A flexible pressure sensor based on cellulose solid electrolyte membrane

Abstract

The present invention relates to a flexible pressure sensor based on a cellulose solid electrolyte membrane, belonging to the field of medical health. A cellulose solid electrolyte membrane and a PI immersion gold electrode using a phosphoric acid and urea phosphate dissolution system are used; phosphoric acid and urea phosphate can be used as both a dissolution system for cellulose and an electrolyte system for the electrolyte membrane, simplifying the preparation steps of the electrolyte membrane while also giving the electrolyte membrane good chemical stability and oxygen resistance. Both phosphoric acid and urea phosphate are completely degradable components and are more environmentally friendly than conventional electrolyte systems. The gold layer, nickel layer, and PI film of the PI immersion gold electrode form an embedded interlocking structure, which is more tightly combined, enhancing stability and mechanical properties while achieving excellent conductive properties.

Description

Technical Field

[0001] The present invention relates to a flexible pressure sensor based on a cellulose solid electrolyte membrane, belonging to the field of medical health. Background Art

[0002] Currently, pressure sensors are mainly divided into three categories: electrochemical pressure sensors based on metal corrosion effects, flexible pressure sensors based on ion paper, and pressure sensors based on MXene materials.

[0003] Electrochemical pressure sensors based on metal corrosion: The working principle is that under pressure, ion migration in a solid electrolyte accelerates the corrosion reaction of different electrodes (such as zinc and carbon electrodes), generating a potential difference change, which is then detected to reflect the pressure. The sensor consists of a solid electrolyte layer and two metal electrodes with different corrosion activities. Pressure causes the contact area between the electrolyte and the electrodes to change, thereby changing the electrochemical reaction rate. Its main disadvantages are slow response time. Since the corrosion reaction takes a certain amount of time, the dynamic response speed of the sensor is limited. Long-term reliability is poor, and the irreversible nature of metal corrosion may lead to degraded sensor performance and a short lifespan.

[0004] Flexible pressure sensor based on ion paper: The pressure is measured by changing the double-layer capacitance caused by the change in the contact area between the folded ion paper and the electrode. The electrode / ion paper / electrode sandwich structure is in face-to-face contact. The electrode is screen-printed with conductive silver paste on the designed area of ​​the ion paper surface to form a specific electrode pattern. The ion paper is folded to form a sensitive area. The mechanical strength is limited: the mechanical strength of the ion paper is low and it is easily damaged under high pressure conditions. There are stability issues. The stability of the ion material is poor and it may decompose or produce side reactions in high temperature, high potential or strong oxidizing environment. There is a risk of environmental pollution. The side reactions or decomposition of the ion material will produce toxic byproducts, which pose a threat to the environment. The preparation cost is high. The liquid ion material and its composite preparation process with the matrix are relatively complicated. The electrode is prepared by screen-printing conductive silver paste, which has poor stability.

[0005] MXene-based pressure sensors utilize the high conductivity and variable resistance of MXene. When pressure is applied to the sensor, the material's microstructure changes, resulting in a change in resistance, thereby detecting pressure. The structure consists of a MXene conductive layer, a flexible substrate (such as PDMS or TPU), and a protective layer. The MXene layer is prepared through coating or printing techniques to form a pressure-sensitive film. MXene materials are easily oxidized in air, causing degradation of electrical properties and affecting the long-term stability of the sensor. The preparation of MXene involves a complex chemical etching process, resulting in high production costs, which limits large-scale commercial applications. Summary of the Invention

[0006] According to the background problem, the problem to be solved by the present invention is:

[0007] How to prepare a pressure sensor with fast response, high stability, oxidation resistance, environmental protection and low cost.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A flexible pressure sensor based on a cellulose solid electrolyte membrane, which uses a cellulose solid electrolyte membrane in a phosphoric acid and urea phosphate dissolution system and a PI immersion gold electrode;

[0010] The preparation steps of the cellulose solid electrolyte membrane are:

[0011] S1. Urea phosphate and cellulose were added to phosphoric acid and completely mixed and dissolved by ultrasonication to obtain a mixed solution 1;

[0012] S2. PVA was added to deionized water, heated to melt at 90-95°C, and the PVA and water were mixed uniformly by stirring to obtain a PVA solution;

[0013] S3. The mixed solution 1 obtained in step S1 is added dropwise to the PVA solution obtained in step S2, with stirring maintained during the addition process; obtaining an electrolyte solution containing cellulose, namely, a mixed solution 2; the mass ratio of the mixed solution 1 added dropwise to the PVA solution is 1:10 to 1.3:10;

[0014] S4. The mixed solution 2 obtained in step S3 is poured into a mold and dried in a constant temperature drying oven at 30 to 35 ° C for 24 to 48 hours to obtain a cellulose solid electrolyte membrane;

[0015] The steps for preparing the PI immersion gold electrode are as follows:

[0016] (1) Cleaning the PI film by ultrasonic wave, placing the cleaned PI film in KOH solution for modification, and obtaining a modified PI film;

[0017] (2) immersing the modified PI film in a nickel sulfate solution at 45-50° C. to adsorb nickel ions on the surface of the PI film, thereby obtaining a PI film adsorbed with nickel ions;

[0018] (3) placing the PI film adsorbed with nickel ions in a sodium borohydride solution to reduce a nickel seed layer on the surface of the PI film to obtain a reduced PI film;

[0019] (4) placing the reduced PI film in a nickel precipitation solution at 85-90°C, a dense nickel layer will grow on the surface of the PI film to obtain a nickel-treated PI film;

[0020] (5) Immerse the nickel-treated PI film in a gold immersion solution at 85-90°C. At this time, a uniform and dense gold layer will grow on the surface of the PI film to obtain a PI gold immersion electrode.

[0021] Preferably, the cellulose solid electrolyte membrane has micro-columnar protrusions on its surface after being dried in a mold.

[0022] Preferably, in step S1, the concentration of phosphoric acid is 85 wt %, and the mass ratio of urea phosphate, cellulose and phosphoric acid solution is 1:2 to 6:1.74.

[0023] Preferably, in step S3, the mass ratio of the amount of the mixed solution 1 added dropwise to the PVA solution is 1:10.

[0024] Preferably, the concentration of the KOH solution in step (1) is 4M, the concentration of the nickel sulfate solution in step (2) is 0.05M, the concentration of the sodium borohydride solution in step (3) is 0.025M, and the nickel precipitation solution and gold precipitation solution are produced by Shenzhen Keslin Surface Treatment Materials Co., Ltd., the nickel precipitation solution model is KS-N110, and the gold precipitation solution model is HAU-99.

[0025] The electrolyte membrane uses the principle of double-layer capacitance. The principle of double-layer capacitance is that when the two electrodes of the capacitor are immersed in an electrolyte and a voltage is applied, the surface of the conductive electrode will adsorb ions with an opposite charge (such as positive charge adsorbing negative ions). The ions in the electrolyte approach the electrode surface, forming a layer of ion-enriched layer. This double layer composed of the charge on the electrode and the ions in the electrolyte is called a double layer. The double layer is transformed into a double-layer capacitor. Its working mechanism is that the electrode surface adsorbs ions with opposite charges to form a double layer. Energy is stored at the interface between the electrode and the electrolyte. No chemical reaction is involved. During the charge and discharge process, the ions only move in the electrolyte and do not participate in the reaction of the electrode material.

[0026] What is used in the present invention is phosphoric acid / urea phosphate system dissolving cellulose, compared with conventional ionic material dissolving cellulose, phosphoric acid is common chemical, raw material is abundant, preparation process is mature, urea phosphate is commonly used in fertilizer, soil conditioner and water treatment field, this mode is lower in cost, and does not require complicated preparation method. Phosphoric acid and urea phosphate are both completely degradable ingredients, more friendly to the environment, phosphoric acid chemical properties are stable, oxidation resistance is strong, the present invention also uses it as electrolyte system, real cellulose solid electrolyte membrane has good chemical stability and oxygen resistance. The electrolyte membrane with the addition of cellulose has high mechanical strength, can withstand greater force, and is not easily damaged.

