A liquid metal composite film with ultra-high strength, its preparation method and application

Abstract

This invention belongs to the field of liquid metal technology, and particularly relates to a liquid metal composite film with ultra-high strength, its preparation method, and its applications. Through the synergistic effect of "crosslinking reinforcement + stretching orientation," an ordered mechanically reinforced structure is constructed, resulting in a tensile strength of 752.0 MPa and a Young's modulus of 38.8 GPa for the composite film. Through a "calendering and fusion" process, isolated liquid metal droplets are broken and fused into continuous liquid metal sheets, which, in conjunction with highly conductive MXene nanosheets, construct a "solid (MXene)-liquid (LM) dual continuous conductive network." This allows the composite film, with a thickness of only 1.8 μm, to achieve an average EMI shielding effect of 31.2 dB and a shielding effectiveness per unit thickness (SSE / t) of 17333.3 dB / mm. The composite film described in this application is suitable for the "lightweight, thin, and efficient" requirements of modern highly integrated electronic devices (such as flexible circuit boards and micro-sensors), solving the contradiction of traditional shielding materials being "heavy when thick and weak when thin." It can also meet the application needs of fields with extremely high strength requirements, such as weaponry, aerospace, and the automotive industry.

Description

Technical Field

[0001] This invention belongs to the field of liquid metal technology, and particularly relates to a liquid metal composite film with ultra-high strength, its preparation method and application. Background Technology

[0002] Eutectic gallium-indium (EGaIn) alloys, as room-temperature liquid metals (LMs), have attracted widespread attention in the field of electromagnetic interference (EMI) shielding due to their excellent environmental stability, good formability, and superior electrical conductivity. To prepare LM-based thin films suitable for practical EMI shielding applications, easily processed polymers are often introduced as structural binders to address the inherent high fluidity and difficulty in shaping LMs, thus aiding in the preparation of macroscopically usable composite films. However, the mechanical properties of polymer / LM composites often significantly decrease due to dilution and disruption of the polymer continuous phase, as well as interfacial debonding, severely limiting their application in fields with high strength requirements such as weaponry, aerospace, and the automotive industry. Therefore, developing LM-based composite materials that combine excellent mechanical properties with efficient EMI shielding performance is not only a significant challenge in current scientific and engineering fields but also possesses important market application value.

[0003] Previous studies have typically used ultrasonic fragmentation to break liquid metal into micro / nano droplets, which are then composited with polymers to prepare liquid metal-based electromagnetic interference (EMI) shielding materials. However, the oxide shell (Ga2O3) formed on the surface of the liquid metal droplets during ultrasonication severely hinders the effective connection of conductive pathways, reducing the conductivity of the composite material and resulting in poor EMI shielding performance. To address this issue, external mechanical loads are often used to promote droplet deformation or fragmentation to construct continuous conductive pathways. For example, studies have shown that a composite film of cellulose nanofibers / ferric oxide / graphene / liquid metal was prepared using vacuum filtration combined with cold pressing, achieving an EMI shielding effectiveness of 36.2 dB at a thickness of 180 μm, but its tensile strength was only 55.3 MPa, which is insufficient for high-strength applications. To further improve mechanical properties, another study combined high-strength aramid nanofibers with liquid metal and two-dimensional transition metal carbonitrides (MXene) via sol-gel-film conversion and hot pressing. The resulting composite film achieved an electromagnetic interference shielding effectiveness of 74.6 dB and a tensile strength of 178.4 MPa at a thickness of 22 μm. Despite numerous attempts, the mechanical properties of most liquid metal composites are still largely limited by the inherent characteristics of the polymers used, making further breakthroughs difficult.

[0004] On the other hand, the development of highly efficient electromagnetic interference shielding materials with excellent mechanical properties using liquid metals still faces three major challenges: First, the weak hydrogen bonding between the oxide shell of the liquid metal droplet and the polymer makes the material prone to microcracks under stress; second, while mechanical loading helps to build a continuous conductive network to improve shielding effectiveness, it also destroys the internal mechanical support structure, leading to a decrease in mechanical properties; third, the shielding effectiveness per unit thickness (SSE) of liquid metal composite materials reported in existing studies is generally low, making it difficult to meet the requirements of modern highly integrated electronic devices. These factors together result in a mutual constraint between mechanical strength and electromagnetic interference shielding performance, and so far, there are no reports of achieving a synergistic improvement between the two. Summary of the Invention

[0005] Based on the above analysis, this invention discloses a liquid metal composite film with ultra-high strength, its preparation method and application, aiming to solve the problems of poor mechanical properties caused by weak interfacial bonding between LM and polymer, and the mutual restriction between mechanical properties and EMI shielding performance.

