A flexible sensing composite fiber membrane with multi-level microstructure and its preparation method and application

Abstract

The present invention discloses a flexible sensing composite fiber membrane with a multi-level microstructure and a preparation method and application thereof. The composite fiber membrane is prepared by dissolving silver trifluoroacetate in an organic solvent and then dissolving thermoplastic polyurethane (TPU) particles therein to obtain an electrospinning solution; a composite fiber membrane containing silver trifluoroacetate is obtained on an aluminum foil on a drum receiver by electrospinning technology. The composite fiber membrane is then reduced in a reducing solution, and a silver nanoparticle / TPU composite fiber membrane with a multi-level microstructure is obtained after drying. The multi-level microstructure prepared by the present invention using electrospinning technology can directly form ridge-like protrusions on the surface of the fiber membrane, and the heights thereof are unequal and the density distribution is uneven. At the same time, the fiber membrane has a hole structure inside, and a continuous and stable conductive network is obtained after reduction, which is suitable for the field of flexible pressure sensors. The multi-level microstructure effectively improves the sensitivity, response time, detection range, etc. of the pressure sensor, and can be used in the fields of wearable devices for human body, human-computer interaction, and health monitoring.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and in particular relates to a flexible sensing composite fiber membrane with a multi-level microstructure, and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of science and technology, the application of flexible pressure sensors in the fields of artificial intelligence, electronic skin, health monitoring, etc. has gradually increased. In order to promote close communication between people and various electronic devices, various flexible wearable sensors have been continuously developed. Flexible pressure sensors convert external forces into electrical signals or other more easily identifiable response output signals. According to different sensing mechanisms, they can be divided into piezoresistive sensors, capacitive sensors, and piezoelectric sensors. Among them, resistive sensors have attracted much attention due to their advantages such as high sensitivity, short response time, and low hysteresis.

[0003] In the process of constructing flexible pressure sensors, in order to improve the sensitivity and linear range of the sensors, researchers usually perform microstructuring on their sensing layers, such as pyramid-shaped, micro-dome, interlocking, micro-sphere and other structures. Compared with traditional planar structures, microstructures deform when stimulated by external forces, increasing the contact area with the electrodes, causing the contact resistance to change rapidly and improving the sensitivity; and in the process of continuous increase in external forces, the conductive network inside and outside the microstructure substrate caused by deformation undergoes graded changes, thereby expanding its detection range. When the external force increases to a certain extent, the conductive path also tends to saturation, the resistance will not change much, and the sensitivity will also decrease. That is, the sensor is required to show significant changes in the conductive network under extremely small deformations, transmit obvious electrical signals, and maintain the connectivity of the conductive network under large deformations.

[0004] Therefore, obtaining sensors with a wide detection range and high sensitivity at the same time is still a hot topic in current research and is also the main technical need faced in practical applications. For example, the invention patent with publication number CN 114777968 A designs a multi-layer flexible pressure sensor with lotus leaf microstructure, using the lotus leaf papilla microstructure as a bionic template, transferring its bionic microstructure to the flexible substrate layer, and using the electrode layer-substrate layer multilayer superposition method to design and prepare a flexible, sensitive, wide linear range piezoresistive pressure sensor, which has a detection range of 0-500kPa and a maximum sensitivity of 2.525kPa. -1 , the response recovery time is 0.05s and 0.1s respectively, and it can monitor pulse, sound, and human gait. Combined with other related research reports, it can be seen that the sensitivity and detection range of sensors can be improved by replicating microstructures or making bionic microstructures. However, when it comes to practical applications, the complexity, ease of use, and cost of the sensor microstructure design and preparation process are all key considerations.

[0005] In summary, designing a flexible pressure sensor with high sensitivity and wide detection range in a simple and efficient way is of great significance for promoting the commercialization of flexible pressure sensor applications. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of low sensitivity, long response time, narrow detection range, inability to mass produce and complex preparation process in the flexible pressure sensors in the existing preparation technology, and to provide a flexible sensing composite fiber membrane with a multi-level microstructure directly prepared by electrospinning technology and a preparation method thereof, so that the film can be applied to sound recognition, limb movement, pulse monitoring and other aspects.

