A coating with high thermal conductivity and high microwave absorption performance and its preparation method

Abstract

This invention discloses a coating with high thermal conductivity and high microwave absorption performance and its preparation method, comprising the following steps: S1, uniformly dispersing stearic acid-coated microwave-absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene, and appropriate amount of additives in deionized water to obtain a coating; S2, spraying the coating obtained in S1 onto the surface of a substrate; S3, allowing it to stand until the stearic acid-coated microwave-absorbing nanoparticles move to the surface of the waterborne coating; S4, segmented heating and drying; low-temperature drying; melting of stearic acid on the surface of the waterborne coating; high-temperature drying to obtain a coating that combines thermal conductivity and microwave absorption; the coating prepared by this invention utilizes the hydrophobic properties of stearic acid to drive the accumulation of microwave-absorbing nanoparticles on the coating surface through static layering, while simultaneously constructing an ordered arrangement of aminated graphene in the coating, resulting in a coating that combines electrothermal performance and microwave absorption performance.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a coating with high thermal conductivity and high microwave absorption performance, and a method for preparing the same. Background Technology

[0002] Microwave absorbing materials can be classified into two types based on their loss mechanism: electrical loss and magnetic loss. Taking ferromagnetic metal micropowder absorbing materials as an example, ferromagnetic metals have excellent magnetic permeability, especially nano-sized or alloyed metal micropowders, including carbonyl iron powder, carbonyl nickel powder, and cobalt-nickel alloys, which all have high magnetic permeability but poor acid and alkali resistance. Nano-absorbing materials include metals, metal oxides, or nano-sized powders. During the refinement process, due to the nano-effect, the activity of nanomaterials gradually increases. Under the influence of an electromagnetic field, the movement of atoms and electrons intensifies, causing them to magnetize and convert into heat energy, thereby absorbing electromagnetic waves. In existing coatings, most absorbing materials are uniformly dispersed within the coating. However, due to the inherent tendency of nanomaterials to agglomerate and disperse, uniform dispersion of the absorbing material is not conducive to achieving stable and uniform performance. Summary of the Invention

[0003] The primary objective of this invention is to provide a method for preparing a coating with high thermal conductivity and high microwave absorption performance. In the preparation process of the coating prepared by this invention, the hydrophobic properties of stearic acid are utilized to drive the accumulation of microwave-absorbing nanoparticles on the coating surface through static layering, while simultaneously constructing an ordered arrangement of aminated graphene in the coating. The resulting coating combines electrothermal performance and microwave absorption performance.

[0004] To solve this technical problem, the technical solution of the present invention is: a method for preparing a coating with high thermal conductivity and high microwave absorption performance, comprising the following steps:

[0005] S1. A coating is obtained by uniformly dispersing stearic acid-coated microwave absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene and appropriate additives in deionized water.

[0006] S2. Spray the coating obtained in S1 onto the surface of the substrate;

[0007] S3. Let stand until the stearic acid-coated microwave-absorbing nanoparticles move to the surface of the water-based coating.

[0008] S4. Segmented heating and drying;

[0009] Low-temperature drying; stearic acid melts on the surface of the water-based coating;

[0010] High-temperature drying yields a coating that combines thermal conductivity and microwave absorption.

[0011] Preferably, the coating comprises the following components in parts by weight:

[0012]

[0013] This invention utilizes stearic acid to coat microwave-absorbing nanoparticles, with deionized water as the dispersed phase in the coating. The hydrophobic properties of stearic acid cause the coated nanoparticles to spontaneously move and accumulate on the coating surface after spraying. In this invention, waterborne epoxy resin acts as an adhesive or film-forming agent. The aggregation of the microwave-absorbing nanoparticles on the resulting coating surface provides microwave absorption properties, and the ordered arrangement of the aminated graphene ensures the thermal efficiency of the coating. The amino group content in the aminated graphene is 15.0 wt% to 25.0 wt%. The abundant amino groups, with their active hydrogen atoms, react with the epoxy groups in the epoxy resin, causing ring-opening to generate hydroxyl groups. These hydroxyl groups then undergo etherification with the epoxy groups, allowing the aminated graphene to participate in the curing of the epoxy resin, forming a network or three-dimensional polymer.