[0006] To achieve the above objectives, the first technical solution of this application discloses a method for preparing a liquid metal composite film with ultra-high strength, comprising the following steps:

[0007] S1. Preparation of PVA / MXene / LM mixed slurry:

[0008] LM was added to the PVA solution, and the mixture was ultrasonically broken down and then uniformly dispersed to obtain a PVA / LM dispersion.

[0009] MXene solution was added dropwise to the PVA / LM dispersion, and LM was continuously stirred to disperse it, resulting in a PVA / MXene / LM mixed slurry, wherein the MXene is nanosheets with the following composition. ;

[0010] S2. Preparation of composite membrane:

[0011] After the PVA / MXene / LM mixed slurry obtained from S1 was prepared into a film, it was soaked in Na2B4O7 solution, stretched and calendered to obtain a liquid metal composite film with ultra-high strength.

[0012] Furthermore, in the PVA / MXene / LM mixed slurry, the mass fraction of LM is 70.4%, the mass fraction of PVA is 8.5%, and the mass fraction of MXene is 21.1%.

[0013] Furthermore, the ultrasonic fragmentation described in S1 involves breaking the LM into nanodroplets with a diameter of approximately 0.2-1.1 μm.

[0014] Furthermore, the lateral dimensions of the MXene nanosheets are 0.2-0.7 μm.

[0015] Furthermore, the component is Ti3C2T X The preparation method of MXene nanosheets is as follows: Ti3AlC2MAX powder is added to the hydrochloric acid solution of LiF, and the reaction product is obtained after mixing and stirring. The reaction product is then purified.

[0016] Furthermore, the concentration of the Na2B4O7 solution in S2 is 4 mg / mL, and the soaking time is 1-2 min.

[0017] Furthermore, the stretching ratio in the stretching step described in S2 is ≤20%.

[0018] And, the liquid metal composite film with ultra-high strength prepared according to the above preparation method.

[0019] The second technical solution of this application discloses the application of the above-mentioned liquid metal composite film with ultra-high strength as an electromagnetic interference shielding material.

[0020] Compared with the prior art, this application has the following beneficial effects:

[0021] ① This application addresses the problem of poor mechanical properties caused by weak interfacial bonding between LM and polymer: by constructing multiple bonding interactions (coordination bonds, hydrogen bonds, and boron ester bonds) to replace the single weak hydrogen bonds in the prior art, the interfacial bonding force is enhanced, microcracks are avoided when the material is under stress, and the mechanical properties of LM-based composite materials are significantly improved.

[0022] ②This application solves the problem of mutual constraint between mechanical properties and EMI shielding performance: through the synergistic process of "stretching orientation-calendering fusion".

[0023] ③ The ultra-high strength liquid metal composite film prepared in this application forms a robust mechanical reinforcement structure and constructs a dense and continuous conductive network, achieving simultaneous improvement in mechanical properties and EMI shielding performance.

[0024] ④ This application addresses the problem of low shielding effectiveness per unit thickness: by optimizing the material composition and structure, a solid-liquid dual continuous conductive network is prepared, which effectively improves the conductivity of the LM-based composite film, thereby increasing SSE / t and meeting the EMI shielding requirements of highly integrated electronic devices. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 SEM image (a) and corresponding EDS image (b) of the cross-section of the PMLM-20% nanocomposite membrane;

[0027] Figure 2 The orientation factors of PVA nanocrystals and MXene nanosheets in PMLM composite films prepared under different stretching ratios, derived from wide-angle X-ray scattering tests;

[0028] Figure 3 (a) Stress-strain curves, (b) tensile strength and strain, and (c) Young's modulus and toughness of OPMLM, SPMLM, PMLM-0%, 10%, 20%, and 30% films.

