A double conductive network porous fiber membrane and its preparation method and application

Abstract

The present invention discloses a dual-conductive network porous fiber membrane, which belongs to the technical field of pressure sensor materials. The components of the dual-conductive network porous fiber membrane include: thermoplastic polyurethane and conductive material; wherein the dual-conductive network porous fiber membrane includes: a thermoplastic polyurethane / conductive material mixed fiber membrane prepared by electrospinning technology as a first conductive network structure; and a second conductive network structure formed by adsorbing the conductive material on the first conductive network structure by vacuum filtration. The present invention also discloses a preparation method and application of the dual-conductive network porous fiber membrane. The dual-conductive network porous fiber membrane of the present invention has a simple preparation process, which can greatly improve the conductive performance of the flexible pressure sensor while also having high sensitivity and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure sensor materials, and in particular to a double-conductive network porous fiber membrane and a preparation method and application thereof. Background Art

[0002] Thermoplastic polyurethane (TPU) strain gauge flexible sensors offer remarkable advantages, such as light weight, a wide strain range, and simple fabrication. They have a wide range of applications and meet the diverse requirements of today's intelligent flexible devices, demonstrating promising application prospects. Existing sensors primarily use conductive fillers such as carbon nanotubes (CNTs), silver nanoparticles (AgNPs), and gold nanoparticles (AuNPs). These nanomaterials are combined with substrate materials through various methods to create conductive network materials.

[0003] Existing techniques have constructed a hierarchical porous structure with a one-dimensional (1D) conductive network through phase inversion of a carbon nanotube / polyurethane (CNT / PU) solution. Silver nanoparticles are then added to the fibers. As the silver nanoparticles (AgNPs) deposit on the microporous surface, a conductive dual path consisting of 0D AgNPs and 1D CNTs is formed, significantly enhancing the conductive properties. However, this method requires multiple steps during the preparation process, resulting in complex operations and high costs. Furthermore, the stability and durability of the conductive network in practical applications still need to be improved. Alternatively, existing techniques have developed a porous stretchable conductive layer by depositing a gold film on the surface of the porous stretchable conductive layer via ion beam sputtering to form a dual conductive sheath fiber (DCSF). This DCSF strain sensor exhibits a fast response time (184 ms) and ultrahigh sensitivity within the 0–100% strain range (with a gauge factor of 184.50 at strains of 0–10%, 10%–30%, and 30%–100%). However, the complex and costly gold film deposition process makes large-scale production difficult. Based on the advantages of high specific surface area and porosity of fiber membranes prepared by current electrospinning technology, existing technologies have prepared high-performance composite nanofiber membranes with a two-dimensional network topology, showing a wide response range and high sensitivity. Although this method has achieved significant progress in conductivity and sensitivity, the nanofiber membranes face the problem of insufficient mechanical strength and durability in practical applications.

[0004] Therefore, it is necessary to provide a conductive network porous fiber membrane with a simple preparation process that enables the flexible pressure sensor to have both high sensitivity and high conductivity to solve the above problems. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a dual-conductive network porous fiber membrane, which enables a flexible pressure sensor to have both high sensitivity and high conductivity.

[0006] The present invention also provides a method for preparing the double conductive network porous fiber membrane.

[0007] The present invention also provides a flexible pressure sensor.

[0008] The first aspect of the present invention provides a double conductive network porous fiber membrane, the components of the double conductive network porous fiber membrane include:

[0009] thermoplastic polyurethane and conductive materials;

[0010] Among them, the dual conductive network porous fiber membrane includes: a thermoplastic polyurethane / conductive material mixed fiber membrane prepared by electrospinning technology as a first conductive network structure; and a second conductive network structure formed by adsorbing conductive material on the first conductive network structure through vacuum filtration.

