A Janus microporous fiber membrane and its preparation method and application

Abstract

The present invention belongs to the technical field of hierarchical Janus microporous fiber membranes, and discloses a Janus microporous fiber membrane and a preparation method and application thereof. After polytetrafluoroethylene with a relative molecular mass greater than 1 million, a modified filler and a processing aid are mixed in proportion, shear blending is performed to make the polytetrafluoroethylene in situ fiberized to obtain a blended product; the blended product is processed into a film, and the processing aid in the film is etched to remove the processing aid, to obtain a PTFE-based composite film with a microporous fiber network structure; one side of the PTFE-based composite film is plasma treated to form a base layer; a MXene conductive two-dimensional material layer is deposited on the surface of the base layer, and the MXene conductive two-dimensional material layer is pressed and formed to obtain a Janus microporous fiber membrane. The PTFE-based substrate layer can not only improve the overall mechanical properties of the Janus film, but also its unique hydrophobicity and chemical resistance protect the MXene layer, thereby improving the service life of the film.

Description

Technical Field

[0001] The invention belongs to the technical field of hierarchical Janus microporous fiber membranes, and specifically relates to a Janus microporous fiber membrane and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the emergence of next-generation communication technology and the continuous updating of portable electronic devices, flexible wearable electronic devices are increasingly integrated into our lives. However, these devices will inevitably generate electromagnetic radiation and interference during operation, which will not only affect the normal operation of the equipment, but also pose a serious threat to human health. Traditional metal materials are favored for their excellent conductivity, but their heavy weight, easy corrosion, difficult processing and lack of flexibility make them less and less suitable for the development needs of modern society.

[0004] In recent years, many researchers have devoted themselves to implanting modified fillers with high conductivity into polymer matrices in an effort to improve the comprehensive performance of flexible electronic devices. However, thin and light conductive polymer materials used in the field of flexible wearables often rely on reflection effects to achieve efficient electromagnetic shielding, which not only fails to effectively alleviate the leakage of electromagnetic radiation, but may also induce secondary pollution. Therefore, there is an urgent need for a material that has both strong shielding and effective anti-reflection, and is thin, light and flexible. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide a Janus microporous fiber membrane and a preparation method and application thereof.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a Janus microporous fiber membrane, comprising the following steps:

[0008] After polytetrafluoroethylene (PTFE) with a relative molecular mass greater than 1 million, modified fillers and processing aids are mixed in proportion, shear blending is performed at a set temperature, wherein the processing aid becomes molten during the blending process, and the generated shear force is transmitted to the PTFE particles, so that the PTFE is untangled and stretched into a nanofiber network structure, thereby capturing a large amount of modified fillers, and finally obtaining a blended product;

[0009] Processing the blended product into a film, and removing the processing aid in the film by etching, to obtain a PTFE-based composite film with a microporous fiber network structure;

[0010] One side of the PTFE-based composite film is encapsulated and protected, and the other side is plasma treated in an inert atmosphere to form a base layer;

[0011] A MXene conductive two-dimensional material layer is deposited on the surface of the substrate layer and pressed into shape to obtain a Janus microporous fiber membrane.

[0012] Preparation of existing porous PTFE membranes, such as electrostatic spinning, sintering etching, stretching pores, etc. The porous PTFE materials produced by the first two have good fiber structures, but due to the addition of fiber-forming aids and other factors, the porous fiber film produced has low strength, low production efficiency, high cost, and is difficult to industrial production. The most commonly used in industrial production is the stretching pore process, and the product produced has high porosity and controllable pore size, and large-scale production has been achieved. However, the process difficulty of the stretching method is high, and the fiber produced has a high degree of orientation. In the process of biaxial or uniaxial stretching, the deformation of the material must be accurately controlled, otherwise it may cause uneven pore structure. In addition, there is a contradiction between the porosity and mechanical properties of the porous PTFE membrane prepared by the stretching pore process, that is, with the increase of porosity, the mechanical strength of the membrane usually decreases, and then it is difficult to meet the needs of the present invention.

