CN113524823B - Flexible composite material with high electromagnetic shielding performance and preparation method thereof - Google Patents

Flexible composite material with high electromagnetic shielding performance and preparation method thereof Download PDF

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CN113524823B
CN113524823B CN202110906367.XA CN202110906367A CN113524823B CN 113524823 B CN113524823 B CN 113524823B CN 202110906367 A CN202110906367 A CN 202110906367A CN 113524823 B CN113524823 B CN 113524823B
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liquid metal
composite material
electromagnetic shielding
polymer composite
metal sheet
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CN113524823A (en
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姚斌
吕晓洲
史尧光
张维强
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Xidian University
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    • B32B25/00—Layered products comprising a layer of natural or synthetic rubber
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    • B32B27/00—Layered products comprising a layer of synthetic resin
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    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0073—Shielding materials
    • H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
    • H05K9/0083—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising electro-conductive non-fibrous particles embedded in an electrically insulating supporting structure, e.g. powder, flakes, whiskers
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    • H05K9/0073—Shielding materials
    • H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
    • H05K9/0088—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising a plurality of shielding layers; combining different shielding material structure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
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    • B32B2250/24—All layers being polymeric
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    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
    • B32B2307/212—Electromagnetic interference shielding
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    • C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
    • C08J2333/04—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters
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    • C08J2353/00—Characterised by the use of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers
    • C08J2353/02—Characterised by the use of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers of vinyl aromatic monomers and conjugated dienes
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    • C08J2433/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
    • C08J2433/04—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters
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    • C08J2453/02—Characterised by the use of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers of vinyl aromatic monomers and conjugated dienes
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Abstract

The invention discloses a flexible composite material with high electromagnetic shielding performance and a preparation method thereof, wherein the preparation method comprises the following steps: obtaining a polymer solution; adding liquid metal into the polymer solution, and mechanically stirring to obtain a mixed emulsion; casting the mixed emulsion to obtain a liquid metal particle/polymer composite material; the obtained material is subjected to equal biaxial stretching, fixing and heat treatment, and the stretching state is kept, so that the liquid metal sheet/polymer composite material is obtained; casting a layer of mixed emulsion on the upper surface of the obtained material, and performing lamination treatment; and repeating tape casting and laminating, and carrying out hot-pressing treatment and heating curing on the obtained material to obtain the flexible composite material with high electromagnetic shielding performance. The flexible composite material with high electromagnetic shielding performance and the preparation method thereof realize the combination of flexibility and high electromagnetic shielding performance, and the prepared material has isotropic electromagnetic shielding performance, excellent flexibility and stretchability and wide application prospect.

Description

Flexible composite material with high electromagnetic shielding performance and preparation method thereof
Technical Field
The invention belongs to the technical field of electromagnetic shielding, and relates to a flexible composite material with high electromagnetic shielding performance and a preparation method thereof.
Background
The development and popularization of the fifth generation communication technology, the internet of things technology and the flexible electronic technology can promote the development of electronic components in the directions of high frequency, miniaturization, multi-functionalization, flexibility and high integration, so that the power density is continuously increased, electromagnetic waves generated in the electronic components and the micro-nano scale interconnection circuit are greatly increased, and the caused electromagnetic interference seriously affects the stability and safety of the operation of the components, pollutes the living environment and harms the health of human bodies. In order to prevent the harm caused by electromagnetic interference, flexible materials with high electromagnetic shielding efficiency are generally adopted to inhibit and shield electromagnetic waves. Generally, the civil field requires the electromagnetic shielding effectiveness of the material to be higher than 20dB, and the military field requires the electromagnetic shielding effectiveness to be higher than 40 dB.
The traditional metal materials with high conductivity, such as copper, aluminum and the like, have excellent electromagnetic shielding performance, but have low mechanical deformation capacity and high elastic modulus, and cannot meet the requirements of flexible electronic technology on large deformation and flexibility. In recent years, in order to improve the flexibility of materials, researchers have developed a number of flexible electromagnetic shielding composite materials using rigid, highly conductive materials (metal particles and fibers, graphene, carbon nanotubes, Mxene sheets, etc.) as functional fillers and highly stretched flexible elastomers as matrices. However, the introduction of the rigid conductive filler not only reduces the flexibility and mechanical deformability of the electro-magnetic shielding composite, but also the stress causes the electrical conductivity of the electro-magnetic shielding composite to be decreased and the thickness to be thin, thereby causing the electro-magnetic shielding performance to be decreased as the strain is increased.
In order to solve the problem that the electromagnetic shielding effectiveness is reduced after stretching, researchers encapsulate the intrinsically flexible liquid metal three-dimensional framework inside the elastomer matrix, and obtain a composite material with both flexibility and high electromagnetic shielding characteristics, but the liquid metal in the material is easy to flow and then flows out to leak, so that performance reduction and environmental pollution risks are caused.
