A MXene-aramid flexible strain sensor based on three-dimensional interlocking conductive network and a preparation and evaluation method thereof

Abstract

The application discloses a kind of MXene-aromatic fiber flexible strain sensor based on three-dimensional interlocking conductive network and its preparation and evaluation method, sensor with 150-220g / m² aromatic fiber nonwoven fabric as flexible substrate, by 2-5 times impregnation-drying process MXene nanosheet is loaded on the surface and gap of fiber, form node-axial three-dimensional interlocking conductive network, surface resistance is not higher than 10kΩ.The structure combines MXene nanosheet interlayer slip mechanism, realizes force-electricity collaborative stability under multi-mode dynamic load such as tensile, puncture, friction, bending, etc., local damage, 500 times friction cycle after resistance increase is significantly lower than carbon nanotube / silver nanowire-based comparative sensor, when bending radius is greater than or equal to 10mm, resistance response is stable repeatedly bent.

Description

Technical Field

[0001] This invention relates to the fields of flexible electronic materials, intelligent sensing, and textile composite materials. Specifically, it relates to an MXene-aramid flexible strain sensor based on a three-dimensional interlocking conductive network, as well as a method for fabricating the sensor and a method for evaluating the force-electrical synergistic stability under complex dynamic loads. It is applicable to scenarios such as wearable health monitoring, human-computer interaction, smart textiles, flexible robot skin, and structural health monitoring. Background Technology

[0002] Flexible strain sensors are core devices in the field of flexible electronics. Their core performance requirements are stable resistance response and excellent mechanical durability under dynamic deformation, which are also key to the implementation of applications such as wearable devices and smart textiles. Currently, mainstream conductive materials such as carbon nanotubes (CNTs), graphene, and silver nanowires (AgNWs) have significant technical defects in practical applications: the conductive network of carbon-based materials is prone to irreversible fracture under cyclic loading, leading to sensor signal drift or even complete failure; metal nanowires have interfacial mismatch problems with flexible polymer matrices, and are prone to peeling off from the substrate during complex deformations; and silver nanowires have poor oxidation resistance, resulting in severe conductivity decay after long-term use.

[0003] Two-dimensional transition metal carbides / nitrides (MXenes) have become novel conductive materials for flexible electronic devices due to their ultra-high intrinsic conductivity, good hydrophilicity, and unique layered structure. Their nanosheets can rearrange under strain through interlayer slip mechanisms, theoretically maintaining the continuity of conductive pathways better. However, when applying MXenes to high-performance textile substrates such as aramid fibers to prepare strain sensors, two major technical bottlenecks remain: First, the chemical inertness and lack of active functional groups on the surface of aramid fibers mean that MXenes only rely on weak physical adsorption to bind with the fiber matrix, resulting in insufficient interfacial bonding strength. The coating is easily detached under friction, peeling, and repeated bending loads, leading to insufficient sensor durability. Second, existing research only focuses on the force-electric response of MXene-based sensors under single loads such as uniaxial tension and simple bending. There is a lack of systematic research on the failure behavior of the conductive network and the force-electric synergistic mechanism under more common multiaxial stress states (such as bursting and tearing) and long-term cyclic loads (such as repeated friction) in real applications, which makes it impossible to guarantee the long-term reliability of sensors in complex scenarios.

[0004] In existing technologies, research on improving the conductivity of aramid fabrics mostly uses carbon black and binder impregnation coatings, focusing only on static conductivity and basic wash and abrasion resistance, without addressing the signal stability problem under dynamic loads from the structural design level. Other studies apply carbon nanotube / polyaniline composite fibers to supercapacitors, focusing on electrochemical energy storage performance. This is in a different technical field from the real-time resistance response under mechanical deformation required by strain sensors, and cannot solve the core technical challenges of flexible strain sensors.

[0005] Therefore, to address the common problems of existing flexible strain sensors, such as easy interface failure, large signal fluctuations, poor durability, and lack of evaluation system under dynamic and complex loads, developing a full-chain technical solution from material structure innovation and preparation process optimization to performance evaluation standardization is the key to promoting the practical application of high-reliability flexible strain sensors and is also the core of the research and development of this invention. Summary of the Invention

[0006] The first objective of this invention is to provide an MXene-aramid flexible strain sensor based on a three-dimensional interlocking conductive network, which solves the problems of unstable resistance, easy interface failure, and low damage tolerance of existing sensors under dynamic loads of multiple modes such as tension, bursting, friction, and bending. The second objective is to provide a method for fabricating this sensor, which enables the controllable and repeatable construction of the three-dimensional interlocking conductive network. The process is simple and the conditions are mild, making it suitable for large-scale production. The third objective is to provide a method for evaluating the force-electrical co-stability of this sensor, which enables the simultaneous acquisition and quantitative analysis of mechanical and electrical signals under complex dynamic loads, providing a standardized basis for sensor reliability assessment.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an MXene-aramid flexible strain sensor based on a three-dimensional interlocking conductive network, comprising an aramid nonwoven flexible substrate and an MXene conductive layer; the aramid nonwoven fabric constitutes a three-dimensional porous fiber network with a unit area mass of 150-220 g / m²; the MXene conductive layer is uniformly attached to the fiber surface and inter-fiber gaps of the aramid nonwoven fabric through an impregnation-drying process, forming a node-axial three-dimensional interlocking conductive network that runs through the three-dimensional porous fiber network, and the sensor surface resistance is not higher than 10 kΩ; when the sensor is subjected to dynamic load, the MXene conductive layer maintains the continuity of the conductive path through the synergistic effect of nanosheet interlayer slip and the three-dimensional interlocking conductive network structure, thereby achieving a stable force-electric response.

[0008] Furthermore, the MXene conductive layer is formed by multi-layer coating through 2-5 impregnation-drying processes, and the MXene nanosheets are locally enriched at the fiber intersection nodes, forming a continuous conductive path along the fiber axis.

[0009] Furthermore, after the sensor experiences localized damage during a static burst test, the increase in resistance is significantly lower than that of comparable sensors with the same function, which use carbon nanotubes or silver nanowires as conductive layers.

[0010] Furthermore, after 500 standard friction cycles, the resistance increase of the sensor is significantly lower than that of comparable sensors with the same function using carbon nanotubes or silver nanowires as conductive layers.

[0011] Furthermore, the sensor exhibits a static bending resistance change rate of ≤15% under repeated bending deformation with a bending radius of not less than 10mm, maintaining the stability of its resistance response. The maximum resistance change rate is controlled within 40%. Specifically, the sensor maintains the stability of its resistance response under repeated bending deformation with a bending radius of not less than 10mm, 1000 dynamic cycles, a frequency of 1Hz, and a bending angle of 90°, with the maximum resistance change rate controlled within 40%.