[0007] The technical solution for achieving the purpose of the present invention is:

[0008] A method for preparing a flexible sensing composite fiber membrane with a multi-level microstructure comprises the following steps:

[0009] 1) Preparation of electrospinning solution: adding silver trifluoroacetate (C2AgF3O2) to a mixed solvent of tetrahydrofuran and N, N-dimethylformamide and mixing evenly, then adding thermoplastic polyurethane (TPU) and continuing to mix evenly to obtain an electrospinning solution;

[0010] 2) preparing C2AgF3O2-TPU composite fiber membrane: using the electrospinning solution prepared in step 1) to prepare C2AgF3O2-TPU composite fiber membrane by using electrospinning technology;

[0011] 3) Preparation of silver nanoparticles (AgNPs) / TPU flexible sensing composite fiber membrane: The composite fiber membrane prepared in step 2) is placed in a reducing solution for reduction reaction, and after drying, a multi-level microstructured AgNPs / TPU flexible sensing composite fiber membrane is obtained.

[0012] In step 1), the mass ratio of tetrahydrofuran to N,N-dimethylformamide is 1-2:1.

[0013] In step 1), the mass ratio of silver trifluoroacetate to thermoplastic polyurethane is 1:2-8.

[0014] In step 1), the model of the thermoplastic polyurethane is: 60~80A.

[0015] The concentration of the electrospinning solution is 10-18% by mass.

[0016] In step 2), the electrospinning parameters are: distance between syringe needle and roller collection device: 9-15 cm; voltage: 15-30 kV; spinning solution feed rate: 1-2 ml / h; feed time: 5-8 h; roller speed 250-350 rpm.

[0017] In step 3), the reducing solution is one of ascorbic acid solution, sodium borohydride solution and hydrazine hydrate solution.

[0018] The ascorbic acid solution is prepared by dissolving ascorbic acid powder in a mixed solvent with ethanol and water in a mass ratio of 1-2:1, and the concentration of the ascorbic acid solution is 5-10 mg / ml. The ascorbic acid solution is used for reduction reaction, and the reaction conditions are: water bath temperature is 60-90°C, and reduction time is 2-6 hours.

[0019] The flexible sensing composite fiber membrane with a multi-level microstructure and its preparation method and application provided by the present invention have the following advantages over the prior art:

[0020] (1) In the preparation of the composite fiber membrane, silver trifluoroacetate is directly introduced into the TPU electrospinning solution, and under specific electrospinning conditions, the electrospinning technology is used to form a multi-level microstructure in situ (one-step method) during the spinning process, so that the composite fiber membrane can be reduced to obtain a continuous and stable conductive network.

[0021] (2) The microstructure in the flexible sensing composite fiber membrane prepared by the present invention is multi-level and multi-layered. The surface of the composite fiber membrane has ridge-like protrusions and the interior has holes of inconsistent sizes. It can be used to construct a porous microstructure with surface ridge-like protrusions and a fiber network inside the active layer of a pressure sensor, which can improve the sensitivity and detection range of the flexible pressure sensor.

[0022] (3) Compared with other special microstructure processing methods in the prior art, the preparation method of the present invention has a simple and efficient preparation process, can realize batch low-cost industrial production, and can be promoted on a large scale commercially.

[0023] (4) When the present invention performs reduction reaction on the composite fiber membrane, the ascorbic acid solution used is prepared by dissolving ascorbic acid powder in a mixed solvent of ethanol and water, and the solvent ratio is 1~2:1. Since the TPU electrospun membrane is hydrophobic, when the solvent is only water, the reduction effect is not good. When the solvent is only ethanol, the water bath reduction solvent is easy to volatilize. Therefore, a mixed solvent of ethanol and water is used to achieve the most ideal reduction effect.

[0024] The flexible sensing composite fiber membrane obtained by the present invention can be used as an active material in flexible wearable electronic devices. After being assembled into a flexible pressure sensor, it can be used in the fields of artificial intelligence, electronic skin, health monitoring, human wearables, etc.