Researchers have attempted to achieve a combination of flexibility, high electromagnetic shielding performance, and structural stability by dispersing liquid metal particles inside an elastomer. However, there are three problems in flexible composites based on liquid metal particles: (1) under the action of no stress, liquid metal particles in the composite material are in dispersion distribution, the connectivity among the particles is very poor, the conductivity is low, and the electromagnetic shielding efficiency of the material is less than 10dB and far lower than the requirement of practical application; (2) although the stretching can cause the electromagnetic shielding performance to be improved, and the liquid metal particles are converted into the oriented fiber structure, the electromagnetic shielding performance presents strong anisotropy, although the electromagnetic shielding performance can be increased to 20-26 dB when the electric field direction of the electromagnetic waves is parallel to the oriented fibers, the electromagnetic shielding efficiency is only about 5dB when the electric field direction of the electromagnetic waves is perpendicular to the fiber direction of the liquid metal, and the application requirement cannot be met; (3) the higher electromagnetic shielding effectiveness along the strain direction can be obtained only under the external stress stretching, and due to the resilience of the polymer matrix, when the external stress is unloaded, the material rebounds to an unstressed state, so that the microstructure and the performance of the material after stretching cannot be kept in an unstressed sample, and the electromagnetic shielding performance of the material still drops below 10 dB.
In conclusion, the application of the composite material based on the liquid metal particles in the actual electromagnetic shielding scene is severely limited by the excessively low electromagnetic shielding effectiveness and the strong anisotropy, and research and development of the flexible composite material with the high electromagnetic shielding effectiveness are urgently needed.
Disclosure of Invention
In order to achieve the above object, embodiments of the present invention provide a flexible composite material with high electromagnetic shielding performance and a preparation method thereof, which achieve the combination of flexibility and high electromagnetic shielding performance, and the preparation method is simple and easy to operate and easy to implement, and the prepared liquid metal sheet/elastomer composite material has a stable structure, an electromagnetic shielding effectiveness that is isotropic, maintains a good electromagnetic shielding effectiveness in an unstressed and stressed state, has excellent flexibility and stretchability, has a wide application prospect, and solves the problems of too low electromagnetic shielding effectiveness and strong anisotropy of composite materials based on liquid metal particles in the prior art.
The technical scheme adopted by the invention is that the preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
the method comprises the following steps: mixing the polymer in a ratio of 1: (10-30) adding the mixture into a solvent according to the mass ratio, and magnetically stirring to obtain a polymer solution;
step two: adding liquid metal into the polymer solution according to the volume ratio of (1-5) to (5-9), and mechanically stirring to obtain a mixed emulsion;
step three: casting the mixed emulsion on a substrate, carrying out vacuum pumping treatment on the substrate carrying the casting, and drying in vacuum to obtain a liquid metal particle/polymer composite material;
step four: biaxially stretching liquid metal particles/polymer composite materials and the like to 50% -600% of surface strain, and then fixing the biaxially stretched liquid metal sheet/polymer composite materials to obtain the liquid metal sheet/polymer composite materials fixed on an equibiaxial stretching platform;
step five: heating the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform for 2-4 h at the temperature of 60-120 ℃, and then naturally cooling to room temperature to obtain the liquid metal sheet/polymer composite material in a stretching state;
step six: casting a layer of the mixed emulsion prepared in the second step on the upper surface of the liquid metal sheet/polymer composite material obtained in the fifth step, heating to 40-60 ℃ at a heating rate of 1-4 ℃/min, and heating for 1-4 h at the temperature to obtain a liquid metal sheet/polymer composite material with semi-solidified upper surface;
step seven: laminating two pieces of liquid metal sheet/polymer composite materials with semi-solidified upper surfaces, wherein the upper surfaces of the two pieces of liquid metal sheet/polymer composite materials are used as laminating contact surfaces to obtain a laminated liquid metal sheet/polymer composite material;
step eight: repeating the casting process in the sixth step and the laminating process in the seventh step to obtain the multilayer laminated liquid metal sheet/polymer composite material with 10-20 layers;
step nine: and placing the multilayer laminated liquid metal sheet/polymer composite material obtained in the step eight in a hot press die, and carrying out hot pressing treatment and heating solidification to obtain the flexible composite material with high electromagnetic shielding performance.
Further, in the first step, the polymer is a thermoplastic elastomer, and the solvent includes any one of dimethylformamide, dimethylacetamide, acetone and butanone.
Still further, the thermoplastic elastomer comprises: any one of hydrogenated styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, polyacrylate, polyester, ethylene propylene diene monomer rubber, nitrile rubber, butyl rubber.
