Janus-structure MXene cellulose nanofiber composite membrane with electromagnetic shielding and thermal management functions and preparation method of Janus-structure MXene cellulose nanofiber composite membrane

Abstract

The invention discloses a Janus structure MXene cellulose nanofiber composite membrane with electromagnetic shielding and thermal management functions and a preparation method thereof, and belongs to the application field of multifunctional composite materials and nanotechnology. The MXene cellulose nanofiber composite membrane provided by the invention comprises a Fe3O4 (at) CPNF composite membrane and a liquid metal (at) MXene deposition layer, the Fe3O4 (at) CPNF composite membrane is prepared by doping Fe3O4 nanoparticles in cellulose / polyacrylonitrile composite nanofibers, and the Fe3O4 (at) CPNF composite membrane is prepared by doping Fe3O4 nanoparticles in the cellulose / polyacrylonitrile composite nanofibers. And the liquid metal (at) MXene deposition layer is prepared by depositing liquid metal (at) MXene on the single side of the Fe3O4 (at) CPNF composite film. According to the invention, a Fe3O4 (at) CPNF composite membrane is adopted as a base material, a Janus structure with Fe3O4 (at) CPNF on one side and liquid metal (at) MXene on the other side is formed after single-side deposition of a liquid metal (at) MXene dispersion liquid, Fe3O4 nanoparticles are completely encapsulated and partially embedded on the surface in a cellulose nanofiber structure to form a magnetic nanofiber network, the polarization charge density can be improved, and the performance of the material is improved. The heterogeneous interface area is increased, and electromagnetic waves are absorbed through dielectric loss and magnetic loss.

Description

Technical Field

[0001] This invention relates to the field of multifunctional composite materials and nanotechnology applications, and in particular to a Janus structure MXene cellulose nanofiber composite membrane that combines electromagnetic shielding and thermal management functions, and its preparation method. Background Technology

[0002] With the rapid development of modern information technology, electromagnetic pollution has become increasingly serious. Strong electromagnetic interference can not only affect the normal operation of precision core components in electronic devices, but also pose a potential threat to human health. Nanofiber-based membrane structures, due to their ultrathin, porous, flexible, and easy-to-assemble structural characteristics, show broad application prospects in flexible wearable electronic devices, intelligent thermal management, pressure sensors, and electromagnetic shielding. Among these, cellulose polymers can significantly improve the stability of the electrospinning process, improve the mechanical properties and morphological defects of nanofibers, and achieve homogeneous control of internal and external structures. MXene, as a special two-dimensional layered material, possesses excellent dispersibility, high specific surface area, outstanding electrical / dielectric properties, and tunable surface chemical composition, giving it unique advantages in preparing porous, isolated, or layered electromagnetic interference (EMI) shielding composite materials. The abundant hydrophilic groups in cellulose molecules facilitate the formation of strong hydrogen bonds with the functional groups on the MXene surface. Such molecular-level interactions can significantly enhance the mechanical strength, electrical conductivity, and interfacial stability of the composite material. In addition, introducing shielding functional components during the spinning process or post-processing stage to construct heterogeneous interface structures to enhance the multiple reflections of electromagnetic waves between fibers has also become an important strategy to promote the development of nanofiber-based electromagnetic shielding film materials.

[0003] However, to meet the increasingly demanding comprehensive performance requirements of electromagnetic shielding composite materials for smart wearable devices, current research still faces two major challenges. First, there are limitations in electromagnetic shielding performance: over-reliance on high filler loading to improve shielding effectiveness has significant limitations in terms of practicality, economy, and environmental friendliness. Second, there is the limitation in application scenarios and functions: in practical use, smart wearable devices may experience infrared camouflage failure and performance damage due to overheating in high-temperature environments; maintaining normal operating performance in low-temperature environments is also a pressing problem. Therefore, developing multifunctional EMI shielding materials with adjustable thermal management performance and responsiveness to different environments is a key direction for solving these problems. Summary of the Invention

[0004] The purpose of this invention is to provide a Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions, and its preparation method, to solve the aforementioned problems in the background art. This invention uses a Fe3O4@CPNF composite membrane as the matrix material. After unilateral deposition of a liquid metal@MXene dispersion, a Janus structure is formed with one side of Fe3O4@CPNF and the other side of liquid metal@MXene. The Fe3O4 nanoparticles within the cellulose nanofiber structure exhibit complete encapsulation and partial surface embedding, forming a magnetic nanofiber network. This helps to increase the polarization charge density and the heterogeneous interface area, allowing electromagnetic waves to be absorbed through dielectric and magnetic losses.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is to provide a Janus-structured MXene cellulose nanofiber composite membrane (LM@MXene / Fe3O4@CPNF composite membrane) that combines electromagnetic shielding and thermal management functions, which includes a Fe3O4@CPNF composite membrane and a liquid metal@MXene deposition layer; The Fe3O4@CPNF composite film was prepared by doping Fe3O4 nanoparticles into cellulose / polyacrylonitrile composite nanofibers. The liquid metal@MXene deposition layer was prepared by depositing liquid metal@MXene on one side of the Fe3O4@CPNF composite membrane using vacuum-assisted filtration technology.

