Porous piezoresistive composite material based on TPU / G / LM and preparation method and application thereof

Abstract

The invention belongs to the technical field of piezoresistive materials, and particularly relates to a TPU / G / LM-based porous piezoresistive composite material and a preparation method and application thereof.The TPU / G / LM-based porous piezoresistive composite material comprises a porous thermoplastic polyurethane elastomer matrix, graphene distributed in and on the surface of a pore channel structure of the matrix and liquid metal embedded in the pore wall of the matrix and the pore channel structure; the graphene and the liquid metal form a conductive network; the mass of the graphene is 11%-19% of the sum of the mass of the graphene and the mass of the thermoplastic polyurethane elastomer matrix; and the volume fraction of the liquid metal accounts for 10-18% of the total volume of the composite material. A graphene nanosheet and liquid metal synergistic conductive system is introduced into a TPU porous skeleton, so that the dispersion and connectivity of a conductive phase in a TPU matrix are remarkably improved, stacking and agglomeration of graphene sheet layers are effectively inhibited, interface adhesion and structural coupling between the conductive phase and TPU pore walls are enhanced, and the conductivity of the TPU is improved. Therefore, the structural stability and the piezoresistive response performance of the composite material are improved.

Description

Technical Field

[0001] This application belongs to the field of piezoresistive materials technology, and particularly relates to a porous piezoresistive composite material based on TPU / G / LM, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible electronics, smart healthcare, human-computer interaction, wearable monitoring, and soft robotics, these fields are placing higher demands on the comprehensive performance of flexible sensing materials. Piezoresistive materials can convert external mechanical stimuli such as pressure and strain into changes in resistance signals. They offer advantages such as easy signal reading, easy structural integration, and ease of large-area arraying, showing broad application prospects in flexible pressure sensors, electronic skin, health monitoring devices, and motion posture recognition. Traditional piezoresistive sensing materials often employ systems such as metal foil / metal thin films and semiconductor silicon-based strain gauges. While these systems offer good sensitivity and stability, they generally suffer from high rigidity, poor stretchability, difficulty in conforming to complex curved surfaces, and limitations in processing and wearing comfort, making it difficult to meet the requirements of flexible wearable devices for thinness, flexibility, and deformability.

[0003] To address the challenge of traditional piezoresistive materials failing to meet the demands of flexible applications, researchers have developed polymer-based flexible piezoresistive composites using polymeric elastomers as the matrix and incorporating conductive fillers to construct conductive functional phases. Among these, thermoplastic polyurethane (TPU) has attracted widespread attention in the field of flexible piezoresistive sensing materials due to its excellent elasticity and toughness, good thermal processability, and favorable biocompatibility. TPU provides stable mechanical support and recoverable deformation capability, and it is easy to construct porous structures through processes such as solution methods, molding / extrusion, foaming, or freeze-drying, thereby achieving higher compressibility and a more significant resistive response.

[0004] However, in actual preparation, insufficient interfacial compatibility and dispersion stability remain between conductive fillers (such as graphene, carbon nanotubes, and carbon black) and the TPU matrix. This can easily lead to phenomena such as layer stacking or agglomeration, discontinuous conductive networks, and high percolation thresholds, thus limiting the effective response range of the material and reducing the consistency and repeatability of the output signal. Simultaneously, during long-term cyclic loading, porous piezoresistive composites are prone to fatigue damage on the pore walls, and the conductive network is susceptible to slippage and irreversible reconstruction, resulting in resistance signal drift, increased hysteresis, and performance degradation. Therefore, achieving a uniform and stable distribution of the conductive phase within the porous TPU framework and constructing a reconfigurable conductive network with high response, low drift, and high cycle durability remains a key technological bottleneck for improving the performance of flexible piezoresistive composites. Summary of the Invention

[0005] To address the problems of uneven distribution of conductive fillers and easy fatigue damage to pore walls in existing technologies, this application provides a porous piezoresistive composite material based on TPU / G / LM and its preparation method.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a porous piezoresistive composite material based on TPU / G / LM, comprising a porous thermoplastic polyurethane elastomer matrix, graphene distributed in the pore structure and on the surface of the pore wall, and liquid metal embedded in the pore wall and pore structure, wherein the graphene and liquid metal form a conductive network.