[0029] Figure 4 (a) X-band (8.2-12.4 GH) for OPMLM, SPMLM, PMLM-0%, 10%, 20%, and 30% thin films. Z (a) EMI shielding effect, (b) average SE R SE A , and SE T (c) Average absorption (A), reflection (R), and transmission (T) power coefficients. Detailed Implementation

[0030] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0031] The “liquid metal (LM)” mentioned in this application refers to a eutectic gallium-indium (EGaIn) alloy composed of 75wt% gallium and 25wt% indium, with a melting point of 16°C. It is a room-temperature liquid and has excellent electrical conductivity and environmental stability.

[0032] The electromagnetic interference (EMI) mentioned in this application refers to the interference caused by electromagnetic waves to the normal operation of electronic equipment, which needs to be blocked or attenuated by shielding materials.

[0033] The "two-dimensional transition metal carbonitride (MXene)" mentioned in this application specifically refers to Ti3C2T XNanosheets, prepared by selective etching of the Ti3AlC2 MAX phase, possess high conductivity and a sheet-like structure, which can assist in the construction of conductive networks. Specific shielding effectiveness per unit thickness (SSE / t) is a comprehensive indicator that measures the shielding performance and thickness of electromagnetic shielding materials. The unit is dB / mm, and a higher value indicates better shielding performance at the same thickness.

[0034] The "total EMI shielding effectiveness (EMISE)" described in this application T "))" is determined by absorption shielding efficiency (SE) A ) and reflection shielding efficiency (SE) R The power coefficients of reflection (R), absorption (A), and transmission (T) are obtained by adding them together; these are parameters obtained by testing the sample with testing equipment and are used to calculate SE. A and SE R。

[0035] The "polyethylene terephthalate (PET)" described in this application is a substrate material used in the preparation of composite films, and it has good heat resistance and mechanical stability.

[0036] The "sodium tetraborate (Na2B4O7)" described in this application is used for crosslinking treatment of composite membranes to form boron ester bonds with polyvinyl alcohol (PVA, a flexible and easily processed polymer material) to regulate the material structure and properties.

[0037] The "ultra-high strength liquid metal composite membrane" described in this application comprises three raw materials: PVA / MXene / LM. Therefore, the prepared nanocomposite membrane is also simply referred to as a PMLM membrane. Different suffixes or prefixes represent different processing techniques, which are described in detail below. For example, PMLM-20% indicates a calendered PMLM membrane prepared at a 20% stretch rate, which has the best performance among all components. The LM content is the same in all PMLM membranes (70.4 wt%) and is much higher than that of other components; therefore, the prepared PMLM composite membrane is also called an LM-based composite membrane.

[0038] The first embodiment of this application discloses a method for preparing a liquid metal composite film with ultra-high strength, comprising the following steps:

[0039] S1. Preparation of PVA / MXene / LM mixed slurry:

[0040] LM was added to the PVA solution, and the mixture was ultrasonically broken down and then uniformly dispersed to obtain a PVA / LM dispersion.

[0041] MXene solution was added dropwise to the PVA / LM dispersion, and LM was continuously stirred to disperse it, resulting in a PVA / MXene / LM mixed slurry, wherein the MXene was in the form of nanosheets with the composition Ti3C2T. X .

[0042] In this embodiment, the PVA raw material used in the PVA / LM dispersion is a specific mass of PVA powder (model 1799, a commercially available general-purpose model), preferably dissolved in deionized water by heating, with a preferred concentration of 60 mg / mL. PVA1799 refers to a type of polyvinyl alcohol, where "17" indicates the degree of polymerization, approximately 1700, and "99" indicates the degree of alcoholysis, approximately 99%. This high degree of alcoholysis gives PVA1799 a large number of hydroxyl groups (-OH), which play a key role in its chemical and physical properties. It is a water-soluble polymer widely used in fields such as architectural coatings.

[0043] In this embodiment, after the LM (75wt% Ga, 25wt% In) is added to the PVA solution, it first needs to be broken into nanodroplets of 0.2-1.1 μm. On the one hand, this allows the LM to be uniformly dispersed in the PVA solution to form a uniform PVA / LM dispersion. On the other hand, after the LM is broken, the surface of the newly formed LM nanoparticles will be quickly oxidized to form a Ga2O3 layer. The Ga2O3 can form preliminary coordination bonds and hydrogen bonds with the hydroxyl groups of the PVA molecular chain, effectively preventing LM leakage.