[0011] The double conductive network porous fiber membrane according to the first embodiment of the present invention has at least the following beneficial effects:

[0012] The dual-conductive network porous fiber membrane of the present invention comprises a thermoplastic polyurethane / conductive material mixed fiber membrane prepared by electrospinning technology as a first conductive network structure; and a second conductive network structure formed by adsorbing a conductive material on the first conductive network structure by vacuum filtration. Conductive fillers are added to the electrospinning solution to construct a layer of conductive network within the fiber membrane, effectively increasing the conductive path within the fiber membrane. Then, a layer of conductive network is constructed on the fiber membrane to prepare a dual-conductive network porous fiber membrane. The construction of the two layers of conductive networks is combined to greatly increase the conductive path of the fiber membrane, increase the effective contact area of ​​the two layers of conductive networks, and improve the conductivity of the pressure sensor. The construction of the two layers of conductive networks enables the sensor to respond faster to tiny strains and more sensitively regulate the performance of the sensor, so that the sensor exhibits high sensitivity and good stability.

[0013] Since the double conductive network structure of the present invention can withstand large deformation without damaging its structure, it has good stretchability and can be flexibly applied to multiple fields, thereby enhancing the reliability and durability of the sensor.

[0014] According to some embodiments of the present invention, the conductive material includes a carbon nanotube material.

[0015] According to some embodiments of the present invention, the conductive material is selected from carbon nanotube powder and carbon nanotube dispersion.

[0016] According to some embodiments of the present invention, the powder has a particle size of 30 μm-150 μm.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned dual conductive network porous fiber membrane, the preparation method comprising the following steps:

[0018] S1, mixing the thermoplastic polyurethane, the conductive material and the solvent to prepare a spinning solution;

[0019] S2, subjecting the spinning solution to electrospinning technology to obtain a mixed fiber membrane;

[0020] S3. Vacuum-filtering the dispersion of the conductive material and adsorbing it on the mixed fiber membrane to obtain the double conductive network porous fiber membrane.

[0021] The preparation method according to the second aspect of the present invention has at least the following beneficial effects:

[0022] The present invention adopts electrospinning and vacuum filtration to prepare a porous fiber membrane material with a double conductive network structure, which provides a good foundation and new research direction for new double conductive porous fiber membrane material sensors.

[0023] The porous fiber membrane with a dual conductive network structure of the present invention is simple to prepare, easy to operate, low-cost, and has excellent performance. The entire preparation process is relatively efficient and highly controllable. By adjusting the spinning solution formulation and spinning parameters, the fiber membrane thickness, pore size and distribution, and conductive properties can be precisely controlled. This precise process control not only improves product quality and consistency, but also helps reduce production costs and resource consumption.

[0024] According to some embodiments of the present invention, in step S1, the solvent includes N,N-dimethylacetamide (DMAC).

[0025] According to some embodiments of the present invention, in step S1, the material-liquid ratio of the conductive material to the solvent is (1-8): 700 g / mL.

[0026] According to some embodiments of the present invention, in step S1, the mass ratio of the thermoplastic polyurethane to the conductive material is (8.76-8.97): (0.03-0.24).

[0027] Preferably, in step S1, the mass ratio of the thermoplastic polyurethane to the conductive material is (8.85-8.91): (0.09-0.15).

[0028] According to some embodiments of the present invention, in step S1, the mass percentage of the conductive material in the spinning solution is 0.1% to 0.8%.

[0029] Preferably, in step S1, the mass percentage of the conductive material in the spinning solution is 0.3% to 0.5%.

[0030] According to some embodiments of the present invention, the mass percentage of the thermoplastic polyurethane and the conductive material in the spinning solution is 28-32%.

[0031] Preferably, the mass percentage of the thermoplastic polyurethane and the conductive material in the spinning solution is 30%.

[0032] According to some embodiments of the present invention, in step S2, the electrospinning voltage is 15-17 kV.

[0033] According to some embodiments of the present invention, in step S2, the round trip distance of the electrospinning is 100-110 mm.

