Layered porous composite membrane with orientation and preparation method and application thereof

Abstract

The invention belongs to the technical field of functional composite materials and electromagnetic shielding films, and particularly relates to an oriented layered porous composite film as well as a preparation method and application thereof. The spinning solution is continuously extruded through a mold with a rectangular slit outlet, and the formed jet flow directly enters a coagulating bath system and is cured through a gelation process to form a continuous gel film; and washing the gel film with water, and subsequently carrying out confinement pre-freezing shaping and freeze drying in sequence to obtain the oriented layered porous composite film. The oriented layered porous composite membrane is obtained on the basis of long runner shearing and confinement freeze drying, the preparation process is continuous, large-area preparation is facilitated, meanwhile, the obtained composite membrane shows a low-density, high-orientation and communicated layered pore structure, good mechanical strength is kept, and meanwhile, the oriented layered porous composite membrane has a good application prospect. Excellent electromagnetic shielding effectiveness and electric heating performance are shown, and a novel high-performance material choice is provided for the field of electromagnetic protection.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials and electromagnetic shielding film technology, and specifically relates to an oriented layered porous composite film, its preparation method and application. Background Technology

[0002] With the rapid development of 5G communication, vehicle-mounted radar, and high-power electronic devices, the operating frequency of electronic systems is constantly increasing, the electromagnetic environment in space is becoming increasingly complex, and electromagnetic radiation pollution is becoming more and more prominent. Long-term exposure to strong electromagnetic fields can not only interfere with the normal operation of precision instruments but may also pose potential health hazards. Therefore, developing novel electromagnetic shielding materials that combine high-efficiency shielding, lightweight flexibility, and ease of processing is of great significance. Polymer-based composite materials are considered ideal candidates for shielding materials due to their low density, ease of processing, and corrosion resistance. By introducing conductive fillers (such as metal particles, carbon nanotubes, graphene, and MXene) into the polymer matrix to construct a conductive network, certain shielding performance can be achieved.

[0003] In existing electromagnetic shielding material fabrication processes, common film-forming methods include vacuum filtration, blade coating, casting, or tape casting. These methods are inefficient and discontinuous, and the resulting materials often have high density, which is not conducive to lightweight design. Furthermore, insufficient multiple reflections and loss paths hinder further enhancement of electromagnetic shielding effectiveness. Therefore, it is crucial to develop new molding processes to construct composite films with oriented layered porous structures while maintaining continuous fabrication capabilities. This would reduce material density, improve conductive network efficiency, and enhance multiple reflections and absorption of electromagnetic waves, ultimately achieving lightweight and efficient electromagnetic shielding. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing electromagnetic shielding material preparation processes by providing a new preparation method that can obtain an oriented layered porous composite membrane while ensuring continuous preparation capability; the obtained oriented layered porous composite membrane has low material density and high-efficiency electromagnetic shielding.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An oriented layered porous composite membrane is obtained by the following method: the spinning solution is continuously extruded through a die with a rectangular slit outlet, and the resulting jet directly enters the coagulation bath system, where it is solidified through a gelation process to form a continuous gel membrane; the gel membrane is washed with water, and then subjected to confined pre-freezing and confined freeze-drying in sequence to obtain an oriented layered porous composite membrane.

[0006] The spinning solution is obtained by mixing a conductive filler dispersion with a gelling material; The conductive filler is one or more of MXene, graphene, or MoS2; the gelling material is one or more of alginate, aramid nanofibers, silk fibroin, cellulose, or chitosan.

[0007] The spinning solution of the present invention exhibits shear-thinning behavior of a non-Newtonian fluid and viscoelastic properties with a storage modulus greater than the loss modulus.

[0008] The flow channel of the spinning solution in the mold is rectangular, and the length-to-diameter ratio of the flow channel is 3-100:1; the preferred length-to-diameter ratio of the flow channel is 60:1.

[0009] The rectangular slit outlet of the mold has a width of 30-100 mm and a height of 0.5-3 mm; preferably, the width of the rectangular slit outlet is 30 mm and the height is 1 mm.

