A linear range adjustable ionization type flexible pressure sensor and preparation method thereof

Abstract

A ion-type flexible pressure sensor with adjustable linear range and a preparation method thereof, belonging to the field of pressure sensing technology. The sensor is composed of an upper PET substrate, a positive electrode, a TPU / ILs ion membrane, a Gr / WPU sponge, a polyurethane sponge frame, a negative electrode and a lower PET substrate from top to bottom. The present invention introduces a Gr / WPU sponge elastomer with adjustable conductivity on the basis of a sandwich structure ion-type pressure sensor, and adjusts the double-layer capacitance of the sensor by changing its resistance range, so that the linear range of the pressure sensor can be adjusted within a wider range; the pressure sensor of the present invention has good cycle stability, fast response recovery speed, and good resolution of small pressures within a wide pressure detection range. The detection range can reach 0~2300 kPa, the linearity is 0.98, and the sensitivity is 1.11 kPa ‑1 , which has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure sensing, and in particular relates to an ion-type flexible pressure sensor with adjustable linear range and a preparation method thereof. Background Art

[0002] Flexible sensors have the characteristics of being stretchable, bendable, and foldable, which greatly broadens the application scenarios of sensors compared to traditional rigid devices. As one of the important components in the field of flexible sensing, flexible pressure sensors can convert external pressure signals into electrical signals.

[0003] The performance of flexible pressure sensors that are generally concerned include sensitivity, response speed, pressure resolution, stability, etc. When sensors are used to monitor human vital signs, different application scenarios have different requirements for sensor performance. For example, monitoring of human physiological signals such as pulse and vocal cord vibration often requires sensors to have higher sensitivity within a narrow detection range. Monitoring of body joint movement requires sensors to have good stability within the medium pressure detection range. Monitoring of plantar pressure of different groups of people requires sensors to have a wider detection range to adapt to people with different foot shapes and different weights.

[0004] Ion-type flexible pressure sensors use the double electric layer formed at the interface between the electrode and the electrolyte layer to greatly increase the capacitance of the sensor. At present, the main method to improve the sensitivity of ion-type flexible pressure sensors is to construct interface microstructures. However, as the load pressure increases, the sensor exhibits strain hardening, the output signal increases slowly and tends to saturation, resulting in the sensor being unable to accurately identify and analyze the signal under high pressure. The balance between the wide detection range and high sensitivity of ion-type pressure sensors has always been the focus of scientific researchers. The research work on expanding the detection range of sensors mainly changes the change in the contact area between the two under load pressure by constructing the interface microstructure between the electrode and the electrolyte layer, thereby slowing down the saturation speed of the pressure sensor capacitance and widening its linear detection range. However, the design process of the microstructure is complex and costly, and the performance of the sensor prepared by the microstructure strategy is relatively single and difficult to control, and cannot adapt to complex and changing application requirements. Therefore, a design strategy for pressure sensors with adjustable linear range is urgently needed to enable the sensor to adapt to different application scenarios. Summary of the invention

[0005] In view of the above problems, the present invention first designs a conductive polyurethane sponge elastomer with adjustable resistance range. By adjusting the change range of resistance of the elastomer under load pressure, the attraction ability of electrons at the interface of the electrode and electrolyte layer to ions is changed, thereby providing an ion-type flexible pressure sensor with adjustable linear range assembled by a conductive polyurethane sponge elastomer and an ion membrane and a preparation method thereof, which realizes the recognition and resolution of small pressures within a wide detection range of the sensor and the precise regulation of the linear range of the sensor, so as to solve the problems of existing ion-type pressure sensors with narrow detection range, low pressure resolution in the high-pressure range, difficult to regulate device performance, and inability to adapt to various application requirements.

[0006] The present invention discloses an ion-type flexible pressure sensor with adjustable linear range, which is composed of an upper PET substrate, a positive electrode, a TPU / ILs ion membrane, a Gr / WPU sponge, a polyurethane sponge frame, a negative electrode and a lower PET substrate from top to bottom; the change in the conductivity of the Gr / WPU sponge can regulate the aggregation amount of ions at the interface between the electrode and the TPU / ILs ion membrane (electrolyte layer), thereby changing the capacitance of the sensor and realizing the controllable linear range of the sensor.

