Flexible pressure sensing film and preparation method thereof

Abstract

The invention discloses a preparation method of a flexible pressure sensing film, which comprises the following steps: mixing dandelion modified cellulose nanofiber dispersion liquid with single-layer graphene dispersion liquid, and stirring at room temperature to obtain a uniform blended solution; and filtering the blended solution through a vacuum filtration method, and obtaining the flexible pressure sensing film through a layer-by-layer self-assembly mode. The flexible pressure sensing film prepared by the invention has high sensitivity, can generate obvious resistance change under small pressure change, and realizes accurate detection of small pressure signals. And meanwhile, the device has quick response and recovery capability, real-time monitoring of dynamic pressure change is facilitated, and the performance stability of the device under the conditions of high-frequency operation and quick loading is improved. The pressure sensing film shows a wide detection range, can maintain good linear response characteristics in low-pressure and high-pressure intervals, effectively overcomes the problems that a traditional flexible pressure sensor is narrow in detection range and easy to saturate, and expands application scenarios.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and in particular relates to a method for preparing a flexible pressure sensing film and a flexible pressure sensing film prepared by the preparation method. Background Art

[0002] Flexible pressure sensors can monitor changes in external pressure in real time without affecting the overall flexibility and wearability of the device. They are widely used in a variety of fields, including electronic skin, health monitoring, intelligent prostheses, motion detection, industrial automation, and intelligent robotics. In the healthcare field, flexible pressure sensors can be used to detect physiological signals such as human pulse, respiratory rate, and gait analysis, assisting in early disease screening and health management. In the field of human-computer interaction, flexible pressure sensors can enable flexible displays, smart gloves, virtual reality devices, etc., to achieve a more natural and precise interactive experience. In the fields of intelligent manufacturing and robotics, flexible pressure sensors can simulate the tactile perception function of human skin, enhancing robots' perception and adaptability to the external environment.

[0003] Currently, the fabrication of flexible pressure sensors on the market generally utilizes a piezoresistive sensing element constructed from a flexible polymer substrate combined with a conductive sensitive material. While these commercially available flexible pressure sensors have achieved significant progress in response speed, flexible design, and miniaturization, they still face challenges in overall performance and application requirements, including insufficient sensitivity and quantitative detection capabilities, limited range coverage, and unstable recovery performance. Some products lack clear recovery time labeling, and exhibit signal drift or hysteresis during continuous loading and unloading, impacting real-time performance and long-term stability. In recent years, research has focused on developing high-performance flexible pressure sensors based on hydrogel materials. While hydrogel-based pressure sensors have achieved breakthroughs in extending their range and improving their flexibility, they suffer from long response and recovery times, insufficient material dehydration and long-term stability, and complex fabrication processes with poor batch controllability, making large-scale, consistent production difficult. Cellulose, due to its renewability, flexibility, and good processability, is widely used in flexible pressure sensor research. However, current flexible pressure sensors fabricated using cellulose struggle to achieve a balanced sensitivity and range, with limited response and recovery speed, microstructural stability, and process consistency.

[0004] Based on the above analysis, a flexible pressure sensing film with higher sensitivity, wider detection range, faster response speed, better mechanical stability and durability, as well as low cost and scalable preparation is urgently needed in the industry.

[0005] Purpose of the Invention

[0006] In response to the problems of insufficient sensitivity, limited detection range, slow response and recovery speed of existing flexible pressure sensors, the present invention provides a flexible thin film pressure sensor and its preparation method, which can significantly improve the pressure sensing sensitivity, produce obvious electrical signal changes (high ΔR / R0) under slight pressure changes, and achieve high-precision detection; expand the detection pressure range, have good response linearity in the low pressure to high pressure range, and realize wide-range continuous monitoring; shorten the response and recovery time of the sensor, improve the dynamic response speed, and meet the application requirements of real-time monitoring and high-frequency change detection.

[0007] The present invention is achieved through the following technical means:

[0008] The present invention first discloses a method for preparing a flexible pressure sensing film, comprising the following steps:

[0009] (1) Preparation of dandelion dry powder

[0010] After removing impurities and rotten leaves from commercially available dandelion raw materials, rinse thoroughly with pure water and dry in a 50°C forced air drying oven. Other drying methods, such as heating or freeze-drying, can also be used. The dried dandelion sample is pulverized and sieved through a 200-mesh sieve to obtain a dried dandelion powder. Store in a cool, dry, and well-ventilated place until ready for use.