[0010] The rectangular flow channel in the mold has a high aspect ratio, which is the ratio of the channel's length to its height. This aspect ratio allows for the application of a planar shear flow field to the high-viscosity spinning solution. Preferably, the width and height of the flow channel are consistent with the width and height of the rectangular slit outlet.

[0011] The flow rate of the spinning solution in the mold is 0.5-10 mL / min; preferably, the flow rate is 2 mL / min.

[0012] Furthermore, the temperature of the coagulation bath system is 10-60℃, and the coagulation time is 1-2 h; preferably, the temperature of the coagulation bath system is 25-30℃.

[0013] The above process can be summarized as "long-channel shear wet spinning", which is a continuous film-forming process that uses a rectangular channel with a high aspect ratio to apply a planar shear flow field to a high-viscosity spinning solution and directly contacts the coagulation bath at the channel outlet to complete gelation. This process can induce the orientation of sheet fillers and polymer chains along the flow direction on a macroscopic scale and fix the orientation structure during the cross-linking and curing process.

[0014] Furthermore, the washed gel film is laid flat between the upper and lower mold plates for subsequent confined pre-freezing and freezing operations. The gap between the upper and lower mold plates is 0.5-3 mm, which is the thickness of the film. Preferably, the gap thickness between the upper and lower mold plates is 1 mm.

[0015] The freezing process of the gel membrane in this invention is an improvement upon existing methods, and it further addresses the shortcomings of current preparation processes, such as warping, wrinkling, and uneven thickness during freeze-drying. These defects include the collapse and wrinkling of internal nanosheets, which disrupts the previously formed orientation structure, resulting in poor membrane smoothness and thickness uniformity, and consequently reduced mechanical properties and conductivity network continuity. Therefore, the above steps, while maintaining the high orientation advantages of long-channel wet spinning, introduce a controllable porous structure and effectively suppress drying shrinkage.

[0016] Furthermore, the pre-freezing temperature is -20 to 0 ℃, and the pre-freezing time is 12 to 24 h; The freeze-drying vacuum degree is 1-10 Pa, the freezing temperature is -50 ℃ to -40 ℃, and the freeze-drying time is 48-72 h.

[0017] The above process can be summarized as "confined freeze-drying". By clamping the wet gel film between two parallel flat molds and limiting the thickness of the gel film with spacers of fixed thickness, the shaping and freeze-drying process is completed in the clamped state. In this process, the gel film is mechanically limited in the thickness direction, thereby effectively avoiding deformation problems such as uneven thickness, warping, wrinkling and edge curling that are common in free freeze-drying.

[0018] The preparation method described in this invention, specifically, most preferably includes the following steps: 1) The conductive filler dispersion and the gelling material are mixed in a certain proportion, stirred evenly, and then vacuum degassed to obtain the spinning solution. The total solid content of the spinning solution is 20-60 mg / ml; the proportion is the mass ratio of conductive filler to gelling material of 1:0.3-9.

[0019] 2) The spinning solution from step 1) is continuously extruded through a rectangular die with a rectangular slit outlet. The spinning solution is fully stretched and oriented under the shearing action of the long flow channel. Then, it enters the coagulation bath directly from the die outlet in the form of a jet. Under the synergistic effect of shearing orientation and cross-linking curing, a gel film is formed. The obtained gel film is washed with water to remove the residual solvent in the coagulation bath. 3) Confined Freeze-drying: The gel membrane obtained in step 2) is laid flat on the surface of the lower mold plate. Spacers of the same thickness as the membrane are placed around the gel membrane. The upper mold plate is then covered, and the upper and lower molds are clamped together using clamps or bolts, so that the gel membrane is held between the two parallel and flat molds. The gap between the molds is limited by the spacers to set the target membrane thickness. The clamping assembly is pre-frozen to allow the aqueous phase inside the gel to grow directionally in the confined space to form an ice crystal layer structure. Subsequently, freeze-drying is performed to sublimate the ice crystals inside the gel, resulting in a composite membrane with controllable thickness, flat surfaces, and an oriented layered porous structure.

