Light absorber and method for producing the same

Abstract

A light absorber includes a plurality of carbon nanotubes, a plurality of carbon particles, and an epoxy resin, the plurality of carbon nanotubes form a carbon nanotube network structure, the epoxy resin is coated on the surface of the plurality of carbon nanotubes, and the plurality of carbon particles are connected through the carbon nanotube network structure coated with the epoxy resin. In addition, the present application also provides a preparation method of the light absorber.

Description

TECHNICAL FIELD

[0001] The present application relates to a light absorber and a preparation method thereof, in particular to a light absorber based on carbon nanotubes and a preparation method thereof. BACKGROUND

[0002] Light absorbers have a wide range of applications, including energy harvesting, stray light shielding, and stealth technology. In the design and manufacture of perfect light absorbers, there is often a trade-off between enhancing the density of micro-nano structures for light absorption and improving the durability and stability of the material. This dichotomy can limit the wider application of these light absorbers, especially in harsh environmental conditions. Currently, there is an urgent need to design perfect light absorbers that can withstand extreme environments, including mechanical stress, extreme temperatures, strong ultraviolet radiation, and other severe challenges. These light absorbers are crucial for applications that require consistent performance in harsh environments, such as aerospace, military operations, and special industries. SUMMARY

[0003] Therefore, it is necessary to provide a light absorber with excellent light absorption performance and excellent durability and stability in harsh environments and a preparation method thereof.

[0004] A light absorber includes a plurality of carbon nanotubes, a plurality of carbon particles, and an epoxy resin, the plurality of carbon nanotubes form a carbon nanotube network structure, the epoxy resin is coated on the surface of the plurality of carbon nanotubes, and the plurality of carbon particles are connected by the carbon nanotube network structure coated with the epoxy resin.

[0005] A preparation method of a light absorber includes the following steps: providing a light absorber pre-liquid, the light absorber pre-liquid includes a solvent, a plurality of carbon nanotubes, a plurality of carbon particles, and an epoxy resin, the plurality of carbon nanotubes form a carbon nanotube network structure, and the plurality of carbon nanotubes and carbon particles are suspended in the solvent in a colloidal state; and spraying the light absorber pre-liquid on a substrate to form a light absorber.

[0006] Compared with the prior art, the light absorber provided by the present application exhibits excellent absorption efficiency under harsh environmental conditions, exceeding 99.9% in a wide spectral range. The combination of carbon nanotubes and epoxy resin as a connector between carbon particles significantly enhances the durability and stability of the light absorber, ensuring consistent performance even under mechanical wear, extreme temperatures, ultraviolet radiation, water impact, and long-term outdoor conditions. Moreover, the preparation method of the light absorber uses a spraying process, which is cost-effective and can be mass-produced. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1A top view SEM image of the light absorber spray coating provided by the embodiment of the present application, with a scale of 500 μm.

[0008] Figure 2 A cross-sectional SEM image of the light absorber spray coating provided by the embodiment of the present application, with a scale of 20 μm.

[0009] Figure 3 A side view SEM image of the light absorber spray coating provided by the embodiment of the present application, with a scale of 500 μm.

[0010] Figure 4 A top view SEM image of the light absorber spray coating provided by the embodiment of the present application, with a scale of 50 μm.

[0011] Figure 5 A top view SEM image of the light absorber spray coating provided by the embodiment of the present application, with a scale of 10 μm.

[0012] Figure 6 An SEM image of the sprayed epoxy resin-free carbon nanotube-carbon black composite material, with a scale of 20 μm.

[0013] Figure 7 A TEM image of the carbon nanotube and epoxy resin dispersed in an ethanol solution provided by the embodiment of the present application, with a scale of 100 nm.

[0014] Figure 8 A flowchart of the preparation method of the light absorber provided by the embodiment of the present application.

[0015] Figure 9 A reflectance spectrum of the light absorber provided by the present application in the visible wavelength range.

[0016] Figure 10 A reflectance spectrum of the light absorber provided by the present application in the near-infrared wavelength range.

[0017] Figure 11 A reflectance spectrum of the light absorber provided by the present application in the mid-infrared wavelength range.

[0018] Figure 12 A function relationship between the specular reflectance and the incident angle of the light absorber provided by the present application measured using non-polarized light with a wavelength of 550 nm.

[0019] Figure 13 A hemispherical reflectance spectrum of the light absorber provided by the present application in the visible wavelength range measured by an integrating sphere.

[0020] Figure 14The hemispherical reflectance spectrum of the light absorber provided by the present application in the near-infrared wavelength range measured by an integrating sphere.

[0021] Figure 15 The reflectance spectrum of the light absorber provided by the present application measured at an incident angle of 15°.