[0011] (2) Preparation of dandelion extract

[0012] Add 10g of dried dandelion powder to a mixture of alcohol and water (ethanol to water volume ratio of 0.2 to 5:1) at a ratio of 100-1000mL. Soak the mixture at 0-35°C for at least 12 hours. After soaking, ultrasonicate the mixture (ultrasound time 20-60 minutes, ultrasonic temperature 50-80°C) to promote the release of the active ingredients.

[0013] (3) Purification of dandelion extract

[0014] The ultrasonically treated extract was vacuum filtered to remove residue using a water-based mixed cellulose membrane with a pore size of less than 1 mm. The filtrate was centrifuged at 4000 rpm for 10 minutes at room temperature, and the supernatant was collected to obtain the purified dandelion extract.

[0015] (4) Preparation of cellulose nanofiber dispersion

[0016] Cellulose nanofibers were added into pure water at a ratio of 2-10 g / 20 mL and stirred at 500 r / min for 8 h at room temperature to disperse them evenly.

[0017] (5) Mixture of cellulose nanofibers and dandelion extract

[0018] Mix 2-10 g of uniformly dispersed cellulose nanofibers with 50 mL of dandelion extract. The mixture was first sonicated in an ultrasonicator for 5 minutes (100 W ultrasonic power, alternating between 2 seconds on and 2 seconds off). The mixture was then stirred at 500 rpm for 20-120 minutes at room temperature to form a homogeneous mixture.

[0019] (6) Centrifugation and freezing of the mixed solution

[0020] The mixture was centrifuged at a speed of more than 2000 r / min for 10 min, the supernatant was discarded, and the viscous solid sample at the lower layer was collected and stored in a frozen state at -20°C.

[0021] (7) Freeze-drying of dandelion-modified cellulose nanofibers

[0022] The frozen sample was placed in a freeze dryer and freeze-dried at below 0°C for more than 12 hours to obtain a dandelion-modified cellulose nanofiber sample with a fluffy porous structure.

[0023] (8) Preparation of dandelion-modified cellulose nanofiber dispersion

[0024] Add 50 mg of freeze-dried dandelion-modified cellulose nanofibers to at least 20 ml of pure water and disperse at room temperature. Alternate stirring and sonication: 3 hours of stirring (500 rpm) followed by 5 minutes of sonication (200 W power, 2 seconds on / 2 seconds off). Repeat this process 2-3 times until the sample is evenly dispersed.

[0025] (9) Preparation of single-layer graphene dispersion

[0026] Monolayer graphene was added to pure water at a mass-to-volume ratio of less than 0.5 mg / mL and dispersed at room temperature. The dispersion process also employed alternating stirring and ultrasonication: stirring for 2 hours (at a stirring speed of 500 rpm) and ultrasonication for 5 minutes (at a power of 200 W, alternating between 2s on and 2s off), with four to five cycles repeated until a uniform and stable monolayer graphene dispersion was formed.

[0027] (10) Preparation of flexible pressure sensing membrane

[0028] 50 mg of a dandelion-modified cellulose nanofiber dispersion was mixed with 7.5-15 mg of a single-layer graphene dispersion and stirred at 500 rpm for 8 hours at room temperature to obtain a homogeneous blend solution. 96 mL of the blend solution was then filtered using a water-based mixed cellulose membrane for at least 10 hours. A flexible pressure sensing film was formed through a layer-by-layer self-assembly process.

[0029] Furthermore, the dandelion dry powder in step (2) is added to an alcohol-water mixed solution at a ratio of 10 g / 400 mL; the volume ratio of the ethanol to water is 3:2, the soaking temperature is 4° C., and the soaking time is 24 h; the ultrasonic treatment time is 40 min, and the ultrasonic temperature is 65° C.

[0030] Furthermore, the pore size of the filter membrane in step (3) is 45 μm.

[0031] Furthermore, the cellulose nanofiber dispersion in step (4) is prepared by the following method:

[0032] Cellulose nanofibers were added into pure water at a ratio of 2-10 g / 20 mL and stirred at 500 r / min for 8 h at room temperature to disperse them evenly.