[0044] In this embodiment, the MXene nanosheets are composed of... The preferred method is to mix LiF hydrochloric acid solution with Ti3AlC2MAX powder and stir to react, selectively etching the Al phase during the reaction; preferably, the reaction product also needs to be purified by washing, separation and other steps, and the lateral size of the obtained MXene nanosheets is 0.2-0.7μm.

[0045] In this embodiment, the advantages of PVA and MXene are: 1. PVA is easy to process and is soluble in water. 2. PVA has abundant surface chemical groups, which easily form hydrogen bonds with MXene, enhancing mechanical properties. 3. PVA can be peeled off from the substrate at a very thin thickness after subsequent soaking in Na2B4O7 solution. MXene is mainly utilized for its high electrical conductivity and abundant surface chemical groups. The above materials are unique and irreplaceable. If they are replaced with similar polymers or MXene, the final material performance will be greatly reduced, and the preparation cost will increase significantly.

[0046] Furthermore, the Na₂B₄O₇ solution primarily functions to crosslink PVA, thereby enhancing its mechanical properties. The main component responsible for this is B(OH)₄. - If other compounds containing B(OH)4 are used... - Replacing Na2B4O7 solution with a solution of [other chemicals] will increase the cost and may also decrease the performance.

[0047] In this embodiment, the PVA / MXene / LM mixed slurry is prepared by adding MXene solution dropwise to the PVA / LM dispersion while continuously stirring. This allows MXene nanosheets to form strong coordination bonds with Ga2O3 on the surface of LM droplets, further stabilizing the LM dispersion and resulting in a uniform mixed slurry.

[0048] In the PVA / MXene / LM mixed slurry, the mass fraction of LM is 70.4%, the mass fraction of PVA is 8.5%, and the mass fraction of MXene is 21.1%.

[0049] S2. Preparation of composite membrane:

[0050] After the PVA / MXene / LM mixed slurry obtained from S1 was prepared into a film, it was soaked in Na2B4O7 solution, stretched and calendered to obtain a liquid metal composite film with ultra-high strength.

[0051] In this embodiment, the method of preparing the PVA / MXene / LM mixed slurry into a film can be selected by coating, such as blade coating, and the substrate is preferably PET.

[0052] The obtained PVA / MXene / LM membrane was immersed in Na2B4O7 solution to carry out a crosslinking reaction, during which borate ester bonds could be formed between PVA molecular chains to complete the crosslinking and obtain a PVA / MXene / LM crosslinked film.

[0053] The cross-linked film is further subjected to a stretching process, which enables the PVA molecular chains, PVA nanocrystals, MXene nanosheets, and LM droplets to be simultaneously oriented, forming an ordered mechanically reinforced structure. The stretching ratio in this stretching step is ≤30%, preferably 20%.

[0054] The isolated LM droplets are then subjected to calendering to break them up and fuse them into continuous LM sheets. These sheets, together with MXene nanosheets, form a solid-liquid dual continuous conductive network, ultimately yielding a PVA / MXene / LM nanocomposite film (PMLM).

[0055] The aforementioned thin film constructs an ordered mechanically enhanced structure through the synergistic effect of "crosslinking reinforcement + stretching orientation": on the one hand, the coordination bonds and hydrogen bonds between LM, MXene, and PVA effectively solve the problem of weak interfacial bonding; on the other hand, the borate ester bonds formed between PVA molecular chains provide an adjustable crosslinking structure, which is conducive to the simultaneous orientation of PVA molecular chains, PVA nanocrystals, MXene nanosheets, and LM nanodroplets induced by stretching. The final prepared PMLM composite film (LM mass fraction 70.4 wt%) has a tensile strength of 752.0 MPa and a Young's modulus of 38.8 GPa, which is a significant improvement compared to existing technologies. As an electromagnetic interference shielding material, it can directly meet the application requirements of fields with extremely high strength requirements such as weaponry, aerospace, and automotive industries, filling the application gap of liquid metal-based materials in high-strength scenarios.

[0056] The technical solutions and effects of this application will be described in detail below through specific embodiments.