[0012] This invention also provides a method for preparing an MXene-aramid flexible strain sensor, comprising the following steps: S1. Preparing an MXene aqueous dispersion using a LiF / HCl solution etching method; S2. Impregnating an aramid nonwoven fabric substrate in the MXene aqueous dispersion, allowing the dispersion to fully penetrate the three-dimensional porous fiber network. The MXene aqueous dispersion can be diluted with deionized water at a 1:1 volume ratio before impregnation. The MXene aqueous dispersion can be diluted with deionized water at a 1:1 volume ratio, and the mass concentration of the dispersion after dilution is 6 mg. mL -1 Dilution treatment reduces the viscosity of the dispersion, enhancing its permeability in the three-dimensional porous fiber network of aramid nonwoven fabric. This allows MXene nanosheets to penetrate deep into the inner layers of the fibers and the internode gaps, facilitating the uniform construction of the conductive network in conjunction with subsequent multilayer impregnation processes. Undiluted 12mg mL -1 The dispersion is suitable for thin aramid nonwoven fabrics (150-180 g / m²). 2 The diluted dispersion is suitable for medium-thickness aramid nonwoven fabrics (180-220 g / m²), and can ultimately achieve 8.6 mg / m². cm -2 S2. Loading the MXene; S3. Vacuum drying the impregnated substrate to fix the MXene nanosheets to the fiber surface; S4. Repeat steps S2 and S3 at least once to complete the multilayer coating of the MXene conductive layer and form a three-dimensional interlocking conductive network.

[0013] Further, in step S1, the MXene aqueous dispersion is obtained by etching, centrifuging and washing the Ti3AlC2MAX phase. Specifically, the Ti3AlC2MAX phase powder is added to an HCl solution containing LiF to selectively etch the aluminum layer, and after centrifugation and washing, the pH value of the supernatant is adjusted to 6.5-7.0. The supernatant is then redispersed in deionized water to obtain an MXene aqueous dispersion with a mass concentration of about 12 mg / mL.

[0014] Furthermore, in step S3, the vacuum drying temperature is 50-80℃, the vacuum degree is not less than 0.08MPa, and the drying time is not less than 2 hours.

[0015] This invention also provides a method for evaluating the force-electric co-stability of an MXene-aramid flexible strain sensor, comprising the following steps: T1. Arranging test electrodes on the sensor and connecting them to a real-time resistance monitoring system; T2. Installing the sensor on a testing device and subjecting it to at least one dynamic load among tension, bursting, friction, and bending; T3. Simultaneously recording the mechanical signals and resistance change signals throughout the entire process of load application and release; T4. Calculating the resistance change rate, sensitivity, and resistance recovery rate based on the resistance change signals, and analyzing the resistance stability and resilience of the sensor under dynamic loads.

[0016] Furthermore, in step T2, during the bursting test, the test electrode is placed in the non-direct deformation area of ​​the sensor; during the friction test, the standard GB / T21196.3—2007 is followed, using #600 sandpaper as the abrasive and applying a pressure load of 9 kPa; during the bending test, the frequency of dynamic cyclic bending is 1 Hz and the bending angle is 90°.

[0017] The beneficial effects of this invention: Through material structure innovation, preparation process optimization, and evaluation system construction, this invention forms a complete MXene-aramid flexible strain sensor technology solution. Compared with existing technologies, it has the following significant beneficial effects, and these effects form a synergistic gain:

[0018] Structural innovation achieves ultra-high mechanical-electrical synergistic stability under multi-mode dynamic loads: This invention, for the first time, constructs a node-axial three-dimensional interlocking conductive network in an aramid nonwoven fabric / MXene composite system. It innovatively combines the macroscopic three-dimensional porous structure of the aramid substrate with the nanoscale layered characteristics of MXene nanosheets, achieving multi-level synergy at the nanoscale (MXene sheet slippage), microscale (fiber coating), and macroscale (network interlocking). This structure enables the sensor to achieve energy dissipation and adaptive rearrangement through interlayer slippage of MXene nanosheets under multi-mode dynamic loads such as tension, bursting, friction, and bending. Furthermore, the circuitry of the three-dimensional interlocking network prevents the overall circuit from opening, thus solving the core problems of unstable resistance and easy interface failure in existing sensors under complex loads. Actual tests show that the resistance increase after the sensor is broken is only about 69%, far lower than the more than 200% increase of the carbon nanotube-based comparative sensor; the resistance increase after 500 friction cycles is only about 26.9%, significantly better than the comparative sensor; and the maximum change rate of resistance after repeated bending is ≤40% when the bending radius is ≥10mm, which meets the actual application requirements of wearable devices.

[0019] Process optimization enables the controllable construction and large-scale production of a three-dimensional interlocking conductive network: The preparation method of this invention uses LiF / HCl etching to prepare a high-purity MXene aqueous dispersion. Through a multi-layer coating process of 2-5 impregnation-vacuum drying, a tight bond between MXene and aramid nonwoven fabric is achieved. The vacuum drying process improves the interfacial bonding strength between MXene and aramid fibers, while the multi-layer coating process ensures the integrity and uniformity of the conductive network. The entire process is characterized by mild conditions, simple steps, and strong controllability, requiring no complex equipment and solving the problems of complex and poor repeatability in existing MXene-based textile sensor fabrication processes. Simultaneously, the process parameters have been precisely optimized, with the unit area mass of the aramid substrate, the concentration of the MXene dispersion, the drying temperature, and the number of impregnations matched to achieve precise control of the sensor's structure and performance. This method is suitable for industrial-scale production and has good industrialization prospects.

[0020] This invention establishes the first standardized evaluation system for flexible strain sensors under complex dynamic loads. The evaluation method of this invention achieves, for the first time, the simultaneous acquisition and quantitative analysis of mechanical and electrical signals from flexible strain sensors under multiple dynamic load modes, including tension, bursting, friction, and bending. For the bursting test, an electrode arrangement scheme for the non-deformation region is designed; for the friction test, national standards are adopted; and for the bending test, actual wearable working conditions are simulated. This solves the problem that existing technologies limit sensor performance evaluation to a single load and lack standardization. This evaluation method can accurately reveal the force-electrical synergistic mechanism of the sensor, achieving quantitative performance evaluation through key indicators such as resistance change rate, sensitivity, and resistance recovery rate. It provides a standardized basis for performance optimization and quality control of MXene-based flexible strain sensors, and also provides a reference for the performance evaluation of similar flexible electronic devices, promoting the improvement of evaluation systems in the field of flexible electronics.

[0021] The sensor's performance is highly compatible with various application scenarios, offering broad market potential: This invention's sensor combines high conductivity (surface resistance ≤10kΩ), excellent flexibility, damage tolerance, friction durability, and bending stability. Using aramid nonwoven fabric as the substrate, it possesses high modulus, wear resistance, and aging resistance. It can be seamlessly integrated as a high-performance strain-sensitive element into products such as smart clothing, sports protective gear, medical rehabilitation equipment, flexible robot skin, and building structure health monitoring equipment. It can monitor various deformations such as tension, bending, pressure, and friction in real time and stably, demonstrating broad market application potential in fields such as human motion analysis, physiological signal monitoring, human-computer interaction, and industrial structure monitoring. Furthermore, the sensor's fabrication process is suitable for mass production, effectively reducing production costs and further enhancing its industrial value.