[0013] The present invention uses polytetrafluoroethylene with a relative molecular mass greater than 1 million. Polytetrafluoroethylene (PTFE) with a larger relative molecular mass is easy to fiberize, mainly because of its unique molecular chain structure and high molecular weight characteristics: 1) Strong interchain force: The molecular chain of PTFE is composed of strong CC and CF bonds. This highly stable chemical structure makes it difficult for its molecular chain to break, increasing the tensile strength of the chain during fiberization. 2) Molecular chain flexibility: Although PTFE has a large molecular weight, its chain structure is still flexible. Under the action of external forces (such as shear force or tensile force), the molecular chain can be rearranged to form a continuous fiberized structure. 3) Molecular weight effect: High molecular weight provides longer chain segments, showing higher mechanical properties and viscoelasticity during the fiberization process, thereby promoting fiberization. Therefore, PTFE with a high relative molecular mass is more suitable for preparing a stable and strong fiber network.

[0014] Since PTFE itself has a high melting point (over 327°C) and does not have fluidity in the molten state, it cannot be directly processed into fibers. Therefore, a processing aid is needed as an intermediate phase to transfer the shear force generated by the screw to pull the PTFE into fibers. The processing aid needs to have adjustable fluidity and viscosity within the melting temperature range to transfer shear force during processing. After processing, the processing aid needs to be removed, and the prepared film has a porous structure by etching away the processing aid.

[0015] The PTFE microporous fiber membrane prepared by the preparation method of the present invention has the advantages of high strength, high porosity, small pore size, etc., and can meet the use requirements of the electromagnetic shielding layer of flexible wearable electronic devices. When the PTFE microporous fiber membrane has a high porosity, it can have good air permeability, thereby improving the comfort of wearing. As the base layer of the MXene conductive two-dimensional material layer, the PTFE microporous fiber membrane needs to have good mechanical properties and environmental resistance.

[0016] In addition, the electromagnetic shielding principle of the Janus microporous fiber membrane of the present invention is: when the electromagnetic wave is incident from the MXene side, the Janus film attenuates the electromagnetic wave through the reflection-absorption mechanism; when the electromagnetic wave is incident from the PTFE-based film side, the Janus film attenuates the electromagnetic wave through the absorption-reflection-reabsorption mechanism. Although there is no difference in shielding effectiveness when electromagnetic waves are incident from different directions, when incident from the PTFE-based side, the film can dissipate more electromagnetic energy through internal absorption, thereby greatly reducing secondary pollution caused by reflection. The filler inside the PTFE-based film mainly plays the role of absorbing electromagnetic waves, so in order to improve the absorption performance of electromagnetic waves, it is necessary to increase the amount of filler as much as possible.

[0017] The inventor has tried a lot of methods of filling fillers in the process of the experiment, such as processing after PTFE raw material powder or emulsion is blended with fillers, but due to the low surface energy of PTFE, the modified filler and the matrix interface are poorly combined and easily reunited. In addition, when PTFE is filled and modified, it is impossible to add a high concentration of modified fillers, otherwise the PTFE processing process stress concentration and fracture will be caused. Therefore, how to add a high-content modified filler in the modification process, the functionalized PTFE porous material with excellent electrical conductivity, thermal conductivity, mechanical property, shielding property, hydrophobicity, light absorption performance, etc., prepared by the intrinsic properties and special structure between PTFE and the modified filler, also becomes a problem.

[0018] The method for preparing the PTFE-based composite film with a microporous fiber network structure of the present invention, during the in-situ fiber-forming process of PTFE, the added modified filler is evenly and firmly fixed in the formed uniform micropores, effectively solving the problem of agglomeration of the modified filler, and can achieve the filling of a large amount of modified filler, thereby helping to improve the electromagnetic wave absorption performance of the Janus microporous fiber membrane.

[0019] In addition, since the PTFE microporous fiber membrane prepared by the present invention has high strength, high porosity and small pore size, a MXene conductive two-dimensional material layer can be deposited on the PTFE-based composite film by vacuum filtration and other methods, and since the micropores in the composite film are evenly distributed, the deposited MXene conductive two-dimensional material layer is relatively flat and uniform, thereby reducing the performance loss caused by local structural defects.

[0020] The present invention strategically regulates the composition and conductivity at different positions of the film, so that the loss mode and path of electromagnetic waves on both sides of the film are different, thereby promoting an efficient electromagnetic wave shielding mechanism of "absorption-reflection-reabsorption". The advantage of this method is that a PTFE-based microporous composite film with a high filler concentration can be obtained through an innovative and simple blending method. The processing process is highly controllable, the equipment cost is low, and the production is efficient, which can be applied to large-scale industrial production; secondly, the PTFE-based composite membrane manufactured by this process has a unique nanofiber network structure, which has a high porosity, a small pore size, and excellent mechanical strength and flexibility, which can support subsequent processing and be used in the field of flexible wearables.

