A color-mixed structural color fabric and a preparation method thereof

Abstract

The application discloses a preparation method of a mixed color structural color fabric, and comprises the following steps: completely dissolving caffeic acid in deionized water, then adding a potassium iodate solution, stirring and reacting, and obtaining poly-caffeic acid nanometer microspheres after centrifugation and water washing; repeating the above steps, and changing the conditions of the caffeic acid and the potassium iodate to obtain poly-caffeic acid nanometer microspheres with different particle sizes; dispersing the poly-caffeic acid nanometer microspheres with different particle sizes in water respectively to obtain microsphere dispersions with different particle sizes; uniformly mixing the microsphere dispersions with different particle sizes to obtain a mixed dispersion, then adding an aqueous polyurethane to obtain a microsphere assembly liquid; and immersing a fabric in the microsphere assembly liquid to obtain a mixed color structural color fabric after self-assembly. According to the preparation method, the poly-caffeic acid nanometer microspheres with different particle sizes are mixed and deposited, and various structural color fabrics can be quickly prepared.

Description

Technical Field

[0001] This invention relates to the field of structural color technology, and in particular to a method for preparing mixed-color structural color fabrics and the mixed-color structural color fabrics prepared by the method. Background Technology

[0002] Structural colors arise from the physical interaction between light and specific periodic microstructures or nanostructures in materials, involving phenomena such as interference, diffraction, and scattering. They are characterized by being green and environmentally friendly, having vibrant colors, and never fading.

[0003] In recent years, microsphere self-assembly has become one of the most commonly used methods for constructing structured colored fabrics due to its high controllability during the assembly process and the superior optical properties of the assembled structure. To achieve vibrant color decorative effects, researchers have been actively developing full-spectrum photonic crystal structured colors.

[0004] The current main approach involves using nanospheres of different sizes to construct photonic crystals with varying photonic band gaps, thereby generating a range of structural colors (e.g., patent applications 202211404041.8 and 202411378179.4). However, producing each structural color requires microspheres of precise dimensions, which complicates the process. Furthermore, some studies have drawn inspiration from additive color mixing of chemical colors, selecting three different sizes (234 nm, 178 nm, 152 nm) of poly(styrene-methyl methacrylate) microspheres to represent the three primary colors (red, green, and blue) (Reference: Surf. Interfaces, 2024, 51, 104805). These microspheres were mixed in pairs and sprayed onto a dark wood matrix in varying proportions, yielding uniform structural colors that covered almost the entire visible spectrum, thus expanding the potential applications of mixed microsphere assemblies in structural color generation. However, obtaining highly saturated mixed structural colors on white fabrics remains a challenge due to the influence of incoherent scattered light.

[0005] When using the most common white fabric as the substrate, the structural color obtained by commonly used microspheres such as polystyrene and silica microspheres is usually whitish. It is necessary to introduce black light-absorbing materials to absorb incoherent scattered light (such as carbon powder and graphene). The addition of these additional materials can easily reduce the uniformity of the structural color, and the amount introduced will affect the saturation of the structural color. Therefore, it is difficult to obtain a bright structural color on the surface of white fabric using only dark-colored microspheres.

[0006] The above background information is provided only to assist in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed before the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0007] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing a mixed-color structured fabric.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a mixed-color structured fabric includes the following steps:

[0010] Caffeic acid was completely dissolved in deionized water, then potassium iodate solution was added, the mixture was stirred and reacted, and after centrifugation and washing with water, polycaffeic acid nanospheres were obtained.

[0011] Repeat the above steps, changing the conditions of caffeic acid and potassium iodate, to obtain polycaffeic acid nanospheres with different particle sizes;

[0012] The polycaffeic acid nanospheres of different sizes were dispersed in water to obtain microsphere dispersions of different sizes.

[0013] Two microsphere dispersions with different particle sizes were mixed evenly to obtain a mixed dispersion, and then waterborne polyurethane was added to obtain a microsphere assembly solution.

[0014] The fabric is immersed in the microsphere assembly solution, and after self-assembly, a mixed-color structured fabric is obtained.

[0015] Compared to coated microspheres, the preparation process of polycaffeic acid nanospheres directly from caffeic acid and potassium iodate in this invention requires only one polymerization step, making it simple and convenient to operate. Furthermore, it primarily uses green, natural phenolic acid polycaffeic acid as raw material, without involving the use of styrene or silica, making it more environmentally friendly.