[0033] Furthermore, in step (5), the amount of cellulose nanofiber used is 5 g; the ultrasonic power is 100 W, and the operation is performed alternately for 2 seconds and the rest for 2 seconds; and the stirring time is 40 minutes.

[0034] Furthermore, the centrifugation condition in step (6) is 4000 r / min for 10 min.

[0035] Furthermore, the freeze-drying condition in step (7) is freeze-drying at -45°C for 72 hours.

[0036] Furthermore, the amount of pure water used in step (8) is 50 ml; the dispersion methods include stirring, homogenization, and ultrasound.

[0037] Furthermore, in step (9), the mass volume ratio of the single-layer graphene to pure water is 11.5 mg / 46 mL; and the dispersion method includes stirring, homogenizing, and ultrasound.

[0038] Furthermore, the amount of the single-layer graphene dispersion in step (10) is 11.5 mg; the filtration time is 10 to 15 hours; and the pore size of the filter membrane is 22 μm.

[0039] The invention also discloses a flexible pressure sensing film prepared according to any one of the above preparation methods.

[0040] The present invention also discloses an application of the above-mentioned flexible pressure sensing film in the fields of health monitoring, electronic skin, smart wearables, and human-computer interaction.

[0041] The beneficial effects of the present invention are:

[0042] This invention significantly improves the overall performance of the flexible pressure sensing membrane by modifying cellulose nanofibers with dandelion extract and combining it with a single-layer graphene to construct a composite flexible film. Specific beneficial effects are as follows:

[0043] 1. The flexible pressure sensing film prepared by the present invention has high sensitivity and can produce obvious resistance changes under slight pressure changes. The ΔR / R0 can reach 250%, which realizes the accurate detection of slight pressure signals and meets the application requirements of high-precision monitoring.

[0044] 2. The sensing film has fast response and recovery capabilities, with a response and recovery time of 20ms, which is conducive to real-time monitoring of dynamic pressure changes and improves the performance stability of the device under high-frequency operation and fast loading conditions.

[0045] 3. The pressure sensing membrane exhibits a wide detection range, covering the low pressure to high pressure range of 5kPa to 600MPa, and can maintain good linear response characteristics in both low and high pressure ranges, effectively overcoming the problems of narrow detection range and easy saturation of traditional flexible pressure sensors, and expanding application scenarios.

[0046] In summary, the flexible pressure sensing membrane provided by the present invention is superior to the existing market and academic research levels in terms of sensitivity, measuring range, response speed and mechanical stability. It can be widely used in health monitoring, electronic skin, smart wearables, human-computer interaction and other fields, and has important application value and promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a flow chart for preparing the pressure sensing film of the present invention;

[0048] Figure 2 This is a sensitivity and stability cycle test diagram of Example 1;

[0049] Figure 3 This is a response / recovery time test diagram of Example 1;

[0050] Figure 4 This is the linear fitting diagram of Example 1. DETAILED DESCRIPTION

[0051] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. For those skilled in the art, the present invention can be implemented without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention.

[0052] Example 1

[0053] A method for preparing a flexible pressure sensing film comprises the following steps:

[0054] (1) Preparation of dandelion dry powder

[0055] After removing impurities and rotten leaves from commercially available dandelion raw materials, rinse thoroughly with pure water and dry in a 50°C forced air drying oven. Other drying methods, such as heating or freeze-drying, can also be used. The dried dandelion sample is pulverized and sieved through a 200-mesh sieve to obtain a dried dandelion powder. Store in a cool, dry, and well-ventilated place until ready for use.

[0056] (2) Preparation of dandelion extract

[0057] Dandelion powder was added to a 400 mL ethanol-water mixture (ethanol:water ratio of 3:2 by volume) at a ratio of 10 g / 400 mL. The mixture was then allowed to soak at 4°C for 24 hours. After soaking, the mixture was ultrasonically treated at 65°C for 40 minutes to promote the release of the active ingredient.

[0058] (3) Purification of dandelion extract

[0059] The ultrasonically treated extract was vacuum filtered to remove residue using a 45 μm pore size aqueous mixed cellulose membrane. The filtrate was centrifuged at 4000 rpm for 10 minutes at room temperature, and the supernatant was collected to obtain the purified dandelion extract.

