A MXene-based bimaterial gradient-driven thin film and a preparation method thereof

Abstract

The application belongs to the technical field of intelligent flexible drivers, and discloses a double-material gradient driving film based on MXene and a preparation method thereof; the gradient driving film comprises three layers of structures of a bottom layer, a middle layer and a top layer arranged in sequence from bottom to top; MXene is used as the matrix and is doped with PMMA and CNF in the three layers of structures; and the concentration of the PMMA gradually decreases and the concentration of the CNF gradually increases from bottom to top; the gradient driving film is prepared by step-by-step vacuum filtration from the bottom layer to the top layer; the application is a bidirectional gradient asymmetric structure, eliminates the obvious interlayer interface, significantly improves the interlayer bonding force and structural stability of the film, realizes triple stimulation response of humidity, light field and electric field, and solves the problems of the interlayer abrupt interface, weak bonding force of the traditional multilayer driver, single driving mode of the driver, slow response speed, low bending curvature, poor deformation recovery and the like.

Description

Technical Field

[0001] This invention belongs to the field of intelligent flexible actuator technology, and relates to a multi-stimulus responsive MXene-based composite actuation film, specifically a dual-material gradient actuation film based on MXene and its preparation method. Background Technology

[0002] Flexible intelligent actuators are a current research hotspot in the fields of intelligent materials and microelectromechanical systems (MEMS). Unlike traditional rigid actuators, they possess advantages such as flexibility, adaptability to complex and irregular working environments, and diverse actuation methods, and are now widely used in biomimetic robots, medical micro-devices, intelligent soft actuators, and smart wearable devices. Currently, mainstream flexible actuator materials include carbon-based materials, polymers, two-dimensional nanomaterials, and composite functional materials. Among these, two-dimensional layered MXene materials, with their high conductivity, excellent photothermal / electrothermal conversion efficiency, good flexibility, and ease of solution processing, have become the preferred core substrate for flexible actuators.

[0003] Currently, most commercially available and laboratory-developed flexible actuators employ bilayer heterogeneous composite structures. The fabrication logic involves combining a stimulus-responsive active material with an inert material and a differentially responsive material. The bending of the thin film is achieved by relying on the deformation mismatch between the two materials under a single external stimulus. To enrich the actuation modes and achieve multi-field responses, existing technologies typically employ multilayer stacking composites, integrating multiple functional materials to construct three or more heterogeneous layered structures.

[0004] However, after reviewing existing technologies and conducting experimental verification, the following technical problems exist with current multilayer and double-layer heterogeneous flexible actuators: 1. Abrupt interlayer interfaces lead to low bonding strength: In traditional bilayer and multilayer actuators, the material layers have clear abrupt interfaces. The surface energy, polarity, and physical properties of different materials vary greatly, and the interlayer bonding relies solely on physical adhesion, without chemical bonding or compositional transition, resulting in weak interlayer adhesion. During long-term cyclic bending and deformation recovery processes, slippage, delamination, and peeling are prone to occur between layers, leading to poor device structural stability and a significantly shortened lifespan.

[0005] 2. Limited driving mode: Conventional dual-layer actuators can achieve bidirectional reversible deformation, but the driving mode is limited; it is difficult to meet the complex and precise control requirements of intelligent robotic arms, bionic actuators, etc.

[0006] 3. Poor material compatibility and weak overall driving performance: Existing multi-material composite actuators have unreasonable material matching and lack functional components with complementary deformation characteristics. They generally have problems such as small bending curvature, slow response, and incomplete deformation recovery. At the same time, some functional materials are expensive to prepare and have complex processing technology, making it difficult to mass-produce them on a large scale.

[0007] 4. Complex manufacturing process and difficult mass production: Existing high-performance flexible actuators mostly adopt manufacturing processes such as high-temperature sintering, chemical vapor deposition, and complex modification synthesis. They rely on high-precision experimental equipment, have high energy consumption, complex processes, and harsh experimental conditions, making it impossible to achieve low-cost, large-scale industrial production.

