MWCNT-rGO-PDMS composite film, and preparation method and application thereof

Abstract

This invention belongs to the field of sensor material preparation technology, specifically relating to a MWCNT-rGO-PDMS composite film, its preparation method, and its applications. The MWCNT-rGO-PDMS composite film consists of a PDMS flexible elastic matrix and multi-walled carbon nanotubes and reduced graphene oxide conductive fillers dispersed within the PDMS flexible elastic matrix. This invention utilizes MWCNTs, rGO, and PDMS to construct a ternary composite pressure-sensitive material. By leveraging the synergistic effect between one-dimensional MWCNTs and two-dimensional rGO, a multi-scale three-dimensional dynamic conductive network is constructed within the PDMS flexible elastic matrix. MWCNTs provide continuous one-dimensional conductive paths, rGO enhances the connection between different conductive units, and the PDMS flexible elastic matrix provides flexible deformation capability and viscoelastic recovery characteristics. Through this design, the MWCNT-rGO-PDMS composite film simultaneously possesses high pressure response sensitivity, a wide pressure detection range, good mechanical flexibility, and good time stability.

Description

Technical Field

[0001] This invention belongs to the field of sensor material preparation technology, specifically relating to a MWCNT-rGO-PDMS composite thin film, its preparation method, and its application. Background Technology

[0002] In recent years, with the accelerating pace of life, increasing work and study pressure, and prolonged use of electronic devices, sleep disorders have become a significant public health issue. Numerous studies have shown that chronic sleep deprivation or poor sleep quality not only leads to short-term effects such as decreased attention, memory loss, and poor mental state, but also increases the risk of various chronic diseases, including hypertension, diabetes, cardiovascular disease, and neurodegenerative diseases. Therefore, long-term, continuous, and accurate monitoring of the human sleep process is of great importance for sleep disorder screening, health management, and chronic disease prevention.

[0003] Currently, sleep monitoring mainly includes two categories: medical-grade sleep monitoring devices and consumer-grade smart wearable devices. Medical-grade sleep monitoring devices use polysomnography (PSG) as the gold standard. It comprehensively analyzes the sleep process by simultaneously collecting multiple physiological signals such as electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), electrocardiography (ECG), respiratory airflow, blood oxygen saturation, and limb movement to accurately assess sleep stages and types of sleep disorders. However, PSG devices are typically expensive and have complex systems. Electrode attachment and device calibration need to be performed by professionals in hospitals or specialized sleep centers. During the testing process, subjects need to connect numerous wires and sensors, which not only affects normal sleep but also easily produces the so-called "first-night effect," leading to a certain deviation between the test results and actual home sleep conditions. Therefore, PSG cannot meet the needs of the general population for long-term, continuous home monitoring.

[0004] With the development of flexible electronics and wearable health monitoring technologies, consumer-grade smart bracelets and smartwatches are increasingly being applied to sleep monitoring. These devices typically utilize sensors such as accelerometers, gyroscopes, and photoplethysmography (PPG) to collect human motion and heart rate information, and combine this with algorithms to infer the user's sleep state. Compared to medical-grade devices, they have advantages such as small size, low cost, and ease of long-term wear. However, existing consumer-grade devices mainly rely on motion detection for sleep analysis, and their results are easily affected by the tightness of the fit, changes in body posture, and environmental factors, resulting in limited monitoring accuracy. Furthermore, smart bracelets and smartwatches often use rigid electronic components and hard straps, which can cause discomfort and affect sleep comfort and user compliance during prolonged wear, making it difficult to meet the requirements of high-quality sleep monitoring.

[0005] Flexible pressure sensors have gained widespread attention in fields such as human motion monitoring, electronic skin, biomedical detection, and health monitoring due to their advantages of being lightweight, flexible, bendable, stretchable, and easy to adhere to human skin. Among them, flexible pressure sensors based on the piezoresistive effect have become an important research direction in the field of sleep monitoring due to their advantages of simple structure, low manufacturing cost, direct output signal, and easy integration. However, for piezoresistive flexible sleep monitoring sensors, their core sensing materials have a series of significant defects in practical applications. This results in existing piezoresistive flexible sleep monitoring sensors still suffering from problems such as complex equipment, insufficient wearing comfort, susceptibility to high-frequency noise interference, limited pressure response range, and insufficient long-term stability when applied to human turning over motion detection, making it difficult to meet the actual needs of long-term home-based, high-reliability, and low-power sleep monitoring.

[0006] Therefore, there is an urgent need to provide a flexible sensor made of new sensing materials for the field of sleep monitoring, which can have a wide pressure response range, high stability and excellent anti-interference ability while ensuring good flexibility and wearing comfort. Summary of the Invention

[0007] The purpose of this invention is to provide a MWCNT-rGO-PDMS composite film, its preparation method, and its applications. A ternary composite pressure-sensitive material is constructed using multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and polydimethylsiloxane (PDMS). PDMS, as a flexible elastic matrix, provides deformable space for the MWCNTs and rGO conductive fillers. MWCNTs, as one-dimensional nano-conductive structures, have a high aspect ratio and can form continuous conductive paths within the matrix. rGO, as a two-dimensional sheet-like conductive material, can form a multi-scale synergistic conductive network with MWCNTs, improving the stability and pressure response of the conductive network. This invention constructs a stable and dense three-dimensional conductive network through a high content of conductive fillers, causing a significant change in resistance when the material is subjected to pressure. This allows the flexible pressure sensor to respond significantly to large-amplitude, long-period movements such as turning over during sleep, while naturally suppressing weak high-frequency disturbances such as breathing, heartbeat, and clothing friction, achieving a "self-filtering" function.

[0008] The present invention is specifically achieved through the following technical solution: a MWCNT-rGO-PDMS composite film proposed according to the present invention is composed of a PDMS flexible elastic matrix and multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) conductive fillers dispersed in the PDMS flexible elastic matrix. The PDMS flexible elastic matrix is ​​formed by mixing and curing a PDMS precursor and a corresponding mass of curing agent.

[0009] In the aforementioned MWCNT-rGO-PDMS composite film, the mass of multi-walled carbon nanotubes (MWCNTs) accounts for 8% of the total mass of the raw materials, and the mass of reduced graphene oxide (rGO) accounts for 0.4% of the total mass of the raw materials. The total mass of the raw materials refers to the sum of the masses of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), PDMS precursor, and curing agent.

[0010] In the aforementioned MWCNT-rGO-PDMS composite film, the mass ratio of the PDMS precursor to the curing agent is 9:1.

