A foam-based flexible tactile sensor and a method of manufacturing the same

Abstract

The application discloses a kind of foam-based flexible tactile sensor and its preparation method, the flexible tactile sensor has three-layer structure, middle layer is PEDOT:pss / rGO composite foam, the composite foam is tactile sensing material, and the upper and lower layers are both flexible PDMS film;The application uses simple and efficient hydrothermal synthesis method and subsequent flash instantaneous irradiation reduction method, and prepares a kind of three-dimensional porous PEDOT:pss / rGO composite foam, can effectively and maximumly keep the composite skeleton structure of original PEDOT:pss / GO foam, and makes PEDOT:pss polymer polymer and rGO sheet closely connected, so that PEDOT:pss / rGO composite foam has better mechanical elasticity and high conductivity, so that flexible tactile sensor has high sensitivity, ultra-low detection lower limit, short response time and good stability and other excellent performance, widely used in human health, motion monitoring and other fields.

Description

Technical Field

[0001] This invention relates to the field of flexible tactile sensing technology, specifically to a foam-based flexible tactile sensor and its preparation method, which uses freeze-drying and flash instantaneous irradiation reduction technology to prepare the foam-based flexible tactile sensor. Background Technology

[0002] With the advent of the information age and the rise of artificial intelligence, wearable electronic devices based on flexible pressure sensors have emerged for health monitoring and medical diagnosis. Traditional pressure sensors primarily use rigid semiconductor materials such as Si, Ge, and GaAs as substrates, making them inflexible and wear-resistant. Flexible pressure sensors, on the other hand, offer advantages such as excellent elasticity, small size, portability, simple manufacturing, and low cost. A pressure sensor is a physical sensor that converts mechanical force into an electrical signal. Based on this sensing principle, pressure sensors typically include piezoresistive, piezoelectric, and triboelectric types. Among these, piezoresistive sensors, due to their convenient data acquisition, high sensitivity, fast response speed, strong stability, and simple manufacturing process, have become ideal candidates for next-generation sensors.

[0003] Sensitivity and range are two crucial parameters for pressure sensors. High sensitivity and large range are highly sought-after, but achieving a balance between the two is difficult. Currently reported pressure sensors exhibit high sensitivity, but their high-sensitivity range is narrow. High-sensitivity and large-range pressure sensors can be obtained through the selection of sensor materials and structural design. Among currently popular piezoresistive sensing materials, graphene has become a research focus due to its excellent properties, such as good conductivity, high mechanical strength, and light weight. Although two-dimensional graphene-based thin-film pressure sensors can easily achieve high sensitivity and fast response, making them suitable for detecting minute deformations, they cannot operate effectively in real time under high pressure and compression. Therefore, the rational construction of foam-based pressure sensors with three-dimensional structures is a solution to the problem of the limited range of two-dimensional graphene pressure sensors. The hydrothermal reduction method, using PEDOT:pss and rGO as raw materials, employs a self-assembly process to easily obtain three-dimensional composite foams, and its simple preparation makes it easy for mass production. The polymer material poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT:pss) has high conductivity and is uniformly dispersed in water and polar organic solvents.