[0008] In summary, there is an urgent need in this field to develop a flexible thin-film actuator that is easy to fabricate, has high interlayer bonding strength, excellent cycle stability, and can achieve bidirectional reversible actuation under multiple field stimuli. This would ensure excellent actuation performance while reducing fabrication costs, simplifying the processing flow, and solving the industry pain points of traditional heterogeneous layered actuators, such as delamination, single actuation mode, and poor stability. Summary of the Invention

[0009] The purpose of this invention is to provide a dual-material gradient driven thin film based on MXene and its preparation method, so as to solve the problems of abrupt interlayer interfaces, weak bonding, single driving mode, slow response speed, low bending curvature and poor deformation recovery of traditional multilayer actuators.

[0010] This invention is achieved through the following technical solution: A dual-material gradient-driven thin film based on MXene includes a three-layer structure consisting of a bottom layer, a middle layer, and a top layer arranged sequentially from bottom to top. Each of the three layers uses MXene as a substrate and is doped with PMMA and CNF. The concentration of PMMA gradually decreases from bottom to top, while the concentration of CNF gradually increases. The three-layer structure has no clear layering interface.

[0011] Preferably, the concentrations of PMMA and CNF in the middle layer are equal, resulting in uniform doping.

[0012] A method for preparing a dual-material gradient-driven thin film based on MXene includes the following steps: Step 1: Prepare MXene dispersion; Step 2: Prepare PMMA@MXene mixed dispersion, CNF & PMMA@MXene ternary mixed dispersion, and CNF@MXene mixed dispersion respectively; Step 3: Prepare gradient-driven thin films from the bottom layer to the top layer using stepwise vacuum filtration.

[0013] Furthermore, the preparation method of MXene dispersion includes: MAX-Ti3AlC2 powder was placed in an etching solution and etched to obtain a multilayer MXene mixture. The multilayer MXene mixture was centrifuged, washed, dried, dried to remove impurities, purified, and then thoroughly mixed with water to obtain an MXene aqueous dispersion.

[0014] Further, to ensure thorough mixing with water, deionized water is added to the purified precipitate, and the mixture is vigorously shaken and sonicated for 20-30 minutes. Then, it is centrifuged at a low speed of 3000-4000 rpm for 3-5 minutes to remove multi-layered stacked particles and collect the upper blackish-brown liquid, which is the MXene aqueous dispersion.

[0015] Furthermore, the preparation method of PMMA@MXene mixed dispersion is as follows: PMMA nanospheres are taken, deionized water is added, and PMMA aqueous dispersion is prepared by thorough stirring; MXene aqueous dispersion and PMMA aqueous dispersion are mixed at a mass ratio of 3~5:1 and ultrasonically dispersed.

[0016] Furthermore, the preparation method of CNF & PMMA@MXene ternary mixed dispersion is to take MXene aqueous dispersion, mix PMMA aqueous dispersion and CNF aqueous dispersion with solid content of 0.5~0.8 wt% at a mass ratio of 15~20:1:1, stir magnetically at room temperature and homogenize by ultrasonication.

[0017] Furthermore, the CNF@MXene mixed dispersion is prepared by taking an MXene aqueous dispersion and mixing it with a CNF aqueous dispersion with a solid content of 0.5~0.8 wt% at a mass ratio of 5~8:1, and then ultrasonically dispersing it evenly.

[0018] Furthermore, the stepwise vacuum filtration process includes: Substrate preparation: The entire PMMA@MXene mixed dispersion was transferred to a vacuum filtration device, with the vacuum level controlled at 0.06~0.08 MPa, and filtered until the membrane was semi-dry. Preparation of the middle layer: While maintaining a constant vacuum negative pressure, the ternary mixed dispersion is slowly and uniformly added to the surface of the bottom film, and the mixture is continuously filtered until it is semi-dry to form a middle layer with a continuous transition of components; Top layer preparation: Under the same vacuum conditions, CNF@MXene mixed dispersion is added dropwise and filtered until the film is completely formed. The three layers of film are tightly bonded by residual moisture and vacuum pressure, without additional drying or heat treatment processes.