[0020] The oriented layered porous composite membrane obtained by the above preparation method has the appearance characteristics of flat surfaces and controllable thickness. It is composed of a gelled material matrix and conductive fillers, and simultaneously constructs an oriented layered porous structure and a two-dimensional conductive network inside. The composite membrane has a highly oriented layered porous structure. The gelled material and conductive fillers are stacked and arranged basically parallel to the membrane surface. Two-dimensional conductive nanosheets are oriented and connected along the layers to form a two-dimensional conductive network, forming a continuous conductive path. The membrane cross-section has a layered porous structure, and through or semi-through sheet-like channels are formed between the layers, which can provide multiple electromagnetic reflection interfaces and interfacial polarization sites.

[0021] This composite membrane exhibits a low-density, high-orientation, and interconnected layered porous structure. While maintaining good mechanical strength, lightweight and flexible properties, it also demonstrates excellent electromagnetic shielding effectiveness and electrothermal performance, providing a new high-performance material option for the field of electromagnetic protection and possessing broad practical application prospects.

[0022] The oriented layered porous composite membrane obtained by this invention can be well applied in electromagnetic protection, thermal management, and wearable electronic devices.

[0023] The preparation principle of this invention is as follows: First, a long-channel shear wet spinning process is used to allow the spinning solution to undergo stable planar shearing and moderate stretching, so that the molecular chains of the gelled material and the two-dimensional nanosheets are aligned along the flow direction and rapidly cross-linked and solidified in a coagulation bath to form a continuous gel membrane with initial orientation; then, a confined freeze-drying process is used to freeze and sublimate within a limited thickness space. During the freezing process, ice crystal layers parallel to the membrane surface are formed. After sublimation, sheet-like channels are left in the gel skeleton, and finally a composite membrane with an internally oriented layered porous structure, controllable thickness, and flat surfaces is obtained.

[0024] In general, the present invention has the following advantages: 1) By adopting the long-channel shear wet spinning process, the high-orientation stacking of two-dimensional conductive nanosheets and gelled materials is achieved on a macroscopic scale through the strong planar shear field of the mold. The resulting gel skeleton provides an ordered template for the subsequent layered porous structure, so that the final composite membrane has a high degree of orientation.

[0025] 2) By using the confined freeze-drying process, the thickness and deformation of the gel membrane are effectively constrained while forming a layered porous structure, avoiding the problems of membrane warping, wrinkling and uneven thickness caused by traditional free freeze-drying. The resulting composite membrane has a smooth surface, controllable thickness and stable dimensions, which facilitates the assembly of actual devices and large-area applications.

[0026] 3) The two-dimensional conductive network constructed from two-dimensional conductive nanosheets, combined with the layered porous structure, provides abundant multiple reflection and interface polarization positions while ensuring high conductivity, thereby further enhancing the electromagnetic shielding performance. High electromagnetic shielding performance can be obtained with low filler content, balancing shielding efficiency and material lightweight.

[0027] 4) Wet spinning is a continuous preparation process that is quick, easy to operate, environmentally friendly, and can be used for large-scale production.

[0028] Compared with the prior art, the present invention has the following advantages: This invention yields an oriented layered porous composite membrane with a continuous preparation process that facilitates large-area fabrication. The resulting composite membrane exhibits low density, high orientation, and a connected layered porous structure. While maintaining good mechanical strength, it also demonstrates excellent electromagnetic shielding effectiveness and electrothermal performance, providing a novel high-performance material option for the field of electromagnetic protection. Attached Figure Description

[0029] Figure 1 The images above and below show actual photos of the mold device and composite film used in the embodiments of the present invention. Figure 2 The images are cross-sectional SEM images of the composite membrane, including (a) Example 1, (b) Example 2, and (c) Example 3; Figure 3 The cross-sectional SEM images of the composite membrane include (a) Comparative Example 2, (b) Comparative Example 3, and (c) Comparative Example 4. Figure 4 Two-dimensional wide-angle X-ray diffraction patterns of the composite films obtained in Examples 1-3; Figure 5 Two-dimensional wide-angle X-ray diffraction patterns of the composite films obtained in Comparative Example 1 and Example 1; Figure 6 This is a density statistics chart of the composite membranes obtained in Examples 1-3; Figure 7 The graph shows the mechanical properties of the composite membranes obtained in Examples 1-3. Figure 8 The graph shows the electrothermal performance of the composite membrane obtained in Example 1. Figure 9 SE of the composite membranes obtained in Examples 1-5 A SE R and SE T A statistical chart of values; Figure 10 SE of the composite membranes obtained in Comparative Example 2 and Example 1 A SE R and SE T A statistical chart of the values. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. Example 1