[0007] When the device is loaded with pressure, in the pressure range of 0~1000 kPa, the low resistance of Gr / WPU sponge leads to a small double-layer capacitance at the interface formed between it and TPU / ILs ion membrane; as the device load pressure increases, the conductivity of Gr / WPU sponge is improved, and more charged electrons on the contact interface between Gr / WPU sponge and TPU / ILs ion membrane can attract charged ions with opposite electrical properties, thereby enhancing the double-layer capacitance. The regulation of the resistance range of Gr / WPU sponge plays a key role in regulating the sensitive range of the sensor. When the device load pressure changes, the double-layer capacitance at the interface between the sensor electrode and the TPU / ILs ion membrane will change. An AC voltage of 1 kHz and 1 V is applied to the sensor, and the capacitance values ​​output by the positive and negative electrodes of the sensor are measured, and the capacitance response and sensitivity of the sensor under different load pressures are calculated. The capacitance response (R) of the pressure sensor is defined as: R = (C-C0) / C0, where C is the capacitance value output by the positive and negative electrodes when the sensor is loaded with different pressures, and C0 is the initial capacitance value output by the positive and negative electrodes when the sensor is not loaded with pressure; the sensitivity (S) of the pressure sensor is defined as: S = ΔR / ΔP, ΔR is the change in capacitance response when the sensor is loaded with different pressures, and ΔP is the change in pressure when the sensor is loaded with different pressures.

[0008] The method for preparing a linear range adjustable ion-type flexible pressure sensor of the present invention comprises the following steps:

[0009] (1) Add 0.02-0.8 g of graphene (Gr) to 20 mL of deionized water and stir at 20-30 °C for 0.5-3 h until the graphene is evenly dispersed; add 0.1-2 g of waterborne polyurethane (WPU) to the obtained solution and stir at 20-30 °C for 1-5 h to obtain a Gr / WPU mixed solution;

[0010] (2) Cut the polyurethane sponge into discs and place them in 10-50 mL of deionized water, ultrasonically clean them for 0.5-2 h, and then dry them at 50-70 °C to obtain polyurethane sponge discs with impurities removed;

[0011] (3) placing the polyurethane sponge disc obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5-3 h and then drying it at 50-70°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge, thereby obtaining a Gr / WPU sponge;

[0012] (4) Add 0.2-0.4 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide (DMF) and stir at 60-80 °C for 1.5-3.0 h until the TPU is completely dissolved to obtain a TPU solution;

[0013] (5) adding 0.2-0.4 g of ionic liquid (ILs) to the TPU solution obtained in step (4), stirring at 60-80 °C for 1.5-3.0 h to obtain a TPU / ILs mixed solution;

[0014] (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it into a polytetrafluoroethylene mold, place it in a ventilated environment and dry it for 8 to 15 h to obtain a TPU / ILs film with a thickness of 0.2 to 0.5 mm, cut it into a circle, and obtain a TPU / ILs ion membrane;

[0015] (7) Cutting two fabric conductive tapes (with metal copper and nickel on the surface) into a shape composed of a circular area and a rectangular area, and attaching them as the positive electrode and negative electrode of the sensor to the lower surface of the upper polyethylene terephthalate (PET) substrate and the upper surface of the lower polyethylene terephthalate (PET) substrate, respectively;

[0016] (8) Cutting off a circular area with the same diameter as the Gr / WPU sponge from the center of the polyurethane sponge to obtain a polyurethane sponge frame; attaching double-sided tape to the upper and lower surfaces of the polyurethane sponge, and embedding the Gr / WPU sponge obtained in step (3) into the polyurethane sponge frame to obtain a pressure-sensitive layer;

[0017] (9) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface prepared in step (7) are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (6) and the pressure-sensitive layer prepared in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular areas of the positive electrode and the negative electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a certain pressure is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0018] Furthermore, in step (2) and step (8), the thickness of the polyurethane sponge is 1-3 mm and the density is 25-60 ppi; in step (2), the diameter of the polyurethane sponge disc is 0.5-1.5 cm; in step (6), the diameter of the TPU / ILs ion membrane is 0.5-1.5 cm; in step (7), the diameter of the circular area of ​​the fabric conductive tape is 0.5-1.5 cm, and the length of the rectangular area is 1.5-2.5 cm and the width is 0.2-0.8 cm; the upper polyethylene terephthalate (PET) substrate and the lower polyethylene terephthalate (PET) substrate are rectangular structures with a length of 3-5.5 cm and a width of 1.5-2.5 cm; in step (9), the flexible pressure sensor is obtained after applying a pressure of 1-3N between the upper and lower substrates.