Further, in the first step, the magnetic stirring is specifically as follows: magnetically stirring at the stirring speed of 100 r/min-400 r/min for 12-48 h at the temperature of 20-60 ℃.
Further, In the second step, the liquid metal is a pure liquid metal or a liquid metal alloy with a melting point lower than 30 ℃, and the composition of the liquid metal comprises at least one of Ga, In, Sn, Bi and Hg.
Further, in the second step, the mechanical stirring is specifically: mechanically stirring for 2 to 12 hours at the stirring speed of 50 to 200r/min under the temperature condition of 20 to 40 ℃.
Further, in the third step, the process conditions of vacuum drying are specifically as follows: the vacuum drying temperature is 60-100 ℃, and the vacuum drying time is 1-4 h.
Further, in the ninth step, the hot pressing treatment specifically comprises: applying 50-100 kPa pressure at 100-120 ℃ to carry out hot pressing treatment for 10-60 min.
Further, in the ninth step, the heating and curing specifically comprises: heating and curing for 1-4 h at the temperature of 60-100 ℃.
Another object of the present invention is to provide a flexible composite material with high electromagnetic shielding performance, which is prepared according to the above preparation method.
The invention has the beneficial effects that:
(1) according to the flexible composite material with high electromagnetic shielding performance, in the processes of equal biaxial stretching and heating remodeling, the liquid metal is changed into a two-dimensional sheet structure from a granular state, and the in-plane direction of the liquid metal micrometer sheet is parallel to the stretching direction to form an in-plane oriented structure, so that the composite material has good electromagnetic shielding characteristics in all directions in a plane; in the invention, the thermoplastic polymer is used as a matrix, and the microstructure of the material in a stretching state is kept to be in a stress-free state through heating and stress remodeling; in the lamination and hot pressing process, the liquid metal/elastomer mixed emulsion is used as an interface bonding material to enhance the bonding property of an interface between layers, so that the mechanical property of the material is improved;
(2) the preparation method of the flexible composite material with high electromagnetic shielding performance provided by the embodiment of the invention is simple and feasible, has low cost, can be used for forming a workpiece with a complex shape, has excellent electromagnetic shielding effect, and has wide application prospect in the fields of intelligent deformable aircrafts, wearable devices and flexible electronics.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is an image of a liquid metal sheet/polymer composite as affixed to an equi-biaxial stretching platform according to an embodiment of the present invention.
Fig. 2 is an optical microscope image of a liquid metal particle/polymer composite obtained in an example of the present invention.
Fig. 3 is a macroscopic image of a liquid metal sheet/polymer composite obtained in an example of the present invention during stretching.
Fig. 4 is an optical microscope image of a liquid metal flake/polymer composite strained to 300% for an example of the invention.
Fig. 5 is a comparison of the electromagnetic shielding performance of the flexible composite material with high electromagnetic shielding performance and the liquid metal particle/polymer composite material according to the embodiment of the present invention.
In the drawings: the device comprises a 1-aluminum alloy ground plate bracket, a 2-aluminum alloy stretching rod and a 3-aluminum alloy clamp.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The idea of the invention is as follows: the preparation method comprises the steps of preparing a liquid metal particle/thermoplastic elastomer composite material by adopting a tape casting process, obtaining the composite material in which liquid metal is uniformly dispersed in a thermoplastic elastomer in a micron sheet structure by an equal biaxial stretching and heating remodeling process, and obtaining the flexible composite material with high electromagnetic shielding performance in all directions in a plane by a laminating and hot pressing process.
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
the method comprises the following steps: mixing the polymer in a ratio of 1: (10-30) adding the mixture into a solvent according to the mass ratio, and magnetically stirring the mixture for 12-48 hours at the stirring speed of 100-400 r/min at the temperature of 20-60 ℃ to dissolve a polymer in the solvent to obtain a polymer solution;
the polymer is a thermoplastic elastomer comprising: any one of hydrogenated styrene-butadiene block copolymer (SEBS), styrene-butadiene-styrene block copolymer (SBS), polyacrylate, polyester, ethylene propylene diene monomer, nitrile rubber, butyl rubber;
the solvent comprises any one of dimethylformamide, dimethylacetamide, acetone and butanone.
Step two: adding liquid metal into a polymer solution according to the volume ratio of (1-5) to (5-9), wherein the sum of the volume percentages of the liquid metal and the polymer solution is 100%, and mechanically stirring for 2-12 h at the stirring speed of 50-200 r/min at the temperature of 20-40 ℃, wherein the mechanical stirring is specifically to stir by a stirring rod on a stirrer, break the liquid metal into liquid metal particles, and uniformly disperse the liquid metal particles in the polymer solution to obtain a mixed emulsion with good fluidity.
The liquid metal is pure liquid metal or liquid metal alloy with melting point lower than 30 ℃, and the component comprises at least one of Ga, In, Sn, Bi and Hg.
