A melamine / silver particle / polydimethylsiloxane metamaterial and its preparation method and application

Abstract

The present invention relates to a melamine / silver particle / polydimethylsiloxane metamaterial, its preparation method, and application. The metamaterial is primarily composed of a composite of melamine foam, silver particles, and polydimethylsiloxane. The acid-etched melamine foam is immersed in a silver slurry to produce an acid-etched conductive melamine foam. The acid-etched conductive melamine foam is then immersed in polydimethylsiloxane solutions of varying concentrations and cured to produce the melamine / silver particle / polydimethylsiloxane metamaterial. Compared to the prior art, the melamine / silver particle / polydimethylsiloxane metamaterial prepared in the present invention not only exhibits electromagnetic double-negative properties, namely negative dielectric constant and negative magnetic permeability, but also can be deformed by applying an external force, thereby regulating the degree of double negativity and the corresponding frequency range. This metamaterial can be applied to the field of tunable metamaterials and help expand the application of metamaterials in areas such as smart switches and adjustable antenna windows.

Description

Technical Field

[0001] The present invention relates to the technical field of supercomposite materials, and in particular to a melamine / silver particle / polydimethylsiloxane supermaterial and a preparation method and application thereof. Background Art

[0002] Since Zhong et al. demonstrated negative dielectric constants in carbon nanofiber (CNF) / polyetherimide (PEI) composites in 2009, researchers have been working to achieve metamaterial properties with negative dielectric constants in polymers by adjusting composition and constructing various microstructures. However, few researchers have been able to fully tune the properties of metamaterials using fabricated samples.

[0003] As a typical polymer with a three-dimensional network structure, melamine foam has broad application prospects and important application value due to its flexibility and adjustable properties. However, pure melamine foam has a positive dielectric constant and positive magnetic permeability, making it difficult to achieve metamaterial properties. The inventor's patent CN110204779 A discloses a method for preparing a composite material with metamaterial properties, providing an acidified carbon tube / conductive silver paste / melamine foam composite material, the frequency range corresponding to the negative dielectric constant and negative magnetic permeability of the composite material is 1M-1GHz. However, the material designed in this patent has a small frequency range and a low operating frequency, making it difficult to apply in emerging communication fields such as 5G and satellite communications. Summary of the Invention

[0004] The purpose of the present invention is to provide a melamine / silver particle / polydimethylsiloxane metamaterial and its preparation method and application in order to overcome the defects of the above-mentioned prior art such as the small frequency range corresponding to the negative dielectric constant and negative magnetic permeability and the application limitations.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] One of the technical solutions of the present invention is a melamine / silver particle / polydimethylsiloxane metamaterial, which is formed by combining melamine foam, silver particles, and polydimethylsiloxane, with the mass ratio of melamine foam to silver particles being 5:1-2. The polydimethylsiloxane provides structural strength to the melamine foam, while the silver particles coat the melamine foam, imparting electromagnetic properties.

[0007] Furthermore, the diameter of the silver particles is 10-40 μm.

[0008] The second technical solution of the present invention is to provide a method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial, comprising the following steps:

[0009] (1) placing the melamine foam in a strong acid for corrosion, rinsing it with deionized water until it is neutral, and then fully impregnating it in a silver paste after primary drying, and then secondary drying to obtain an acid-etched conductive melamine foam;

[0010] (2) mixing a polydimethylsiloxane prepolymer and a curing agent, and adding a diluent to dilute the mixture to prepare a high-concentration polydimethylsiloxane solution and a low-concentration polydimethylsiloxane solution, respectively;

[0011] (3) The acid-etched conductive melamine foam prepared in step (1) is first placed in a low-concentration polydimethylsiloxane solution, and is completely immersed and then cured once; the solidified material after the primary curing is then placed in a high-concentration polydimethylsiloxane solution, and is completely immersed and then cured twice, and after the secondary curing, a melamine / silver particle / polydimethylsiloxane metamaterial is prepared.

[0012] Furthermore, in step (1), the pKa of the strong acid is less than 1, and the etching time is 5-45 minutes. The strong acid can corrode the melamine foam structure, thereby creating gaps in the network structure, forming micro-capacitors, and supporting the generation of negative magnetic permeability. Erosion times that are too short or too long will not corrode the melamine foam skeleton into the ideal structure with split open resonant rings.

[0013] Further preferably, in step (1), the time for the first drying is 8-24 hours, and the time for the second drying is 12-24 hours.