[0060] (4) Preparation of cellulose nanofiber dispersion

[0061] Cellulose nanofibers were added into pure water at a ratio of 4 g / 20 mL and stirred at 500 r / min for 8 h at room temperature to make them dispersed evenly.

[0062] (5) Mixture of cellulose nanofibers and dandelion extract

[0063] 4 g of uniformly dispersed cellulose nanofibers were mixed with 50 mL of dandelion extract. The mixed solution was first sonicated in an ultrasonicator for 5 minutes (ultrasound power 100 W, alternating between 2 seconds on and 2 seconds off), and then stirred at 500 rpm for 40 minutes at room temperature to form a homogeneous mixture.

[0064] (6) Centrifugation and freezing of the mixed solution

[0065] The mixture was centrifuged at 4000 r / min for 10 min, the supernatant was discarded, and the viscous solid sample at the bottom layer was collected and stored in a freezer at -20°C.

[0066] (7) Freeze-drying of dandelion-modified cellulose nanofibers

[0067] The frozen sample was placed in a freeze dryer and freeze-dried at -45°C for 72 hours to obtain a dandelion-modified cellulose nanofiber sample with a fluffy porous structure.

[0068] (8) Preparation of dandelion-modified cellulose nanofiber dispersion

[0069] 50 mg of freeze-dried dandelion-modified cellulose nanofibers were added to 50 ml of pure water and dispersed at room temperature. The dispersion process used alternating stirring and sonication: stirring for 3 hours (at 500 rpm) and sonication for 5 minutes (at 200 W, alternating between 2 seconds on and 2 seconds off). This process was repeated 2-3 times until the sample was uniformly dispersed.

[0070] (9) Preparation of single-layer graphene dispersion

[0071] Monolayer graphene was added to pure water at a mass-to-volume ratio of 11.5 mg / 46 mL and dispersed at room temperature. The dispersion process also employed alternating stirring and ultrasonication: stirring for 2 hours (at a stirring speed of 500 rpm) and ultrasonication for 5 minutes (at a power of 200 W, alternating between 2 seconds on and 2 seconds off), with four to five cycles repeated until a uniform and stable monolayer graphene dispersion was formed.

[0072] (10) Preparation of flexible pressure sensing membrane

[0073] 50 mg of a dandelion-modified cellulose nanofiber dispersion was mixed with 11.5 mg of a single-layer graphene dispersion and stirred at 500 rpm for 8 hours at room temperature to obtain a uniform blend solution. 96 mL of the blend solution was then vacuum filtered for 15 hours using a 22 μm pore size aqueous mixed cellulose membrane. A flexible pressure sensing film was formed through a layer-by-layer self-assembly process.

[0074] Example 2

[0075] A method for preparing a flexible pressure sensing film comprises the following steps:

[0076] (1) Preparation of dandelion dry powder

[0077] After removing impurities and rotten leaves from commercially available dandelion raw materials, rinse thoroughly with pure water and dry in a 50°C forced air drying oven. Other drying methods, such as heating or freeze-drying, can also be used. The dried dandelion sample is pulverized and sieved through a 200-mesh sieve to obtain a dried dandelion powder. Store in a cool, dry, and well-ventilated place until ready for use.

[0078] (2) Preparation of dandelion extract

[0079] Dandelion powder was added to an alcohol-water mixture (ethanol:water volume ratio of 0.2:1) at a ratio of 10g / 100mL and allowed to soak at 15°C for 36 hours. After soaking, the mixture was ultrasonically treated (ultrasound time 20 minutes, ultrasonic temperature 80°C) to promote the release of the active ingredients.

[0080] (3) Purification of dandelion extract

[0081] The ultrasonically treated extract was vacuum filtered to remove residue using a 45 μm pore size aqueous mixed cellulose membrane. The filtrate was centrifuged at 4000 rpm for 10 minutes at room temperature, and the supernatant was collected to obtain the purified dandelion extract.

[0082] (4) Preparation of cellulose nanofiber dispersion

[0083] Cellulose nanofibers were added into pure water at a ratio of 2 g / 20 mL and stirred at 500 r / min for 8 h at room temperature to make them dispersed evenly.