[0019] The advantages of the present invention are:

[0020] 1. The present invention introduces a Gr / WPU sponge elastomer with adjustable conductivity on the basis of a sandwich structure ion-type pressure sensor, and adjusts the double-layer capacitance of the sensor by changing its resistance range, so that the linear range of the pressure sensor can be adjusted in a wider range;

[0021] 2. The structure, material and preparation process of the flexible pressure sensor in the present invention have the advantages of being highly controllable, repeatable and low-cost;

[0022] 3. The flexible pressure sensor with adjustable linear range designed by the present invention can be used to specifically design pressure sensors by adjusting the resistance range of Gr / WPU sponge, for example, to design a sensor that is sensitive to low pressure but not to high pressure, a sensor that is insensitive to low pressure but responsive to high pressure, or a sensor that is linearly sensitive in a wide pressure range;

[0023] 4. The flexible pressure sensor with adjustable linear range designed by the present invention has good cycle stability, fast response recovery speed, and good resolution of small pressures within a wide pressure detection range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic structural diagram of a flexible pressure sensor prepared in Examples 1 to 5 of the present invention;

[0025] Figure 2 is a schematic structural diagram of a flexible pressure sensor prepared in Example 6 of the present invention;

[0026] Figure 3 is a curve showing the change of capacitance of the ionization type pressure sensor prepared in Examples 1 to 6 of the present invention with respect to load pressure;

[0027] Figure 4 is a curve showing the change of capacitance response of the ionization type pressure sensor prepared in Example 3 and Example 4 of the present invention with respect to load pressure;

[0028] Figure 5 It is the capacitance response and recovery curve of the ionization type pressure sensor prepared in Example 3 of the present invention under the cycle test of different load pressures;

[0029] Figure 6 1 is the response time and recovery time curve of the ionization type pressure sensor prepared in Example 3 of the present invention at a load of 1000 kPa;

[0030] Figure 7 The capacitance response curve and recovery curve of the ionization type pressure sensor prepared in Example 3 of the present invention when a load of 600 kPa is applied 3500 times;

[0031] Figure 8 is the response curve of the ionization type pressure sensor prepared in Example 3 of the present invention to a load of 35 kPa under a reference pressure of 50 kPa;

[0032] Fig. 9 is the response curve of the ionization type pressure sensor prepared in Example 3 of the present invention to a load of 35 kPa under a reference pressure of 1300 kPa;

[0033] Fig.10 3 is the response curve of the ionization type pressure sensor prepared in Example 3 of the present invention to a load of 35 kPa under a reference pressure of 2050 kPa. DETAILED DESCRIPTION

[0034] Example 1: (1) 0.05 g of graphene (Gr) was added to 20 mL of deionized water and stirred at 25°C for 1 h until the graphene was evenly dispersed; 0.4 g of waterborne polyurethane (WPU) was added to the obtained solution and stirred at 25°C for 3 h to obtain a Gr / WPU mixed solution;

[0035] (2) Cut the polyurethane sponge (thickness 2 mm, density 45 ppi) into a disc with a diameter of 1 cm and place it in 30 mL of deionized water. Ultrasonic cleaning was performed for 0.5 h and then dried at 60 °C to obtain a circular polyurethane sponge with impurities removed.

[0036] (3) placing the circular polyurethane sponge obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5 h and then drying it at 60°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge to obtain a Gr / WPU sponge;

[0037] (4) Add 0.35 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide (DMF) and stir at 70 °C for 2 h until the TPU is completely dissolved to obtain a TPU solution;

[0038] (5) Add 0.35 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ILs) to the TPU solution obtained in step (4), and stir at 70°C for 2 h to obtain a TPU / ILs mixed solution;

[0039] (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it on a polytetrafluoroethylene mold (size 2*6 cm 2 ) and placed in a ventilated place to dry for 10 h to obtain a TPU / ILs film (thickness 0.3 mm); the TPU / ILs film was cut into a circle with a diameter of 1 cm to obtain a TPU / ILs ion membrane;

[0040] (7) Cut a fabric conductive tape (with a surface made of metal copper and nickel, 0.1 mm thick and 20 mm wide) into a shape composed of a circle and a rectangle, with a diameter of 1 cm and a length of 2 cm and a width of 0.5 cm for the rectangle. Attach the positive electrode and negative electrode of the sensor to the lower surface of the upper polyethylene terephthalate (PET) substrate with a length of 5 cm and a width of 1.5 cm and to the upper surface of the lower polyethylene terephthalate (PET) substrate, respectively.