[0007] The mass of the graphene is 11% to 19% of the sum of the mass of the graphene and the thermoplastic polyurethane elastomer matrix; the volume fraction of the liquid metal accounts for 10% to 18% of the total volume of the composite material.

[0008] In some embodiments, the mass of the graphene is 15% of the sum of the mass of the graphene and the thermoplastic polyurethane elastomer matrix, and the volume fraction of the liquid metal accounts for 14% of the total volume of the composite material.

[0009] This application also provides a method for preparing a porous piezoresistive composite material based on TPU / G / LM, including the following steps:

[0010] (1) Thermoplastic polyurethane elastomer is dissolved in 1,4-dioxane to obtain TPU solution;

[0011] (2) Graphene was added to 1,4-dioxane and dispersed in an ultrasonic bath to obtain a graphene / 1,4-dioxane dispersion;

[0012] (3) The graphene / 1,4-dioxane dispersion was added to the TPU solution and stirred to obtain the TPU / G precursor solution;

[0013] (4) Add liquid metal to the TPU / G precursor solution and stir to obtain TPU / G / LM precursor solution;

[0014] (5) The TPU / G / LM precursor liquid is rapidly injected into the mold, pre-frozen and freeze-dried to obtain TPU / G / LM porous piezoresistive composite material.

[0015] In some embodiments, steps (1) and (3) are both performed under heating conditions.

[0016] In some embodiments, after adding liquid metal in step (4), heating is stopped or the temperature is lowered.

[0017] In some embodiments, after adding liquid metal in step (4), heating is stopped or the temperature is lowered, and stirring is performed when the system temperature drops to 30~35 ℃.

[0018] In some embodiments, the pre-freezing is freezing at -20 °C for 12 h, and the freeze-drying time is 24 h.

[0019] In some embodiments, the ultrasound treatment time in step (2) is 1 h.

[0020] The application of the composite material provided in this application as a piezoresistive material.

[0021] The composite material provided in this application is used as a thermistor material.

[0022] Beneficial effects: This invention significantly improves the dispersion and connectivity of the conductive phase in the TPU matrix by introducing a synergistic conductive system of graphene nanosheets and liquid metal into the porous TPU framework, effectively inhibits the stacking and agglomeration of graphene sheets, and enhances the interfacial adhesion and structural coupling between the conductive phase and the TPU pore walls, thereby improving the structural stability and piezoresistive response performance of the composite material.

[0023] By employing a freeze-drying process to construct a stable porous structure, the resulting composite material maintains its flexibility while possessing low density and good deformation response, significantly enhancing the material's mechanical flexibility and its ability to transfer and amplify stress.

[0024] By employing a freeze-drying process to construct a stable three-dimensional interconnected porous structure, the resulting composite material maintains flexibility and compressibility while possessing low density and rapid deformation recovery capability. During loading, the porous framework can effectively transfer stress and promote the reconstruction of the conductive network, thereby amplifying changes in resistance signal and improving the sensing response amplitude and adaptability to the operating range.

[0025] The preparation method provided by this invention is simple to operate, the process is controllable, the raw materials used are readily available, and it is suitable for large-scale production. At the same time, this method can achieve synergistic control between porous structures and conductive networks, providing a feasible technical path for the engineering application of flexible piezoresistive sensing materials.

[0026] Compared with existing technologies, the TPU / G / LM porous piezoresistive composite material constructed in this invention exhibits superior performance in terms of piezoresistive response and stability. It is suitable for applications such as flexible pressure sensing, temperature sensing, and monitoring of human motion and physiological signals, and has good promotional value and application prospects. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a porous piezoresistive composite material structure;

[0028] Figure 2 This is a schematic diagram of the preparation process of porous piezoresistive composite materials;

[0029] Figure 3 SEM image and EDS elemental mapping image of the porous piezoresistive composite material prepared in Example 1;

[0030] Figure 4 The piezoresistive response curve and sensitivity piecewise fitting results of the porous piezoresistive composite material prepared in Example 1 are shown.

