PVDF / CNT@PVDF / PTFE composite nanofiber membrane, and preparation method and application thereof

Abstract

The application provides a PVDF / CNT@PVDF / PTFE composite nanofiber membrane and a preparation method and application thereof, and belongs to the technical field of electrostatic spinning.The application greatly improves the performance of the fiber membrane by adding CNT particles and PTFE; and the two components are made into a core-shell structure, so that the advantages of the two materials can be maximally utilized, and the core-shell structure can also improve the performance of the fiber membrane.The dispersed CNT solution is coated on the surface of the nanofiber membrane for modification, so that the thermal stability and sensitivity of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane can be further enhanced.The wearable strain sensor prepared from the PVDF / CNT@PVDF / PTFE composite nanofiber membrane has high mechanical performance, thermal stability and sensitivity, is environment-friendly, and has the ability to work in harsh environments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrospinning, in particular to a PVDF / CNT@PVDF / PTFE composite nanofiber membrane and a preparation method and application thereof. BACKGROUND

[0002] Artificial smart fabrics can harvest a variety of biomechanical energy from human motion and effectively convert it into stable electrical energy. Using artificial smart fabrics to prepare wearable strain sensors is an effective method that can sustainably drive wearable electronic devices in a clean, safe and efficient manner. Moreover, in addition to the energy collection function, these smart fabrics can be integrated with daily clothing to sense the amplitude of human motion, serving as high-sensitivity sensors for human motion and posture. These features also provide a basis for the widespread application of artificial smart fabrics in smart textiles and the next generation of wearable electronic products.

[0003] In recent years, many experts and scholars have published articles on wearable strain sensors, but they all have certain limitations and cannot maintain good mechanical properties and thermal stability, and some are greatly affected by harsh environments. Therefore, constructing smart textiles that can generate electrical energy through human mechanical motion is a good solution and an important progress in realizing fully wearable power in a clean, safe and sustainable manner. SUMMARY

[0004] The purpose of the present application is to provide a PVDF / CNT@PVDF / PTFE composite nanofiber membrane and a preparation method and application thereof. The wearable strain sensor prepared by the PVDF / CNT@PVDF / PTFE composite nanofiber membrane has high mechanical properties, thermal stability and sensitivity, and is environmentally friendly and capable of working in harsh environments.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a PVDF / CNT@PVDF / PTFE composite nanofiber membrane, comprising the following steps:

[0007] (1) dissolving PVDF and CNT in DMF and acetone to obtain a first solution;

[0008] (2) dissolving PVDF and PTFE concentrated solution in a mixed solution of DMF and acetone to obtain a second solution;

[0009] (3) preparing nanofiber membrane: the first solution and the second solution are coaxially connected, placed in a spinning device, woven to form a core-shell structure, the core layer is PVDF / PTFE, and the shell layer is PVDF / CNT, and after weaving, the nanofiber membrane is taken out of the receiving device and dried to obtain the nanofiber membrane;

[0010] (4) modifying the nanofiber membrane: after the CNT is dispersed in a solvent, the nanofiber membrane is coated on the surface of the nanofiber membrane, and the modified PVDF / CNT@PVDF / PTFE composite nanofiber membrane is dried.

[0011] Further, in step (1), the mass ratio of the PVDF, the CNT, the DMF and the acetone is PVDF:CNT:DMF:acetone = 1-2 g:0.001-0.1 g:3-6 mL:1-3 mL.

[0012] Further, in step (2), the mass volume ratio of the PVDF, the PTFE, the DMF and the acetone is PVDF:PTFE:DMF:acetone = 1-2 g:50-150 muL:3-6 mL:1-3 mL, and the concentration of the PTFE is 60%.

[0013] Further, in step (3), the volume ratio of the first solution and the second solution is 1-2:1-2, and the receiving device is attached with an adherend.

[0014] Further, in step (4), the mass volume ratio of the CNT and the solvent is 0.025-0.1 g:6-24 mL, the solvent is one of ethanol, DMF and PVP, and the coating amount is 0.5-1.5 g / m 2 The coating includes drop coating or spin coating.

[0015] The application further provides a PVDF / CNT@PVDF / PTFE composite nanofiber membrane prepared by the preparation method of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane.