Step three: under the condition of room temperature, the mixed emulsion is cast on any one of a PET film belt, a PTFE substrate and a glass substrate, the movement speed of a push rod in the casting process is 0.5-2 mm/s, the thickness of a casting object is controlled by adjusting the height of a scraper of a casting machine, the thickness of the casting object is 0.5-3 mm, the substrate carrying the casting object is transferred into a vacuum oven for vacuum pumping treatment until no bubbles are generated on the surface of the casting object, and then the casting object is dried in vacuum for 1-4 h under the temperature condition of 60-100 ℃ so as to be cured, and the liquid metal particle/polymer composite material is obtained.
Step four: placing and clamping the liquid metal particle/polymer composite material on an equal biaxial stretching platform, firstly stretching the liquid metal particle/polymer composite material and the like to 50-600% of plane strain, and then fixing the equal biaxial stretched liquid metal sheet/polymer composite material to obtain the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform.
When biaxial stretching platform, as shown in fig. 1, including the aluminium alloy tray support 1 of inside trompil, be provided with eight aluminium alloy tensile poles 2 along the adjustable length of centre gripping direction on the aluminium alloy tray support 1, every aluminium alloy tensile pole 2 all is provided with an aluminium alloy anchor clamps 3 towards the tip at aluminium alloy tray support 1 center for the centre gripping sample. The liquid metal particle/polymer composite material is clamped by the eight aluminum alloy clamps 3, the aluminum alloy clamps 3 which are used for clamping the liquid metal particle/polymer composite material are screwed tightly by screws, the eight aluminum alloy stretching rods 2 move outwards at equal intervals at the same time for a certain distance, the strain borne by the sample can be controlled, the isotropic surface strain is applied to the material, and the equal biaxial stretching of the liquid metal particle/polymer composite material is realized.
The working principle of the step is as follows: the liquid metal particles in the liquid metal particle/polymer composite material are converted into a two-dimensional metal sheet structure through equal biaxial stretching, and the in-plane direction of the liquid metal sheet is parallel to the stretching direction. In the process of equal biaxial stretching, the liquid metal particles are subjected to the stress transmitted by the elastomer matrix and gradually change into a two-dimensional sheet structure. Compared with a particle structure, the two-dimensional sheet structure has a larger surface area, and meanwhile, the in-plane direction of the sheet structure is parallel to the stretching direction, so that after electromagnetic waves are incident on the surface of a material, the reflection and absorption effects of the surface of the sheet structure on the electromagnetic waves are better.
Step five: and transferring the equal biaxial stretching platform and the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform into a heating device, heating for 2-4 h at the temperature of 60-120 ℃, naturally cooling to room temperature, and taking down the liquid metal sheet/polymer composite material subjected to heat treatment from the equal biaxial stretching platform to obtain the liquid metal sheet/polymer composite material in a stretching state.
The working principle of the step is as follows: in the heat treatment process of the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform, under the combined action of heating and stretching stress, the thermoplastic elastomer in the liquid metal particle/elastomer composite material can be reshaped, when the stress is relaxed and the temperature is reduced to room temperature, the material can keep the stretching state of the material not to rebound, so that the shape and microstructure of the liquid metal in the stretching state are successfully kept in a sample with external stretching stress removed, compared with the liquid metal particles, the two-dimensional sheet structure of the liquid metal obtained by remolding has larger surface area, meanwhile, the in-plane direction of the sheet structure is parallel to the stretching direction, and after electromagnetic waves are incident to the surface of the material, the reflection and absorption effects of the surface of the sheet structure on the electromagnetic waves are better.
Step six: and (4) placing the liquid metal sheet/polymer composite material obtained in the fifth step on a casting machine, then casting a layer of mixed emulsion prepared in the second step on the upper surface of the liquid metal sheet/polymer composite material, wherein the casting thickness is 0.04-0.1 mm, the temperature of the casting machine is raised to 40-60 ℃ at the temperature raising rate of 1-4 ℃/min, and the liquid metal sheet/polymer composite material with the semi-solidified upper surface is obtained after heating for 1-4 hours at the temperature.
The working principle of the step is as follows: during heating, the solvent in the mixed emulsion cast on the upper surface of the liquid metal sheet/polymer composite material in a stretched state can re-dissolve the upper surface of the liquid metal sheet/polymer composite material in a stretched state, so that the upper surface of the liquid metal sheet/polymer composite material in a stretched state and the mixed emulsion cast thereon are mixed together, and strong connection is formed between the liquid metal sheet/polymer composite material in a stretched state and a new cast layer cast thereon in a heating and curing process, thereby greatly enhancing the bonding degree of an interlayer interface. If the step is not added, the next lamination is directly carried out, the interface strength between layers is low, and the product performance is poor.