[0014] Further preferably, the strong acid is selected from one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid and permanganic acid.

[0015] Furthermore, in step (1), the silver paste is composed of polyethylene terephthalate and silver particles, and the mass of the silver particles accounts for 50%-80% of the mass of the silver paste. The silver particles are attached to the melamine foam skeleton, providing electrical conductivity to the melamine / silver particle / polydimethylsiloxane metamaterial.

[0016] Furthermore, in step (2), the curing agent is selected from hydrogen silicone oil or ethyl orthosilicate; and the diluent is selected from any one of acetone, toluene, and chloroform.

[0017] Furthermore, in step (2), the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is 8-15:1.

[0018] Furthermore, in step (2), the high-concentration polydimethylsiloxane solution is a polydimethylsiloxane solution with a mass fraction of 70-90%, and the low-concentration polydimethylsiloxane solution is a polydimethylsiloxane solution with a mass fraction of 40-60%. The low-concentration polydimethylsiloxane solution has a low viscosity and can completely fill the gaps in the melamine foam, while the high-concentration polydimethylsiloxane solution can prevent the test electromagnetic wave from bypassing the sample and causing leakage and provide better mechanical elasticity.

[0019] Furthermore, in step (3), the temperature of the primary curing and the secondary curing is 60-120° C., and the time is 1-12 hours.

[0020] A third technical solution of the present invention is to provide an application of a melamine / silver particle / polydimethylsiloxane metamaterial, wherein the melamine / silver particle / polydimethylsiloxane metamaterial is applied in the field of adjustable metamaterials.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention uses polydimethylsiloxane as a substrate, so that the melamine / silver particle / polydimethylsiloxane metamaterial has excellent mechanical properties and good elasticity, can deform under different stresses, and can regulate the frequency range and intensity of negative dielectric constant and negative magnetic permeability through deformation.

[0023] (2) The present invention adopts an acid etching method to control the fracture density of the melamine foam skeleton by changing the strength of the acid and the etching time, thereby affecting the content of silver particles in the melamine foam, and then controlling the electromagnetic properties of the melamine / silver particle / polydimethylsiloxane metamaterial.

[0024] (3) The melamine / silver particle / polydimethylsiloxane metamaterial of the present invention has electromagnetic double negative properties, namely negative dielectric constant and negative magnetic permeability. The frequency range corresponding to the negative dielectric constant and negative magnetic permeability of the undeformed melamine / silver particle / polydimethylsiloxane metamaterial is 2-7.15 GHz.

[0025] (4) The melamine / silver particle / polydimethylsiloxane metamaterial of the present invention has stress adjustability. By changing the morphology of the melamine / silver particle / polydimethylsiloxane metamaterial, its negative dielectric constant, negative magnetic permeability, and corresponding frequency range can be controlled. The frequency range corresponding to the negative dielectric constant and negative magnetic permeability of the melamine / silver particle / polydimethylsiloxane metamaterial with a deformation of 15% is 5.3-18 GHz.

[0026] (5) The melamine / silver particle / polydimethylsiloxane metamaterial of the present invention can be applied to the field of adjustable metamaterials, providing a possibility for the preparation of controllable composite electromagnetic metamaterials, and also helping to expand the application of metamaterials in the fields of smart switches, adjustable antenna windows, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram of the mediation constant performance of Example 1.

[0028] Figure 2 This is the magnetic permeability performance diagram of Example 1. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0031] The silver paste is 8000A conductive silver paste produced by Shenzhen Baojiayi Technology Co., Ltd.; the polydimethylsiloxane prepolymer is Dow Corning DC184 / PDMS prepolymer transparent optical adhesive from the United States.

[0032] Example 1:

[0033] This embodiment provides a method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial, comprising the following steps:

[0034] (1) The cleaned melamine foam is placed in a strong acid for corrosion, wherein the strong acid is concentrated sulfuric acid with a mass fraction of 96%. After standing for 10 minutes, it is repeatedly rinsed with deionized water until it is neutral. After drying for 8 hours, it is placed in a silver paste with a silver particle content of 65% and a diameter of 20 μm and fully immersed. After drying for 12 hours, it is made into an acid-etched conductive melamine foam.

