scale using methods such as hydrothermal synthesis, physical vapor deposition, and polymer phase separation exhibit weak mechanical stability, insufficient to meet the needs of most practical applications. Furthermore, there are few reports on constructing robust multilayer hydrophobic surface structures that maintain stable sliding angles during wear through chemical deposition, layer-by-layer deposition, colloidal assembly, or electrospinning modification methods. The design of long-lasting superhydrophobic materials is based on the self-healing potential of low surface energy substances or surface microstructures. Currently, there are two main methods for constructing long-lasting superhydrophobic coating materials: one is to construct a superhydrophobic system capable of replenishing low surface energy components, and the other is to construct a superhydrophobic system capable of reconstructing multi-level micro / nano structures. A common method is to graft fluorine-containing segments or load other low surface energy substances into the material bulk, utilizing the material's pores or microcapsules as storage sites for these low surface energy substances. However, existing durable superhydrophobic microcapsules suffer from poor self-release effects, low modification efficiency, and low controllability, failing to achieve long-lasting and stable self-cleaning functions. Summary of the Invention

[0004] To address the problems of weak durability and short lifespan of superhydrophobic microcapsules prepared using traditional techniques, which easily lose their original self-cleaning and anti-fouling functions under adverse external environments, and the low production efficiency and poor effectiveness of traditional microcapsule modification methods, hindering the widespread application of long-lasting superhydrophobic microcapsules, this application provides a long-lasting superhydrophobic microcapsule, its preparation method, and its application. The invention designs and prepares core-shell structured microcapsules containing hexamethylene diisocyanate as a self-healing core material, providing the microcapsule surface with durable, regenerative superhydrophobic properties to promptly repair damage to surface components or structures caused by friction and wear. Furthermore, the sol-gel method is used to modify the microcapsule surface with PDMS@TEOS to improve hydrophobicity and toughness, enhancing the material's self-cleaning and anti-friction and wear capabilities. This allows the superhydrophobic properties of the coating material to be restored in coating applications, extending the lifespan of the microcapsules.

[0005] The technical solution adopted in this application is as follows:

[0006] A long-lasting superhydrophobic microcapsule, the long-lasting superhydrophobic microcapsule comprising a shell and a reactive core material encapsulated inside the shell;

[0007] The outer surface of the shell is a rough surface formed by dispersed particle protrusions;

[0008] The particle protrusions are formed by the accumulation of several nanoparticles.

[0009] The outer surface of the shell is covered with a cross-linked polymer network;

[0010] The cross-linked polymer network is a polydimethylsiloxane-functionalized SiO2 nanoparticle network.

[0011] The shell material is selected from at least one of polyurea formaldehyde and polyurethane;

[0012] The reactive core material is selected from at least one of hexamethylene diisocyanate, 1,4-diisocyanate butane, and 1,8-diisocyanate octane.

[0013] The methods and concepts proposed in this application can be applied to other similar core-shell material combinations, such as a shell material of polyurethane (PU) and a core material of 1,4-diisocyanate butane or 1,8-diisocyanate octane.

[0014] Preferably, the shell is made of polyurea formaldehyde, and the reactive core material is hexamethylene diisocyanate.

[0015] Optionally, the material of the stack of several nanoparticles with granular protrusions is the same as that of the shell.

[0016] Optionally, the rough surface formed by the particle protrusions constitutes an ultra-low surface energy protective layer, which is formed by the chemical reaction between the reactive core material expanding to the outer surface of the shell and the polar groups on the shell surface.

[0017] Optionally, the polydimethylsiloxane-functionalized SiO2 nanoparticle network is a cross-linked structure formed by the reaction of polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS), wherein the tetraethoxysilane forms the SiO2 nanoparticle network during hydrolysis and condensation in the reaction process.

[0018] The long-lasting superhydrophobic microcapsules in this application possess the characteristic of reactive core material self-diffusion from the shell. Hexamethylene diisocyanate (HDI) self-diffusion from the shell and its reaction with hydrophilic groups on the shell surface is key to achieving long-lasting hydrophobicity. During the preparation process, the protrusions in the polyurea-formaldehyde (PUF) nanoparticles are due to the precipitation of the prepolymer from the aqueous suspension. During use, when hydrophilic groups are present on the outside of the microcapsules, the core material HDI diffuses to the microcapsule surface and reacts with it, also forming a hydrophobic polymer.

[0019] According to another aspect of this application, a method for preparing the above-mentioned long-lasting superhydrophobic microcapsules is provided, comprising the following steps:

[0020] S1. Adjust the pH of the formaldehyde aqueous solution to alkaline, then mix it with urea to obtain a shell raw material solution, heat it to react, and obtain a prepolymer of urea-formaldehyde aqueous suspension;

[0021] S2. Add all of the prepolymer of the urea-formaldehyde aqueous suspension from step S1 to a mixture of ethyl methacrylate (EMA) aqueous solution and water, stir I, then add hexamethylene diisocyanate (HDI) dropwise, stir II to form an emulsion, adjust the pH to acidic, and obtain superhydrophobic microcapsules.