[0031] An oriented layered porous electromagnetic shielding composite film is prepared by the following steps: 1) Preparation of spinning solution: Aqueous dispersion of monolayer MXene nanosheets was collected by in-situ etching with LiF / HCl to obtain MXene dispersion of 15 mg / mL. SA powder was added to MXene dispersion at a mass ratio of 1:1 of MXene and sodium alginate (SA). After magnetic stirring for 12 h, vacuum degassing was performed to obtain spinning solution with a total solid content of 30 mg / mL.

[0032] 2) Load the spinning solution obtained in step 1) into a syringe and inject it through a metering pump. Figure 1 In the long channel mold with a rectangular slit outlet shown (the length of the channel in the mold is 60 mm, the width is 30 mm, the height is 1 mm, and the length-to-diameter ratio of the channel is 60:1; the width of the rectangular outlet is 30 mm and the height is 1 mm), the injection rate is 2 mL / min, and the flow rate of the spinning solution in the mold is 2 mL / min. The spinning solution is continuously extruded from the mold, and the resulting jet directly enters a 5 wt% CaCl2 solution (the solvent is water and isopropanol in a volume ratio of 3:1, and the temperature is 25℃). It then rapidly crosslinks into a continuous gel film. After crosslinking and coagulating in a coagulation bath for 1 h, the gel film is washed with water three times, each time for 2 h.

[0033] 3) The gel membrane obtained in step 2) is laid flat on the surface of the lower mold plate. Spacers are placed around the gel membrane, and the upper mold plate is covered. The upper and lower molds are clamped together using clamps, so that the gel membrane is held between the two parallel and flat molds. The mold gap is limited by 1 mm spacers to control the thickness. The mold is pre-frozen in a refrigerator at -20°C for 12 h, and then transferred to a freeze dryer for 72 h (vacuum degree of 1 Pa, temperature of -50°C) to obtain an oriented layered porous MXene / SA composite membrane, labeled M. 1.5 S 1.5 Composite film. Example 2

[0034] An oriented layered porous electromagnetic shielding composite film is prepared in a manner different from that in Example 1, in step 1), the concentrations of MXene and sodium alginate in the spinning solution are both 10 mg / mL, the total solid content of the spinning solution is 20 mg / mL, and the resulting sample is labeled as M1S1 composite film. All other aspects are the same as in Example 1. Example 3

[0035] An oriented layered porous electromagnetic shielding composite film is prepared in a manner different from that in Example 1, in step 1), the concentrations of MXene and sodium alginate in the spinning solution are both 20 mg / mL, the total solid content of the spinning solution is 40 mg / mL, and the resulting sample is labeled as M2S2 composite film. All other aspects are the same as in Example 1. Example 4

[0036] An oriented layered porous electromagnetic shielding composite film is prepared in a manner different from that in Example 1, in step 1), the mass ratio of MXene and sodium alginate is 1:2 (the total solid content is still 30 mg / mL), and the resulting sample is labeled as M1S2 composite film. All other aspects are the same as in Example 1. Example 5

[0037] An oriented layered porous electromagnetic shielding composite membrane was prepared in a method that differed from that in Example 1 in that: in step 1), the mass ratio of MXene to sodium alginate was 7:3 (the total solid content remained at 30 mg / mL), and the resulting sample was labeled as M. 2.1 S 0.9 Everything else is the same as in Example 1.

[0038] Comparative Example 1 Using the same spinning solution as in Example 1, an MXene / SA gel membrane was prepared by a blade coating process, followed by confined freeze-drying according to step 3) to obtain a composite membrane, labeled M. 1.5 S 1.5 @B.