[0057] Example 1: Preparation of a liquid metal composite film with ultra-high strength (PVA / MXene / LM nanocomposite film, PMLM)

[0058] The raw materials used in this embodiment were sourced as follows: Liquid metal (LM, composed of 75 wt% gallium and 25 wt% indium, melting point 16℃) was purchased from Dongguan Huatai Metal Materials Technology Co., Ltd. Ti3AlC2MAX powder (400 mesh, 98%) was purchased from Jilin Yiyi Technology Co., Ltd. Polyvinyl alcohol (PVA, 1799) and sodium tetraborate decahydrate (Na2B4O7·10H2O, 99.9%) were purchased from Shanghai Maclean Biochemical Co., Ltd. Concentrated hydrochloric acid (HCl, 37 wt%) and lithium fluoride (LiF, 99.9%) were purchased from China National Pharmaceutical Chemical Reagent Co., Ltd.

[0059] S1. Preparation of PVA / MXene / LM mixed slurry

[0060] (1) MXene (Ti3C2T) XPreparation of nanosheets: 1 g of LiF powder was slowly added to 20 mL of 9 M hydrochloric acid (HCl) solution and stirred at room temperature for 20 min until completely dissolved; then 1.0 g of Ti3AlC2MAX powder (400 mesh, 98% purity) was added and stirred continuously at 45 °C for 48 h to selectively etch the Al phase; the reaction product was centrifuged at 4000 rpm for 5 min to remove the acid solution, and washed repeatedly with deionized water until the pH of the supernatant was ≈7; the washed precipitate was redispersed in deionized water, sonicated at 300 W power for 2 h under ice bath conditions, and then centrifuged at 3500 rpm for 20 min. The supernatant (containing a few layers of MXene) was collected, diluted to 12 mg / mL, and stored at 4 °C for later use. The lateral size of the obtained MXene nanosheets was 0.2-0.7 μm.

[0061] (2) Preparation of PVA solution: Add a specific mass of PVA powder (model 1799) to 20 mL of deionized water and stir continuously at 90 °C until completely dissolved to prepare a PVA solution with a concentration of 60 mg / mL.

[0062] (3) Preparation of LM dispersion: Add 4g of LM (75wt% Ga, 25wt% In) to the above PVA solution, and sonicate with a probe sonicator at 840W power for 5min under ice bath conditions to break the LM into nanodroplets with a diameter of about 0.6μm, forming a uniform PVA / LM mixture; continuously stir with magnetic force to allow the Ga2O3 on the surface of the LM droplets to form preliminary coordination bonds and hydrogen bonds with the hydroxyl groups of the PVA molecular chains, so as to prevent LM leakage.

[0063] (4) Preparation of PVA / MXene / LM mixed slurry: 40 mL of MXene solution (12 mg / mL) was added dropwise to the PVA / LM mixture and stirred continuously for 30 min to form strong coordination bonds between MXene nanosheets and Ga2O3 on the surface of LM droplets, further stabilizing the LM dispersion and obtaining a uniform mixed slurry.

[0064] S2. Preparation of PVA / MXene / LM nanocomposite films

[0065] Blade coating: Using blade coating (coating gap 300μm), the above mixed slurry is uniformly coated on the PET substrate, and then placed in a 50℃ oven to dry and remove the solvent (water) to obtain a pre-dried PVA / MXene / LM film.

[0066] Crosslinking treatment: Immerse the dried film in a 4 mg / mL Na2B4O7 solution for 1-2 min to form borate ester bonds between PVA molecular chains and complete crosslinking; then peel the film off the PET substrate.

[0067] Stretching and Orientation: The peeled cross-linked film is fixed on a custom fixture and stretched and fixed at a specific stretching ratio (0%, 10%, 20%, 30%) at room temperature; during the stretching process, PVA molecular chains, PVA nanocrystals, MXene nanosheets, and LM droplets are simultaneously oriented to form an ordered mechanically reinforced structure.