[0022] S3. In a closed environment, the superhydrophobic microcapsules obtained in step S2 are subjected to steam treatment using a solution containing polydimethylsiloxane and tetraethoxysilane, and then subjected to sol-gel reaction in a catalyst solution vapor environment to obtain the long-lasting superhydrophobic microcapsules.

[0023] Optionally, in step S3, the weight ratio of polydimethylsiloxane to tetraethoxysilane is 1 to 8:1;

[0024] Optionally, in step S3, the catalyst solution is a liquid of propanol and ammonia, wherein the volume ratio of propanol to ammonia is 3 to 5:1.

[0025] Optionally, in step S3, the conditions for the sol-gel reaction include: a reaction temperature of 35–55°C, a reaction time of 0.5–1 h, and a curing time of 6–12 h after the reaction; this process is a catalyst solution vapor treatment process.

[0026] Optionally, the steam treatment conditions include a steam treatment time of 10–30 min. This process is a steam treatment of a PDMS@TEOS mixed solution, with ambient temperature and pressure conditions.

[0027] Optionally, the conditions for the sol-gel reaction may further include controlling the pH of the catalyst solution to be 8.5 to 9.5.

[0028] Optionally, during the steam treatment process, the superhydrophobic microcapsules are placed on a 250-350 mesh fabric.

[0029] Optionally, in step S1, the shell material liquid contains 5 to 9 parts by weight of 37 wt% formaldehyde aqueous solution and 2.5 to 4.5 parts by weight of urea.

[0030] Optionally, in step S1, the conditions for adjusting the pH to alkaline include: adding triethanolamine (TEA) to adjust the pH of the formaldehyde aqueous solution to 7.5-9.5;

[0031] Optionally, in step S1, the conditions for the heating reaction include: a reaction temperature of 60–80°C and a reaction time of 60–90 min.

[0032] Optionally, in step S1, the shell material liquid is in a stirred state during the heating reaction process.

[0033] Optionally, in step S2, the mixture contains 12 to 22 parts by weight of a 3.0 wt% aqueous solution of ethyl methacrylate and 30 to 50 parts by weight of water;

[0034] Optionally, in step S2, 5 to 15 parts by weight of hexamethylene diisocyanate are added dropwise;

[0035] Optionally, in step S2, the conditions for stirring I include: stirring for 10 to 20 minutes at 20 to 25°C and 250 to 350 rpm;

[0036] Optionally, in step S2, the conditions for stirring II include: stirring for 10 to 20 minutes at 20 to 25°C and a speed of 700 to 1000 rpm;

[0037] Optionally, in step S2, the conditions for adjusting the pH to acidity include: after the emulsion has stabilized for 20 to 30 minutes, adjusting the pH of the emulsion to 1 to 2 using a citric acid aqueous solution with a pH of 0.3.

[0038] Optionally, in step S2, the mixture may further include 0.2 to 0.3 parts by weight of resorcinol.

[0039] Optionally, in step S2, after adjusting the pH to acidic, the reaction is continued for 1 to 2 hours at 40–50°C and 100–200 rpm.

[0040] The sol-gel surface treatment technology provided in this application for generating durable and robust superhydrophobic microcapsule coatings is an advanced and efficient method for material surface modification. This technology forms a dense and uniform coating on the surface of microcapsules through a sol-gel process, thereby significantly improving the mechanical strength and durability of the microcapsules. The core of the sol-gel technology of this invention lies in gelling the hydrophobic layer PDMS@TEOS under appropriate conditions, ultimately forming a micro / nano-scale protective coating on the surface of the microcapsules. This coating not only endows the microcapsules with excellent superhydrophobicity, effectively preventing the penetration of water and other liquids, but also possesses good self-cleaning properties. Furthermore, due to the unique micro / nano structure of this coating and its good physical / chemical stability, the microcapsules can maintain their functionality even when subjected to mechanical friction or chemical erosion. By improving the service life and reliability of materials through this sol-gel surface treatment technology, superhydrophobic microcapsule coatings suitable for various environments can be prepared, with wide applications in waterproofing, antifouling, and anti-corrosion fields. Therefore, sol-gel treated reactive microcapsules are a promising method for developing multifunctional, robust, and durable self-cleaning coatings.

[0041] This application utilizes a cross-linked polymer network (composed of PDMS@TEOS) to provide a robust, hierarchical superhydrophobic surface on reactive microcapsules. This network, composed of polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS), forms a cross-linked structure through a chemical reaction. First, PDMS provides excellent flexibility and hydrophobicity, resulting in an ultra-low surface energy. Meanwhile, TEOS forms a silica network during hydrolysis and condensation reactions, enhancing the overall mechanical strength and stability of the structure. Through this cross-linked polymer network, the microcapsule surface not only possesses superhydrophobicity but also exhibits significant wear resistance. This hierarchical structure further optimizes the functionality of the microcapsules, providing multi-layered protection and maintaining stable performance even in harsh physical and chemical environments. The application of the PDMS@TEOS cross-linked polymer network provides an innovative surface treatment method for microcapsule technology, significantly enhancing its application prospects in industrial coatings, waterproofing materials, and self-cleaning surfaces. This method allows microcapsules to maintain high functionality while achieving longer service life and higher reliability, meeting diverse practical application requirements.