Step seven: and (3) laminating the two liquid metal sheets/polymer composite materials with the upper surfaces semi-solidified, wherein the upper surfaces of the two liquid metal sheets/polymer composite materials are used as laminating contact surfaces, so as to obtain the laminated liquid metal sheet/polymer composite material.
The working principle of the step is as follows: the upper surface of the semi-solidified mixed emulsion is used as a contact surface between layers, the two semi-solidified liquid metal sheets/polymer composite materials on the upper surfaces form a laminated structure, and the semi-solidified mixed emulsion has cohesiveness, so that the upper surfaces of the two semi-solidified liquid metal sheets/polymer composite materials on the upper surfaces are bonded when being contacted with each other, and the composite material with a double-layer structure is obtained. The two layers of liquid metal foil when laminated in this step do not require corresponding angles because the liquid metal foil/polymer composite is isotropic in-plane.
Step eight: repeating the casting process in the sixth step and the laminating process in the seventh step to obtain the multilayer laminated liquid metal sheet/polymer composite material with 10-20 layers; when the multilayer is laminated in the step, the corresponding angle is not required, because the liquid metal sheet is isotropic in the plane, and different laminating angles do not influence the performance of the final product.
Step nine: and placing the multilayer laminated liquid metal sheet/polymer composite material obtained in the step eight in a hot press mold, applying 50-100 kPa pressure at the temperature of 100-120 ℃, carrying out hot pressing treatment for 10-60 min, transferring the hot-pressed multilayer laminated liquid metal sheet/polymer composite material into a heating device, and carrying out heating and curing for 1-4 h at the temperature of 60-100 ℃ so as to completely cure the semi-cured mixed emulsion of the casting layer in the multilayer laminated liquid metal sheet/polymer composite material, thereby obtaining the flexible composite material with high electromagnetic shielding performance.
Example 1
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
(1) 30g of a hydrogenated styrene-butadiene block copolymer was added to 600g of dimethylformamide, and magnetically stirred at a stirring rate of 250r/min at a temperature of 40 ℃ for 30 hours to obtain a polymer solution.
(2) Adding gallium-indium eutectic alloy (EGaIn) liquid metal with the melting point of 15 ℃ into the polymer solution according to the volume ratio of 3:7, and mechanically stirring for 7 hours at the temperature of 30 ℃ and the stirring speed of 125r/min to obtain a mixed emulsion.
(3) And (2) casting the mixed emulsion on a PET film belt substrate at room temperature, controlling the movement speed of a push rod to be 1.25mm/s in the casting process, controlling the thickness of a casting object to be 1.75mm by adjusting the height of a scraper of a casting machine, transferring the substrate carrying the casting object into a vacuum oven, vacuumizing, and then vacuum-drying for 2.5 hours at the temperature of 80 ℃ to obtain a liquid metal particle/polymer composite material, wherein the micro-morphology of the liquid metal particle/polymer composite material is shown in figure 2.
(4) The liquid metal particle/polymer composite is placed and clamped on an equi-biaxial stretching platform, the liquid metal particle/polymer composite is first equi-biaxially stretched to 300% plane strain, and then the equi-biaxially stretched liquid metal sheet/polymer composite is fixed to obtain the liquid metal sheet/polymer composite fixed on the equi-biaxial stretching platform as shown in fig. 3.
(5) And transferring the equibiaxial stretching platform and the liquid metal sheet/polymer composite material fixed on the equibiaxial stretching platform into a heating device, heating for 3h at the temperature of 90 ℃, naturally cooling to room temperature, and taking down the liquid metal sheet/polymer composite material subjected to heat treatment from the equibiaxial stretching platform to obtain the liquid metal sheet/polymer composite material in a stretching state, wherein the micro-morphology of the liquid metal sheet/polymer composite material is shown in fig. 4.
(6) And (3) placing the liquid metal sheet/polymer composite material obtained in the step (5) on a casting machine, then casting a layer of mixed emulsion prepared in the step (2) on the upper surface of the liquid metal sheet/polymer composite material, wherein the casting thickness is 0.06mm, the temperature of the casting machine is increased to 50 ℃ at the temperature increasing rate of 2.5 ℃/min, and the liquid metal sheet/polymer composite material with the semi-solidified upper surface is obtained after heating for 2.5 hours at the temperature.
(7) And (3) laminating the two liquid metal sheets/polymer composite materials with the upper surfaces semi-solidified, wherein the upper surfaces of the two liquid metal sheets/polymer composite materials are used as laminating contact surfaces, so as to obtain the laminated liquid metal sheet/polymer composite material.
(8) Repeating the casting and laminating processes in (6) and (7) to obtain a liquid metal foil/polymer composite material laminated with 15 layers.