[0021] In some embodiments, the processing aid is selected from polyethylene, polylactic acid, polyvinyl chloride, polyamide, polyvinyl alcohol, polyethylene glycol, polystyrene, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate or paraffin.

[0022] In some embodiments, the modified filler is a conductive filler, a magnetic filler, a thermally conductive filler, an optical modifier, a fluorescent agent, a lubricant, or a toughening agent.

[0023] Preferably, the conductive filler is selected from carbon fiber, liquid metal, carbon nanotube, graphene or two-dimensional MXene.

[0024] Preferably, the magnetic filler is selected from ferrosoferric oxide or iron-cobalt alloy.

[0025] Preferably, the thermally conductive filler is selected from boron nitride, metal oxide or graphite.

[0026] Preferably, the optical modifier is selected from silicon dioxide or titanium dioxide.

[0027] In some embodiments, the PTFE is added in the form of PTFE emulsion or PTFE powder.

[0028] Preferably, in the blended product, the mass fraction of PTFE is 1-50%, preferably 10-40%.

[0029] In some embodiments, the shear blending temperature is 10-60°C higher than the melting point of the processing aid, the shear rate is 60-140 rpm, and the shear blending time is 5-30 minutes, so as to ensure that the PTFE can be fully fiberized and the polymer will not be carbonized, thereby regulating factors such as the fiberization degree and porosity of the PTFE-based composite film.

[0030] Preferably, the shear blending equipment is a twin-screw extruder, an internal mixer or an open mixer.

[0031] In some embodiments, the compression molding method is molding or roller pressing.

[0032] Preferably, the molding or rolling pressure is 80-120 MPa, the temperature is 40-60° C., and the time is 20-40 minutes.

[0033] Specifically, the pressure is 100 MPa, the temperature is 50°C, and the time is 30 minutes to improve the stability of the Janus film structure.

[0034] In some embodiments, the Janus microporous fiber membrane has a thickness of 0.01-3 mm.

[0035] In some embodiments, solvent etching is used to remove the processing aid in the thin film, and the solvent is selected from water, chloroform, dimethylformamide, dimethyl sulfoxide, xylene, methanol, ethanol, dichloromethane, acetone or carbon tetrachloride.

[0036] Preferably, the etching method is Soxhlet extraction, which is specifically as follows: the film to be etched is placed in an extraction tube, a solvent for dissolving the processing aid is added to the extraction bottle, and the solvent is heated to vaporize, thereby repeatedly washing the film to completely remove the processing aid.

[0037] In some embodiments, when one side of the PTFE-based composite film is subjected to plasma treatment, the plasma treatment time is 15-30 minutes.

[0038] Through plasma treatment, functional groups are grafted onto one side of the PTFE film, making the plasma-treated side hydrophilic and the other side hydrophobic. The hydrophilic side is firmly bonded to the MXene conductive two-dimensional material layer, effectively preventing the MXene conductive two-dimensional material layer from falling off.

[0039] The plasma is an ionized gas composed of electrons, ions, atoms and molecules, etc., and has high reactivity. Polar groups can be introduced into the surface of the PTFE-based composite film, thereby improving the wettability, adhesion and other properties of the material.

[0040] In some embodiments, the method of depositing a MXene conductive two-dimensional material layer on the surface of the substrate layer is: 3 AlC 2 Ti is etched by heating in a mixed solution of hydrochloric acid and lithium fluoride. 3 AlC 2 The mass ratio of lithium fluoride to lithium fluoride is 1:1.6, the etching temperature is 35-40°C, the etching time is 48 hours, and the etched solid is washed to a pH value greater than 6.

[0041] To prevent MXene from oxidation during treatment, it was ultrasonically treated in an ice bath for 30–60 min and exfoliated to obtain a few-layer MXene (1–10 layers) dispersion;

[0042] The few-layer MXene dispersion is deposited on the substrate by vacuum filtration to obtain the MXene. The few-layer MXene has a large interlamellar spacing and a high specific surface area, which is conducive to constructing a porous structure and improving filtration efficiency and selectivity. The few-layer MXene has more exposed active groups (such as -OH, -F, -O) on the surface, which is conducive to its combination with the PTFE-based composite film.