[0042] The long-lasting superhydrophobic microcapsules provided in this application achieve a sustainably low surface energy in the microcapsule shell primarily due to the diffusion mechanism of the reactive core material, a process that can occur at room temperature. When the core material diffuses to the microcapsule surface, it spontaneously reacts chemically with polar groups on the shell surface. These polar groups are typically hydrophilic functional groups remaining from the shell material during preparation or from the external environment; through reaction with the core material, these polar groups are effectively neutralized. Due to the high reactivity of the core material, this diffusion and reaction process can proceed rapidly and efficiently, forming a protective layer with ultra-low surface energy on the microcapsule surface. This results in excellent hydrophobicity and antifouling properties, while simultaneously enhancing the stability and durability of the microcapsules under various environmental conditions. Since this process can be carried out at room temperature without additional heating or complex processing steps, it offers high economic efficiency and operability. This innovative surface modification method provides new possibilities for the promotion and application of microcapsule technology in demanding application scenarios, significantly improving the functionality and market competitiveness of microcapsules.

[0043] According to another aspect of this application, at least one of the above-described long-lasting superhydrophobic microcapsules or the long-lasting superhydrophobic microcapsules prepared by the above-described preparation method is provided for use in industrial coatings, waterproof materials or self-cleaning coatings.

[0044] Optionally, the application includes spraying a primer onto the surface of the target product, and then spraying long-lasting superhydrophobic microcapsules onto the primer.

[0045] Optionally, microcapsule powder can be sprayed using a powder coating instrument.

[0046] Optionally, the primer is not strictly limited and can be selected as needed, such as epoxy resin materials.

[0047] Optionally, the surface of the target product is a metal substrate.

[0048] In this application:

[0049] PUF stands for polyurea formaldehyde.

[0050] HDI stands for hexamethylene diisocyanate.

[0051] PDMS stands for polydimethylsiloxane.

[0052] TEOS is tetraethoxysilane.

[0053] WCA is the water contact angle.

[0054] SA is the sliding angle.

[0055] The beneficial effects that this application can produce include:

[0056] The long-lasting superhydrophobic microcapsules provided in this application integrate PDMS-functionalized SiO2 nanoparticles through sol-gel treatment on the microcapsule shell, enabling the microcapsules to exhibit excellent thermal stability at high temperatures up to 217°C and also demonstrate excellent superhydrophobicity. In the preferred embodiment, the water contact angle (WCA) can reach 165.2±0.4°, and the sliding angle (SA) can reach 2.6±1.5°. In addition to excellent heat resistance and superhydrophobicity, the long-lasting superhydrophobic microcapsules of this application maintain superhydrophobic surface stability even after wear tests, water immersion tests under a wide range of conditions, and aging tests after exposure to high-intensity ultraviolet light. These properties provide a good solution for developing long-lasting self-cleaning microcapsule coatings with excellent thermal stability and anti-aging properties.

[0057] This application presents a method for preparing long-lasting superhydrophobic microcapsules. The process is simple, widely applicable, and low-cost, making it suitable for large-scale preparation of durable and robust superhydrophobic microcapsules. Furthermore, the design and manufacturing of the microcapsules emphasize enhancing their long-lasting hydrophobicity. By optimizing the selection of shell materials and the preparation process, the microcapsules release enhanced hydrophobic substances during service, maintaining their hydrophobic function. This not only extends the lifespan of the microcapsules but also ensures their stability and reliability under complex environmental conditions. Therefore, it is of great significance for solving the problem of microcapsule hydrophobic function failure caused by environmental factors and provides a more durable and efficient solution for the practical application of hydrophobic microcapsules. Attached Figure Description

[0058] Figure 1This paper describes the preparation principle and process of long-lasting superhydrophobic microcapsules, including: (a) a schematic diagram of constructing a hydrophobic PDMS@TEOS layer on HDI microcapsules via sol-gel vapor deposition in a sealed reaction chamber; (b) and (c) schematic mechanisms of constructing a hydrophobic PDMS@TEOS layer on HDI microcapsules via sol-gel vapor deposition; and (d) a schematic diagram of fabricating a sol-gel-treated microcapsule assembly coating on a metal substrate. An epoxy resin matrix was selected as the primer coating.

[0059] Figure 2 This is a schematic diagram illustrating the mechanism by which sol-gel treated microcapsules transform from hydrophilic to superhydrophobic as aging time increases.

[0060] Figure 3 The superhydrophobic stability tests of untreated and sol-gel treated microcapsule coatings are shown in the following figures: (a) is a visual image of blue-dyed water droplets on a metal substrate; (b) is a visual image of water droplets on a sol-gel treated microcapsule coating (1 day); (c) is a visual image of water jets on the surface of an untreated microcapsule coating (1 day); (d) is a visual image of water jets on the surface of a sol-gel treated microcapsule coating (1 day); (e) is a camera photograph of a 5 ml water droplet contacting, deforming, and leaving the surface of a sol-gel treated microcapsule coating; (f) and (g) are graphs showing the relationship between the aging time of the untreated microcapsules and the sol-gel treated microcapsule coatings at room temperature and the changes in WCA and SA.