[0039] Comparative Example 2 Using the same spinning solution and wet spinning process as in Example 1 (i.e., according to steps 1 and 2), a composite film was subsequently obtained by conventional freeze-drying, denoted as M. 1.5 S 1.5 @F.

[0040] Comparative Example 3 Using the same spinning solution and wet spinning process as in Example 2, a composite membrane was obtained by conventional freeze drying, labeled M1S1@F.

[0041] Comparative Example 4 Using the same spinning solution and wet spinning process as in Example 3, a composite membrane was obtained by conventional freeze drying, labeled M2S2@F.

[0042] The morphology of the composite film was characterized using scanning electron microscopy; the orientation of the composite film was characterized using wide-angle X-ray diffraction; the mechanical properties of the composite film were characterized using a universal tensile testing machine; the electrothermal properties of the composite film were characterized using an infrared camera; and the electromagnetic shielding properties of the composite film were characterized using a vector network analyzer.

[0043] (a) Structural characterization Figure 2 The images shown are cross-sectional SEM images of the composite membranes obtained in Examples 1-3. It can be seen that under the synergistic effect of long-channel shear wet spinning and confined freeze-drying, the composite membrane exhibits a regular layered porous structure. The two-dimensional conductive nanosheets are clearly oriented along the extrusion direction, and the pores show good interlayer connectivity in the thickness direction. The overall thickness of the membrane is uniform and the interface is clear, indicating that the confined conditions effectively suppress the volume shrinkage and structural collapse during the freeze-drying process.

[0044] Figure 3 The cross-sectional SEM images of the composite membranes obtained in Comparative Examples 2-4 show that when using the traditional free freeze-drying method, the gel membrane generates significant shrinkage stress during sublimation, leading to warping, wrinkling, and local collapse of the composite membrane. The internal pore structure becomes disordered, the layered orientation structure is destroyed, the membrane thickness distribution is uneven, and the overall structural stability is poor.

[0045] contrast Figure 2 and Figure 3 It can be seen that the confined freeze-drying strategy effectively constrains the thickness and deformation of the gel membrane while ensuring the formation of the porous structure, thus successfully constructing a layered porous composite membrane structure with good orientation, stable structure and uniform thickness.

[0046] (ii) Performance Characterization Figure 4 The two-dimensional wide-angle X-ray diffraction results of the composite films obtained in Examples 1-3 show that as the viscosity of the spinning solution increases, the orientation degree of the filler first increases and then decreases. Among them, the Hermann orientation factor corresponding to Example 1 is the highest, reaching 0.65, indicating that moderate rheological properties are beneficial to achieving full orientation of nanosheets in a long flow channel shear field.

[0047] Figure 5Comparative results of two-dimensional wide-angle X-ray diffraction for Example 1 and Example 1 show that the Hermann orientation factor of the composite film prepared by the blade coating process is 0.57, while the orientation factor of the composite film prepared by the long-channel wet spinning process is increased to 0.65, and the half-width of the diffraction peak is reduced. This indicates that the continuous planar shearing effect in the long channel can significantly enhance the orientation degree of the two-dimensional conductive filler.

[0048] Figure 6 The density statistics of the composite membranes obtained in Examples 1-3 show that the layered porous structure formed after confined freeze-drying significantly reduced the overall density of the composite membrane (0.31 g / cm³). 3 This demonstrates the material's excellent lightweight characteristics, which is beneficial for the application of flexible devices and wearable electromagnetic protection materials.

[0049] Figure 7 The statistical results of the tensile stress-strain curves of the composite membranes obtained in Examples 1-3 show that, with the increase of the viscosity of the spinning solution, the tensile strength and elongation at break of the composite membrane first increase and then decrease. This trend is consistent with the orientation of the filler, indicating that the orientation structure plays a key role in enhancing load transfer efficiency and improving the interfacial bonding strength within the membrane.

[0050] Figure 8 The results of the Joule heating performance test of the composite film obtained in Example 1 show that as the applied voltage increases, the surface temperature of the composite film rises rapidly, reaching approximately 115 °C under a 4 V voltage condition. This indicates that the continuously oriented two-dimensional conductive network is conducive to the rapid conduction of current and the uniform release of heat, giving the composite film good electrothermal performance.