[0016] According to some preferred embodiments of the present invention, the conditions for changing caffeic acid and potassium iodate are as follows: the concentration ratio of potassium iodate to caffeic acid is fixed, the concentration of caffeic acid is increased, and the particle size of the polycaffeic acid microspheres is increased.

[0017] According to some preferred embodiments of the present invention, the conditions for changing caffeic acid and potassium iodate are as follows: keeping the concentration of caffeic acid constant, increasing the concentration ratio of potassium iodate to caffeic acid, and the particle size of the polycaffeic acid microspheres first increases and then decreases. Specifically, when the concentration ratio of potassium iodate to caffeic acid is in the range of 0.2:1 to 0.7:1, the particle size gradually increases, and when it is in the range of 0.7:1 to 3:1, the particle size gradually decreases.

[0018] According to some preferred embodiments of the invention, the concentration of caffeic acid is 4-15 mmol / L.

[0019] According to some preferred embodiments of the present invention, the concentration ratio of potassium iodate to caffeic acid is 0.2:1-3:1.

[0020] According to some preferred embodiments of the present invention, the reaction temperature of the stirring reaction is 50-100°C, and the reaction time is 1-6 hours.

[0021] According to some preferred embodiments of the invention, the polycaffeic acid microspheres have a particle size of 150-300 nm.

[0022] According to some preferred embodiments of the invention, the mass fraction of the microsphere dispersion is 3%-10%.

[0023] According to some preferred embodiments of the present invention, when the mixed dispersion contains two types of polycaffeic acid nanospheres with different particle sizes, the volume ratio between the dispersion of polycaffeic acid nanospheres with smaller particle sizes and the dispersion of polycaffeic acid nanospheres with larger particle sizes is 0.3:1 to 5:1. It is preferable to mix microspheres with two different particle sizes and color systems; if three particle sizes are mixed, the degree of disorder is too high, making it difficult to produce structural colors. Furthermore, the intermediate color between two primary colors formed after mixing two types of microspheres with different particle sizes and color systems is called a mixed color.

[0024] According to some preferred embodiments of the present invention, it is preferable that the particle size difference between the two polycaffeic acid nanospheres with different particle sizes is more than 20 nm, so that the two polycaffeic acid nanospheres with different particle sizes can be compounded in different proportions to form a richer color, and avoid the two primary colors being too different to achieve the color mixing effect.

[0025] According to some preferred embodiments of the invention, the amount of aqueous polyurethane added is 5%-20% of the total mass of the microsphere assembly solution.

[0026] According to some preferred embodiments of the invention, the self-assembly conditions are gravity self-assembly at 40-90°C for 1-5 hours.

[0027] According to some preferred embodiments of the invention, the fabric is made of wool, silk, cotton, polyester, or nylon.

[0028] In some embodiments of the present invention, the method for preparing mixed-color structured fabrics specifically includes the following steps:

[0029] Step S1: Dissolve caffeic acid completely in deionized water, then add potassium iodate solution, stir and react, and after centrifugation and washing with water, obtain polycaffeic acid nanospheres of the corresponding particle size.

[0030] Step S1 was repeated, and the concentration of caffeic acid or the ratio of potassium iodate to caffeic acid was varied to obtain polycaffeic acid nanospheres of different sizes. Specifically, under a fixed ratio of potassium iodate to caffeic acid, the particle size of the polycaffeic acid nanospheres increased with increasing caffeic acid concentration. Under a fixed caffeic acid concentration, the particle size of the polycaffeic acid nanospheres first increased and then decreased with increasing ratio of potassium iodate to caffeic acid.

[0031] Step S2: Disperse the polycaffeic acid nanospheres of different particle sizes in water to obtain microsphere dispersions of different particle sizes. The mass fraction of the microsphere dispersions is 3%-10%.

[0032] Step S3: Mix two polycaffeic acid nanosphere dispersions of different particle sizes at a certain volume ratio to obtain a mixed dispersion. Then add aqueous polyurethane to obtain a microsphere assembly solution.

[0033] Step S4: Immerse the fabric in the microsphere assembly solution and perform gravity self-assembly at 40-90℃ for 1-5 hours to obtain a mixed-color structured fabric.

[0034] The present invention also provides a mixed-color structured fabric prepared according to the above-described preparation method.