[0084] (5) Mixture of cellulose nanofibers and dandelion extract

[0085] 2 g of uniformly dispersed cellulose nanofibers were mixed with 50 mL of dandelion extract. The mixed solution was first sonicated in an ultrasonic disruptor for 5 minutes (ultrasound power 100 W, alternating between 2 seconds on and 2 seconds off), and then stirred at 500 rpm for 20 minutes at room temperature to form a homogeneous mixture.

[0086] (6) Centrifugation and freezing of the mixed solution

[0087] The mixture was centrifuged at 3000 r / min for 10 min, the supernatant was discarded, and the viscous solid sample at the bottom layer was collected and stored in a freezer at -20°C.

[0088] (7) Freeze-drying of dandelion-modified cellulose nanofibers

[0089] The frozen sample was placed in a freeze dryer and freeze-dried at below -25°C for 90 hours to obtain a dandelion-modified cellulose nanofiber sample with a fluffy porous structure.

[0090] (8) Preparation of dandelion-modified cellulose nanofiber dispersion

[0091] 50 mg of freeze-dried dandelion-modified cellulose nanofibers were added to 40 ml of pure water and dispersed at room temperature. The dispersion process used alternating stirring and sonication: stirring for 3 hours (at 500 rpm) and sonication for 5 minutes (at 200 W, alternating between 2 seconds on and 2 seconds off). This process was repeated 2-3 times until the sample was evenly dispersed.

[0092] (9) Preparation of single-layer graphene dispersion

[0093] Monolayer graphene was added to pure water at a mass-to-volume ratio of 0.4 mg / mL and dispersed at room temperature. The dispersion process also employed alternating stirring and ultrasonication: stirring for 2 hours (at a stirring speed of 500 rpm) and ultrasonication for 5 minutes (at a power of 200 W, alternating between 2 seconds on and 2 seconds off), with four to five cycles repeated until a uniform and stable monolayer graphene dispersion was formed.

[0094] (10) Preparation of flexible pressure sensing membrane

[0095] 50 mg of a dandelion-modified cellulose nanofiber dispersion was mixed with 7.5 mg of a single-layer graphene dispersion and stirred at 500 rpm for 8 hours at room temperature to obtain a uniform blend solution. 96 mL of the blend solution was then vacuum filtered for 12 hours using a 22 μm pore size aqueous mixed cellulose membrane. A flexible pressure sensing film was formed through a layer-by-layer self-assembly process.

[0096] Example 3

[0097] A method for preparing a flexible pressure sensing film comprises the following steps:

[0098] (1) Preparation of dandelion dry powder

[0099] After removing impurities and rotten leaves from commercially available dandelion raw materials, rinse thoroughly with pure water and dry in a 50°C forced air drying oven. Other drying methods, such as heating or freeze-drying, can also be used. The dried dandelion sample is pulverized and sieved through a 200-mesh sieve to obtain a dried dandelion powder. Store in a cool, dry, and well-ventilated place until ready for use.

[0100] (2) Preparation of dandelion extract

[0101] Dandelion powder was added to an alcohol-water mixture (ethanol:water volume ratio of 5:1) at a ratio of 10g / 1000mL and allowed to soak at 35°C for 36 hours. After soaking, the mixture was ultrasonically treated (ultrasound time 60 minutes, ultrasonic temperature 50°C) to promote the release of the active ingredients.

[0102] (3) Purification of dandelion extract

[0103] The ultrasonically treated extract was vacuum filtered to remove residue using a 50 μm pore size aqueous mixed cellulose membrane. The filtrate was centrifuged at 4000 rpm for 10 minutes at room temperature, and the supernatant was collected to obtain the purified dandelion extract.

[0104] (4) Preparation of cellulose nanofiber dispersion

[0105] Cellulose nanofibers were added into pure water at a ratio of 8 g / 20 mL and stirred at 500 r / min for 8 h at room temperature to make them dispersed evenly.

[0106] (5) Mixture of cellulose nanofibers and dandelion extract

[0107] Mix 10 g of uniformly dispersed cellulose nanofibers with 50 mL of dandelion extract. The mixture was first sonicated in an ultrasonicator for 5 minutes (100 W ultrasonic power, alternating between 2 seconds on and 2 seconds off). The mixture was then stirred at 500 rpm at room temperature for 20 to 120 minutes (preferably 40 minutes) to form a homogeneous mixture.