[0031] Figure 5 The dynamic response curves of the porous piezoresistive composite material prepared in Example 1 under different pressure loading / unloading conditions;

[0032] Figure 6 Cyclic stability test curves of the porous piezoresistive composite material prepared in Example 1;

[0033] Figure 7 Current-voltage (IV) characteristic curves of porous piezoresistive composite materials with different liquid metal volume fractions;

[0034] Figure 8 The response curves and sensitivity piecewise fitting results of the composite materials prepared in Example 6 are shown.

[0035] Figure 9 Cyclic stability test curves of the composite material prepared in Example 6;

[0036] Figure 10 The response / recovery time curve of the composite material prepared in Example 1 under a load of 25 kPa pressure is shown.

[0037] Figure 11 The response / recovery time curve of the composite material prepared in Example 6 under a load of 25 kPa pressure is shown.

[0038] Figure 12 This is a temperature change curve of the composite material prepared in Example 1 under heating and cooling treatment;

[0039] Figure 13 The graph shows the resistance change of the composite material prepared in Example 1 during the heating and cooling process. Detailed Implementation

[0040] The present application will be further described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without making creative changes are within the protection scope of the present application.

[0041] Material selection in the embodiments:

[0042] Graphene nanosheets (G): particle size 1~5 μm, Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.;

[0043] Thermoplastic polyurethane elastomer (TPU): Dongguan Langfeng Plastic Raw Materials Co., Ltd.;

[0044] Liquid metal (LM): Gallium-indium-tin eutectic alloy; containing 62% gallium, 25% indium and 13% tin by mass, melting point: 3 ℃, Shenyang Jiabei Commercial and Trade Company.

[0045] Example 1

[0046] A schematic diagram of a TPU / G / LM porous piezoresistive composite material and its preparation method, specifically including as follows: Figure 2 The following steps are shown:

[0047] (1) Thermoplastic polyurethane elastomer (TPU) was dissolved in 1,4-dioxane and magnetically stirred at 45°C for 2 h to obtain a TPU solution, with the TPU concentration controlled at 14 wt%;

[0048] (2) Graphene (G) was added to 1,4-dioxane, wherein the mass ratio of graphene to 1,4-dioxane was 1:3. The graphene was first premixed to allow it to be initially wetted and dispersed. Then it was placed in an ultrasonic bath and ultrasonically dispersed for 1 h to break the agglomeration between the graphene nanosheets and improve its dispersion uniformity in the solvent, so as to obtain a stable graphene / 1,4-dioxane dispersion.

[0049] (3) The above dispersion was slowly added to the TPU solution at a mass of 15% of the sum of the mass of graphene and thermoplastic polyurethane elastomer, and continuous stirring was maintained during the addition process to avoid re-agglomeration caused by excessive local concentration. Then, stirring was continued at 1000 rpm for 12 h at 45 °C to fully mix the TPU matrix and graphene nanosheets and achieve uniform dispersion, so as to obtain a uniform TPU / G precursor solution.

[0050] (4) Add a predetermined amount of liquid metal (LM) to the TPU / G precursor liquid, and control the volume fraction of liquid metal to account for 14% of the total volume of the composite material. During the addition process, keep the stirring slow and continuous to avoid local aggregation of liquid metal. After the addition is completed, stop heating immediately and cool the system to 30 °C. Let the viscosity of the system gradually rise to facilitate the stable distribution of liquid metal in the TPU / G precursor liquid. Then stir at 600 rpm for 15 min to make the liquid metal uniformly dispersed in the form of microdroplets or microareas and fully contact the graphene conductive network to obtain the TPU / G / LM precursor liquid.

[0051] (5) The TPU / G / LM precursor liquid is injected into the mold and frozen at -20 ℃ for 12 h, followed by freeze drying for 24 h to obtain a porous TPU / G / LM porous piezoresistive composite material with a porous structure.