[0006] The Janus structure of this invention refers to a Fe3O4@CPNF composite film on one side and a liquid metal@MXene deposition layer on the other side. The Fe3O4@CPNF composite film side possesses stronger photothermal conversion capabilities, while the liquid metal@MXene deposition layer side serves as an electrothermal layer and an infrared radiation modulation surface. This invention uses the Fe3O4@CPNF composite film layer as a mechanical framework, which endows the composite film with both flexibility and strength.

[0007] Preferably, the liquid metal in the liquid metal@MXene deposition layer comprises gallium, indium, and tin in a mass ratio of 60~70:20~30:8~12; and the MXene in the liquid metal@MXene deposition layer is Ti3C2T. x .

[0008] Preferably, the thickness of the MXene cellulose nanofiber composite membrane is 70 μm; the loading density of the liquid metal@MXene deposition layer on the MXene cellulose nanofiber composite membrane is 1-5 mg / cm³. 2 (Based on the planar area of ​​the composite membrane).

[0009] The second technical solution of the present invention provides a method for preparing the above-mentioned Janus structure MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions, comprising the following steps: Microcrystalline cellulose (MCC) and polyacrylonitrile (PAN) were mixed in a solvent using a co-solvent method, and then Fe3O4 nanoparticles were doped by ultrasonic dispersion to obtain a spinning solution. Electrospinning was then performed to obtain the Fe3O4@CPNF composite film. Liquid metal@MXene dispersion was deposited onto one side of the Fe3O4@CPNF composite membrane using vacuum-assisted filtration technology to obtain the MXene cellulose nanofiber composite membrane.

[0010] Preferably, the solvent contains lithium chloride and dimethylacetamide; the mass ratio of microcrystalline cellulose to polyacrylonitrile is 3:13; the concentration of microcrystalline cellulose in the spinning solution is 4-5 wt%; and the concentration of Fe3O4 nanoparticles in the spinning solution is 2-6 wt%. The method for doping Fe3O4 nanoparticles is ultrasonic dispersion, wherein the ultrasonic dispersion power is 200~400W and the time is 5~15 hours.

[0011] Preferably, the parameters of the electrospinning are: voltage range of 15~20kV, spinning distance of 10~20cm, extrusion speed of injection pump of 0.5~1mL / h, and receiver rotation speed of 200~500r / min.

[0012] Preferably, the preparation method of the liquid metal@MXene dispersion includes the following steps: mixing liquid metal with a dispersant to obtain a liquid metal dispersion; Hydrochloric acid and lithium fluoride were mixed, then MXene powder was added, the mixture was sonicated, and the supernatant was collected by centrifugation to obtain an MXene dispersion. The liquid metal dispersion is mixed with the MXene dispersion to obtain the liquid metal@MXene dispersion.

[0013] Preferably, the mass-to-volume ratio of liquid metal to dispersant in the liquid metal dispersion is 25-35 mg:1 mL; the mass-to-volume ratio of MXene powder to raw materials other than MXene powder in the MXene dispersion is 25-35 mg:1 mL; the MXene powder is Ti3AlC2 powder; and the volume ratio of liquid metal dispersion to MXene dispersion is 1-2:1-2.

[0014] The third technical solution of the present invention provides an application of the above-mentioned Janus structure MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions in the fields of electromagnetic protection or thermal management.

[0015] The technical principle of this invention is as follows: This invention constructs a Janus-structured LM@MXene / Fe3O4@CPNF composite film, using Fe3O4@CPNF as the matrix material. Fe3O4 nanoparticles are fully encapsulated and partially embedded in the polymer matrix via a co-solvent method, thereby increasing the polarization charge density and expanding the heterogeneous surface area. This allows for the absorption of electromagnetic waves through dielectric and magnetic losses, while maintaining stable dielectric and magnetic properties under mechanical loads. A Janus-structured composite film is formed by the unilateral deposition of a liquid metal@MXene dispersion, with one side being Fe3O4@CPNF and the other being liquid metal@MXene. Thanks to the hydrogen bonding between the cellulose and MXene components, the two layers exhibit good compatibility, forming a dense interfacial bond. The LM (liquid metal) and MXene form a sandwich structure between a conductive electrode plate and a dielectric, creating numerous microcapacitors within the composite film. This promotes multiple transmissions and rapid attenuation of electromagnetic energy between the MXene nanosheet layers. This structure facilitates multiple reflections of electromagnetic waves between impedance-mismatched layers.

[0016] Furthermore, the asymmetric product structure of this invention results in completely different properties on both sides of the composite film. For example, when the Fe3O4@CPNF side, which has a stronger photothermal conversion capability, faces outward, it helps absorb sunlight for heating, while the LM@MXene side, acting as an electrothermal layer and infrared radiation modulation side, faces inward to reduce internal heat loss. The composite film can also be used as a heat dissipation layer for electronic devices: the photothermal side converts local hotspot heat into radiative heat dissipation in the planar direction, and the infrared radiation modulation side prevents external heat radiation from flowing back. In addition, the infrared emissivity ε of the liquid metal@MXene layer surface is only 0.27, classifying it as a low-infrared-emission material. In cold environments, the low-infrared-emissivity surface reduces the thermal signal of the target, thus achieving an infrared radiation modulation effect.