[0022] Figure 16 The reflectance spectrum of the light absorber provided by the present application measured at an incident angle of 30°.

[0023] Figure 17 The reflectance spectrum of the light absorber provided by the present application measured at an incident angle of 45°.

[0024] Figure 18 The reflectance spectrum of the light absorber provided by the present application measured at an incident angle of 60°.

[0025] Figure 19 The schematic diagram of the binding mechanism between the carbon black particles and the carbon nanotubes added with the epoxy resin in the spray coating of the light absorber provided by the present application.

[0026] Figure 20 The comparative schematic diagram before and after the scratch area of the spray coating of the light absorber adhered by the adhesive tape in the embodiment of the present application.

[0027] Figure 21 The abrasion track photo of the carbon nanotube-CB particle layer without adding the epoxy resin after 500 abrasion cycles in the embodiment of the present application.

[0028] Figure 22 The microscope image of the abrasion track of the carbon nanotube-CB particle layer without adding the epoxy resin after 500 abrasion cycles in the embodiment of the present application.

[0029] Figure 23 The photo of the abrasion track of the spray coating of the light absorber provided by the embodiment of the present application after 500 abrasion cycles.

[0030] Figure 24 The microscope image of the abrasion track of the spray coating of the light absorber provided by the embodiment of the present application after 500 abrasion cycles.

[0031] Figure 25 The schematic diagram of the linear abrasion test on the spray coating of the light absorber provided by the embodiment of the present application using the sandpaper.

[0032] Figure 26 The schematic diagram of preparing the spray coating on the cloth as the light absorber.

[0033] Figure 27A schematic diagram for testing the specular reflectivity of the light absorber spray coating of the present embodiment under harsh environment with a wavelength of 550 nm.

[0034] Explanation of main element symbols

[0035] No

[0036] The following detailed description will further illustrate the present application in conjunction with the above-mentioned figures. DETAILED DESCRIPTION

[0037] The light absorber and the preparation method thereof provided by the present application will be further described in detail below in conjunction with the figures and specific embodiments.

[0038] The present embodiment provides a light absorber, which comprises a plurality of carbon nanotubes, a plurality of carbon particles and an epoxy resin. The plurality of carbon nanotubes form a carbon nanotube network structure, the epoxy resin is coated on the surface of the plurality of carbon nanotubes, and the plurality of carbon particles are connected through the epoxy resin and the carbon nanotube network structure. That is, the plurality of carbon particles are connected through the carbon nanotube network structure coated with the epoxy resin, the carbon particles are wrapped by the carbon nanotube and the epoxy resin, and there is a gap between the carbon nanotube-carbon particle aggregates. The addition of the epoxy resin in the light absorber significantly enhances the connection between the carbon nanotubes and the carbon particles, and the addition of the epoxy resin significantly strengthens the interfacial bonding between the carbon nanotubes and the carbon particles. The carbon nanotubes can be single-walled carbon nanotubes, double-walled carbon nanotubes or multi-walled carbon nanotubes. The carbon particles can be carbon particles with a diameter ranging from 100 nm to 100 um, and the epoxy resin can be a variety of alcohol-soluble epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenolic epoxy resin, multifunctional glycidyl ether epoxy resin, etc.

[0039] Further, the light absorber can also comprise a substrate for supporting the light absorber. The type, shape, thickness, etc. of the substrate are not limited. The substrate can be quartz, polymer, metal, ceramic or cloth, etc. The surface of the substrate can be a plane, a curved surface, or an irregular surface. In the present embodiment, the substrate is quartz.

[0040] Still further, the light absorber can also comprise a curing agent, which is selected according to the corresponding epoxy resin and can be aliphatic amine, aromatic amine, polyamide, etc.

[0041] In the present embodiment, the light absorber comprises a plurality of carbon nanotubes, a plurality of carbon particles, an epoxy resin and a curing agent. The carbon nanotubes are multi-walled carbon nanotubes with an average diameter of 20 nm. The carbon particles are carbon black (CB) particles, the epoxy resin is E51, and the curing agent is diethylene triamine.

[0042] AsFigure 1 As shown, the morphology of the light absorber coating in this embodiment is very similar to that of the epoxy-free light absorber coating. Carbon black particles are uniformly dispersed on the surface of the light absorber, and the carbon nanotube-carbon black composite material extensively covers the light absorber coating. This observation indicates that a carbon nanotube-CB particle composite coating can be manufactured via a spraying process by adding appropriate epoxy resin and curing agent. This method maintains the entire carbon nanomaterial system and its surface morphology, laying the foundation for superior absorption properties and ensuring the stability and durability of the light absorber coating.