[0041] (8) Cut a polyurethane sponge (thickness 2 mm, density 45 ppi) into a rectangle with a length of 5 cm and a width of 1.5 cm, and cut off a circular area with a diameter of 1 cm at the center of the rectangle, taking the remaining frame part to obtain a polyurethane sponge frame; attach double-sided tape to the upper and lower surfaces of the polyurethane sponge frame, respectively, and embed the Gr / WPU sponge obtained in step (3) into the frame to obtain a pressure-sensitive layer;

[0042] (9) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface prepared in step (7) and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (6) and the pressure-sensitive layer prepared in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular area of ​​the electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a pressure of 2 N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0043] Example 2: (1) 0.1 g of graphene (Gr) was added to 20 mL of deionized water and stirred at 25°C for 1 h until the graphene was evenly dispersed; 0.4 g of waterborne polyurethane (WPU) was added to the obtained solution and stirred at 25°C for 3 h to obtain a Gr / WPU mixed solution;

[0044] (2) Cut the polyurethane sponge (thickness 2 mm, density 45 ppi) into a disc with a diameter of 1 cm and place it in 30 mL of deionized water. Ultrasonic cleaning was performed for 0.5 h and then dried at 60 °C to obtain a circular polyurethane sponge with impurities removed.

[0045] (3) placing the circular polyurethane sponge obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5 h and then drying it at 60°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge to obtain a Gr / WPU sponge;

[0046] (4) Add 0.35 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide (DMF) and stir at 70 °C for 2 h until the TPU is completely dissolved to obtain a TPU solution;

[0047] (5) Add 0.35 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ILs) to the TPU solution obtained in step (4), and stir at 70°C for 2 h to obtain a TPU / ILs mixed solution;

[0048] (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it on a polytetrafluoroethylene mold (size 2*6 cm 2 ) and placed in a ventilated place to dry for 10 h to obtain a TPU / ILs film (thickness 0.3 mm); the TPU / ILs film was cut into a circle with a diameter of 1 cm to obtain a TPU / ILs ion membrane;

[0049] (7) Cut the fabric conductive tape (with copper and nickel on the surface, 0.1 mm thick and 20 mm wide) into a shape composed of a circle and a rectangle, with a diameter of 1 cm for the circle and a length of 2 cm and a width of 0.5 cm for the rectangle, and attach the positive electrode and negative electrode of the sensor to the lower surface of the upper polyethylene terephthalate (PET) substrate with a length of 5 cm and a width of 1.5 cm and to the upper surface of the lower polyethylene terephthalate (PET) substrate, respectively;

[0050] (8) Cut a polyurethane sponge (thickness 2 mm, density 45 ppi) into a rectangle with a length of 5 cm and a width of 1.5 cm, and cut off a circular area with a diameter of 1 cm at the center of the rectangle, taking the remaining frame part to obtain a polyurethane sponge frame; attach double-sided tape to the upper and lower surfaces of the polyurethane sponge frame, respectively, and embed the Gr / WPU sponge obtained in step (3) into the frame to obtain a pressure-sensitive layer;

[0051] (9) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface prepared in step (7) and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (6) and the pressure-sensitive layer prepared in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular area of ​​the electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a pressure of 2 N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0052] Example 3: (1) 0.2 g of graphene (Gr) was added to 20 mL of deionized water and stirred at 25°C for 1 h until the graphene was evenly dispersed; 0.4 g of waterborne polyurethane (WPU) was added to the obtained solution and stirred at 25°C for 3 h to obtain a Gr / WPU mixed solution;

[0053] (2) Cut the polyurethane sponge (thickness 2 mm, density 45 ppi) into a disc with a diameter of 1 cm and place it in 30 mL of deionized water. Ultrasonic cleaning was performed for 0.5 h and then dried at 60 °C to obtain a circular polyurethane sponge with impurities removed.

[0054] (3) placing the circular polyurethane sponge obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5 h and then drying it at 60°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge to obtain a Gr / WPU sponge;

[0055] (4) Add 0.35 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide (DMF) and stir at 70 °C for 2 h until the TPU is completely dissolved to obtain a TPU solution;

[0056] (5) Add 0.35 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ILs) to the TPU solution obtained in step (4), and stir at 70°C for 2 h to obtain a TPU / ILs mixed solution;

[0057] (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it on a polytetrafluoroethylene mold (size 2*6 cm 2 ) and placed in a ventilated place to dry for 10 h to obtain a TPU / ILs film (thickness 0.3 mm); the TPU / ILs film was cut into a circle with a diameter of 1 cm to obtain a TPU / ILs ion membrane;