[0017] The beneficial technical effects of the present invention are as follows: 1. This invention constructs a Janus-structured MXene / cellulose nanofiber composite membrane. Using a Fe3O4@CPNF composite membrane as the matrix material, a Janus structure is formed by unilateral deposition of a liquid metal@MXene dispersion, with one side consisting of Fe3O4@CPNF and the other side of liquid metal@MXene. Fe3O4 nanoparticles within the cellulose nanofiber structure exhibit complete encapsulation and partial surface embedding, forming a magnetic nanofiber network. The addition of Fe3O4 nanoparticles helps increase the polarization charge density and the heterogeneous interface area, facilitating electromagnetic wave absorption through dielectric and magnetic losses. In this system, cellulose nanofibers effectively provide structural support and matrix stabilization. The introduction of the liquid metal@MXene deposition layer demonstrates good compatibility through hydrogen bonding between the multiple components of cellulose and MXene, forming a dense interfacial bond. The sandwich structure configuration of LM and MXene forming a conductive electrode plate and a dielectric layer creates numerous microcapacitors within the composite membrane, thereby enhancing the multiple reflections and attenuation of electromagnetic waves at impedance mismatched interlayer surfaces. Furthermore, the asymmetrical structure allows the two sides of the composite membrane to exhibit completely different properties. The Fe3O4@CPNF side, which has a stronger photothermal conversion capability, faces outward to absorb sunlight and provide heat, while the LM@MXene side, which serves as an electrothermal layer and infrared radiation control layer, faces inward to reduce internal heat loss. This makes it suitable for lightweight temperature control in polar expeditions or winter sports equipment.

[0018] 2. The microcrystalline cellulose (MCC) spinning solution prepared in this invention can efficiently dissociate the strong hydrogen bonds between microcrystalline cellulose molecules, significantly improving its solubility and spinning solution uniformity, and optimizing the stability and spinning performance of the spinning solution. This is a key process step to ensure stable material performance. Fe3O4 nanoparticles are introduced into the MCC spinning solution using ultrasonic dispersion technology. The cavitation effect effectively breaks up the nanoparticle aggregates, achieving uniform distribution in the matrix. This avoids nozzle clogging during electrospinning and reduces the use of dispersants without damaging the cellulose molecular chain structure. Vacuum-assisted filtration technology is used for one-sided deposition, achieving uniform and dense deposition of the mixed solution, reducing bubble defects, and preserving the original flexibility and permeability of the spun membrane through one-sided functionalization. Simultaneously, it enhances the synergistic effect of liquid metal and MXene, making the operation highly efficient and controllable, and easily adaptable for large-scale preparation.

[0019] 3. To achieve electromagnetic shielding and intelligent thermal management, this invention develops a method for preparing a Janus-structured MXene / cellulose nanofiber composite membrane that combines electromagnetic shielding and bidirectional thermal management functions. This preparation process ensures the uniformity and stability of the materials used, providing a guarantee for meeting the increasingly demanding comprehensive performance requirements of nanofiber-based EMI shielding composite materials in subsequent intelligent wearable devices. Furthermore, the selected process parameters can be flexibly adjusted according to different requirements, exhibiting good adaptability and process scale-up potential. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The images show SEM images and diameter distribution histograms of nanofibers with different MCC / PAN blend ratios in Example 1 of this invention. Among them, (a) is P13 fiber, (b) is C2 / P14 fiber, (c) is C3 / P13 fiber, (d) is C4 / P12 fiber, and (e) is C5 / P11 fiber.

[0022] Figure 2 The electromagnetic shielding performance variation curves are shown for the LM@MXene / Fe3O4@CPNF composite film of Example 1 and the MXene / Fe3O4@CPNF composite film of Comparative Example 2.

[0023] Figure 3 The temperature change curves on both sides of the LM@MXene / Fe3O4@CPNF composite membrane in Example 1 are shown.

[0024] Figure 4 The temperature change curve of the Fe3O4@CPNF surface of the LM@MXene / Fe3O4@CPNF composite film in Example 1 within 30 seconds of light irradiation is shown.

[0025] Figure 5 Infrared images of tin foil, carbon fiber cloth, CPNF nanofiber membrane, the Fe3O4@CPNF side of the LM@MXene / Fe3O4@CPNF composite membrane of Example 1, and the LM@MXene side of the LM@MXene / Fe3O4@CPNF composite membrane before and after 30 minutes on a constant temperature heating stage.

[0026] Figure 6 SEM images and tensile mechanical property diagrams of Fe3O4@CPNF composite films with different Fe3O4 doping amounts in Example 2 and CPNF nanofiber films in Comparative Example 1 are shown. (a) is the CPNF nanofiber film; (b) is 1%; (c) is 2%; (d) is 3%; (e) is 4%; (f) is 5%; (g) is 6%; (h) is a 4% SEM image at a higher magnification; and (i) is the tensile mechanical property diagram.