[0108] (6) Centrifugation and freezing of the mixed solution

[0109] The mixture was centrifuged at 6000 r / min for 10 min, the supernatant was discarded, and the viscous solid sample at the bottom layer was collected and stored in a frozen state at -20°C.

[0110] (7) Freeze-drying of dandelion-modified cellulose nanofibers

[0111] The frozen sample was placed in a freeze dryer and freeze-dried at below -25°C for 60 hours to obtain a dandelion-modified cellulose nanofiber sample with a fluffy porous structure.

[0112] (8) Preparation of dandelion-modified cellulose nanofiber dispersion

[0113] 50 mg of freeze-dried dandelion-modified cellulose nanofibers were added to 100 ml of pure water and dispersed at room temperature. The dispersion process used alternating stirring and sonication: stirring for 3 hours (at 500 rpm) and sonication for 5 minutes (at 200 W, alternating between 2 seconds on and 2 seconds off). This process was repeated 2-3 times until the sample was evenly dispersed.

[0114] (9) Preparation of single-layer graphene dispersion

[0115] Monolayer graphene was added to pure water at a mass-to-volume ratio of 0.2 mg / mL and dispersed at room temperature. The dispersion process also employed alternating stirring and ultrasonication: stirring for 2 hours (at a stirring speed of 500 rpm) and ultrasonication for 5 minutes (at a power of 200 W, alternating between 2s on and 2s off), with four to five cycles repeated until a uniform and stable monolayer graphene dispersion was formed.

[0116] (10) Preparation of flexible pressure sensing membrane

[0117] 50 mg of a dandelion-modified cellulose nanofiber dispersion was mixed with 15 mg of a single-layer graphene dispersion and stirred at 500 rpm for 8 hours at room temperature to obtain a uniform blend solution. 96 mL of the blend solution was then vacuum filtered for 24 hours using a 22 μm pore size aqueous mixed cellulose membrane. A flexible pressure sensing film was formed through a layer-by-layer self-assembly process.

[0118] Test Example 1

[0119] The flexible pressure sensing film prepared by the present invention has high sensitivity and can produce significant resistance changes under slight pressure changes. The ΔR / R0 can reach 250%, realizing accurate detection of slight pressure signals and meeting the application requirements of high-precision monitoring. Figure 2 The X-axis represents time (0-420s), and the Y-axis represents normalized resistance change (ΔR / R0). The main graph demonstrates the sensor's stability over extended periods of operation, with resistance values ​​remaining stable and the resistance change rate (ΔR / R0) reaching 250%. The inset shows that the sensor's response to periodic pressure signals remains consistent over two specific time periods, demonstrating excellent repeatability. This demonstrates that the pressure sensing membrane exhibits excellent signal stability and cyclic response repeatability, and the high ΔR / R0 also demonstrates its high sensitivity.

[0120] Test Example 2

[0121] The sensing film has a fast response and recovery capability, with a response and recovery time of 20ms, which is conducive to the real-time monitoring of dynamic pressure changes and improves the performance stability of the device under high-frequency operation and fast loading conditions. Figure 3 After the sensor is subjected to pressure (the purple area during the pressurization phase), ΔR / R0 rapidly rises to a steady state and recovers quickly after unloading. The measured response and recovery times in the figure are both approximately 20ms. This demonstrates that the sensing membrane has rapid response and recovery capabilities, supporting real-time monitoring of dynamic pressure changes.

[0122] Test Example 3

[0123] The pressure sensing membrane exhibits a wide detection range, covering the low pressure to high pressure range of 5kPa to 600MPa, and maintains good linear response characteristics in both low and high pressure ranges, effectively overcoming the problems of narrow detection range and easy saturation of traditional flexible pressure sensors, and expanding application scenarios. Figure 4 : ΔR / R0 shows a bilinear response characteristic with the applied pressure. The low pressure range (5kPa~50kPa) and the high pressure range (50kPa~600MPa) are fitted with good linear relationships (R 2 >0.98). This shows that the sensing membrane has a wide detection range, can accurately sense changes from micro pressure (5kPa) to extremely high pressure (600MPa), and maintains good linearity within different pressure ranges, solving the problem of easy saturation and narrow linear region of traditional flexible pressure sensors.