[0019] The beneficial effects of this invention compared to the prior art are as follows: This invention utilizes a stepwise vacuum filtration process to construct a bidirectional gradient asymmetric structure with synergistic distribution of PMMA and CNF along the thickness direction of an MXene film. This allows the composite film to bend to one side under humidity stimulation and in the opposite direction under light or electrical stimulation, thus achieving reversible bidirectional actuation. Unlike traditional bilayer structure actuators, this invention achieves continuous component transition through a gradient interface, eliminating obvious interlayer boundaries and significantly improving the interlayer bonding and structural stability of the film. This method offers a simple fabrication process, and the resulting actuator possesses advantages such as excellent actuation performance, rapid response, and high cycle stability. Specifically: 1. Structural design advantages, completely solving the problem of interlayer stability. This invention employs a stepwise vacuum filtration process to construct a continuous compositional gradient structure, resulting in a smooth transition between PMMA and CNF content within the film, eliminating the abrupt interfaces common in traditional multilayer structures. No adhesive is required for bonding; instead, vacuum pressure and residual moisture achieve tight interlayer bonding, significantly enhancing interlayer strength. After 2000 cycles of use, no delamination, slippage, or detachment occurs, demonstrating structural stability far exceeding that of traditional bilayer and multilayer composite actuators, substantially extending device lifespan. By avoiding the abrupt interfaces found in traditional bilayer or multilayer structures and significantly strengthening interlayer bonding, this invention solves the problems of easy delamination and short lifespan in multilayer actuators.

[0020] 2. Excellent driving performance, enabling precise bidirectional controllable deformation. Leveraging the differentiated deformation properties of CNF (hydrophilic swelling) and PMMA (high thermal expansion), combined with MXene's excellent photothermal and electrothermal conversion performance, it achieves a triple stimulus response to humidity, light field, and electric field. The bending direction is opposite to that under humidity and light / electric stimulation, completing reversible bidirectional drive. The maximum bending angle can reach 470°, the deformation recovery rate is close to 100%, and there is no residual deformation, which can meet the precise control requirements of intelligent robotic arms and precision actuators.

[0021] 3. Raw materials are inexpensive, and the preparation process is simple and easy to mass-produce. The MXene, PMMA, and CNF used in this invention are all commercially available materials with low procurement costs. The entire process employs room-temperature solution mixing and vacuum filtration molding, eliminating the need for high-temperature sintering, high-pressure reactions, and expensive precision equipment. The preparation process is simple and energy-efficient. The preparation time for a single film is no more than 2 hours, and batch production is possible, resulting in high production efficiency. This makes it suitable for industrial-scale mass production and has a low barrier to entry for industrialization.

[0022] 4. Wide range of applicable scenarios and strong environmental compatibility. The thin film driving method of this invention is diversified, including low-voltage electric driving, non-contact optical driving, and environmental humidity driving, which can be adapted to different working scenarios. The film is thin, flexible, and lightweight, and can be cut into any shape. It can not only be used to make intelligent robotic arms to perform grasping, transferring, and releasing actions, but also applied to fields such as micro sensors, bionic soft robots, intelligent temperature control films, and medical micro actuators. It has extremely strong environmental compatibility.

