Preparation method of aramid nanofiber-based Janus composite membrane

Abstract

This invention discloses a method for preparing an aramid nanofiber-based Janus composite membrane. Modified iron tetroxide (Fe3O4) and boron nitride nanosheets (BNNS), modified silicon carbide nanowires (SiCnw), and reduced graphene oxide (rGO) are electrostatically self-assembled in pairs to form a two-component hybrid filler. This filler is then combined with aramid nanofibers (ANF) to form a bilayer structure. The components in the prepared Janus composite membrane exhibit synergistic effects, and each of the upper and lower layers possesses independent functional characteristics, ultimately achieving integrated insulation, electromagnetic shielding, and thermal conductivity properties. This invention provides a novel technical path for the design and preparation of novel aramid nanofiber-based Janus composite membranes. The preparation process is simple and convenient, and the resulting composite membrane material has broad application prospects in practical engineering fields such as thermal conductivity and electromagnetic shielding.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive and electromagnetically shielding composite materials, specifically to a method for preparing a lightweight, highly thermally conductive, and highly electromagnetically shielding aramid nanofiber-based Janus composite film. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization, high density, and high power, the integration of internal electronic components is constantly increasing. During operation, these devices not only generate a large amount of heat but also release complex electromagnetic radiation. If this heat cannot be dissipated in time, it will lead to performance degradation and shortened lifespan of electronic devices; while electromagnetic radiation can interfere with the normal operation of surrounding electronic devices and may also pose potential health hazards. Therefore, the development of multifunctional composite film materials that combine excellent insulation, efficient electromagnetic shielding, and good thermal conductivity has become an urgent need in fields such as electronics, information technology, and aerospace.

[0003] Traditional metallic materials face a series of challenges when used as thermal conductive and electromagnetic interference shielding materials, including susceptibility to corrosion, high density, poor processability, and lack of flexibility. These shortcomings significantly limit their application in aerospace and modern electronic devices. Using traditional metals as fillers also restricts their application in highly integrated electronic devices due to their inherent high density, processing difficulty, and weak corrosion resistance. Correspondingly, the emergence of low-density, easily processed, and high-performance nanofillers such as boron nitride nanosheets (BNNS), carbon nanotubes (CNTs), and reduced graphene oxide (rGO) has greatly promoted the development of aramid nanofiber-based integrated electromagnetic shielding and thermal conductive materials. In particular, rGO possesses high electrical and thermal conductivity, while BNNS exhibits excellent insulation and thermal conductivity, demonstrating enormous potential in next-generation integrated electromagnetic shielding and thermal conductive materials.

[0004] Aramid nanofibers (ANFs) are a highly promising high-performance matrix material, widely used in numerous fields due to their excellent mechanical properties, high-temperature resistance, low density, and superior insulation. This makes ANFs an excellent alternative to traditional thermally conductive shielding materials such as metals. Furthermore, ANFs' inherent flexibility, high-temperature resistance, and insulation properties offer significant advantages in electromagnetic shielding, electronic packaging, and insulation protection. However, pure ANF films have poor thermal conductivity and lack electromagnetic shielding capabilities. Their singular functional characteristics limit ANFs' potential applications in many practical industries, especially in scenarios where synergistic requirements exist for thermal conductivity, electromagnetic shielding, and insulation. In such cases, the multifunctional integration of materials demands strict stability. Therefore, designing and manufacturing ANF composite films with high mechanical flexibility, excellent insulation, and simultaneously possessing thermal conductivity and efficient electromagnetic shielding properties remains a significant challenge.

[0005] Existing modification technologies often employ single fillers or random mixtures of multi-component fillers, making it difficult to achieve synergistic optimization of insulation, electromagnetic shielding, and thermal conductivity. They either prioritize insulation and thermal conductivity at the expense of electromagnetic shielding, or prioritize electromagnetic shielding and thermal conductivity at the expense of insulation. Furthermore, in some multi-component modification schemes, the compatibility between the filler and the matrix is ​​poor, making it difficult for the components to form effective synergies, and problems such as poor impedance matching and unstable electromagnetic shielding efficiency easily arise. Janus structural materials, with their independent functions in both the upper and lower layers and the ability to achieve synergistic effects, offer a new approach to solving these technical challenges. Therefore, developing an aramid nanofiber-based Janus composite membrane with a simple preparation process and excellent performance has become an urgent technical problem to be solved. Summary of the Invention

[0006] To overcome the problem of limited functionality of traditional aramid nanofiber materials in the field of flexible electronic devices, this invention provides a method for preparing a multifunctional synergistically enhanced aramid nanofiber-based Janus composite film.