[0004] Chinese patent CN109273273A discloses a PAN-GO / PEDOT:PSS supercapacitor electrode material based on nanofiber yarn and its preparation method, including a skin layer and a core layer. The skin layer is twisted along the axial direction of the core layer to form a core-spun yarn structure. The skin layer is composed of PAN nanofibers and graphene oxide, the core layer is conductive cotton yarn, and conductive polymer PEDOT:PSS particles are attached to the surface of the skin layer. Using conductive cotton yarn as the core yarn and PAN-GO nanofibers wound and wrapped together as the skin layer to form a core-spun yarn, and then grafting PEDOT:PSS conductive organic material onto the surface layer, a supercapacitor electrode material with good cycle stability and high energy storage is prepared, and the cost is low. Chinese patent CN105905985A discloses the preparation and application of a graphene oxide GO / poly(3,4-ethylenedioxythiophene) PEDOT:poly(p-phenylene sulfonate) PSS modified graphite felt electrode for use in heterogeneous electro-Fenton systems. The modified graphite felt electrode is prepared using degreased and decontaminated graphite felt material as the working electrode, a platinum wire electrode as the counter electrode, a saturated calomel electrode as the reference electrode, and a mixture of graphene oxide suspension, 3,4-ethylenedioxythiophene, and poly(p-phenylene sulfonate) as the electrolyte. The modified graphite felt electrode is prepared using a cyclic voltammetric electropolymerization method. The modified graphite felt electrode applied to a heterogeneous electro-Fenton system can significantly improve the cathode conductivity and the catalytic activity of the redox reaction to generate H2O2. It can effectively improve the degradation and removal capacity of cationic dye wastewater; the modified electrode modification process is simple and easy to operate, with a long service life and strong stability, and has good application prospects; Chinese patent CN115891136A discloses a 3D printing ink and printing method for flexible organic electrochemical transistors, belonging to the field of organic electrochemical transistor technology; the base ink is a crosslinking agent obtained by mixing nanofiber cellulose NFC / polyvinyl alcohol PVA hydrogel with glutaraldehyde and then treating it with acid; the electrode ink is a reduced graphene oxide rGO / CNT electrode prepared by graphene oxide / carbon nanotube CNT; the active layer ink includes channel active layer ink and gate active layer ink; both the channel active layer ink and the gate active layer ink include PEDOT:PSS material; the insulating layer ink includes PDMS, but considering that the existing technology uses chemical reagents (such as hydrazine hydrate, citric acid, etc.) to reduce GO, the existing technology is slightly insufficient.

[0005] Chinese patent CN112713007A discloses an aerogel-based electrode, comprising reduced graphene oxide (rGO) and PEDOT:PSS. The aerogel formed by rGO and PEDOT:PSS is pressed to form an electrode sheet, with PEDOT:PSS incorporated into the interconnect structure of the rGO sheet. In the electrode, rGO primarily acts as the active material, while PEDOT:PSS serves as a separator and crosslinking agent between the rGO sheets, effectively preventing stacking between rGO layers and reducing the resistance at the rGO junctions. The layered structure of graphene and the excellent conductivity of PEDOT:PSS both contribute to the rapid transport of electrolyte ions. However, considering the differences in reduction methods, the reduction method in this application is significantly shorter and more efficient than existing technologies, which are somewhat lacking in the latter. Summary of the Invention

[0006] Technical problems to be solved: This application proposes a foam-based flexible tactile sensor and its preparation method to solve the problems of existing technologies, such as inability to bend or wear, difficulty in reconciling high sensitivity and large range, narrow high sensitivity range, inability to work effectively in real time under strong pressure and large compression, and small range of two-dimensional graphene pressure sensors.

[0007] Technical solution:

[0008] A foam-based flexible tactile sensor has a three-layer structure. The middle layer is a circular thin sheet of PEDOT:pss / rGO composite foam, which is the tactile sensing material. Two electrodes are provided on the tactile sensing material, and the two electrodes are respectively led to the outside of the foam-based flexible tactile sensor by wires. The upper and lower layers are both flexible PDMS films.

[0009] This application also discloses a method for preparing a foam-based flexible tactile sensor. The lower flexible PDMS film has a circular depression. A circular sheet of PEDOT:pss / rGO composite foam is embedded into the circular depression of the lower flexible PDMS film and covered with an upper flexible PDMS film to obtain a flexible tactile sensor.

[0010] As a preferred technical solution of this application, the circular sheet PEDOT:pss / rGO composite foam is prepared by freeze-drying and flash instantaneous irradiation reduction.