[0034] According to some embodiments of the present invention, in step S2, the electrospinning winding speed is 110-120 mm / s.

[0035] According to some embodiments of the present invention, in step S2, the collection speed of the electrospinning is 110-120 mm / s.

[0036] According to some embodiments of the present invention, in step S2, the receiving distance of the electrospinning is 13-15 cm.

[0037] According to some embodiments of the present invention, in step S2, the electrospinning extrusion rate is 1-2 mL / h.

[0038] According to some embodiments of the present invention, in step S2, the humidity of the electrospinning environment is 45%-60%.

[0039] According to some embodiments of the present invention, in step S3, the concentration of the conductive material dispersion is 0.01% to 0.05%.

[0040] Preferably, in step S3, the concentration of the conductive material dispersion is 0.01%.

[0041] According to some embodiments of the present invention, in step S3, the thickness of the conductive material dispersion adsorbed on the mixed fiber membrane is 0.01-0.02 μm.

[0042] A third aspect of the present invention provides a flexible pressure sensor comprising the above-mentioned double conductive network porous fiber membrane.

[0043] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0045] Figure 1 This is a flow chart of the preparation process in Example 1 of the present invention;

[0046] Figure 2 is an ultra-depth-of-field morphology image of the dual-conductive network porous fiber membrane prepared in Examples 1 to 4 of the present invention;

[0047] Figure 3 1 is a graph showing the resistance change rate of the dual conductive network porous fiber membranes prepared in Examples 1 to 4 of the present invention;

[0048] Figure 4 Graph showing the stability of the dual conductive network porous fiber membranes prepared in Examples 1 to 4 of the present invention;

[0049] Figure 5 Graph showing the conductive properties of the dual conductive network porous fiber membranes prepared in Examples 1 to 4 of the present invention;

[0050] Figure 6 1 is a graph showing the sensitivity test results of the dual conductive network porous fiber membranes prepared in Examples 1 to 4 of the present invention. DETAILED DESCRIPTION

[0051] The embodiments of the present invention are described in detail below. The same or similar reference numerals throughout the embodiments represent the same or similar elements or elements with the same or similar functions. The embodiments described below are exemplary and are only used to explain the present invention and are not to be construed as limiting the present invention.

[0052] In the description of the present invention, if there is a description of first, second, etc., it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0053] The terms "preferably," "more preferably," and the like, used herein refer to embodiments of the present invention that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the present invention.

[0054] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0055] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of the present invention.

[0056] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0057] Example 1

[0058] This embodiment provides a dual conductive network porous fiber membrane, the preparation method of which includes the following steps:

[0059] (1) Preparation of TPU / CNT mixed spinning solution: First, add 21g of pure DMAC to a beaker and keep it in a slightly heated stirring state and stir thoroughly (to facilitate the dissolution of CNT). Then weigh 0.15g of CNT powder and gradually add it to the DMAC solution. After each addition, wait until the powder is evenly dispersed in the solution before adding more. The material-liquid ratio of CNT powder to solvent is 5:700g / mL, so that the CNT is fully dissolved). Finally, add 8.85g of weighed TPU particles. Place the prepared mixed solution with a CNT mass fraction of 0.5% in a magnetic stirrer and stir for 12h to ensure that the TPU is completely dissolved in the DMAC to form a uniform black TPU / CNT polymer mixed spinning solution.

[0060] (2) Electrospinning: Electrospinning was performed using an electrospinning machine. The prepared TPU / CNT mixed spinning solution was added to a 10 ml plastic syringe with a spinneret. To prevent the jet from shifting up and down during spinning, conductive copper foil tape was used to create a horn shape to control the spinneret range, ensuring good uniformity of the spun fiber membrane. After spinning for 5 hours, a TPU / CNT electrospun membrane was obtained. Spinning voltage: 15-17 kV, extrusion volume of 1 mL / h, round-trip distance of 100 mm, winding speed of 120 mm / s, collection speed of 120 mm / s, receiving distance of 15 cm, and spinning at 45%-60% humidity.