[0007] The present invention has simple and easy-to-operate steps, and the aramid nanofiber-based Janus composite film obtained has excellent thermal conductivity and electromagnetic shielding properties, while maintaining good mechanical properties while ensuring high electromagnetic shielding and high thermal conductivity.

[0008] The technical solution of the present invention is as follows: A method for preparing an aramid nanofiber-based Janus composite membrane includes: (1) Preparation of ANF dispersion Aramid fibers (AF) and potassium hydroxide (KOH) were added to dimethyl sulfoxide (DMSO) solvent, and then isopropanol (IPA) was added dropwise. The mixture was stirred at room temperature to obtain an ANF (aramid nanofiber) dispersion. In this step, ANF is prepared by deprotonation-induced stripping. The preferred mass ratio of aramid fiber, potassium hydroxide, dimethyl sulfoxide, and isopropanol is 1:1.5:80~100:10~13; It is preferable to use magnetic stirring at 500 rpm for 2-4 hours at room temperature; In the obtained ANF dispersion, the preferred mass fraction of ANF is 0.8-1%; (2) Positively modified iron(III) oxide and silicon carbide nanowires Take iron(III) oxide (Fe3O4) and silicon carbide nanowires (SiCnw), add polydiallyldimethylammonium chloride (PDDA) respectively, stir evenly, then centrifuge and wash, freeze dry to obtain modified iron(III) oxide and modified silicon carbide nanowires. The preferred method is to mix ferric oxide and polydiallyldimethylammonium chloride at a mass ratio of 1:20, and use mechanical stirring at a speed of 500 rpm for 4-6 hours. Silicon carbide nanowires are preferably mixed with polydiallyldimethylammonium chloride at a mass ratio of 1:20, and the mixture is stirred magnetically at a speed of 600 rpm for 4 to 6 hours. Specifically, centrifuge at 8000 rpm for 10 min, then wash with deionized water; centrifuge and wash 3 times. (3) Preparation of hybrid fillers of iron oxide and boron nitride nanosheets The modified iron(II) oxide and boron nitride nanosheets (BNNS) obtained in step (2) were ultrasonically dispersed evenly in deionized water to obtain Fe3O4@BNNS dispersion; The mass ratio of modified iron oxide and boron nitride nanosheets is 7:3 to 2:8; The preferred ultrasonic dispersion settings are 300 W power, 60 kHz frequency, and 20-30 min time. Boron nitride nanosheets were prepared by ball milling, specifically: hexagonal boron nitride (h-BN) and isopropanol were mixed at a ratio of 1 g: 20 mL, ball milled at 300 rpm for 12 h, centrifuged, washed, and dried to obtain boron nitride nanosheets; (4) Preparation of hybrid fillers of silicon carbide nanowires and graphene oxide The modified silicon carbide nanowires and graphene oxide (GO) obtained in step (2) were ultrasonically dispersed evenly in deionized water to obtain SiCnw@GO dispersion. The mass ratio of modified silicon carbide nanowires to graphene oxide is 7:3 to 2:8. The preferred ultrasonic dispersion settings are 300 W power, 60 kHz frequency, and 20-30 min time. (5) Preparation of a co-dispersion of ANF and Fe3O4@BNNS Take the ANF dispersion obtained in step (1) and add it to the Fe3O4@BNNS dispersion obtained in step (3). Disperse it evenly by ultrasonication to obtain a blended dispersion I. The mass ratio of ANF to Fe3O4@BNNS is 2:8~8:2; The preferred ultrasonic dispersion settings are 300 W power, 60 kHz frequency, and 15 min time. (6) Preparation of ANF and SiCnw@GO blend dispersion II Take another ANF dispersion obtained in step (1) and add it to the SiCnw@GO dispersion obtained in step (4). Stir evenly to obtain a blended dispersion II. The mass ratio of ANF to SiCnw@GO is 2:8 to 8:2; It is preferable to use magnetic stirring at 600 rpm for 20 min; (7) Preparation of Janus composite membrane The blended dispersion I from step (5) was poured into a sand core funnel pre-placed with a filter membrane, and a wet membrane was prepared by vacuum-assisted filtration. Then, the blended dispersion II from step (6) was poured into the same sand core funnel, and a double-layer wet membrane was prepared by vacuum-assisted filtration. The double-layer wet membrane was immersed in sodium ascorbate solution, dried at 80°C, washed (soaked in deionized water for 30 min), mechanically molded (50 kPa), and dried (at room temperature) to obtain the Janus composite membrane. Specifically, PVDF filter membranes are selected, and the vacuum degree is controlled at -0.08 to -0.1 MPa during filtration. The preferred sodium ascorbate solution (solvent is deionized water) has a mass fraction of 5%.