[0052] Example 2

[0053] Based on Example 1, the volume fraction of liquid metal was controlled at 10 vol%, and the mass fraction of graphene was controlled at 15 wt% (based on the sum of the masses of graphene and TPU). The remaining preparation steps and parameters were the same as in Example 1.

[0054] Example 3

[0055] Based on Example 1, the volume fraction of liquid metal was controlled at 12 vol%, and the mass fraction of graphene was controlled at 15 wt%. The remaining preparation steps and parameters were the same as in Example 1.

[0056] Example 4

[0057] Based on Example 1, the volume fraction of liquid metal was controlled at 16 vol%, and the mass fraction of graphene was controlled at 15 wt%. The remaining preparation steps and parameters were the same as in Example 1.

[0058] Example 5

[0059] Based on Example 1, the volume fraction of liquid metal was controlled at 18 vol%, and the mass fraction of graphene was controlled at 15 wt%. The remaining preparation steps and parameters were the same as in Example 1.

[0060] Example 6

[0061] Based on Example 1, the volume fraction of liquid metal was controlled at 14 vol%, and the mass fraction of graphene was controlled at 11 wt%. The remaining preparation steps and parameters were the same as in Example 1.

[0062] Example 7

[0063] Based on Example 1, the volume fraction of liquid metal was controlled at 14 vol%, the mass fraction of graphene was 19 wt%, and the remaining preparation steps and parameters were the same as in Example 1.

[0064] The TPU / G / LM porous piezoresistive composite material prepared in Example 1 was characterized by scanning electron microscopy (SEM), and the distribution of the liquid metal and graphene conductive phases was analyzed by energy dispersive spectroscopy (EDS) elemental mapping. The results are as follows: Figure 3As shown in the figure. The results show that the material exhibits a three-dimensional interconnected porous framework structure, with graphene mainly attached to the pore walls and forming a continuous conductive network on the framework surface; liquid metal is embedded in the pore walls and channels in the form of microdroplets or microregions, forming a multi-scale synergistic conductive pathway with the graphene network, and the elemental distribution is uniform, thus achieving reconfigurable and stable modulation of the conductive pathway during compression deformation. Its simulated structure is shown in the figure. Figure 1 As shown. The porous piezoresistive composite materials prepared in Examples 2-7 also exhibited the above structures after SEM and EDS analysis.

[0065] Comparative Example 1

[0066] (1) Thermoplastic polyurethane elastomer (TPU) was dissolved in 1,4-dioxane and magnetically stirred at 45 °C for 2 h to obtain a uniform TPU solution. (2) Graphene nanosheets were added to 1,4-dioxane and dispersed in an ultrasonic bath for 1 h to obtain a graphene / 1,4-dioxane dispersion. (3) The graphene dispersion was then added to the TPU solution, wherein the mass of graphene was 15% of the sum of the mass of graphene and TPU, and stirred at 1000 rpm for 12 h at 45 °C to obtain a TPU / G precursor solution. (4) After adding a predetermined amount of liquid metal (LM) to the TPU / G precursor liquid, the volume fraction of the liquid metal is controlled to account for 14% of the total volume of the composite material. The system is ultrasonically treated for 1 min at 45 °C using an ultrasonic disruptor to achieve forced dispersion of the liquid metal. After ultrasonic treatment, the system is kept at 45 °C and stirred at 600 rpm for 5 min to obtain the TPU / G / LM precursor liquid. (5) The precursor liquid is frozen at -20 °C for 12 h and then freeze-dried for 24 h to obtain the TPU / G / LM porous piezoresistive composite material.

[0067] Comparative Example 2

[0068] The ultrasonic fragmentation time for the liquid metal was controlled to be 2 minutes. Other conditions were the same as in Comparative Example 1.

[0069] Comparative Example 3

[0070] The ultrasonic fragmentation time for the liquid metal was controlled to be 3 minutes. Other conditions were the same as in Comparative Example 1.