[0043] like Figure 2 As shown, a cross-sectional view of the light absorber coating reveals that the CB particles are encapsulated by carbon nanotubes and epoxy resin. The light absorber composite material is tightly packed, establishing a layered structure, much like bricks bonded with mortar, where the CB particles are connected by a network of carbon nanotubes integrated with the resin. This network endows the light absorber coating with strong mechanical properties and stability. Figure 3 The side-view SEM image of the light absorber coating depicts an undulating yet uniform topography with gaps of tens of nanometers between the carbon nanotube-CB aggregates, which offer significant advantages for light absorption in the visible to infrared spectral range. Furthermore, from a design perspective, the integration of CB particles enhances the scattering and absorption capabilities of the light absorber surface. Figure 4 As shown, the surface morphology of the light absorber coating consists of stacked carbon nanotube-CB particle composites with gaps between them. The integration of these particles, especially in all-carbon nanomaterials, effectively increases the gap density in local areas. This increased gap density effectively reduces the equivalent refractive index of the light absorber surface, thereby promoting a reduction in reflection. Furthermore, the addition of epoxy resin to the carbon nanotube-CB particle composite produces unique properties not observed in resin-free layers, such as... Figure 5 As shown, the presence of epoxy resin imparts a smoother surface texture to the carbon nanotube-CB particles, indicating that the carbon nanotubes and CB particles are completely encapsulated by the resin. This characteristic is achieved through… Figure 6 The images presented further confirm the absence of a resin-coated coating.

[0044] Carbon nanotubes exhibit high efficiency as absorbers and connectors linking carbon particles within light-absorbing coatings, thus creating multi-scale, all-carbon-based nanomaterials.

[0045] It is understood that the light absorber may be composed of multiple carbon nanotubes, multiple carbon particles, and epoxy resin.

[0046] In addition, embodiments of the present invention provide a method for preparing a light absorber, which includes the following steps:

[0047] S1, providing a light absorber pre-liquid, the light absorber pre-liquid comprising a solvent, carbon nanotubes, carbon particles and epoxy resin, the carbon nanotubes forming a network structure, the carbon nanotubes and the carbon particles being suspended in the solvent in a colloidal state.

[0048] In the light absorber pre-liquid, the carbon nanotubes and the carbon particles exhibit the ability to remain stable for a long time, sometimes even for months, without forming aggregates.

[0049] S2, spraying the light absorber pre-liquid on a substrate to form a light absorber.

[0050] In step S1, the method for preparing the light absorber pre-liquid comprises the following steps:

[0051] S11, providing carbon nanotubes;

[0052] S12, dispersing the carbon nanotubes into the solvent, performing flocculation treatment to obtain a carbon nanotube suspension;

[0053] S13, adding the epoxy resin and the carbon particles into the carbon nanotube suspension, performing ultrasonic dispersion to form the light absorber pre-liquid.

[0054] In step S11, the method for preparing the carbon nanotubes is not limited, such as arc discharge method, laser evaporation method or chemical vapor deposition method, etc. In the embodiment, the chemical vapor deposition method is used to prepare the carbon nanotubes, which comprises the following steps:

[0055] S111, growing a carbon nanotube array on a growth substrate; and

[0056] S112, using a blade or other tools to scrape the carbon nanotube array from the growth substrate to obtain carbon nanotubes.

[0057] In step S111, the length of the carbon nanotubes in the carbon nanotube array is not limited. Preferably, the length of the carbon nanotubes is greater than 100 μm (microns). The carbon nanotubes are substantially parallel to each other and substantially perpendicular to the surface of the growth substrate. The carbon nanotube array provided in the embodiment is one of a single-walled carbon nanotube array, a double-walled carbon nanotube array and a multi-walled carbon nanotube array.

[0058] In this embodiment, the carbon nanotube array is prepared by chemical vapor deposition. The steps include: (a) providing a flat growth substrate, which can be a P-type or N-type silicon substrate, or a silicon substrate with an oxide layer, and preferably an 8-inch silicon substrate; (b) forming a catalyst layer on the surface of the growth substrate, which can be made of iron (Fe), cobalt (Co), nickel (Ni), or an alloy of any combination thereof; (c) annealing the growth substrate with the catalyst layer in air at 700-900°C for about 30-90 minutes; (d) placing the treated growth substrate in a reaction furnace, heating it to 500-740°C in a protective gas environment, and then introducing a carbon source gas to react for about 5-30 minutes to grow the carbon nanotube array with a height greater than 100 microns. The carbon nanotube array is a pure carbon nanotube array formed by a plurality of carbon nanotubes that are parallel to each other and perpendicular to the growth substrate. Due to the long length of the generated carbon nanotubes, some of the carbon nanotubes can be intertwined. By controlling the growth conditions as described above, the carbon nanotube array is substantially free of impurities such as amorphous carbon or residual catalyst metal particles. In this embodiment, the carbon source gas can be a chemically active hydrocarbon such as acetylene, and the protective gas can be nitrogen, ammonia, or an inert gas.