[0016] The application further provides an application of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane in preparing a wearable strain sensor.

[0017] Further, the method for preparing the wearable strain sensor is as follows:

[0018] The two ends of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane are connected to electrodes, and the electrodes are fixed by conductive silver paste to obtain the wearable strain sensor.

[0019] Further, the electrodes include conductive adhesive tape, thin copper wire or fiber membrane.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] (1) The CNT has very good conductivity, mechanical properties, flexibility and heat transfer performance, etc., and the PTFE is called the king of plastics, has good chemical stability, corrosion resistance, sealing property and high lubrication non-stickiness, etc., and the performance of the fiber membrane is greatly improved by adding the CNT particles and the PTFE; and the two components are made into a core-shell structure, so that the advantages of the two materials can be maximally utilized, and the core-shell structure can also improve the performance of the fiber membrane. The well-dispersed CNT solution is coated on the surface of the nanofiber membrane for modification, so that the thermal stability and sensitivity of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane can be further enhanced.

[0022] (2) In the preparation of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane, different properties of the attached materials can be attached on the receiving device, so that the application range of the nanofiber membrane is greatly increased.

[0023] (3) In the preparation of the wearable strain sensor, the electrode of the sensor can be changed according to different needs, so that the application field of the wearable strain sensor is greatly increased. The prepared wearable strain sensor has high mechanical performance, thermal stability and sensitivity, is environment-friendly, and has the ability to work in harsh environments. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0025] Figure 1 SEM diagram of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane prepared for Example 1;

[0026] Figure 2 Thermal stability test of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane prepared for Example 1, wherein A is the sample of the present application, B is the PVDF / MWCNTs@PVDF / PTFE nanofiber membrane, and C is the PVDF / MWCNTs nanofiber membrane;

[0027] Figure 3 Resistance response of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane prepared for Example 1 under different stretching voltages;

[0028] Figure 4Resistance response of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane prepared in Example 1 under different strains;

[0029] Figure 5 Resistance response of the wearable strain sensor prepared in Example 1 before and after being immersed in water for 24 h;

[0030] Figure 6 Resistance response of the wearable strain sensor prepared in Example 1 after being cut;

[0031] Figure 7 Resistance response of the wearable strain sensor prepared in Example 1 for testing pulse beats;

[0032] Figure 8 Cyclic stability of the wearable strain sensor prepared in Example 1;

[0033] Figure 9 Structural schematic diagram of the wearable strain sensor prepared in Example 1. DETAILED DESCRIPTION

[0034] The embodiments of the present application are described in detail below, which are intended to explain the present application, and cannot be understood as a limitation of the present application. The specific techniques or conditions not mentioned in the embodiments are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The reagents or instruments used are not marked with the manufacturer, and are all conventional products that can be obtained by purchase.

[0035] The various exemplary embodiments of the present application are described in detail below, which should not be considered as a limitation of the present application, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present application.

[0036] The specific techniques or conditions not mentioned in the embodiments are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The reagents or instruments used are not marked with the manufacturer, and are all conventional products that can be obtained by purchase.

[0037] The present application provides a PVDF / CNT@PVDF / PTFE composite nanofiber membrane, which specifically comprises the following steps:

[0038] (1) Dissolve PVDF and CNT in a mixed solution of DMF and acetone to obtain a first solution; wherein PVDF:CNT:DMF:acetone = 1-2 g:0.001-0.1 g:3-6 mL:1-3 mL, and the most preferred is 1 g:0.005 g:3.315 g:1.42 g.

[0039] (2) the second solution is obtained by dissolving the PVDF and PTFE concentrated solution in a mixed solution of DMF and acetone, wherein PVDF: PTFE: DMF: acetone = 1-2 g: 50-150 μL: 3-6 mL: 1-3 mL, and the most preferred ratio is 1 g: 50 μL: 3.315 g: 1.42 g; the concentration of the PTFE is 60%.

[0040] Both the first solution and the second solution are subjected to heating and stirring until uniform, and the heating includes magnetic vibration heating or ultrasonic vibration heating.