[0035] Compared with existing traditional technologies, the advantages of this invention are as follows: The method for preparing mixed-color structural fabrics of this invention uses polycaffeic acid nanospheres of different particle sizes for mixed deposition, which can rapidly prepare fabrics with multiple structural colors. At the same time, the excellent light absorption properties of polycaffeic acid nanospheres avoid the influence of incoherent scattered light in the microsphere assembly structure, and vibrant structural colors can be constructed on the surface of white fabrics without the need for additional black additives. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 These are the reflectance spectra of the three mixed-structure dyed fabrics prepared in Example 1 of this invention;

[0038] Figure 2 These are scanning electron microscope images of the surfaces of the three colored fabrics prepared in Example 1 of this invention;

[0039] Figure 3 These are the reflection spectra of the three mixed-structured colored fabrics prepared in Example 2 of this invention. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0041] The present invention provides a method for preparing mixed-color structural fabrics, which utilizes the mixed deposition of polycaffeic acid nanospheres of different particle sizes to rapidly prepare fabrics with multiple structural colors. The synthesis of polycaffeic acid microspheres is simple and environmentally friendly. Furthermore, the excellent light absorption properties of the polycaffeic acid nanospheres avoid the influence of incoherent scattered light in the microsphere assembly structure, thereby improving the color saturation of the structural colors. This solves the problem in existing technologies of being unable to rapidly obtain structurally colored fabrics with a complete color spectrum and vibrant colors.

[0042] Specifically, the method for preparing the mixed-color structured fabric of the present invention includes the following steps:

[0043] Step S1: Dissolve caffeic acid completely in deionized water, then add potassium iodate solution, stir and react, and after centrifugation and washing with water, obtain polycaffeic acid nanospheres of the corresponding particle size.

[0044] The concentration of caffeic acid was 4-15 mmol / L; the concentration ratio of potassium iodate to caffeic acid was 0.2:1-3:1; the reaction temperature was 50-100℃ and the reaction time was 1-6 h. The particle size of the prepared polycaffeic acid nanospheres was 150-300 nm.

[0045] Repeat step S1 and change the concentration of caffeic acid or the ratio of potassium iodate to caffeic acid to obtain polycaffeic acid nanospheres with different particle sizes.

[0046] Specifically, under a fixed potassium iodate to caffeic acid concentration ratio, the particle size of polycaffeic acid microspheres increases with increasing caffeic acid concentration. Under the same caffeic acid concentration, the particle size of polycaffeic acid microspheres initially increases and then decreases with increasing potassium iodate to caffeic acid concentration ratio. Specifically, the particle size gradually increases when the potassium iodate to caffeic acid concentration ratio is in the range of 0.2:1 to 0.7:1, and gradually decreases when it is in the range of 0.7:1 to 3:1.

[0047] Compared to coated microspheres, the preparation process of polycaffeic acid nanospheres directly from caffeic acid and potassium iodate in this invention requires only one polymerization step, making it simple and convenient to operate. Furthermore, it primarily uses green, natural phenolic acid polycaffeic acid as raw material, without involving the use of styrene or silica, making it more environmentally friendly.

[0048] Step S2: Disperse polycaffeic acid nanospheres of different particle sizes in water to obtain microsphere dispersions of different particle sizes. The mass fraction of the microsphere dispersions is 3%-10%.

[0049] Step S3: Mix two polycaffeic acid nanosphere dispersions of different particle sizes at a certain volume ratio to obtain a mixed dispersion. Then add aqueous polyurethane to obtain a microsphere assembly solution.

[0050] The solid content of the waterborne polyurethane is 15-20%, preferably 16%. The amount of waterborne polyurethane added is 5%-20% of the total mass of the microsphere assembly solution.

[0051] When the mixed dispersion contains two types of polycaffeic acid nanospheres with different particle sizes, the volume ratio between the dispersion of polycaffeic acid nanospheres with smaller particle sizes and the dispersion of polycaffeic acid nanospheres with larger particle sizes is 0.3:1-5:1. Preferably, the particle sizes of the two types of polycaffeic acid nanospheres differ by more than 20 nm, so that when the two types of polycaffeic acid nanospheres with different particle sizes are mixed in different proportions, a richer range of colors can be formed, avoiding the situation where the difference between the two primary colors is too small to achieve a color mixing effect.