[0061] Figure 4 The abrasion resistance tests were conducted on untreated and sol-gel treated microcapsule coatings, where: (a) is a schematic diagram of the abrasion tester; (b) and (c) show the changes in the contact angles of the untreated microcapsule coating and the sol-gel treated microcapsule coating with blue-dyed water and orange-dyed ethylene glycol before and after 4500 abrasion cycles; (d) and (e) show the changes in the sliding angles of the untreated microcapsule coating and the sol-gel treated microcapsule coating with water and ethylene glycol. Before testing, both the untreated and sol-gel treated microcapsules were aged at room temperature for 8 days.

[0062] Figure 5 These are SEM images of untreated and sol-gel treated microcapsule coatings before and after wear, where: (a) is an overview of the untreated microcapsule coating before wear; (b) is a magnified image of spherical microcapsules with hierarchical surface shells; (c) is an overview of the untreated microcapsule coating after 4500 sandpaper cycles of wear; (d) is a magnified image of flat microcapsules with damaged surface structures; (e) is an overview of the sol-gel treated microcapsule coating before wear; (f) is a magnified image of sol-gel treated microcapsules with solid shells; (g) is an overview of the sol-gel treated microcapsule coating after 4500 sandpaper cycles of wear; and (h) is a magnified image of sol-gel treated microcapsules showing a rough shell structure after wear.

[0063] Figure 6 The UV aging tests were conducted on untreated and sol-gel treated microcapsule coatings, where (a) and (b) show the effects of UV aging on WCAs and SAs of the untreated and sol-gel treated microcapsule coatings, respectively. Before testing, the untreated and sol-gel vapor-treated microcapsules were aged at room temperature for 8 days; images of the coatings for the antifouling test are shown in: (c) untreated microcapsules (before water flow test), (d) untreated microcapsules (after water flow test), (e) sol-gel treated microcapsules (before water flow test), and (f) sol-gel treated microcapsules (after water flow test).

[0064] Figure 7 These are SEM images of HDI microcapsules, where: (a) is an overview of the spherical HDI microcapsules; (b) is a magnified view of a single microcapsule showing its rough outer surface; (c) shows the accumulation of PUF nanoparticles on the outside of the HDI microcapsules; and (d) is an extended view of the PUF nanoparticles on the microcapsule wall.

[0065] Figure 8 SEM images of the complete sol-gel treated microcapsules obtained at different reaction times are shown, where: (a) is the SEM image at 0 min reaction time, (b) is the SEM image at 20 min reaction time and (c) is the SEM image at 60 min reaction time, and the magnified image on the right panel was taken at a higher magnification; (d) and (e) are the AFM 3D surface structures, (f) and (g) are the corresponding 2D images, and (h) and (i) are the cross-sectional roughness profiles; (d), (f), and (h) are the surface of the HDI microcapsules and (e), (g), and (i) are the surface of the sol-gel treated microcapsules. The synthesis conditions for the sol-gel modified microcapsules were a reaction at 55 °C for 60 min and a TEOS / PDMS mass ratio of 5.

[0066] Figure 9 The effect of the PDMS@TEOS mass ratio on the water contact angle (WCA) of the sol-gel modified microcapsule assembly coating during temperature changes is investigated.

[0067] Figure 10 The test is a thermal stability test, in which: (a) the residual weight of HDI microcapsules and sol-gel treated HDI microcapsules changes with temperature, and (b) the residual weight of pure HDI and sol-gel treated microcapsules changes with time. Detailed Implementation

[0068] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0069] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0070] Unless otherwise specified, all test methods are conventional and all instrument settings are those recommended by the manufacturer.

[0071] The specific preparation method and conditions for the long-lasting superhydrophobic microcapsule coating used in the test example were as follows: The surface of an aluminum substrate (6cm × 6cm) was ultrasonically cleaned with 99.5% acetone for later use. A layer of polyurethane primer (500μm) was first sprayed onto the aluminum substrate using a 0.5mm diameter Taiwan KL3 spray gun at a pressure of 50psi, followed by spraying 0.1g of superhydrophobic microcapsules onto the primer to form a long-lasting superhydrophobic microcapsule coating.

[0072] The superhydrophobic stability test was conducted using the Biolin Attension Theta Lite contact angle tester.

[0073] The abrasion resistance test was conducted using a Taber 1700 abrasion tester.

[0074] The instrument used for the ultraviolet aging test was the Q-Lab QUV accelerated aging tester.

[0075] The self-cleaning performance test was conducted using a gray standard sample of a building coating with a stain resistance test. The contaminated coating was mounted on a support at a 45° angle. The surface was cleaned using a 150 mL water spray at a pressure of 1 bar and a distance of 25–30 cm to study its self-cleaning effect.

[0076] The thermal stability test was conducted using a TA Instruments Q500 thermogravimetric analyzer.