[0051] Figure 9 SE of the composite membranes obtained in Examples 1-5 A SE R and SE T The statistical chart of values ​​shows that each sample exhibits stable electromagnetic shielding performance, and the shielding effectiveness gradually increases with the increase of MXene content. When the mass ratio of MXene to sodium alginate is 7:3 (corresponding to Example 5), the total electromagnetic shielding effectiveness can reach 55.1 dB, indicating that the oriented layered porous structure significantly enhances the electromagnetic wave attenuation capability under the synergistic effect of multiple reflections and interface polarization.

[0052] Figure 10 SE of the composite membranes obtained in Comparative Example 2 and Example 1 A SE R and SE TThe statistical chart shows that the total shielding effectiveness of the composite film obtained by traditional freeze-drying is only 23.71 dB, while the shielding effectiveness of the composite film obtained by adopting the confined freeze-drying strategy is improved to 39.11 dB. This indicates that confined freeze-drying can effectively maintain the continuity of the orientation structure and conductive network formed during wet spinning, thereby significantly improving the electromagnetic shielding performance of the composite film.

Claims

1. A method for preparing a layered porous composite membrane having an orientation, characterized by, The spinning dope is continuously extruded through a long runner die with a rectangular slit outlet, and the jet formed is directly introduced into a coagulation bath system to form a continuous gel film through a gelation process; The gel film is washed with water, and then sequentially subjected to confined pre-freezing shaping and confined freeze-drying to obtain an oriented layered porous composite film.

2. The method of claim 1, wherein the oriented layered porous composite membrane is prepared by the steps of: The flow channel of the spinning dope in the die is rectangular, and the length-diameter ratio of the flow channel is 30-100:

1. Optionally, the length-diameter ratio of the flow channel is 60:

1.

3. The method of claim 2, wherein the oriented layered porous composite membrane is prepared by the steps of: The rectangular slit outlet of the die has a width of 30-100 mm and a height of 0.5-3 mm. Optionally, the rectangular slit outlet has a width of 30 mm and a height of 1 mm.

4. The method for preparing an oriented layered porous composite membrane as described in claim 2, characterized in that, The flow rate of the spinning dope in the die is 0.5-10 mL / min. Optionally, the flow rate is 2 mL / min.

5. The method for preparing an oriented layered porous composite membrane as described in claim 1, characterized in that, The coagulation bath system temperature is 10-60 o C, coagulation time is 1-2 h; Optionally, the coagulation bath system temperature is 25-30 o C.

6. The method of producing an oriented layered porous composite membrane according to any one of claims 1 to 5, wherein The washed gel film is laid between the upper and lower die platens for subsequent confined pre-freezing and freezing, and the gap thickness between the upper and lower die platens is 0.5-3 mm. Optionally, the gap thickness between the upper and lower die platens is 1 mm.

7. The method of claim 6, wherein the oriented layered porous composite membrane is prepared by the steps of: The pre-freezing shaping temperature is -20-0 ℃, and the pre-freezing time is 12-24 h. The vacuum degree of the freeze-drying is 1-10 Pa, the freezing temperature is -50 ℃ to -40 ℃, and the freeze-drying time is 48-72 h. Optionally, the spinning dope is obtained by mixing an electrically conductive filler dispersion liquid and a gelation material: The electrically conductive filler is one or more of MXene, graphene or MoS2; and the gelation material is one or more of alginate, aramid nanofiber, silk fibroin, cellulose or chitosan.

8. The oriented layered porous composite film obtained by the preparation method of any one of claims 1-7.

9. The oriented layered porous composite membrane of claim 8, wherein, The composite film is composed of a gelation material matrix and an electrically conductive filler, and has a highly oriented layered porous structure in the film layer, in which the gelation material and the electrically conductive filler are stacked and arranged substantially parallel to the film surface, the two-dimensional conductive nanosheet is oriented and connected along the layer surface to form a two-dimensional conductive network, and the film cross section has a layered pore structure, and through or semi-through sheet-shaped pore channels are formed between the layers.

10. The oriented layered porous composite film of claim 8 for use in electromagnetic protection, thermal management and wearable electronic devices.

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