[0059] In step S12, the plurality of carbon nanotubes are dispersed in a solvent, and the flocculation treatment can be performed by ultrasonic dispersion or high-intensity stirring to obtain a carbon nanotube suspension. Preferably, the plurality of carbon nanotubes are dispersed in an ethanol solvent, and ultrasonic dispersion is performed for 10-30 minutes. Due to the large specific surface area of carbon nanotubes and the strong van der Waals force between intertwined carbon nanotubes, the flocculation treatment does not completely disperse the carbon nanotubes in the carbon nanotube raw material in the solvent. The carbon nanotubes are attracted and intertwined by van der Waals force to form a network structure, which can also be referred to as a flocculent structure. In this embodiment, the carbon nanotubes are dispersed in an ethanol solution, and the carbon nanotubes are connected to form a network structure. It is crucial to maintain the colloidal suspension state of the carbon nanotubes in the ethanol solvent. A higher carbon nanotube concentration can increase the viscosity of the solution, which can damage the subsequent spray coating process, while a lower carbon nanotube concentration can reduce the efficiency of the light absorber preparation. Preferably, 0.1-0.8 grams of carbon nanotubes are dispersed in 200 milliliters of ethanol.

[0060] In step S12, preferably, a dispersant can be added during the process of dispersing the plurality of carbon nanotubes in the solvent, and then a carbon nanotube suspension is formed by using an ultrasonic cell disruptor for tip ultrasonic dispersion of the carbon nanotubes.

[0061] In step S13, after adding the epoxy resin to the carbon nanotube suspension and thoroughly mixing, the epoxy resin is uniformly distributed between the carbon nanotubes, such as Figure 7It is apparent that the carbon nanotubes are surrounded by the epoxy resin, which accumulates at the junctions of the carbon nanotubes, forming a uniform composite of carbon nanotubes and epoxy resin, which is crucial for the structural integrity and performance of the light absorber. The epoxy resin is added to the carbon nanotube suspension as an adhesive, and the dispersion of the carbon nanotubes in the epoxy resin is crucial for enhancing the stability and durability of the light absorber. The use of appropriate dispersion techniques can ensure that the epoxy resin is uniformly distributed throughout the carbon nanotube suspension, maximizing the interaction between the carbon nanotubes and the epoxy resin, and thereby improving the performance of the light absorber. In this embodiment, the epoxy resin used is E51, which can be dissolved in various organic solvents, including ethanol, and the concentration of E51 is 0.1-0.4 grams per 200 milliliters.

[0062] Due to the small amount of resin added to the carbon nanotube suspension, the basic properties of the carbon nanotube suspension are not substantially changed. This ensures that the subsequently sprayed light absorber is still mainly composed of carbon nanomaterials, thereby retaining the light capture and absorption properties of the light absorber.

[0063] Carbon particles are added to the carbon nanotube suspension to achieve a mass ratio of carbon nanotubes to carbon particles of 4:5 to 4:70. The amount of solvent can be adjusted according to actual conditions to ensure that the light absorber pre-liquid can be subjected to the spraying process. Preferably, the solvent is 200 mL, the carbon nanotubes are 0.4 g, and the carbon particles are 0.5 g to 7 g. The carbon nanotubes are well dispersed in the ethanol solution, with most of the carbon nanotubes separated as individuals.

[0064] Preferably, a curing agent can be added to the carbon nanotube suspension, which is selected according to the corresponding epoxy resin and can be a fatty amine, an aromatic amine, a polyamide, etc.

[0065] In step S2, the spraying method is not limited and can use a spray gun with a diameter of 1 mm, a carrier gas of nitrogen at a pressure of 0.3 MPa, an effective spraying range of about 150 mm, and a solution consumption of 100 mL per minute. The spraying process is carried out in a closed exhaust hood, and the sample is removed when the surface is completely dry a few minutes after spraying, without any subsequent heating process, and finally forms a sprayed layer as a light absorber. The sprayed layer is characterized by its ultra-light property, with a density as low as 3.6 x 10 -6 grams per square millimeter, which is particularly advantageous in space or military operations.

[0066] Please refer to Figure 8 The present embodiment provides a method for preparing a light absorber, which specifically comprises the following steps:

[0067] First, a carbon nanotube array with a height of 285 microns is grown on an 8-inch silicon wafer, and the carbon nanotube array is scraped off the silicon wafer.

[0068] Secondly, 0.4 g of the carbon nanotubes were put into 200 mL of ethanol solvent, PVP was added, the concentration of PVP was 0.1 g PVP per 200 mL of ethanol solvent, and the carbon nanotube suspension was obtained by ultrasonic flocculation treatment using an ultrasonic cell disruptor. Each carbon nanotube in this embodiment was multi-walled, and the average diameter was 20 nm.