[0043] Preferably, per gram of Ti 3 AlC 2 20 mL of 9 mol / L hydrochloric acid is required.

[0044] Preferably, the thickness of the MXene conductive two-dimensional material layer is 5-35 μm.

[0045] In a second aspect, the present invention provides a Janus microporous fiber membrane prepared by the preparation method.

[0046] In a third aspect, the present invention provides the use of the Janus microporous fiber membrane in the preparation of an electromagnetic shielding element.

[0047] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0048] 1) The PTFE-based microporous fiber membrane prepared by direct blending does not require a series of complex processes such as pre-extrusion, calendering, aging, stretching, and sintering in traditional processes; the equipment investment is small and does not require a large number of expensive equipment in traditional processes;

[0049] The unique shear-induced in-situ fiber-forming process can introduce a high content of modified fillers into the PTFE-based composite film, thereby effectively improving the electromagnetic wave absorption performance of the composite film; the resulting PTFE-based composite film has high porosity, small pore size, and good strength and flexibility.

[0050] 2) Most MXene films / papers have poor mechanical properties and are easily damaged by oxidation in humid environments due to their inherent rigidity, brittleness and poor chemical stability, which greatly limits their application in the field of flexible wearables. The PTFE-based substrate layer can not only improve the overall mechanical properties of the Janus film, but also has excellent hydrophobicity and chemical corrosion resistance. During use, the hydrophobic and chemically resistant PTFE-based substrate layer can be placed outward to resist the entry of water vapor and external corrosive gases, which can prevent the MXene layer from being damaged by oxidation and protect the MXene layer, thereby increasing the service life of the film.

[0051] 3) The MXene conductive reflective layer is compounded with the PTFE-based electromagnetic wave absorption layer. The two sides of the film of the present invention have different protection characteristics against electromagnetic waves. When the electromagnetic wave is incident from the MXene side, the Janus film attenuates the electromagnetic wave through the reflection-absorption mechanism; when the electromagnetic wave is incident from the PTFE-based film side, the Janus film attenuates the electromagnetic wave through the absorption-reflection-reabsorption mechanism. Although there is no difference in shielding effectiveness when electromagnetic waves are incident from different directions, when incident from the PTFE-based side, the film can dissipate more electromagnetic energy through internal absorption, thereby greatly reducing secondary pollution caused by reflection. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0053] Figure 1 It is a process flow chart of the preparation of the Janus microporous fiber membrane provided in an embodiment of the present invention.

[0054] Figure 2 This is a real picture of the CNT / PTFE-MXene film sample prepared in Example 1.

[0055] Figure 3 This is a microscopic electron microscope image of the MXene side in the CNT / PTFE-MXene film prepared in Example 1.

[0056] Figure 4 This is a microscopic electron microscope image of the CNT / PTFE side in the CNT / PTFE-MXene film prepared in Example 1.

[0057] Figure 5 The CNT / Fe prepared in Example 2 3 O 4 / Real photos of PTFE-MXene film samples.

[0058] Figure 6 The CNT / Fe prepared in Example 2 3 O 4 CNT / Fe / PTFE-MXene film 3 O 4 / Microscopic electron microscope image of PTFE side.

[0059] Figure 7 The TiO prepared in Example 3 2 / SiO 2 / Real photos of PTFE-MXene film samples.

[0060] Figure 8The TiO prepared in Example 3 2 / SiO 2 TiO in PTFE-MXene films 2 / SiO 2 / Microscopic electron microscope image of PTFE side.

[0061] Fig. 9 The TiO prepared in Example 3 2 / SiO 2 Water contact angle of / PTFE superhydrophobic film. DETAILED DESCRIPTION

[0062] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0063] The present invention will be further described below in conjunction with the embodiments.

[0064] Example 1

[0065] A method for preparing a Janus microporous fiber membrane with excellent electromagnetic shielding performance, such as Figure 1 As shown, the specific preparation steps are as follows:

[0066] Take carbon nanotubes (CNT) as conductive modified filler, polyvinyl alcohol (PVA, whose melting temperature is 190℃) as processing aid and PTFE for extrusion to prepare CNT / PTFE microporous composite film. PVA, PTFE and CNT are dried in an oven at 65℃ for 24 hours. The blending device is a mixer, the film making device is a hot press, and the washing agent is water.