[0025] Technical principle of the present invention: electrospinning technology is to make TPU spray thin streams to the collecting device to form nanofiber felt under the action of high-voltage electric field to overcome surface tension. Silver trifluoroacetate is a silver salt. When the content of silver trifluoroacetate added increases and the mass ratio with TPU reaches 2~4:8, under the specific electrospinning parameters given in the claims, the addition of high-content silver trifluoroacetate increases the viscosity of the electrospinning solution and the charge density. Silver ions are prone to migration and aggregation during electrospinning due to their high surface energy, which affects the formation of a stable Taylor cone in the electrospinning solution, and then causes the electrospinning solution to have an unstable jet. With the volatilization of the solvent, a composite fiber membrane with a multi-level microstructure is formed on the collecting device at one time. The ridge-like protrusions on its surface can increase the contact resistance between the interdigital electrodes, and it is easy to deform under a small force to cause resistance changes, thereby obtaining high sensitivity; its internal fiber structure and hole structure help to improve the sensitivity of the sensor under high pressure. Therefore, the flexible sensing composite fiber membrane-based pressure sensor prepared by this process has both high sensitivity and a wide detection range. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a surface SEM image of the AgNPs / TPU flexible sensing composite fiber membrane with a multi-level microstructure in the present invention;

[0027] Figure 2 This is a cross-sectional SEM image of the AgNPs / TPU flexible sensing composite fiber membrane with a multi-level microstructure in the present invention;

[0028] Figure 3 Schematic diagram of the structure and sensing mechanism of the AgNPs / TPU flexible sensing composite fiber membrane-based pressure sensor with multi-level microstructure in the present invention;

[0029] Figure 4 is a sensitivity diagram of the AgNPs / TPU composite fiber membrane-based flexible pressure sensor prepared in Example 2;

[0030] Figure 5 Response time diagram of the AgNPs / TPU composite fiber membrane-based flexible pressure sensor prepared in Example 2;

[0031] Figure 6 The AgNPs / TPU composite fiber membrane-based flexible pressure sensor prepared in Example 2 is used for pulse detection. Implementation

[0032] The present invention is further described below with reference to the accompanying drawings and embodiments, but the present invention is not limited thereto. Example

[0033] A method for preparing a flexible sensing composite fiber membrane with a multi-level microstructure comprises the following steps:

[0034] (1) Preparation of electrospinning solution: 0.5 g of silver trifluoroacetate was added to a mixed solvent of 10 ml of tetrahydrofuran and 10 ml of N,N-dimethylformamide. After magnetic stirring for 2 h, 4 g of thermoplastic polyurethane particles (60A) were added and magnetic stirring was continued for 12 h. During the stirring process, the mouth of the beaker was sealed with plastic wrap to prevent the solvent from evaporating until the electrospinning solution was completely dissolved.

[0035] (2) Electrospinning film forming process: inject the above electrospinning solution into the syringe, install it on the nozzle holder of the electrospinning instrument, and clamp the high-voltage power supply clip in the middle of the needle. Turn on the switch of the electrospinning instrument, and set the parameters of the electrospinning process as follows: the distance between the syringe needle and the roller collection device is 15 cm, the voltage is 15 kV, the spinning solution feed rate is 2 ml / h, the feed time is 6 h, and the roller speed is 300 rpm; finally, the C2AgF3O2-TPU composite fiber film is obtained, and the fiber film is naturally air-dried for 12 h.

[0036] (3) Preparation of AgNPs / TPU composite fiber membrane: The C2AgF3O2-TPU composite fiber membrane obtained in step (2) was cut into 2*2 cm size, then placed in a 5 mg / ml ascorbic acid solution, and reduced in a water bath at 90°C for 6 h to obtain an AgNPs / TPU composite fiber membrane. After the residue on the surface was washed off with deionized water, the membrane was placed in an oven at 60°C for 6 h. The ascorbic acid solution is prepared by dissolving ascorbic acid powder in a mixed solvent of ethanol and water in a mass ratio of 1:1.

[0037] (4) Preparation of a composite fiber membrane-based flexible pressure sensor: The AgNPs / TPU composite fiber was cut into 0.5×0.5 mm 2 The size of the flexible sensing composite film is covered on the interdigital electrode with a multi-level microstructure on the surface, and then fixed with PU tape. The specific structure from top to bottom is: PU tape, composite fiber membrane, interdigital electrode, and the two sides of the electrode are connected to the measurement unit through welding wires. By testing the change value of the electrical signal under different pressures, a series of sensing properties such as sensitivity, response time, detection range, and detection limit of the flexible sensing composite film are evaluated. At the same time, the flexible pressure sensor is used to monitor a series of signals such as pulse, finger bending, and blowing, to prove that it has a wide range of applications.

