Cement-based super-hydrophobic coating with anti-freezing and anti-icing properties, and preparation method and application thereof

Abstract

This invention discloses a cement-based superhydrophobic coating with antifreeze and anti-icing properties, its preparation method, and its application, belonging to the technical field of coating compositions. The cement-based superhydrophobic coating of this invention is made from the following raw materials in the indicated mass percentages: propyltrimethoxysilane 12%–16%, hydroxyl-terminated polydimethylsiloxane 3%–5%, alkaline silica sol 30%–35%, and deionized water 47%–52%; the total proportion of all components is 100%. This coating exhibits good permeability and breathability, and excellent superhydrophobic properties. The coating is non-toxic and environmentally friendly, possesses anti-icing properties, and can reduce the adhesion between ice and cement-based materials, improving de-icing efficiency. The preparation method of this invention requires no complex equipment and is simple and efficient. The cement-based superhydrophobic coating is easy to use and can significantly reduce the damage to cement-based materials caused by freeze-thaw cycles, improving the durability of building structures in cold regions.

Description

Technical Field

[0001] This invention relates to the field of coating composition technology, and in particular to a cement-based superhydrophobic coating with antifreeze and anti-icing properties, its preparation method and application. Background Technology

[0002] Cement-based materials have advantages such as abundant raw materials, low price, and high compressive strength, making them one of the most consumed and widely used building materials. However, the service environments of cement-based materials are relatively complex, and the requirements for durability vary.

[0003] In cold climates, the accumulation and freezing of ice and snow often pose serious risks to the stability and service life of cement-based materials. Removing the ice layer frozen to the material surface is a major challenge. Traditional de-icing methods, such as mechanical and chemical de-icing, while solving the problem quickly, suffer from material damage, high energy consumption, and environmental pollution. Simultaneously, freeze-thaw cycles also threaten the lifespan of cement-based materials. Moisture enters the cement-based material through pores, and after repeated ice-water cycles, the internal pore pressure gradually increases, eventually leading to structural damage. Currently, there are two main treatment methods: the first is to increase the material's density and improve freeze-thaw resistance by adding cementitious materials to reduce the water-cement ratio, but this does not change the inherent hydrophilicity of cement-based materials. The second is to apply organic coatings to reduce water penetration into the structural surface, but these organic coatings have limited durability, and some coatings may blister and peel off in humid environments. Traditional improvement methods have not effectively solved the problem of performance degradation of cement-based materials in cold regions, making the search for new protective methods of great significance.

[0004] For example, Chinese invention patent CN105131830A discloses a long-lasting nano-hydrophobic coating composition and its preparation method, comprising the following components in a certain weight percentage: fluorochlorosilane, nano-silica, polyorganosiloxane, rare earth salt, film-forming agent, and alcohol solvent. The preparation method involves adding the fluorochlorosilane, polyorganosiloxane, rare earth salt, and film-forming agent to the nano-silica sol at 30-70°C, mixing and reacting to obtain the long-lasting nano-hydrophobic coating. This coating is convenient to use; after spraying the coating onto a clean, dry glass surface, it is wiped evenly with a dry cloth, forming a transparent nano-hydrophobic coating with a strong water-repellent effect. The effective time after one wipe can reach more than 3 months, and the glass becomes clearer and brighter. However, this coating composition is designed for glass applications and has insufficient permeability when used on cement-based materials. Furthermore, its preparation requires the use of organic solvents, resulting in high costs and potential adverse environmental impacts.

[0005] Chinese invention patent CN113292896A discloses a topcoat for coatings, with the following composition by weight: 47-60 parts of alkali-resistant emulsion, 0-30 parts of silica sol, 0.5-1 part of bactericide, 0.5-1 part of wetting agent, 2-4 parts of film-forming aid, 0.5-1 part of defoamer, 0.5-1 part of thickener, 15-40 parts of deionized water, and 1-2 parts of hydrophobic agent. This topcoat completely overcomes the shortcomings of existing topcoats on the market, such as poor water resistance, weather resistance, and yellowing over time. The coating uses deionized water as a solvent, combined with additives to form the coating, and utilizes alkaline silica sol to increase the coating's adhesion and hardness. However, this increased hardness leads to increased brittleness, causing damage and peeling under repeated freeze-thaw cycles due to ice crystal expansion and compression, making it unsuitable for applications in cold regions.