[0067] In the first step, CNT particles and PTFE powder (the relative molecular mass of PTFE is 4×10 6 g / mol), PVA particles were mixed evenly in a sealed bag, and then the internal mixer was preheated to 190°C.

[0068] The second step is to turn on the screw rotation switch of the internal mixer after the preheating is completed, and gradually add the evenly mixed raw materials into the internal mixer through the feeding port. The processing time is set to 10 minutes and the shear rate is controlled to 80 rpm.

[0069] The third step is to open the internal mixer after the cycle is completed. After the molten blend is cooled and solidified, it is rolled into a film at 180°C through an open mixer to obtain a blend film with a thickness of 0.1 mm.

[0070] In the fourth step, the film was cut into a circle with a radius of 3 cm, and then placed in a flowing water source for 4 hours to completely remove the PVA in the blend. After washing, the CNT / PTFE composite film was taken out and then dried at room temperature. One side of the film was encapsulated for protection, and the other side was facing up and plasma treated in a nitrogen environment for 15 minutes.

[0071] Step 5: Add 30 mL of concentrated hydrochloric acid to 10 mL of deionized water to prepare a 9 mol / L hydrochloric acid solution, then add 3.2 g of lithium fluoride and stir for 30 minutes. 3 AlC 2 Slowly add it into the above mixed solution, stir in a 40°C water bath for 48 hours, and set the stirring speed to 400 rpm.

[0072] Step 6: After etching, remove the excess acid solution on the upper layer, and wash the lower black solid with deionized water for 10 times until the pH of the upper clear liquid is greater than 6. The centrifuge speed is gradually increased from 2000 rpm to 10000 rpm with the number of washings. The washed multilayer MXene is ultrasonically treated in an ice bath for 40 minutes to obtain a few-layer MXene dispersion, which is then diluted with deionized water to a concentration of 2 g / mL.

[0073] In the seventh step, the hydrophilic CNT / PTFE film after plasma treatment was placed on one side facing up, and then 15 mL of the few-layer MXene solution was deposited on the film by vacuum filtration.

[0074] In the eighth step, the film was pressed on a hot press at 10 MPa and 50°C for 30 minutes. After the pressing, the Janus film was taken out and dried in a vacuum oven at 120°C.

[0075] In this embodiment, the obtained CNT / PTFE-MXene-based electromagnetic shielding film is as follows Figure 2 As shown, the film exhibits an obvious Janus structure, in which the CNT / PTFE side is hydrophobic with a water contact angle of about 142°, and the MXene side is hydrophilic with a water contact angle of about 47°.

[0076] The side surface of MXene is smooth and flat, with uniform morphology and structure. Figure 3 The porous fiber structure inside the CNT / PTFE side is shown in Figure 4As shown, PTFE fibers and thinner CNT fibers are interlaced in the surrounding gaps. According to the measurement, the porosity of the CNT / PTFE side film is about 76%, the overall tensile strength of the film is about 30 MPa, the elongation at break is greater than 50%, the conductivity of the CNT / PTFE side is about 5 S / cm, the conductivity of the MXene side is about 474 S / cm, the shielding effectiveness of the film is 42 dB, and the absorption coefficient is 0.06 when the electromagnetic wave is incident from the MXene side, and the absorption coefficient is 0.28 when it is incident from the CNT / PTFE side. It can be seen that the absorption capacity of the film has been improved to a certain extent when incident from the CNT / PTFE side.

[0077] Example 2

[0078] A method for preparing a Janus microporous fiber membrane with excellent electromagnetic shielding performance comprises the following steps:

[0079] Carbon nanotubes (CNT, outer diameter between 1.2-2nm) and ferroferric oxide (Fe 3 O 4 , particle size of about 50nm) as modified filler, polylactic acid (PLA) as processing aid and PTFE were blended and extruded to prepare CNT / Fe 3 O 4 / PTFE microporous composite film as an example. 3 O 4 , PTFE (the relative molecular mass of PTFE is 4×10 6 g / mol), CNT was dried in an oven at 65°C for 24 hours. The blending device was a twin-screw extruder, the film-making device was a hot press, and the washing agent was dichloromethane.