(9) And (3) placing the multilayer laminated liquid metal sheet/polymer composite material obtained in the step (8) in a hot press mold, applying 75kPa pressure at the temperature of 110 ℃ for hot pressing for 35min, transferring the multilayer laminated liquid metal sheet/polymer composite material subjected to hot pressing into a heating device, and heating and curing at the temperature of 80 ℃ for 2.5h to obtain the flexible composite material with high electromagnetic shielding performance.
Example 2
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
(1) 40g of polyacrylate is added into 400g of acetone, and magnetic stirring is carried out for 12h at the temperature of 20 ℃ and the stirring speed of 100r/min, so as to obtain a polymer solution.
(2) Adding gallium-indium eutectic alloy (EGaIn) liquid metal with the melting point of 15 ℃ into the polymer solution in a volume ratio of 1:9, and mechanically stirring for 2 hours at the stirring speed of 50r/min under the temperature condition of 20 ℃ to obtain a mixed emulsion.
(3) And (2) casting the mixed emulsion on a glass substrate at room temperature, controlling the movement speed of a push rod to be 0.5mm/s and the thickness of casting to be 0.5mm in the casting process, transferring the substrate carrying the casting into a vacuum oven, vacuumizing, and then vacuum-drying for 4 hours at the temperature of 60 ℃ to obtain the liquid metal particle/polymer composite material.
(4) Placing and clamping the liquid metal particle/polymer composite material on an equal biaxial stretching platform, first biaxially stretching the liquid metal particle/polymer composite material to 50% plane strain, and then fixing the equal biaxial stretched liquid metal sheet/polymer composite material to obtain the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform.
(5) And transferring the equal biaxial stretching platform and the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform into a heating device, heating for 4h at the temperature of 60 ℃, naturally cooling to room temperature, and taking down the liquid metal sheet/polymer composite material subjected to heat treatment from the equal biaxial stretching platform to obtain the liquid metal sheet/polymer composite material in a stretching state.
(6) And (3) placing the liquid metal sheet/polymer composite material obtained in the step (5) on a casting machine, casting a layer of mixed emulsion prepared in the step (2) on the upper surface of the liquid metal sheet/polymer composite material, wherein the casting thickness is 0.04mm, the temperature of the casting machine is increased to 40 ℃ at the temperature increasing rate of 1 ℃/min, and the liquid metal sheet/polymer composite material with the semi-solidified upper surface is obtained by heating for 4 hours at the temperature.
(7) And (3) laminating the two liquid metal sheets/polymer composite materials with the upper surfaces semi-solidified, wherein the upper surfaces of the two liquid metal sheets/polymer composite materials are used as laminating contact surfaces, so as to obtain the laminated liquid metal sheet/polymer composite material.
(8) Repeating the casting and laminating processes in (6) and (7) to obtain a 10 layer laminated liquid metal foil/polymer composite.
(9) And (3) placing the 10-layer laminated liquid metal sheet/polymer composite material obtained in the step (8) in a hot press mold, applying 50kPa pressure at the temperature of 100 ℃, carrying out hot pressing treatment for 60min, transferring the hot-pressed 10-layer laminated liquid metal sheet/polymer composite material to a heating device, and carrying out heating curing for 4h at the temperature of 60 ℃ to obtain the flexible composite material with high electromagnetic shielding performance.
Example 3
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
(1) 25g of a styrene-butadiene-styrene block copolymer was added to 750g of dimethylacetamide, and magnetically stirred at a stirring rate of 400r/min at a temperature of 60 ℃ for 12 hours to obtain a polymer solution.
(2) Adding gallium indium tin eutectic alloy (EGaInSn) liquid metal at 6 ℃ into the polymer solution in a volume ratio of 5:5, and mechanically stirring for 2 hours at a stirring speed of 200r/min under the temperature condition of 40 ℃ to obtain a mixed emulsion with good fluidity.
(3) And (2) casting the mixed emulsion on a PTFE substrate at room temperature, controlling the movement speed of a push rod to be 2mm/s and the thickness of casting to be 3mm in the casting process, transferring the substrate carrying the casting into a vacuum oven, vacuumizing, and then drying in vacuum for 1h at the temperature of 100 ℃ to obtain the liquid metal particle/polymer composite material.
(4) Placing and clamping the liquid metal particle/polymer composite material on an equal biaxial stretching platform, first biaxially stretching the liquid metal particle/polymer composite material to 600% plane strain, and then fixing the equal biaxial stretched liquid metal sheet/polymer composite material to obtain the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform.
(5) And transferring the equal biaxial stretching platform and the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform into a heating device, heating for 2h at the temperature of 120 ℃, naturally cooling to room temperature, and taking down the liquid metal sheet/polymer composite material subjected to heat treatment from the equal biaxial stretching platform to obtain the liquid metal sheet/polymer composite material in a stretching state.
