A flexible piezoresistive sensor based on porous network two-dimensional material and its preparation method

Abstract

The present invention belongs to the field of flexible sensors, specifically a flexible piezoresistive sensor based on a porous network two-dimensional material and its preparation method. The method comprises the following steps: S100 - preparing an SDS surfactant solution, wherein the solvent is a mixture of water and ethanol; S200 - using sandpaper as a template, dripping the SDS surfactant solution onto the sandpaper surface; S300 - pouring the PDMS mixture onto the sandpaper and SDS surfactant surfaces, heating and curing, and then removing the PDMS from the sandpaper surface to form a porous network PDMS substrate; S400 - ultrasonically immersing the prepared porous network PDMS substrate in a two-dimensional material dispersion and drying; S500 - preparing electrodes and encapsulating them, thereby completing the preparation of a flexible piezoresistive sensor based on a porous network two-dimensional material. The present invention uses sandpaper as a substrate and creates a uniform porous structure in the PDMS by dripping an SDS surfactant onto the sandpaper surface. Compared to preparation techniques using sacrificial templates, this technique has the advantages of no residue, simple experimental operation, and low preparation cost.

Description

Technical Field

[0001] The present invention belongs to the field of flexible sensors, and in particular relates to a flexible piezoresistive sensor based on a porous network two-dimensional material and a preparation method thereof. Background Art

[0002] Flexible piezoresistive sensors, with their simple structure, fast response, and high stability, hold broad application prospects in areas such as human motion detection, biomimetic electronic skin, and human-computer interaction. However, achieving low cost, high sensitivity, and a wide detection range remain key challenges for their future development. Research into novel sensing mechanisms, the integration of novel functional nanomaterials, and novel fabrication processes for flexible devices are key areas of research.

[0003] Three-dimensional porous materials are widely used in the preparation of flexible piezoresistive sensors due to their excellent performance and ease of integration. In 2017, Luo et al. grew a graphene network on nickel foam using a chemical vapor deposition process. By controlling the reaction time, the thickness of the graphene could be precisely controlled. They then cast PDMS and corroded the nickel foam with hydrochloric acid to produce a graphene-PDMS pore structure. The sensitivity and detection range of this sensor reached 15.9 kPa, respectively. -1 and 0~60 kPa ( Adv. Mater ., 2017, 29(40): 1702675.). In 2019, Sengupta et al. prepared PDMS sponge using sugar cubes as sacrificial templates and graphene as conductive material to prepare flexible piezoresistive sensors ( ACS Appl. Mater. Interfaces , 2019, 11(38): 35201-35211.). Patent CN111378205A proposes a flexible strain sensor prepared using sugar cubes as a template and chemically reduced graphene oxide as a conductive material. Patent CN112834089A uses sandpaper as a template to increase the roughness of the PDMS surface and NaCl as a sacrificial template to prepare a flexible piezoresistive sensor. The above technologies all use sacrificial template technology, which has a relatively complex preparation process and high cost. In addition, the sacrificial template will produce residues in the flexible substrate, which will have a significant impact on the performance of the sensor. Patent CN110701992B uses a sandpaper surface microstructure as a template for the preparation of a capacitive strain sensor. In this method, the sandpaper only serves as a template for forming a microstructure on the polydimethylsiloxane surface. In addition, this technology has the problems of complex preparation method, high cost, and narrow detection range. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a flexible piezoresistive sensor based on porous network two-dimensional material and a preparation method thereof.

[0005] The present invention adopts the following technical scheme: a flexible piezoresistive sensor based on a porous network two-dimensional material and a preparation method thereof, comprising the following steps: S100 ~ preparing an SDS surfactant solution, wherein the solvent is a mixture of water and ethanol; S200 ~ using sandpaper as a template, dripping the SDS surfactant solution onto the surface of the sandpaper; S300 ~ pouring a PDMS mixture on the surface of the sandpaper and the SDS surfactant, heating and curing, and then removing the PDMS from the sandpaper surface to obtain a porous network PDMS substrate; S400 ~ placing the obtained porous network PDMS substrate in a two-dimensional material dispersion for ultrasonic immersion and drying; S500 ~ preparing electrodes and encapsulating them to complete the preparation of the flexible piezoresistive sensor based on the porous network two-dimensional material.