[0035] (2) The polydimethylsiloxane prepolymer and the curing agent hydrogenated silicone oil were mixed in a mass ratio of 10:1, and different proportions of diluents were added to prepare high-concentration and low-concentration polydimethylsiloxane solutions respectively. Toluene was selected as the diluent solvent. Among them, the mass fraction of the high-concentration polydimethylsiloxane solution was 75%, and the mass fraction of the low-concentration polydimethylsiloxane solution was 50%. The acid-etched melamine foam was first placed in the low-concentration polydimethylsiloxane solution, completely immersed and then cured. The cured product was then placed in the high-concentration polydimethylsiloxane solution, completely immersed and then cured. The temperature of the two curing processes was 80°C, and the curing time was 1.5 hours. A melamine foam / silver particle / polydimethylsiloxane metamaterial was prepared, wherein the mass ratio between the melamine foam and the silver particles was 5:1.

[0036] In this example, a melamine foam / silver particle / polydimethylsiloxane metamaterial with metamaterial properties was prepared. The melamine foam / silver particle / polydimethylsiloxane metamaterials were named, according to the degree of deformation, as MF / Ag / PDMS-undeformed, MF / Ag / PDMS-15% deformed, MF / Ag / PDMS-30% deformed, and PMF / Ag / PDMS-45% deformed.

[0037] The dielectric constant and magnetic permeability of the melamine foam / silver particles / polydimethylsiloxane metamaterial prepared in this embodiment were tested using Agilent 16453A. Figure 1 It can be seen that within the test frequency range of 2-18 GHz, the dielectric constants of the melamine foam / silver particles / polydimethylsiloxane metamaterials are all negative, and as the degree of deformation increases, the negative dielectric properties increase. Figure 2 It can be seen that within the test frequency range of 2-18 GHz, the magnetic permeability of MF / Ag / PDMS-undeformed is negative in the range of 2-7.15 GHz, with the minimum value reaching -3.07, and the magnetic permeability of MF / Ag / PDMS-15% deformed is negative in the range of 5.3-18 GHz, with the minimum value reaching -0.87.

[0038] Example 2

[0039] This embodiment provides a method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial, comprising the following steps:

[0040] (1) The cleaned melamine foam is placed in a strong acid corrosion, wherein the strong acid is concentrated sulfuric acid with a mass fraction of 96%. After standing for 5 minutes, it is repeatedly rinsed with deionized water until it is neutral. After drying for 12 hours, it is placed in a silver paste with a silver particle content of 50% and a diameter of 10 μm and fully immersed. After drying for 18 hours, the acid-etched conductive melamine foam is prepared.

[0041] (2) The polydimethylsiloxane prepolymer and the curing agent ethyl orthosilicate were mixed in a mass ratio of 8:1, and different proportions of diluents were added to prepare high-concentration and low-concentration polydimethylsiloxane solutions respectively. Acetone was selected as the diluent solvent. Among them, the mass fraction of the high-concentration polydimethylsiloxane solution was 70%, and the mass fraction of the low-concentration polydimethylsiloxane solution was 40%. The acid-etched conductive melamine foam was first placed in the low-concentration polydimethylsiloxane solution, completely immersed and then cured. The cured product was then placed in the high-concentration polydimethylsiloxane solution, completely immersed and then cured. The temperature of the two curing processes was 60°C, and the curing time was 1 hour. A melamine foam / silver particle / polydimethylsiloxane metamaterial was prepared, wherein the mass ratio between melamine foam and silver particles was 5:2.

[0042] This example controls the degree of fracture of the melamine foam skeleton by controlling the type and duration of acid treatment, while maintaining mechanical elasticity under the action of polydimethylsiloxane, enabling deformation under varying stresses. Using an immersion-compounding method, the acid-etched melamine foam is immersed in a silver paste, introducing highly conductive silver particles into the melamine foam skeleton. The resulting melamine foam / silver particle / polydimethylsiloxane metamaterial exhibits negative dielectric constant and negative magnetic permeability. The metamaterials are designated, according to their degree of deformation, as MF / Ag / PDMS (undeformed), MF / Ag / PDMS (15% deformed), MF / Ag / PDMS (30% deformed), and PMF / Ag / PDMS (45% deformed).

[0043] Example 3:

[0044] This embodiment provides a method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial, comprising the following steps:

[0045] (1) The cleaned melamine foam is placed in a strong acid corrosion, wherein the strong acid is concentrated nitric acid with a mass fraction of 68%. After standing for 45 minutes, it is repeatedly rinsed with deionized water until it is neutral. After drying for 18 hours, it is placed in a silver paste with a silver particle content of 80% and a diameter of 40 μm and fully immersed. After drying for 20 hours, the acid-etched conductive melamine foam is prepared.