[0077] According to one embodiment of this application, an example diagram of the vapor deposition process for preparing sol-gel treated microcapsules by hydrolyzing and condensing PDMS@TEOS sol at different reaction temperatures in a sealed chamber is shown below. Figure 1 As shown in Figure a, the prepared HDI microcapsules were cured through two vapor deposition processes to obtain long-lasting superhydrophobic sol-gel modified HDI microcapsules. A highly elastic cross-linked PDMS@TEOS nanoshell was formed on the microcapsules using a mild sol-gel vapor surface modification method. This simple atomization application method is expected to significantly improve the coverage quality of the sol-gel solution (PDMS@TEOS) on the microcapsule surface. To stabilize the rough surface composed of aggregated PUF particles, PDMS@TEOS was synthesized via a condensation reaction of TEOS and PDMS as a hydrophobic precursor for modifying the microcapsules (reaction process as shown in Figure a). Figure 1b). Because PDMS is a hydrophobic, superelastic silicone rubber, and the combination of the mixed solution (PDMS@TEOS) can impart good adhesion and stability to the nanolayer, thus enabling better adhesion to the HDI microcapsules (attachment structure diagram shown). Figure 1 c). By spraying sol-gel modified microcapsules onto substrates such as epoxy resin and then applying them to metal substrates, sol-gel modified microcapsule coatings with superhydrophobic properties can be easily synthesized (the process is as follows). Figure 1 d). This elastic polyurea nanolayer structure is attributed to the inward-outward diffusion of the core material (microcapsule core material), followed by a spontaneous room-temperature chemical change on the microcapsule surface, consuming the hydrophilic groups on the PUF particle surface and continuously generating additional hydrophobic polyurea layers on the silica shell (reaction mechanism as follows). Figure 2 When external hydrophilic groups, such as -OH and -NH2, come into contact with the surface of the microcapsule, HDI containing -NCO groups diffused from the surface reacts with these hydrophilic groups to form a polyurea or polyurethane layer, which enhances the hydrophobicity of the microcapsule surface.

[0078] According to one embodiment of this application, a highly elastic cross-linked PDMS@TEOS nanoshell is formed on HDI microcapsules, thereby achieving excellent and durable self-cleaning properties. The diffusion-reactive core material eliminates polar groups on the microcapsule shell, achieving sustainable ultra-low surface energy, thus preparing durable superhydrophobic microcapsules. This invention provides a convenient and low-cost method for preparing durable superhydrophobic microcapsules. This method has simple preparation steps, is easy to operate, and features adjustable microcapsule size and water contact angle, overcoming the shortcomings of existing physical deposition methods, template methods, and layer-by-layer electrostatic self-organization methods. Therefore, the scalable manufacturing method of this invention for preparing durable and stable superhydrophobic microcapsules has significant commercial implications.

[0079] According to one embodiment of this application, synthesizing elastically deformable layered structures with ultra-low surface energy has the potential to improve the toughness and long-term stability of coatings. Promising layered synthesis strategies include elastomers, functional composites, and fluorosilane-based coatings. Among these, cross-linked polymer networks are extremely robust polymers. They consist of multiple polymer networks interlocked at the molecular level by mutual covalent bonds. Choosing cross-linked networks with polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) is a good option for synthesizing advanced solvent-protected superhydrophobic coatings. Currently, the realization of PDMS@TEOS structures on microcapsule surfaces to construct long-lasting superhydrophobic microcapsules for self-cleaning has not been investigated.

[0080] Example

[0081] (a) Preparation of HDI microcapsules (untreated microcapsules)

[0082] The pH of 7.0 g of 37 wt.% formaldehyde aqueous solution was adjusted to approximately 8.5 using triethanolamine (TEA). Then, 3.5 g of urea was added to a 20 mL vial and then to the alkaline aqueous solution. The vial was magnetically stirred in hot water at a preset temperature of 70°C. After 75 minutes of reaction, a prepolymer of urea-formaldehyde aqueous suspension was obtained.

[0083] 17 g of 3.0 wt.% EMA aqueous solution and 40 g of deionized water were poured into a 250 mL beaker. The prepolymer of the urea-formaldehyde aqueous suspension was added, and a 0.9 wt.% EMA aqueous solution was prepared by stirring at a gentle stirring speed of 300 rpm for 15 minutes at 22 °C using a three-bladed paddle stirrer. Subsequently, to initiate the emulsification process, the oil phase (HDI) was added dropwise to the 22 °C aqueous solution, and the stirring speed was increased to 900 rpm for 15 minutes. After stabilizing the emulsion system for 25 minutes, the pH of the system was controlled to approximately 1.5 using a citric acid aqueous solution with pH = 0.3 to initiate and promote in-situ polymerization. To increase the stability of the shell, 0.25 g of resorcinol was added to the synthesis system. To monitor the stability of the HDI microcapsules, the stirring speed was reduced to 300 rpm, and the mixture was stirred at 25 °C for 25 minutes. The reaction apparatus was then transferred back to a water bath, and the reaction was further carried out at 45 °C and 150 rpm for 1.5 hours. When the system cooled to room temperature, the reaction finally stopped, yielding HDI microcapsules, which were then washed and filtered five times with deionized water.