[0027] Figure 7 This is a macroscopic view of the liquid metal dispersion of Example 1.

[0028] Figure 8 This is a macroscopic view of the MXene dispersion from Example 1.

[0029] Figure 9 This is a macroscopic view of the LM@MXene / Fe3O4@CPNF composite membrane of Example 1. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0031] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0033] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0034] This invention discloses a Janus-structured MXene cellulose nanofiber composite membrane that combines electromagnetic shielding and thermal management functions, comprising a Fe3O4@CPNF composite membrane and a liquid metal@MXene deposition layer; The Fe3O4@CPNF composite film was prepared by doping Fe3O4 nanoparticles into cellulose / polyacrylonitrile composite nanofibers. The liquid metal@MXene deposition layer was prepared by depositing liquid metal@MXene on one side of the Fe3O4@CPNF composite membrane using vacuum-assisted filtration technology.

[0035] Furthermore, the liquid metal in the liquid metal@MXene deposition layer comprises gallium, indium, and tin in a mass ratio of 60~70:20~30:8~12, more preferably a eutectic gallium indium tin alloy (EGaInSn) in a mass ratio of 68.5:21.5:10; the MXene in the liquid metal@MXene deposition layer is Ti3C2T. x .

[0036] In this invention, the addition of liquid metal can improve the electromagnetic interference shielding performance of the composite film.

[0037] Furthermore, the thickness of the MXene cellulose nanofiber composite membrane is 70 μm; the loading density of the liquid metal@MXene deposition layer on the MXene cellulose nanofiber composite membrane is 1-5 mg / cm³. 2 (Based on the planar area of ​​the composite membrane).

[0038] This invention also discloses a method for preparing the Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions, comprising the following steps: (1) Microcrystalline cellulose (MCC) and polyacrylonitrile (PAN) are mixed in a solvent by co-solvent method, and then Fe3O4 nanoparticles are doped by ultrasonic dispersion to obtain spinning solution. Electrospinning is then performed to obtain the Fe3O4@CPNF composite film. (2) Liquid metal@MXene dispersion was deposited on one side of the Fe3O4@CPNF composite membrane by vacuum-assisted filtration technology to obtain the MXene cellulose nanofiber composite membrane.

[0039] Furthermore, the solvent contains lithium chloride (LiCl) and dimethylacetamide (DMAc); the mass ratio of microcrystalline cellulose to polyacrylonitrile is 3:13; the concentration of microcrystalline cellulose in the spinning solution is 4-5 wt%; and the concentration of Fe3O4 nanoparticles in the spinning solution is 2-6 wt%.

[0040] This invention uses a LiCl / DMAc system to dissolve MCC, which can break the binding forces between cellulose molecules, thereby dispersing MCC at the molecular level in the solvent system to form a homogeneous solution.

[0041] Further, in step (1): the mixing includes the following steps: placing microcrystalline cellulose in a solvent, activating it at 110~130℃, and then mixing it with polyacrylonitrile.

[0042] Furthermore, the ultrasonic dispersion power is 200~400W, and the time is 5~15 hours.

[0043] Furthermore, the concentration of Fe3O4 nanoparticles in the spinning solution is 2-6 wt%, more preferably 3-5 wt%, and even more preferably 4 wt%.

[0044] This invention controls the content of Fe3O4 nanoparticles within the above-mentioned range, enabling the spun film to have a uniform morphology, high magnetic content, and satisfactory mechanical properties.

[0045] Furthermore, the parameters of the electrospinning are as follows: voltage range of 15~20kV, more preferably 15~17kV; spinning distance of 10~20cm, more preferably 16~18cm; extrusion speed of the injection pump of 0.5~1mL / h, more preferably 0.8~1mL / h, and even more preferably 0.51mL / h; and rotation speed of the receiver of 200~500r / min, more preferably 200~300r / min.

[0046] By controlling the spinning parameters within the above-mentioned range, the present invention can achieve better spinning results.

[0047] Furthermore, the preparation method of the Fe3O4@CPNF composite film includes the following steps: Lithium chloride and a portion of dimethylacetamide are mixed to obtain a solvent; Microcrystalline cellulose is placed in the solvent, heated and activated at 100-120°C and stirred for 1-2 hours, and then stirred for another 1-2 hours at room temperature to obtain a cellulose solution; polyacrylonitrile is added to the cellulose solution, and the remaining small amount of DMAc is added again to obtain a mixture; Fe3O4 nanoparticles were added to the mixture to achieve a concentration of 4wt%, and then ultrasonic ice bath treatment was performed at a power of 400W for 10-13 hours to obtain a spinning solution. Electrospinning was then performed to obtain the Fe3O4@CPNF composite film.