[0014] Preferably, the microwave absorbing nanoparticles are β-Ni(OH)2 or β-FeOOH. The microwave absorbing nanoparticles used in this invention are magnetically depleted nanoparticles, which are enriched on the surface of the coating, providing uniform microwave absorption performance while effectively improving the wear resistance of the resulting coating.

[0015] The preferred process conditions for coating stearic acid-coated microwave absorbing nanoparticles are as follows:

[0016] Microwave-absorbing nanoparticles are uniformly dispersed in molten stearic acid, and ultrasonic vibration effectively coats the surface of the nanoparticles with stearic acid. This invention removes stearic acid to a certain extent during the segmented drying process. Therefore, by using the simplest physical coating, the chemical bonds between stearic acid and the nanoparticles are reduced, facilitating stearic acid removal.

[0017] Preferably, the coating obtained after spraying and drying the coating material comprises a thermally conductive layer and a microwave-absorbing layer sequentially from the substrate surface towards the air in the thickness direction. This invention utilizes stearic acid to drive the microwave-absorbing nanoparticles, achieving not only the enrichment of the nanoparticles on the coating surface but also organizing the ordered arrangement of the central amino-graphene, resulting in an electrothermal layer and a microwave-absorbing layer distributed along the thickness direction. Preferably, the substrate in this invention is an aluminum alloy or stainless steel.

[0018] The preferred process conditions for S2 spraying are as follows: reciprocating speed of 10 m / min to 12 m / min, spraying flow rate of 300 cc / min, and spraying thickness of 0.5 mm to 1.0 mm. This invention utilizes multiple spraying processes to effectively ensure that the stearic acid-coated microwave-absorbing nanoparticles are impacted to the lower-middle position of the resulting coating, thereby ensuring the sorting and arrangement of the aminated graphene during the floating process.

[0019] The preferred low-temperature drying temperature in S4 is 80°C to 90°C, and the time is 15 min to 25 min;

[0020] The high-temperature drying temperature in S4 is 100℃ to 120℃, and the time is 20 min to 30 min.

[0021] The coating, which has been dried by S4 staged heating, is preferably wiped 3 to 5 times with an ethanol-deionized water mixture to remove residual stearic acid from the coating surface. This invention removes stearic acid, and even if a small amount remains on the coating surface, the hydrophobic properties of stearic acid prevent water from accumulating and remaining on the coating, thus avoiding damage to the coating structure due to the hydrophilicity of aminated graphene.

[0022] The preferred composition of the ethanol-deionized water mixture is as follows:

[0023] The mass ratio of ethanol to deionized water is 1:(1 to 3);

[0024] Ethanol and deionized water were ultrasonically dispersed until homogeneous.

[0025] This invention utilizes an ethanol-deionized water mixture to remove residual stearic acid from the surface.

[0026] The second objective of this invention is to provide a coating with high thermal conductivity and high microwave absorption performance, wherein the coating obtained by this invention combines electrothermal performance and microwave absorption performance.

[0027] To solve this technical problem, the technical solution of the present invention is as follows:

[0028] The coating prepared by the method provided by the present invention.

[0029] By adopting the above technical solution, the beneficial effects of the present invention are:

[0030] This invention involves coating microwave-absorbing nanoparticles with stearic acid and uniformly dispersing them with waterborne epoxy resin, curing agent, and aminated graphene in deionized water. The mixture is then sprayed onto a substrate surface. After spraying, the stearic acid-coated microwave-absorbing nanoparticles, due to their hydrophobicity, migrate to the surface of the coating during the post-spraying settling phase, forming an accumulation. Then, during the segmented heating and drying process, taking advantage of the fact that stearic acid has a melting point of 67°C to 72°C, the stearic acid melts during the low-temperature drying process and remains on the surface of the waterborne coating. Finally, high-temperature drying is performed, and the moisture evaporates slowly, resulting in a coating with microwave-absorbing nanoparticles enriched on the surface.

[0031] The coating obtained by this invention also includes sheet-like aminated graphene. As the stearic acid drives the microwave-absorbing nanoparticles to move from bottom to top within the coating, the originally randomly distributed sheet-like aminated graphene is organized, and the aminated graphene forms an orderly arrangement, resulting in uniform and stable electrothermal properties of the coating.