[0084] In this embodiment, HDI-containing microcapsules with rough-walled polyurethane foam (PUF) were prepared via in-situ polycondensation in a water-in-oil emulsion. The typical formation process of the HDI microcapsules was recorded using an optical microscope. The obtained optical microscope images and SEM images of the synthesized HDI microcapsules show that they have a spherical morphology. Figure 7 a) This is likely primarily due to the interaction of fluid-induced shear forces. Figure 1 At higher magnification ( Figure 7 (b) It can be clearly observed that the surface of the microcapsules is covered with particulate deposits, which should be PUF particles. With increasing molecular weight, the formation of PUF nanoparticles is likely due to the precipitation of prepolymers from an aqueous suspension. Their accumulation and deposition on the capsule surface leads to a roughness in the outer layer of the PUF shell, such as… Figure 7 As shown in c to d.

[0085] (II) Preparation of sol-gel treated HDI microcapsules

[0086] 10-15g of untreated HDI microcapsules from step (I) were evenly placed on a 300-mesh screen and then vapor-treated with a PDMS@TEOS mixed solution in a sealed chamber for 20 minutes to obtain pretreated HDI microcapsules. To form a PDMS@TEOS nanolayer, an alkaline-catalyzed sol-gel reaction of the pretreated HDI microcapsules was then carried out in a sealed chamber filled with catalyst solution vapor (propanol:ammonia = 4:1, v / v). The pH was controlled at 9 at different equilibrium temperatures. To perform this sol-gel vapor surface modification, the reaction time was increased to 1 hour. The microcapsules were then air-dried overnight in a fume hood, finally yielding robust, long-lasting, superhydrophobic sol-gel modified HDI microcapsules. Figure 8 As shown in (a)-(c). Furthermore, the effect of PDMS@TEOS mixed colloidal particles on the surface morphology of the microcapsules was evaluated using AFM. The morphological characteristics of untreated microcapsules and sol-gel treated microcapsules were measured using corresponding three-dimensional (3D), two-dimensional (2D) images and cross-sectional roughness profiles, as shown in... Figure 8 As shown in (d)-(i), the surface of the untreated microcapsules is very rough, with a root mean square roughness (RMS) of 1.74 nm. This is due to the presence of micro-aggregates of PUF resin particles. In contrast, the morphology of the microcapsules on the PDMS@TEOS superhydrophobic surface is significantly altered, with the hill-like protrusions of the PUF nanoparticles on the surface stabilized by a "wrinkled" structure caused by the co-hydrolysis and condensation reaction of PDMS and TEOS. Due to this unique structural feature, the RMS has been reduced to 1.14 nm. Therefore, the distance between the protrusions is crucial for trapping air in the recessed locations when water jumps off the microcapsule coating surface. The mass ratio of PDMS@TEOS and the alkali-catalyzed sol-gel reaction temperature vary, as shown in Table 1.

[0087] Table 1

[0088]

[0089]

[0090] Test Example 1: Hydrophobicity of Materials under Different Preparation Conditions

[0091] To obtain the optimal superhydrophobic coating, the effects of the PDMS@TEOS mass ratio and the alkali-catalyzed sol-gel reaction temperature on the wetting properties of the sol-gel modified microcapsule coating were carefully measured. The results are as follows: Figure 9As shown, the formulation and reaction temperature of PDMS@TEOS are crucial for generating appropriate PDMS@TEOS particles to control surface wetting behavior and enhance surface roughness. At the reaction temperature, the WCA of the microcapsule coating initially decreased as the mass ratio of TEOS to PDMS increased from 1:1 to 2:1, and then increased sharply as the mass ratio further increased from 2:1 to 5:1. No further improvement was observed when the mass ratio exceeded 5:1. Most interestingly, at a mass ratio of 5:1, the WCA gradually increased from 35°C to 55°C. Finally, at 55°C, the highest WCA of 165.2 ± 0.4°C was observed at a TEOS to PDMS mass ratio of 5:1, demonstrating the successful formation of a significantly superhydrophobic surface.

[0092] Test Example 2: Water Wetting Behavior Stability

[0093] The HDI microcapsules from Example 15 and the sol-gel treated HDI microcapsules were subjected to water wetting behavior stability tests. Water droplet testing on the original metal plate showed that the metal substrate is hydrophilic, with a water contact angle (WCA) of 45.2 ± 0.2°. Figure 3 a). In contrast, water droplets on the sol-gel treated microcapsule coating (1 day) remained stable and exhibited a spherical shape, with a WCA of 165.2 ± 0.4°. Figure 3 b). When water was sprayed onto the treated microcapsule coating (1 day) using a syringe needle, the water droplets easily slid off the coating surface without leaving a trace, and the corresponding slip angle (SA) was measured to be 2.6 ± 1.5°. Figure 3 d). In contrast, the coating containing untreated microcapsules exhibited poorer slip properties, with a WCA of 59 ± 1.2° and an SA of 30 ± 1.2°. Figure 3 c). These images and data demonstrate the water wetting behavior stability of untreated and sol-gel treated microcapsule coatings over aging time.

[0094] like Figure 3 As shown in e, even if a water droplet suspended on the needle tip approaches the surface of the superhydrophobic coating, the water droplet can still completely detach from the superhydrophobic surface despite the deformation and contact process caused by external force.

