Method for preparing conductive polymer composite with quantum dot assistance and conductive polymer composite

Abstract

The application relates to the technical field of functional materials, and discloses a method for preparing a conductive polymer composite with the aid of quantum dots and the conductive polymer composite, which comprises the following steps: providing an oil phase solution comprising an organic solvent and a polymer and a water phase solution comprising water, quantum dots, reduced graphene oxide and carbon nanotubes; mixing the oil phase solution with the water phase solution, performing homogenization treatment, and obtaining a Pickering emulsion which can be stored stably for more than 30 days; freezing the Pickering emulsion at a preset temperature, then continuously injecting high-pressure CO2 at the preset temperature to remove the organic solvent, and then performing freeze-drying to remove water, so that a conductive polymer composite with an isolated conductive network structure and high conductivity is obtained; and the conductivity of the conductive polymer composite is as high as 240 S.m ‑1 .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional materials, in particular to a method for preparing a conductive polymer composite material assisted by quantum dots and a conductive polymer composite material. BACKGROUND

[0002] Conductive polymer composites (CPCs) are formed by single or mixed conductive fillers dispersed in a polymer matrix, which have been widely used in sensors, antistatic materials, electromagnetic shielding, etc. in recent years. In order to achieve high electrical conductivity, conductive fillers need to be randomly distributed in the polymer matrix to prepare conductive polymer composites, which usually requires a high load of conductive fillers, resulting in poor elasticity and processing performance of the conductive polymer composite material, and high production cost. The conductive fillers of the conductive polymer composite material with isolated conductive network are distributed on the surface of the polymer particles, which can achieve high electrical conductivity at a lower amount of conductive fillers.

[0003] In the emulsion template method, the conductive fillers can be uniformly coated on the surface of the polymer particles, have good dispersibility, and the conductive network structure is easy to control, which is expected to achieve high conductivity at a low amount of conductive fillers, and is an effective method for preparing isolated conductive polymer composite materials. However, this method usually requires a large amount of surfactants to stabilize the emulsion, and the surfactants are usually insulating and difficult to remove, which affects the conductivity of the conductive polymer composite material.

[0004] Reduced graphene oxide has high conductivity, but it cannot be used alone to stabilize the emulsion. Therefore, if reduced graphene oxide is used as a stabilizer to prepare a conductive polymer composite material by the emulsion template method, it has important significance in improving the electrical conductivity of the conductive polymer composite material and providing a new type of emulsion stabilizer.

[0005] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0006] Based on the above shortcomings of the prior art, the purpose of the present application is to provide a method for preparing a conductive polymer composite material assisted by quantum dots and a conductive polymer composite material, which aims to solve the problems that the emulsion template method usually requires a large amount of nearly insulating surfactants to stabilize the emulsion, resulting in poor conductivity of the prepared conductive polymer composite material, and reduced graphene oxide cannot be used alone as an emulsion stabilizer.

[0007] The technical scheme of the present application is as follows:

[0008] In a first aspect of the present application, a method for preparing a conductive polymer composite material assisted by quantum dots is provided, which comprises the following steps:

[0009] An oil phase solution and an aqueous phase solution are provided, wherein the oil phase solution comprises an organic solvent and a polymer, and the aqueous phase solution comprises water, quantum dots, reduced graphene oxide, and carbon nanotubes;

[0010] The oil phase solution and the aqueous phase solution are mixed and homogenized to obtain a Pickering emulsion.

[0011] The Pickering emulsion is frozen at a preset temperature, and then high-pressure CO2 is injected at the preset temperature to remove organic solvents. Then, it is freeze-dried to remove water, thereby obtaining the conductive polymer composite material.

[0012] The high-pressure CO2 is CO2 with a pressure of 7.5~15 MPa.

[0013] Optionally, the quantum dots include at least one of carbon quantum dots, graphene quantum dots, graphene oxide quantum dots, and reduced graphene oxide quantum dots.

[0014] Optionally, the concentration of the quantum dots in the aqueous solution is 0.05~5 mg·mL. -1 The concentration of the reduced graphene oxide is 0.1~20 mg·mL. -1 .

[0015] Optionally, the concentration of the polymer in the oil phase solution is 10~300 mg·mL. -1 ;

[0016] The polymer includes at least one of polyethylene terephthalate, polybutylene terephthalate, polypropylene, polyamide, polystyrene, polymethyl methacrylate, nitrocellulose, cellulose acetate, synthetic rubber, polyethylene, polylactic acid, polyvinyl chloride, polyphenylene ether, polyurethane, polyimide, polysulfone, polyethersulfone, polyacrylonitrile, and polyvinyl alcohol.

[0017] The organic solvent includes at least one selected from benzene, ethyl acetate, chloroform, cyclohexane, n-hexane, cyclohexanone, toluene, and xylene.