[0023] 5. Good material synergy, and adjustable and controllable overall performance. By simply adjusting the doping ratio of PMMA and CNF, the humidity-driven or photo / electric-driven performance can be optimized to suit different operating conditions; there is no chemical repulsion between the materials, the physicochemical properties are stable, they are resistant to room temperature oxidation and mild acid and alkali corrosion, the storage and use conditions are flexible, and the daily maintenance cost is low. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of the MXene-based composite thin film with dual material composition gradients according to the present invention. Figure 2 This is a schematic diagram of the multi-field driving principle of the MXene-based driver prepared in this invention; Figure 3 The diagram shows the response performance of the driving film prepared in this invention under humidity, light field and electric field stimulation (top row: humidity stimulation; middle row: light field stimulation; bottom row: electric field stimulation); in the diagram, PMM is PMMA@MXene&MXene; CMM is CNF@MXene&MXene; PMCM is PMMA@MXene&CNF@MXene; Figure 4 This diagram illustrates the process of grasping, transferring, and releasing a target object using an intelligent robotic hand fabricated with the MXene-based actuator prepared in this invention. Detailed Implementation

[0025] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0026] This invention selects MXene as a conductive, photothermal, and electrothermal substrate material, and combines it with hydrophilic cellulose nanofiber (CNF) and hydrophobic polymethyl methacrylate (PMMA) nanospheres as dual-gradient modification materials. A three-layer continuous gradient composite film is prepared through a stepwise vacuum filtration process. The compositional gradient change pattern along the film thickness direction is as follows: the bottom layer has high PMMA and low CNF, the middle layer has uniformly doped PMMA and CNF, and the top layer has high CNF and low PMMA, with no clear layer interface. The bidirectional driving is achieved by utilizing the differential deformation properties of the materials: under humidity stimulation, CNF absorbs moisture and swells, causing the film to bend towards the PMMA side; under light / electric stimulation, MXene completes energy conversion and generates heat, and the high thermal expansion properties of PMMA trigger reverse bending, ultimately achieving reversible bidirectional driving under multiple stimuli.

[0027] This invention proposes a method for preparing bidirectional driven thin films based on a dual-material gradient structure of MXene, specifically including the following steps: Step 1: Preparation of MXene Dispersion 1. Preparation of etching solution: Measure 20-25 mL of concentrated hydrochloric acid into a polytetrafluoroethylene beaker, slowly add 1-2 g of lithium fluoride under stirring at room temperature, and continue stirring for 30 min until the lithium fluoride is completely dissolved to form a uniform etching solution. 2. High-temperature etching: Slowly add 2 g of MAX-Ti3AlC2 powder to the etching solution, heat to 35~40 ℃, and continuously stir and etch at a constant temperature for 36~48 h to remove the aluminum atom layer and obtain a multilayer MXene mixture; 3. Centrifugation and washing: Transfer the etched mixture into a centrifuge tube and centrifuge at 10,000-12,000 rpm for 10-15 minutes. Discard the acidic supernatant. Add 35-40 mL of deionized water to the precipitate, shake to mix, and then sonicate in an ultrasonic machine for 10-15 minutes. Centrifuge again with the same parameters. Repeat the washing operation until the pH of the supernatant stabilizes at 5-6. 4. Organic solvent stripping: Discard the supernatant after water washing, and dry the lower precipitate in a vacuum oven at 60 ℃ for 12 h; add 20~40 mL of anhydrous ethanol to the dried precipitate, sonicate at a constant temperature for 1 h, centrifuge at 10000~12000 rpm for 10~15 min to remove impurities, and collect the lower purified precipitate. 5. Preparation of MXene aqueous dispersion: Add 20-25 mL of deionized water to the purified precipitate, shake vigorously to mix, sonicate for 20-30 min, centrifuge at 3000-4000 rpm for 3-5 min, remove multi-layer stacked particles, and collect the upper black-brown liquid, which is the MXene aqueous dispersion. 6. Concentration calibration: Accurately measure 4~6 mL of MXene dispersion, vacuum filter, dry at 60 ℃ to constant weight, weigh the solid mass, calculate the mass concentration of the dispersion, and set aside for later use.