[0095] like Figure 3As shown in f, after one day of room temperature aging, the untreated microcapsules still exhibited hydrophilicity, with a WCA of 59.0 ± 1.2° and an SA of 30.0 ± 1.2°. With increasing aging time, the WCA of the untreated microcapsule coating gradually increased, while the SA gradually decreased, reaching a stable trend of 145.2 ± 2.2° and 18.4 ± 1.5° after 8 days. This result indicates that the untreated microcapsule coating can achieve superhydrophobicity after 6 days of aging. The internal and external diffusion of the low surface energy reactive core material (HDI) and its spontaneous chemical changes on the microcapsule surface at room temperature are considered the reasons for the development of superhydrophobicity. Due to the chemical reaction between HDI and hydrophilic groups, the surface gradually transforms from hydrophilic to superhydrophobic.

[0096] like Figure 3 As shown in g, the sol-gel treated microcapsules exhibited significant superhydrophobicity after aging at room temperature for 1 day, with WCA of 165.2±0.4° and SA of 2.6±1.5°. Furthermore, they maintained superhydrophobicity after aging at room temperature for 8 days (WCA=165.9±0.5°, SA=2.2±1.2°), indicating that their wetting properties have excellent stability.

[0097] Test Example 3: Abrasion Resistance Test

[0098] Abrasion resistance tests were performed on the HDI microcapsules in Example 15 and the sol-gel treated HDI microcapsules. A schematic diagram of the abrasion resistance tester is shown below. Figure 4 As shown in figure a, the mechanical elasticity of the microcapsule coating against external forces was evaluated to assess its superhydrophobic properties. Figure 4 The differences before and after the wear test are shown. The results indicate that the surface of the untreated microcapsule coating degraded significantly after only 4500 cycles of friction. The water contact angles (WCAs) and glycol contact angles (CAs) decreased significantly from 145.2 ± 2.2° to 64.3 ± 1.2° and from 136.5 ± 0.6° to 59.6 ± 1.1°, respectively. Figure 4 b). In contrast, the sol-gel treated microcapsule coatings maintained a WCA angle above 150° after 4500 cycles of friction. Figure 4 c).

[0099] Figure 4 As shown in d, the water slip angle of the untreated MCs coating and the slip angle of ethylene glycol increased from 18.4±1.5° to 48.9±2.2° and from 21.9±2.6° to 58.6±2.4°, respectively.

[0100] Figure 4 As shown in e, the sliding angle of MCs treated with sol-gel to water and ethylene glycol remained below 10° after 4500 cycles of friction, demonstrating robust wear resistance.

[0101] Test Example 4: Self-cleaning performance

[0102] The self-cleaning properties of the HDI microcapsules in Example 15 and the sol-gel treated HDI microcapsules were tested. After 8 days of exposure in an aging chamber, the WCAs of the untreated microcapsule coating decreased from 145.2±2.2° to 119.6±2.1°, and the corresponding SAs decreased from 18.4±1.5° to 31.2±0.9°. Figure 6 a). The WCAs of the sol-gel treated microcapsule coating remained almost unchanged, decreasing from 165.9 ± 0.5° to 163.5 ± 1.04°, while the corresponding SAs only decreased from 2.2 ± 1.2° to 4.5 ± 1.2° after 8 days of exposure. Figure 6 b). For example Figure 6 As shown in Figure cf, after water rinsing, the untreated microcapsule coating on a galvanized stainless steel substrate still retained a significant amount of powdery contaminants. In contrast, most of the contaminants were washed away from the sol-gel treated microcapsule coating. These results demonstrate that the microcapsule coating treated with sol-gel vapor surface modification possesses durable self-cleaning properties.

[0103] Test Example 5 Thermal Stability

[0104] Thermal stability tests were performed on the HDI microcapsules in Example 15 and the sol-gel treated HDI microcapsules. Figure 10 (a) As can be seen, pure HDI begins to evaporate at 109℃, while untreated microcapsules lose weight at 202℃, indicating that microencapsulated HDI has better thermal stability than pure HDI. The decomposition temperature of the sol-gel surface-treated microcapsules is 217℃. The highly cross-linked PDMS@TEOS shell surface structure prevents leakage of the core material of the sol-gel treated microcapsules during heating, thereby improving thermal stability. During a 100-minute isothermal process at 100℃, the residual weights of pure HDI and sol-gel treated microcapsules change over time as follows: Figure 10 As shown in (b), pure HDI lost approximately 68 wt.% of the original sample weight, while the sol-gel treated microcapsules lost only approximately 0.5 wt.% during the isothermal process. This result indicates that the sol-gel treated microcapsules have a lower evaporation rate, further confirming that the PDMS@TEOS shell imparts better heat resistance to the sol-gel treated microcapsules than pure HDI.