[0038] (5) The flexible pressure sensor prepared by the above method has been tested for performance. Its sensitivity is 1.3 kPa in the range of 0-40 kPa. -1 ; 40-60kPa, sensitivity is 3.46 kPa -1; 60-82 kPa, sensitivity 0.38 kPa -1 ; The response time is 200ms. Example

[0039] (1) Preparation of electrospinning solution: Add 2 g of silver trifluoroacetate to a mixed solvent of 10 ml of tetrahydrofuran and 10 ml of N,N-dimethylformamide. After magnetic stirring for 2 h, add 4 g of thermoplastic polyurethane particles (70A) and continue magnetic stirring for 12 h. During the stirring process, seal the mouth of the beaker with plastic wrap to prevent the solvent from evaporating until the solution is completely dissolved to obtain the electrospinning solution.

[0040] (2) Electrospinning film forming process: Inject the above electrospinning solution into a syringe and install it on the nozzle holder of the electrospinning instrument, and clamp the high-voltage power supply clip in the middle of the needle. Turn on the switch of the electrospinning instrument, and set the parameters of the electrospinning process as follows: the distance between the syringe needle and the roller collection device is 10 cm, the voltage is 27 kV, the spinning solution feed rate is 2 ml / h, the feed time is 6 h, and the roller speed is 300 rpm. Finally, the C2AgF3O2-TPU composite film is obtained and air-dried for 12 h.

[0041] (3) Preparation of AgNPs / TPU composite fiber membrane: The obtained C2AgF3O2-TPU composite fiber membrane was cut into 2*2cm size, then placed in 10mg / ml ascorbic acid solution, and reduced in a water bath at 90℃ for 6h to obtain AgNPs / TPU composite fiber. After the surface residue was washed off with deionized water, it was placed in a 60℃ oven and dried for 6h. The ascorbic acid solution is prepared by dissolving ascorbic acid powder in a mixed solvent of ethanol and water in a mass ratio of 1:1.

[0042] (4) Preparation of a composite fiber membrane-based flexible pressure sensor: The AgNPs / TPU composite fiber was cut into 0.5×0.5 mm 2 The size of the flexible sensing composite film is covered on the interdigital electrode with a multi-level microstructure on the surface, and then fixed with PU tape. The specific structure from top to bottom is: PU tape, composite fiber membrane, interdigital electrode, and the two sides of the electrode are connected to the measurement unit through welding wires. By testing the change value of the electrical signal under different pressures, a series of sensing properties such as sensitivity, response time, detection range, and detection limit of the flexible sensing composite film are evaluated. At the same time, the flexible pressure sensor is used to monitor a series of signals such as pulse, finger bending, and blowing, to prove that it has a wide range of applications.

[0043] (5) The flexible pressure sensor prepared by the above method has been tested for performance. Its sensitivity is 8.3 kPa in the range of 0-40 kPa. -1 ; 40-60kPa, sensitivity is 8.87 kPa-1 ; 60-82kPa, sensitivity is 2.24 kPa -1 ; The response time is 78ms; and the pulse can be detected. Example

[0044] (1) Preparation of electrospinning solution: Add 2 g of silver trifluoroacetate to a mixed solvent of 10 ml of tetrahydrofuran and 10 ml of N,N-dimethylformamide. After magnetic stirring for 2 h, add 4 g of thermoplastic polyurethane particles (80A) and continue magnetic stirring for 12 h. During the stirring process, seal the mouth of the beaker with plastic wrap to prevent the solvent from evaporating until the solution is completely dissolved to obtain the electrospinning solution.

[0045] (2) Electrospinning film forming process: Inject the above electrospinning solution into a syringe and install it on the nozzle holder of the electrospinning instrument, and clamp the high-voltage power supply clip in the middle of the needle. Turn on the switch of the electrospinning instrument, and set the parameters of the electrospinning process as follows: the distance between the syringe needle and the roller collection device is 10 cm, the voltage is 27 kV, the spinning solution feed rate is 2 ml / h, the feed time is 6 h, and the roller speed is 300 rpm. Finally, the C2AgF3O2-TPU composite film is obtained and air-dried for 12 h.