[0061] (3) Preparation of conductive filler: Prepare 200 ml of 0.01% carbon nanotube dispersion (carbon nanotube diameter <10 μm) using a 5% mass fraction carbon nanotube dispersion (Suzhou Tanfeng Graphene Technology Co., Ltd.). Fill a 1 L beaker with deionized water, use a syringe to extract the dispersion and inject it into the deionized water to prepare 200 ml of carbon nanotube dispersion diluted to 0.01%. Use ultrasonic equipment to sonicate at 12 degrees Celsius for 15 minutes, with an ultrasonic power of 240 W, to ensure uniform dispersion of the carbon nanotube dispersion.

[0062] (4) 200 ml of 0.01% carbon nanotube aqueous dispersion was evenly filtered and adsorbed on a 5 cm x 5 cm TPU / CNT hybrid fiber membrane by a vacuum filter to form a CNT / TPU / CNT dual conductive network structure porous fiber membrane. The specific preparation process is as follows: Figure 1 shown.

[0063] This embodiment also provides a flexible pressure sensor, including the above-mentioned CNT / TPU / CNT dual conductive network structure porous fiber membrane as a sensing element. The specific preparation method is as follows: a small amount of conductive silver paste is applied to the left and right sides of the porous fiber membrane of the CNT / TPU / CNT dual conductive network structure, and then the copper wire and the conductive copper foil tape are bonded together and fixed on the side of the fiber membrane. Finally, the electrodes are welded and encapsulated with polydimethylsiloxane as the packaging material to form a pressure sensor.

[0064] Example 2

[0065] This embodiment provides a dual conductive network porous fiber membrane, which differs from Example 1 in that the mass fraction of CNTs in the mixed spinning solution is 0.1%.

[0066] Example 3

[0067] This embodiment provides a dual conductive network porous fiber membrane, which differs from Example 1 in that the mass fraction of CNTs in the mixed spinning solution is 0.3%.

[0068] Example 4

[0069] This embodiment provides a dual conductive network porous fiber membrane, which differs from Example 1 in that the mass fraction of CNTs in the mixed spinning solution is 0.8%.

[0070] Comparative Example 1

[0071] This comparative example provides a 30 wt% pure TPU electrospinning membrane prepared according to the same steps as Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a TPU / CNT hybrid fiber membrane. Unlike Example 1, this one does not vacuum-filter the conductive material for adsorption, i.e., it does not incorporate a secondary conductive network structure. Because the CNT concentration in the mixed solution is relatively low, the conductivity and sensitivity of the hybrid fiber membrane cannot be measured.

[0074] Test Example 1

[0075] The double conductive network structure porous fiber membrane samples of Examples 1 to 4 were fixed on the microscope sample stage, and the morphology was observed using a super depth of field microscope with a magnification of 2000 times. The morphology was photographed using a super depth of field three-dimensional microscope. Figure 2 shown.

[0076] Figure 2 (a) is the 30wt% pure TPU in Comparative Example 1, with uniform fibers and no obvious conductive material; Figure 2 Middle (b) is 0.1wt% CNT in Example 2, where CNTs begin to appear on the outside of the fiber, but are sparsely distributed; Figure 2 Middle (c) is 0.3wt% CNT in Example 3, where CNT distribution is more obvious on the fiber surface; Figure 2 Middle (d) is 0.5wt% CNT in Example 1, and CNT begins to agglomerate on the fiber surface; Figure 2 In Example (e), at 0.8 wt% CNT, significant CNT agglomeration was observed in Example 4, affecting fiber performance. Therefore, CNTs were present on the exterior of the fibers in this embodiment, and as the CNT concentration increased, CNT agglomeration also occurred on the exterior of the fibers. However, excessively high CNT concentrations can cause CNT agglomeration, impacting fiber performance.