[0048] Furthermore, the preparation method of the liquid metal@MXene dispersion includes the following steps: mixing 300 mg of liquid metal with a dispersant, sonicating in an ice bath using a cell sonicator for 1-2 hours, then adjusting the pH to weakly alkaline, continuing to stir at 300 rpm at room temperature for 12-24 hours, and finally centrifuging and washing at 10000 rpm to obtain the liquid metal dispersion; 40 mL of hydrochloric acid and 3.2 g of lithium fluoride were stirred at room temperature for 30 min. Then, 2 g of MXene powder was added to the HCl / LiF mixture, and the mixture was heated and stirred at 40 °C for 42-48 hours. The reaction solution was then washed by centrifugation to pH 6 and sonicated in an ice bath for 3-5 hours. After sonication, the mixture was centrifuged at 5000 rpm for 30 min, and the black supernatant was collected to obtain the MXene dispersion. The liquid metal dispersion was mixed with the MXene dispersion and ultrasonically treated in an ice bath for 15-30 minutes to obtain the liquid metal@MXene dispersion.

[0049] This invention uses the fluoride salt method to prepare MXene dispersions, which can give them good dispersibility and conductivity, while adding a large number of active oxygen-containing groups to their surface.

[0050] Further, the mass-to-volume ratio of liquid metal to dispersant in the liquid metal dispersion is 25-35 mg:1 mL, more preferably 30 mg:1 mL; the mass-to-volume ratio of MXene powder to the remaining raw materials other than MXene powder in the MXene dispersion is 25-35 mg:1 mL, more preferably 30 mg / mL; the MXene powder is Ti3AlC2 powder; the volume ratio of liquid metal dispersion to MXene dispersion is 1-2:1-2, more preferably 1:1.

[0051] This invention limits the proportions of liquid metal and MXene within the aforementioned range, enabling more thorough dispersion.

[0052] This invention limits the volume ratio of liquid metal dispersion and MXene dispersion within the above-mentioned range, which enables the composite film to have a suitable liquid metal content, thereby better forming a multi-scale structure design of microcapacitance → high porosity → asymmetric layering, and making efficient use of the functional filler in the composite film.

[0053] Further, the single-sided deposition includes the following steps: cutting the Fe3O4@CPNF composite membrane into 5cm×5cm sheets and placing them on a microporous filter membrane. Then, using vacuum-assisted filtration, the liquid metal@MXene dispersion is deposited onto one side of the Fe3O4@CPNF composite membrane. The membrane is then peeled off from the microporous filter membrane and dried to obtain the MXene cellulose nanofiber composite membrane, with one side being gray Fe3O4@CPNF and the other side being silver-purple liquid metal@MXene.

[0054] The present invention does not impose any special limitations on the peeling operation; any peeling technique known to those skilled in the art can be used.

[0055] Furthermore, the drying time is 10-20 hours.

[0056] The MXene cellulose nanofiber composite membrane prepared by this invention still has excellent electromagnetic protection and thermal management functions despite being relatively thin and lightweight. It can be applied to fields such as flexible smart wearable devices and has great potential for application in extreme environments.

[0057] The present invention does not impose any special limitations on the operation of the MXene cellulose nanofiber composite film in the fields of electromagnetic protection and thermal management. Any technical solution for the application of composite films in the fields of electromagnetic protection and thermal management that is well known to those skilled in the art can be used.

[0058] The present invention also discloses the application of the above-mentioned Janus structure MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions in the fields of electromagnetic protection or thermal management.

[0059] Unless otherwise specified, "ice bath" in this invention refers to the operation of using an ice-water mixture as a cooling medium to maintain the temperature of the reaction system at around 0°C.

[0060] Unless otherwise specified, "room temperature" in this invention refers to 10-30°C.

[0061] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0062] Example 1 A method for preparing a Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions, comprising the following steps: (1) Weigh 0.8g of lithium chloride (LiCl) and add it to 9.2g of dimethylacetamide (DMAc) to prepare a LiCl / DMAc solvent with a concentration of 8wt%. Then add 0.4g / 0.6g / 0.8g / 1.0g of microcrystalline cellulose powder (MCC) and activate and stir at 120℃. Add 6.8g of DMAc to the cellulose solution for the second time, and then add 2.8g / 2.6g / 2.4g / 2.2g of polyacrylonitrile powder (PAN). Let it stand for 12 hours to obtain a mixture. According to the mass ratio of MCC and PAN in the mixture, the samples are named C2 / P14, C3 / P13, C4 / P12 and C5 / P11, respectively. The spinning solution with 13wt% PAN and 4wt% LiCl added is used as a control and named P13. The relevant solution preparations are shown in Table 1.

[0063] Subsequently, 8g of the C3 / P13 mixture was taken, and 0.081g of Fe3O4 nanoparticles were added. The mixture was ultrasonically dispersed for 12h to obtain a spinning solution with a Fe3O4 mass fraction of 1wt%. The electrospinning conditions were set as follows: spinning voltage 15~17 kV, spinning distance 18 cm, feed speed 0.8 mL / h, receiver rotation speed 300 rpm, spinning temperature 25~30℃, and ambient humidity 30%~50%. Electrospinning was then performed to prepare Fe3O4@CPNF composite films. (In addition, spinning experiments were conducted under the same spinning conditions using P13, C2 / P14, C3 / P13, C4 / P12, and C5 / P11 as spinning solutions, and the obtained fiber samples were designated as P13 fiber, C2 / P14 fiber, C3 / P13 fiber, C4 / P12 fiber, and C5 / P11 fiber, respectively.)