(6) And (3) placing the liquid metal sheet/polymer composite material obtained in the step (5) on a casting machine, then casting a layer of mixed emulsion prepared in the step (2) on the upper surface of the liquid metal sheet/polymer composite material, wherein the casting thickness is 0.1mm, the temperature of the casting machine is increased to 60 ℃ at the temperature increasing rate of 4 ℃/min, and the liquid metal sheet/polymer composite material with the semi-solidified upper surface is obtained after heating for 1h at the temperature.
(7) And (3) laminating the two liquid metal sheets/polymer composite materials with the upper surfaces semi-solidified, wherein the upper surfaces of the two liquid metal sheets/polymer composite materials are used as laminating contact surfaces, so as to obtain the laminated liquid metal sheet/polymer composite material.
(8) Repeating the casting and laminating processes in (6) and (7) to obtain a liquid metal foil/polymer composite material with 20 laminated layers.
(9) And (3) placing the 20-layer laminated liquid metal sheet/polymer composite material obtained in the step (8) in a hot press mold, applying 100kPa pressure at the temperature of 120 ℃ for hot pressing for 10min, transferring the hot-pressed multilayer laminated liquid metal sheet/polymer composite material into a heating device, and heating and curing at the temperature of 100 ℃ for 1h to obtain the flexible composite material with high electromagnetic shielding performance.
Example 4
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
except that (4) the liquid metal particle/polymer composite is equi-biaxially stretched to 180% area strain.
The rest is the same as in example 1.
Example 5
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
except that (4) the liquid metal particle/polymer composite is equi-biaxially stretched to 500% face strain.
The rest is the same as in example 1.
Example 6
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
except that in (1), the polymer is polyester;
the rest is the same as in example 1.
Example 7
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
the polymer in the step (1) is ethylene propylene diene monomer;
the rest is the same as in example 1.
Example 8
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
except that the polymer in (1) is nitrile butadiene rubber;
the rest is the same as in example 1.
Example 9
The preparation method of the flexible composite material with high electromagnetic shielding performance comprises the following steps:
the polymer in the step (1) is butyl rubber;
the rest is the same as in example 1.
Comparative example 1
A method for preparing a liquid metal particle/polymer composite comprising the steps of:
and (3) directly placing the liquid metal particle/polymer composite material obtained in the step (3) on a casting machine without the step (4) and the step (5), then casting a layer of mixed emulsion prepared in the step (2) on the upper surface of the liquid metal particle/polymer composite material, wherein the casting thickness is 0.06mm, the temperature of the casting machine is increased to 50 ℃ at the temperature increasing rate of 2.5 ℃/min, and the liquid metal particle/polymer composite material with semi-solidified upper surface is obtained by heating the casting machine for 2.5h at the temperature.
The rest is the same as in example 1.
Comparative example 2
The preparation method of the flexible composite material comprises the following steps:
and (4) placing and clamping the liquid metal particle/polymer composite on a uniaxial stretching platform to obtain the liquid metal sheet/polymer composite fixed on the uniaxial stretching platform.
The rest is the same as in example 1.
Comparative example 3
The preparation method of the flexible composite material comprises the following steps:
and (3) directly laminating the two pieces (5) of the obtained liquid metal sheet/polymer composite material without the step (6) to obtain the laminated liquid metal sheet/polymer composite material.
The rest is the same as in example 1.
Comparative example 4
The preparation method of the flexible composite material comprises the following steps:
and (3) obtaining the liquid metal sheet/polymer composite material with 8 laminated layers.
The rest is the same as in example 1.
Examples of the experiments
The electromagnetic shielding effectiveness of the flexible composite materials prepared in the examples 1 to 9 and the comparative examples 1 to 4 was tested at the frequency range of 8GHz to 12.4GHz, and the test results are shown in table 1. The results of comparing the electromagnetic shielding efficiency of the flexible composite material having high electromagnetic shielding performance obtained in example 3 with that of the liquid metal particle/polymer composite material obtained in comparative example 1 are shown in fig. 5.
TABLE 1 electromagnetic shielding effectiveness test results of the flexible composite materials prepared in examples 1 to 9
Item Electromagnetic shielding effectiveness (dB) Item Electromagnetic shielding effectiveness (dB)
Example 1 41.6 Example 8 41.4
Example 2 26 Example 9 41.5
Example 3 62 Comparative example 1 10.1
Example 4 32.2 Comparative example 2 22
Example 5 51.7 Comparative example 3 31.3
Example 6 41.4 Comparative example 4 23.9
Example 7 41.5
As can be seen from Table 1: the electromagnetic shielding effectiveness of the liquid metal sheet/elastomer composite material obtained by equal biaxial stretching is far higher than that of the liquid metal particle/elastomer composite material and that of the liquid metal/elastomer composite material obtained by uniaxial stretching; the electromagnetic shielding performance of the liquid metal sheet/elastomer composite material is improved along with the increase of the content of the liquid metal, the number of laminated layers and the strain of the equal biaxial stretching surface; the electromagnetic shielding performance of the liquid metal sheet/elastomer composite material is higher than 20dB, the application requirement in the civil field is met, and when the content of the liquid metal is higher, the electromagnetic shielding performance is higher than 40dB, and the requirement in the military field is met.