[0011] This invention also provides a method for preparing MWCNT-rGO-PDMS composite films, which specifically includes the following steps: S1. Weigh a certain amount of reduced graphene oxide (rGO) and place it in an agate mortar for thorough grinding to form a uniform powder. Then, weigh a certain amount of multi-walled carbon nanotubes (MWCNTs) and add them to the aforementioned agate mortar, along with an appropriate amount of PDMS precursor and a corresponding mass of curing agent. Mechanically grind the reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), PDMS precursor, and curing agent in the agate mortar to ensure that all components are thoroughly mixed and homogeneous, thus obtaining a black composite slurry. S2. The obtained black composite paste is scraped onto a stainless steel mold. The black composite paste is gradually filled into the stainless steel mold through multiple scraping processes, ensuring that the final composite film has a uniform thickness and a smooth surface. S3. Place the stainless steel mold containing the black composite slurry in an oven for heat treatment. After the heat treatment is completed, turn off the heating device and allow the sample to cool naturally to room temperature with the oven. S4. Peel the cooled and solidified sample from the stainless steel mold to obtain the MWCNT-rGO-PDMS composite film.

[0012] In the aforementioned method for preparing MWCNT-rGO-PDMS composite films, in step S1, the mass of multi-walled carbon nanotubes (MWCNTs) accounts for 8% of the total mass of the raw materials, and the mass of reduced graphene oxide (rGO) accounts for 0.4% of the total mass of the raw materials. The total mass of the raw materials refers to the sum of the masses of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), PDMS precursor, and curing agent.

[0013] In the aforementioned method for preparing MWCNT-rGO-PDMS composite films, in step S1, the mass ratio of PDMS precursor to curing agent is 9:1.

[0014] In the aforementioned method for preparing the MWCNT-rGO-PDMS composite film, step S3 includes three stages of heat treatment: the first stage is heat treatment at 60 ℃ for 10 h, the second stage is heat treatment at 80 ℃ for 2 h, and the third stage is heat treatment at 120 ℃ for 2 h.

[0015] This invention also provides an application of the MWCNT-rGO-PDMS composite film prepared according to the aforementioned method in a flexible pressure sensor. The flexible pressure sensor includes a MWCNT-rGO-PDMS composite film, an upper surface conductor, a lower surface conductor, and an encapsulation layer for protecting the MWCNT-rGO-PDMS composite film. One end of the upper and lower surface conductors is bent to form a closed ring structure, forming a ring contact end. The ring contact ends of the upper and lower surface conductors are respectively attached to the upper and lower surfaces of the same MWCNT-rGO-PDMS composite film. A fixing adhesive piece is used to adhere and fix the ring contact ends to the MWCNT-rGO-PDMS composite film, ensuring stable contact between the upper and lower surface conductors and the MWCNT-rGO-PDMS composite film. The upper and lower surface conductors are led out in opposite directions along the MWCNT-rGO-PDMS composite film. The encapsulation layer is used to encapsulate the upper and lower surfaces of the MWCNT-rGO-PDMS composite film, resulting in a flexible pressure sensor. The encapsulation layer is made of polypropylene film. The initial resistance of this flexible pressure sensor is 12kΩ, and its sensitivity is 2.92kPa. -1 .

[0016] Compared with the prior art, the present invention has at least the following advantages: (1) This invention utilizes multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and polydimethylsiloxane (PDMS) to construct a ternary composite pressure-sensitive material. By leveraging the synergistic effect between one-dimensional MWCNTs and two-dimensional rGO, a multi-scale three-dimensional dynamic conductive network is constructed within a flexible PDMS matrix. Specifically, MWCNTs provide continuous one-dimensional conductive paths, the rGO sheet structure enhances the connection between different conductive units, and the flexible PDMS matrix provides flexible deformation capability and viscoelastic recovery properties. Through this design, the MWCNT-rGO-PDMS composite film simultaneously possesses high pressure response sensitivity, a wide pressure detection range, good mechanical flexibility, and good time stability.

[0017] (2) This invention constructs a stable, dense, and dynamically reconfigurable three-dimensional conductive network using high-content conductive fillers, enabling the MWCNT-rGO-PDMS composite film to exhibit significant resistance changes under pressure. When the MWCNT-rGO-PDMS composite film is subjected to pressure loading or unloading, a resistance overshoot response with obvious time characteristics is generated due to the viscoelastic deformation of the PDMS matrix, the friction between conductive fillers, the adjustment of the network topology, and the dynamic change of the tunneling distance. This includes: the resistance overshoot peak caused by pressure disturbance at the moment of pressure loading, the resistance overshoot peak caused by pressure unloading at the moment of pressure release, and the resistance overshoot response caused by overload under high pressure conditions. Traditional flexible pressure sensors typically employ a fast recovery design, and their output signals are easily affected by high-frequency, low-amplitude signals. However, this invention utilizes the minute-level slow recovery characteristics of the MWCNT-rGO-PDMS composite film after unloading, enabling the flexible pressure sensor to naturally possess a function similar to a low-pass filter. Therefore, high-frequency, small-amplitude noise cannot generate obvious resistance overshoot peaks, while large pressure changes and long-duration human turning movements can activate significant overshoot signals. Therefore, this invention realizes a hardware-level signal filtering method based on material physical properties, which can reduce the complexity of back-end signal processing and improve the reliability of sleep monitoring.

[0018] (3) This invention breaks through the traditional design concept of minimizing hysteresis effect in piezoresistive sensors. It utilizes the resistance overshoot phenomenon generated by the reconstruction of the conductive network and the viscoelasticity of the polymer in the high-filler-load composite system, and transforms this phenomenon into a characteristic dynamic pressure recognition signal. This allows the flexible pressure sensor to respond significantly to large-amplitude, long-period movements such as turning over during human sleep, while naturally suppressing high-frequency weak disturbances such as human breathing, heartbeat, and clothing friction. The flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite film has good flexibility and bendability, and can be attached to the back of the hand, forearm, or knee joint to collect pressure change signals caused by changes in human posture during sleep, thereby enabling human sleep monitoring. Attached Figure Description

[0019] Figure 1 These are physical images (a) of the flexible pressure sensor assembled according to the present invention and (b) of the flexible pressure sensor in a bent state.

[0020] Figure 2 This is a curve showing the change in resistance of a flexible pressure sensor as a function of the MWCNT mass fraction.

[0021] Figure 3 This is a curve showing the change in sensitivity of the flexible pressure sensor as a function of the MWCNT mass fraction.