[0077] Test Example 2

[0078] Flexible tensile test method: Cut the CNT / TPU / CNT porous fiber membrane with a dual conductive network structure obtained in Examples 1 to 4 and Comparative Example 1 into a size of 3cm×1cm, paste copper foil on both sides, and make the distance between the two copper foils in the middle be 20mm. Turn on the flexible electronic tester switch, adjust the stretching rate, number of times and other parameters, and set the stretching parameters as follows: stretching speed 1mm / s, stretching elongation 5%, 10% and 25% are stretching 1mm, 2mm and 5mm respectively, and the number of stretching is 20 times. At the same time, connect copper wires on both sides of the flexible tester, clamp the copper sheet at the end, clamp the cut CNT / TPU / CNT dual conductive structure sensor on the flexible tensile tester, connect wires on both sides to connect the copper sheet, and the results are as follows Figure 3 shown.

[0079] from Figure 3It can be seen that the resistance change rate increases significantly with increasing tensile strain. This demonstrates that the dual-conductive flexible sensor exhibits excellent response performance to varying tensile strains. Generally speaking, the greater the stretching distance, the greater the sensor strain, and the greater the response strength. As the tensile strain increases, the sensor's response strength also increases, which is consistent with our expectations. This may be due to the external force acting on the flexible sensor: the deformation (such as stretching or compression) is proportional to the stress it experiences, and the force generated by this deformation is in turn greater. Changes in the material's internal structure: Through flexible stretching, the molecular chains of the CNTs attached to the sensor move more violently, resulting in changes in resistance. It should be noted that excessive stretching distances can also lead to rupture of the sensor film and failure of the CNT conductive network, which in turn affects test accuracy.

[0080] Test Example 3

[0081] Stability test: The stability test of the CNT / TPU / CNT porous fiber membrane with dual conductive network structure in Example 1 was carried out. The flexibility tensile test was repeated 300 times under the condition of 10% strain and the stretching speed was set at 40 mm / s on the flexibility tester. The results are shown in the figure. Figure 4 shown.

[0082] from Figure 4 It can be seen that with the increase of time and the increase of the number of stretching, the signal peak value maintains a stable trend, the relative change of resistance between 1092 and 1505Ω and the sensor response intensity remain almost unchanged, which shows that the CNT / TPU / CNT dual conductive structure flexible sensor has good stability and repeatability and has a good service life.

[0083] Test Example 3

[0084] Conductive performance: First, connect the positive and negative poles of a multimeter with two wires, then adjust the knob on the multimeter to the resistance indication position, then use the probes of the two wires to touch the two ends of the sample, and use the multimeter to test the static resistance of the porous fiber membranes with double conductive network structures of Examples 1 to 4 and Comparative Example 1. The results are as follows: Figure 5 shown.

[0085] from Figure 5 It can be seen that in Example 1, the CNT mass fraction is 0.5%, and its static resistance is reduced by 87.4% compared with the static resistance of the single conductive structure of pure TPU. Therefore, the porous fiber membrane with a double conductive network structure with a CNT mass fraction of 0.5% has good conductivity.

[0086] Test Example 4

[0087] Sensitivity test: This test example uses the gauge factor (GF) of the strain-type flexible sensor to represent the sensitivity coefficient of the flexible sensor with a double conductive network structure. The calculation formula for GF is as follows:

[0088] ;

[0089] in:

[0090] GF is the sensing coefficient, also known as sensitivity;

[0091] R0 is the resistance value of the sensor in the initial state / Ω;

[0092] R is the real-time resistance graph of the sensor under tensile deformation / Ω;

[0093] ∆R is the rate of change of resistance value / Ω;

[0094] L0 is the length of the sensor in the initial state / mm;

[0095] L is the real-time length of the sensor under tensile deformation / mm;