[0080] In the first step, CNT particles, PTFE powder, and Fe 3 O 4 The pellets and PLA pellets were mixed evenly in a sealed bag, and then the twin-screw extruder was preheated to 190°C.

[0081] The second step is to turn on the screw switch of the twin-screw extruder after the preheating is completed, adjust the extrusion mode to the circulation mode, and then gradually add the evenly mixed raw materials into the twin-screw extruder. The blending time is set to 12 minutes and the shear rate is 100 rpm.

[0082] The third step is to start the extrusion mode, and after the molten blend is cooled and solidified, transfer it to a hot press and press it at a pressure of 10 MPa to obtain a blend film with a thickness of 0.2 mm.

[0083] In the fourth step, the film was cut into a circle with a radius of 3.5 cm, and then immersed in 500 mL of dichloromethane for 10 hours, and then repeatedly washed with a Soxhlet extraction device to completely remove the PLA phase in the blend. 3 O 4 / PTFE composite film, and then dried at room temperature. One side of the film was encapsulated for protection, and the other side was facing up and treated in a nitrogen plasma environment for 15 minutes.

[0084] The subsequent preparation steps and hot pressing process of the few-layer MXene dispersion are consistent with those in Example 1.

[0085] In this example, the obtained CNT / Fe 3 O 4 / PTFE-MXene based electromagnetic shielding films such as Figure 5 As shown, the film exhibits an obvious Janus structure, in which CNT / Fe 3 O 4 / PTFE side is hydrophobic, with a water contact angle of about 148°, and MXene side is hydrophilic, with a water contact angle of about 52°. 3 O 4 / PTFE side internal fiber porous structure such as Figure 6 As shown, Fe 3 O 4 The nanoparticles are firmly bound in the nanofiber network.

[0086] It was determined that CNT / Fe 3 O 4 The porosity of the film on the CNT / PTFE side is about 71%, the overall tensile strength of the film is about 27 MPa, the elongation at break is greater than 45%, and the saturation magnetization of the film is 22.24 emu / g. 3 O 4 The conductivity of the CNT / PTFE side is about 0.1 S / cm, the conductivity of the MXene side is about 462 S / cm, the shielding effectiveness of the film is 47 dB, the absorption coefficient of the electromagnetic wave is 0.09 when it is incident from the MXene side, and the absorption coefficient is 0.51 when it is incident from the CNT / PTFE side. 3 O 4 Nanoparticles greatly improve the electromagnetic wave absorption capacity of Janus film through the attenuation mode of magnetic loss and enhance the overall shielding effectiveness of the film.

[0087] Example 3

[0088] A method for preparing a Janus microporous fiber membrane with excellent electromagnetic shielding performance, the specific steps are as follows: titanium dioxide (TiO 2, average particle size 50nm) and silicon dioxide (SiO 2 , average particle size 200nm) as modified filler, polymethyl methacrylate (PMMA) as processing aid and PTFE were blended and extruded to prepare TiO 2 / SiO 2 / PTFE microporous composite film as an example. 2 ,PTFE,TiO 2 The mixture was dried in an oven at 65°C for 24 hours. The blending device was a twin-screw extruder, the film-making device was a hot press, and the washing agent was N,N-dimethylformamide.

[0089] The first step is to pre-mix SiO 2 Particles, TiO 2 The pellets, PTFE powder and PLA pellets were mixed evenly in a sealed bag, and then the twin-screw extruder was preheated to 210°C.

[0090] The second step is to turn on the screw switch of the twin-screw extruder after the preheating is completed, adjust the extrusion mode to the circulation mode, and then gradually add the evenly mixed raw materials into the twin-screw extruder, set the blending time to 12 minutes, and control the shear rate to 60 rpm.

[0091] The third step is to start the extrusion mode. After the molten blend is cooled and solidified, it is transferred to a hot press and pressed at a pressure of 10 Mpa to obtain a blend film with a thickness of 1 mm.

[0092] In the fourth step, the film was cut into squares with a side length of 5 cm, and then immersed in 500 mL of DMF for 12 h, and then repeatedly washed with clean DMF to completely remove the PLA phase in the blend. 2 / SiO 2 / PTFE composite film, and then dried at room temperature. One side of the film was encapsulated for protection, and the other side was facing up and treated in a nitrogen plasma environment for 15 minutes.