[0022] Figure 4This is a curve showing the change in resistance of a flexible pressure sensor as a function of the mass fraction of rGO.

[0023] Figure 5 This is a curve showing the sensitivity of the flexible pressure sensor as a function of the rGO mass fraction.

[0024] Figure 6 The image shows a physical diagram of the MWCNT-rGO-PDMS composite film prepared in Example 8, where (a) is a schematic diagram of its rough surface, (b) is a schematic diagram of its smooth surface, and (c) is a schematic diagram of its bent state.

[0025] Figure 7 This is a schematic diagram of three conductivity mechanisms in the MWCNT-rGO-PDMS composite film.

[0026] Figure 8 This is the resistance variation trend of a flexible pressure sensor assembled with MWCNT-rGO-PDMS composite thin film under different placement times.

[0027] Figure 9 This is an exponential fitting curve of the resistance of a flexible pressure sensor assembled with MWCNT-rGO-PDMS composite film as a function of placement time at different placement times.

[0028] Figure 10 This is a comparison of the sensitivity of the flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite film prepared in Example 8 with that of a conventional flexible pressure sensor.

[0029] Figure 11 The flexible pressure sensor is assembled based on the MWCNT-rGO-PDMS composite film prepared in Example 8. The dynamic resistance test curve is obtained by simulating limb movements during sleep by pressing down and raising the human arm.

[0030] Figure 12 The dynamic resistance test curves were obtained from the flexible pressure sensor assembled based on the MWCNT-rGO-PDMS composite thin film prepared in Example 8, using a 6.8 kg weight for pressurization and depressurization experiments. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Unless otherwise specified, all conditions in the following examples were performed under conventional conditions or conditions recommended by the manufacturer. Raw materials and reagents whose manufacturers are not specified are all commercially available products. Unless otherwise stated, the scientific and technical terminology and experimental methods of this invention are based on the conventional understanding and existing standard methods of those skilled in the art.

[0033] The MWCNT-rGO-PDMS composite film proposed in this invention is composed of a PDMS flexible elastic matrix and multi-walled carbon nanotubes and reduced graphene oxide conductive fillers dispersed in the PDMS flexible elastic matrix. The PDMS flexible elastic matrix is ​​formed by mixing and curing a PDMS precursor and a corresponding mass of curing agent. Specifically, the MWCNT-rGO-PDMS composite film is prepared according to the following method: S1. Weigh a certain amount of reduced graphene oxide (rGO) and place it in an agate mortar for thorough grinding to form a uniform powder. Then, weigh a certain amount of multi-walled carbon nanotubes (MWCNTs) and add them to the aforementioned agate mortar. Add an appropriate amount of Dow SYLGARD 184 PDMS precursor and a corresponding mass of curing agent. Mechanically grind rGO, MWCNT, PDMS precursor and curing agent in the agate mortar for 5-7 minutes to ensure that the components are fully mixed and obtain a black composite slurry with uniform color, glossy surface and consistent texture. S2. The obtained black composite paste is scraped onto a stainless steel mold. The black composite paste is gradually filled into the stainless steel mold through multiple scraping processes, ensuring that the final composite film has a uniform thickness and a smooth surface. S3. Place the stainless steel mold containing the black composite slurry in an oven for heat treatment. First, heat treat at 60 ℃ for 10 hours to achieve preliminary curing, then heat treat at 80 ℃ for 2 hours to achieve further curing, and finally heat treat at 120 ℃ for 2 hours. After the heat treatment is completed, turn off the heating device and allow the sample to cool naturally to room temperature with the oven. S4. Peel the cooled and solidified sample from the stainless steel mold to obtain the MWCNT-rGO-PDMS composite film.

[0034] Preferably, in step S1 above, the mass of reduced graphene oxide accounts for 0.4% of the total mass of the raw materials, the mass of multi-walled carbon nanotubes accounts for 8% of the total mass of the raw materials, and the mass ratio of PDMS precursor to curing agent is 9:1. The total mass of raw materials refers to the sum of the masses of reduced graphene oxide, multi-walled carbon nanotubes, PDMS precursor, and curing agent.

[0035] The present invention will now be described in detail with reference to specific embodiments: Example 1 S1. Weigh 0.07g of multi-walled carbon nanotubes (MWCNTs) and add them to an agate mortar. Add 3.087g of Dow SYLGARD184 PDMS precursor and 0.343g of curing agent. The mass ratio of PDMS precursor to curing agent is 9:1. The mass of MWCNT accounts for 2% of the total mass of MWCNT, PDMS precursor and curing agent. Mechanically grind the mixture of MWCNT, PDMS precursor and curing agent in the agate mortar for 5 minutes to fully mix the components and obtain a black composite slurry with uniform color, glossy surface and consistent texture. S2. The obtained black composite slurry is scraped into a stainless steel mold. The black composite slurry is gradually filled into the stainless steel mold through multiple scraping processes to ensure that the final composite film has a uniform thickness and a smooth surface. The film-forming space of the stainless steel mold is 100 mm × 40 mm × 0.3 mm (length × width × thickness). S3. Place the stainless steel mold containing the black composite slurry in an oven for heat treatment. First, heat treat at 60 ℃ for 10 hours to achieve preliminary curing, then heat treat at 80 ℃ for 2 hours to achieve further curing, and finally heat treat at 120 ℃ for 2 hours. After the heat treatment is completed, turn off the heating device and allow the sample to cool naturally to room temperature with the oven. S4. Peel the cooled and solidified sample from the stainless steel mold to obtain the MWCNT-PDMS composite film. Cut it into 30 mm × 30 mm square flexible piezoresistive films for later use.

[0036] Example 2 In step S1, the masses of MWCNT, PDMS precursor, and curing agent are 0.14g, 3.024g, and 0.336g, respectively. The mass of MWCNT accounts for 4% of the total mass of MWCNT, PDMS precursor, and curing agent. The remaining operation steps are the same as in Example 1. The MWCNT-PDMS composite film is obtained and cut into 30 mm × 30 mm square flexible piezoresistive films for later use.

[0037] Example 3 In step S1, the masses of MWCNT, PDMS precursor, and curing agent are 0.21g, 2.961g, and 0.329g, respectively. The mass of MWCNT accounts for 6% of the total mass of MWCNT, PDMS precursor, and curing agent. The grinding time is 6min. The remaining operation steps are the same as in Example 1. The MWCNT-PDMS composite film is obtained and cut into 30mm×30mm square flexible piezoresistive films for later use.