[0006] In step S100 , the concentration of the SDS solution and the type of solvent will greatly affect the number and size of bubbles. The mass fraction of SDS in the SDS solution is 10%, and the solvent is a mixture of 75% alcohol and 25% water.

[0007] In step S200, the volume of the SDS solution affects the yield of bubbles. The sandpaper used has a size of 15 mm*10 mm, and the volume of the added SDS solution is 100 μL.

[0008] In step S200, sandpaper is used as a template. The roughness of its surface affects the amount of air trapped at the interface between PDMS and sandpaper during PDMS casting, which in turn affects the amount of blistering. 240-grit sandpaper is the optimal choice.

[0009] In step S300, the curing process of the PDMS mixture, that is, the heating temperature and time, will affect the distribution of bubbles. The curing process of the PDMS mixture adopts a heating temperature of 70°C and a time of 45 minutes.

[0010] In step S400, the two-dimensional material is graphene or transition metal sulfide or boron nitride or a combination of any two of graphene, transition metal sulfide and boron nitride or a combination of graphene, transition metal sulfide and boron nitride.

[0011] In step S400 , the concentration of the two-dimensional material solution is 2 mg / mL, and the solvent is N,N-dimethylformamide.

[0012] In step S400, the prepared porous network PDMS substrate is placed in a two-dimensional material dispersion and ultrasonically immersed for 20 minutes, and then dried at 75°C. The process is repeated 6 times to allow the two-dimensional material to be saturated in the porous network PDMS substrate and the initial resistance to stabilize.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) This invention develops a method for preparing a porous network structured flexible substrate without a sacrificial template. Using sandpaper as the substrate, a uniform porous structure is generated in PDMS by dripping SDS surfactant onto the sandpaper surface. Compared to preparation techniques with sacrificial templates, this technique has the advantages of no residue, simple experimental operation, and low preparation cost.

[0015] (2) The present invention ultrasonically immerses the porous network structured flexible substrate in a graphene solution, resulting in a highly sensitive sensor. The resulting flexible piezoresistive sensor has the advantages of high sensitivity and a wide detection range, and has promising application prospects in fields such as speech recognition and motion monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the preparation process of a flexible piezoresistive sensor based on porous network two-dimensional materials;

[0017] Figure 2 This is the SEM image of porous network graphene;

[0018] Figure 3 The relationship between the relative resistance change and pressure of the flexible piezoresistive sensor of porous network two-dimensional materials;

[0019] Figure 4 Repeatability results of flexible piezoresistive sensors based on porous network two-dimensional materials;

[0020] Figure 5 Figure 1 shows the detection of speech by a flexible piezoresistive sensor made of porous network two-dimensional materials;

[0021] Figure 6 Figure II shows the detection of speech by a flexible piezoresistive sensor made of porous network two-dimensional materials. DETAILED DESCRIPTION

[0022] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and specific embodiments. The following examples or drawings are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0023] S1. Preparation of porous network PDMS flexible substrate:

[0024] First, cut a piece of sandpaper with a mesh size of 15 mm x 10 mm and a mesh size of 240. Prepare a 10% SDS solution with a mass fraction of 10% and a solvent of 75% ethanol. Use a pipette to drop 100 μL of the SDS solution onto the sandpaper surface and let it sit for 1 minute.

[0025] Mix PDMS solution A and solution B in a mass ratio of 10:1 and stir thoroughly. Pour the PDMS mixture onto a sandpaper surface and dry it in a drying oven at 70°C for 45 minutes. Separate the PDMS from the sandpaper surface to form a porous network PDMS flexible substrate. Figure 1 Steps 1 through 3 illustrate the substrate preparation process. During the preparation process, sandpaper is used as a template. Due to the uneven surface of the sandpaper, air is trapped between the PDMS and the sandpaper during PDMS pouring. This is when the surfactant SDS on the sandpaper surface generates air bubbles. During the PDMS curing process, these bubbles remain stable within the flexible substrate, forming a porous network structure. Figure 1 Steps 1 to 3 in the figure show the preparation process of porous network PDMS.