[0071] Comparative Example 4

[0072] The ultrasonic fragmentation time for the liquid metal was controlled to be 5 min. Other conditions were the same as in Comparative Example 1.

[0073] Comparative Example 5

[0074] The ultrasonic fragmentation time for the liquid metal was controlled to be 10 min. Other conditions were the same as in Comparative Example 1.

[0075] Comparative Example 6

[0076] Based on Example 1, without adding liquid metal, only TPU / G porous materials were prepared. The remaining preparation steps and parameters were the same as in Example 1.

[0077] Comparative Example 7

[0078] Based on Example 1, the TPU / G / LM precursor solution was directly cast into a film and the solvent was removed by evaporation under vacuum to obtain a TPU / G / LM composite film. All other conditions were the same as in Example 1.

[0079] Performance testing

[0080] The sample materials prepared in each embodiment and comparative example were cut into 2 cm × 2 cm samples with a thickness of 0.5 mm, and clamped between the upper and lower metal electrodes to ensure stable initial contact. The resistance R was collected in real time under a constant test voltage (1 V), and R0 represents the resistance under zero load.

[0081] The piezoresistive response curve was obtained by applying a periodic compressive load (0-300 kPa) at a frequency of 1 Hz and recording the change of ΔR / R0 with pressure P. Piecewise linear fitting was performed on the curve for different pressure ranges, and the slope is the sensitivity S. Sensitivity S characterizes the relative change in the sensor's output electrical signal under pressure changes, and its mathematical expression is:

[0082] S=| |

[0083] Where ΔR represents the change in the sensor's electrical signal caused by pressure loading, R0 represents the electrical signal value under the initial state (zero pressure), and ΔP represents the pressure change. For a piezoresistive sensor, when the resistance is used as the output signal, the segmented sensitivities S1, S2, and S3 are respectively taken as the slopes of the fitted straight lines within the corresponding pressure intervals.

[0084] The piezoresistive performance of the sample obtained in Example 1 was tested, and the piezoresistive response curve of the relative resistance change ΔR / R0 as a function of pressure P was obtained. Piecewise linear fitting was performed for different pressure ranges. Figure 4 As can be seen, the curve exhibits different linear response characteristics in the low-pressure region (0-5 kPa), the medium-pressure region (5-75 kPa), and the high-pressure region (75-300 kPa), with corresponding piecewise sensitivities S of S1 = 4.46 kPa. -1 S2 = 0.672 kPa -1 And S3 = 0.197 kPa -1 The above results indicate that the sensor exhibits differentiated response slopes across different pressure ranges, and piecewise fitting can be used to characterize the variation of its electrical response within each pressure range.

[0085] In Comparative Example 6, no liquid metal was added. The piezoresistive response curve and sensitivity piecewise fitting results of the prepared material sample are as follows: Figure 8 As shown, the sensitivity S1 = 2.15 kPa in the low-pressure region (0-5 kPa). -1 Sensitivity in the medium pressure zone (5-75 kPa) is S² = 0.45 kPa. -1 Sensitivity S3 in the high-pressure zone (75-300 kPa) is 0.04 kPa. -1 Compared to the composite material prepared in Example 1, the sensitivity of each region decreased significantly.

[0086] The dynamic response curve is obtained by recording ΔR / R0 and time under different pressure loading / unloading conditions (three repeated loading / unloading cycles at different pressures). For example... Figure 5 As shown, the material sample prepared in Example 1 exhibits a reversible ΔR / R0 step response with monotonically increasing amplitude as the load increases over a wide pressure range from Pa to 50 kPa, and the waveforms are consistent across multiple loading / unloading operations, indicating that it possesses excellent low-pressure response capability, range coverage, and repeatability.