[0069] Then, epoxy resin E51 was added to the carbon nanotube suspension, 0.2 g of E51 was added per 200 mL of ethanol solvent, and additional 30 minutes of ultrasonic dispersion was performed to enhance the combination of the carbon nanotubes and the epoxy resin E51. Subsequently, 7 g of carbon black particles were added to the carbon nanotube suspension, and diethylenetriamine was added as a curing agent to obtain a stable light absorber pre-liquid.

[0070] Finally, the light absorber pre-liquid was sprayed on a substrate to form a light absorber. Specifically, a spray gun was used for spraying.

[0071] To quantitatively evaluate the performance of the epoxy-containing sprayed layer as an absorber, we obtained the reflectance spectrum in the wavelength range of 400 nm to 20 μm. Considering that the sprayed carbon nanotube surface lacks periodicity or geometric surface features, the reflectance behavior is expected to be independent of the polarization state of the incident light. The reflectance spectrum of the light absorber sprayed layer prepared under normal incidence is shown in detail in Figures 9 to 11 In view of the fact that the measurement equipment and comparison standards of the reflectance spectrum in different studies can be different, especially in the case of low reflectance measurement, the carbon nanotube array was selected as the reference for the reflectance measurement in the entire wavelength range in the current work as the most effective light absorber.

[0072] As Figure 9As shown, the carbon nanotube spray coating without added carbon black particles and integrated with epoxy resin exhibits nearly uniform reflectance in the visible wavelength region, approximately 0.19%. This represents a modest decrease compared to the reflectance of 0.32% for the pure carbon nanotube layer prepared previously. The decrease in reflectance is attributed to the increased surface roughness due to the incorporation of epoxy resin, which reduces specular reflection. As a benchmark, the carbon nanotube array of 285 microns height used in this study exhibits a reflectance of 0.05% as measured by the equipment used in this study. By systematically increasing the mass of carbon black particles added to each 200 milliliters of carbon nanotube solution, from 3 grams to 7 grams, a gradual decrease in reflectance of the light absorber spray coating was observed. Notably, the minimum reflectance reached 0.063% after adding 7 grams of carbon black particles, a value very close to the reflectance level of the absorber model of carbon nanotube array. Furthermore, since both carbon nanotubes and CB particles are composed of all-carbon nanomaterials, the integration of epoxy resin into the mixture does not negatively impact the light absorption capability. Therefore, the reflectance performance of the light absorber spray coating exhibits significant consistency across the visible spectral range.

[0073] In the infrared wavelength range, as shown in FIGS. 6A and 6B, the reflectance spectra exhibit a similar decreasing trend as the number of CB particles increases. The incorporation of epoxy resin does not change this trend, corresponding to the near-infrared (NIR) and mid-infrared (MIR) wavelength ranges. For wavelengths beyond 1 micron, the carbon nanotube array exhibits a minimum reflectance of 0.02%, establishing a reference benchmark. With the gradual increase in carbon black content in the carbon nanotube suspension, the reflectance of the spray coating containing 7 grams of CB particles and epoxy resin reaches approximately 0.05% in the near-infrared range. This performance is comparable to the carbon nanotube-CB composite without epoxy resin, indicating that the presence of epoxy resin does not significantly affect the absorption characteristics of the light absorber in this wavelength range. Figure 10 Figure 11 As shown, the carbon nanotube spray coating without added carbon black particles and integrated with epoxy resin exhibits nearly uniform reflectance in the visible wavelength region, approximately 0.19%. This represents a modest decrease compared to the reflectance of 0.32% for the pure carbon nanotube layer prepared previously. The decrease in reflectance is attributed to the increased surface roughness due to the incorporation of epoxy resin, which reduces specular reflection. As a benchmark, the carbon nanotube array of 285 microns height used in this study exhibits a reflectance of 0.05% as measured by the equipment used in this study. By systematically increasing the mass of carbon black particles added to each 200 milliliters of carbon nanotube solution, from 3 grams to 7 grams, a gradual decrease in reflectance of the light absorber spray coating was observed. Notably, the minimum reflectance reached 0.063% after adding 7 grams of carbon black particles, a value very close to the reflectance level of the absorber model of carbon nanotube array. Furthermore, since both carbon nanotubes and CB particles are composed of all-carbon nanomaterials, the integration of epoxy resin into the mixture does not negatively impact the light absorption capability. Therefore, the reflectance performance of the light absorber spray coating exhibits significant consistency across the visible spectral range.