[0009] Compared with the prior art, the present invention has the following beneficial effects: The aramid nanofibers (ANF) used in this invention possess high strength, high modulus, and high temperature resistance. The composite membrane preparation method is simple and easy to operate. By adjusting the ratio of Fe3O4 to BNNS on one side of the Janus composite membrane, this invention effectively improves the thermal conductivity of the composite membrane while simultaneously maintaining electrical insulation, allowing the Fe3O4@BNNS hybrid filler to disperse within the ANF matrix, thus enhancing membrane flexibility. By adjusting the ratio of SiCnw to GO on the other side of the Janus composite membrane, impedance matching is optimized while reducing graphene oxide to improve conductivity, effectively enhancing the electromagnetic shielding and thermal conductivity of the composite membrane. The Janus composite membrane obtained through filtration is uniform and dense. On the Fe3O4@BNNS filler side, Fe3O4 also provides a certain amount of hysteresis loss. This invention's Janus composite membrane synergistically enhances thermal conductivity and electromagnetic shielding effectiveness while maintaining mechanical strength. Attached Figure Description

[0010] Figure 1 Flowchart of Janus composite membrane preparation. Detailed Implementation

[0011] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0012] In the following embodiments, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry; the methods in the following embodiments are conventional methods in the art unless otherwise specified.

[0013] The raw material, aramid fiber (AF), was purchased from DuPont, USA, under the trade name Kevlar fiber, with dimensions of 6 mm in length and 10-20 μm in width.

[0014] The PVDF membrane filter was purchased from Haining Yanguan Longshun Filtration Equipment Factory; diameter: 50 mm; pore size: 0.22 μm.

[0015] Example 1

[0016] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0017] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0018] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 8 mg of modified Fe3O4 and 32 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0019] (4) Add 8 mg of modified SiCnw and 32 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0020] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0021] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0022] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0023] Example 2

[0024] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0025] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0026] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 8 mg of modified Fe3O4 and 32 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0027] (4) Add 12 mg of modified SiCnw and 28 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0028] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0029] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0030] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0031] Example 3

[0032] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0033] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0034] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 12 mg of modified Fe3O4 and 28 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0035] (4) Add 8 mg of modified SiCnw and 32 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0036] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0037] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0038] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0039] Example 4

[0040] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0041] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0042] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 12 mg of modified Fe3O4 and 28 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0043] (4) Add 12 mg of modified SiCnw and 28 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0044] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0045] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0046] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0047] Example 5

[0048] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0049] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0050] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 12 mg of modified Fe3O4 and 28 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0051] (4) Add 20 mg of modified SiCnw and 20 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0052] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0053] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0054] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0055] Example 6

[0056] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0057] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0058] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 12 mg of modified Fe3O4 and 28 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0059] (4) Add 28 mg of modified SiCnw and 12 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0060] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0061] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0062] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0063] Example 7

[0064] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0065] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0066] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 20 mg of modified Fe3O4 and 20 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0067] (4) Add 8 mg of modified SiCnw and 32 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0068] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0069] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0070] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0071] Example 8

[0072] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0073] (2) Weigh 1 g of iron(II,III) oxide (Fe3O4), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash; weigh 1 g of silicon carbide nanowires (SiCnw), add 20 g of polydiallyldimethylammonium chloride (PDDA) modifier, stir evenly, centrifuge and wash.