[0064] (2) Mix 300 mg of liquid metal (LM) with a dispersant (1 mg / mL dopamine hydrochloride solution), and sonicate the mixture in an ice bath using a cell sonicator for 1 hour to adjust the pH of the dispersion to weakly alkaline. Stir at 300 rpm for 24 hours at room temperature, and finally centrifuge and wash at 10,000 rpm to obtain a liquid metal dispersion with a concentration of 30 mg / mL (see...). Figure 7 ).

[0065] 40 mL of 9 mol / L hydrochloric acid and 3.2 g of lithium fluoride were stirred at room temperature for 30 min. Then, 2 g of Ti3AlC2 powder was slowly added, and the mixture was continuously heated and stirred in a 40 °C water bath for 42 h. After the reaction was completed, the mixture was washed with deionized water until the pH value reached 6, and then sonicated in an ice bath for 3 h. After sonication, the mixture was centrifuged at 5000 rpm for 30 min, and the black upper layer was collected to obtain a 30 mg / mL MXene dispersion (see...). Figure 8 ).

[0066] The liquid metal dispersion and the MXene dispersion were mixed at a volume ratio of 1:1 and ultrasonically treated in an ice bath for 30 min to obtain the liquid metal@MXene dispersion.

[0067] (3) The Fe3O4@CPNF composite membrane was cut into 5cm×5cm sheets and placed on a microporous filter membrane. Then, using vacuum-assisted filtration, a liquid metal@MXene dispersion was deposited onto one side of the Fe3O4@CPNF composite membrane. The membrane was then peeled off from the microporous filter membrane, dried, and a Janus-structured LM@MXene / Fe3O4@CPNF composite membrane was formed (see...). Figure 9 One side is gray Fe3O4@CPNF, and the other side is silver-purple liquid metal@MXene.

[0068] Comparative Example 1 A method for preparing CPNF nanofiber membranes: Take 8g of the mixture C3 / P13 from Example 1 and ultrasonically disperse it for 12h to obtain the spinning solution. Set the electrospinning conditions as follows: spinning voltage 15~17 kV, spinning distance 18 cm, feed speed 0.8 mL / h, receiver rotation speed 300 rpm, spinning temperature 25~30℃, and ambient humidity 30%~50% to conduct electrospinning and obtain CPNF nanofiber membrane.

[0069] Comparative Example 2 The only difference from Example 1 is that the addition of liquid metal is omitted, and the MXene dispersion is directly deposited onto one side of the Fe3O4@CPNF composite membrane in step (3). The resulting product is denoted as MXene / Fe3O4@CPNF composite membrane.

[0070] Example of effect 1 Table 1. Preparation of mixed spinning solutions with different MCC / PAN blend ratios SEM images and diameter distribution histograms of nanofibers with different MCC / PAN blend ratios are shown below. Figure 1 Among them, (a) is P13 fiber, (b) is C2 / P14 fiber, (c) is C3 / P13 fiber, (d) is C4 / P12 fiber, and (e) is C5 / P11 fiber.

[0071] Depend on Figure 1 It is evident that the C3 / P13 composite nanofibers obtained when the MCC to PAN blend ratio is 3:13 have a bead-free, most uniform diameter distribution, and a tree-like orientation microstructure. They can support inorganic / metal nanoparticles and MXene nanomaterials, providing a robust substrate for the synergistic construction of high-performance electromagnetic shielding composite nanofiber materials.

[0072] Figure 2 The electromagnetic shielding performance variation curves are shown for the LM@MXene / Fe3O4@CPNF composite film of Example 1 and the MXene / Fe3O4@CPNF composite film of Comparative Example 2.

[0073] In this invention, the intercalation strategy of LM@PDA nanoparticles and the fluidity of LM itself optimize the stacking of Ti3C2T. x The contact resistance between MXene nanosheets, through "surface-to-point" contact, effectively improves the electronic conductivity of the electrode and reduces the percolation threshold, enabling the monolithic LM@MXene / Fe3O4@CPNF composite film to achieve an extremely thin thickness of 70 μm and a percolation resistance of 0.762 g / cm³. 3At low densities, the shielding effectiveness SSE / t (considering the effects of both thickness and density on SE) reaches a maximum of 8870.8 dB·cm in the X-band. 2 / g, such as Figure 2 .

[0074] pass Figure 2 The curves showing the change in electromagnetic shielding performance before and after the introduction of liquid metal show that after the introduction of liquid metal, it can form a multi-scale structural design with Mxene, which is characterized by microcapacitance, high porosity, and asymmetric layering. This allows for more efficient utilization of the functional fillers in the composite membrane, promoting the synergistic effect of percolation network conductivity loss, microcapacitance polarization effect, and dielectric layer dipole polarization. Compared with before the introduction of liquid metal, the total shielding effectiveness has more than doubled.