[0038] Example 4 In step S1, the masses of MWCNT, PDMS precursor, and curing agent are 0.28g, 2.898g, and 0.322g, respectively. The mass of MWCNT accounts for 8% of the total mass of MWCNT, PDMS precursor, and curing agent. The grinding time is 7min. The remaining operation steps are the same as in Example 1. The MWCNT-PDMS composite film is obtained and cut into 30mm×30mm square flexible piezoresistive films for later use.

[0039] Example 5 In step S1, the masses of MWCNT, PDMS precursor, and curing agent are 0.35g, 2.835g, and 0.315g, respectively. The mass of MWCNT accounts for 10% of the total mass of MWCNT, PDMS precursor, and curing agent. The grinding time is 7min. The remaining operation steps are the same as in Example 1. The MWCNT-PDMS composite film is obtained and cut into 30mm×30mm square flexible piezoresistive films for later use.

[0040] The square flexible piezoresistive films prepared in Examples 1-5 were assembled into flexible pressure sensors, and the specific steps are as follows: (1) Select two copper enameled wires, remove the insulating varnish layer at both ends of the copper enameled wires to expose the internal copper conductors, and then bend the exposed copper conductor at one end of each copper enameled wire to form a closed ring structure, forming a ring contact end, to obtain the upper surface conductor and the lower surface conductor. Both the upper surface conductor and the lower surface conductor have only one end as the ring contact end. (2) The circular contact ends of the upper surface wire and the lower surface wire are respectively attached to the upper and lower surfaces of the same square flexible piezoresistive film. The circular contact ends are fixed to the flexible piezoresistive film by the square fixing adhesive piece, so that the upper surface wire and the lower surface wire maintain stable contact with the flexible piezoresistive film. The other ends of the upper surface wire and the lower surface wire are respectively led out in opposite directions along the flexible piezoresistive film. (3) The upper and lower surfaces of the flexible piezoresistive film obtained in step (2) are encapsulated using an encapsulation layer to obtain a flexible pressure sensor, such as... Figure 1 As shown.

[0041] Figure 1 In the image, (a) is a physical image of the assembled flexible pressure sensor, and (b) is a physical image of the flexible pressure sensor in a bent state. In this flexible pressure sensor, the circular contact ends of the upper and lower surface wires are respectively attached to the upper and lower surfaces of the same square flexible piezoresistive film to collect the resistance change signal during the material being subjected to force; the other ends of the upper and lower surface wires are led out in opposite directions along the flexible piezoresistive film to connect to external resistance testing equipment, current acquisition equipment, or wireless signal transmission modules. Figure 1As can be clearly seen in (b), the flexible pressure sensor remains in good condition under bending conditions and does not break.

[0042] In one embodiment, the fixing adhesive sheet can be selected as polyimide tape.

[0043] In one embodiment, the encapsulation layer is made of transparent polypropylene film. The flexible piezoresistive film, the annular contact ends of the upper and lower surface wires, and the fixing adhesive pad are encapsulated by the encapsulation layer to improve the sensor's structural stability and environmental adaptability. The assembled flexible pressure sensor has a square sheet structure with good flexibility and bendability, and can be attached to the back of the hand, forearm, or knee joint to collect pressure change signals caused by changes in body posture during sleep.

[0044] The square flexible piezoresistive films prepared in Examples 1-5 were assembled into flexible pressure sensors according to the sensor assembly method described above. The initial resistance and sensitivity of different flexible pressure sensors were tested. The resistance test method was carried out in accordance with the national standard GB / T 15662-1995 and the international standard ASTM D991. The sensitivity was calculated by the rate of change of resistance under unit pressure. s=(ΔR / R0) / (F / A) Where s represents sensitivity, in Pa. -1 R0 represents the initial resistance value, in ohms (Ω); ΔR represents the change in resistance, in ohms (Ω); F represents the pressure, in newtons (N); A represents the area of ​​force application, in square meters (m²). 2 ).

[0045] Plot a graph with the percentage of MWCNT mass in the total mass of MWCNT, PDMS precursor, and curing agent in Examples 1-5 as the x-axis and the initial resistance as the y-axis, as shown below. Figure 2 As shown. Simultaneously, a graph was plotted with the percentage of MWCNT mass in the total mass of MWCNT, PDMS precursor, and curing agent in Examples 1-5 as the x-axis and the test sensitivity as the y-axis, as shown. Figure 3 As shown, without reduced graphene oxide (rGO), the initial resistance of the flexible pressure sensor gradually decreases with increasing mass percentage of MWCNT (from 5198 kΩ to 84 kΩ), indicating that with increasing MWCNT content, a large number of conductive paths are gradually formed, and the conductivity of the composite material is significantly enhanced. Sensitivity first increases and then decreases with increasing mass percentage of MWCNT. When the mass percentage of MWCNT accounts for 8% of the total mass of MWCNT, PDMS precursor, and curing agent, the assembled flexible pressure sensor has a relatively low initial resistance (203 kΩ) while also possessing high sensitivity (0.83 kPa).-1 Therefore, preferably, the percentage of MWCNT mass in the flexible piezoresistive film is 8% of the total mass of MWCNT, PDMS precursor, and curing agent.

[0046] Example 6 In step S1, the masses of MWCNT, PDMS precursor, and curing agent are 0.28g, 2.927g, and 0.293g, respectively. The mass of MWCNT accounts for 8% of the total mass of MWCNT, PDMS precursor, and curing agent. The mass ratio of PDMS precursor to curing agent is 10:1. The grinding time is 7min. The remaining operation steps are the same as in Example 4. A MWCNT-PDMS composite film is obtained, which is cut into 30mm×30mm square flexible piezoresistive films and assembled into a flexible pressure sensor. The initial resistance is tested using the same method and is 261 kΩ with an error of 84 kΩ. In contrast, the initial resistance of the flexible pressure sensor assembled from the flexible piezoresistive film obtained in Example 4 (with a mass ratio of PDMS precursor to curing agent of 9:1) is 203kΩ with an error of 51kΩ. Therefore, the flexible pressure sensor assembled from the flexible piezoresistive film prepared with a mass ratio of PDMS precursor to curing agent of 9:1 in this invention has better stability.