[0026] S2. Fabrication of Flexible Piezoresistive Sensors Based on Porous Network 2D Materials:

[0027] The two-dimensional material used in the present invention is one or more of transition metal sulfides and boron nitride. Preferably, graphene is used as the two-dimensional material. A 2 mg / mL solution of the two-dimensional material is prepared in DMF. A flexible substrate is ultrasonically immersed in the two-dimensional material solution for 20 minutes, followed by drying at 75°C. This process is repeated six times. Interdigitated electrodes are drawn on the surface of a biaxially oriented polypropylene film using conductive silver paste and then encapsulated to produce a flexible piezoresistive sensor using a porous network two-dimensional material. Figure 1 Steps 3 to 5 in the figure show the preparation process of flexible piezoresistive sensors made of porous network two-dimensional materials. Figure 2 The figure shows an SEM image of porous network graphene. It can be seen from the figure that the graphene sheet has relatively uniform pores.

[0028] S3. Test results of the relative change in resistance of a flexible piezoresistive sensor based on porous network graphene at different pressures. ΔR is the resistance change, and R0 is the initial resistance. According to the sensitivity definition of piezoresistive sensors, the maximum sensitivity of this sensor reaches 52.24 kPa. -1 . Figure 3 The figure shows the relative change in resistance of the sensor under different pressures.

[0029] S4. Verification of Reproducibility:

[0030] like Figure 4 As shown in the figure, a certain pressure is applied to the sensor, and the initial resistance and real-time resistance change during the measurement process are collected using electrical measurement equipment, and a time-resistance change curve is plotted. This proves that the sensor has excellent repeatability.

[0031] S5. Voice Measurement:

[0032] like Figure 5 、 6 As shown, the flexible stress sensor is attached to the subject's hand and throat, and the pronunciations of "Hello", "Goodbye" and "Happy Birthday, Taiyuan University of Technology" are repeated. The initial resistance and real-time resistance changes during the measurement process are collected using electrical measuring equipment, and the time-resistance change rate curve is drawn as the voice signal curve.

[0033] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible piezoresistive sensor based on a porous network two-dimensional material, characterized by: The following steps are included: S100~preparing an SDS surfactant solution, wherein the solvent is a mixture of water and ethanol; S200~Using sandpaper as a template, add SDS surfactant solution to the sandpaper surface; S300~ The PDMS mixture is poured onto the surface of sandpaper and SDS surfactant. The surfactant SDS on the sandpaper surface will generate bubbles. During the PDMS heating and curing process, the bubbles are stably present in the flexible substrate. After curing at 70°C for 45 minutes, the PDMS is removed from the sandpaper surface to prepare a porous network PDMS substrate. S400~Place the prepared porous network PDMS substrate in the two-dimensional material dispersion and ultrasonically immerse for 20 minutes, then dry at 75°C, and repeat this process 6 times; S500~Prepare electrodes and encapsulate them to complete the preparation of flexible piezoresistive sensors based on porous network two-dimensional materials.

2. The method for preparing a flexible piezoresistive sensor based on a porous network two-dimensional material according to claim 1, characterized in that: In step S100, the mass fraction of SDS in the SDS solution is 10%, and the solvent is a mixture of 75% alcohol and 25% water.

3. The method for preparing a flexible piezoresistive sensor based on a porous network two-dimensional material according to claim 1, characterized in that: In the step S200, the size of the sandpaper used is 15 mm*10 mm, and the volume of the added SDS solution is 100 μL.

4. The method for preparing a flexible piezoresistive sensor based on a porous network two-dimensional material according to claim 1, characterized in that: In the step S200, the sandpaper is 240 mesh.

5. The method for preparing a flexible piezoresistive sensor based on a porous network two-dimensional material according to claim 1, characterized in that: In step S400, the two-dimensional material is one of graphene, transition metal sulfide, and boron nitride, or a combination of any two of graphene, transition metal sulfide, and boron nitride, or a combination of graphene, transition metal sulfide, and boron nitride.

6. The method for preparing a flexible piezoresistive sensor based on a porous network two-dimensional material according to claim 5, characterized in that: In the step S400, the concentration of the two-dimensional material dispersion is 2 mg / mL, and the solvent is N,N-dimethylformamide.

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