[0074] (3) Weigh 1 g of hexagonal boron nitride (h-BN), add 20 mL of isopropanol (IPA), ball mill for 12 h, centrifuge, wash and dry to obtain BNNS; add 20 mg of modified Fe3O4 and 20 mg of BNNS to a beaker containing 40 mL of deionized water, and disperse by ultrasonication.

[0075] (4) Add 12 mg of modified SiCnw and 28 mg of GO to a beaker containing 40 mL of deionized water and disperse by ultrasonication.

[0076] (5) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (3) and stir until homogeneous.

[0077] (6) Add 6 mL of ANF dispersion to the mixed dispersion obtained in step (4) and stir until homogeneous.

[0078] (7) The blended dispersions from steps (5) and (6) are poured into a sand core funnel in sequence. A composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane. The vacuum degree is controlled at -0.09 MPa. The prepared composite membrane is immersed in 10 mL of 5% sodium ascorbate solution, placed in an 80℃ oven for 6 h to dry, and then washed with deionized water. The composite membrane is then mechanically molded and dried under 50 kPa to obtain the aramid nanofiber-based electromagnetic shielding and thermally conductive Janus composite membrane.

[0079] Comparative Example 1

[0080] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain a 1 wt% ANF dispersion.

[0081] (2) Take 20 mL of the ANF dispersion from step (1) and add DMSO dilution solution until the ANF concentration is 0.3 wt%, and stir evenly.

[0082] (3) Prepare a composite membrane by vacuum filtration of the ANF dispersion from step (2); use a PVDF membrane as the filter membrane and control the vacuum degree at -0.09 MPa.

[0083] (4) The membrane is molded at 50 kPa and dried at room temperature to obtain the ANF membrane.

[0084] Comparative Example 2

[0085] (1) Weigh 1 g of aramid fiber (AF) and 1.5 g of potassium hydroxide (KOH), add them to 100 mL of dimethyl sulfoxide (DMSO), stir evenly, add 13 mL of isopropanol (IPA) dropwise, stir for 4 h, and obtain 1 wt% ANF dispersion.

[0086] (2) Add 80 mg of GO to a beaker containing 80 mL of deionized water and disperse by ultrasonication.

[0087] (3) Add 12 mL of ANF dispersion to the GO dispersion obtained in step (2) and stir until homogeneous.

[0088] (4) While the blended dispersion is still hot, it is poured into a sand core funnel and a composite membrane is prepared by vacuum-assisted filtration, using a PVDF membrane as the filter membrane and the vacuum degree is controlled at -0.09 MPa. The wet membrane is immersed in 10 mL of 5% sodium ascorbate solution, GO is reduced in an oven at 80℃, and then washed with ethanol.

[0089] (5) The composite film is mechanically molded and dried at 50 kPa to obtain the thermally conductive electromagnetic shielding composite film.

[0090] The composite membrane samples of Examples 1-8 and Comparative Examples 1-2 were subjected to performance tests, and the test results are shown in Table 1: Table 1. Measurement results of composite membranes in Examples 1-8 and Comparative Examples 1-2

[0091] This invention prepares a Janus composite membrane with insulation, electromagnetic shielding and thermal conductivity by introducing electrostatic self-assembly of iron(III) oxide (Fe3O4), boron nitride nanosheets (BNNS), silicon carbide nanowires (SiCnw) and reduced graphene oxide (rGO) into aramid nanofibers (ANF) and using a double-layer membrane filtration method.