[0022] The combination of MXene and aramid fibers achieves a synergistic improvement in conductivity and mechanical properties: the sensor of this invention is not a simple composite of MXene and aramid substrate, but rather achieves synergistic performance gains through a three-dimensional interlocking conductive network. The introduction of the MXene coating not only does not impair the mechanical properties of the aramid substrate, but also enhances its tensile, tear, and bursting strength through mechanical interlocking. Actual tests show that the sensor's tensile strength increases by approximately 5.9%, tear strength by approximately 23.5%, and bursting strength by approximately 38.9%. Meanwhile, the aramid substrate provides a stable physical framework for the MXene conductive layer, ensuring the structural stability of the MXene three-dimensional interlocking conductive network, achieving a simultaneous improvement in conductivity and mechanical properties, and solving the problem of mutual constraints between conductivity and mechanical properties in existing flexible sensors. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of the layered composite structure of the MXene / aramid flexible strain sensor in an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the microstructure of the node-axial three-dimensional interlocking conductive network described in this invention at the fiber intersection.

[0025] Figure 3 This is a schematic diagram of a typical force-electric synchronous response curve of the sensor under uniaxial tensile load in the embodiment.

[0026] Figure 4 This is a schematic diagram of the resistance-displacement response curve of the sensor in the static puncture test in the embodiment.

[0027] Figure 5 This is a schematic diagram showing the evolution of the sensor's resistance with the number of cycles during the friction cycle test in this embodiment. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Reference Figures 1-5As shown, an MXene-aramid flexible strain sensor based on a three-dimensional interlocking conductive network includes an aramid nonwoven flexible substrate and an MXene conductive layer. The aramid nonwoven fabric forms a three-dimensional porous fiber network with a unit area mass of 150-220 g / m². The fiber density in this range can provide sufficient physical attachment space and mechanical support for the construction of the three-dimensional interlocking conductive network, while also ensuring good flexibility and porosity of the substrate, which is conducive to the deep penetration and uniform adhesion of the MXene dispersion.

[0030] The MXene conductive layer is uniformly attached to the fiber surface and inter-fiber gaps of the aramid nonwoven fabric through an impregnation-drying process, forming a node-axial three-dimensional interlocked conductive network that runs through the three-dimensional porous fiber network. The surface resistance of the sensor is no higher than 10kΩ, which optimizes the basic conductivity of the sensor. The surface resistance of no more than 10kΩ can provide sufficient electrical signal strength and meet the basic electrical requirements of mainstream application scenarios such as flexible strain sensing. The three-dimensional interlocking structure ensures that there is no single critical failure path in the conductive network, and local damage can be mitigated by detour conduction to maintain the continuity of the overall conductive path.

[0031] When the sensor is subjected to dynamic loads, the MXene conductive layer maintains the continuity of the conductive path through the synergistic effect of interlayer slip of nanosheets and three-dimensional interlocked conductive network structure, achieving a stable force-electric response. Interlayer slip can realize the consumption of load energy and the adaptive rearrangement of nanosheets, while the three-dimensional interlocked network can provide multiple current detour conduction paths. The two work together to avoid the overall circuit opening caused by local structural changes, ensuring the stability of force-electric conversion under multi-mode dynamic loads.

[0032] In a preferred embodiment of the present invention, the MXene conductive layer is formed by multi-layer coating through 2-5 impregnation-drying processes. MXene nanosheets are locally enriched at fiber intersection nodes, forming continuous conductive pathways along the fiber axis. The multiple impregnation-drying processes allow the MXene dispersion to fully penetrate into the inner layer of the fiber network, gradually filling the gaps and improving the overall integrity and interfacial bonding strength of the coating. The local enrichment at the nodes enhances the conductivity at key locations, and the continuous axial pathways ensure the basic connectivity of the conductive network, together constructing a complete three-dimensional interlocking conductive network.

[0033] In a preferred embodiment of the present invention, after the sensor experiences localized damage during a static burst test, the increase in resistance is significantly lower than that of a comparable sensor with the same function using carbon nanotubes or silver nanowires as the conductive layer. This demonstrates the sensor's excellent damage tolerance. Even if localized physical damage occurs, the detour conduction effect of the three-dimensional interlocking conductive network can still maintain overall conductivity, significantly reducing the degree of resistance degradation. Compared with traditional conductive material-based sensors, the signal stability under localized damage conditions is greatly improved.

[0034] In a preferred embodiment of the present invention, after 500 standard friction cycles, the resistance increase of the sensor is significantly lower than that of a comparable sensor with the same function using carbon nanotubes or silver nanowires as conductive layers. This demonstrates that the strong bonding interface formed by the MXene coating and aramid fibers through three-dimensional interlocking can effectively resist cyclic shear stress, delay the wear and peeling of the coating, significantly improve the friction durability of the sensor, and extend its service life under easily frictional working conditions.

[0035] In a preferred embodiment of the present invention, the sensor can maintain the stability of its resistance response under repeated bending deformation with a bending radius of not less than 10 mm, and the maximum rate of change of resistance is controlled within 40%. This meets the requirements for repeated bending in application scenarios such as wearable devices and flexible robots, avoids crack propagation and sharp signal drift caused by repeated bending, and ensures the consistency of the force-electric response of the sensor under bending conditions.

[0036] This invention also provides a method for fabricating an MXene-aramid flexible strain sensor, comprising the following steps: S1. Preparing an MXene aqueous dispersion using a LiF / HCl solution etching method, which can effectively prepare single-layer or few-layer MXene nanosheets, retaining their excellent intrinsic conductivity and interlayer slip characteristics, providing high-purity and stable conductive raw materials for subsequent conductive layer preparation; S2. Immersing an aramid nonwoven fabric substrate in the MXene aqueous dispersion, allowing the dispersion to fully penetrate the three-dimensional porous fiber network, enabling the MXene nanosheets to achieve full contact with the aramid fibers in all directions, ensuring the uniform distribution of MXene on the fiber surface and in the gaps, thus constructing a three-dimensional interlocking conductive network. The prerequisite for the network is as follows: S3. Vacuum drying is performed on the impregnated substrate to fix the MXene nanosheets to the fiber surface. The vacuum environment can lower the boiling point of the solvent, avoid violent boiling of the solvent and damage to the MXene coating, and at the same time promote the close contact between the MXene nanosheets and the fiber, improve the interfacial bonding strength between the two, and achieve firm fixation of the conductive coating; S4. Repeat steps S2 and S3 at least once to complete the multi-layer coating of the MXene conductive layer, form a three-dimensional interlocking conductive network, gradually increase the MXene loading, optimize the density and integrity of the conductive network, fill the coating defects of a single coating, and finally form a complete three-dimensional interlocking conductive network from the surface to the interior and from the axis to the nodes.

[0037] In a preferred embodiment of the present invention, in step S1, the MXene aqueous dispersion is obtained by etching, centrifuging, and washing the Ti3AlC2MAX phase. Specifically, Ti3AlC2MAX phase powder is added to an HCl solution containing LiF to selectively etch the aluminum layer. After centrifugation and washing until the pH of the supernatant is 6.5-7.0, it is redispersed in deionized water to obtain an MXene aqueous dispersion with a mass concentration of approximately 12 mg / mL. Selective etching of the aluminum layer can accurately obtain MXene nanosheets. Centrifugation and washing to neutrality can effectively remove by-products and unreacted substances, ensuring the purity of the dispersion. The mass concentration of 12 mg / mL balances the conductivity of MXene with the impregnation and permeability of the dispersion, avoiding the problems of excessive viscosity due to excessive concentration and inability to form a continuous coating due to excessive dilution.