[0058] (7) Cut the fabric conductive tape (with copper and nickel on the surface, 0.1 mm thick and 20 mm wide) into a shape composed of a circle and a rectangle, with a diameter of 1 cm for the circle and a length of 2 cm and a width of 0.5 cm for the rectangle, and attach the positive electrode and negative electrode of the sensor to the lower surface of the upper polyethylene terephthalate (PET) substrate with a length of 5 cm and a width of 1.5 cm and to the upper surface of the lower polyethylene terephthalate (PET) substrate, respectively;

[0059] (8) Cut a polyurethane sponge (thickness 2 mm, density 45 ppi) into a rectangle with a length of 5 cm and a width of 1.5 cm, and cut off a circular area with a diameter of 1 cm at the center of the rectangle, taking the remaining frame part to obtain a polyurethane sponge frame; attach double-sided tape to the upper and lower surfaces of the polyurethane sponge frame, respectively, and embed the Gr / WPU sponge obtained in step (3) into the frame to obtain a pressure-sensitive layer;

[0060] (9) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface prepared in step (7) and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (6) and the pressure-sensitive layer prepared in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular area of ​​the electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a pressure of 2 N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0061] Example 4: (1) 0.4 g of graphene (Gr) was added to 20 mL of deionized water and stirred at 25°C for 1 h until the graphene was evenly dispersed; 0.4 g of waterborne polyurethane (WPU) was added to the obtained solution and stirred at 25°C for 3 h to obtain a Gr / WPU mixed solution;

[0062] (2) Cut the polyurethane sponge (thickness 2 mm, density 45 ppi) into a disc with a diameter of 1 cm and place it in 30 mL of deionized water. Ultrasonic cleaning was performed for 0.5 h and then dried at 60 °C to obtain a circular polyurethane sponge with impurities removed.

[0063] (3) placing the circular polyurethane sponge obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5 h and then drying it at 60°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge to obtain a Gr / WPU sponge;

[0064] (4) Add 0.35 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide (DMF) and stir at 70 °C for 2 h until the TPU is completely dissolved to obtain a TPU solution;

[0065] (5) Add 0.35 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ILs) to the TPU solution obtained in step (4), and stir at 70°C for 2 h to obtain a TPU / ILs mixed solution;

[0066] (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it on a polytetrafluoroethylene mold (size 2*6 cm 2 ) and placed in a ventilated place to dry for 10 h to obtain a TPU / ILs film (thickness 0.3 mm); the TPU / ILs film was cut into a circle with a diameter of 1 cm to obtain a TPU / ILs ion membrane;

[0067] (7) Cut a fabric conductive tape (with a surface made of metal copper and nickel, 0.1 mm thick and 20 mm wide) into a shape composed of a circle and a rectangle, with a diameter of 1 cm and a length of 2 cm and a width of 0.5 cm for the rectangle. Attach the positive electrode and negative electrode of the sensor to the lower surface of the upper polyethylene terephthalate (PET) substrate with a length of 5 cm and a width of 1.5 cm and to the upper surface of the lower polyethylene terephthalate (PET) substrate, respectively.

[0068] (8) Cut a polyurethane sponge (thickness 2 mm, density 45 ppi) into a rectangle with a length of 5 cm and a width of 1.5 cm, and cut off a circular area with a diameter of 1 cm at the center of the rectangle, taking the remaining frame part to obtain a polyurethane sponge frame; attach double-sided tape to the upper and lower surfaces of the polyurethane sponge frame, respectively, and embed the Gr / WPU sponge obtained in step (3) into the frame to obtain a pressure-sensitive layer;

[0069] (9) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface prepared in step (7) and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (6) and the pressure-sensitive layer prepared in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular area of ​​the electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a pressure of 2 N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0070] Example 5: (1) 0.6 g of graphene (Gr) was added to 20 mL of deionized water and stirred at 25°C for 1 h until the graphene was evenly dispersed; 0.4 g of waterborne polyurethane (WPU) was added to the obtained solution and stirred at 25°C for 3 h to obtain a Gr / WPU mixed solution;

[0071] (2) Cut the polyurethane sponge (thickness 2 mm, density 45 ppi) into a disc with a diameter of 1 cm and place it in 30 mL of deionized water. Ultrasonic cleaning was performed for 0.5 h and then dried at 60 °C to obtain a circular polyurethane sponge with impurities removed.