[0011] As a preferred technical solution of this application, the specific steps of the preparation method of the circular thin-sheet PEDOT:pss / rGO composite foam are as follows:

[0012] Step 1: Mix PEDOT:pss solution and GO solution at a mass ratio of 1:5-20 to obtain a mixture;

[0013] Step 2: Disperse the mixture ultrasonically for 15 minutes to obtain a homogeneous mixed solution;

[0014] Step 3: Transfer the homogeneous mixed solution to a sealed hydrothermal reactor with a Teflon liner, and react it in an electrically heated drying oven at 130°C for 9 hours to synthesize a hydrogel-like cylinder.

[0015] Step 4: Freeze the formed hydrogel cylinder at -69°C in a freezer for 20 hours;

[0016] Step 5: Then freeze-dry in a vacuum freeze dryer at -69℃ for 13 hours to obtain lightweight and dense PEDOT:pss / GO composite foam;

[0017] Step 6: Prepare a fluffy and porous PEDOT:pss / rGO composite foam by instantaneous flash irradiation of lightweight and dense PEDOT:pss / GO composite foam;

[0018] Step 7: Cut the fluffy and porous PEDOT:pss / rGO composite foam into circular thin sheets to obtain circular thin sheet PEDOT:pss / rGO composite foam.

[0019] As a preferred technical solution of this application, the ratio of PEDOT:pss solution is PEDOT:pss = 1.5:100, and the conductivity is 800 S / cm.

[0020] As a preferred embodiment of this application, the concentration of the GO solution is 2 mg / mL, and the mass ratio of PEDOT:pss solution to GO solution is 1:10.

[0021] As a preferred technical solution of this application, the circular sheet PEDOT:pss / rGO composite foam is connected to both sides of the PEDOT:pss / rGO composite foam using conductive silver paste, and then solidified at 100°C for 10 minutes.

[0022] As a preferred embodiment of this application, the Teflon liner has a capacity of 50 mL.

[0023] As a preferred technical solution of this application, the instantaneous flash irradiation involves charging the Heymann lamp to a discharge voltage of 380V and then discharging it instantaneously to release 6000 joules of energy in the form of a flash.

[0024] As a preferred technical solution of this application, the diameter of the circular sheet is 1-2 cm and the thickness is 0.2-0.6 cm.

[0025] The technical principle of this application is that both the formation mechanism of composite foam and the working mechanism of tactile sensors are applicable.

[0026] Working mechanism of the tactile sensor: When pressure is applied, the effective deformation volume of the pores in the PEDOT:pss / rGO composite foam sensitive material of the tactile sensor decreases with the increase of compression. The PEDOT:pss polymer and rGO sheet in the composite foam skeleton structure generate more contact points, reducing the contact resistance. When the pressure is removed, the PEDOT:pss / rGO composite foam gradually restores its original skeleton structure, and the contact resistance increases. The pore deformation of the composite foam leads to a change in resistance, which provides the sensor with high sensitivity.

[0027] Beneficial effects:

[0028] 1. This application employs a simple and efficient hydrothermal synthesis method followed by a flash instantaneous irradiation reduction method to prepare a three-dimensional porous PEDOT:pss / rGO composite foam. This instantaneous reduction process can effectively and maximally maintain the original composite skeleton structure of the PEDOT:pss / GO foam and tightly bond the PEDOT:pss polymer with the rGO sheet, thereby giving the prepared PEDOT:pss / rGO composite foam good mechanical elasticity and high electrical conductivity. In addition, the composite foam has a unique three-dimensional porous structure. These characteristics enable the prepared flexible tactile sensor to have excellent performance such as high sensitivity, large range, ultra-low detection limit, short response time and good stability.

[0029] 2. The flexible tactile sensor of this application will be widely used in fields such as human health and motion monitoring. Attached Figure Description

[0030] Figure 1 A detailed flowchart illustrating the fabrication of the foam-based flexible tactile sensor of this application;

[0031] Figure 2 This is a scanning electron microscope (SEM) image of the PEDOT:pss / rGO composite foam of this application;

[0032] Figure 3 This is a sensitivity diagram of the foam-based flexible tactile sensor of this application;

[0033] Figure 4 This is a multi-cycle piezoresistive response diagram of the foam-based flexible tactile sensor under different pressures according to this application;

[0034] Figure 5This is a diagram showing the minimum detectable limit of the foam-based flexible tactile sensor in this application;

[0035] Figure 6 This is a diagram illustrating the periodic pulse signal generated by the foam-based flexible tactile sensor used in this application for monitoring pulse.