[0093] The subsequent preparation steps and hot pressing process of the few-layer MXene dispersion are consistent with those in Example 1.

[0094] In this example, the TiO 2 / SiO 2 / PTFE-MXene based electromagnetic shielding films such as Figure 7 As shown, the film exhibits an obvious Janus structure, in which TiO 2 / SiO 2 / PTFE film water contact angle is about 152°, reaching a super hydrophobic state, such as Fig. 9shown.

[0095] TiO 2 / SiO 2 / PTFE film internal fiber porous structure such as Figure 8 As shown, the smaller TiO 2 Nanoparticles and larger SiO 2 The nanoparticles are firmly bound in the nanofiber network. 2 / SiO 2 The porosity of the PTFE film is about 81%, and the water vapor permeability of the film as a whole is 7934.51 g·m -2 ·24h -1 The overall tensile strength of the film is about 34 MPa, the elongation at break is greater than 60%, the electrical conductivity of the MXene film is about 512 S / cm, and the overall shielding effectiveness of the film is 39 dB.

[0096] Comparative Example 1

[0097] Compared with Example 2, the difference is that a MXene dispersion is first prepared, as in Example 1, and then freeze-dried for 48 hours to prepare a MXene powder.

[0098] In step 1, CNT particles, PTFE powder, and Fe 3 O 4 The particles, MXene powder, and PLA particles are directly twin-screw blended to prepare CNT / Fe 3 O 4 / MXene / PTFE homogeneous film.

[0099] In this comparative example, CNT / Fe 3 O 4 The water contact angle of the / MXene / PTFE film is about 93°, the tensile strength is about 17 MPa, the elongation at break is greater than 35%, the film saturation magnetization is 23.92 emu / g, the electrical conductivity is about 72 S / cm, the film shielding effectiveness is 31 dB, and the absorption coefficient when electromagnetic waves are incident is 0.21.

[0100] Compared with Example 2, the hydrophobic angle and mechanical strength of the homogeneous film are greatly reduced due to the introduction of MXene, and the MXene layer will oxidize during high-temperature thermal processing, thereby greatly reducing the electromagnetic shielding performance of the film. This comparative example highlights the importance of preparing the MXene conductive layer by layered filtration.

[0101] Comparative Example 2

[0102] Compared with Example 2, the difference is that in step 4, CNT / Fe3 O 4 Both sides of the PTFE / PTFE composite film were plasma treated in a nitrogen atmosphere for 15 minutes, and then 7.5 mL of the few-layer MXene solution was deposited on both sides of the film by a vacuum filtration device.

[0103] The film was then pressed on a hot press at 10 MPa and 50°C for 30 minutes, and then taken out and dried in a vacuum oven at 120°C. The prepared film does not have a janus structure, and both sides of the film are covered with hydrophilic MXene.

[0104] In this comparative example, the water contact angle on both sides of the film is 53°, and the film as a whole is not hydrophobic. The overall tensile strength of the film is about 25 MPa, the elongation at break is greater than 44%, the film saturation magnetization is 20.19 emu / g, the conductivity is about 349 S / cm, the film shielding effectiveness is 44 dB, and the absorption coefficient when electromagnetic waves are incident is 0.11.

[0105] Compared with Example 2, the film without the Janus structure not only has no PTFE-based hydrophobic layer to protect it, but also most of the electromagnetic waves will be reflected due to the strong impedance mismatch effect at the interface between the MXene layer and the air, which is likely to cause secondary electromagnetic pollution. This comparative example highlights the superiority of the Janus structure.

[0106] Comparative Example 3

[0107] Compared with Example 2, the difference is that no modified filler is added to PTFE, and only PTFE powder and PLA particles with a mass ratio of 10:80 are directly twin-screw blended, and then prepared into a pure PTFE homogeneous film after subsequent pressing and etching, and cut into a circle with a radius of 3 cm.

[0108] 5 mg of CNT particles and 5 mg of Fe 3 O 4 50 mg of particles and 30 mg of MXene powder were ultrasonically treated in deionized water for 30 minutes, and then deposited on the plasma-treated side through a vacuum filtration device to prepare PTFE-CNT / Fe 3 O 4 / MXene film.