[0074] ​With increasing CB particle concentration, the epoxy-resin-containing carbon nanotube-7g CB particle composite coating achieved a reflectance of approximately 0.05% in the near-infrared range. This performance is comparable to that of the epoxy-free carbon nanotube-CB particle composite. Furthermore, in the mid-infrared (MIR) range, the carbon nanotube array exhibited an exceptionally low reflectance of 0.005%, demonstrating the uniformity of its absorption capacity. The epoxy-resin-added 7g CB particle coating achieved a reflectance of 0.01%. The reflectance variation trend remained consistent across the visible, near-infrared, and mid-infrared wavelength ranges. These observations strongly suggest that the addition of epoxy resin did not negatively impact the absorption efficiency of the carbon nanotube-CB particle composite light absorber. Even with the addition of epoxy resin, the light absorption performance of the carbon nanotube-carbon black light absorber remained consistently strong across the visible, near-infrared, and mid-infrared wavelength ranges. This performance is comparable to that of vertically aligned carbon nanotube (VA carbon nanotube) arrays.

[0075] In practical applications, achieving omnidirectional absorption is a key characteristic of light absorbers, which presents a significant challenge for existing technologies. To evaluate the stability of the omnidirectional light reflection performance of epoxy resin-containing spray coatings, such as... Figures 15-18 As shown, reflectance spectra were obtained within the visible light wavelength range at incident angles from 0° to 60°. The reflectance measurements of all samples were consistent, demonstrating the excellent omnidirectional absorption capability of the epoxy resin-containing carbon nanotube-CB particle composite coating in the visible spectrum, regardless of the incident angle. At a wavelength of 550 nm, the specular reflectance at different incident angles is as follows: Figure 12 As shown, the light intensity is close to the midpoint of the visible spectrum. The addition of epoxy resin plays a crucial role in maintaining the surface morphology of carbon nanotube-CB particles, which is essential for ensuring the robust absorption performance of carbon nanomaterials in the coating. At an incident angle of 60°, the reflectivity of the coating increases slightly from 0.05% under normal incidence to 0.09%, suggesting that the absorptivity of the coating may exceed 99.9%. The addition of epoxy resin maintains the scattering centers and gaps between carbon black particles on the surface of the carbon nanotube coating, which is beneficial for light absorption. Carbon nanotubes with added epoxy resin are not only crucial for light absorption but also for more effectively binding carbon black particles.

[0076] To assess the overall absorption performance of the spray coating in the visible and near-infrared wavelength range, the hemispherical reflectance spectra were measured using an integrating sphere. Carbon nanotube arrays are highly efficient in promoting light absorption, with hemispherical reflectance consistently below 0.5%. Previous studies have shown that the addition of carbon black particles to carbon nanotube spray coatings creates a combination of micron-scale undulations and nanoscale gaps on the surface, resulting in hemispherical reflectance of 0.75%. It was experimentally demonstrated that the addition of epoxy resin can maintain the surface morphology of carbon nanotube-carbon black particle spray coatings, preserving the key micron-scale and nanoscale gaps that contribute to light capture and absorption. As shown in FIGS. 1-2, Figure 13 , Figure 14 hemispherical reflectance of the spray coating with added epoxy resin reached 0.74% in the visible range and 0.85% in the near-infrared range. These results indicate comparable performance to the spray coating without added epoxy resin, indicating wavelength independence.

[0077] As shown in FIG. 3, Figure 19 The carbon nanotubes were coated with epoxy resin before being wrapped with CB particles to form the composite, which strengthened their role as a binder between CB particles. This treatment made the carbon nanotubes more robust, effectively "fixing" the micro- and nanostructures after the curing process. The epoxy-coated carbon nanotubes provided significant support to the CB particles, significantly enhancing the mechanical stability and durability of the composite. First, the addition of epoxy resin did not alter the morphology of the spray coating, thus preserving the exceptional absorption properties of all carbon nanomaterials, as established by previous experiments. Second, the epoxy resin facilitated cross-linking and physical entanglement between carbon nanotube-CB particles, providing forces beyond van der Waals forces, greatly enhancing the mechanical performance of the spray coating. When the carbon nanotubes were impregnated with resin, they served as strong connectors between carbon black particles, a feature that was crucial for large-scale production of light absorbers. This addition was essential for altering the surface morphology and strengthening the interconnections between carbon nanotube-CB particles. Finally, this preparation process was well-suited for large-scale application through the spray method.