[0036] Figure 7 The foam-based flexible tactile sensor of this application is used to monitor the vibrations generated in the throat during vocalization;

[0037] Figure 8 This application presents a foam-based flexible tactile sensor for monitoring vibrations generated by mouse clicks. Detailed Implementation

[0038] The embodiments of this application are described in detail below. These embodiments are implemented based on the technical solution of this application, and detailed implementation methods and specific operation processes are given. The protection scope of this application is limited to the following examples.

[0039] Example 1:

[0040] like Figure 1 As shown, the fabrication method of the foam-based flexible tactile sensor includes the following specific steps:

[0041] First, PEDOT:pss / GO composite foam was obtained by freeze-drying: PEDOT:pss solution and GO solution were mixed at mass ratios of 1:20, 1:10 and 1:5, respectively; then the mixture was ultrasonically dispersed for 15 minutes to obtain a homogeneous solution; subsequently, the homogeneous solution was transferred to a sealed hydrothermal reactor with a 50 mL Teflon liner and reacted in an electrically heated drying oven at 130°C for 9 hours to synthesize a shaped hydrogel-like cylinder; subsequently, the shaped hydrogel-like cylinder was frozen at -69°C for 20 hours in a freezer, and then freeze-dried in a vacuum freeze dryer at -69°C for 13 hours to obtain a lightweight and dense PEDOT:pss / GO composite foam; finally, a fluffy and porous PEDOT:pss / rGO composite foam was prepared by instantaneous flash irradiation of the lightweight and dense PEDOT:pss / GO composite foam. For comparison, pure rGO foam was manufactured using the same process route.

[0042] The surface morphology and internal microstructure of the prepared PEDOT:pss / rGO composite foam were observed and analyzed by SEM, such as... Figure 2As shown in the SEM images, the PEDOT:pss / rGO composite foam exhibits a distinctly uneven wrinkled structure. The foam interior displays a 3D porous structure. The PEDOT:pss polymer significantly enhances the protrusions and depressions of the PEDOT:pss / rGO composite foam, which is highly beneficial for improving the pressure sensitivity of the sensor. SEM images of the PEDOT:pss / rGO composite foam reveal that spindle-shaped PEDOT:pss polymers are tightly interwoven within pure PEDOT:pss, and multiple PEDOT:pss and rGO polymers combine to form a tangled layered structure within the PEDOT:pss / rGO composite foam.

[0043] To fabricate a flexible pressure sensor, the prepared PEDOT:pss / rGO composite foam was cut into circular thin sheets, and copper wires were connected to both sides of the PEDOT:pss / rGO composite foam using conductive silver paste. The foam was then solidified at 100°C for 10 minutes.

[0044] A flexible tactile sensor is fabricated by embedding a circular sheet of PEDOT:pss / rGO composite foam into a circular recess in a lower flexible PDMS film and then covering it with an upper flexible PDMS film.

[0045] To evaluate the sensing performance of a foam-based flexible tactile sensor under external force, the change in relative resistance (ΔR / R0) during a continuous increase in external force was investigated. Figure 3 As shown, the fabricated foam-based flexible tactile sensor exhibits three different linearity ranges within pressure ranges of 0–0.3 kPa, 0.3–1 kPa, and 1–2.7 kPa, with sensitivities of 2.32, 0.39, and 0.06 kPa, respectively. -1 It can be observed that, since the skeleton and pores of the PEDOT:pss / rGO composite foam have been compressed to a minimum, the resistance of the prepared pressure sensor almost reaches saturation under a pressure of 1 kPa.