[0046] (3) Preparation of AgNPs / TPU composite fiber membrane: The obtained C2AgF3O2-TPU composite fiber membrane was cut into 2*2 cm size, and then placed in a 10 mg / ml sodium borohydride solution, whose solvent was ethanol and water in a ratio of 1:1, and reduced under magnetic stirring for 1 h to obtain AgNPs / TPU composite fibers. After rinsing the surface residue with deionized water, the membrane was placed in a 60°C oven and dried for 6 h.

[0047] (4) Preparation of a composite fiber membrane-based flexible pressure sensor: The AgNPs / TPU composite fiber was cut into 0.5×0.5 mm 2 The size of the flexible sensing composite film is covered with the side with ridge-like protrusions on the surface, and then fixed with PU tape. The specific structure from top to bottom is: PU tape, composite fiber membrane, and forked electrode. The two sides of the electrode are connected to the measurement unit through welding wires. By testing the change value of the electrical signal under different pressures, the sensitivity, response time, detection range, detection limit and other sensing properties of the flexible sensing composite film are evaluated. At the same time, the flexible pressure sensor is used to monitor a series of signals such as pulse, finger bending, and blowing to prove that it has a wide range of applications.

[0048] (5) The flexible pressure sensor prepared by the above method has been tested for performance. Its sensitivity is 3.3 kPa in the range of 0-40 kPa. -1 ; 40-60kPa, sensitivity is 6.58 kPa-1 ; 60-82kPa, sensitivity is 1.24kPa -1 ; The response time is 123ms; and the pulse can be detected.

Claims

1. A method for preparing a flexible sensing composite fiber membrane with a multi-level microstructure, characterized in that: The steps include: 1) Preparing an electrospinning solution: adding silver trifluoroacetate to a mixed solvent of tetrahydrofuran and N,N-dimethylformamide and mixing evenly, then adding thermoplastic polyurethane and continuing to mix evenly to prepare an electrospinning solution; 2) preparing C2AgF3O2-TPU composite fiber membrane: using the electrospinning solution prepared in step 1) to prepare C2AgF3O2-TPU composite fiber membrane by using electrospinning technology; 3) Preparing silver nanoparticles / TPU flexible sensing composite fiber membrane: placing the composite fiber membrane prepared in step 2) in a reducing solution for reduction reaction, and obtaining a multi-level microstructured AgNPs / TPU flexible sensing composite fiber membrane after drying; In step 1), the mass ratio of silver trifluoroacetate to thermoplastic polyurethane is 1:2-8; In step 3), the reducing solution is one of ascorbic acid solution, sodium borohydride solution, and hydrazine hydrate solution; The concentration of the electrospinning solution is 10-18% by mass; In step 2), the electrospinning parameters are: distance between syringe needle and roller collection device: 9-15 cm; voltage: 15-30 kV; spinning solution feed rate: 1-2 mL / h; feed time: 5-8 h; roller speed 250-350 rpm.

2. The method for preparing a flexible sensing composite fiber membrane with a multi-level microstructure according to claim 1, characterized in that: In step 1), the model of the thermoplastic polyurethane is: 60~80A.

3. The method for preparing a flexible sensing composite fiber membrane with a multi-level microstructure according to claim 1, characterized in that: The ascorbic acid solution is prepared by dissolving ascorbic acid powder in a mixed solvent with ethanol and water in a mass ratio of 1-2:1, and the concentration of the ascorbic acid solution is 5-10 mg / mL. The ascorbic acid solution is used for reduction reaction, and the reaction conditions are: water bath temperature is 60-90°C, and reduction time is 2-6 hours.

4. A flexible sensing composite fiber membrane with a multi-level microstructure, characterized in that: Prepared by the method described in any one of claims 1 to 3.

5. Application of the flexible sensing composite fiber membrane with a multi-level microstructure as claimed in claim 4 in the field of flexible electronic sensing or wearable electronic devices.

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