[0018] Optionally, the mass ratio of carbon nanotubes in the aqueous solution to polymers in the oil solution is (0.5~20):100, and the volume ratio of the oil solution to the aqueous solution is (1~10):(1~10).

[0019] Optionally, the aqueous solution further includes an electrolyte, which includes at least one selected from sodium chloride, potassium chloride, magnesium chloride, and lithium chloride; the concentration of the electrolyte in the aqueous solution is 0-20 mg / mL. -1 .

[0020] Optionally, the method for preparing the aqueous solution includes the following steps:

[0021] Quantum dots were added to water and stirred to obtain a dispersion.

[0022] Reduced graphene oxide is added to the dispersion, and the mixture is sonicated at a power of 150-1500 W for 5-60 min. Then, carbon nanotubes are added, and the mixture is stirred to obtain an aqueous solution. Alternatively, reduced graphene oxide is added to the dispersion, and the mixture is sonicated at a power of 150-1500 W for 5-60 min. Then, carbon nanotubes and an electrolyte are added, and the mixture is stirred to obtain an aqueous solution.

[0023] Optionally, the homogenization process conditions are as follows:

[0024] The rotation speed is 300~10000 rpm, and the time is 0.5~30 min.

[0025] Optionally, the preset temperature is -86 to 0 ℃; the injection time of the high-pressure CO2 is 1 to 8 h;

[0026] The freeze-drying process conditions are as follows:

[0027] The temperature ranges from -86 to -10 ℃, and the time ranges from 0.5 to 48 h.

[0028] In a second aspect, the present invention provides a conductive polymer composite material, wherein the conductive polymer composite material is prepared by the method of the present invention described above for preparing conductive polymer composite materials using quantum dots.

[0029] Beneficial Effects: This invention utilizes quantum dots to assist in the dispersion of conductive reduced graphene oxide. The Pickering emulsion prepared using quantum dots and reduced graphene oxide as stabilizers has a particle size range of 30-200 μm and can be stably stored for over 30 days, avoiding the use of insulating surfactants or poorly conductive stabilizers such as graphene oxide. Then, using the prepared Pickering emulsion as a template, the microstructure of the emulsion is maintained by freezing, preventing the collapse of the emulsion droplet structure during solvent removal. Subsequently, high-pressure CO2 is continuously injected under frozen conditions to remove organic solvents. Finally, water is removed by freeze-drying. This process maximizes the preservation of the network structure constructed by reduced graphene oxide and carbon nanotube conductive fillers in the Pickering emulsion template, avoiding the problems of agglomeration and network inhomogeneity that occur during solvent removal. Simultaneously, it expands the range of organic solvents that can be selected, thereby expanding the range of polymers that can be selected, resulting in broad applicability. Since quantum dots themselves do not affect the conductivity of the conductive polymer composite material, a conductive polymer composite material with an isolated conductive network structure and high conductivity can be obtained without further processing. Even with low conductive filler content, the conductivity reaches as high as 240 S·m.-1 The method provided by this invention is simple, energy-saving, environmentally friendly, and low-cost. Attached Figure Description

[0030] Figure 1 The figures show the test results of the Pickering emulsion prepared in Example 1, where (a) is an optical microscope image and (b) is a particle size distribution diagram.

[0031] Figure 2 The figures show the test results of the carbon quantum dot-assisted multilayer reduced graphene oxide stabilized Pickering emulsion prepared in Example 2, where (a) is an optical microscope image and (b) is a particle size distribution diagram.

[0032] Figure 3 This is a scanning electron microscope image of the conductive polymer composite material prepared in Example 2.

[0033] Figure 4 The figures show the test results of the graphene quantum dot-assisted few-layer reduced graphene oxide stabilized Pickering emulsion prepared in Example 3, where (a) is an optical microscope image and (b) is a particle size distribution diagram.

[0034] in, Figure 1 (b) Figure 2 (b) and Figure 4 In (b) of the diagram, D represents the average particle size. Detailed Implementation

[0035] This invention provides a method for preparing conductive polymer composite materials using quantum dots and the conductive polymer composite materials themselves. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0037] In the inventors' previous research, a Pickering emulsion stabilized with graphene oxide was used as a template to prepare conductive polymer composites. This allowed for the use of a smaller amount of stabilizer, addressing the problem of requiring a large amount of insulating surfactant in existing emulsion template methods. However, the stabilizer graphene oxide has poor conductivity and remains in the conductive polymer composite, hindering further improvement in its conductivity. Reduced graphene oxide (RGO) is obtained by chemically or thermally reducing some of the oxygen-containing groups in graphene oxide (GO), restoring some of the sp² structure of graphene and exhibiting good conductivity. Applying RGO to the Pickering emulsion template method for preparing conductive polymer composites would significantly improve their conductivity. However, although RGO still retains defects and a small number of functional groups, its dispersibility is insufficient, making it unsuitable as a stabilizer for the Pickering emulsion. Therefore, this invention provides a method for preparing conductive polymer composites using quantum dots, comprising the following steps:

[0038] S1. Provide an oil phase solution and an aqueous phase solution, wherein the oil phase solution comprises an organic solvent and a polymer, and the aqueous phase solution comprises water, quantum dots, reduced graphene oxide, and carbon nanotubes;

[0039] S2. The oil phase solution and the aqueous phase solution are mixed and homogenized to obtain Pickering emulsion;

[0040] S3. The Pickering emulsion is frozen at a preset temperature, and then high-pressure CO2 is injected at the preset temperature to remove the organic solvent. Then, the water is removed by freeze drying to obtain the conductive polymer composite material.