[0046] (2) The polydimethylsiloxane prepolymer and the curing agent hydrogenated silicone oil were mixed in a mass ratio of 15:1, and different proportions of diluents were added to prepare high-concentration and low-concentration polydimethylsiloxane solutions respectively. Chloroform was selected as the diluent solvent. Among them, the mass fraction of the high-concentration polydimethylsiloxane solution was 90%, and the mass fraction of the low-concentration polydimethylsiloxane solution was 60%. The acid-etched conductive melamine foam was first placed in the low-concentration polydimethylsiloxane solution, completely immersed and then cured. The cured product was then placed in the high-concentration polydimethylsiloxane solution, completely immersed and then cured. The temperature of the two curing processes was 120°C, and the curing time was 12 hours. A melamine foam / silver particle / polydimethylsiloxane metamaterial was prepared, in which the mass ratio between melamine foam and silver particles was 5:1.

[0047] In this embodiment, the degree of fracture of the melamine foam skeleton is controlled by controlling the type and duration of acid, while maintaining mechanical elasticity under the action of polydimethylsiloxane, allowing it to deform under different stresses. An immersion composite method is used to immerse the acid-etched melamine foam in silver paste, thereby introducing silver particles with excellent conductivity into the melamine foam skeleton. The melamine foam is then cured and formed with polydimethylsiloxane to prepare a melamine foam / silver particle / polydimethylsiloxane metamaterial with negative dielectric constant and negative magnetic permeability.

[0048] Example 4:

[0049] This embodiment provides a method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial, comprising the following steps:

[0050] (1) The cleaned melamine foam is placed in a strong acid for corrosion, wherein the strong acid is 72% by mass of perchloric acid, and after standing for 30 minutes, it is repeatedly rinsed with deionized water until it is neutral, and after drying for 24 hours, it is placed in a silver paste with a silver particle content of 60% and a diameter of 30 μm and fully immersed, and after drying for 24 hours, an acid-etched conductive melamine foam is prepared.

[0051] (2) The polydimethylsiloxane prepolymer and the curing agent hydrogenated silicone oil were mixed in a mass ratio of 12:1, and different proportions of diluents were added to prepare high-concentration and low-concentration polydimethylsiloxane solutions respectively. Toluene was selected as the diluent solvent. Among them, the mass fraction of the high-concentration polydimethylsiloxane solution was 80%, and the mass fraction of the low-concentration polydimethylsiloxane solution was 50%. The acid-etched conductive melamine foam was first placed in the low-concentration polydimethylsiloxane solution, completely immersed and then cured. The cured product was then placed in the high-concentration polydimethylsiloxane solution, completely immersed and then cured. The temperature of the two curings was 100°C and the curing time was 5h. A melamine foam / silver particle / polydimethylsiloxane metamaterial was prepared, wherein the mass ratio between melamine foam and silver particles was 5:2.

[0052] In this embodiment, the degree of fracture of the melamine foam skeleton is controlled by controlling the type and duration of acid, while maintaining mechanical elasticity under the action of polydimethylsiloxane, allowing it to deform under different stresses. An immersion composite method is used to immerse the acid-etched melamine foam in silver paste, thereby introducing silver particles with excellent conductivity into the melamine foam skeleton. The melamine foam is then cured and formed with polydimethylsiloxane to prepare a melamine foam / silver particle / polydimethylsiloxane metamaterial with negative dielectric constant and negative magnetic permeability.

[0053] Example 5:

[0054] The process is similar to that of Example 4 except that, in step (2), the polydimethylsiloxane prepolymer and the curing agent hydrogenated silicone oil are mixed in a mass ratio of 10:1, and acetone is used as the diluent.

[0055] Example 6:

[0056] Most aspects are the same as those of Example 4, except that in step (2), the mass fraction of the high-concentration polydimethylsiloxane solution is 70%, and the mass fraction of the low-concentration polydimethylsiloxane solution is 60%.

[0057] Example 7:

[0058] The method is similar to Example 4 in most respects, except that the strong acid in step (1) is 70% by mass of permanganate, and the mass ratio of melamine foam to silver particles in the prepared melamine foam / silver particles / polydimethylsiloxane metamaterial is 5:1.

[0059] Comparative Example 1:

[0060] Compared with Example 1, most of the steps are the same, except that the concentrated sulfuric acid with a mass fraction of 96% is replaced by dilute sulfuric acid with a mass fraction of 30%.