[0052] In this invention, when two microspheres of different sizes are mixed and assembled, the average particle size of the microspheres in the assembled structure changes, thereby altering the maximum reflection wavelength of the structurally colored fabric. Therefore, the color of the mixed-color structurally colored fabric is determined by the particle size and ratio of the two mixed microspheres, and the color of the mixed-color structurally colored fabric is an intermediate color between the corresponding colors of the two mixed microspheres. For example, when microspheres with a particle size of 198±10nm (green) and microspheres with a particle size of 256±10nm (purple-red) are mixed and assembled in ratios of 0.3:1, 1:1, and 3:1, the resulting colors are pink, orange, and yellow, respectively.

[0053] Step S4: Immerse the fabric in the microsphere assembly solution and perform gravity self-assembly at 40-90℃ for 1-5 hours to obtain a mixed-color structural fabric. The fabric material is wool, silk, cotton, polyester, or nylon.

[0054] Example 1

[0055] The method for preparing the mixed-color structured fabric in this embodiment includes the following steps:

[0056] 0.936 g of caffeic acid was added to a round-bottom flask containing 630 mL of deionized water and stirred continuously at 80 °C until completely dissolved. Then, 20 mL of pre-dissolved potassium iodate solution (1.113 g) was slowly added, and the mixture was magnetically stirred at 80 °C for 3 h. After the reaction was complete, the reaction solution was centrifuged at 8000 rpm / min for 10 min, and then washed three times with deionized water to obtain polycaffeic acid nanospheres with a particle size of 198 ± 10 nm. Similarly, by changing the amount of caffeic acid to 1.638 g and the amount of potassium iodate to 1.947 g, while keeping other reaction conditions unchanged, polycaffeic acid microspheres with a particle size of 256 ± 10 nm were obtained.

[0057] The two types of microspheres with different particle sizes were ultrasonically dispersed in deionized water to obtain a nanosphere dispersion with a mass fraction of 4%. Subsequently, 1.5 mL, 1 mL, and 0.5 mL of microsphere dispersion with a particle size of 198±10 nm were mixed with 0.5 mL, 1 mL, and 1.5 mL of microsphere dispersion with a particle size of 256±10 nm, respectively. Then, 300 μL of aqueous polyurethane emulsion (solid content 16%) was added to each of the three mixed dispersions, and the mixture was ultrasonicated for 30 min to ensure uniform mixing, thus obtaining the final mixed assembly solution.

[0058] Then, 2 mL of each of the three mixed assembly solutions was added to three petri dishes (3.5 cm in diameter) containing white cotton fabric samples; after self-assembly at a constant temperature (80 °C) for 3 hours, yellow, orange, and pink structural colors were obtained on the surface of the cotton fabric, respectively.

[0059] Furthermore, the above three sets of mixed assembly solutions can be used in different areas of the same fabric to form structural colors of yellow, orange, and pink. That is, green (198±10nm microspheres) and purple-red (256±10nm microspheres) microspheres can be compounded in different proportions to obtain a variety of different intermediate colors and applied to the fabric.

[0060] Figure 1 The reflectance spectra of the three mixed-structure dyed fabrics prepared in Example 1 are shown. Figure 2 Scanning electron microscope (SEM) images of the surfaces of the three colored fabrics prepared in Example 1. Figure 1 It can be seen that the reflection peaks of the three mixed-color fabrics are located between green and purplish-red, indicating that the three colors are intermediate colors between green (198±10nm microspheres) and purplish-red (256±10nm microspheres). Figure 2 Scanning electron microscopy images show that the surfaces of the three mixed-color fabrics contain two different sizes of microspheres, and the proportion of larger microspheres gradually increases from yellow and orange to pink.

[0061] Example 2

[0062] The method for preparing the mixed-color structured fabric in this embodiment includes the following steps:

[0063] 1.638 g of caffeic acid was added to a round-bottom flask containing 630 mL of deionized water and stirred continuously at 80 °C until completely dissolved. Then, 20 mL of pre-dissolved potassium iodate solution (1.947 g) was slowly added, and the mixture was magnetically stirred at 80 °C for 3 h. After the reaction was complete, the reaction solution was centrifuged at 8000 rpm / min for 10 min, and then washed three times with deionized water to obtain polycaffeic acid nanospheres with a particle size of 256 ± 10 nm. Similarly, by changing the amount of caffeic acid to 0.585 g and the amount of potassium iodate to 0.696 g, while keeping other reaction conditions unchanged, polycaffeic acid microspheres with a particle size of 154 ± 10 nm were obtained.