[0041] The high-pressure CO2 is CO2 with a pressure of 7.5~15 MPa (for example, the pressure can be 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa or 15 MPa, etc.).

[0042] In this invention, during the homogenization process of mixing the oil phase solution and the aqueous phase solution, quantum dots are introduced to improve the dispersibility of reduced graphene oxide. Quantum dots assist reduced graphene oxide and carbon nanotubes in self-assembly at the oil-water interface through non-covalent π-π interactions and encapsulate them on the surface of oil droplets (the oil droplets contain dissolved polymers). The oil droplets with quantum dots, reduced graphene oxide, and carbon nanotubes on their surface are dispersed in water to form a quantum dot-assisted reduced graphene oxide stabilized Pickering emulsion (oil-in-water type). This emulsion serves as a template for preparing conductive polymer composite materials. Then, the mixture is frozen and high-pressure CO2 is injected under frozen conditions to remove organic solvents. Water is removed by freeze-drying (i.e., lyophilization) to obtain a conductive polymer composite material with an isolated conductive network structure and high conductivity (wherein, carbon nanotubes and reduced graphene oxide are uniformly distributed on the surface of polymer particles as conductive fillers to form an isolated conductive network).

[0043] This invention utilizes quantum dots to assist in the dispersion of conductive reduced graphene oxide, specifically by introducing quantum dots to improve the dispersibility of reduced graphene oxide. The Pickering emulsion prepared using quantum dots and reduced graphene oxide as stabilizers has a particle size range of 30–200 μm and can be stably stored for over 30 days, avoiding the use of insulating surfactants or poorly conductive stabilizers such as graphene oxide. Then, using the prepared Pickering emulsion as a template, the microstructure of the emulsion is maintained through freezing, preventing the collapse of the emulsion droplet structure during solvent removal. Subsequently, high-pressure CO2 is continuously injected under frozen conditions to remove organic solvents, and finally, water is removed by freeze-drying. Therefore, the network structure constructed by reduced graphene oxide and carbon nanotube conductive fillers in the Pickering emulsion template can be maintained to the maximum extent, avoiding the problems of agglomeration and network inhomogeneity that occur during solvent removal. Since quantum dots themselves do not affect the conductivity of the conductive polymer composite material, a conductive polymer composite material with an isolated conductive network structure and high conductivity can be obtained without further processing. Its conductivity reaches as high as 240 S·m even with low conductive filler content. -1 The method provided by this invention is simple, energy-saving, environmentally friendly, and low-cost.

[0044] In existing emulsion template methods for preparing conductive polymer composites, low-boiling-point organic solvents (boiling point <100 °C) are typically used for the oil phase solution. These low-boiling-point organic solvents are difficult to dissolve high-modulus and high-molecular-weight polymers, thus limiting the choice of polymers. Furthermore, organic solvents capable of dissolving high-modulus and high-molecular-weight polymers often have very high boiling points, making them difficult to remove through solvent evaporation (because water in the aqueous phase boils), thus further limiting the choice of organic solvents. In the inventors' previous research, supercritical CO2 drying was used to remove organic solvents from the oil phase, which solved the above problems and improved the range of organic solvents and polymers that could be selected. However, the conductivity of the resulting conductive polymer composites still fell short of practical requirements. This was mainly because the emulsion was relatively prone to instability during organic solvent removal, leading to a need for further improvement in the stability of the constructed network structure. Therefore, to maintain the microstructure of the emulsion and prevent the collapse of the emulsion droplet structure during organic solvent removal, this invention first freezes the Pickering emulsion to maintain its microstructure and prevent the collapse of the emulsion droplet structure during organic solvent removal. Then, the organic solvent is removed by high-pressure CO2 under frozen conditions, and finally, water is removed by freeze-drying. This method can not only completely remove organic solvents and water and maintain the three-dimensional filler network structure, avoiding the problems of agglomeration and network inhomogeneity that exist during solvent removal, but also expand the selection range of organic solvents (the boiling points of the organic solvents used can be not only below 100 ℃, but also above 100 ℃), thereby expanding the selection range of polymers and making it widely applicable.