[0047] With a fixed percentage of MWCNT in the total raw material mass of 8% and a PDMS precursor to curing agent mass ratio of 9:1, the effect of varying the amount of reduced graphene oxide added on the final performance of the flexible pressure sensor was investigated, as follows: Example 7 S1. Weigh 0.007g of reduced graphene oxide (rGO) and grind it thoroughly in an agate mortar until it forms a uniform powder. Then weigh 0.28g of multi-walled carbon nanotubes (MWCNTs) and add them to the aforementioned agate mortar, along with 2.892g of Dow Sylgard 184 PDMS precursor and 0.321g of curing agent, so that the mass of rGO accounts for 0.2% of the total mass of the raw materials, the mass of MWCNTs accounts for 8% of the total mass of the raw materials, and the mass ratio of PDMS precursor to curing agent is 9:1. The total mass of the raw materials refers to the sum of the masses of reduced graphene oxide, multi-walled carbon nanotubes, PDMS precursor, and curing agent. The mixture of rGO, MWCNT, PDMS precursor, and curing agent was mechanically ground in an agate mortar for 6 minutes to ensure thorough mixing of the components and obtain a black composite slurry with uniform color, glossy surface, and consistent texture. The remaining operation steps were the same as steps S2-S4 in Example 1 to obtain the MWCNT-rGO-PDMS composite film, which was then cut into 30 mm × 30 mm square flexible piezoresistive films for later use.

[0048] Example 8 S1. Weigh 0.014g of reduced graphene oxide (rGO) and grind it thoroughly in an agate mortar until it forms a uniform powder. Then weigh 0.28g of multi-walled carbon nanotubes (MWCNTs) and add them to the aforementioned agate mortar, along with 2.885g of Dow Sylgard 184 PDMS precursor and 0.321g of curing agent, so that the mass of rGO accounts for 0.4% of the total mass of raw materials, the mass of MWCNT accounts for 8% of the total mass of raw materials, and the mass ratio of PDMS precursor to curing agent is 9:1. The remaining operation steps are the same as steps S2-S4 of Example 1 to obtain a MWCNT-rGO-PDMS composite film, which is then cut into 30mm × 30mm square flexible piezoresistive films for later use.

[0049] Example 9 S1. Weigh 0.021g of reduced graphene oxide (rGO) and grind it thoroughly in an agate mortar until it forms a uniform powder. Then weigh 0.28g of multi-walled carbon nanotubes (MWCNTs) and add them to the aforementioned agate mortar, along with 2.88g of Dow Sylgard 184 PDMS precursor and 0.32g of curing agent, so that the mass of rGO accounts for 0.6% of the total mass of raw materials, the mass of MWCNT accounts for 8% of the total mass of raw materials, and the mass ratio of PDMS precursor to curing agent is 9:1. The remaining operation steps are the same as steps S2-S4 of Example 1 to obtain a MWCNT-rGO-PDMS composite film, which is then cut into 30mm × 30mm square flexible piezoresistive films for later use.

[0050] Following the aforementioned sensor assembly method, the square flexible piezoresistive films prepared in Examples 7-9 were assembled into flexible pressure sensors. The initial resistance and sensitivity of different flexible pressure sensors were tested using the same method. A graph was plotted with the percentage of rGO mass in Examples 7-9 relative to the total mass of rGO, MWCNT, PDMS precursor, and curing agent as the x-axis and the tested initial resistance as the y-axis. The results are shown below. Figure 4 As shown. Simultaneously, a graph was plotted with the percentage of rGO mass in the total mass of rGO, MWCNT, PDMS precursor, and curing agent in Examples 7-9 as the x-axis and the test sensitivity as the y-axis. The results are as follows. Figure 5 As shown.

[0051] Figure 4 and Figure 5In the above, when the rGO mass percentage is 0%, the test results of the flexible pressure sensor assembled from the flexible piezoresistive film prepared in Example 4 are shown. It can be seen that the initial resistance of the flexible pressure sensor gradually decreases with the increase of the rGO mass percentage (from 203 kΩ to 3 kΩ), indicating that the rGO sheet structure can further connect the discontinuous regions between MWCNTs, improving the overall conductivity. However, the sensitivity of the flexible pressure sensor first increases and then decreases with the increase of the rGO mass percentage. This may be because an excessively high rGO content leads to an overly dense conductive network, reducing the network reconstruction space due to pressure changes, thus decreasing sensitivity. When the rGO mass percentage of the total mass of rGO, MWCNTs, PDMS precursor, and curing agent is 0.4%, the assembled flexible pressure sensor has a small initial resistance (12 kΩ) while maintaining high sensitivity (2.92 kPa). -1 Therefore, preferably, the mass percentage of rGO in the MWCNT-rGO-PDMS composite film is 0.4% of the total mass of rGO, MWCNT, PDMS precursor, and curing agent, while the mass percentage of MWCNT is 8% of the total mass of rGO, MWCNT, PDMS precursor, and curing agent.

[0052] Figure 6 The images shown are of the MWCNT-rGO-PDMS composite film fabricated in Example 8. (a) is a schematic diagram of its rough surface, (b) is a schematic diagram of its smooth surface, and (c) is a schematic diagram of its bent state. The rough surface of the flexible piezoresistive film is the side of the slurry facing upwards in the stainless steel mold. This surface exhibits a certain rough structure due to direct contact with the scraper. The smooth surface is the side of the slurry in contact with the stainless steel mold, and this surface is relatively smooth. Figure 6 Figure (c) shows that the flexible piezoresistive film prepared in Example 8 has good flexibility, can achieve various deformations such as rolling and bending, has good mechanical adaptability, and can bend and deform with human movement.

[0053] The MWCNT-rGO-PDMS composite film prepared in this invention uses PDMS as a flexible elastic matrix to provide deformable space for the conductive filler; MWCNT, as a one-dimensional nano-conductive structure, has a high aspect ratio and can form continuous conductive paths within the matrix; rGO, as a two-dimensional sheet-like conductive material, can form a multi-scale synergistic conductive network with MWCNT, improving the stability and pressure response of the conductive network. MWCNT and rGO intertwine in the PDMS matrix to form a conductive network with a three-dimensional topological structure, such as... Figure 7As shown, the change in internal resistance of the material is mainly affected by the following three conductivity mechanisms: (1) direct contact conductivity between conductive fillers; (2) quantum tunneling effect caused by the change in spacing between conductive fillers; and (3) change in the overall topology of the conductive network.

[0054] Unlike traditional pressure sensors that rely solely on resistance changes under stable pressure, this invention utilizes transient resistance overshoot behavior during pressure loading and unloading as a characteristic signal to identify human movement processes. Based on the external pressure change process, the flexible pressure sensor (hereinafter referred to as the "sensor") assembled from the MWCNT-rGO-PDMS composite thin film prepared in this invention mainly exhibits the following three resistance overshoot modes.