[0032] This invention utilizes aminated graphene and a curing agent to jointly participate in the curing of waterborne epoxy resin. The epoxy resin film forms a positioning effect on the microwave absorbing nanoparticles and graphene materials, and the resulting coating combines microwave absorption performance with electrothermal performance. Attached Figure Description

[0033] Figure 1 This invention relates to a process flow diagram for preparing a coating with high thermal conductivity and high microwave absorption performance;

[0034] Figure 2 This is a schematic diagram of the structure of the coating obtained by the present invention;

[0035] Figure 3 yes Figure 2 Enlarged view of point A in the middle.

[0036] In the picture:

[0037] Substrate 1; Coating 2; Thermally conductive layer 21; Aminated graphene 211; Wave-absorbing layer 22; Wave-absorbing nanoparticles 221. Detailed Implementation

[0038] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0039] Example 1

[0040] This embodiment discloses a method for preparing a coating with high thermal conductivity and high microwave absorption performance, such as... Figure 1 As shown, it includes the following steps:

[0041] S1. Stearic acid-coated microwave absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene and appropriate amount of additives are uniformly dispersed in deionized water to obtain a coating. The dosage of each component is shown in Table 1.

[0042] The microwave absorbing nanoparticles are β-Ni(OH)2.

[0043] The process conditions for coating the stearic acid-coated microwave-absorbing nanoparticles in this embodiment are as follows:

[0044] The microwave-absorbing nanoparticles are uniformly dispersed in molten stearic acid, and the stearic acid is effectively coated on the surface of the microwave-absorbing nanoparticles by ultrasonic oscillation.

[0045] S2. Spray the coating obtained in S1 onto the surface of the tinplate substrate;

[0046] The process conditions for S2 spraying are as follows: reciprocating speed is 10m / min, spraying flow rate is 150cc / min, and spraying thickness is 0.8mm.

[0047] S3. Let stand until the stearic acid-coated microwave-absorbing nanoparticles move to the surface of the water-based coating.

[0048] S4. Segmented heating and drying;

[0049] Low-temperature drying; stearic acid melts on the surface of the water-based coating;

[0050] The low-temperature drying temperature is 80℃, and the time is 25 minutes;

[0051] High-temperature drying yields a coating that combines thermal conductivity and microwave absorption; the high-temperature drying temperature is 100℃ and the time is 20 minutes.

[0052] The coating obtained after the paint is sprayed and dried includes, from the substrate surface towards the air, a thermally conductive layer and a wave-absorbing layer, as shown below. Figure 2 and Figure 3 As shown.

[0053] In this embodiment, the coating, which has been dried by S4 segmented heating, was wiped three times with an ethanol-deionized water mixture to remove residual stearic acid from the coating surface.

[0054] The composition of the ethanol-deionized water mixture in this embodiment is as follows:

[0055] The mass ratio of ethanol to deionized water is 1:2;

[0056] Ethanol and deionized water were ultrasonically dispersed until homogeneous.

[0057] Example 2

[0058] This embodiment discloses a method for preparing a coating with high thermal conductivity and high microwave absorption performance, such as... Figure 1 As shown, it includes the following steps:

[0059] S1. Stearic acid-coated microwave absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene and appropriate amount of additives are uniformly dispersed in deionized water to obtain a coating. The dosage of each component is shown in Table 1.

[0060] The microwave absorbing nanoparticles are β-Ni(OH)2.

[0061] The process conditions for coating the stearic acid-coated microwave-absorbing nanoparticles in this embodiment are as follows:

[0062] The microwave-absorbing nanoparticles are uniformly dispersed in molten stearic acid, and the stearic acid is effectively coated on the surface of the microwave-absorbing nanoparticles by ultrasonic oscillation.

[0063] S2. Spray the coating obtained in S1 onto the surface of the tinplate substrate;

[0064] The process conditions for S2 spraying are as follows: reciprocating speed is 12m / min, spraying flow rate is 300cc / min, and spraying thickness is 0.8mm.

[0065] S3. Let stand until the stearic acid-coated microwave-absorbing nanoparticles move to the surface of the water-based coating.