[0041] (3) preparation of the nanofiber membrane: the first solution and the second solution are coaxially connected and placed in a spinning device to weave a core-shell structure, wherein the core layer is PVDF / PTFE and the shell layer is PVDF / CNT, and then the woven product is taken out from the receiving device and vacuum dried to remove residual solvents to obtain the nanofiber membrane;

[0042] The spinning device includes a receiving device, a coaxial mechanism, a high-voltage power supply and a syringe pump, wherein the receiving device includes a roller, and a layer of adhesion is attached to the receiving device.

[0043] (4) modification of the nanofiber membrane: the prepared fiber membrane is taken out and cut, and the CNT is dispersed in a solvent and coated on the surface of the nanofiber membrane, and then vacuum dried to obtain the modified PVDF / CNT@PVDF / PTFE composite nanofiber membrane;

[0044] The solvent is one of ethanol, DMF and PVP, the dispersion method is first magnetic stirring for 5 h and then ultrasonic oscillation for 1-2 h, the modification is coating the dispersed CNT solution on the surface of the fiber, the coating includes drop coating or spin coating, or the cut fiber membrane is placed in the solution and subjected to ultrasonic oscillation, and the coating amount is 0.5-1.5 g / m 2 .

[0045] The application provides a method for preparing a wearable strain sensor by using a PVDF / CNT@PVDF / PTFE composite nanofiber membrane, which specifically includes the following steps:

[0046] (5) the PVDF / CNT@PVDF / PTFE composite nanofiber membrane is connected to electrodes at both ends and fixed by conductive silver paste; the electrodes can be thin copper wires or other types of fiber membranes.

[0047] Example 1

[0048] The application provides a method for preparing a wearable strain sensor, which specifically includes the following steps:

[0049] (1) 0.005 g CNT particles and 1 g PVDF powder were dissolved in a mixed solution obtained by mixing 3.315 mL of DMF and 1.42 mL of acetone, then magnetic stirring at room temperature for 6 h, ultrasonic vibration for 2 h, until uniformly dispersed, to obtain a first solution;

[0050] (2) 50 μL of PTFE concentrated solution and 1 g of PVDF were dissolved in a mixed solution obtained by mixing 3.315 mL of DMF and 1.42 mL of acetone, then magnetic stirring at 60°C for 6 h, until uniformly dispersed, to obtain a second solution.

[0051] (3) Two clean syringes with a volume of 5 mL were taken, the first solution and the second solution were respectively taken into the syringes, then the two syringes were connected by a special coaxial needle. The second solution was sprayed from the inner needle as the core layer material, and the first solution was sprayed from the outer needle as the shell layer material.

[0052] Then set the parameters, the distance between the receiving device and the nozzle is 12.5 cm, the voltage is 20 kv, the feeding speed of the main pump and the auxiliary pump is 0.0007 mm / s, the relative humidity is about 60%, the temperature is about 25°C, a layer of tin foil paper is covered on the roller to receive the fiber, and finally the spinning is started, to obtain a fiber membrane. The obtained fiber membrane is placed in a vacuum drying box for drying for 2 h, the temperature is set to 70°C, to remove the residual solvent, and the dried fiber membrane is taken out and cut into a rectangular sample of 7 cm*4 cm, to obtain a nanofiber membrane.

[0053] (4) 0.025 g of CNT particles were dispersed in 6 ml of ethanol solution, first magnetic stirring at room temperature for 10 min, then ultrasonic vibration for 2 h, and the water was replaced every half hour to ensure the water temperature uniform, finally the dispersed CNT was coated on the prepared sample, the coating amount was 1.5 g / m 2 . Then dry at 60°C for 1 h to obtain a modified PVDF / CNT@PVDF / PTFE composite nanofiber membrane.

[0054] (5) The conductive tape was pasted on both sides of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane to serve as an electrode, and conductive silver paste was coated between the conductive tape and the fiber membrane, then dried at 60°C for 1 h to obtain a wearable strain sensor.

[0055] The prepared wearable strain sensor was tested for performance, such as sensitivity, mechanical properties, thermal stability, etc., and the results are shown in Figures 1-8 , and the structure diagram is shown in Figure 9 .

[0056] From Figure 1It can be seen that all the fibers in the fiber membrane show random orientation, the fibers are all smooth and flat on the surface, and are naturally stacked with each other to form a 3D porous network structure, and a large number of particles are adhered to the fiber surface due to the coating of a layer of MWCNTs on the fiber surface, which directly indicates that the coating of MWCNTs is successful.