[0055] (1) Pressure disturbance resistance overshoot mechanism (instantaneous response upon pressure application) When the sensor is subjected to external transient pressure, the PDMS elastic matrix first undergoes rapid viscoelastic deformation. Due to localized shear deformation and the Poisson effect within the material during the initial stage of pressure loading, lateral displacement occurs in some areas, increasing the distance between the MWCNT and rGO, which were originally in a stable contact state. At this time, some conductive contact points separate, the number of conductive pathways decreases, and the tunneling distance between the fillers increases. Therefore, at the instant pressure is applied, the material resistance increases rapidly, forming a significant positive resistance spike.

[0056] As pressure continues to increase, the conductive filler undergoes overall compression, leading to the re-establishment of more contact points between the MWCNT and rGO, a shortened tunneling distance, and a gradual densification of the conductive network. Ultimately, the material resistance rapidly decreases and enters a stable low-resistance state. Therefore, during pressurization, the flexible pressure sensor exhibits the following characteristics: instantaneous high resistance peak → rapid decrease → stable low-resistance state. This characteristic can serve as an important identification signal for the downward pressure of a human arm, body contact, or the initiation of a rollover.

[0057] (2) Pressure unloading resistor overshoot mechanism (instantaneous response upon release) When external pressure is suddenly released, the PDMS elastic matrix quickly recovers its original shape due to its elastic recovery capability. However, because this invention uses a high-content conductive filler system, there are strong inter-nanomaterial friction, steric hindrance, and network structure constraints within the conductive network. Therefore, the recovery speed of the conductive filler network is significantly lower than the instantaneous recovery speed of the PDMS matrix. Shortly after pressure release, the PDMS rapidly expands and recovers, while the MWCNT-rGO network remains stretched and loose, increasing the distance between fillers and causing a rapid rise in tunneling impedance. Consequently, the material resistance exceeds its initial pressure-free state resistance, resulting in a significant "unloading resistance overshoot" phenomenon. Subsequently, as the conductive network gradually readjusts to a stable state, the material resistance slowly decreases according to an exponential decay law, eventually recovering to a stable state. This process manifests as: low resistance state → instantaneous high resistance overshoot peak → slow recovery over several minutes. Because this recovery process lasts for a relatively long time, it can effectively distinguish itself from high-frequency weak disturbances such as human breathing and heartbeat, thus possessing natural anti-interference capabilities.

[0058] (3) Pressure overload resistance overshoot mechanism (abnormal pressure response) When a material is subjected to extremely high pressure, its internal conductive network undergoes more dramatic structural changes. Under overload pressure, the PDMS matrix experiences excessive vertical compression and lateral expansion while maintaining its volume. The conductive filler is subjected to strong compression and lateral displacement, resulting in large stress gradients in localized areas. Significant slippage and network distortion occur between the MWCNT and rGO. Due to excessive mechanical action, the conductive network in some areas may experience transient or even irreversible damage, reducing the number of conductive paths. Therefore, even with continuous external pressure, the material resistance may still show a nonlinear increase, resulting in a pressure overload resistance overshoot response. This mechanism enables the sensor to have a larger pressure detection range, avoiding the problem of rapid saturation of traditional high-sensitivity piezoresistive materials under high pressure.

[0059] The three resistance overshoot mechanisms mentioned above do not exist independently, but rather work together under different pressure conditions. The pressure loading phase mainly exhibits resistance overshoot due to pressure disturbance; the pressure release phase mainly exhibits resistance overshoot due to unloading; and the extreme pressure state exhibits resistance overshoot due to overload. These three mechanisms collectively determine the sensor's dynamic response characteristics to pressure changes. Since different human actions correspond to different pressure change processes, the flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite thin film prepared in this invention can not only detect the magnitude of pressure, but also distinguish between the pressure generation process, the pressure release process, the duration of the action, and the intensity of the action.

[0060] To evaluate the stability of the MWCNT-rGO-PDMS composite film during long-term use, this invention further investigated the aging-related changes in the resistance of the MWCNT-rGO-PDMS composite film. During the experiment, the initial resistance of the MWCNT-rGO-PDMS composite film samples was continuously tested at different placement times. The resistance tests were conducted according to the national standard GB / T 15662-1995 and the international standard ASTM D991. The changes in the internal conductive network of the MWCNT-rGO-PDMS composite film over time were analyzed.

[0061] The MWCNT-rGO-PDMS composite film prepared in Example 8 was cut and assembled into a flexible pressure sensor. Its resistance value was then measured after being placed for different number of days. A graph was plotted with the energization time during resistance testing as the x-axis and resistance as the y-axis. The results are as follows: Figure 8 As shown, during the energization process of the composite film, the resistance gradually decreases with increasing energization time, eventually stabilizing within 200 seconds. This is because during electron transport, the conductive fillers MWCNT and rGO undergo a certain degree of positional reconfiguration due to the electric field force. Once this reconfiguration process is complete, the MWCNT-rGO-PDMS composite film reaches a stable operating state. Furthermore, resistance tests conducted on the MWCNT-rGO-PDMS composite film after different placement times indicate that the initial resistance initially increases rapidly with increasing placement time, then gradually stabilizes. Therefore, the flexible pressure sensor made from this MWCNT-rGO-PDMS composite film requires a brief energization before use, after which it enters a stable operating state.

[0062] To describe this change pattern and eliminate data noise during the testing process, this invention uses a first-order exponential model to fit the resistance change process of the above experiment. The fitting formula is as follows: R(t) = AB × e^(-t / τ) Where: R(t) represents the resistance of the material at time t, in kiloohms (kΩ); A represents the resistance plateau value after stabilization, in kiloohms (kΩ); B represents the resistance difference between the initial and steady-state states, in kiloohms (kΩ); t represents time, in seconds (s); τ represents the time constant of resistance change, in seconds (s). The fitting results show that the experimental data and the theoretical curve have a high degree of agreement (see...). Figure 8 The R in the upper right corner 2 In the first 10 days after preparation, the resistance of the MWCNT-rGO-PDMS composite thin film material showed a significant increasing trend, and then gradually stabilized, eventually settling at around 12.3 kΩ.