[0006] Therefore, it is necessary to research a cement-based superhydrophobic coating for cold regions. Utilizing the superhydrophobic properties of the coating, ice and snow are unlikely to form a stable adhesion on the surface of cement-based materials, thus achieving efficient de-icing and reducing building maintenance costs. Simultaneously, by effectively preventing the adhesion and penetration of moisture on the material surface, the possibility of moisture entering the interior of the cement-based material is reduced at the source, improving the overall freeze-thaw resistance. This is of great significance for comprehensively enhancing the durability and safety of cement-based materials in cold environments. Summary of the Invention

[0007] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a cement-based superhydrophobic coating with antifreeze and anti-icing properties, simple to use, and environmentally friendly and pollution-free is provided, the raw materials of which include the following components in mass percentage:

[0008] Propyltrimethoxysilane 12%–16%, hydroxyl-terminated polydimethylsiloxane 3%–5%, alkaline silica sol 30%–35%, deionized water 47%–52%; the total proportion of the above components is 100%.

[0009] Preferably, the alkaline silica sol is composed of 25% to 30% by mass of nano-silica, with an average particle size of 20 to 30 nm and a pH of 10 to 12.

[0010] In a second aspect of the present invention, a simple and efficient method for preparing a cement-based superhydrophobic coating is provided, comprising the following steps:

[0011] (1) Mix the proportions of propyltrimethoxysilane, hydroxyl-terminated polydimethylsiloxane, alkaline silica sol and deionized water to obtain a raw material mixture;

[0012] (2) The raw material mixture is stirred at a certain temperature and speed to obtain a cement-based superhydrophobic coating.

[0013] Preferably, in step (2), the temperature is 28–32°C.

[0014] Preferably, in step (2), the stirring rate is 750 to 1000 rpm.

[0015] Preferably, in step (2), the stirring treatment lasts for 3 to 4.5 hours.

[0016] In the preparation process, the reaction temperature and rotation speed primarily affect the degree of hydrolysis of the siloxane; different degrees of hydrolysis result in different numbers of hydroxyl groups generated. Complete hydrolysis results in a siloxane molecule carrying three hydroxyl groups (the hydrolysis product is silanol), facilitating subsequent dehydration condensation reactions. Furthermore, temperature and rotation speed influence the degree of reaction between silanol and polysiloxane with the silica sol, thereby affecting the formation of subsequent secondary structures. Therefore, to obtain the structure required by this invention, the preparation parameters need to be controlled within a specific range. If the coating preparation is not carried out within this range, the subsequent secondary structures may not form, or the number of hydroxyl groups in the coating may be too low, weakening the adhesion to the substrate.

[0017] Furthermore, when the raw materials are first mixed, polysiloxane may float on top. However, after a certain period of high-speed stirring, the raw materials react, and this phenomenon disappears. Under long-term storage conditions, although this invention uses hydrophobic components, the resulting coating is not an oil-water two-phase system and does not exhibit stratification. This is because the ratio of raw materials, temperature, time, and stirring speed are controlled, allowing the siloxane to completely hydrolyze and react with the polysiloxane and nano-silica in the silica sol to form a stable bond, thus obtaining a stable product. If the reaction is carried out outside the recommended preparation conditions, the product will become unstable and stratified.

[0018] In a third aspect of the invention, the application of the cement-based superhydrophobic coating of the first aspect of the invention or the cement-based superhydrophobic coating prepared by the method of the second aspect of the invention is provided, specifically, its application as a coating material in improving the freeze-thaw resistance of cement-based materials.

[0019] Preferably, the specific operation of the application is as follows: applying a cement-based superhydrophobic coating to the surface of a cement-based material, curing it at room temperature, and forming a freeze-thaw resistant superhydrophobic coating through self-assembly.