[0124] While the embodiments of the present invention are described above, these embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to make good use of the present invention and its modifications and uses. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible pressure sensing film, comprising: (1) Preparation of dandelion modified cellulose nanofiber dispersion: The freeze-dried dandelion-modified cellulose nanofibers were added into pure water and uniformly dispersed at room temperature to obtain a dandelion-modified cellulose nanofiber dispersion for later use; (2) Preparation of single-layer graphene dispersion: Adding a single-layer graphene to pure water and dispersing it evenly at room temperature to obtain a single-layer graphene dispersion for later use; (3) Preparation of blend solution: The dandelion-modified cellulose nanofiber dispersion and the single-layer graphene dispersion were mixed and stirred at room temperature to obtain a uniform blend solution; (4) Preparation of flexible pressure sensing membrane: 96 mL of the blended solution was filtered by vacuum filtration for more than 10 hours. The filter membrane used was an aqueous mixed cellulose membrane. A flexible pressure sensing film was obtained by layer-by-layer self-assembly.

2. The preparation method according to claim 1, wherein: The freeze-dried dandelion-modified cellulose nanofibers in step (1) are prepared by the following method: ①Preparation of dandelion extract 10g of dandelion dried powder was added to 100-1000ml of a mixed solution of alcohol and water, and the mixture was soaked and allowed to stand at 0-35°C for more than 12 hours. The mixture was ultrasonically treated and the residue was removed by vacuum filtration using a water-based mixed cellulose membrane. The filtrate after filtration was centrifuged at room temperature, and the supernatant was collected to obtain the dandelion extract. ② Preparation of cellulose nanofiber dispersion 2-10 g of cellulose nanofibers were added to 20 mL of pure water and stirred at 500 rpm for 8 h at room temperature to obtain a cellulose nanofiber dispersion for later use. ③ Mixture of cellulose nanofibers and dandelion extract 2-10 g of cellulose nanofiber dispersion was mixed with 50 mL of dandelion extract. The mixed solution was first sonicated in an ultrasonic disruptor for 5 minutes, then stirred at 500 rpm for 20-120 minutes at room temperature, and then centrifuged at a speed of more than 2000 rpm for 10 minutes. The supernatant was discarded and the solid sample at the bottom was collected. ④ Preparation of freeze-dried dandelion-modified cellulose nanofibers The lower solid sample is frozen at -20°C, and the frozen sample is placed in a freeze dryer and freeze-dried at below 0°C for more than 12 hours to obtain the product.

3. The preparation method according to claim 1, wherein: Step ① The volume ratio of ethanol to water in the alcohol-water mixed solution is 0.2 to 5:1; The ultrasonic treatment time is 20 to 60 minutes, and the temperature is 50 to 80°C; The pore size of the filter membrane is less than 1 mm; The centrifugal treatment speed is 4000 r / min and the centrifugal time is 10 min.

4. The preparation method according to claim 1, wherein: The ultrasonic treatment conditions in step ③ are: ultrasonic power 100 W, working 2 seconds / stopping 2 seconds alternately.

5. The preparation method according to claim 1, wherein: In step (1), the amount of freeze-dried dandelion modified cellulose nanofibers is 50 mg, and the amount of pure water is more than 20 mL; The dispersion at room temperature is carried out by alternating stirring and ultrasonic treatment, including: Stirring speed: 500 r / min for 3 h; The ultrasonic power was 200 W, with 2 s on and 2 s off alternating, and the treatment lasted for 5 min; The dispersion is completed in 2 to 3 cycles.

6. The preparation method according to claim 1, wherein: The mass volume ratio of the monolayer graphene to pure water in step (2) is less than 0.5 mg / mL; The dispersion method includes stirring, homogenizing, and ultrasonication, and the dispersion temperature is controlled at 0° C. to 35° C.

7. The preparation method according to claim 1, wherein: The mass ratio of the dandelion modified cellulose nanofiber dispersion in step (3) is 50:7.5-15 mg; The stirring condition is: stirring at 500 r / min for 8 h at room temperature to obtain a uniform blend solution.

8. The preparation method according to claim 1, wherein: The filtration time in step (4) is 15 hours; The pore size of the filter membrane used was 22 μm.

9. A flexible pressure sensing membrane prepared according to the preparation method according to any one of claims 1 to 8.

10. Application of the flexible pressure sensing film according to claim 9 in the fields of health monitoring, electronic skin, smart wearables, and human-computer interaction.

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