[0061] Testing of the sample produced in this comparative example showed that within the test range of 2-18G, only the dielectric constant produced a negative value, while the magnetic permeability did not. Therefore, using strong acid corrosion to artificially create a broken skeleton and produce an open resonant ring is a key step.

[0062] Comparative Example 2:

[0063] Compared with Example 1, most aspects are the same except that the dipping and curing in the high-concentration polydimethylsiloxane solution are omitted.

[0064] The samples prepared in this comparative example were tested and found to have no dielectric constant or permeability after responsiveness to electromagnetic waves within the 2-18G test range. This is because the sample lacks a high-concentration polydimethylsiloxane matrix. During testing, some electromagnetic waves pass directly through the sample gaps, preventing the sample from responsiveness to electromagnetic waves. Therefore, using high- and low-concentration polydimethylsiloxane solutions for impregnation and curing is also a key step.

[0065] Comparative Example 3:

[0066] Compared with Example 1, most aspects are the same except that the dipping and curing in the low-concentration polydimethylsiloxane solution are omitted.

[0067] The samples made in this comparative example were tested and found to have no negative dielectric constant and permeability values ​​in the test range of 2-18G. The reason is that the high-concentration polydimethylsiloxane solution, due to its high viscosity, cannot completely fill the gaps in the foam during the impregnation process, resulting in a large number of bubbles still inside the sample after curing. These bubbles destroy the structure that can produce negative electromagnetic parameters. The low-concentration polydimethylsiloxane solution has a lower viscosity and can completely fill the gaps in the melamine foam. Therefore, using a low-concentration polydimethylsiloxane solution for impregnation and curing is also a key step.

[0068] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial, characterized in that: The steps include: (1) placing the melamine foam in a strong acid for corrosion, rinsing it with deionized water until it is neutral, and then fully impregnating it in a silver paste after primary drying, and then secondary drying to obtain an acid-etched conductive melamine foam; (2) mixing a polydimethylsiloxane prepolymer and a curing agent, and adding a diluent to dilute the mixture to prepare a high-concentration polydimethylsiloxane solution and a low-concentration polydimethylsiloxane solution, respectively; (3) placing the acid-etched conductive melamine foam obtained in step (1) in a low-concentration polydimethylsiloxane solution, and performing a primary curing after complete immersion; then placing the solidified material after the primary curing in a high-concentration polydimethylsiloxane solution, and performing a secondary curing after complete immersion; and finally, preparing a melamine / silver particle / polydimethylsiloxane metamaterial after the secondary curing; Wherein, in step (1), the pKa of the strong acid is less than 1, and the corrosion time is 5-45 min; In step (2), the high-concentration polydimethylsiloxane solution is a polydimethylsiloxane solution with a mass fraction of 70-90%, and the low-concentration polydimethylsiloxane solution is a polydimethylsiloxane solution with a mass fraction of 40-60%.

2. The method for preparing the melamine / silver particle / polydimethylsiloxane metamaterial according to claim 1, characterized in that: The melamine / silver particle / polydimethylsiloxane metamaterial is formed by compounding melamine foam, silver particles and polydimethylsiloxane, and the mass ratio between the melamine foam and the silver particles is 5:1-2.

3. The method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial according to claim 1, characterized in that: The diameter of the silver particles is 10-40 μm.

4. The method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial according to claim 1, characterized in that: In step (1), the silver paste is composed of polyethylene terephthalate and silver particles, and the mass of the silver particles accounts for 50%-80% of the mass of the silver paste.

5. The method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial according to claim 1, characterized in that: In step (2), the curing agent is selected from hydrogen silicone oil or ethyl orthosilicate; and the diluent is selected from any one of acetone, toluene, and chloroform.

6. The method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial according to claim 1, characterized in that: In step (2), the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is 8-15:

1.

7. The method for preparing a melamine / silver particle / polydimethylsiloxane metamaterial according to claim 1, characterized in that: In step (3), the temperature of the primary curing and the secondary curing is 60-120° C., and the time is 1-12 hours.

8. An application of a melamine / silver particle / polydimethylsiloxane metamaterial, characterized in that: The melamine / silver particle / polydimethylsiloxane metamaterial is prepared by the preparation method according to any one of claims 1 to 7, and the melamine / silver particle / polydimethylsiloxane metamaterial is applied in the field of adjustable metamaterials.

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