[0087] The cyclic stability test involves repeatedly loading and unloading the sample at a frequency of 1 Hz under a fixed pressure (100 kPa), recording ΔR / R0 and the number of cycles. During cyclic compression, when ΔR / R0 is detected to be saturated and fixed for a long period, and the resistance R signal simultaneously becomes fixed and tends to the lower limit of the instrument, it indicates that the electrical response has failed, and recording is stopped. The corresponding number of cycles at this point is the final number of compression cycles. Figure 6 As shown, the material sample prepared in Example 1 can operate stably for up to 20,000 cycles, and the output morphology remains highly consistent before and after cycling, reflecting the fatigue resistance and long-term reliability of the porous framework and conductive network. The cyclic stability test curve of the material prepared in Comparative Example 6 is shown below. Figure 9 As shown, since the conductive network is composed only of graphene nanosheet contacts, it is prone to interfacial damage under repeated compression, leading to continuous degradation of the conductive pathways. Figure 9 The results show that the TPU / G porous piezoresistive material prepared in Comparative Example 6 maintained a continuous and effective ΔR / R0 output within approximately 8000 cycles under cyclic compression, exhibiting a regular and repeatable peak-valley response. However, it also showed significant amplitude drift, baseline drift, and inter-cycle dispersion, indicating relatively poor stability of the piezoresistive signal output. In contrast, the TPU / G / LM prepared in Example 1 maintained a continuous, repeatable, and more stable piezoresistive signal output even during longer cycles, demonstrating superior cycle durability and long-term service reliability.

[0088] Figure 7The current-voltage (IV) characteristic curves of TPU / G / LM porous piezoresistive composites with different liquid metal volume fractions prepared in Examples 1-5 are shown. The IV curves of samples with different LM volume fractions (samples prepared in Examples 1-5) are approximately linear and the slope increases with the increase of LM content. This indicates that the composite material system has stable ohmic conductivity and the conductivity path can be tunably enhanced by introducing LM. This provides an electrical basis for obtaining highly consistent and calibrable piezoresistive signal output.

[0089] In addition, from Figure 10 and 11 It can be seen that under 25 kPa loading / unloading conditions, the TPU / G / LM composite material prepared in Example 1 can complete the response within 1 ms and recover within 4 ms, showing a significant millisecond-level fast follow-up. In contrast, the response and recovery of the TPU / G composite material prepared in Comparative Example 6 are approximately 56 ms and 64 ms, respectively, with a significantly longer time scale. This indicates that the introduction of LM makes the conductive path more continuous and can be quickly reconstructed, while also having a buffering effect on the viscoelastic hysteresis of the skeleton, thereby significantly improving the dynamic response capability under high load.

[0090] The piezoresistive response properties and compression cycle number of the composite porous piezoresistive materials prepared in Examples 1-5 and Comparative Examples 1-7 are shown in Table 1:

[0091] Table 1

[0092]

[0093] Compared to Comparative Examples 1-5, which used ultrasonic dispersion after the addition of liquid metal, this invention terminates heating promptly after the introduction of liquid metal, allowing the system viscosity to recover. Under gentle stirring conditions, it promotes the uniform distribution and effective anchoring of the liquid metal within the porous framework, thereby reducing local aggregation and subsequent migration at the pore walls and interfaces. This improves the electrical response stability of the material during cyclic loading and reduces performance fluctuations during the preparation process. As shown in Table 1, the compression cycles in Examples 1-5 all exceeded 2500, especially in Examples 1, 2, and 6, reaching 20000, 9000, and 15000 cycles respectively. Compared to the ultrasonic dispersion method used in Comparative Examples 1-5, the number of cycles is significantly increased. This is because excessively long ultrasonic dispersion of liquid metal can lead to excessive droplet fragmentation and a sparse conductive network, resulting in increased resistance, decreased sensitivity, and reduced cyclic stability.

[0094] When the volume fraction of liquid metal is low, insufficient conductive bridging prevents the formation of a stable network and hinders stress transmission and dissipation. This limits the reconstruction range of the conductive network, resulting in a smaller change in ΔR / R0 and decreased sensitivity. Conversely, when the volume fraction is too high, liquid metal droplets are more prone to coalescence and localized seepage, causing the conductive pathways to become "short-circuited" and leading to unstable contact states during cycling. This results in decreased sensitivity or increased signal drift. Furthermore, the liquid metal content gradually decreases during cycling, irreversibly damaging the conductive network and causing pore structure collapse. Within a suitable liquid metal content range, the liquid metal is effectively constrained by the porous framework, providing a continuous conductive path and stress buffer while preventing uncontrolled seepage, thus significantly improving the material's cycling stability. Under the process conditions of this invention, a liquid metal volume fraction of 14 vol% achieves a better balance between sensitivity and stability.

