High-conductivity low-infrared-emissivity silver nanowire gel film, preparation method and application

Abstract

The invention discloses a high-conductivity and low-infrared-emissivity silver nanowire gel film, a preparation method and application. Polyvinyl alcohol is adopted as a matrix, high-conductivity silver nanowires are adopted as functional filler, a porous framework structure is constructed through a repeated freezing-thawing method, system moisture is removed through freeze drying treatment, and it is guaranteed that the whole film is light and high in strength; and high-conductivity silver nanowires are uniformly filled among the frameworks, so that a bridging effect is achieved, and internal conductive network lapping is realized. The prepared gel film with high conductivity has the characteristics of low density and high strength, the infrared emissivity can be lower than 0.3, the conductivity can reach 104 S / m, and the preparation method has the characteristics of simplicity in operation, easiness in raw material obtaining and easiness in popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible highly conductive and low infrared emissivity materials, and particularly relates to a highly conductive and low infrared emissivity gel film filled with silver nanowires, a preparation method and an application thereof. Background Art

[0002] Infrared stealth technology refers to changing the radiation signal characteristics of the object surface to make it close to the background radiation signal, so that the detector cannot identify and track it. By reducing the emissivity of the object surface material and then weakening the target radiation signal, the possibility of the target being detected and tracked by infrared can be effectively reduced, and the stealth performance of the target can be improved. This is crucial for stealth devices and equipment in the military, aerospace and other fields, so it has become a relatively common infrared stealth technology method at present.

[0003] Low infrared emissivity materials are a class of materials with special infrared radiation characteristics. These materials show excellent performance in absorbing and emitting infrared radiation, so they have received extensive attention and applications in many fields. Currently, the mainstream infrared stealth materials are low infrared emissivity coatings, which mainly rely on the excellent conductivity of metal fillers to achieve low infrared emissivity.

[0004] CN 114835153A discloses a preparation method of a ZnO-based high-temperature ultra-low infrared emissivity material. First, a zinc salt and a cerium salt are added to a solvent to prepare a reaction nitrate solution; a precipitant solution is prepared by adding a precipitant to the solvent, and then the precipitant solution is added dropwise to the mixed nitrate solution to form a sol precursor. After drying, a dry gel precursor is obtained, and after calcination, a ZnO-based high-temperature ultra-low infrared emissivity material is obtained. The infrared emissivity of the ZnO material prepared by this process is reduced to below 0.15 in the 3-5μm band. However, the raw materials in this method are toxic or have other usage hazards, making it difficult to promote to practical applications.

[0005] One-dimensional metal silver nanowires (AgNWs) have high electrical conductivity and processability and can be used as filling materials for low infrared emissivity materials. CN 110229552A discloses a preparation and film-forming method of an infrared stealth coating. The infrared stealth coating includes: silver nanowires, a transparent organic substance, a dispersant and / or a coloring filler. Among them, the concentration of the silver nanowire dispersion is 1-60mg / mL, and the corresponding dispersant is water or isopropanol, and the transparent organic substance is one of polymethyl methacrylate, poly-4-methylpentene, polyethylene, polyethylene terephthalate, polyurethane and polystyrene ester. This coating has a lower infrared emissivity, but this method uses a large number of raw materials and the preparation process is relatively complex. Summary of the Invention

[0006] The objective of the present invention is to provide a silver nanowire gel film that is flexible, has excellent mechanical properties, high conductivity, and low infrared emissivity.

[0007] A highly conductive and low infrared emissivity silver nanowire gel film provided by the present invention is composed of silver nanowires as conductive fillers distributed on a film with polyvinyl alcohol as the matrix, and it has a porous structure.

[0008] Furthermore, the gel film has an infrared emissivity lower than 0.3, and the film conductivity is as high as 10 4 S / m.

[0009] Furthermore, the silver nanowires account for 1 - 10 wt.% of the mass of the gel film, preferably 10 wt.%.