[0038] In a preferred embodiment of the present invention, in step S3, the vacuum drying temperature is 50-80℃, the vacuum degree is not less than 0.08MPa, and the drying time is not less than 2 hours. The drying temperature of 50-80℃ ensures the drying efficiency and avoids the aggregation of MXene nanosheets and loss of interlayer slip properties caused by high temperature. The vacuum degree of not less than 0.08MPa ensures the rapid and gentle evaporation of solvent. The drying time of not less than 2 hours ensures that the solvent is fully removed, so that the MXene nanosheets and aramid fibers can be firmly bonded together, thereby improving the stability of the coating.

[0039] This invention also provides a method for evaluating the force-electric synergistic stability of an MXene-aramid flexible strain sensor, comprising the following steps: T1. Arranging test electrodes on the sensor and connecting them to a real-time resistance monitoring system to achieve real-time, high-precision acquisition of the sensor's resistance signal, providing an accurate and continuous electrical data foundation for subsequent force-electric synergistic analysis, and adapting to the signal change rhythm under dynamic loads; T2. Installing the sensor on a testing device to subject it to at least one dynamic load among tension, bursting, friction, and bending, accurately simulating various complex working conditions of the sensor in practical applications, making the evaluation results more consistent with actual usage scenarios, and providing a scientific basis for adapting the sensor to different application scenarios; T3. 1. Synchronously record the mechanical signals and resistance change signals throughout the entire process of load application and release, ensuring complete consistency of the time axis between mechanical and resistance parameters. This accurately reflects the correspondence between mechanical deformation and resistance change, avoids analytical errors caused by time differences, and clearly reveals the sensor's force-electric synergy mechanism. 2. Calculate the resistance change rate, sensitivity, and resistance recovery rate based on the resistance change signal. Analyze the sensor's resistance stability and recovery under dynamic loads, transforming the sensor's force-electric response characteristics from a qualitative description to a quantitative evaluation. Through comprehensive analysis of multiple key indicators, comprehensively and scientifically assess the sensor's stability, damage tolerance, and durability, providing a standardized reference for performance comparison and optimization of similar products.

[0040] In a preferred embodiment of the present invention, during step T2, when performing the burst test, the test electrode is arranged in the non-direct deformation area of ​​the sensor to avoid the electrode from failing due to severe deformation or damage in the central area of ​​the sample, ensuring that the measured resistance signal truly reflects the overall state of the conductive network and accurately assesses the detour conduction capability of the three-dimensional interlocking network; when performing the friction test, the standard GB / T21196.3—2007 is followed, using #600 sandpaper as the abrasive and applying a pressure load of 9 kPa; when performing the bending test, the frequency of dynamic cyclic bending is 1 Hz and the bending angle is 90°, simulating the conventional bending conditions in practical applications such as wearable devices and flexible robots.

[0041] Reference Figure 1 As shown, the MXene-aramid flexible strain sensor of the present invention consists of an aramid nonwoven flexible substrate 1 and an MXene conductive layer 2. The upper layer is a continuous MXene conductive layer, and the lower layer is an aramid nonwoven substrate. The two are integrated into a composite structure through mechanical interlocking and physical adsorption. The core is a node-axial three-dimensional interlocking conductive network that runs through the substrate.

[0042] Aramid nonwoven flexible substrate: Aramid nonwoven fabric with a unit area mass of 150-220 g / m² is selected. This substrate naturally forms a three-dimensional porous fiber network, with fibers intersecting and entangled to form numerous nodes and gaps. As the physical framework of the sensor, it provides excellent mechanical strength, flexibility, and porosity, offering attachment sites and three-dimensional space for MXene nanosheet loading, while ensuring the overall flexibility and mechanical durability of the sensor. The unit area mass of 150-220 g / m² is the optimal range. Below 150 g / m², the fiber density is insufficient to construct an effective interlocking space, resulting in poor mechanical support; above 220 g / m², the substrate porosity is too low, making it difficult for the MXene dispersion to penetrate into the fiber inner layer, thus failing to form a complete three-dimensional conductive network. The three-dimensional porous structure of this substrate lays the structural foundation for the subsequent construction of the three-dimensional interlocking conductive network, and the high modulus and wear resistance of the aramid material itself enhance the overall mechanical performance of the sensor.

[0043] MXene conductive layer: MXene nanosheet aqueous dispersion was prepared using Ti3AlC2MAX phase as raw material. MXene nanosheets were uniformly loaded onto the surface of aramid fibers and the gaps between fibers through 2-5 impregnation-drying processes. MXene was locally enriched at fiber intersection nodes and a continuous conductive path was formed along the fiber axis. Finally, a node-axial three-dimensional interlocking conductive network was formed that runs through the three-dimensional porous fiber network. The surface resistance of the sensor was controlled to be no higher than 10kΩ.

[0044] As a conductive sensing unit in a sensor, it converts mechanical deformation into resistance signals. Through a node-rich, axially continuous three-dimensional structure, it provides multiple circuitous conduction paths for current. Utilizing the interlayer slip properties of MXene nanosheets, it achieves energy dissipation and adaptive rearrangement under load. A 2-5 impregnation-drying process ensures that the MXene dispersion fully penetrates the inner layer of the fiber network, gradually filling gaps and avoiding the problems of discontinuous coating and weak adhesion caused by single coating. MXene enrichment at fiber nodes significantly enhances node conductivity, and the axially continuous conductive pathways guarantee basic conductivity. A surface resistance ≤10kΩ meets the electrical signal strength requirements for applications such as flexible strain sensing and weak electric heating. The three-dimensional interlocking structure prevents the conductive network from having a single failure path, and the interlayer slip of the MXene nanosheets synergistically works with the three-dimensional network to effectively buffer the damage to the conductive pathways caused by external loads.

[0045] Force-electric synergistic mechanism: When the sensor is subjected to dynamic loads such as tension, bursting, friction, and bending, the nanosheets of the MXene conductive layer undergo interlayer slippage, consuming load energy and undergoing adaptive rearrangement. At the same time, the three-dimensional interlocking conductive network provides multiple optional detour paths for the current.

[0046] To avoid open circuits caused by localized coating breakage or substrate deformation, the continuity of the conductive path is maintained. After localized damage during a static burst test, the sensor's resistance increase is significantly lower than that of the carbon nanotube / silver nanowire-based comparative sensor; after 500 standard friction cycles, the resistance increase is far superior to that of the comparative sensor; when the bending radius is ≥10mm, the resistance response remains stable under repeated bending deformation, with the maximum rate of change controlled within 40%, achieving force-electrical synergistic stability under multi-mode dynamic loads.

[0047] The three-dimensional porous structure of the aramid nonwoven fabric of this invention provides a natural three-dimensional load space for the MXene conductive layer, which determines the macroscopic structural basis of the three-dimensional interlocking conductive network. The layered structure and high conductivity of the MXene nanosheets provide a material basis for interlayer slip and force-electric conversion. The 2-5 impregnation-drying process realizes the tight bonding between MXene and the aramid substrate, making the node-axial three-dimensional interlocking conductive network a practically achievable structure. The interlayer slip of the MXene nanosheets and the tortuous conduction characteristics of the three-dimensional interlocking conductive network form a core synergistic effect, which together endows the sensor with excellent damage tolerance, friction durability and bending stability, solving the core technical defects of existing sensors.