[0046] Figure 4 The study demonstrates the relative resistance change of a foam-based flexible tactile sensor under different external forces, specifically through dynamic loading and unloading cycles with varying pressures applied to the sensor. Clearly, the relative resistance changes differently under different pressures, increasing with increasing pressure. Simultaneously, under the same pressure conditions, the relative resistance change remains stable, exhibiting a highly regular waveform. Therefore, the proposed PEDOT:pss / rGO composite foam pressure sensor can clearly detect different pressure levels.

[0047] Whether a pressure sensor can detect subtle changes in behavior depends on its detection limit. To obtain the lowest detection limit for a foam-based flexible tactile sensor, a sheet of lightweight paper was used as a weak external force to detect the sensor's piezoresistive response. Figure 5 As can be seen, the piezoresistive signal of the sensor can respond to the pressure of a sheet of paper being converted into approximately 3 Pa, indicating that the prepared PEDOT:pss / rGO composite foam pressure sensor can detect extremely small pressures in practical applications.

[0048] In summary, the fabricated foam-based flexible tactile sensor exhibits excellent performance, including high sensitivity, wide operating range, and good stability, and can be used to monitor some key physiological signals and subtle human movements. Pulse is an important indicator of health; therefore, pulse signal detection is helpful for real-time cardiovascular monitoring. The flexible PEDOT:pss / rGO composite foam pressure sensor is tightly attached to the volunteer's wrist to record signal changes generated by pulses. From the periodic pulse signal ( Figure 6 Three distinct peaks were clearly observed in the waveform: a percussion (P) wave, a tidal (T) wave, and a diploid (D) wave. To verify the sensor's speech recognition capability, the proposed PEDOT:pss / rGO composite foam pressure sensor was adhered to the throat. When the word "Nanjing" was repeated, the pressure sensor recorded a series of regular waveforms. Figure 7 Two significant characteristic peaks can be observed from one cycle of the signal, caused by the contraction and vibration of the throat during phonation. Furthermore, the proposed sensor was attached to the index finger to detect minute mouse clicks in real time. Figure 8 As shown.

[0049] Example 2:

[0050] A foam-based flexible tactile sensor has a three-layer structure. The middle layer is a circular thin-film PEDOT:pss / rGO composite foam, which serves as the tactile sensing material. Two electrodes are mounted on the tactile sensing material and are connected to the outside of the foam-based flexible tactile sensor via wires. The upper and lower layers are both flexible PDMS films. The method for fabricating the foam-based flexible tactile sensor involves embedding the circular thin-film PEDOT:pss / rGO composite foam into a circular recess in the lower flexible PDMS film, and then covering it with the upper flexible PDMS film, thus obtaining the flexible tactile sensor. The circular thin-film PEDOT:pss / rGO composite foam is prepared by freeze-drying and flash instantaneous irradiation reduction. The specific steps of the preparation method are as follows:

[0051] Step 1: Mix the PEDOT:pss solution and GO solution at a mass ratio of 1:10 to obtain a mixture;

[0052] Step 2: Disperse the mixture ultrasonically for 15 minutes to obtain a homogeneous mixed solution;

[0053] Step 3: Transfer the homogeneous mixed solution to a sealed hydrothermal reactor with a Teflon liner, and react it in an electrically heated drying oven at 130°C for 9 hours to synthesize a hydrogel-like cylinder.

[0054] Step 4: Freeze the formed hydrogel cylinder at -69°C in a freezer for 20 hours;

[0055] Step 5: Then freeze-dry in a vacuum freeze dryer at -69℃ for 13 hours to obtain lightweight and dense PEDOT:pss / GO composite foam;

[0056] Step 6: Prepare a fluffy and porous PEDOT:pss / rGO composite foam by instantaneous flash irradiation of lightweight and dense PEDOT:pss / GO composite foam;

[0057] Step 7: Cut the fluffy and porous PEDOT:pss / rGO composite foam into circular thin sheets to obtain circular thin sheet PEDOT:pss / rGO composite foam.