[0064] The two types of microspheres with different particle sizes were ultrasonically dispersed in deionized water to obtain a nanosphere dispersion with a mass fraction of 4%. Subsequently, 1.5 mL, 1 mL, and 0.5 mL of microsphere dispersion with a particle size of 154±10 nm were mixed with 0.5 mL, 1 mL, and 1.5 mL of microsphere dispersion with a particle size of 256 nm, respectively. Then, 300 μL of aqueous polyurethane emulsion (solid content 16%) was added to each of the three mixed dispersions, and the mixture was ultrasonicated for 30 min to ensure uniform mixing, thus obtaining the final mixed assembly solution.

[0065] Then, 2 mL of each of the three mixed assembly solutions was added to three petri dishes (3.5 cm in diameter) containing white cotton fabric samples; after self-assembly at a constant temperature (80 °C) for 3 hours, green, yellow-green, and light red structural colors were obtained on the surface of the cotton fabric, respectively.

[0066] Figure 3 The figure shows the reflection spectra of the three mixed-structure fabrics prepared in Example 2. As can be seen from the figure, the reflection peaks of the three colors are located between blue and magenta, indicating that the three colors are intermediate colors between blue (154±10nm microspheres) and magenta (256±10nm microspheres).

[0067] Example 3

[0068] The method for preparing the mixed-color structured fabric in this embodiment includes the following steps:

[0069] 0.936 g of caffeic acid was added to a round-bottom flask containing 630 mL of deionized water and stirred continuously at 80 °C until completely dissolved. Then, 20 mL of pre-dissolved potassium iodate solution (1.113 g) was slowly added, and the mixture was magnetically stirred at 80 °C for 3 h. After the reaction was complete, the reaction solution was centrifuged at 8000 rpm / min for 10 min, followed by washing three times with deionized water to obtain polycaffeic acid nanospheres with a particle size of 198 ± 10 nm. Similarly, by changing the amount of caffeic acid to 0.585 g and the amount of potassium iodate to 0.696 g, while keeping other reaction conditions unchanged, polycaffeic acid microspheres with a particle size of 154 ± 10 nm were obtained.

[0070] The two types of microspheres with different particle sizes were ultrasonically dispersed in deionized water to obtain a nanosphere dispersion with a mass fraction of 4%. Subsequently, 1.5 mL, 1 mL, and 0.5 mL of microsphere dispersion with a particle size of 154±10 nm were mixed with 0.5 mL, 1 mL, and 1.5 mL of microsphere dispersion with a particle size of 198±10 nm, respectively. Then, 300 μL of aqueous polyurethane emulsion (solid content 16%) was added to each of the three mixed dispersions, and the mixture was ultrasonicated for 30 min to ensure uniform mixing, thus obtaining the final mixed assembly solution.

[0071] Then, 2 mL of each of the three mixed assembly solutions was added to three petri dishes (3.5 cm in diameter) containing white silk fabric samples. After self-assembly at a constant temperature (80 °C) for 3 hours, light blue, cyan, and light green structural colors were obtained on the surface of the silk fabric, respectively. The three colors were a mixed structural color of blue (154±10 nm microspheres) and green (198±10 nm microspheres).

[0072] The structurally colored fabric prepared by patent CN113106759A uses polycaffeic acid-coated polystyrene microspheres as the basic unit. The preparation of these microspheres requires two complex steps: the synthesis of the polystyrene microspheres and the coating of their surface with polycaffeic acid. Furthermore, only six colors are obtained, with each microsphere size corresponding to one structurally colored fabric. The preparation process of the polysulfide resin microspheres used in the examples of patent CN202310699804.4 is also very complex and uses the organic solvent acetone. In contrast, the method of this invention uses polycaffeic acid microspheres directly polymerized from caffeic acid, resulting in a simpler and faster preparation process. Moreover, in the method of this invention, two microsphere sizes can yield more than two structural colors, broadening the structural color chromatogram. In this invention, the preparation process of the polycaffeic acid microspheres does not require the addition of organic solvents, only caffeic acid and potassium iodate as raw materials, making the preparation simpler and more environmentally friendly.

[0073] The microspheres of different particle sizes in this invention can be combined in any mixing ratio to produce different colors. Mixing green and red microspheres can yield many intermediate colors between green and red. Preparing these intermediate colors using only one particle size of microspheres is extremely difficult, as each color requires separate preparation of microspheres with the corresponding particle size. The particle size difference between microspheres corresponding to two similar colors may only be 1-3 nm, which is difficult to control during preparation; generally, 10-20 nm is relatively easier. Therefore, in existing technologies, it is difficult to obtain similar intermediate colors using microspheres of a single particle size. However, the method in this application can easily produce similar intermediate colors through compounding, and the operation is simple and environmentally friendly. Furthermore, the polycaffeic acid microspheres are single-component and simple to synthesize, requiring no coating of polystyrene microspheres and no additional black additives to construct vibrant structural colors on the surface of white fabrics.