[0075] To evaluate the photothermal conversion and infrared modulation performance of the composite film, xenon lamp irradiation experiments were conducted on both its front and back sides. Specific experimental conditions were as follows: the composite film was mounted on the inner wall of a dark chamber, and a high-pressure short-arc xenon lamp was placed 20 cm directly above the film surface to simulate a power density of 200 mW / cm². 2 Concentrated sunlight.

[0076] Infrared thermal imaging analysis under xenon lamp irradiation showed that, with irradiation time continuing for up to 30 min, the temperatures of the LM@MXene and Fe3O4@CPNF surfaces of the composite film gradually increased from room temperature, stabilizing at 40.9℃ and 51.6℃, respectively (see...). Figure 3 The results indicate that the strong extinction coefficient and broadband absorption characteristics of MXene, along with the surface plasmon resonance effect of liquid metal, jointly promote the photothermal conversion capability of the composite film.

[0077] Furthermore, the integration of nano-sized Fe3O4 particles with nanofibers significantly increases the specific surface area of ​​the material, enabling the Fe3O4@CPNF surface to exhibit excellent light absorption and photothermal conversion efficiency. Within only 30 seconds of illumination, its surface temperature rapidly increased from 25.2℃ to 40.7℃ (see...). Figure 4 This demonstrates high photothermal conversion efficiency.

[0078] Figure 5 Infrared images of tin foil, carbon fiber cloth, CPNF nanofiber membrane, the Fe3O4@CPNF side of the LM@MXene / Fe3O4@CPNF composite membrane of Example 1, and the LM@MXene side of the LM@MXene / Fe3O4@CPNF composite membrane before and after 30 minutes on a constant temperature heating stage.

[0079] Figure 5 In Chinese, "Tinfoil" refers to tin foil, and "Carbon fiber fabric" refers to carbon fiber cloth.

[0080] After being placed on a 37°C constant-temperature heating stage used to simulate human body temperature for 30 minutes, the surface temperature of the LM@MXene side of the LM@MXene / Fe3O4@CPNF composite film in Example 1 increased by only 0.2°C, almost indistinguishable from room temperature, demonstrating infrared emissivity modulation performance similar to that of metal (tin foil). This indicates that LM@MXene can effectively reflect thermal infrared radiation, so the temperature of the LM@MXene side of the composite film did not change significantly. Figure 5 Infrared emissivity testing showed that the infrared emissivity ε of the LM@MXene side of the composite film in Example 1 was only 0.27, which is lower than that of other carbon-based materials such as carbon fiber cloth, and it belongs to the category of low infrared emissivity materials (ε<0.5).

[0081] The Fe3O4@CPNF composite film without the introduction of liquid metal exhibits stronger thermal conductivity and higher infrared emissivity (ε=0.74), and its surface temperature rapidly rises to the same temperature as the heating stage in a very short time. Figure 5 In the infrared thermal phase diagram, it appears as the same red color as the heating stage, making it difficult to achieve the purpose of controlling the infrared emissivity.

[0082] Example 2 A method for preparing a Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions, comprising the following steps: Weigh 0.8g LiCl and add it to 9.2g DMAc to prepare an 8wt% LiCl / DMAc solvent. Then add 0.6g microcrystalline cellulose powder (MCC) and activate the solution at 120℃ with stirring. Add 6.8g DMAc to the cellulose solution for the second time, followed by 2.6g polyacrylonitrile powder (PAN). Let the solution stand for 12 hours to obtain a mixed solution.

[0083] Subsequently, 8g of the above mixture was taken, and different masses of Fe3O4 nanoparticles were added respectively. The mixture was ultrasonically dispersed for 12h to obtain spinning solutions with Fe3O4 mass fractions of 1wt% / 2wt% / 3wt% / 4wt% / 5wt% / 6wt%. The electrospinning conditions were set as follows: spinning voltage 15~17 kV, spinning distance 18 cm, feed speed 0.8 mL / h, receiver rotation speed 300 rpm, spinning temperature 25~30℃, and ambient humidity 30%~50%. Electrospinning was then performed to obtain Fe3O4@CPNF composite films (referred to as 1%, 2%, 3%, 4%, 5%, and 6% according to the different Fe3O4 mass fractions).

[0084] Example 2 Figure 6SEM images and tensile mechanical property diagrams of Fe3O4@CPNF composite films with different Fe3O4 doping amounts in Example 2 and CPNF nanofiber films in Comparative Example 1 are shown. (a) is the CPNF nanofiber film; (b) is 1%; (c) is 2%; (d) is 3%; (e) is 4%; (f) is 5%; (g) is 6%; (h) is a 4% SEM image at a higher magnification; and (i) is the tensile mechanical property diagram.

[0085] Figure 6 The data in (i) concerning 0% refers to CPNF nanofiber membranes.

[0086] Depend on Figure 6 It can be seen that, without Fe3O4 doping, the CPNF nanofiber membrane exhibits a smooth surface and an interconnected dendritic structure. Doping with Fe3O4 nanoparticles at a concentration of 1–4 wt% results in a uniform distribution of particles along the fiber axis, forming a unique "beaded chain" morphology. However, when the Fe3O4 nanoparticle doping concentration in the spinning solution reaches 5–6 wt%, particle agglomeration becomes more pronounced, manifesting as large aggregates between fibers. Furthermore, during electrospinning, frequent needle blockage prevents continuous solution ejection, severely impairing the process stability and mechanical properties of the resulting composite fiber, leading to a rapid decrease in fiber breaking strength. Comprehensive analysis indicates that a Fe3O4 nanoparticle concentration of 4% in the spinning solution is the optimal ratio for achieving uniform morphology, high magnetic content, and satisfactory mechanical properties.