[0020] As a water-based coating, the cement-based superhydrophobic coating of this invention has the advantage of short curing time. For example, in practical use, it can be fully cured in just 24 hours. This may be because the prepared coating still contains some hydrolyzed hydroxyl groups, which are highly reactive and will attract Ca from hydration products such as calcium hydroxide. 2+ Surrounding OH -A dehydration condensation reaction occurs, and the amount of -OH carried by the designed ratio may be appropriate, which promotes the reaction to occur relatively quickly and completely, and then forms a bond and solidifies.

[0021] The organosilicon material used in this invention has good air permeability. The superhydrophobic structure built on the surface of the cement-based material after curing is not completely closed. This protective structure will not block the capillaries of the material, maintain the overall air permeability of the material, and avoid the blistering and cracking phenomenon of traditional organic protective coatings.

[0022] Based on the above technical solutions, the concept of this invention is to use propyltrimethoxysilane, hydroxyl-terminated polydimethylsiloxane, and alkaline silica sol in a designed ratio as the main raw materials in an aqueous environment. During the preparation of the superhydrophobic coating, the hydrogen-containing functional groups of propyltrimethoxysilane hydrolyze in water to generate silanol. The silanol and hydroxyl-terminated polydimethylsiloxane react with the -OH groups from the silica sol, dispersing and fixing the nano-silica particles. By designing the reactant ratio, after the coating is applied to the surface of the cementitious material, some of the nano-silica will form local agglomerates, creating a two-stage rough structure, which improves the stability of the air layer within the subsequent superhydrophobic structure. Simultaneously, the silanol and hydroxyl-terminated polydimethylsiloxane react with the -OH groups of hydration products, such as calcium silicate hydrate and calcium hydroxide, firmly attaching the superhydrophobic structure to the surface of the cementitious material. The two-stage superhydrophobic structure on the material surface spontaneously forms after coating through a dehydration condensation reaction, requiring simple application and no complex equipment.

[0023] The superhydrophobic coating of this invention can impart excellent water resistance to cement-based materials. When the coating comes into contact with water, the water exerts water pressure on the superhydrophobic structure and gradually penetrates it. The two hierarchically rough microstructures can slow down the escape of air from the cushion structure and prolong the transition process from the Wenzel state to the Cassie-Baxter state on the superhydrophobic surface. The hydrophobic low surface energy groups and this dual-roughness structure work synergistically to reduce the water absorption rate of the cement-based material after coating.

[0024] Superhydrophobic coatings can significantly reduce the porosity near the surface of cementitious materials, decreasing the number of harmful pores and increasing the number of harmless pores. The number of these harmful pores (greater than 100 nm) directly impacts the freeze-thaw resistance of cementitious materials, as they serve as effective pathways and storage spaces for water or other liquids to penetrate. Simultaneously, the double-roughened structure significantly reduces the water absorption rate of cementitious materials, preventing excessive water infiltration into the material's interior. These two properties combined limit the formation and expansion of ice crystals during freeze-thaw cycles, effectively mitigating damage caused by freezing and subsequent expansion.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] This invention provides a cement-based superhydrophobic coating with good permeability and breathability, and excellent superhydrophobic properties. The coating is non-toxic and environmentally friendly, and has antifreeze and anti-icing properties, which can reduce the adhesion between ice and cement substrate materials and improve de-icing efficiency.

[0027] This invention provides a method for preparing cement-based superhydrophobic coatings. The process does not require complex equipment and has the advantages of being simple and efficient.

[0028] This invention provides an application of a cement-based superhydrophobic coating, which is simple to use and can significantly reduce the damage of freeze-thaw cycles to cement-based materials, thereby improving the durability of building structures in cold regions. Attached Figure Description

[0029] Figure 1 Photographs showing the surface wettability of the cement-based superhydrophobic coating in Example 3; (a) is the contact angle of the droplet on the coating surface; (b) is the roll-off angle of the droplet on the coating surface; (c) is the morphology of the droplet on the superhydrophobic coating surface.

[0030] Figure 2 The images show the microstructure of the cement-based superhydrophobic coating surface in Example 3; (a) is magnified at 5000x; (b) at 10000x; and (c) at 25000x.