[0010] The preparation method of the above-mentioned highly conductive and low infrared emissivity silver nanowire gel film adopts a method combining solution casting, repeated freeze-thawing, and freeze-drying methods, and specifically includes the following steps:

[0011] (1) Stir the polyvinyl alcohol particles at 80 - 100 °C to dissolve them in deionized water to prepare an aqueous polyvinyl alcohol solution, add silver nanowires to this solution, and continue stirring for a period of time to obtain a mixed solution;

[0012] (2) After degassing the mixed solution in step (1), cast it in a horizontally placed polytetrafluoroethylene mold. After it cools to room temperature, place it in a freezer for freezing;

[0013] (3) After the freezing is completed, take out the sample, place it at room temperature until the sample is completely thawed, and then repeat the freezing process in step (2) under the same conditions;

[0014] (4) Take out the sample in step (3) and perform freeze-drying treatment to obtain the gel film.

[0015] Furthermore, the degree of polymerization of polyvinyl alcohol is 500 - 1200, and the degree of alcoholysis is 50% - 99%.

[0016] Furthermore, the diameter of the silver nanowires is 5 - 50 nm, and the length is 5 - 20 μm.

[0017] Furthermore, in step (1), the stirring rate is 400 - 800 r / min; when adding the silver nanowires to this solution, stir for at least 8 h to obtain a mixed solution.

[0018] Furthermore, in step (2), freeze at -5 °C for 20 h.

[0019] Furthermore, in step (3), repeat the freezing process 0 - 2 times.

[0020] Further, in step (4), the process conditions for freeze-drying treatment are as follows: the freezing temperature is -55°C, the vacuum degree is 1.00 MPa, and the freeze-drying time is 4 hours.

[0021] Compared with the existing invention, the advantages of the present invention are as follows:

[0022] 1. The preparation process is simple, without complex operations, and the size of the prepared sample is only affected by the sample mold, enabling mass preparation of samples.

[0023] 2. Silver nanowires with high electrical conductivity are selected as the conductive filler, which can easily achieve the role of a bridging network inside the gel film. In addition, a conductive network will be constructed on the surface and inside of the gel film, ensuring its high electrical conductivity while meeting the requirement of low infrared emissivity.

[0024] 3. While having excellent electrical conductivity and low infrared emissivity, the gel sample also has the advantages of flexibility and strong mechanical properties, and can fully adapt to various usage environments. Description of the Drawings

[0025] Figure 1 It is the internal porous framework structure of the gel film prepared for Comparative Example 1.

[0026] Figure 2 It is the surface microstructure of the silver nanowire gel film prepared for Example 12. Specific Embodiments

[0027] Now, the silver nanowire gel film with high electrical conductivity and low infrared emissivity of the present invention and its preparation method will be described in more detail by way of exemplary embodiments. These embodiments are provided to make this specification more complete and full, so that those skilled in the art can fully understand and implement the invention patent, but the present invention is not limited to the listed exemplary embodiments.

[0028] The present invention obtains a gel film with high electrical conductivity and low infrared emissivity through a combination of solution casting, repeated freeze-thawing, and freeze-drying methods.

[0029] Example 1:

[0030] (1) Using a 50-ml three-necked flask, add 20.0 ml of deionized water, weigh 2.0 g of polyvinyl alcohol and 0.22 g of highly conductive silver nanowires, and transfer them to the flask. Heat to 95°C and mechanically stir for 10 h to obtain a mixed solution at a rotation speed of 700 r / min.

[0031] (2) After degassing the solution, cast it in a horizontally placed polytetrafluoroethylene mold with a sample thickness of 3.0 mm inside the mold. After it cools to room temperature, place it in a freezer at -5°C and freeze it for 20 h.

[0032] (3) The sample is subjected to freeze-drying treatment after 20 h. The freezing temperature is -55 °C and the vacuum degree is 1.00 MPa. The freeze-drying is completed after 4 h of treatment with a freeze-dryer to obtain a gel film. The conductivity of the film is 2.1*10 2 S / m, and the infrared emissivity is 0.32.

[0033] Example 2:

[0034] Other processes are the same as in Example 1, except that: in step (1), 0.44 g of highly conductive silver nanowires are added.

[0035] Example 3:

[0036] Other processes are the same as in Example 1, except that: in step (1), 1.1 g of highly conductive silver nanowires are added.

[0037] Example 4:

[0038] Other processes are the same as in Example 1, except that: in step (1), 2.2 g of highly conductive silver nanowires are added.