[0105] In summary, the superhydrophobic sol-gel treated microcapsules synthesized using the technical solution of this application possess convincingly durable, damage-recoverable superhydrophobicity, which significantly outperforms most superhydrophobic materials in the literature. The chemical inertness of PDMS and its high adhesion to the substrate are also major contributing factors. The PDMS surface coating synergistically interacts with micro-aggregated silica to form a uniform, dense surface with hierarchical roughness. In conclusion, sol-gel treated microcapsules with an internally highly reactive core material and an external hydrophobic nano / microstructure represent an effective design strategy for improving the wear resistance and extending the service life of superhydrophobic microcapsule coatings.

[0106] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing long-lasting superhydrophobic microcapsules, characterized in that, Includes the following steps: S1. Adjust the pH of the formaldehyde aqueous solution to alkaline, then mix it with urea to obtain a shell raw material solution, heat it to react, and obtain a prepolymer of urea-formaldehyde aqueous suspension; S2. Add all of the prepolymer of the urea-formaldehyde aqueous suspension from step S1 to a mixture of ethyl methacrylate aqueous solution and water, stir I, then add hexamethylene diisocyanate dropwise, stir II to form an emulsion, adjust the pH to acidic, and obtain superhydrophobic microcapsules. S3. In a closed environment, the superhydrophobic microcapsules obtained in step S2 are subjected to steam treatment using a solution containing polydimethylsiloxane and tetraethoxysilane, and then subjected to sol-gel reaction in a catalyst solution vapor environment to obtain the long-lasting superhydrophobic microcapsules. In step S3, the catalyst solution is a liquid of propanol and ammonia, and the volume ratio of propanol to ammonia is 3~5:

1. The conditions for the sol-gel reaction include: a reaction temperature of 35~55℃, a reaction time of 0.5~1h, and a curing time of 6~12h after the reaction; The conditions for steam treatment include: steam treatment time of 10-30 minutes.

2. The method for preparing long-lasting superhydrophobic microcapsules according to claim 1, characterized in that, The long-lasting superhydrophobic microcapsule includes a shell and a reactive core material encapsulated inside the shell; The outer surface of the shell is a rough surface formed by dispersed particle protrusions; The particle protrusions are formed by the accumulation of several nanoparticles. The outer surface of the shell is covered with a cross-linked polymer network; The cross-linked polymer network is a polydimethylsiloxane-functionalized SiO2 nanoparticle network. The shell is made of polyurea-formaldehyde; The reactive core material is selected from hexamethylene diisocyanate.

3. The method for preparing long-lasting superhydrophobic microcapsules according to claim 2, characterized in that, The polydimethylsiloxane-functionalized SiO2 nanoparticle network is a cross-linked structure formed by the reaction of polydimethylsiloxane and tetraethoxysilane, wherein the tetraethoxysilane forms the SiO2 nanoparticle network through hydrolysis and condensation during the reaction.

4. The preparation method according to claim 1, characterized in that, In step S3, the weight ratio of polydimethylsiloxane to tetraethoxysilane is 1~8:

1.

5. The preparation method according to claim 1, characterized in that, In step S1, the shell material liquid contains 5-9 parts by weight of 37 wt% formaldehyde aqueous solution and 2.5-4.5 parts by weight of urea.

6. The preparation method according to claim 1, characterized in that, In step S1, the conditions for adjusting the pH to alkaline include: adding triethanolamine to adjust the pH of the formaldehyde aqueous solution to 7.5-9.

5.

7. The preparation method according to claim 1, characterized in that, In step S1, the conditions for the heating reaction include: a reaction temperature of 60~80℃ and a reaction time of 60~90min.

8. The preparation method according to claim 1, characterized in that, In step S2, the mixture contains 12-22 parts by weight of a 3.0 wt% aqueous solution of ethyl methacrylate and 30-50 parts by weight of water.

9. The preparation method according to claim 1, characterized in that, In step S2, 5-15 parts by weight of hexamethylene diisocyanate are added dropwise.

10. The preparation method according to claim 1, characterized in that, In step S2, the conditions for stirring I include: stirring for 10 to 20 minutes at 20 to 25°C and a speed of 250 to 350 rpm.

11. The preparation method according to claim 1, characterized in that, In step S2, the conditions for stirring II include: stirring for 10 to 20 minutes at 20 to 25°C and a speed of 700 to 1000 rpm.

12. The preparation method according to claim 1, characterized in that, In step S2, the conditions for adjusting the pH to acidity include: after the emulsion has stabilized for 20-30 minutes, adjusting the pH of the emulsion to 1-2 using a citric acid aqueous solution with a pH of 0.

3.

13. The preparation method according to claim 8, characterized in that, In step S2, the mixture also includes 0.2 to 0.3 parts by weight of resorcinol.

14. The preparation method according to claim 1, characterized in that, In step S2, after adjusting the pH to acidic, the reaction continues for 1-2 hours at 40-50°C and 100-200 rpm.

15. The application of the long-lasting superhydrophobic microcapsules prepared by any one of claims 1 to 14 in industrial coatings, waterproofing materials or self-cleaning coatings.

16. The application according to claim 15, characterized in that, The application includes spraying a primer onto the surface of the target product, and then spraying long-lasting superhydrophobic microcapsules onto the primer.

17. The application according to claim 16, characterized in that, The surface of the target product is a metal substrate.

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