[0063] To further illustrate the time stability of the MWCNT-rGO-PDMS composite film, the MWCNT-rGO-PDMS composite film prepared in Example 8 was cut and assembled into a flexible pressure sensor. Its resistance was then measured after being placed for different number of days, and exponential fitting curves of the resistance of the MWCNT-rGO-PDMS composite film over time were obtained for different placement times, as shown below. Figure 9 As shown, the formula used to fit the relationship between resistance and time is as follows: R(t) = C + D × [1 - e^(-t / τ)] Where: R(t) represents the resistance value of the material at time t, in kiloohms (kΩ); C represents the resistance plateau value after stabilization, in kiloohms (kΩ); D represents the resistance difference between the initial state and the steady state, in kiloohms (kΩ); t represents time, in days (d); τ represents the time constant of resistance change, in days (d). Figure 9 In C=4.2671 kΩ, D=8.0009 kΩ, τ=3.31 d.

[0064] This first-order exponential model effectively reflects the time stability of the material, while the resistance change during this process mainly originates from the further relaxation of the PDMS molecular chains and the spontaneous adjustment of the composite conductive network from a non-equilibrium state to a low-energy stable state. Figure 9 Overall, over time, the reference resistance of the MWCNT-rGO-PDMS composite film gradually increases, the conductive network structure tends to stabilize, and the resistance recovery curve gradually flattens. These results indicate that the MWCNT-rGO-PDMS composite film prepared in Example 8 of this invention possesses good long-term stability, and the sensor assembled from it can meet the application requirements of long-term sleep monitoring.

[0065] To verify the performance advantages of the flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite film prepared in Example 8 of this invention, its sensitivity was compared with that of a previously published flexible pressure sensor, such as... Figure 10 As shown. Figure 10 In this study, the sensitivity data of samples 1, 2, and 3 are obtained from published research literature (10.1016 / j.mtnano.2024.100512, 10.1007 / s40820-019-0288-7). Sample 5 corresponds to the test results of the flexible pressure sensor assembled with the MWCNT-rGO-PDMS composite film (Example 8) of this invention based on the resistance overshoot effect. Sample 4 corresponds to the test results of the flexible pressure sensor of sample 5 after the resistance overshoot effect occurs.

[0066] Figure 10This indicates that the sensitivity of sample 4 (after the resistance overshoot effect of the flexible pressure sensor in sample 5) is 0.32 kPa. -1 The sensitivity of sample 5 (based on the resistance overshoot effect) was significantly improved to 2.92 kPa. -1 Compared to previously reported results, the sensitivity of Sample 1 was 0.41 kPa. -1 The sensitivity of sample 2 was 0.68 kPa. -1 The sensitivity of sample 3 was 1.62 kPa. -1 This indicates that the MWCNT-rGO-PDMS composite film prepared in Example 8 of this invention exhibits significantly higher pressure response capability. The main reasons for its excellent response are: firstly, MWCNTs provide a continuous one-dimensional conductive path; secondly, the rGO sheet structure can connect the local fracture regions between MWCNTs, improving the integrity of the conductive network; simultaneously, the multi-scale conductive network formed by these two components has a larger structural adjustment space under pressure, enabling the material to achieve high sensitivity while maintaining a wide operating range; furthermore, the competitive relationship among the three conductive mechanisms and the rational application of the resistance overshoot effect greatly enhance the material's ability to respond to external forces.

[0067] Human turning over typically involves two parallel physical processes: "pressure increase" and "pressure release." One limb lifting off the bed causes pressure release, while the other limb touching the bed causes pressure increase. Therefore, during these pressure increase and release processes, the flexible pressure sensor outputs resistance overshoot signals with different characteristics. To verify the application effect of the flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite film prepared in Example 8 of this invention in detecting human movements during sleep, the assembled flexible pressure sensor was used to perform dynamic resistance tests on pressure changes during simulated sleep turning over. Pressure increase and pressure release groups were set up separately during the test. Figure 11 The dynamic resistance test curve is obtained by simulating limb movements during sleep by pressing down and raising the human arm. The specific operation steps include: fixing the assembled flexible pressure sensor to the wrist; placing the elbow of the arm with the flexible pressure sensor attached on a flat table; allowing the forearm to fall naturally onto the table and holding it there for 20 seconds, with the flexible pressure sensor pressed under the wrist to simulate a pressure state; then slowly raising the forearm to simulate a pressure release state, holding it there for 20 seconds as well; repeating this method alternately. Figure 11 In the text, pressurization group 1, pressurization group 2, and pressurization group 3 represent flexible pressure sensors assembled from different batches of MWCNT-rGO-PDMS composite films produced according to Example 8. Pressurization group 1 and depressurization group 1 are the same sample, pressurization group 2 and depressurization group 2 are the same sample, and pressurization group 3 and depressurization group 3 are the same sample.

[0068] Figure 12 The dynamic resistance test curve is obtained by conducting pressure and decompression experiments using a 6.8 kg weight to simulate the effect of a relatively large pressure. The specific operating steps include: placing the flexible pressure sensor on a flat table, pressing the 6.8 kg weight onto the flexible pressure sensor and holding it for 20 seconds to simulate the pressure state, and then removing the 6.8 kg weight and holding it for 20 seconds to simulate the decompression state. Figure 12 In the text, pressurization group 4 and pressurization group 5 represent flexible pressure sensors assembled from different batches of MWCNT-rGO-PDMS composite films produced according to Example 8. Pressurization group 4 and pressure relief group 4 are the same sample, and pressurization group 5 and pressure relief group 5 are the same sample.

[0069] exist Figure 11 and Figure 12 In the pressurization experiment (pressurization group 1-pressurization group 5), the sensor was initially in a pressure-free state for the first 20 seconds. When pressure was applied at approximately 20 seconds, all pressurization groups showed a significant transient resistance increase peak (resistance overshoot effect). Subsequently, due to the continuous application of pressure, the PDMS matrix continued to compress, the MWCNT and rGO conductive networks gradually reconnected, the tunneling distance decreased, and therefore, the pressure disturbance resistance overshoot ended, the resistance rapidly decreased (in the last 20 seconds), and remained stable.

[0070] All pressure groups (1-5) exhibit the same pattern: a sharp upward peak is generated at the moment of pressure application (resistance overshoot effect), followed by a rapid decline into a stable low-resistance state. This transient peak can serve as a trigger signal for judging the downward pressure of a human arm or the contact action of the body. The peaks in pressure groups 4 and 5 are sharper than those in pressure groups 1-3 because the process of pressing down a heavy object is more stable and involves greater force than the actual downward pressure of an arm.