[0057] Figure 2 The shrinkage conditions of three different fiber membranes (sample size: a circle with a diameter of 3.5 cm) after standing at 140℃, 160℃ and 180℃ for 30 min are compared. At 140℃, it can be seen that the three fiber membranes all remain unchanged, and the appearance basically has no change. At 160℃, the sample fiber membrane in the application still has little change, while the PVDF / MWCNTs@PVDF / PTFE fiber membrane without coating has some small curling and some edge lifting, but the overall appearance has not changed much, and the PVDF / MWCNTs fiber membrane has obvious wrinkles and shrinkage. At 180℃, the sample fiber membrane in the application can still maintain a good appearance, the PVDF / MWCNTs@PVDF / PTFE fiber membrane without coating has obvious curling, and the curling of the PVDF / MWCNTs fiber membrane is more obvious, and even the edge of the fiber membrane has serious shrinkage, resulting in a huge change in the overall appearance of the fiber membrane. Therefore, it can be seen that the sample fiber membrane in the application has good heat resistance and can maintain a good fiber appearance at 180℃, basically without curling and shrinkage.

[0058] Figure 3 It can be seen from the figure that the flexible strain sensor assembled by the sample fiber membrane in the application has good stability and repeatability of the resistance response at different stretching rates, and the waveforms are also stable and normal. The resistance responses at different stretching rates are stably at about 2.5, 2.7 and 4.2 respectively, and the curve fluctuation frequency also increases with the increase of the stretching rate in the same time. It can be seen from the figure that the resistance response value also increases continuously with the increase of the stretching rate, because the greater the stretching rate, the greater the deformation of the sensor, that is, the fiber is lengthened to increase the real-time resistance of the fiber, and the change of the fiber resistance will directly affect the real-time resistance of the sensor. At the same time, the response time is relatively stable, and can increase with the increase of the stretching frequency without affecting the stability of the response time.

[0059] From Figure 4It can be seen from the figure that the sensor assembled by the sample fiber membrane in the application has good stability and repeatability, and the resistance response value also increases with the increase of the strain in the same time. It can be seen from the figure that the resistance response value also increases continuously with the increase of the tensile strain, because the greater the tensile strain, the greater the deformation of the sensor, and the greater the change of the resistance response value. The resistance response value increases from 2.2 to about 8.3, and the resistance response value remains very stable under each strain.

[0060] From Figure 5 It can be seen from the figure that the sensor assembled by the sample fiber membrane in the application has better stability and repeatability, and the resistance response value is stable at about 1.5, the waveform has obvious fluctuation rule, and there is no slow change of the waveform. However, after 24h of immersion, the resistance response value decreases slightly and is stable at about 1.3, because the hydrophobicity of the composite fiber membrane coated with MWCNTs is slightly poor, and the immersion has a slight effect on the sensor, but it can be seen from the figure that the effect is very small, which basically does not affect the normal use of the sensor.

[0061] From Figure 6 It can be seen from the figure that the sensor assembled by the sample fiber membrane in the application has better stability and repeatability, and the resistance response value is stable at about 1.5, the waveform has obvious fluctuation rule, and there is no slow change of the waveform. However, after 24h of immersion, the resistance response value decreases slightly and is stable at about 1.3, because the hydrophobicity of the composite fiber membrane coated with MWCNTs is slightly poor, and the immersion has a slight effect on the sensor, but it can be seen from the figure that the effect is very small, which basically does not affect the normal use of the sensor.

[0062] Figure 7 In order to test the waveform of pulse beat, it can be seen from the test result that it completely conforms to the number of pulse beats per minute (60-100 times / min) of normal people, and has good stability and repeatability, and the resistance response value is stable at about 1.002. The resistance response value is very low because the pulse beat cannot cause large deformation of the sensor. However, it can be seen from the waveform that the waveform is slightly different, because the skin at the wrist may have slight vibration during the test, and the test environment may cause errors.

[0063] Figure 8The cycle stability test chart of the sensor is shown in the figure, the test speed is 1 cycle / s, it can be seen from the figure that good stability and repeatability are still possessed after 40000 times of stretching and releasing, the change of the waveform has good stability and repeatability, and the resistance response is always kept at about 20, which indicates that the sensor prepared in the application has a long service life and can maintain good stability in long-term work. However, it can also be seen from the figure that some waveforms have certain defects, which is because the test equipment is placed in the air and the test time is relatively long, resulting in certain errors, which is a normal phenomenon.