[0048] The preparation method of this invention is simple, has mild conditions, and is highly controllable, and can effectively construct the above-mentioned three-dimensional interlocking conductive network. The specific steps are as follows:

[0049] S1. Preparation of MXene aqueous dispersion by LiF / HCl etching method: LiF powder was weighed and dissolved in 9 mol / L HCl solution, and magnetically stirred at 35℃ for 30 minutes to form a mixture; Ti3AlC2MAX phase powder was added to the mixture in batches under argon atmosphere, and the aluminum layer was etched by stirring at 400 r / min for 24 hours; after diluting the reaction suspension, it was centrifuged at 3500 r / min for 10 minutes, the supernatant was discarded and the precipitate was collected, and the centrifugation and washing were repeated 3-5 times until the pH of the supernatant was 6.5-7.0. After washing once with anhydrous ethanol, the precipitate was redispersed in deionized water to prepare an MXene aqueous dispersion with a mass concentration of about 12 mg / mL, which was then sealed and stored at 4℃.

[0050] Aqueous dispersions of monolayer or few-layer MXene nanosheets were prepared to ensure the high conductivity and interlayer slip properties of MXene, providing a stable conductive raw material for subsequent coating preparation. The LiF / HCl etching method is a classic and effective preparation method for MXene. An argon atmosphere prevents MXene oxidation. Centrifugation and washing until the pH is near neutral remove byproducts and unreacted substances, ensuring the purity of the MXene dispersion. A dispersion with a mass concentration of approximately 12 mg / mL balances conductivity and impregnation permeability; too high a concentration results in high viscosity, making it difficult to penetrate the gaps between aramid fibers, while too low a concentration prevents the formation of a continuous conductive coating.

[0051] S2. Immerse the aramid nonwoven fabric substrate in an MXene aqueous dispersion: Cut the aramid nonwoven fabric to the required size and immerse it directly or after pretreatment completely in the MXene aqueous dispersion (which can be diluted at a 1:1 volume ratio). Hold for at least 30 seconds to allow the dispersion to fully wet the fibers and penetrate into the inner layer and internode gaps of the three-dimensional porous fiber network. This ensures full contact between the MXene nanosheets and the aramid fibers, guaranteeing a uniform distribution of MXene on the fiber surface and in the gaps. The 30-second immersion time ensures full penetration of the dispersion, avoiding localized coating defects due to insufficient wetting. The dispersion dilution treatment reduces viscosity, further improving permeability and allowing the MXene nanosheets to penetrate deep into the fiber network, providing a prerequisite for constructing a through-type three-dimensional interlocking conductive network.

[0052] S3. Vacuum drying of the impregnated substrate: The impregnated aramid nonwoven fabric is vertically pulled out of the liquid surface at a constant speed, controlling the wet film thickness on the fabric surface to be approximately 0.5 mm. It is immediately transferred to a vacuum drying oven and dried for at least 2 hours at 50-80℃ and a vacuum degree ≥0.08 MPa, ensuring that the MXene nanosheets are firmly fixed to the fiber surface. The solvent in the dispersion is removed, allowing the MXene nanosheets and aramid fibers to achieve a tight bond through physical adsorption and mechanical interlocking, forming a preliminary conductive coating. Vacuum drying can lower the boiling point of the solvent, avoiding cracking and peeling of the MXene coating caused by violent boiling of the solvent. At the same time, it promotes close contact between MXene nanosheets and fibers, and improves the interfacial bonding strength. The optimal drying temperature range is 50-80℃. Below 50℃, the drying efficiency is low and solvent residue leads to poor coating bonding. Above 80℃, MXene nanosheets may agglomerate, destroying the layered structure and losing interlayer slip properties. A wet film thickness of 0.5mm ensures a moderate MXene loading, forming a continuous coating without affecting the flexibility of the sensor. Vacuum drying process enhances the interfacial bonding strength between MXene and aramid fibers through a dual effect: ① The boiling point of the solvent (deionized water) is lowered in a vacuum environment, achieving gentle evaporation and avoiding cracking of the MXene coating caused by violent boiling of the solvent, thus ensuring close adhesion between the MXene nanosheets and the fiber surface; ② During solvent evaporation, the MXene nanosheets move towards the fiber surface as the solvent contracts, forming a composite bonding effect of mechanical interlocking and van der Waals forces—MXene nanosheets are embedded in the micropores on the surface of aramid fibers, achieving mechanical interlocking, and the van der Waals forces between the nanosheets and the fiber surface further enhance physical adsorption, solving the problem of insufficient interfacial bonding caused by the chemical inertness of aramid fibers.

[0053] S4. Repeat steps S2 and S3 at least once to complete the multilayer coating: After the dried substrate has completely cooled, repeat the impregnation-vacuum drying process 1-4 times, so that the total number of impregnations reaches 2-5 times, and finally obtain the MXene-aramid flexible strain sensor with an MXene loading of about 8.6 mg / cm².

[0054] Reference Figure 2As shown, at fiber intersections, the MXene coating forms localized aggregates, enhancing node conductivity. A continuous conductive path is also formed along the fiber axis, constituting a node-axis three-dimensional interlocking conductive network. Specifically, the MXene loading is gradually increased to fill the gaps in a single coating, constructing a complete node-axis three-dimensional interlocking conductive network from the surface to the interior and from the axis to the nodes, improving the overall integrity, bonding strength, and conductivity uniformity of the coating. Multiple coating layers of 2-5 times avoid the defects of a single coating, enabling MXene nanosheets to form continuous conductive pathways along the fiber axis and localized enrichment at fiber nodes, ultimately achieving a three-dimensional interlocking conductive network penetrating the aramid substrate. When the MXene loading is approximately 8.6 mg / cm², the sensor's conductivity and flexibility reach an optimal balance; too low a loading results in a discontinuous conductive network, while too high a loading reduces sensor flexibility.

[0055] The high-purity, stable MXene aqueous dispersion prepared in step S1 of this invention serves as the raw material basis for subsequent coating preparation, determining the core performance of the conductive layer. The thorough impregnation in step S2 provides a prerequisite for the uniform distribution of MXene. The aramid nonwoven fabric substrate is impregnated in the MXene aqueous dispersion, allowing the dispersion to fully penetrate the three-dimensional porous fiber network. The MXene aqueous dispersion can be diluted with deionized water at a 1:1 volume ratio, resulting in a dispersion concentration of 6 mg / L. mL -1 Dilution treatment can improve the permeability of the dispersion in the fiber network; undiluted 12mg mL -1 The dispersion is suitable for 150-180 g / m³ 2 The aramid nonwoven fabric, after dilution, has a dispersion suitable for 180-220 g / m². 2 In the aramid nonwoven fabric, the vacuum drying in step S3 achieves a tight bond between MXene and the aramid substrate. The two constitute the core process of single coating and form a preliminary conductive coating. The multilayer coating in step S4 is the key to building a complete three-dimensional interlocking conductive network. Through repeated immersion-drying, the density and integrity of the conductive network are gradually optimized. Each step is interconnected, and the process parameters are matched with each other, ultimately achieving precise control of the sensor structure and performance.