[0078] The perfect light absorber in harsh environments was conceptualized as an ideal material that could effectively absorb a large portion of incident light. It was designed to maintain its structural integrity and performance under the harsh conditions typically encountered in these environments without degrading. To determine the adhesion performance of the light absorber spray coating, a varnish cross-cut test standardized to ASTM D3359 was employed. The initial step was to create a 1 x 1 square millimeter grid on the light absorber spray coating using a cross-cut tester, ensuring complete penetration to the substrate. Afterwards, adhesive tape (3M brand) was firmly adhered to the scored area, then quickly removed, a process repeated until there was no detectable residue on the tape. This ensured a comprehensive assessment of adhesion performance. Subsequently, the grid squares were carefully inspected for peeling behavior, as shown in FIG. 4. Figure 20No residue was left on the tape after the final iteration, confirming the strong adhesion of the light absorber spray coating to the substrate. Adhesion tests showed that the light absorber spray coating adhered firmly to the substrate, achieving an adhesion rating of 5B according to the ASTM D3359 standard. This exceptional adhesion is primarily attributed to the strong binding capacity of the carbon nanotube-CB particles encapsulated within the epoxy resin. This interconnected network not only ensures strong adhesion of the light absorber spray coating but also maintains the stability of the micro- and nanostructures. Maintaining this stability is crucial for all carbon nanomaterials to effectively capture and absorb radiation, making them ideal absorbers.

[0079] Furthermore, to evaluate the mechanical durability of the spray coating, a wear analysis test was conducted. The test began with a ball-on-disc sliding test, which was performed using a universal micro-tribometer (UMT-5, Bruker) in a linear mode. The light absorber spray containing 7 grams of CB particles was sprayed on a steel ball, which was paired with a bearing ball having a diameter of 4 millimeters and a hardness of 700 HV. Prior to the test, the bearing ball was ultrasonically cleaned in a bath of acetone and ethanol for 10 minutes to eliminate any residual contaminants. The friction test was performed under a normal load of 0.5 N, with a frequency of 1 Hz over a range of 7 millimeters for a total of 500 cycles. The purpose of this method was to examine the tribological behavior of the material. To ensure the reliability of the results, the test was conducted three times to ensure repeatability and was performed under ambient conditions at 23 °C. The steel ball was passed over the surface at a frequency of 1 Hz to create a wear track and evaluate the wear resistance, as shown in Figures 21-24 The wear track of the light absorber spray coating of the present embodiment was significantly shallower compared to the wear track of the layer of carbon nanotube-CB particles without the addition of epoxy resin, indicating that the light absorber spray coating with the addition of epoxy resin had better resistance to wear. In contrast, the steel substrate was exposed in the wear track of the layer of carbon nanotube-CB particles without the addition of epoxy resin. The addition of epoxy resin resulted in a significant reduction in the wear track, reflecting the contribution of the epoxy resin to improving the wear resistance of the light absorber spray coating.

[0080] To comprehensively evaluate the mechanical durability and wear resistance of the light absorber spray coating, a wear analysis test was conducted using sandpaper. The test was performed using 800-grit sandpaper under a load of 100 grams, as shown in Figure 25 After 100 wear cycles, the spray coating showed sustained stability and strong adhesion, with no apparent damage or detachment. One significant advantage of the spray coating process is that it can form the light absorber pre-liquid on substrates with curved surfaces, irregular shapes, or uneven surfaces. As shown in Figure 26 The light absorber pre-liquid can be effectively sprayed onto a cloth substrate, resulting in a large-scale flexible absorber that maintains excellent mechanical stability. This feature means that the light absorber spray coating integrated with the resin can withstand the severe tests of friction and wear in practical applications.

[0081] This invention also included thermal shock testing to evaluate the ability of the light absorber coating to withstand sudden and extreme temperature changes. This evaluation is crucial for determining the thermal stability and structural integrity of materials, especially for applications in industries such as aerospace, electronics, and ceramics, where materials frequently encounter rapid temperature variations. The test began with the light absorber coating applied to a steel substrate and then exposed to a hot plate at 150°C for two hours. Throughout the heating process, the light absorber coating exhibited excellent stability, showing no signs of peeling or damage. Subsequently, thermal cycling testing was conducted to further evaluate the thermal shock resistance of the light absorber coating. This test involved alternating exposure to 150°C and immersion in liquid nitrogen. After the substrate was uniformly heated to 150°C, the light absorber coating was rapidly immersed in liquid nitrogen, and after a short interval, the sample was returned to the hot plate at 150°C, and this process was repeated. The results of this test demonstrate that the light absorber coating maintains significant thermal shock resistance under rapid temperature changes. This is primarily due to the thermal stability of the in-layer carbon nanomaterials and epoxy resin composite material. The absence of cracks, deformation, or other damage indicating temperature-induced stress confirms that the light absorber coating is suitable for environments with frequent and sudden temperature fluctuations.