[0064] Figure 9 The structure schematic diagram of the sensor is shown in the figure, the prepared solution is sucked out by a syringe, then a PVDF / MWCNTs@PVDF / PTFE nanofiber membrane with a core-shell structure is prepared by a coaxial electrospinning method, a layer of MWCNTs is coated on the surface of the fiber membrane, then a conductive tape is connected as an electrode, and finally the PDMS is encapsulated.

[0065] Embodiment 2

[0066] The wearable strain sensor is prepared by adopting the preparation method of the wearable strain sensor in embodiment 1, and the difference from embodiment 1 is that a layer of conductive fabric is covered on the roller of the receiving device in embodiment 2, which is used for directly receiving the fiber and can further improve the conductivity.

[0067] Embodiment 3

[0068] The wearable strain sensor is prepared by adopting the preparation method of the wearable strain sensor in embodiment 1, and the difference from embodiment 1 is that the prepared fiber membrane is soaked in the dispersed CNTs, and then ultrasonic oscillation is performed for 1 h, so that the CNTs can be well adsorbed on the surface of the fiber.

[0069] Embodiment 4

[0070] The wearable strain sensor is prepared by adopting the preparation method of the wearable strain sensor in embodiment 4, and the difference from embodiment 1 is that other types of fiber membranes are used as electrodes, and then copper wires are led out, which can be used as a nanometer friction generator, greatly increasing the application field.

[0071] The above only describes the preferred embodiments of the application, and it should be noted that for ordinary skilled persons in the art, some improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be regarded as the protection scope of the application.

Claims

1. A method for preparing a PVDF / CNT@PVDF / PTFE composite nanofiber membrane, characterized in that, Includes the following steps: (1) Dissolve PVDF and CNT in a mixed solution of DMF and acetone to obtain the first solution; (2) Dissolve the concentrated PVDF and PTFE solution in a mixed solution of DMF and acetone to obtain a second solution; (3) Preparation of nanofiber membrane: The first solution and the second solution are coaxially connected and placed in a spinning device to form a core-shell structured fiber with a core layer of PVDF / PTFE and a shell layer of PVDF / CNT. The core-shell structured fiber enters the receiving device, is taken out from the receiving device, and dried to obtain a nanofiber membrane. (4) Modification of nanofiber membrane: CNTs are dispersed in a solvent and coated on the surface of a nanofiber membrane. After drying, a modified PVDF / CNT@PVDF / PTFE composite nanofiber membrane is obtained. The mass-to-volume ratio of PVDF, CNT, DMF, and acetone in step (1) is PVDF:CNT:DMF:acetone = 1~2 g:0.001~0.1 g:3~6 mL:1~3 mL; In step (2), the mass-to-volume ratio of PVDF, PTFE, DMF, and acetone is: PVDF:PTFE:DMF:acetone = 1~2 g: 50~150 μL: 3~6 mL: 1~3 mL; the concentration of PTFE is 60%. In step (3), the volume ratio of the first solution to the second solution is 1~2:1~2; the receiving device is covered with a layer of deposit; In step (4), the mass-to-volume ratio of CNT to solvent is 0.025~0.1g:6~24mL; the solvent is one of ethanol, DMF, and PVP; and the amount coated is 0.5~1.5g. Coating includes drop coating or spin coating.

2. A PVDF / CNT@PVDF / PTFE composite nanofiber membrane prepared by the method of claim 1.

3. The application of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane according to claim 2 in the preparation of wearable strain sensors.

4. The application of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane according to claim 3 in the fabrication of wearable strain sensors, characterized in that, The method for preparing the wearable strain sensor is as follows: A wearable strain sensor was obtained by connecting both ends of a PVDF / CNT@PVDF / PTFE composite nanofiber membrane to electrodes and fixing it with conductive silver paste.

5. The application of the PVDF / CNT@PVDF / PTFE composite nanofiber membrane according to claim 4 in the fabrication of wearable strain sensors, characterized in that, The electrode comprises conductive tape, fine copper wire, or fiber membrane.

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