[0066] S4. Segmented heating and drying;

[0067] Low-temperature drying; stearic acid melts on the surface of the water-based coating;

[0068] The low-temperature drying temperature is 90℃, and the time is 25 minutes;

[0069] High-temperature drying yields a coating that combines thermal conductivity and microwave absorption; the high-temperature drying temperature is 120℃ and the time is 30 minutes.

[0070] The coating obtained after the paint is sprayed and dried includes, from the substrate surface towards the air, a thermally conductive layer and a wave-absorbing layer, as shown below. Figure 2 and Figure 3 As shown.

[0071] In this embodiment, the coating, which has been dried by S4 segmented heating, was wiped three times with an ethanol-deionized water mixture to remove residual stearic acid from the coating surface.

[0072] The composition of the ethanol-deionized water mixture in this embodiment is as follows:

[0073] The mass ratio of ethanol to deionized water is 1:2;

[0074] Ethanol and deionized water were ultrasonically dispersed until homogeneous.

[0075] Example 3

[0076] This embodiment discloses a method for preparing a coating with high thermal conductivity and high microwave absorption performance, such as... Figure 1 As shown, it includes the following steps:

[0077] S1. Stearic acid-coated microwave absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene and appropriate amount of additives are uniformly dispersed in deionized water to obtain a coating. The dosage of each component is shown in Table 1.

[0078] The microwave absorbing nanoparticles are β-FeOOH.

[0079] The process conditions for coating the stearic acid-coated microwave-absorbing nanoparticles in this embodiment are as follows:

[0080] The microwave-absorbing nanoparticles are uniformly dispersed in molten stearic acid, and the stearic acid is effectively coated on the surface of the microwave-absorbing nanoparticles by ultrasonic oscillation.

[0081] S2. Spray the coating obtained in S1 onto the surface of the tinplate substrate;

[0082] The process conditions for S2 spraying are as follows: reciprocating speed is 10m / min, spraying flow rate is 200cc / min, and spraying thickness is 0.8mm.

[0083] S3. Let stand until the stearic acid-coated microwave-absorbing nanoparticles move to the surface of the water-based coating.

[0084] S4. Segmented heating and drying;

[0085] Low-temperature drying; stearic acid melts on the surface of the water-based coating;

[0086] The low-temperature drying temperature is 80℃, and the time is 25 minutes;

[0087] High-temperature drying yields a coating that combines thermal conductivity and microwave absorption; the high-temperature drying temperature is 100℃ and the time is 20 minutes.

[0088] The coating obtained after the paint is sprayed and dried includes, from the substrate surface towards the air, a thermally conductive layer and a wave-absorbing layer, as shown below. Figure 2 and Figure 3 As shown.

[0089] In this embodiment, the coating, which has been dried by S4 segmented heating, was wiped three times with an ethanol-deionized water mixture to remove residual stearic acid from the coating surface.

[0090] The composition of the ethanol-deionized water mixture in this embodiment is as follows:

[0091] The mass ratio of ethanol to deionized water is 1:2;

[0092] Ethanol and deionized water were ultrasonically dispersed until homogeneous.

[0093] Example 4

[0094] This embodiment discloses a method for preparing a coating with high thermal conductivity and high microwave absorption performance, such as... Figure 1 As shown, it includes the following steps:

[0095] S1. Stearic acid-coated microwave absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene and appropriate amount of additives are uniformly dispersed in deionized water to obtain a coating. The dosage of each component is shown in Table 1.

[0096] The microwave absorbing nanoparticles are β-FeOOH.

[0097] The process conditions for coating the stearic acid-coated microwave-absorbing nanoparticles in this embodiment are as follows:

[0098] The microwave-absorbing nanoparticles are uniformly dispersed in molten stearic acid, and the stearic acid is effectively coated on the surface of the microwave-absorbing nanoparticles by ultrasonic oscillation.

[0099] S2. Spray the coating obtained in S1 onto the surface of the tinplate substrate;

[0100] The process conditions for S2 spraying are as follows: reciprocating speed is 10m / min, spraying flow rate is 200cc / min, and spraying thickness is 0.8mm.

[0101] S3. Let stand until the stearic acid-coated microwave-absorbing nanoparticles move to the surface of the water-based coating.