[0096] is strain; the results are as follows Figure 6 As shown;

[0097] from Figure 6 It can be seen that in the range of 0~0.8% CNT content, the sensitivity coefficient first increases and then decreases with the increase of CNT mass proportion. Figure 2 The super-depth-of-field topography reveals that as CNT concentration increases, CNTs may agglomerate, affecting their synergistic effect with the subsequently deposited conductive network. A flexible sensor with a dual conductive network structure, when the CNT mass fraction is 0.5%, achieves high sensitivity, a 520% ​​improvement over a flexible sensor with a single conductive network structure made of pure TPU. Therefore, the flexible sensor with a dual conductive network structure described in this application exhibits high sensitivity.

[0098] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A double conductive network porous fiber membrane, characterized in that: The components of the double conductive network porous fiber membrane include: thermoplastic polyurethane and conductive materials; The dual-conductive network porous fiber membrane comprises: a thermoplastic polyurethane / conductive material mixed fiber membrane prepared by electrospinning technology as a first conductive network structure; a second conductive network structure formed by adsorbing a conductive material on the first conductive network structure by vacuum filtration; the conductive material is a dispersion of carbon nanotube powder; the particle size of the powder is 30μm-150μm; the preparation method of the dual-conductive network porous fiber membrane comprises the following steps: S1, mixing the thermoplastic polyurethane, the conductive material and the solvent to prepare a spinning solution; S2, subjecting the spinning solution to electrospinning technology to obtain a mixed fiber membrane; S3, vacuum filtering and adsorbing the dispersion of the conductive material on the mixed fiber membrane to obtain the double conductive network porous fiber membrane; The mass ratio of the thermoplastic polyurethane to the conductive material is (8.76-8.97): (0.03-0.24); the concentration of the conductive material dispersion is 0.01%-0.05%; in step S3, the thickness of the conductive material dispersion adsorbed on the mixed fiber membrane is 0.01-0.02 μm.

2. A method for preparing a double conductive network porous fiber membrane according to claim 1, characterized in that: The preparation method comprises the following steps: S1, mixing the thermoplastic polyurethane, the conductive material and the solvent to prepare a spinning solution; S2, subjecting the spinning solution to electrospinning technology to obtain a mixed fiber membrane; S3. Vacuum-filtering the dispersion of the conductive material and adsorbing it on the mixed fiber membrane to obtain the double conductive network porous fiber membrane.

3. The preparation method according to claim 2, characterized in that In step S1, the solvent includes N,N-dimethylacetamide.

4. The preparation method according to claim 2, characterized in that In step S1, the material-liquid ratio of the conductive material to the solvent is (1-8): 700 g / mL.

5. The preparation method according to claim 2, characterized in that In step S1, the mass percentage of the conductive material in the spinning solution is 0.1% to 0.8%.

6. The preparation method according to claim 2, characterized in that In step S1, the mass percentage of the thermoplastic polyurethane and the conductive material in the spinning solution is 28-32%.

7. The preparation method according to claim 2, characterized in that In step S2, the electrospinning voltage is 15-17 kV.

8. The preparation method according to claim 2, characterized in that In step S2, the round trip distance of the electrospinning is 100-110 mm.

9. The preparation method according to claim 2, characterized in that In step S2, the electrospinning winding speed is 110-120 mm / s.

10. The preparation method according to claim 2, characterized in that In step S2, the collection speed of the electrospinning is 110-120 mm / s.

11. The preparation method according to claim 2, characterized in that In step S2, the receiving distance of the electrospinning is 13-15 cm.

12. The preparation method according to claim 2, characterized in that In step S2, the electrospinning extrusion rate is 1-2 mL / h.

13. The preparation method according to claim 2, characterized in that In step S2, the humidity of the electrospinning environment is 45%-60%.

14. A flexible pressure sensor, characterized in that: It comprises the double conductive network porous fiber membrane as claimed in claim 1.

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