[0072] (3) placing the circular polyurethane sponge obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5 h and then drying it at 60°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge to obtain a Gr / WPU sponge;

[0073] (4) Add 0.35 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide (DMF) and stir at 70 °C for 2 h until the TPU is completely dissolved to obtain a TPU solution;

[0074] (5) Add 0.35 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ILs) to the TPU solution obtained in step (4), and stir at 70°C for 2 h to obtain a TPU / ILs mixed solution;

[0075] (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it on a polytetrafluoroethylene mold (size 2*6 cm 2 ) and placed in a ventilated place to dry for 10 h to obtain a TPU / ILs film (thickness 0.3 mm); the TPU / ILs film was cut into a circle with a diameter of 1 cm to obtain a TPU / ILs ion membrane;

[0076] (7) Cut a fabric conductive tape (with a surface made of metal copper and nickel, 0.1 mm thick and 20 mm wide) into a shape composed of a circle and a rectangle, with a diameter of 1 cm and a length of 2 cm and a width of 0.5 cm for the rectangle. Attach the positive electrode and negative electrode of the sensor to the lower surface of the upper polyethylene terephthalate (PET) substrate with a length of 5 cm and a width of 1.5 cm and to the upper surface of the lower polyethylene terephthalate (PET) substrate, respectively.

[0077] (8) Cut a polyurethane sponge (thickness 2 mm, density 45 ppi) into a rectangle with a length of 5 cm and a width of 1.5 cm, and cut off a circular area with a diameter of 1 cm at the center of the rectangle, taking the remaining frame part to obtain a polyurethane sponge frame; attach double-sided tape to the upper and lower surfaces of the polyurethane sponge frame, respectively, and embed the Gr / WPU sponge obtained in step (3) into the frame to obtain a pressure-sensitive layer;

[0078] (9) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface prepared in step (7) and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (6) and the pressure-sensitive layer prepared in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular area of ​​the electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a pressure of 2 N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0079] Example 6: (1) 0.35 g of thermoplastic polyurethane (TPU) was added to 3 mL of N,N-dimethylformamide (DMF), and stirred at 70°C for 2 h until the TPU was completely dissolved to obtain a TPU solution;

[0080] (2) adding 0.35 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ILs) to the TPU solution obtained in step (1), stirring at 70° C. for 2 h to obtain a TPU / ILs mixed solution;

[0081] (3) Take 2 mL of the TPU / ILs mixed solution obtained in step (2) and evenly drop it on a polytetrafluoroethylene mold (size 2*6 cm 2 ) and placed in a ventilated place to dry for 10 h to obtain a TPU / ILs film (thickness 0.3 mm); the TPU / ILs film was cut into a circle with a diameter of 1 cm to obtain a TPU / ILs ion membrane;

[0082] (4) Cut the conductive fabric tape (with copper and nickel on the surface, 0.1 mm thick and 20 mm wide) into a shape composed of a circle and a rectangle, with a diameter of 1 cm and a length of 2 cm and a width of 0.5 cm for the circle and the negative electrode as the sensor, respectively, on the lower surface of the upper polyethylene terephthalate (PET) substrate with a length of 5 cm and a width of 1.5 cm and on the upper surface of the lower polyethylene terephthalate (PET) substrate;

[0083] (5) The upper polyethylene terephthalate (PET) substrate with a positive electrode on the lower surface and the lower polyethylene terephthalate (PET) substrate with a negative electrode on the upper surface prepared in step (4) are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane prepared in step (3) is placed between the positive electrode and the negative electrode, so that the circular area of ​​the electrode and the position of the TPU / ILs ion membrane are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (4), and a pressure of 2 N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

[0084] The structural schematic diagram of the flexible pressure sensor prepared in Examples 1 to 5 is shown in FIG. Figure 1 The names of the parts are: upper PET substrate 1, positive electrode 2, TPU / ILs ion membrane 3, Gr / WPU sponge 4, polyurethane sponge frame 5, negative electrode 6, lower PET substrate 7; TPU / ILs ion membrane 3 is placed in the middle upper layer in contact with the positive electrode 2, and the combination of Gr / WPU sponge 4 and polyurethane sponge frame 5 is placed in the middle lower layer in contact with the negative electrode 6.

[0085] The structural schematic diagram of the flexible pressure sensor prepared in Example 6 is shown in FIG. Figure 2 The names of the parts are: upper PET substrate 1, positive electrode 2, TPU / ILs ion membrane 3, negative electrode 4, lower PET substrate 5; TPU / ILs ion membrane 3 is placed between positive electrode 2 and negative electrode 6 as a sensitive layer.