[0102] S4. Segmented heating and drying;

[0103] Low-temperature drying; stearic acid melts on the surface of the water-based coating;

[0104] The low-temperature drying temperature is 80℃, and the time is 20 minutes;

[0105] High-temperature drying yields a coating that combines thermal conductivity and microwave absorption; the high-temperature drying temperature is 110℃ and the time is 30 minutes.

[0106] The coating obtained after the paint is sprayed and dried includes, from the substrate surface towards the air, a thermally conductive layer and a wave-absorbing layer, as shown below. Figure 2 and Figure 3 As shown.

[0107] In this embodiment, the coating, which has been dried by S4 segmented heating, was wiped three times with an ethanol-deionized water mixture to remove residual stearic acid from the coating surface.

[0108] The composition of the ethanol-deionized water mixture in this embodiment is as follows:

[0109] The mass ratio of ethanol to deionized water is 1:2;

[0110] Ethanol and deionized water were ultrasonically dispersed until homogeneous.

[0111] Comparative Example

[0112] This comparative example discloses a method for preparing a coating with high thermal conductivity and high microwave absorption performance, such as... Figure 1 As shown, it includes the following steps:

[0113] S1, microwave absorbing nanoparticles, waterborne epoxy resin, curing agent, aminated graphene and appropriate amount of additives are uniformly dispersed in deionized water to obtain a coating. The dosage of each component is shown in Table 1.

[0114] The microwave absorbing nanoparticles are β-Ni(OH)2.

[0115] S2. Spray the coating obtained in S1 onto the surface of the tinplate substrate;

[0116] The process conditions for S2 spraying are as follows: reciprocating speed is 12m / min, spraying flow rate is 300cc / min, and spraying thickness is 0.8mm.

[0117] S3, let stand for 10 minutes;

[0118] S4. Segmented heating and drying;

[0119] The low-temperature drying temperature is 90℃, and the time is 25 minutes;

[0120] The high-temperature drying temperature is 120℃ and the time is 30 minutes; the coating is obtained.

[0121] Table 1 shows the composition and dosage of the coatings corresponding to Examples 1 to 4 and the comparative examples.

[0122] project Example 1 Example 2 Example 3 Example 4 Comparative Example stearic acid 2.5 3.0 3.5 4.0 / Wave-absorbing nanoparticles 50 60 70 80 60 Waterborne epoxy resin 300 400 500 400 400 curing agent 100 180 200 140 180 Aminographene 60 70 80 90 70 Deionized water 400 500 600 600 500 Additives 20 25 30 25 25

[0123] The frequencies of common electromagnetic radiation sources in daily life generally range from 10MHz to 3000MHz. The operating frequencies of typical experimental or industrial equipment are approximately 10MHz to 30MHz, televisions emit radiation at 250MHz, refrigerators at 900MHz, and microwave ovens at 3000MHz. For electromagnetic radiation frequently encountered in daily life, the coatings obtained in Examples 1 to 4 and the comparative example were tested for shielding effectiveness at specific frequencies according to GB / T 25471-2010 "Test Method for Shielding Effectiveness of Electromagnetic Shielding Coatings". The thermal conductivity was measured using a thermal conductivity analyzer, and the contact angle of water on the obtained coatings before and after friction was measured using a contact angle meter. Specific data are shown in Table 2. The friction conditions were as follows: the obtained coatings were rubbed along a straight line for 500cm on 120-grit sandpaper under a 500g weight.

[0124] Table 2 Performance indicators of the coatings obtained in Examples 1 to 4 and comparative examples.

[0125]

[0126] Combining the data recorded in Tables 1 and 2, it can be seen that the coating obtained by the present invention combines microwave absorption performance and thermal conductivity while also possessing good hydrophobic properties. Comparing the performance of the coating obtained in the comparative example with the coatings obtained in Examples 1 to 4, the comparative example disperses the microwave absorbing material and aminated graphene in an aqueous epoxy resin through a mixing and dispersion method. The resulting coating contains microwave absorbing nanoparticles and aminated graphene within its thickness range. The aminated graphene participates in the curing of the epoxy resin, and the contact angle between the resulting coating and water is 56°, while the contact angle between the coatings obtained in Examples 1 to 4 and water is greater than 90°. That is, the coating obtained by the present invention has hydrophobic properties, fundamentally reducing contact with water and effectively protecting the structure of the coating. Moreover, the contact angle of the coating obtained by the present invention remains basically unchanged before and after friction. The main reason is that the microwave absorbing layer has good wear resistance, avoiding the loss of film thickness due to friction. In addition, the reasons for the hydrophobic properties of the coating obtained by the present invention also include:

[0127] The accumulation of microwave-absorbing nanoparticles on the coating surface, combined with the curing of epoxy resin, results in a coating with a micro-nano structure due to the particle structure and distribution of the microwave-absorbing nanoparticles. This macroscopically manifests as a hydrophobic coating, which effectively reduces the contact between the coating and water, thus helping to maintain the stability of the coating structure. On the other hand, although the stearic acid accumulated on the surface volatilizes and is wiped away during the drying process, the unavoidable residue of stearic acid on the coating surface also contributes to the hydrophobic properties of the coating to a certain extent.

[0128] The microwave absorption performance of the coating obtained by this invention is significantly better than that of the comparative example. Comparing the coatings obtained by the comparative example and Example 2, the main difference is that the comparative example did not use stearic acid to coat the microwave-absorbing nanoparticles. Therefore, the components in the comparative example coating are relatively dispersed under stirring. There is no process in this invention where the hydrophobic properties of stearic acid drive the microwave-absorbing nanoparticles to accumulate on the coating surface using an aqueous dispersion system. Consequently, there is no sorting and arrangement of the sheet-like aminated graphene in the coating. In contrast, the coating obtained by this invention has a microwave-absorbing layer enriched on the coating surface and a thermally conductive layer with orderly arranged aminated graphene oxide. The orderly arranged aminated graphene, together with the microwave-absorbing layer, further attenuates electromagnetic waves. This invention effectively improves the microwave absorption performance through the combined effect of the enrichment of microwave-absorbing nanoparticles and the orderly arrangement of sheet-like aminated graphene, while also taking into account the electrothermal performance.

Claims

1.A method for preparing a coating with high thermal conductivity and high wave absorption performance, comprising the following steps: S1, uniformly dispersing stearic acid-coated wave-absorbing nanoparticles, water-based epoxy resin, curing agent, amino-functionalized graphene, and appropriate additives in deionized water to obtain a coating; S2, spraying the coating obtained in S1 on the surface of a substrate; S3, standing until the stearic acid-coated wave-absorbing nanoparticles move to the surface of the water-based coating; S4, drying by heating in stages; low-temperature drying; melting of the stearic acid on the surface of the water-based coating; high-temperature drying to obtain a coating with both thermal conductivity and wave absorption; the temperature for low-temperature drying in S4 is 80-90℃, and the time is 15-25 min; the temperature for high-temperature drying in S4 is 100-120℃, and the time is 20-30 min; the coating comprises the following components by mass fraction: stearic acid 2.5-4.0 parts; wave-absorbing nanoparticles 50-80 parts; water-based epoxy resin 300-500 parts; curing agent 100-200 parts; amino-functionalized graphene 60-90 parts; deionized water 400-600 parts; and additives 20-30 parts; the coating obtained after spraying and drying comprises a thermal conductivity layer and a wave absorption layer in the thickness direction from the surface of the substrate to the air; the coating dried by heating in stages in S4 is wiped 3-5 times with an ethanol-deionized water mixture to remove residual stearic acid on the surface of the coating; the wave-absorbing nanoparticles are β-Ni(OH) 2 or β-FeOOH; the process conditions for coating the wave-absorbing nanoparticles with stearic acid are as follows: uniformly dispersing the wave-absorbing nanoparticles in molten stearic acid and ultrasonically oscillating the stearic acid to effectively coat the surface of the wave-absorbing nanoparticles; the process conditions for spraying in S2 are as follows: reciprocating speed 10-12 m / min, spraying flow rate 150-300 cc / min, and spraying thickness 0.5-1.0 mm; the composition of the ethanol-deionized water mixture is as follows: mass ratio of ethanol to deionized water 1: (1-3) ; and the ethanol and deionized water are ultrasonically dispersed uniformly; and 6. A coating prepared by the method of any one of claims 1-5. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein: ​ 3. The method of claim 1, wherein: ​ ​ 4. The method of claim 1, wherein: ​ 5. The method of claim 1, wherein: ​ ​ ​ ​

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