All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. The preparation method of the flexible composite material with high electromagnetic shielding performance is characterized by comprising the following steps:
the method comprises the following steps: the mass ratio of the polymer to the solvent is 1: (10-30) mixing, and magnetically stirring to obtain a polymer solution;
step two: mixing liquid metal and polymer solution according to the volume ratio of (1-5) to (5-9), and mechanically stirring to obtain a mixed emulsion;
step three: casting the mixed emulsion on a substrate, carrying out vacuum pumping treatment on the substrate carrying the casting, and drying in vacuum to obtain a liquid metal particle/polymer composite material;
step four: biaxially stretching liquid metal particles/polymer composite materials and the like to 50% -600% of surface strain, and then fixing the biaxially stretched liquid metal sheet/polymer composite materials to obtain the liquid metal sheet/polymer composite materials fixed on an equibiaxial stretching platform;
step five: heating the liquid metal sheet/polymer composite material fixed on the equal biaxial stretching platform for 2-4 h at the temperature of 60-120 ℃, and then naturally cooling to room temperature to obtain the liquid metal sheet/polymer composite material in a stretching state;
step six: casting a layer of the mixed emulsion prepared in the second step on the upper surface of the liquid metal sheet/polymer composite material obtained in the fifth step, heating to 40-60 ℃ at a heating rate of 1-4 ℃/min, and heating for 1-4 h at the temperature to obtain 1 layer of liquid metal sheet/polymer composite material with semi-solidified upper surface;
step seven: laminating two liquid metal sheet/polymer composite materials with semi-solidified upper surfaces, wherein the upper surfaces of the two liquid metal sheet/polymer composite materials are used as laminating contact surfaces to obtain a laminated liquid metal sheet/polymer composite material;
step eight: repeating the casting process in the sixth step and the laminating process in the seventh step to obtain a multilayer laminated liquid metal sheet/polymer composite material, wherein the number of layers is 10-20;
step nine: and placing the multilayer laminated liquid metal sheet/polymer composite material obtained in the step eight in a hot press die, and carrying out hot pressing treatment and heating solidification to obtain the flexible composite material with high electromagnetic shielding performance.
2. The method for preparing a flexible composite material with high electromagnetic shielding performance according to claim 1, wherein in the first step, the polymer is a thermoplastic elastomer, and the solvent comprises any one of dimethylformamide, dimethylacetamide, acetone and butanone.
3. The method of claim 2, wherein the thermoplastic elastomer comprises: any one of hydrogenated styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, polyacrylate, polyester, ethylene propylene diene monomer rubber, nitrile rubber, butyl rubber.
4. The method for preparing a flexible composite material with high electromagnetic shielding performance according to claim 1, wherein in the first step, the magnetic stirring is specifically: magnetically stirring at the stirring speed of 100 r/min-400 r/min for 12-48 h at the temperature of 20-60 ℃.
5. The method for preparing a flexible composite material with high electromagnetic shielding performance according to claim 1, wherein In the second step, the liquid metal is a pure liquid metal or a liquid metal alloy with a melting point lower than 30 ℃, and the composition includes at least one of Ga, In, Sn, Bi, and Hg.
6. The method for preparing a flexible composite material with high electromagnetic shielding performance according to claim 1, wherein in the second step, the mechanical stirring is specifically: mechanically stirring for 2 to 12 hours at the stirring speed of 50 to 200r/min under the temperature condition of 20 to 40 ℃.
7. The method for preparing the flexible composite material with high electromagnetic shielding performance according to claim 1, wherein in the third step, the vacuum drying process conditions are specifically as follows: the vacuum drying temperature is 60-100 ℃, and the vacuum drying time is 1-4 h.
8. The method for preparing the flexible composite material with high electromagnetic shielding performance according to claim 1, wherein in the ninth step, the hot pressing treatment specifically comprises: applying 50-100 kPa pressure at 100-120 ℃ to carry out hot pressing treatment for 10-60 min.
9. The method for preparing the flexible composite material with high electromagnetic shielding performance according to claim 1, wherein in the ninth step, the heating and curing specifically comprises: heating and curing for 1-4 h at the temperature of 60-100 ℃.
10. Flexible composite material with high electromagnetic shielding performance, characterized by being prepared according to the preparation method of any one of claims 1 to 9.
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