[0028] Step 2 and 3: Preparation of functional mixed dispersions 1. PMMA@MXene mixed dispersion: Weigh 0.1 g of PMMA nanospheres with a particle size of 400 nm, add 10 mL of deionized water, and stir magnetically at room temperature for 3 h to obtain a 10 mg / mL PMMA aqueous dispersion; Mix the MXene aqueous dispersion and the PMMA aqueous dispersion at a mass ratio of 4:1, and sonicate for 15~20 min to ensure uniform dispersion of particles without agglomeration or precipitation; 2. CNF & PMMA@MXene ternary mixed dispersion: Take MXene aqueous dispersion, mix PMMA aqueous dispersion and CNF aqueous dispersion with 0.5 wt% solid content at a mass ratio of 20:1:1, stir magnetically at room temperature for 20 min, and sonicate for 10 min to prepare homogeneous ternary mixed dispersion. 3. CNF@MXene mixed dispersion: Take 3 mL of the standardized MXene aqueous dispersion and mix it with CNF aqueous dispersion with a solid content of 0.5 wt% at a mass ratio of 6:1. Disperse evenly by sonication for 15 min to obtain a mixed solution with high CNF content.

[0029] Step 3: Preparation of gradient thin films by stepwise vacuum filtration 1. Bottom layer preparation: Transfer the entire PMMA@MXene mixed dispersion to a vacuum filtration device, control the vacuum degree at 0.06~0.08 MPa, and filter until the film is semi-dry (no free-flowing water on the surface, and the texture is moist and not cracked). 2. Preparation of intermediate transition layer: While maintaining a constant vacuum negative pressure, the ternary mixed dispersion is slowly and uniformly added to the surface of the bottom film, and the mixture is continuously filtered until semi-dry to form an intermediate layer with continuous component transition; 3. Top layer preparation: Under the same vacuum conditions, CNF@MXene mixed dispersion is added dropwise and filtered until the film is completely formed. The three layers of film are tightly bonded by residual moisture and vacuum pressure, without additional drying or heat treatment processes. 4. Post-processing: After filtration, remove the composite membrane from the filter bottle and place it in a ventilated place at room temperature to air dry naturally. Control the total thickness of the membrane to be 20~25 μm to finally obtain a dual-material gradient MXene-based driven membrane.

[0030] Step 4: Thin Film Driven Performance Test The specific steps are as follows: the prepared gradient film is cut into standard strip samples of 20 mm × 5 mm, one end is fixed and the other end is suspended, and humidity, near-infrared light and low voltage electrical stimulation tests are performed respectively. The ambient temperature is kept constant at 25 ℃. The film bending angle, response time, recovery time and number of cycles are recorded.

[0031] The specific details are as follows: 1. Humidity-driven: CNF contains a large number of hydroxyl groups, exhibiting excellent hydrophilicity and water absorption swelling capacity; while PMMA is a hydrophobic polymer with extremely weak water absorption capacity. When humidity increases, the CNF-rich side of the film (i.e., the top layer) absorbs moisture and expands much more than the PMMA-rich side (i.e., the bottom layer), resulting in asymmetric swelling and causing the film to bend towards the PMMA-rich side. When humidity decreases, the CNF side dehydrates and shrinks, and the film returns to its flat state. This is how the composite film achieves humidity-driven growth.

[0032] 2. Light-driven: MXene exhibits excellent photothermal conversion effects. When a light field (such as near-infrared light) is applied, MXene converts light energy into heat energy, causing the overall temperature of the film to rise. PMMA has a significantly higher coefficient of thermal expansion than CNF and MXene. Therefore, during the heating process, the side rich in PMMA (the bottom layer) experiences greater thermal expansion, resulting in asymmetric expansion and causing the film to bend towards the CNF-rich side. When the light stimulus is removed, the film cools and contracts, returning to its flat state. Thus, the composite film achieves light-driven operation.

[0033] 3. Electrodynamic Drive: MXene also exhibits excellent electrothermal conversion effects. When an electric field (such as a low voltage) is applied, MXene converts electrical energy into heat energy, causing the overall temperature of the film to rise. PMMA has a significantly higher coefficient of thermal expansion than CNF and MXene. Therefore, during the heating process, the side rich in PMMA (the bottom layer) experiences greater thermal expansion, resulting in asymmetric expansion and causing the film to bend towards the CNF-rich side. When the electrical stimulation is removed, the film cools and contracts, returning to its flat state. This is how the composite film achieves electrodynamic drive.