[0045] Quantum dots on reduced graphene oxide (PBO) sheets can enhance the water dispersibility and dispersion stability of PBO. First, quantum dots act as physical spacers, preventing PBO aggregation. Specifically, quantum dots adhere to the PBO surface through electrostatic interactions and van der Waals forces, physically preventing close face-to-face contact between PBO sheets. This effectively inhibits aggregation caused by π-π stacking, ensuring that PBO exists in a more discrete nanoscale sheet form, allowing it to adsorb at the oil-water interface. Second, quantum dots have a mild reducing ability, moderately increasing the hydrophobicity of PBO, which is beneficial for its migration to the oil-water interface. Finally, quantum dots and PBO synergistically stabilize Pickering emulsions; the partially hydrophilic and partially oleophilic structure significantly reduces interfacial energy, ensuring its stability at the oil-water interface. Simultaneously, quantum dots and PBO form a composite particle stabilizer, enhancing steric hindrance and making it more difficult for oil droplets to coalesce upon collision, thus significantly improving emulsion stability.

[0046] In this invention, quantum dots, reduced graphene oxide, and carbon nanotubes (which act as both stabilizers and conductive fillers) are used in combination as stabilizers in a Pickering emulsion, creating a stronger interfacial barrier through a synergistic effect. Specifically, quantum dots act as physical spacers to prevent the aggregation of reduced graphene oxide. Carbon nanotubes bridge the reduced graphene oxide sheets, preventing them from overlapping or agglomerating. Carbon nanotubes can embed themselves into any gaps that may exist between the reduced graphene oxide sheets, further improving the density of the conductive network. The combined zero-dimensional (quantum dots), one-dimensional (carbon nanotubes), and two-dimensional (reduced graphene oxide) structure enhances the mechanical strength of the interfacial film, more effectively resisting instability caused by oil droplet collisions and compression. The carbon nanotubes form physical cross-linking points through van der Waals forces and entanglement, imparting elasticity to the network. The strong π-π conjugated interaction and physical entanglement between reduced graphene oxide and carbon nanotubes make it difficult for them to desorb from the interface, resulting in stronger stability of the emulsion droplets when faced with external disturbances such as temperature changes, pH changes and mechanical shearing.

[0047] In steps S1 and S2, it is not necessary to limit the specific type of reduced graphene oxide. For example, in some embodiments, the reduced graphene oxide includes at least one of monolayer reduced graphene oxide (for example, its particle size can be 0.5~5 μm or 0.5~10 μm), few-layer reduced graphene oxide (for example, its particle size can be 10~50 μm), and multilayer reduced graphene oxide (for example, its particle size can be 10~50 μm).

[0048] This invention does not limit the specific category of quantum dots. For example, in some embodiments, the quantum dots include at least one of carbon quantum dots, graphene quantum dots, graphene oxide quantum dots, and reduced graphene oxide quantum dots, but are not limited thereto.

[0049] In some specific embodiments, the carbon quantum dots include at least one of undoped carbon quantum dots and doped carbon quantum dots, wherein the doped carbon quantum dots include nitrogen-doped carbon quantum dots; the graphene quantum dots include at least one of undoped graphene quantum dots and doped graphene quantum dots, wherein the doped graphene quantum dots include nitrogen-doped graphene quantum dots; the graphene oxide quantum dots include at least one of undoped graphene oxide quantum dots and doped graphene oxide quantum dots, wherein the doped graphene oxide quantum dots include nitrogen-doped graphene oxide quantum dots; the reduced graphene oxide quantum dots include at least one of undoped reduced graphene oxide quantum dots and doped reduced graphene oxide quantum dots, wherein the doped reduced graphene oxide quantum dots include nitrogen-doped reduced graphene oxide quantum dots.

[0050] This invention does not limit the specific type of carbon nanotubes. For example, in some embodiments, the carbon nanotubes may be at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0051] Among them, single-walled carbon nanotubes can be at least one of functionalized single-walled carbon nanotubes and unfunctionalized single-walled carbon nanotubes; functionalized single-walled carbon nanotubes can be at least one of carboxylated single-walled carbon nanotubes, hydroxylated single-walled carbon nanotubes and aminated single-walled carbon nanotubes, but are not limited thereto; multi-walled carbon nanotubes can be at least one of functionalized multi-walled carbon nanotubes and unfunctionalized multi-walled carbon nanotubes; functionalized multi-walled carbon nanotubes can be at least one of carboxylated multi-walled carbon nanotubes, hydroxylated multi-walled carbon nanotubes and aminated multi-walled carbon nanotubes, but are not limited thereto.

[0052] In some embodiments, the concentration of the quantum dots in the aqueous solution is 0.05~5 mg·mL. -1 For example, it can be 0.05 mg·mL -1 0.1 mg·mL -1 0.2 mg·mL -1 0.5 mg·mL -1 0.8 mg·mL -1 1 mg·mL -1 1.5 mg·mL -1 2 mg·mL -1 2.5 mg·mL -1 3 mg·mL -1 3.5 mg·mL -1 4 mg·mL -1 4.5 mg·mL -1 Or 5 mg·mL -1 wait.