[0039] Example 5:

[0040] Other processes are the same as in Example 1, except that: in step (2), after the freezing is completed, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process of step (2) is repeated 1 time under the same conditions.

[0041] Example 6:

[0042] Other processes are the same as in Example 2, except that: in step (2), after the freezing is completed, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process of step (2) is repeated 1 time under the same conditions.

[0043] Example 7:

[0044] Other processes are the same as in Example 3, except that: in step (2), after the freezing is completed, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process of step (2) is repeated 1 time under the same conditions.

[0045] Example 8:

[0046] Other processes are the same as in Example 4, except that: in step (2), after the freezing is completed, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process of step (2) is repeated 1 time under the same conditions.

[0047] Example 9:

[0048] Other procedures are the same as in Example 1, except that: in step (2), after freezing, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process in step (2) is repeated 2 times under the same conditions.

[0049] Example 10:

[0050] Other procedures are the same as in Example 2, except that: in step (2), after freezing, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process in step (2) is repeated 2 times under the same conditions.

[0051] Example 11:

[0052] Other procedures are the same as in Example 3, except that: in step (2), after freezing, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process in step (2) is repeated 2 times under the same conditions.

[0053] Example 12:

[0054] Other procedures are the same as in Example 4, except that: in step (2), after freezing, the sample is taken out and placed at room temperature until the sample is completely thawed, and then the freezing process in step (2) is repeated 2 times under the same conditions.

[0055] Comparative Example 1:

[0056] Other procedures are the same as in Example 1, except that: highly conductive silver nanowires are not added in step (1).

[0057] Comparative Example 2:

[0058] Other procedures are the same as in Example 12, except that: "2.0 g of polyvinyl alcohol" in step (1) is changed to "3.0 g of polyvinyl alcohol".

[0059] Comparative Example 3:

[0060] Other procedures are the same as in Example 12, except that: "2.0 g of polyvinyl alcohol" in step (1) is changed to "1.0 g of polyvinyl alcohol".

[0061] Comparative Example 4:

[0062] Other procedures are the same as in Example 12, except that: step (3) is not carried out, that is, freeze-drying treatment is not carried out.

[0063] The important process parameters and test results of the above examples and comparative examples are summarized in Table 1.

[0064] Table 1

[0065]

Claims

1. A highly conductive and low infrared emissivity silver nanowire gel film, characterized in that, It is composed of silver nanowires as conductive fillers distributed on a film with polyvinyl alcohol as the matrix, and it has a porous structure.

2. The gel film according to claim 1, characterized in that, The gel film has an infrared emissivity lower than 0.3, and the film conductivity is up to 10 4 S / m.

3. The gel film according to claim 1, characterized in that, The silver nanowires account for 1-10 wt.%, preferably 10 wt.%, of the mass of the gel film.

4. A method for preparing the gel film according to any one of claims 1-3, characterized in that, It includes the following steps: (1) Stir polyvinyl alcohol particles at 80-100 °C to dissolve them in deionized water to prepare an aqueous polyvinyl alcohol solution. Add silver nanowires to this solution and continue stirring for a period of time to obtain a mixed solution; (2) After degassing the mixed solution in step (1), cast it in a horizontally placed polytetrafluoroethylene mold. After it cools to room temperature, put it into a freezer for freezing; (3) After the freezing is completed, take out the sample and place it at room temperature until the sample is completely thawed, and then repeat the freezing process in step (2) under the same conditions; (4) Take out the sample in step (3) and perform freeze-drying treatment to obtain the gel film.

5. The method according to claim 4, characterized in that, The degree of polymerization of polyvinyl alcohol is 500-1200, and the degree of alcoholysis is 50%-99%.

6. The method according to claim 4, characterized in that, The diameter of the silver nanowires is 5-50 nm, and the length is 5-20 µm.

7. The method according to claim 4, characterized in that, In step (2), freeze at -5 °C for 20 h.

8. The method according to claim 4, characterized in that, In step (3), repeat the freezing process 0-2 times.

9. The method according to claim 4, characterized in that, In step (4), the process conditions for freeze-drying treatment are: freezing temperature -55 °C, vacuum degree 1.00 MPa, and freeze-drying time 4 hours.

10. Use of the gel film according to any one of claims 1-3 as an infrared stealth material.

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