[0086] The capacitance variation curves of the flexible pressure sensors prepared in Examples 1 to 6 as a function of load pressure are shown in FIG. Figure 3As shown. It can be seen that the capacitance of the flexible pressure sensor prepared in Example 6 shows a saturation trend when the capacitance value is above 100 kPa, while the capacitance value of the flexible pressure sensor prepared in Examples 1 to 5 is significantly reduced in the low-pressure range due to the effect of the Gr / WPU sponge, which effectively delays the degree to which the sensor tends to saturate. Examples 1 to 5 adjust the resistance change range and rate of the Gr / WPU sponge under pressure by regulating the load of the Gr / WPU sponge Gr. The Gr content corresponding to Example 5 is relatively high, so its capacitance changes slowly in the low-pressure range, but in the high-pressure range, it has the same change trend as Example 6, which proves that increasing the resistance of the Gr / WPU sponge and slowing down its speed of approaching the minimum resistance can further slow down the rate at which the capacitance value tends to saturate. The flexible pressure sensors prepared in Examples 3 and 4 have good linearity in the pressure detection range of 0~2300 kPa.

[0087] The capacitance response curves of the flexible pressure sensors prepared in Example 3 and Example 4 as a function of pressure are shown in FIG. Figure 4 The flexible pressure sensor prepared in Example 3 exhibits a pressure of 1.11 kPa -1 The sensitivity and linearity of the flexible pressure sensor prepared in Example 4 showed a sensitivity of 0.59 kPa -1 The sensitivity of Example 3 is 0.01 and the linearity is 0.95. Compared with Example 4, Example 3 shows higher sensitivity and linearity.

[0088] The dynamic capacitance response and recovery curves of the flexible pressure sensor prepared in Example 3 were repeatedly cycled for 10 times at 80 kPa, 250 kPa, 400 kPa, 650 kPa, 900 kPa, 1200 kPa, and 1400 kPa pressures. Figure 5 As shown, the sensor exhibits a stable and consistent capacitive response to the same load pressure and has good resolution for different load pressures. The capacitive response gradually increases with the increase of load pressure, indicating that the sensor has good repeatability and stability.

[0089] The response time and recovery time curves of the flexible pressure sensor prepared in Example 3 under a load of 1000 kPa are shown in FIG. Figure 6 As shown. The response and recovery time is defined as the time required for the capacitance value of the sensor to change to 90% of the stable value. It can be seen that the flexible pressure sensor exhibits a fast response and recovery under load pressure, with a time of 390 ms and 130 ms, respectively, indicating that the sensor can respond and recover quickly to external stimuli even under large pressure.

[0090] The stability test of the flexible pressure sensor prepared in Example 3 is as follows: Figure 7The sensor was subjected to 600 kPa pressure for 3500 cycles. During the multiple loading and releasing processes, the baseline of the sensor remained stable, and the capacitance response changed slightly. The capacitance response curves of the first 30 s and the last 30 s of the test were extracted and calculated along with the pressure change. The maximum deviation of the capacitance response was about 8%, proving that the sensor has good stability and durability during long-term use.

[0091] The pressure resolution test of the flexible pressure sensor prepared in Example 3 under a reference pressure of 50 kPa is as follows: Figure 8 When the reference pressure is 50 kPa, the sensor is loaded with a force of 35 kPa four times in a stepwise manner. From the enlarged graph of the curve, it can be seen that the sensor exhibits a stable and step-increasing capacitance response to 35 kPa, proving that the sensor has good resolution for 35 kPa pressure in the low pressure range of the detection range.

[0092] The pressure resolution test of the flexible pressure sensor prepared in Example 3 under a reference pressure of 1300 kPa is as follows: Fig. 9 When the reference pressure is 1300 kPa, the sensor is loaded with a force of 35 kPa four times in a stepwise manner. From the enlarged curve, it can be seen that the sensor exhibits a stable and step-increasing capacitance response to 35 kPa, proving that the sensor has good resolution capability for 35 kPa pressure in the medium pressure range of the detection range.

[0093] The pressure resolution test of the flexible pressure sensor prepared in Example 3 under a reference pressure of 2050 kPa is as follows: Fig.10 As shown. When the reference pressure is 2050 kPa, the sensor is loaded with a force of 35 kPa four times in a stepwise manner. From the enlarged curve, it can be seen that the sensor exhibits a stable and step-increasing capacitance response to 35 kPa, proving that the sensor has good resolution for 35 kPa pressure in the high pressure range of the detection range. It proves that the sensor detects smaller pressure signals in a wide pressure range.