[0053] In some embodiments, the concentration of the reduced graphene oxide is 0.1~20 mg·mL. -1 For example, it can be 0.1 mg·mL -1 0.5 mg·mL -1 1 mg·mL -1 1.5 mg·mL -1 2 mg·mL -1 5 mg·mL -1 8 mg·mL -1 10 mg·mL -1 12 mg·mL -1 15 mg·mL -1 18 mg·mL -1Or 20 mg·mL -1 wait.

[0054] In some embodiments, the aqueous solution further includes an electrolyte, which includes at least one selected from sodium chloride, potassium chloride, magnesium chloride, and lithium chloride. In this embodiment, adding an electrolyte to the aqueous solution can shield electrostatic forces.

[0055] In some embodiments, the concentration of the electrolyte in the aqueous solution is 0-20 mg / mL. -1 For example, it can be 0 mg·mL -1 0.1 mg·mL -1 1 mg·mL -1 2 mg·mL -1 5 mg·mL -1 10 mg·mL -1 15 mg·mL -1 Or 20 mg·mL -1 wait.

[0056] In some embodiments, the method for preparing the aqueous solution includes the following steps:

[0057] Quantum dots were added to water and stirred to obtain a dispersion.

[0058] Reduced graphene oxide is added to the dispersion, and the mixture is sonicated at a power of 150-1500 W (e.g., 150 W, 200 W, 300 W, 400 W, 500 W, 600 W, 700 W, 800 W, 900 W, 1000 W, 1100 W, 1200 W, 1300 W, 1400 W, or 1500 W, etc.) for 5-60 min (e.g., 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, etc.). Then, carbon nanotubes are added, and the mixture is stirred to obtain an aqueous solution. Alternatively, reduced graphene oxide is added to the dispersion, and the mixture is sonicated at a power of 150-1500 W for 5-60 min. Then, carbon nanotubes and an electrolyte are added, and the mixture is stirred to obtain an aqueous solution.

[0059] In some embodiments, the concentration of the polymer in the oil phase solution is 10-300 mg·mL. -1 For example, it can be 10 mg·mL -1 20 mg·mL -1 50 mg·mL -1 60 mg·mL -1 100 mg·mL -1 120 mg·mL-1 150 mg·mL -1 200 mg·mL -1 250 mg·mL -1 Or 300 mg·mL -1 wait.

[0060] In some embodiments, the polymer includes, but is not limited to, at least one of polyethylene terephthalate, polybutylene terephthalate, polypropylene, polyamide, polystyrene, polymethyl methacrylate, nitrocellulose, cellulose acetate, synthetic rubber, polyethylene, polylactic acid, polyvinyl chloride, polyphenylene ether, polyurethane, polyimide, polysulfone, polyethersulfone, polyacrylonitrile, and polyvinyl alcohol.

[0061] In this invention, both low-boiling-point and high-boiling-point organic solvents can be selected. In some embodiments, the organic solvent includes at least one of benzene, ethyl acetate, chloroform, cyclohexane, n-hexane, cyclohexanone, toluene, and xylene, but is not limited thereto.

[0062] In this invention, both low-boiling-point and high-boiling-point organic solvents can be selected. For example, in some embodiments, the organic solvent includes at least one of benzene, ethyl acetate, chloroform, cyclohexane, n-hexane, cyclohexanone, toluene, and xylene, but is not limited thereto.

[0063] In some embodiments, the mass ratio of carbon nanotubes in the aqueous solution to polymers in the oil solution is (0.5~20):100, for example, it can be 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 12:100, 15:100, 18:100 or 20:100, etc.

[0064] In some embodiments, the volume ratio of the oil phase solution to the aqueous phase solution is (1~10):(1~10), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc.

[0065] In step S2, in some embodiments, the homogenization process uses the following conditions:

[0066] The rotation speed is 300~10000 rpm, and the time is 0.5~30 min.

[0067] For example, the rotational speed can be 300 rpm, 400 rpm, 500 rpm, 800 rpm, 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, or 10000 rpm, etc., and the time can be 0.5 min, 1 min, 2 min, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min, etc.

[0068] In step S3, in some embodiments, the preset temperature is -86 to 0 ℃; the injection time of the high-pressure CO2 is 1 to 8 h.

[0069] In this embodiment, the process conditions allow for better and more thorough removal of organic solvents and prevent the collapse of the emulsion droplet structure, thus maximally maintaining the network structure constructed by the reduced graphene oxide and carbon nanotube conductive fillers in the Pickering emulsion template. For example, the preset temperature (i.e., the temperature used for freezing) can be -86 ℃, -85 ℃, -80 ℃, -75 ℃, -70 ℃, -65 ℃, -60 ℃, -55 ℃, -40 ℃, -30 ℃, -20 ℃, -10 ℃, or 0 ℃. The high-pressure CO2 injection time can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h.