[0031] Figure 3 A schematic diagram of the double roughness structure formed by self-assembly on the surface after the application of a cement-based superhydrophobic coating;

[0032] Figure 4 Photographs showing the self-cleaning properties of the cement-based superhydrophobic coating surface in Example 3;

[0033] Figure 5 Comparison of ice residue on the surface of the samples after de-icing in Example 3 and Comparative Example 1; (a) Surface morphology of Example 3 after de-icing; (b) Surface morphology of Comparative Example 1 after de-icing;

[0034] Figure 6 The following is a comparison of the surface macromorphology of Example 3 and Comparative Example 1 before and after 126 freeze-thaw cycles: (a) Surface macromorphology of Comparative Example 1 before freeze-thaw cycles; (b) Surface macromorphology of Comparative Example 1 after 126 freeze-thaw cycles; (c) Surface macromorphology of Example 3 before freeze-thaw cycles; (d) Surface macromorphology of Example 3 after 126 freeze-thaw cycles. Detailed Implementation

[0035] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0036] In the following embodiments:

[0037] Alkaline silica sol, a silica sol product of Nanjing Haitai Nanomaterials Co., Ltd., is composed of 25% to 30% by mass of nano-silica, with an average particle size of 20 to 30 nm and a pH of 10 to 12.

[0038] Example 1

[0039] Cement-based superhydrophobic coatings are prepared using the following method:

[0040] (1) 12 wt.% propyltrimethoxysilane, 5 wt.% hydroxyl-terminated polydimethylsiloxane, 35 wt.% alkaline silica sol and 48 wt.% deionized water were added to a reaction vessel and mixed to obtain a raw material mixture;

[0041] The alkaline silica sol is composed of 25% by mass of nano-silica with an average particle size of 25 nm and a pH of 12.

[0042] (2) Place the reaction vessel in a constant temperature water bath environment at 32°C and use a magnetic stirrer to stir the liquid mixture at a speed of 1000 rpm for 3 hours to obtain a milky white solution, namely cement-based superhydrophobic coating, and seal it for storage.

[0043] The obtained cement-based superhydrophobic coating is smoothly applied to the surface of the cement-based material. After drying at room temperature for 24 hours, the cement-based material with a superhydrophobic coating is finally formed through self-assembly.

[0044] Example 2

[0045] Cement-based superhydrophobic coatings are prepared using the following method:

[0046] (1) 14 wt.% propyltrimethoxysilane, 4 wt.% hydroxyl-terminated polydimethylsiloxane, 32 wt.% alkaline silica sol and 50 wt.% deionized water were added to a reaction vessel and mixed to obtain a raw material mixture;

[0047] The alkaline silica sol is composed of 30% by mass of nano-silica with an average particle size of 30 nm and a pH of 10.

[0048] (2) Place the reaction vessel in a constant temperature water bath environment at 30°C and use a magnetic stirrer to stir the liquid mixture at a speed of 850 rpm for 3 hours to obtain a milky white solution, namely cement-based superhydrophobic coating, and seal it for storage.

[0049] The obtained cement-based superhydrophobic coating is smoothly applied to the surface of the cement-based material. After drying at room temperature for 24 hours, the cement-based material with a superhydrophobic coating is finally formed through self-assembly.

[0050] Example 3

[0051] Cement-based superhydrophobic coatings are prepared using the following method:

[0052] (1) 15 wt.% propyltrimethoxysilane, 3 wt.% hydroxyl-terminated polydimethylsiloxane, 30 wt.% alkaline silica sol and 52 wt.% deionized water were added to a reaction vessel and mixed to obtain a raw material mixture;

[0053] The alkaline silica sol is composed of 25% by mass of nano-silica with an average particle size of 30 nm and a pH of 12.

[0054] (2) Place the reaction vessel in a constant temperature water bath environment at 30°C and use a magnetic stirrer to stir the liquid mixture at a speed of 780 rpm for 3 hours to obtain a milky white solution, namely cement-based superhydrophobic coating, and seal it for storage.

[0055] The obtained cement-based superhydrophobic coating is smoothly applied to the surface of the cement-based material. After drying at room temperature for 24 hours, the cement-based material with a superhydrophobic coating is finally formed through self-assembly.