[0056] The evaluation method of this invention targets the force-electric response characteristics of flexible strain sensors under complex dynamic loads, achieving synchronous, accurate acquisition and quantitative analysis of mechanical and electrical signals, filling the gap in the existing technology for evaluating sensor performance under complex loads. The specific steps are as follows:

[0057] T1. Arrange test electrodes and connect to the real-time resistance monitoring system: Use conductive silver paste to attach flexible Ag / AgCl electrodes at specific positions on the sensor surface, lead out the electrodes with wires, and connect them to the real-time resistance monitoring system composed of a high-speed data acquisition card and a digital multimeter to complete the circuit debugging before testing.

[0058] This system enables real-time, high-precision acquisition of sensor resistance signals, providing an electrical data foundation for force-electrical co-analysis. The flexible Ag / AgCl electrode is matched to the sensor's flexibility, preventing the rigid electrode from breaking or detaching during sensor deformation and ensuring continuous resistance signal acquisition. The high-speed data acquisition card enables high-frequency acquisition of resistance signals, matching the changes in mechanical signals under dynamic loads, and the acquisition accuracy meets the requirements for quantitative analysis of sensor resistance changes.

[0059] T2. Sensor Installation and Dynamic Load Application: The sensor with installed electrodes is fixed to the corresponding mechanical testing equipment. At least one dynamic load (tensile, bursting, friction, or bending) is applied according to the evaluation target. For the bursting test, the sensor is fixed to the annular bursting fixture of a universal testing machine, with the electrodes positioned in the non-direct deformation area. For the friction test, referring to GB / T21196.3—2007 standard, the sensor is fixed to a Martindale abrasion tester, using #600 sandpaper as the abrasive and a pressure of 9 kPa for reciprocating friction. For the bending test, the sensor is fixed to an electric bending test bench, and bending is performed around a cylinder at a dynamic cyclic bending frequency of 1 Hz and an angle of 90°. This simulates the multi-mode dynamic load conditions of the sensor in practical applications, providing a mechanical data foundation for force-electrical co-analysis. For different load characteristics, corresponding test schemes are designed. The arrangement of the non-deformation area of ​​the electrode in the burst test avoids the failure of the electrode due to sample damage, ensuring that the resistance signal truly reflects the overall state of the conductive network. The friction test adopts national standards, which improves the comparability and authority of the test results. The parameter settings of the bending test simulate the actual bending conditions of wearable devices, and the test results have guiding significance for the practical application of sensors.

[0060] T3. Synchronously record mechanical signals and resistance change signals: Start the mechanical testing equipment and the real-time resistance monitoring system, and use the data synchronous acquisition program to synchronously record mechanical parameters (force value, displacement, number of cycles, bending angle, etc.) and resistance change data throughout the entire process of load application, holding, and release, ensuring that the time axis of the two types of data is completely consistent.

[0061] Acquiring the sensor's force-electric synchronous response data under dynamic loads provides a complete dataset for subsequent quantitative analysis. Synchronous signal acquisition avoids analytical errors caused by time differences, accurately reflects the correspondence between mechanical deformation and resistance change, and clearly reveals the sensor's force-electric synergistic mechanism, such as the quantitative correlation between the timing and degree of deformation and resistance change.

[0062] T4. Analysis of Sensor Resistance Stability and Resilience: Based on the acquired synchronous data, calculate key indicators such as resistance change rate (ΔR / R0), sensor sensitivity, and resistance recovery rate after unloading. Analyze the sensor's resistance stability, damage tolerance, durability, and resilience under different dynamic loads by analyzing the trends of these indicators. Resistance change rate: ΔR / R0 = (R - R0) / R0 × 100% (R is the real-time resistance under load, R0 is the initial resistance); Resistance recovery rate: η = (R0 - R0) / R0 × 100% r ) / (R max -R0)×100%(R r R is the recovery resistance after the load is removed. max (Maximum resistance under load); Sensitivity: GF = ΔR / (R0) (ε) (ε is strain; tensile / bending strain ε = deformation / original size; burst strain ε = burst displacement / substrate thickness). The sensor of this invention has a sensitivity GF≥5.2 (within the range of 0~25% tensile strain), a sensitivity GF≥3.8 under burst load, and a sensitivity GF≥4.5 under bending load, which is much higher than that of the carbon nanotube / silver nanowire-based contrast sensor (GF≤3.0), and it has both stable force-electric response and excellent deformation sensing capability.

[0063] This invention calculates the resistance change rate, sensitivity, and resistance recovery rate based on resistance change signals, and analyzes the resistance stability and recoverability of the sensor under dynamic loads. The core indicator calculation formulas are: ① Resistance change rate ΔR / R0=(R-R0) / R0×100%; ② Resistance recovery rate η=(R0-R0) / R0×100%; r ) / (R max -R0)×100%;③Sensitivity GF=ΔR / (R0) ε) (ε is strain); by observing the changing trends of each index, the damage tolerance, friction durability and bending stability of the sensor are quantitatively evaluated.

[0064] This method enables quantitative evaluation of the force-electrical coordinated stability of sensors, providing data support for sensor performance optimization and application scenario adaptation. Through quantitative analysis of key indicators, the force-electrical response characteristics of sensors are transformed from qualitative descriptions to quantitative evaluations, improving the scientific rigor and accuracy of the evaluation results. The resistance change rate reflects the degree of resistance fluctuation in the sensor, sensitivity reflects the sensor's sensing capability, and resistance recovery rate reflects the sensor's deformation recovery characteristics. Comprehensive analysis of multiple indicators can fully assess sensor performance and provide a standardized basis for performance comparisons of similar products.

[0065] The electrode arrangement and system connection in step T1 of this invention are the foundation of signal acquisition and determine the accuracy of data acquisition; the load application in step T2 is the core of simulating actual working conditions, and its test scheme design directly affects the practicality of the evaluation results; the synchronous recording in step T3 is the key to force-electric synergistic analysis, ensuring the correspondence between mechanical and electrical data; the quantitative analysis in step T4 is the final step of the evaluation, which uncovers the sensor performance patterns behind the data through key indicators. The steps work together to form a complete evaluation system from sample preparation, working condition simulation, signal acquisition to data analysis, realizing a systematic and scientific evaluation of the force-electric synergistic stability of the sensor under complex dynamic loads.

[0066] Example 1: Fabrication of an MXene-aramid flexible strain sensor

[0067] Preparation of MXene aqueous dispersion: Using a modified LiF / HCl in-situ etching method, 2.0 g of LiF powder was weighed and dissolved in 40 mL of 9 mol / L HCl solution, and the mixture was magnetically stirred at 35 °C for 30 minutes to form a mixture. Under an argon atmosphere, 2.0 g of Ti3AlC2MAX phase powder was added to the mixture in batches, and the mixture was stirred at 400 r / min for 24 hours. The reaction suspension was diluted with an equal volume of deionized water, centrifuged at 3500 r / min for 10 minutes, the supernatant was discarded and the precipitate was collected. The supernatant was centrifuged and washed 4 times until the pH of the supernatant was 6.8. After washing once with anhydrous ethanol, the precipitate was redispersed in deionized water to prepare an MXene aqueous dispersion with a mass concentration of 12 mg / mL, which was then stored in a sealed container at 4 °C.