[0070] In some embodiments, the freeze-drying process conditions are as follows:

[0071] The temperature ranges from -86 to -10 ℃, and the time ranges from 0.5 to 48 h.

[0072] For example, the temperature can be -86 ℃, -85 ℃, -80 ℃, -75 ℃, -70 ℃, -65 ℃, -60 ℃, -55 ℃, -40 ℃, -30 ℃, -20 ℃ or -10 ℃, etc., and the time can be 0.5 h, 1 h, 2 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h or 48 h, etc.

[0073] This invention also provides a conductive polymer composite material, wherein the conductive polymer composite material is prepared using the quantum dot-assisted preparation method described above. The conductive polymer composite material provided by this invention has an isolated conductive network structure and high conductivity; when the conductive filler carbon nanotubes account for 10 wt% of the polymer mass, the conductivity of the conductive polymer composite material can reach 240 S·m.-1 .

[0074] The present invention will be further described below through specific embodiments.

[0075] Unless otherwise specified, the materials and equipment used in the following embodiments are all commercially available products.

[0076] The ultrasonic dispersing rod was purchased from Shanghai Yanyong Ultrasonic Equipment Co., Ltd., model NBK-1500; the disperser was purchased from IKA GmbH, Germany, model T25.

[0077] The carbon quantum dots (i.e. undoped carbon quantum dots) were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with item number 102632 and serial number XF253.

[0078] The graphene quantum dots (i.e., undoped graphene quantum dots) were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with item number 100803 and serial number XF152.

[0079] Multi-walled carbon nanotubes (i.e., unfunctionalized multi-walled carbon nanotubes) were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with item number 100234 and serial number XFM04.

[0080] The multilayer reduced graphene oxide (RGO) was purchased from Suzhou CarbonFeng Graphene Technology Co., Ltd. The product name is chemically produced multilayer graphene (reduced oxide RGO), and its specifications are: 6-10 layers, thickness 3-8 nm, and specific surface area 50-100 m². 2 / g, with a sheet diameter of 10~50 μm.

[0081] The few-layer reduced graphene oxide (RGO) was purchased from Suzhou CarbonFeng Graphene Technology Co., Ltd. The product name is chemically produced few-layer graphene (reduced oxide RGO), and its specifications are: 1-5 layers, thickness 3-8 nm, and specific surface area 150-350 m². 2 / g, with a sheet diameter of 10~50 μm.

[0082] Low-density polyethylene was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No.: 9002-88-4.

[0083] Example 1

[0084] To demonstrate that carbon quantum dots can assist in stabilizing Pickering emulsions with reduced graphene oxide, this embodiment uses carbon quantum dots and multilayer reduced graphene oxide as stabilizers to prepare a Pickering emulsion, specifically including the following steps:

[0085] (1) Add carbon quantum dots to deionized water and stir until homogeneous to obtain a concentration of 0.8 mg / mL.-1 Carbon quantum dot dispersion.

[0086] (2) Add multilayer reduced graphene oxide to the carbon quantum dot dispersion obtained in step (1), and sonicate it with an ultrasonic dispersing rod at a power of 900 W for 30 min. Then add NaCl and stir until homogeneous to obtain an aqueous solution. The concentration of multilayer reduced graphene oxide in the aqueous solution is 8 mg·mL. -1 The concentration of NaCl is 1 mg·mL -1 .

[0087] (3) Add polyphenylene ether to xylene, stir to dissolve, and obtain an oil phase solution. The concentration of polyphenylene ether in the oil phase solution is 80 mg·mL. -1 .

[0088] (4) The oil phase solution obtained in step (3) is mixed with the aqueous phase solution obtained in step (2), with a volume ratio of 1:2 between the oil phase solution and the aqueous phase solution. After homogenization using a disperser (10,000 rpm for 10 min), a Pickering emulsion (specifically, a carbon quantum dot-assisted multilayer reduced graphene oxide stabilized Pickering emulsion) is obtained.

[0089] Optical micrograph of the obtained Pickering emulsion is shown below. Figure 1 As shown in (a) above, the particle size distribution diagram is as follows: Figure 1 As shown in (b), carbon quantum dots can assist in stabilizing Pickering emulsions by multilayer reduced graphene oxide.

[0090] Example 2

[0091] This embodiment provides a method for preparing a conductive polymer composite material, including the following steps:

[0092] (1) Add 32 mg of carbon quantum dots to 40 mL of deionized water and stir until homogeneous to obtain a carbon quantum dot dispersion.

[0093] (2) Add 150 mg of multilayer reduced graphene oxide to 40 mL of carbon quantum dot dispersion, and use an ultrasonic dispersing rod to sonicate at 900 W for 30 min. Then add 340 mg of KCl and 80 mg of multi-walled carbon nanotubes, stir evenly, and obtain an aqueous solution.