[0068] Calendering and Fusion: The stretched and oriented film was calendered in a two-roll press at room temperature. During calendering, isolated LM droplets broke and fused to form continuous LM sheets, which, together with MXene nanosheets, constructed a solid-liquid dual-continuous conductive network, ultimately yielding a PVA / MXene / LM nanocomposite film (PMLM). For simplicity, PMLM nanocomposite films prepared at different stretching ratios are denoted as PMLM-x, where x represents the stretching ratio (0%, 10%, 20%, 30%). As a comparison, a PMLM film without stretching and calendering was also prepared and named OPMLM. Furthermore, a sample that underwent only 20% stretching without calendering was also prepared as a comparison sample and named SPMLM.

[0069] like Figure 1 The image shows the SEM image and corresponding EDS image of the cross-section of the PMLM-20% nanocomposite film. In the prepared PMLM composite film (PMLM-20%), LM nanodroplets deform under stress to form continuous LM sheets, while MXene nanosheets are more clearly arranged along the stretching direction, forming a solid-liquid dual-continuous conductive network.

[0070] like Figure 2 The figure shows the orientation factors (f) of PVA nanocrystals and MXene nanosheets in PMLM composite films prepared under different stretching ratios, derived from wide-angle X-ray scattering tests. When the stretching ratio increases from 0% to 30%, the values ​​of the orientation factors (f) of PVA nanocrystals and MXene nanosheets in the PMLM film increase from 0.22 and 0.33 to 0.79 and 0.89, respectively, which strongly confirms the appearance of an orientation structure in the PMLM nanocomposite film.

[0071] like Figure 3The figures show (a) stress-strain curves, (b) tensile strength and strain, and (c) Young's modulus and toughness of OPMLM, SPMLM, PMLM-0%, 10%, 20%, and 30% films. The OPMLM film exhibits the worst mechanical properties, with a tensile strength of 172.3 MPa, a toughness of 8.7 MJ / m³, and a Young's modulus of 4.5 GPa. In contrast, the SPMLM film shows a significant improvement in performance: a tensile strength of 392.3 MPa, a toughness of 11.6 MJ / m³, and a Young's modulus of 24.1 GPa, indicating that the stretch-induced multi-orientation structure effectively enhances the mechanical properties of the PMLM nanocomposite film. Furthermore, the PMLM-0% film shows slightly better mechanical properties than the OPMLM film, with a tensile strength of 269.6 MPa, a toughness of 17.4 MJ / m³, and a Young's modulus of 6.1 GPa. This improvement can be attributed to the denser structure formed by the calendering process. With increasing stretching ratio during film preparation, the tensile strength, toughness, and Young's modulus of PMLM nanocomposite films initially increase and then decrease, while their fracture strain decreases monotonically. The PMLM-20% film exhibits the highest mechanical properties: tensile strength of 752.0 MPa, toughness of 33.0 MJ / m³, and Young's modulus of 38.8 GPa. Its superior performance is mainly attributed to the enhanced, dense, multi-oriented structure and multiple bonding within the LM nanocomposite film. The decrease in mechanical properties of the PMLM-30% film may be attributed to excessive stretching during preparation, which damages the internal microstructure and creates stress concentration points. Furthermore, the decrease in fracture strain with increasing stretching ratio is mainly attributed to the gradually enhanced multi-oriented structure and increased bonding sites, which restrict the movement of PVA chains.

[0072] like Figure 4 The figures show the EMI shielding performance of OPMLM, SPMLM, PMLM-0%, 10%, 20%, and 30% thin films in the X-band (8.2–12.4 GHz) and the average SE. R SE A , and SE T (c) Average absorption (A), reflection (R), and transmission (T) power coefficients: SE of OPMLM and SPMLM films in the X-band T With shielding strengths of only 7.0 dB and 14.5 dB respectively, they exhibit poor EMI shielding performance. It is worth noting that PMLM-0% SE... T The SE was significantly improved to 24.2 dB, exceeding the standard for commercial EMI shielding materials (>20 dB). As the elongation increased from 10% to 20% and 30%, the SE of the PMLM nanocomposite film also improved. TThe SE of the PMLM nanocomposite membrane increased from 27.8 dB for PMLM-10% to 31.2 dB for PMLM-20%, and then to 35.3 dB for PMLM-30%. T The growth comes from its SE R and SE A The synchronous growth of SE A The increase was significantly greater. Specifically, as the stretching ratio increased from 0% to 30%, the SE of the PMLM nanocomposite film... A It increased by 8.6 dB (15.8-24.4 dB), while SE R The increase was only 2.5 dB (8.4–10.9 dB). This phenomenon is mainly attributed to the perfect conductive network constructed by LM lamellae and MXene nanosheets, which increases the ohmic loss of electromagnetic waves as they penetrate the PMLM nanocomposite film.