[0058] The PEDOT:pss solution has a ratio of PEDOT:pss = 1.5:100, a conductivity of 800 S / cm, a GO solution concentration of 2 mg / mL, and a mass ratio of PEDOT:pss solution to GO solution of 1:10. The instantaneous flash irradiation involves charging the Heymann lamp to its discharge voltage of 380V and then discharging it instantaneously, releasing 6000 joules of energy in the form of a flash.

[0059] The circular sheet of PEDOT:pss / rGO composite foam is made by connecting copper wires to both sides of the PEDOT:pss / rGO composite foam using conductive silver paste, and then solidified at 100°C for 10 minutes. The diameter of the circular sheet is 1-2 cm and the thickness is 0.2-0.6 cm.

[0060] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for fabricating a foam-based flexible tactile sensor, characterized in that: This foam-based flexible tactile sensor has a three-layer structure. The middle layer is a circular thin-film PEDOT:pss / rGO composite foam, which serves as the tactile sensing material. Two electrodes are mounted on this tactile sensing material, and these electrodes are connected to the outside of the foam-based flexible tactile sensor via wires. The upper and lower layers are both flexible PDMS films. The lower flexible PDMS film has a circular recess. The circular thin-film PEDOT:pss / rGO composite foam is embedded into this circular recess, and then the upper flexible PDMS film is covered, thus obtaining the flexible tactile sensor. The circular thin-film PEDOT:pss / rGO composite foam is prepared by freeze-drying and flash instantaneous irradiation reduction. The specific steps are as follows: Step 1: Mix PEDOT:pss solution and GO solution at a mass ratio of 1:5-20 to obtain a mixture; Step 2: Disperse the mixture ultrasonically for 15 minutes to obtain a homogeneous mixed solution; Step 3: Transfer the homogeneous mixed solution to a sealed hydrothermal reactor with a Teflon liner, and react it in an electrically heated drying oven at 130°C for 9 hours to synthesize a hydrogel-like cylinder. Step 4: Freeze the formed hydrogel cylinder at -69°C in a freezer for 20 hours; Step 5: Then freeze-dry in a vacuum freeze dryer at -69℃ for 13 hours to obtain lightweight and dense PEDOT:pss / GO composite foam; Step 6: Prepare fluffy and porous PEDOT:pss / rGO composite foam by instantaneous flash irradiation of lightweight and dense PEDOT:pss / GO composite foam; Step 7: Cut the fluffy and porous PEDOT:pss / rGO composite foam into circular thin sheets to obtain circular thin sheet PEDOT:pss / rGO composite foam.

2. The method for preparing the foam-based flexible tactile sensor according to claim 1, characterized in that: The PEDOT:pss solution has a ratio of PEDOT:pss = 1.5:100 and a conductivity of 800 S / cm.

3. The method for preparing the foam-based flexible tactile sensor according to claim 1, characterized in that: The concentration of the GO solution is 2 mg / mL, and the mass ratio of PEDOT:pss solution to GO solution is 1:

10.

4. The method for preparing the foam-based flexible tactile sensor according to claim 1, characterized in that, The circular sheet PEDOT:pss / rGO composite foam is connected to both sides of the PEDOT:pss / rGO composite foam using conductive silver paste, and then solidified at 100 °C for 10 minutes.

5. The method for preparing the foam-based flexible tactile sensor according to claim 1, characterized in that, The Teflon liner has a capacity of 50 mL.

6. The method for preparing the foam-based flexible tactile sensor according to claim 1, characterized in that, The instantaneous flash irradiation involves charging the Heymann lamp to its discharge voltage of 380 V, and then discharging it instantaneously to release 6000 joules of energy in the form of a flash.

7. The method for preparing the foam-based flexible tactile sensor according to claim 1, characterized in that, The diameter of the circular sheet is 1-2 cm and the thickness is 0.2-0.6 cm.

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