[0094] (3) Polystyrene was added to xylene and stirred until dissolved to obtain an oil phase solution. The concentration of polystyrene in the oil phase solution was 80 mg·mL. -1 .

[0095] (4) Take 10 mL of oil phase solution and add it to the aqueous phase solution obtained in step (2). After homogenization using a disperser (rotation speed of 8000 rpm, time of 10 min), carbon quantum dot-assisted multilayer reduced graphene oxide stabilized Pickering emulsion is obtained.

[0096] (5) The carbon quantum dot-assisted multilayer reduced graphene oxide stabilized Pickering emulsion obtained in step (4) was frozen at -18 °C for 4 h, and then CO2 at 9 MPa was continuously injected at -18 °C for 3 h to remove xylene. Then it was freeze-dried at -86 °C for 24 h to remove water, and a conductive polymer composite material (multi-walled carbon nanotubes account for 10 wt% of the mass of polystyrene) was obtained.

[0097] Test results:

[0098] (1) An optical microscope image of the carbon quantum dot-assisted multilayer reduced graphene oxide stabilized Pickering emulsion prepared in Example 2 is shown below. Figure 2 As shown in (a) above, the particle size distribution diagram is as follows: Figure 2 As shown in (b) of the diagram.

[0099] (2) The carbon quantum dot-assisted multilayer reduced graphene oxide stabilized Pickering emulsion prepared in Example 2 was left at room temperature for 30 days and showed no significant change.

[0100] (3) Scanning electron microscope image of the conductive polymer composite material prepared in Example 2 is shown below. Figure 3 As shown.

[0101] (4) The conductive polymer composite material (powder) prepared in Example 2 was hot-pressed using a hot press to obtain a test sample with dimensions of 4 cm × 4 cm × 1 mm (i.e., length 4 cm, width 4 cm, and thickness 1 mm). The conductivity of the test sample was measured to be 240 S·m using a four-probe tester. -1 .

[0102] Example 3

[0103] This embodiment provides a method for preparing a conductive polymer composite material, including the following steps:

[0104] (1) Add 15 mg of graphene quantum dots to 30 mL of deionized water and stir until homogeneous to obtain a graphene quantum dot dispersion.

[0105] (2) Add 150 mg of few-layer reduced graphene oxide to 30 mL of graphene quantum dot dispersion, and use an ultrasonic dispersing rod to sonicate at 600 W for 60 min. Then add 100 mg of NaCl and 60 mg of multi-walled carbon nanotubes, stir evenly, and obtain an aqueous solution.

[0106] (3) Low-density polyethylene was added to benzene and stirred until dissolved to obtain an oil phase solution. The concentration of polyethylene in the oil phase solution was 100 mg·mL. -1 .

[0107] (4) Take 7.5 mL of oil phase solution and add it to the aqueous phase solution obtained in step (2). After homogenization using a disperser (speed 10000 rpm, time 10 min), a graphene quantum dot-assisted few-layer reduced graphene oxide stabilized Pickering emulsion is obtained.

[0108] (5) The graphene quantum dot-assisted few-layer reduced graphene oxide stabilized Pickering emulsion obtained in step (4) was frozen at -10 °C for 5 h, and then CO2 at 8 MPa was continuously injected at -10 °C for 4 h to remove benzene. Then it was freeze-dried at -86 °C for 24 h to remove water, and a conductive polymer composite material (multi-walled carbon nanotubes account for 8 wt% of the polyethylene mass) was obtained.

[0109] Test results:

[0110] (1) An optical microscope image of the graphene quantum dot-assisted few-layer reduced graphene oxide stabilized Pickering emulsion prepared in Example 3 is shown below. Figure 4 As shown in (a) above, the particle size distribution diagram is as follows: Figure 4 As shown in (b) of the diagram.

[0111] (2) The graphene quantum dot-assisted few-layer reduced graphene oxide stabilized Pickering emulsion prepared in Example 3 was left at room temperature for 30 days and showed no significant change.

[0112] (3) The conductive polymer composite material (powder) prepared in Example 3 was hot-pressed using a hot press to obtain a test sample with dimensions of 4 cm × 4 cm × 1 mm (i.e., length 4 cm, width 4 cm, and thickness 1 mm). The conductivity of the test sample was measured to be 201 S·m using a four-probe tester. -1 .