[0073] This invention constructs an ordered mechanically reinforced structure through the synergistic effect of "crosslinking reinforcement + stretching orientation": on the one hand, the coordination and hydrogen bonding between LM, MXene, and PVA effectively solves the problem of weak interfacial bonding; on the other hand, the borate ester bonds formed between PVA molecular chains provide an adjustable crosslinking structure, which is beneficial for stretching-induced synchronous orientation of PVA molecular chains, PVA nanocrystals, MXene nanosheets, and LM nanodroplets. The optimal PMLM composite film (LM mass fraction 70.4 wt%, stretching ratio 20%) finally prepared has a tensile strength of 752.0 MPa and a Young's modulus of 38.8 GPa, which is a significant improvement compared to existing technologies. It is expected to directly meet the application needs of fields with extremely high strength requirements such as weaponry, aerospace, and automotive industries, filling the application gap of liquid metal-based materials in high-strength scenarios.

[0074] This invention utilizes a "calendering-fusion" process to break up and fuse isolated LM droplets into continuous LM sheets, which are then synergistically combined with highly conductive MXene nanosheets to construct a "solid (MXene)-liquid (LM) dual continuous conductive network." Electrons can be rapidly transported through the MXene sheets and conduct across scales through the LM sheets, significantly improving the conductivity of the composite film. The prepared PMLM composite film, with a thickness of only 1.8 μm, achieves an average EMI shielding effect of 31.2 dB, and a shielding effectiveness per unit thickness (SSE / t) of 17333.3 dB / mm, superior to most reported EMI shielding materials. Its excellent EMI shielding performance meets the "thin, light, and efficient" requirements of modern highly integrated electronic devices (such as flexible circuit boards and micro-sensors), resolving the contradiction of traditional shielding materials being "heavy when thick and weak when thin."

[0075] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for preparing a liquid metal composite film with ultra-high strength, characterized in that, Includes the following steps: S1. Preparation of PVA / MXene / LM mixed slurry: LM was added to the PVA solution, and the mixture was ultrasonically broken down and then uniformly dispersed to obtain a PVA / LM dispersion. MXene solution was added dropwise to the PVA / LM dispersion, and LM was continuously stirred to disperse it, resulting in a PVA / MXene / LM mixed slurry, wherein the MXene was a nanosheet with the composition Ti3C2Tx; S2. Preparation of composite membrane: After the PVA / MXene / LM mixed slurry obtained from S1 was prepared into a film, it was soaked in Na2B4O7 solution, stretched and calendered to obtain a liquid metal composite film with ultra-high strength.

2. The preparation method according to claim 1, characterized in that, In the PVA / MXene / LM mixed slurry, the mass fraction of LM is 70.4%, the mass fraction of PVA is 8.5%, and the mass fraction of MXene is 21.1%.

3. The preparation method according to claim 1, characterized in that, The ultrasonic fragmentation described in S1 involves breaking the LM into nanodroplets with a diameter of 0.2-1.1 μm.

4. The preparation method according to claim 1, characterized in that, The MXene nanosheets described in S1 have a lateral dimension of 0.2-0.7 μm.

5. The preparation method according to claim 1, characterized in that, The component is Ti3C2T. X The preparation method of MXene nanosheets is as follows: Ti3AlC2MAX powder is added to the hydrochloric acid solution of LiF, and the reaction product is obtained after mixing and stirring. The reaction product is then purified.

6. The preparation method according to claim 1, characterized in that, The concentration of the Na2B4O7 solution in S2 is 4 mg / mL, and the soaking time is 1-2 min.

7. The preparation method according to claim 1, characterized in that, The stretching ratio in the stretching step described in S2 is ≤30%.

8. A liquid metal composite membrane with ultra-high strength prepared by any one of the preparation methods according to claims 1-7.

9. The application of the ultra-high strength liquid metal composite film according to claim 8 as an electromagnetic interference shielding material.

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