[0056] Example 4

[0057] Cement-based superhydrophobic coatings are prepared using the following method:

[0058] (1) 13 wt.% propyltrimethoxysilane, 5 wt.% hydroxyl-terminated polydimethylsiloxane, 35 wt.% alkaline silica sol and 47 wt.% deionized water were added to a reaction vessel and mixed to obtain a raw material mixture;

[0059] The alkaline silica sol is composed of 25% by mass of nano-silica with an average particle size of 30 nm and a pH of 12.

[0060] (2) Place the reaction vessel in a constant temperature water bath environment at 28°C and use a magnetic stirrer to stir the liquid mixture at a speed of 750 rpm for 4.5 hours to obtain a milky white solution, namely cement-based superhydrophobic coating, and seal it for storage.

[0061] The obtained cement-based superhydrophobic coating is smoothly applied to the surface of the cement-based material. After drying at room temperature for 24 hours, the cement-based material with a superhydrophobic coating is finally formed through self-assembly.

[0062] Example 5

[0063] Cement-based superhydrophobic coatings are prepared using the following method:

[0064] (1) 16 wt.% propyltrimethoxysilane, 3 wt.% hydroxyl-terminated polydimethylsiloxane, 30 wt.% alkaline silica sol and 51 wt.% deionized water were added to a reaction vessel and mixed to obtain a raw material mixture;

[0065] The alkaline silica sol is composed of 25% by mass of nano-silica with an average particle size of 30 nm and a pH of 12.

[0066] (2) Place the reaction vessel in a constant temperature water bath environment at 30°C and use a magnetic stirrer to stir the liquid mixture at a speed of 1000 rpm for 3 hours to obtain a milky white solution, namely cement-based superhydrophobic coating, and seal it for storage.

[0067] The obtained cement-based superhydrophobic coating is smoothly applied to the surface of the cement-based material. After drying at room temperature for 24 hours, the cement-based material with a superhydrophobic coating is finally formed through self-assembly.

[0068] Comparative Example 1

[0069] This comparative example is a cement-based material without coating, serving as a blank group for comparison with the examples.

[0070] Performance tests were conducted on some representative embodiments and Comparative Example 1. The test items and methods are as follows:

[0071] Wettability testing: The contact angles of the examples and comparative examples were measured using an optical contact angle meter (DSA 100, Krüss, Germany). Five random points were selected on the test surface of each sample, and the average value of the obtained contact angles was calculated as the test result. The roll-off angles of the examples and comparative examples were measured using an optical contact angle meter (OCA 20, Dataphysics, Germany). All wettability tests were performed at room temperature using 4 μL of deionized water.

[0072] Self-cleaning test: Simulated contaminants, such as sand particles, are covered on the surface of the coated sample. Water droplets are used to impact the surface contaminants, and the self-cleaning performance of the coating is tested by observing the amount of contaminants remaining.

[0073] Water absorption rate and freeze-thaw cycle test: The test shall be conducted in accordance with the requirements of GBT 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete".

[0074] Penetration depth test: The test was conducted in accordance with the requirements of JTS153-2015 "Durability Design Standard for Water Transport Engineering Structures".

[0075] De-icing thrust test: A bottomless cubic mold with a side length of 20 mm is filled with water and placed on the sample surface. After being placed in a refrigerator at -17℃ for 4 hours, the ice is pushed off the sample surface using a digital thrust meter to test the de-icing thrust.

[0076] The test results are shown in Table 1.

[0077] Table 1:

[0078]

[0079] Note: " / " in the table indicates that there are no actual measurable points.