[0082] Using ultraviolet (UV) irradiation to evaluate the photodegradation resistance of the light-absorbing coating is crucial for ensuring the coating's protection against UV radiation and solar radiation. At 200 W / m... 2 After exposing the light absorber coating to ultraviolet radiation for two hours at a given optical power density, the coating maintained its durability, and reflectance measurements showed stability. This result is consistent with previous studies demonstrating that the light absorption properties of carbon nanomaterials are essentially unaffected in the ultraviolet wavelength range. The epoxy resin used in this invention exhibits significant resistance to ultraviolet radiation, thus giving the coating excellent UV stability. Furthermore, from another perspective, when carbon nanotubes and carbon black particles are integrated into the epoxy resin, they can function as both UV stabilizers and absorbers. This dual role helps protect the epoxy resin from the harmful effects of ultraviolet radiation.

[0083] In addition, water impact testing was conducted to evaluate the ability of the light absorber coating to withstand the forces associated with high-speed water impact, which is crucial for applications that may be exposed to such conditions. The water pressure was set to approximately 2 kg / mm². 2and applied to the substrate using a spray nozzle. Throughout the testing, the light absorber spray coating exhibited superior durability, and any residual moisture evaporated easily, allowing the light absorber spray coating to return to its original state without any observable damage or delamination. To further enhance the evaluation, the light absorber spray coating was also subjected to a 10-hour water immersion test. After immersion, the light absorber spray coating was dried and subjected to a tactile inspection, and no signs of flaking were observed. Under these rigorous water exposure conditions, the light absorber spray coating demonstrated superior durability and reliability in real-world applications.

[0084] Finally, a real-world evaluation of the outdoor stability and durability of the light absorber spray coating was performed when installed on a vehicle. The light absorber spray coating was attached to the front windshield of the vehicle, and the vehicle was operated under standard conditions and exposed to various weather elements, including wind, rain, and solar radiation. After a 30-day test period, the light absorber spray coating maintained its durability.

[0085] As shown in FIG. 6, the specular reflectance of the light absorber spray coating of the present embodiment was tested at a wavelength of 550 nm under harsh environmental conditions, and the reflectance measurements indicated consistent performance. Figure 27

[0086] The light absorber provided by the present application exhibits superior absorption efficiency under harsh environmental conditions, exceeding 99.9% over a wide spectral range. The combination of carbon nanotubes with epoxy resin as a connector between carbon particles significantly enhances the durability and stability of the light absorber, ensuring consistent performance even under mechanical wear, extreme temperatures, UV radiation, water impact, and long-term outdoor conditions. Moreover, the use of a spray process is cost-effective and allows for large-scale production.

[0087] In addition, other variations to the disclosed embodiments can be apparent to those skilled in the art, and it is intended to encompass such variations as fall within the scope of the appended claims.​​​​​​

Claims

1. A light absorber comprising a plurality of carbon nanotubes, a plurality of carbon particles and an epoxy resin, the plurality of carbon nanotubes forming a carbon nanotube network structure, the epoxy resin coating the surface of the plurality of carbon nanotubes, the plurality of carbon particles being connected by the carbon nanotube network structure coated with the epoxy resin.

2. The light absorber according to claim 1, wherein There is a gap between the carbon nanotube-carbon particle aggregates.

3. The light absorber of claim 1, wherein The light absorber further comprises a curing agent.

4. The light absorber of claim 1, wherein The light absorber further comprises a substrate, the plurality of carbon nanotubes, the plurality of carbon particles and the epoxy resin being located on the surface of the substrate, the surface of the substrate being a flat surface, a curved surface or the substrate having an irregular surface.

5. The light absorber as claimed in claim 1, wherein The light absorber is composed of the plurality of carbon nanotubes, the plurality of carbon particles and the epoxy resin.

6. The light absorber of claim 1, wherein The mass ratio of the plurality of carbon nanotubes to the plurality of carbon particles is 4:5 to 4:

70.

7. A method for preparing a light absorber, comprising the steps of: providing a light absorber precursor solution comprising a solvent, a plurality of carbon nanotubes, a plurality of carbon particles and an epoxy resin, the plurality of carbon nanotubes forming a carbon nanotube network structure, the plurality of carbon nanotubes and carbon particles being suspended in the solvent in a colloidal state; spraying the light absorber precursor solution on a substrate to form a light absorber.

8. The method for producing a light absorber according to claim 7, wherein The method for preparing the light absorber precursor solution comprises the steps of: providing a plurality of carbon nanotubes; dispersing the plurality of carbon nanotubes in a solvent, performing flocculation treatment to obtain a carbon nanotube suspension; adding an epoxy resin and carbon particles to the carbon nanotube suspension, performing ultrasonic dispersion to form a light absorber precursor solution.

9. The method for producing a light absorber according to claim 7, wherein The mass ratio of the carbon nanotubes to the carbon particles is 4:5 to 4:

70.

10. The method for producing a light absorber according to claim 7, wherein The concentration of the epoxy resin is 0.1-0.4 grams of epoxy resin per 200 milliliters of solvent.

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