[0034] To verify the technical superiority of the gradient structure, material ratio, and preparation process of this invention, three sets of examples with different material ratios and two sets of comparative examples with traditional structures were set up. All samples were prepared under identical environmental and testing conditions, and the testing standards were uniform: ambient temperature 25 ℃, normal pressure, humidity stimulation range 33%~100%RH, and light stimulation using 808 nm near-infrared light with a power of 20~200 mW / cm². 2 Electrical stimulation uses a low DC voltage of 0~1.7 V. Example 1

[0035] Following steps one through three above, the thin film was prepared using the following process: MXene etching temperature 35 ℃, etching time 48 h; PMMA microsphere particle size 400 nm; MXene aqueous dispersion to PMMA aqueous dispersion mass ratio 4:1; MXene aqueous dispersion, PMMA aqueous dispersion and CNF aqueous dispersion with 0.5 wt% solid content mixed at a mass ratio of 20:1:1; MXene aqueous dispersion and CNF aqueous dispersion with 0.5 wt% solid content mixed at a mass ratio of 6:1; total film thickness 22 μm; three-layer stepwise vacuum filtration, vacuum degree 0.07 MPa; and air-dried at room temperature.

[0036] Example 2 (PMMA doping level increased by 20%) Based on Example 1, the mass ratio of MXene aqueous dispersion to PMMA aqueous dispersion was adjusted to 3:1, while the other raw material parameters, preparation process, and film thickness remained unchanged, to prepare a high PMMA doping gradient film.

[0037] Example 3 (CNF doping level increased by 20%) Based on Example 1, the mass ratio of MXene aqueous dispersion to CNF aqueous dispersion was adjusted to 5:1, while the other raw material parameters, preparation process, and film thickness remained unchanged, to prepare a high CNF doping gradient film.

[0038] Comparative Example 1 (Traditional bilayer structure thin film) Using a traditional two-layer preparation process, a PMMA@MXene film was prepared as the first layer and a CNF@MXene film was prepared as the second layer. After the two layers were independently filtered and dried, they were bonded together with polyvinyl alcohol adhesive to form a clearly layered two-layer heterogeneous film. The total thickness of the film was controlled to be 22 μm, and the total doping amount of the material was completely consistent with that in Example 1.

[0039] Comparative Example 2 (Hybrid Thin Film without Gradient) All MXene, PMMA, and CNF materials from Example 1 were mixed at once, and a homogeneous dispersion was prepared by ultrasonic stirring. A gradient-free homogeneous composite film was prepared by single vacuum filtration. The film thickness was 22 μm, and the total mass of all materials was the same as in Example 1.

[0040] The performance test results are shown in the table below: ; Test Result Analysis: Analysis of the advantages of gradient structure: Examples 1-3 are all gradient structure films. Compared with the conventional double-layer adhesive comparative example 1 and the homogeneous non-gradient comparative example 2, the bending angle is increased by 22%~200% and the response time is shortened by more than 50%. Moreover, the gradient structure has no obvious interlayer interface and the cycle service life is more than 4 times that of the conventional double-layer structure, which proves that the continuous gradient transition structure can effectively improve the interlayer bonding force and driving performance.

[0041] Effect of material ratio on performance: In Example 2, increasing the PMMA doping amount improved the bending angle of optical and electrical driving, but reduced the humidity driving performance; In Example 3, increasing the CNF doping amount resulted in the best humidity driving performance, but reduced optical / electrical driving deformation; Example 1 was the optimal ratio, with balanced performance of the three driving methods and the strongest overall adaptability.

[0042] Comparative example defect verification: Comparative example 1 has a significant abrupt interface in its double-layer adhesive structure. After repeated use, the adhesive ages and the interlayer peels off, resulting in a rapid decline in driving performance. Comparative example 2 has a homogeneous film with no compositional differences, which makes it impossible to form asymmetric deformation. The bending angle is extremely small, and it does not have bidirectional driving capability, further verifying the necessity of the gradient design of this invention.