[0087] In summary, this invention achieves a multifunctional MXene / cellulose nanofiber composite membrane by depositing liquid metal@MXene on one side of the Fe3O4@CPNF composite membrane. The Fe3O4@CPNF composite membrane improves the mechanical brittleness and interlayer structural defects of MXene, ensuring both flexibility and breathability. The liquid metal and MXene form a sandwich structure of conductive electrode plates and dielectric, creating numerous microcapacitors within the composite membrane and promoting multiple reflections of electromagnetic waves across the impedance-mismatched interlayer layers. This bilayer structure not only achieves a multi-scale structural design of microcapacitors → high porosity → layering, but also further optimizes the conductivity and dielectric properties of the functional filler, promoting multiple reflections of electromagnetic waves within the layers and maximizing absorption loss (SE). A This effectively reduces impedance mismatch at the gas-film interface. Furthermore, based on the bifacial anisotropy of infrared emissivity and thermal conductivity, the Janus-structured composite membrane of this invention can achieve flexible infrared radiation adjustment according to different environments, realizing bidirectional thermal management. Compared to the limited performance and singular application scenarios and functions of traditional electromagnetic shielding, this design achieves superior electromagnetic shielding performance and thermal management efficiency.

[0088] The embodiments herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0089] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0090] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A Janus-structured MXene cellulose nanofiber composite membrane that combines electromagnetic shielding and thermal management functions, characterized in that, It includes a Fe3O4@CPNF composite film and a liquid metal@MXene deposition layer; The Fe3O4@CPNF composite film was prepared by doping Fe3O4 nanoparticles into cellulose / polyacrylonitrile composite nanofibers. The liquid metal@MXene deposition layer was prepared by depositing liquid metal@MXene on one side of the Fe3O4@CPNF composite film.

2. The Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions according to claim 1, characterized in that, The liquid metal in the liquid metal@MXene deposition layer contains gallium, indium, and tin in a mass ratio of 60~70:20~30:8~12; the MXene in the liquid metal@MXene deposition layer is Ti3C2T. x .

3. The Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions according to claim 1, characterized in that, The thickness of the MXene cellulose nanofiber composite membrane is 70 μm; the loading density of the liquid metal@MXene deposition layer on the MXene cellulose nanofiber composite membrane is 1-5 mg / cm³. 2 .

4. A method for preparing a Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions as described in any one of claims 1-3, characterized in that, Includes the following steps: Microcrystalline cellulose and polyacrylonitrile were mixed in a solvent, and then Fe3O4 nanoparticles were doped to obtain a spinning solution. Electrospinning was then performed to obtain the Fe3O4@CPNF composite film. Liquid metal@MXene dispersion was deposited onto one side of the Fe3O4@CPNF composite membrane to obtain the MXene cellulose nanofiber composite membrane.

5. The preparation method according to claim 4, characterized in that, The solvent contains lithium chloride and dimethylacetamide; the mass ratio of microcrystalline cellulose to polyacrylonitrile is 3:13; the concentration of microcrystalline cellulose in the spinning solution is 4-5 wt%; the concentration of Fe3O4 nanoparticles in the spinning solution is 2-6 wt%. The method for doping Fe3O4 nanoparticles is ultrasonic dispersion, wherein the ultrasonic dispersion power is 200~400W and the time is 5~15 hours.

6. The preparation method according to claim 4, characterized in that, The electrospinning parameters are as follows: voltage range of 15~20kV, spinning distance of 10~20cm, extrusion speed of injection pump of 0.5~1mL / h, and receiver rotation speed of 200~500r / min.

7. The preparation method according to claim 4, characterized in that, The preparation method of the liquid metal@MXene dispersion includes the following steps: mixing liquid metal with a dispersant to obtain a liquid metal dispersion; Hydrochloric acid and lithium fluoride were mixed, then MXene powder was added, the mixture was sonicated, and the supernatant was collected by centrifugation to obtain an MXene dispersion. The liquid metal dispersion is mixed with the MXene dispersion to obtain the liquid metal@MXene dispersion.

8. The preparation method according to claim 7, characterized in that, The liquid metal dispersion has a mass-to-volume ratio of liquid metal to dispersant of 25-35 mg:1 mL; the MXene dispersion has a mass-to-volume ratio of MXene powder to raw materials other than MXene powder of 25-35 mg:1 mL; the MXene powder is Ti3AlC2 powder; and the volume ratio of liquid metal dispersion to MXene dispersion is 1-2:1-2.

9. The application of a Janus-structured MXene cellulose nanofiber composite membrane with both electromagnetic shielding and thermal management functions as described in any one of claims 1-3 in the fields of electromagnetic protection or thermal management.

Images