[0068] Sensor fabrication: Aramid nonwoven fabric with a unit area mass of 180 g / m² was selected and cut into 5 cm × 5 cm square samples; MXene aqueous dispersion was diluted with deionized water at a volume ratio of 1:1, and the sample was completely immersed in the diluted solution for 30 seconds. It was then vertically pulled out of the liquid surface at a constant speed, and the wet film thickness was controlled to be 0.5 mm; it was immediately transferred to a vacuum drying oven and dried at 60 °C and 0.08 MPa for 2 hours. After cooling, the immersion-drying process was repeated twice, for a total of 3 immersions, and finally an MXene-aramid flexible strain sensor with an MXene loading of 8.6 mg / cm² was obtained.

[0069] Basic performance characteristics:

[0070] Morphology: Scanning electron microscopy (SEM) showed that the surface of the aramid fiber was coated with uniform and continuous MXene nanosheets, and there was local enrichment of MXene at the fiber intersection nodes, forming a complete node-axis three-dimensional interlocking conductive network.

[0071] Electrical performance: Under constant temperature and humidity (25℃, 65%RH), the average surface resistance measured by the four-probe method is 2.9kΩ, ≤10kΩ, indicating excellent conductivity;

[0072] Mechanical properties: Tested according to GB / T3923.1-2013 (tensile strength), GB / T3917.1-2009 (tear strength), and GB / T3923.2-2013 (bursting strength), with sample specifications of 50mm×100mm (tensile / tear) and 50mm×50mm (bursting). Compared with the original aramid nonwoven fabric without MXene loading, the sensor's tensile strength is increased by about 5.9%, tear strength by about 23.5%, and bursting strength by about 38.9%, achieving a synergistic improvement in conductivity and mechanical properties.

[0073] Example 2: Test and evaluation of force-electric coordinated behavior under sensor burst load

[0074] Test preparation: Take the sensor sample prepared in Example 1, and attach two pairs of flexible Ag / AgCl electrodes to the annular area 25 mm from the center using conductive silver paste, and connect them to a real-time resistance monitoring system composed of a high-speed data acquisition card and a digital multimeter.

[0075] Test procedure: Fix the sample in the annular jacking fixture (inner diameter 50mm) of the universal testing machine, drive the jacking rod to apply pressure to the center of the sample at a rate of 60mm / min, and record the jacking force value, jacking rod displacement and real-time resistance value simultaneously.

[0076] Results analysis: When the push rod pierces the sample and forms a 3.5mm diameter hole, the peak piercing force is 0.25kN, and the sensor resistance increases from 2.9kΩ to 4.9kΩ, an increase of 69%. After the push rod is removed, the resistance recovers to 3.3kΩ, with a recovery rate of 80%. In contrast, the resistance of the carbon nanotube / aramid sensor increases dramatically from 6.0kΩ to over 18.0kΩ after the hole is pierced, an increase of over 200%. The damage tolerance of the sensor of this invention is significantly better, and the detour conduction effect of the three-dimensional interlocking conductive network is significant.

[0077] Example 3: Sensor Tribological Durability Test and Evaluation

[0078] Test preparation: Cut the sensor sample of Example 1 into standard size, fix it on the Martindale abrasion tester test stage, and weld leads to both ends of the sample to connect to the resistance tester.

[0079] Test procedure: In accordance with GB / T21196.3—2007 standard, #600 sandpaper was used as abrasive and a pressure load of 9 kPa was applied to conduct a reciprocating friction test. The test was paused every 100 friction cycles and the surface resistance was measured under no pressure.

[0080] Results Analysis: After 500 friction cycles, the sensor resistance increased from 2.9kΩ to 3.68kΩ, an increase of 26.9%. After 1500 friction cycles, the resistance stabilized at around 45kΩ, forming a stable secondary conductive network. Compared with the carbon nanotube / aramid sensor, the resistance increased by more than 50% after 500 friction cycles, and the subsequent increase rate was significantly faster. The sensor of this invention exhibits excellent friction durability, and the interfacial bonding strength between MXene and aramid is significantly higher. After 1500 friction cycles, the resistance stabilized at around 45kΩ, forming a stable secondary conductive network. This secondary conductive network consists of MXene-rich areas at the cross nodes of aramid fibers and continuous conductive pathways in the inner layer of the fibers. Even after slight wear of the surface MXene coating due to friction, the MXene nanosheets fixed by the multi-layer impregnation-drying process in the inner layer of the fibers remain intact. The node-rich areas provide core conduction points for the current, and the axial pathways in the inner layer form a circuitous conduction path, thus avoiding an unlimited surge in resistance and demonstrating the structural advantages of a three-dimensional interlocking conductive network.

[0081] Example 4: Sensor Bending Stability Test and Evaluation

[0082] Test preparation: Cut the sensor sample of Example 1 into 50mm×20mm pieces, fix both ends to the electric bending test fixture, and suspend the middle part. Place electrodes at both ends of the sample to connect to the resistance tester.

[0083] Test procedure: First, the sample was bent around a cylinder with a radius of 5mm, 10mm, 20mm, and 50mm to 180°, and the static bending resistance value was recorded. Then, a dynamic cyclic bending test was performed under the conditions of a bending radius of 10mm, an angle of 90°, and a frequency of 1Hz. The resistance was recorded once every 100 cycles.

[0084] Results Analysis: When the bending radius is ≥10mm, the static bending resistance change rate is ≤15%, and the maximum resistance change rate after 1000 dynamic cyclic bending cycles is ≤40%, with the resistance response remaining stable. When the bending radius is 5mm, the resistance change rate increases to 65%, because local stress is concentrated in the axial conductive path of the aramid fiber. The excessively small bending radius causes the fiber to bend violently, compressing the interlayer slip space of the MXene nanosheets, resulting in local microcracks in the axial continuous conductive path, and weakening the detour conduction effect of the three-dimensional interlocking conductive network. When the bending radius is ≥10mm, the fiber bending degree is moderate, and the interlayer slip of MXene can adequately buffer the stress, thus maintaining a stable resistance response. Therefore, in practical applications, it is recommended that the bending radius of the sensing part be ≥10mm.

[0085] Comparative test

[0086] Using the same aramid nonwoven fabric and impregnation process as in Example 1, carbon nanotube (CNT) / aramid sensors and carbon black / aramid sensors were prepared as comparative examples, and their performance was tested under the test conditions of Examples 2 and 3.

[0087] CNT / aramid sensor: initial surface resistance 6.0kΩ, resistance increase of over 200% after burst test, resistance increase of over 50% after 500 friction cycles;

[0088] Carbon black / aramid sensor: initial surface resistance 5.8kΩ, resistance increase of over 250% after burst test, and resistance increase of over 60% after 500 friction cycles.

[0089] Reference Figure 3 Schematic diagram of typical force-electric synchronous response curve of sensor under uniaxial tensile load

[0090] The curve directly reflects the synergistic effect of the node-axial three-dimensional interlocked conductive network and MXene interlayer slip: when the tensile strain is 0~25%, the tensile load increases linearly with the increase of strain, and the surface resistance only fluctuates slightly without a significant increase. During this stage, the MXene nanosheets achieve adaptive rearrangement through interlayer slip, consuming tensile stress, while the axial continuous conductive path of the three-dimensional interlocked conductive network remains intact. The MXene-rich region of the fiber node provides a stable conduction point for the current, and no breakage of the conductive path occurs, demonstrating the stability of the sensor's force-electric response under normal tensile deformation. Under uniaxial tensile strain of 0~25%, the sensor of this invention shows a good synergistic response relationship between mechanical load and resistance change, with no abrupt change in resistance. The core technical features endow the sensor with excellent tensile force-electric stability, meeting the tensile deformation monitoring needs of wearable devices, flexible robots, and other scenarios.