[0074] The purpose of this invention is to prepare a single structural color by mixing microspheres of various particle sizes. Different structural colors can be obtained by mixing and depositing microspheres of different sizes in different proportions. The method for preparing the mixed-color structural color fabric of this invention involves completely dissolving caffeic acid in deionized water, then adding potassium iodate solution, and stirring at an appropriate temperature to obtain polycaffeic acid nanospheres. Next, dispersions of nanospheres of different particle sizes are mixed in pairs, and aqueous polyurethane is added to obtain a microsphere assembly solution. The fabric is then immersed in the microsphere assembly solution and subjected to gravity self-assembly under appropriate temperature conditions to obtain the mixed-color structural color fabric. The preparation method provided by this invention is rapid, convenient, and low-cost. The prepared mixed-color structural color fabric has a complete color spectrum and vibrant colors, effectively broadening the color range of structural color fabrics and having significant application value in textile coloring. Compared with existing technologies, the caffeic acid used in this invention has a wide range of sources and good biocompatibility, making it green and environmentally friendly for the preparation of structural color fabrics. The polycaffeic acid nanospheres have excellent light absorption properties and can construct bright structural colors on the surface of white fabrics without the need for additional black additives. The preparation of mixed-color structural color fabrics is simple, the conditions are easy to control, and the color saturation is high. The method of this invention is applicable to a variety of fabrics, including polyester, silk, wool, nylon, etc.

[0075] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a mixed-color structured fabric, characterized in that: Includes the following steps: Caffeic acid was completely dissolved in deionized water, then potassium iodate solution was added, the mixture was stirred and reacted, and after centrifugation and washing with water, polycaffeic acid nanospheres were obtained. Repeat the above steps, changing the concentration of caffeic acid or the ratio of potassium iodate to caffeic acid, to obtain polycaffeic acid nanospheres with different particle sizes ranging from 150 to 300 nm. Two types of polycaffeic acid nanospheres with different particle sizes were dispersed in water to obtain two microsphere dispersions with different particle sizes; the particle sizes of the two types of polycaffeic acid nanospheres differed by more than 20 nm. Two microsphere dispersions with different particle sizes were mixed evenly to obtain a mixed dispersion, and then waterborne polyurethane was added to obtain a microsphere assembly solution; wherein the volume ratio between the microsphere dispersion with smaller particle size and the microsphere dispersion with larger particle size was 0.3:1-5:

1. The fabric is immersed in the microsphere assembly solution, and after self-assembly, a mixed-color structured fabric is obtained.

2. The preparation method according to claim 1, characterized in that: The conditions for changing caffeic acid and potassium iodate are as follows: the concentration ratio of potassium iodate to caffeic acid is fixed, the concentration of caffeic acid is increased, and the particle size of the polycaffeic acid microspheres increases.

3. The preparation method according to claim 1, characterized in that: The conditions for changing caffeic acid and potassium iodate are as follows: the concentration of caffeic acid is fixed, the concentration ratio of potassium iodate to caffeic acid is increased, and the particle size of the polycaffeic acid microspheres first increases and then decreases.

4. The preparation method according to claim 1, characterized in that: The concentration of caffeic acid is 4-15 mmol / L.

5. The preparation method according to claim 1, characterized in that: The concentration ratio of potassium iodate to caffeic acid is 0.2:1-3:

1.

6. The preparation method according to claim 1, characterized in that: The reaction temperature of the stirring reaction is 50-100℃, and the reaction time is 1-6h.

7. The preparation method according to claim 1, characterized in that: The mass fraction of the microsphere dispersion is 3%-10%.

8. The preparation method according to claim 1, characterized in that: The amount of waterborne polyurethane added is 5%-20% of the total mass of the microsphere assembly solution.

9. The preparation method according to claim 1, characterized in that: The self-assembly conditions are gravity self-assembly at 40-90℃ for 1-5 hours.

10. The preparation method according to claim 1, characterized in that: The fabric is made of wool, silk, cotton, polyester, or nylon.

11. A mixed-color structural fabric prepared by the preparation method according to any one of claims 1-10.

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