[0109] In this comparative example, the film exhibits an obvious Janus structure, in which the PTFE side is hydrophobic with a water contact angle of about 138°, and the CNT / Fe 3 O 4 / MXene side is hydrophilic, and the water contact angle is about 61°. According to the measurement, the porosity of the PTFE side film is about 65%, the overall tensile strength of the film is about 26 MPa, the elongation at break is greater than 42%, and the saturation magnetization of the film is 21.52 emu / g. One side of the film is insulating, and the other side is conductive. 3 O 4 The conductivity of the / MXene side is about 479 S / cm, and the overall shielding effectiveness of the film is 45 dB. Electromagnetic waves are incident from both sides of the film, making the absorption coefficient basically consistent, both around 0.14.

[0110] Compared with Example 2, when CNT and Fe 3 O 4 When added to MXene, since pure PTFE film has almost no effect on electromagnetic shielding performance, the composite film cannot form an "absorption-reflection-reabsorption" electromagnetic shielding mechanism, and most electromagnetic waves are re-reflected into free space by the high-conductivity MXene layer. This comparison reflects the differences in the synergy between the components and highlights the importance of rationally allocating the location of the modified filler.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a Janus microporous fiber membrane, characterized in that: The steps include: After mixing polytetrafluoroethylene with a relative molecular mass greater than 1 million, a modified filler and a processing aid in proportion, shear blending is performed to make the polytetrafluoroethylene in situ fiberized to obtain a blended product; the processing aid is selected from polyethylene, polylactic acid, polyvinyl chloride, polyamide, polyvinyl alcohol, polyethylene glycol, polystyrene, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate or paraffin; Processing the blended product into a film, and removing the processing aid in the film by etching, to obtain a PTFE-based composite film with a microporous fiber network structure; One side of the PTFE-based composite film is encapsulated and protected, and the other side is plasma treated in an inert atmosphere to form a base layer; A MXene conductive two-dimensional material layer is deposited on the surface of the substrate layer, and the layer is pressed into shape to obtain a Janus microporous fiber membrane; The filler inside the PTFE-based composite film mainly plays the role of absorbing electromagnetic waves.

2. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: The modified filler is a conductive filler or a magnetic filler; The conductive filler is selected from carbon fiber, liquid metal, carbon nanotube, graphene or two-dimensional MXene; The magnetic filler is selected from ferrosoferric oxide or iron-cobalt alloy.

3. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: The PTFE is added in the form of PTFE emulsion or PTFE powder; In the blended product, the mass fraction of PTFE is 5%-50%.

4. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: The shear blending temperature is 10-60° C. higher than the melting point of the processing aid, the shear rate is 60-140 rpm, and the shear blending time is 5-30 minutes.

5. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: The compression molding method is molding or rolling; the molding or rolling pressure is 80-120 MPa, the temperature is 40-60° C., and the time is 20-40 minutes.

6. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: The processing aid in the film is removed by solvent etching, wherein the solvent is selected from water, chloroform, dimethylformamide, dimethyl sulfoxide, xylene, methanol, ethanol, dichloromethane, acetone or carbon tetrachloride; The etching method is Soxhlet extraction, which is as follows: the film to be etched is placed in an extraction tube, a solvent is added to an extraction bottle, and the solvent is heated to vaporize, thereby repeatedly washing the film to completely remove the processing aid.

7. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: When one side of the PTFE-based composite film is subjected to plasma treatment, the plasma treatment time is 15-30 minutes.

8. The method for preparing the Janus microporous fiber membrane according to claim 1, characterized in that: The method for depositing a MXene conductive two-dimensional material layer on the surface of the substrate layer is as follows: heating and etching Ti3AlC2 in a mixed solution of hydrochloric acid and lithium fluoride, the mass ratio of Ti3AlC2 to lithium fluoride being 1:1.5-2, the etching temperature being 35-40°C, the etching time being 48h, washing the etched solid to a pH value greater than 6, and then ultrasonically treating it in an ice bath for 30-60 minutes, and peeling off to obtain a few-layer MXene dispersion; The few-layer MXene dispersion is deposited on the substrate layer by vacuum filtration to obtain the product.

9. A Janus microporous fiber membrane, characterized in that: Prepared by the preparation method described in any one of claims 1 to 8.

10. Use of the Janus microporous fiber membrane according to claim 9 in the preparation of electromagnetic shielding elements.

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