[0071] In the pressure relief experiments (pressure relief groups 1-5), the sensors were initially in a low-resistance state under pressure. When the pressure was suddenly released after approximately 20 seconds, all test groups exhibited significant resistance overshoot. At the moment of pressure release, due to the rapid recovery of the PDMS and the lag in the recovery of the conductive network, the material resistance rose rapidly. Subsequently, the MWCNT and rGO networks gradually rearranged, the internal stress of the material was gradually released, and the conductive path gradually recovered. Therefore, the resistance overshoot ended during pressure relief, and the resistance exhibited an exponential decay recovery process lasting more than 20 seconds, eventually returning to a steady state.

[0072] Decompression groups 1 through 5 exhibited consistent decompression overshoot peaks. Compared to the sharp peaks that appeared during the pressurization process, the peaks that appeared during the decompression process were wider and recovered more slowly. This characteristic indicates that the flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite thin film prepared in Example 8 of this invention can generate action characteristic signals with significant time-scale differences by utilizing the material's own recovery kinetics.

[0073] This invention utilizes multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and polydimethylsiloxane (PDMS) to construct a ternary composite pressure-sensitive material. By leveraging the synergistic effect between one-dimensional MWCNTs and two-dimensional rGO, a multi-scale three-dimensional dynamic conductive network is constructed within a flexible PDMS matrix. Through this structural design, the MWCNT-rGO-PDMS composite film simultaneously possesses high pressure response sensitivity, a wide pressure detection range, good mechanical flexibility, and good temporal stability. This invention breaks through the traditional design approach of minimizing hysteresis in piezoresistive sensors. It utilizes the resistance overshoot phenomenon generated by the reconstruction of the conductive network and the viscoelasticity of the polymer in a high-filler-load composite system, transforming this phenomenon into a characteristic dynamic pressure recognition signal. This allows the flexible pressure sensor to produce a significant response to large-amplitude, long-period movements such as turning over during sleep, while naturally suppressing simultaneous high-frequency, weak disturbances such as breathing, heartbeat, and clothing friction. The flexible pressure sensor assembled from the MWCNT-rGO-PDMS composite film is characterized by its thinness, high flexibility, bendability, and ease of attachment to the human body. It can be attached to the back of the hand, forearm, or knee joint to collect pressure change signals caused by changes in human posture during sleep, thereby enabling human sleep monitoring.

[0074] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A MWCNT-rGO-PDMS composite film, characterized in that, It is composed of a PDMS flexible elastic matrix and multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) conductive fillers dispersed in the PDMS flexible elastic matrix. The PDMS flexible elastic matrix is ​​formed by mixing and curing a PDMS precursor and a corresponding mass of curing agent.

2. The MWCNT-rGO-PDMS composite film as described in claim 1, characterized in that, The mass of multi-walled carbon nanotubes (MWCNTs) accounts for 8% of the total mass of the raw materials, and the mass of reduced graphene oxide (rGO) accounts for 0.4% of the total mass of the raw materials. The total mass of the raw materials refers to the sum of the masses of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), PDMS precursor, and curing agent.

3. The MWCNT-rGO-PDMS composite film as described in claim 1 or 2, characterized in that, The mass ratio of PDMS precursor to curing agent is 9:

1.

4. A method for preparing a MWCNT-rGO-PDMS composite thin film, characterized in that, Includes the following steps: S1. Weigh a certain amount of reduced graphene oxide (rGO) and place it in an agate mortar for thorough grinding to form a uniform powder. Then, weigh a certain amount of multi-walled carbon nanotubes (MWCNTs) and add them to the aforementioned agate mortar, along with an appropriate amount of PDMS precursor and a corresponding mass of curing agent. Mechanically grind the reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), PDMS precursor, and curing agent in the agate mortar to ensure that all components are thoroughly mixed and homogeneous, thus obtaining a black composite slurry. S2. The obtained black composite paste is scraped onto a stainless steel mold. The black composite paste is gradually filled into the stainless steel mold through multiple scraping processes, ensuring that the final composite film has a uniform thickness and a smooth surface. S3. Place the stainless steel mold containing the black composite slurry in an oven for heat treatment. After the heat treatment is completed, turn off the heating device and allow the sample to cool naturally to room temperature with the oven. S4. Peel the cooled and solidified sample from the stainless steel mold to obtain the MWCNT-rGO-PDMS composite film.

5. The method for preparing the MWCNT-rGO-PDMS composite thin film as described in claim 4, characterized in that, In step S1, the mass of multi-walled carbon nanotubes (MWCNTs) accounts for 8% of the total mass of the raw materials, and the mass of reduced graphene oxide (rGO) accounts for 0.4% of the total mass of the raw materials. The total mass of the raw materials refers to the sum of the masses of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), PDMS precursor, and curing agent.

6. The method for preparing the MWCNT-rGO-PDMS composite thin film as described in claim 4, characterized in that, In step S1, the mass ratio of PDMS precursor to curing agent is 9:

1.

7. The method for preparing the MWCNT-rGO-PDMS composite thin film as described in claim 4, characterized in that, In step S3, the heat treatment includes three stages: the first stage is heat treatment at 60 ℃ for 10 h, the second stage is heat treatment at 80 ℃ for 2 h, and the third stage is heat treatment at 120 ℃ for 2 h.

8. The application of the MWCNT-rGO-PDMS composite film prepared by the method described in claim 4 in a flexible pressure sensor.

9. The application as described in claim 8, characterized in that, The flexible pressure sensor includes a MWCNT-rGO-PDMS composite film, an upper surface wire, a lower surface wire, and an encapsulation layer for protecting the MWCNT-rGO-PDMS composite film. One end of the upper and lower surface wires is bent to form a closed ring structure, forming a ring contact end. The ring contact ends of the upper and lower surface wires are respectively attached to the upper and lower surfaces of the same MWCNT-rGO-PDMS composite film. The ring contact ends are glued and fixed to the MWCNT-rGO-PDMS composite film by a fixing adhesive piece, so that the upper and lower surface wires maintain stable contact with the MWCNT-rGO-PDMS composite film. The upper and lower surface wires are led out in opposite directions along the MWCNT-rGO-PDMS composite film. The upper and lower surfaces of the MWCNT-rGO-PDMS composite film are encapsulated by the encapsulation layer to obtain the flexible pressure sensor. The encapsulation layer is made of polypropylene film.

10. The application as described in claim 8 or 9, characterized in that, The flexible pressure sensor has an initial resistance of 12kΩ and a sensitivity of 2.92kPa. -1 .

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