Claims

1. A method for preparing an ion-type flexible pressure sensor with adjustable linear range, characterized in that: The steps are as follows: (1) Add 0.02-0.8 g of graphene Gr into 20 mL of deionized water and stir at 20-30 °C for 0.5-3 h until the graphene is evenly dispersed; add 0.1-2 g of waterborne polyurethane WPU to the obtained solution and stir at 20-30 °C for 1-5 h to obtain a Gr / WPU mixed solution; (2) Cut the polyurethane sponge into discs and place them in 10-50 mL of deionized water, ultrasonically clean them for 0.5-2 h, and then dry them at 50-70 °C to obtain polyurethane sponge discs with impurities removed; (3) placing the polyurethane sponge disc obtained in step (2) in the Gr / WPU mixed solution obtained in step (1), immersing it in ultrasonic bath for 0.5-3 h and then drying it at 50-70°C, using WPU as a binder to uniformly wrap Gr on the surface of the polyurethane sponge, thereby obtaining a Gr / WPU sponge; (4) Add 0.2-0.4 g of thermoplastic polyurethane (TPU) into 3 mL of N,N-dimethylformamide and stir at 60-80 °C for 1.5-3.0 h until the TPU is completely dissolved to obtain a TPU solution; (5) adding 0.2-0.4 g of ionic liquid ILs to the TPU solution obtained in step (4), stirring at 60-80 °C for 1.5-3.0 h to obtain a TPU / ILs mixed solution; (6) Take 2 mL of the TPU / ILs mixed solution obtained in step (5) and evenly drop it into a polytetrafluoroethylene mold, place it in a ventilated environment and dry it for 8 to 15 h to obtain a TPU / ILs film with a thickness of 0.2 to 0.5 mm, cut it into a circle, and obtain a TPU / ILs ion membrane; (7) cutting two fabric conductive tapes into a shape composed of a circular area and a rectangular area, and attaching them to the lower surface of the upper polyethylene terephthalate substrate and the upper surface of the lower polyethylene terephthalate substrate as the positive electrode and the negative electrode of the sensor, respectively; (8) Cutting off a circular area with the same diameter as the Gr / WPU sponge from the center of the polyurethane sponge to obtain a polyurethane sponge frame; attaching double-sided tape to the upper and lower surfaces of the polyurethane sponge, and embedding the Gr / WPU sponge obtained in step (3) into the polyurethane sponge frame to obtain a pressure-sensitive layer; (9) The upper polyethylene terephthalate substrate with a positive electrode on the lower surface produced in step (7) and the lower polyethylene terephthalate substrate with a negative electrode on the upper surface are used as the top layer and the bottom layer respectively, and the TPU / ILs ion membrane produced in step (6) and the pressure-sensitive layer produced in step (8) are placed between the positive electrode and the negative electrode in a top-down order, so that the circular areas of the positive electrode and the negative electrode, the TPU / ILs ion membrane, and the Gr / WPU sponge are aligned, and the sensor is bonded together using the double-sided tape on both sides of the pressure-sensitive layer in step (8), and a certain pressure is applied between the upper and lower substrates to obtain the flexible pressure sensor.

2. The method for preparing a linear range adjustable ionization type flexible pressure sensor according to claim 1, characterized in that: The thickness of the polyurethane sponge in step (2) and step (8) is 1-3 mm, and the density is 25-60 ppi.

3. The method for preparing a linear range adjustable ionization type flexible pressure sensor according to claim 1, characterized in that: The diameter of the polyurethane sponge disc in step (2) is 0.5-1.5 cm, and the diameter of the TPU / ILs ion membrane in step (6) is 0.5-1.5 cm.

4. The method for preparing a linear range adjustable ionization type flexible pressure sensor according to claim 1, characterized in that: In step (7), the diameter of the circular area of ​​the fabric conductive tape is 0.5-1.5 cm, the length of the rectangular area is 1.5-2.5 cm, and the width is 0.2-0.8 cm; the upper polyethylene terephthalate substrate and the lower polyethylene terephthalate substrate are rectangular structures with a length of 3-5.5 cm and a width of 1.5-2.5 cm.

5. The method for preparing a linear range adjustable ionization type flexible pressure sensor according to claim 1, characterized in that: In step (9), a pressure of 1-3N is applied between the upper and lower substrates to obtain the flexible pressure sensor.

6. An ion-type flexible pressure sensor with adjustable linear range, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 5.

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