[0113] In summary, this invention provides a method for preparing conductive polymer composite materials using quantum dots as an aid, and the conductive polymer composite materials themselves. This invention utilizes quantum dots to assist in the dispersion of conductive reduced graphene oxide. The Pickering emulsion prepared using quantum dots and reduced graphene oxide as stabilizers has a particle size range of 30-200 μm and can be stably stored for more than 30 days, avoiding the use of insulating surfactants or poorly conductive stabilizers such as graphene oxide. Then, using the prepared Pickering emulsion as a template, the microstructure of the emulsion is maintained by freezing to prevent the collapse of the emulsion droplet structure during solvent removal. Subsequently, high-pressure CO2 is continuously injected under frozen conditions to remove organic solvents. Finally, water is removed by freeze-drying. This process maximizes the preservation of the network structure constructed by the reduced graphene oxide and carbon nanotube conductive fillers in the Pickering emulsion template, avoiding the problems of agglomeration and network inhomogeneity that exist during solvent removal. Simultaneously, it expands the range of organic solvents that can be selected, thereby expanding the range of polymers that can be selected, resulting in broad applicability. Since quantum dots themselves do not affect the conductivity of conductive polymer composites, conductive polymer composites with isolated conductive network structures and high conductivity can be obtained without subsequent processing. These composites achieve a conductivity as high as 240 S·m even with low conductive filler content. -1 The method provided by this invention is simple, energy-saving, environmentally friendly, and low-cost.

[0114] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing conductive polymer composite materials using quantum dots, characterized in that, Includes the following steps: An oil phase solution and an aqueous phase solution are provided, wherein the oil phase solution comprises an organic solvent and a polymer, and the aqueous phase solution comprises water, quantum dots, reduced graphene oxide, and carbon nanotubes; The oil phase solution and the aqueous phase solution are mixed and homogenized to obtain a Pickering emulsion. The Pickering emulsion is frozen at a preset temperature, and then high-pressure CO2 is injected at the preset temperature to remove the organic solvent. Then, it is freeze-dried to remove water to obtain the conductive polymer composite material. The high-pressure CO2 is CO2 with a pressure of 7.5~15 MPa.

2. The method for preparing conductive polymer composite materials using quantum dots according to claim 1, characterized in that, The quantum dots include at least one of carbon quantum dots, graphene quantum dots, graphene oxide quantum dots, and reduced graphene oxide quantum dots.

3. The method for preparing conductive polymer composite materials using quantum dots according to claim 1, characterized in that, In the aqueous solution, the concentration of the quantum dots is 0.05~5 mg·mL. -1 The concentration of the reduced graphene oxide is 0.1~20 mg·mL. -1 .

4. The method for preparing conductive polymer composite materials using quantum dots according to claim 3, characterized in that, In the oil phase solution, the concentration of the polymer is 10~300 mg·mL. -1 ; The polymer includes at least one of polyethylene terephthalate, polybutylene terephthalate, polypropylene, polyamide, polystyrene, polymethyl methacrylate, nitrocellulose, cellulose acetate, synthetic rubber, polyethylene, polylactic acid, polyvinyl chloride, polyphenylene ether, polyurethane, polyimide, polysulfone, polyethersulfone, polyacrylonitrile, and polyvinyl alcohol. The organic solvent includes at least one selected from benzene, ethyl acetate, chloroform, cyclohexane, n-hexane, cyclohexanone, toluene, and xylene.

5. The method for preparing conductive polymer composite materials using quantum dots according to claim 4, characterized in that, The mass ratio of carbon nanotubes in the aqueous solution to polymers in the oil solution is (0.5~20):100, and the volume ratio of the oil solution to the aqueous solution is (1~10):(1~10).

6. The method for preparing conductive polymer composite materials using quantum dots according to any one of claims 1-5, characterized in that, The aqueous solution further includes an electrolyte, which includes at least one of sodium chloride, potassium chloride, magnesium chloride, and lithium chloride; the concentration of the electrolyte in the aqueous solution is 0-20 mg / mL. -1 .

7. The method for preparing conductive polymer composite materials using quantum dots according to claim 1, characterized in that, The method for preparing the aqueous solution includes the following steps: Quantum dots were added to water and stirred to obtain a dispersion. Reduced graphene oxide was added to the dispersion, and the mixture was sonicated at a power of 150-1500 W for 5-60 min. Then, carbon nanotubes were added, and the mixture was stirred to obtain an aqueous solution.

8. The method for preparing conductive polymer composite materials using quantum dots according to claim 6, characterized in that, The method for preparing the aqueous solution includes the following steps: Quantum dots were added to water and stirred to obtain a dispersion. Reduced graphene oxide was added to the dispersion, and the mixture was sonicated at a power of 150-1500 W for 5-60 min. Then, carbon nanotubes and electrolytes were added, and the mixture was stirred to obtain an aqueous solution.

9. The method for preparing conductive polymer composite materials using quantum dots according to claim 1, characterized in that, The homogenization process conditions are as follows: The rotation speed is 300~10000 rpm, and the time is 0.5~30 min.

10. The method for preparing conductive polymer composite materials using quantum dots according to claim 1, characterized in that, The preset temperature is -86~0 ℃; the high-pressure CO2 injection time is 1~8 h; The freeze-drying process conditions are as follows: The temperature ranges from -86 to -10 ℃, and the time ranges from 0.5 to 48 h.

11. A conductive polymer composite material, characterized in that, The conductive polymer composite material is prepared by the method of quantum dot-assisted preparation of conductive polymer composite materials as described in any one of claims 1-10.

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