[0095] In Comparative Example 7, the solvent was removed by direct evaporation under vacuum conditions. However, due to the shrinkage that easily occurs during the evaporation drying process, which causes the pore structure to collapse and the conductive filler to be unevenly distributed, it is difficult to form a stable porous conductive network. As a result, the output resistance increases, the sensitivity decreases, and the stability of the compression cycle deteriorates, with only 100 compression cycles.

[0096] From Table 1 above and Figures 4-11 The results show that the TPU / G / LM porous piezoresistive composite material constructed in this invention has high sensitivity in the low-pressure region and maintains a usable operating range in the medium and high-pressure regions.

[0097] Furthermore, the TPU / G / LM porous piezoresistive material prepared in this invention also exhibits a thermosensitive effect. For example... Figure 12 As shown, the material sample obtained in Example 1 was subjected to a heating-cooling treatment within the range of 20-60℃, and the change in its resistance value was detected simultaneously. The results are as follows. Figure 13 As shown, the resistance of the material decreases with increasing temperature and increases with decreasing temperature, indicating that this material can be used as a negative temperature coefficient (NTC) thermistor.

[0098] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this application.

Claims

1. A porous piezoresistive composite material based on TPU / G / LM, characterized in that, It includes a porous thermoplastic polyurethane elastomer matrix, graphene distributed within and on the surface of the matrix's pore structure, and liquid metal embedded in the pore walls and pore structure of the matrix, wherein the graphene and liquid metal form a conductive network. The mass of the graphene is 11% to 19% of the sum of the mass of the graphene and the thermoplastic polyurethane elastomer matrix; the volume fraction of the liquid metal accounts for 10% to 18% of the total volume of the composite material.

2. The TPU / G / LM porous piezoresistive composite material according to claim 1, characterized in that, The mass of the graphene is 15% of the sum of the mass of the graphene and the thermoplastic polyurethane elastomer matrix, and the volume fraction of the liquid metal accounts for 14% of the total volume of the composite material.

3. The method for preparing a porous piezoresistive composite material based on TPU / G / LM according to any one of claims 1 to 2, characterized in that, Includes the following steps: (1) Thermoplastic polyurethane elastomer is dissolved in 1,4-dioxane to obtain TPU solution; (2) Graphene was added to 1,4-dioxane and dispersed in an ultrasonic bath to obtain a graphene / 1,4-dioxane dispersion; (3) The graphene / 1,4-dioxane dispersion was added to the TPU solution and stirred to obtain the TPU / G precursor solution; (4) Add liquid metal to the TPU / G precursor solution and stir to obtain TPU / G / LM precursor solution; (5) The TPU / G / LM precursor liquid is rapidly injected into the mold, pre-frozen and freeze-dried to obtain TPU / G / LM porous piezoresistive composite material.

4. The preparation method according to claim 3, characterized in that, Both steps (1) and (3) are performed under heating conditions.

5. The preparation method according to claim 3 or 4, characterized in that, After adding liquid metal in step (4), heating is stopped or the temperature is lowered.

6. The preparation method according to claim 5, characterized in that, After adding liquid metal in step (4), heating should be stopped or the temperature should be lowered. Stirring should be carried out when the system temperature drops to 30~35 ℃.

7. The preparation method according to claim 3, characterized in that, The pre-freezing is freezing at -20 ℃ for 12 h, and the freeze-drying time is 24 h.

8. The preparation method according to claim 3, characterized in that, The ultrasound treatment time in step (2) is 1 hour.

9. The application of the composite material according to any one of claims 1 to 2 as a piezoresistive material.

10. The application of the composite material according to any one of claims 1 to 2 as a thermistor material.

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