[0080] As shown in Table 1, the superhydrophobic coatings described in Examples 1 to 3 exhibit excellent performance. When applied to the surface of cement-based materials, the contact angle is above 150° and the roll-off angle is below 10°, which meets the superhydrophobic standard. Among them, Example 3 has the best overall performance. Figure 1 The image shows the surface wettability of the cement-based superhydrophobic coating in Example 3. The liquid is spherical, and the coating surface exhibits excellent superhydrophobic properties. Figure 2 This is a microscopic morphology image of the cement-based superhydrophobic coating surface in Example 3. At maximum magnification, a double-roughness structure can be seen formed on the superhydrophobic surface. Figure 3 This diagram illustrates the double-rough structure formed by the self-assembly of a cement-based superhydrophobic coating surface after application. Combined with microscopic morphology images, this rough structure of the superhydrophobic surface contains an air layer, which can reduce the adhesion between liquid and solid contaminants and the coating surface. Figure 4 As shown, the cement-based superhydrophobic coating has self-cleaning properties. Droplets falling on the surface can quickly sweep away contaminants. This property can keep the building's appearance clean and tidy, improve its aesthetics, and reduce maintenance costs.

[0081] Compared to the comparative example, the water absorption rate of Examples 1-3 decreased significantly, reaching a minimum of 1.15%, a reduction of 70.66%. This greatly improves the waterproof performance of the cement-based material and reduces the risk of various types of damage caused by water penetration. The penetration depth of Examples 1-3 all exceeded 3.5 mm, indicating that the coating surface still exhibits a certain degree of hydrophobicity after wear, effectively improving the durability of the structure. Regarding de-icing, the de-icing thrust of Examples 1-3 was lower than that of the comparative example, with the maximum thrust value reduced by approximately 58%. Figure 5 As shown in the comparison, no obvious ice residue remained on the surface of the sample after de-icing in Example 3. Compared with the comparative examples, Examples 1-3 showed slower mass loss and less surface damage after multiple freeze-thaw cycles, which can be seen from... Figure 6 The surface macromorphology was observed before and after 126 freeze-thaw cycles.

[0082] The above test results may be due to the fact that the alkaline silica sol in the raw materials provides a large number of nano-silica particles, which helps to form a rough surface structure in the coating. Polydimethylsiloxane contains a large number of low surface energy groups, which can improve the contact angle and roll-off angle of the superhydrophobic coating. At the same time, this raw material has excellent low-temperature resistance, allowing for long-term use in low-temperature environments, greatly contributing to the antifreeze and anti-icing properties of the coating. Propyltrimethoxysilane and polydimethylsiloxane work synergistically to improve the dispersion of nano-silica and promote the formation of a rough surface structure. In addition, propyltrimethoxysilane can also provide some low surface energy groups, further improving the hydrophobicity of the coating. After the reaction, these raw materials can penetrate into the material to form a dense hydrophobic network structure, extending the service life of the coating.

[0083] The properties demonstrated in the tests of the above embodiments will provide advantages for the antifreeze and anti-icing properties of cement-based materials in cold regions. This proves that the cement-based superhydrophobic coating provided by this invention can protect cement-based materials from damage in extreme environments, which will reduce the occurrence of some safety accidents and also reduce the cost of material repair and maintenance.

[0084] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A cement-based superhydrophobic coating, characterized in that, Its raw materials include the following components by mass percentage: Propyltrimethoxysilane 12%~16%, hydroxyl-terminated polydimethylsiloxane 3%~5%, alkaline silica sol 30%~35%, deionized water 47%~52%; the total proportion of the above components is 100%. The alkaline silica sol is composed of 25% to 30% by mass of nano-silica, with an average particle size of 20 to 30 nm and a pH of 10 to 12. The preparation method of the cement-based superhydrophobic coating includes the following steps: (1) Mix the proportions of propyltrimethoxysilane, hydroxyl-terminated polydimethylsiloxane, alkaline silica sol and deionized water to obtain a raw material mixture; (2) The raw material mixture is stirred at a certain temperature and speed to obtain a cement-based superhydrophobic coating; the temperature is 28~32 ℃, the stirring speed is 750~1000 rpm, and the stirring time is 3~4.5 h.

2. An application of the cement-based superhydrophobic coating as described in claim 1, characterized in that: Application as a coating material in improving the freeze-thaw resistance of cement-based materials.

3. The application according to claim 2, characterized in that, The specific operation is as follows: apply cement-based superhydrophobic coating to the surface of cement-based material, cure at room temperature and form a freeze-thaw resistant superhydrophobic coating through self-assembly.

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