[0043] Verification of bidirectional driving effect: All gradient thin film samples (Examples 1-3) achieved bending towards the PMMA side due to humidity and bending in the opposite direction towards the CNF side due to light / electricity, demonstrating significant bidirectional reversible deformation effect; while the comparative sample did not have a stable reverse driving law and the deformation was highly random.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dual-material gradient-driven thin film based on MXene, characterized in that, It includes a three-layer structure arranged from bottom to top: a bottom layer, a middle layer, and a top layer; all three layers use MXene as the matrix and are doped with PMMA and CNF; the concentration of PMMA gradually decreases from bottom to top, and the concentration of CNF gradually increases; the three-layer structure has no clear layer interface.

2. The dual-material gradient-driven thin film based on MXene according to claim 1, characterized in that, The concentrations of PMMA and CNF in the middle layer are equal, resulting in uniform doping.

3. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 1 or 2, characterized in that, Includes the following steps: Step 1: Prepare MXene dispersion; Step 2: Prepare PMMA@MXene mixed dispersion, CNF & PMMA@MXene ternary mixed dispersion, and CNF@MXene mixed dispersion respectively; Step 3: Prepare gradient-driven thin films from the bottom layer to the top layer using stepwise vacuum filtration.

4. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 3, characterized in that, Methods for preparing MXene dispersions include: MAX-Ti3AlC2 powder was placed in an etching solution and etched to obtain a multilayer MXene mixture. The multilayer MXene mixture was centrifuged, washed, dried, dried to remove impurities, purified, and then thoroughly mixed with water to obtain an MXene aqueous dispersion.

5. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 4, characterized in that, To ensure thorough mixing with water, add deionized water to the purified precipitate, shake vigorously to mix, sonicate for 20-30 minutes, centrifuge at 3000-4000 rpm for 3-5 minutes, remove multi-layered stacked particles, and collect the upper blackish-brown liquid, which is the MXene aqueous dispersion.

6. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 3, characterized in that, The preparation method of PMMA@MXene mixed dispersion is as follows: PMMA nanospheres are taken, deionized water is added, and PMMA aqueous dispersion is prepared by stirring thoroughly; MXene aqueous dispersion and PMMA aqueous dispersion are mixed at a mass ratio of 3~5:1 and ultrasonically dispersed.

7. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 6, characterized in that, The preparation method of CNF&PMMA@MXene ternary mixed dispersion is to take MXene aqueous dispersion, mix PMMA aqueous dispersion and CNF aqueous dispersion with solid content of 0.5~0.8 wt% at a mass ratio of 15~20:1:1, stir magnetically at room temperature and homogenize by ultrasonication.

8. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 7, characterized in that, The method for preparing CNF@MXene mixed dispersion is to take MXene aqueous dispersion and mix it with CNF aqueous dispersion with a solid content of 0.5~0.8 wt% at a mass ratio of 5~8:1, and then ultrasonically disperse it evenly.

9. The method for preparing a dual-material gradient-driven thin film based on MXene according to claim 3, characterized in that, The steps of using stepwise vacuum filtration include: Substrate preparation: The entire PMMA@MXene mixed dispersion was transferred to a vacuum filtration device, with the vacuum level controlled at 0.06~0.08 MPa, and filtered until the membrane was semi-dry. Preparation of the middle layer: While maintaining a constant vacuum negative pressure, the ternary mixed dispersion is slowly and uniformly added to the surface of the bottom film, and the mixture is continuously filtered until it is semi-dry to form a middle layer with a continuous transition of components; Top layer preparation: Under the same vacuum conditions, CNF@MXene mixed dispersion is added dropwise and filtered until the film is completely formed. The three layers of film are tightly bonded by residual moisture and vacuum pressure, without additional drying or heat treatment processes.

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