[0092] The composite film consists of an upper layer of ANF / Fe3O4@BNNS and a lower layer of ANF / SiCnw@rGO. The Janus composite film has integrated thermal conductivity and synergistic electromagnetic shielding. The upper layer of Fe3O4@BNNS provides surface insulation while Fe3O4 has a certain hysteresis loss. The lower layer of SiCnw@rGO provides thermal conductivity and electromagnetic shielding while SiCnw can provide a large number of heterogeneous interfaces within the rGO sheets, effectively adjusting impedance matching. The components of this composite film work synergistically, and the upper and lower layers each have independent functional characteristics, achieving the effects of insulation, electromagnetic shielding, and thermal conductivity.

[0093] Our research provides a new approach for designing and manufacturing a novel aramid nanofiber composite membrane. The preparation process is simple, and the resulting aramid nanofiber-based Janus composite membrane shows promising application prospects in practical fields such as thermal conductivity and electromagnetic shielding.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for preparing an aramid nanofiber-based Janus composite membrane, characterized in that, The method includes: (1) Preparation of ANF dispersion Aramid fibers and potassium hydroxide were added to dimethyl sulfoxide solvent, and then isopropanol was added dropwise. The mixture was stirred at room temperature to obtain an ANF dispersion. (2) Positively modified iron(III) oxide and silicon carbide nanowires Take iron oxide and silicon carbide nanowires, add polydiallyldimethylammonium chloride respectively, stir evenly, then centrifuge and wash, freeze dry to obtain modified iron oxide and modified silicon carbide nanowires. (3) Preparation of hybrid fillers of iron oxide and boron nitride nanosheets The modified iron(III) oxide and boron nitride nanosheets obtained in step (2) were ultrasonically dispersed evenly in deionized water to obtain Fe3O4@BNNS dispersion; (4) Preparation of hybrid fillers of silicon carbide nanowires and graphene oxide The modified silicon carbide nanowires and graphene oxide obtained in step (2) were ultrasonically dispersed evenly in deionized water to obtain SiCnw@GO dispersion; (5) Preparation of a co-dispersion of ANF and Fe3O4@BNNS Take the ANF dispersion obtained in step (1) and add it to the Fe3O4@BNNS dispersion obtained in step (3). Disperse it evenly by ultrasonication to obtain a blended dispersion I. (6) Preparation of ANF and SiCnw@GO blend dispersion II Take another ANF dispersion obtained in step (1) and add it to the SiCnw@GO dispersion obtained in step (4). Stir evenly to obtain a blended dispersion II. (7) Preparation of Janus composite membrane The blended dispersion I from step (5) was poured into a sand core funnel pre-placed with a filter membrane, and a wet membrane was prepared by vacuum-assisted filtration. Then, the blended dispersion II from step (6) was poured into the same sand core funnel, and a double-layer wet membrane was prepared by vacuum-assisted filtration. The double-layer wet membrane was immersed in sodium ascorbate solution, dried at 80°C, and then washed, mechanically molded, and dried to obtain the Janus composite membrane.

2. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (1), the mass ratio of aramid fiber, potassium hydroxide, dimethyl sulfoxide, and isopropanol is 1:1.5:80~100:10~13.

3. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (2), iron oxide and polydiallyldimethylammonium chloride are mixed at a mass ratio of 1:20; silicon carbide nanowires and polydiallyldimethylammonium chloride are mixed at a mass ratio of 1:

20.

4. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (3), the mass ratio of modified iron oxide and boron nitride nanosheets is 7:3 to 2:

8.

5. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (3), boron nitride nanosheets are prepared by ball milling. The method is as follows: hexagonal boron nitride and isopropanol are mixed at a ratio of 1 g: 20 mL, ball milled at 300 rpm for 12 h, centrifuged, washed, and dried to obtain boron nitride nanosheets.

6. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (4), the mass ratio of modified silicon carbide nanowires to graphene oxide is 7:3 to 2:

8.

7. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (5), the mass ratio of ANF to Fe3O4@BNNS is 2:8~8:

2.

8. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (6), the mass ratio of ANF to SiCnw@GO is 2:8 to 8:

2.

9. The method for preparing the aramid nanofiber-based Janus composite membrane as described in claim 1, characterized in that, In step (7), the mass fraction of sodium ascorbate solution is 5%.

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