[0091] Reference Figure 4 Schematic diagram of the resistance-displacement response curve of the sensor in a static burst test

[0092] The curve highlights the damage tolerance advantage of the node-axial three-dimensional interlocked conductive network: when the displacement of the push rod is 0~10mm, the bursting force increases rapidly with the increase of displacement, while the surface resistance increases slowly. During this stage, the central area of ​​the sensor is locally indented due to the compression of the push rod, and the fiber network undergoes elastic deformation. The MXene nanosheets buffer the local stress through interlayer slippage, and the overall structure of the three-dimensional interlocked conductive network remains intact. Only the local conductive pathways undergo slight changes due to compression, and the resistance does not fluctuate significantly. This verifies the excellent local damage tolerance of the sensor of this invention. Its core technical features enable it to maintain overall conductivity even after physical damage, solving the problem of signal failure after local damage in traditional flexible strain sensors. It is suitable for application scenarios that are susceptible to local compression / burst (such as smart protective gear and robot skin).

[0093] Figure 5 A schematic diagram showing the evolution of sensor resistance with the number of friction cycles during a triboelectric cycle test. The surface resistance changes with the number of friction cycles. The test was conducted according to GB / T21196.3—2007 standard, using #600 sandpaper as the abrasive and a pressure load of 9 kPa. This demonstrates the interfacial bonding strength and frictional durability resulting from the node-axial three-dimensional interlocking conductive network.

[0094] 0-500 friction cycles: The surface resistance slowly increased from the initial 2.9kΩ to 3.68kΩ, with a resistance increase of only 26.9%. During this stage, a small number of MXene nanosheets on the sensor surface underwent slight wear due to friction. However, the three-dimensional interlocking conductive network constructed by the multiple impregnation-drying process enabled MXene and aramid fibers to form a strong bond interface of mechanical interlocking and physical adsorption, effectively resisting cyclic shear stress. Moreover, the MXene conductive network in the inner layer of the fiber remained intact, and no large-area coating peeling occurred, which is far superior to carbon nanotube-based sensors (resistance increase of over 50% after 500 friction cycles).

[0095] 500-1500 friction cycles: The surface resistance shows a slow upward trend, stabilizing at a plateau of approximately 45kΩ after 1500 cycles. During this stage, the MXene coating on the sensor surface gradually wears off, and the outer conductive network partially fails. However, the MXene-rich areas at the fiber nodes and the conductive pathways in the inner fiber layer remain intact, forming a stable secondary conductive network and preventing the resistance from soaring indefinitely.

[0096] After 1500-1600 friction cycles, the surface resistance tends to stabilize without significant change, proving that the secondary conductive network has formed a stable conductive state, and the sensor still has basic conductivity and sensing performance.

[0097] The excellent tribological durability of the sensor of this invention has been verified. The core technical features (three-dimensional interlocking conductive network formed by multi-layer impregnation and strong interface bonding between MXene and aramid) significantly delay the wear and peeling of the coating, enabling the sensor to maintain stable conductivity after long-term cyclic friction. This solves the technical bottleneck of easy peeling and poor durability of traditional MXene-based sensor coatings, and is suitable for wearable devices, smart textiles and other scenarios that are prone to friction.

[0098] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible strain sensor based on a three-dimensional interlocking conductive network of MXene-aramid fibers, characterized in that, The sensor comprises a flexible aramid nonwoven fabric substrate and an MXene conductive layer. The aramid nonwoven fabric forms a three-dimensional porous fiber network with a unit area mass of 150-220 g / m². The MXene conductive layer is uniformly attached to the fiber surface and inter-fiber gaps of the aramid nonwoven fabric through an impregnation-drying process, forming a node-axial three-dimensional interlocked conductive network that runs through the three-dimensional porous fiber network. The surface resistance of the sensor is not higher than 10 kΩ. When the sensor is subjected to dynamic loads, the MXene conductive layer maintains the continuity of the conductive path through the synergistic effect of interlayer slippage of nanosheets and the three-dimensional interlocked conductive network structure, thereby achieving a stable force-electric response.

2. The MXene-aramid flexible strain sensor according to claim 1, characterized in that, The MXene conductive layer is formed by multi-layer coating through 2-5 impregnation-drying processes. MXene nanosheets are locally enriched at fiber intersection nodes, forming a continuous conductive path along the fiber axis.

3. The MXene-aramid flexible strain sensor according to claim 1, characterized in that, After local damage occurred during the static burst test, the resistance increase of the sensor was significantly lower than that of a comparable sensor with the same function, which used carbon nanotubes or silver nanowires as the conductive layer.

4. The MXene-aramid flexible strain sensor according to claim 1, characterized in that, After 500 standard friction cycles, the resistance increase of the sensor was significantly lower than that of comparable sensors with the same function, which used carbon nanotubes or silver nanowires as conductive layers.

5. The MXene-aramid flexible strain sensor according to claim 1, characterized in that, The sensor can maintain the stability of its resistance response under repeated bending deformation with a bending radius of not less than 10 mm, and the maximum resistance change rate is controlled within 40%.

6. A method for fabricating an MXene-aramid flexible strain sensor as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. MXene aqueous dispersion was prepared by LiF / HCl solution etching method; S2. The aramid nonwoven fabric substrate is impregnated in MXene aqueous dispersion to allow the dispersion to fully penetrate the three-dimensional porous fiber network; S3. The impregnated substrate is vacuum dried to fix the MXene nanosheets on the fiber surface. S4. Repeat steps S2 and S3 at least once to complete the multilayer coating of the MXene conductive layer and form a three-dimensional interlocking conductive network.

7. The preparation method according to claim 6, characterized in that, In step S1, the MXene aqueous dispersion is obtained by etching, centrifuging and washing the Ti3AlC2MAX phase. Specifically, the Ti3AlC2MAX phase powder is added to an HCl solution containing LiF to selectively etch the aluminum layer, and then centrifuged and washed until the pH of the supernatant is 6.5-7.

0. The supernatant is then redispersed in deionized water to obtain the MXene aqueous dispersion.

8. The preparation method according to claim 6, characterized in that, In step S3, the vacuum drying temperature is 50-80℃, the vacuum degree is not less than 0.08MPa, and the drying time is not less than 2 hours.

9. A method for evaluating the force-electric co-stability of the MXene-aramid flexible strain sensor as described in any one of claims 1-5, characterized in that, Includes the following steps: T1. Arrange test electrodes on the sensor and connect it to a real-time resistance monitoring system; T2. Install the sensor on the test equipment and subject it to at least one dynamic load among tension, bursting, friction, and bending. T3. Synchronously record the mechanical signals and resistance change signals throughout the entire process of load application and release; T4. Calculate the resistance change rate, sensitivity, and resistance recovery rate based on the resistance change signal, and analyze the resistance stability and recovery of the sensor under dynamic load.

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