[0027] A solid electrolyte membrane with added cellulose material is prepared into a micro-column through a mold. Under the action of pressure, the electrolyte membrane will deform, causing the contact area between the electrolyte membrane and the electrode to change. A double-layer capacitor will be formed in the contact part between the electrolyte membrane and the electrode. The change in capacitance can reflect the change in force. The advantage is that the charging and discharging speed is fast, so the response speed is fast. The ions only move in the electrolyte, there is no chemical reaction, and the long-term reliability is good.

[0028] The present invention adopts a PI thin film gold-immersion electrode. The principle is that potassium carboxylate will be produced on the surface of the PI thin film under the modification effect of the strong alkaline solution KOH. When the KOH-modified PI film is immersed in a NiSO4 solution, ion exchange will occur between K+ and Ni2-. After the ion exchange is completed, the nickel ions will be embedded in the surface structure of the PI film. Then, the reducing property of NaBH4 can be used to reduce Ni2+ to a Ni seed layer. On the basis of the seed layer, the PI surface is treated with a nickel-immersion solution to obtain a uniform and dense Ni metal layer. Subsequently, limited redox replacement occurs on the PI surface through the gold-immersion solution to obtain AuNPS deposited on the Ni-P layer. As the reaction time increases, a dense and stable Au layer is formed.

[0029] The gold layer, nickel layer, and PI film form an embedded interlocking structure, which is more tightly bonded, enhancing stability and mechanical properties, and achieving excellent conductivity. The thickness of the PI immersion gold electrode depends on the thickness of the PI film and can reach 25 microns, which is lighter and thinner, while retaining the excellent flexibility of the PI film.

[0030] The beneficial effects of the present invention are:

[0031] 1. Phosphoric acid and urea phosphate can be used as both a dissolving system for cellulose and an electrolyte system for the electrolyte membrane, which simplifies the preparation steps of the electrolyte membrane and at the same time makes the electrolyte membrane have good chemical stability and oxygen resistance.

[0032] 2. Phosphoric acid and urea phosphate are both completely degradable components and are more environmentally friendly than conventional electrolyte systems.

[0033] 3. The gold layer, nickel layer and PI film of the PI immersion gold electrode will form an embedded interlocking structure, which is more tightly combined, enhancing the stability and mechanical properties while achieving excellent conductive properties.

[0034] 4. The flexible pressure sensor obtained by the present invention adopts a cellulose solid electrolyte membrane and a PI immersion gold electrode, which makes the flexible pressure sensor respond faster, have higher stability, be more resistant to oxidation, and have low environmental cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1Pressure-capacitance relationship diagram of the flexible pressure sensor made from the cellulose solid electrolyte membrane sample of Example 1

[0036] Figure 2 Response and recovery time diagram of the flexible pressure sensor made from the cellulose solid electrolyte membrane sample of Example 1

[0037] Figure 3 Pressure-capacitance relationship diagram of the flexible pressure sensor made from the cellulose solid electrolyte membrane sample of Example 2

[0038] Figure 4 Response and recovery time diagram of the flexible pressure sensor made from the cellulose solid electrolyte membrane sample of Example 2

[0039] Figure 5 Pressure-capacitance relationship diagram of the flexible pressure sensor made from the cellulose solid electrolyte membrane sample of Example 3

[0040] Figure 6 Response and recovery time diagram of the flexible pressure sensor made from the cellulose solid electrolyte membrane sample of Example 3 DETAILED DESCRIPTION

[0041] In the following examples, the basic structure of the flexible sensor is as follows: the top and bottom layers are PI immersion gold electrodes with a thickness of 25 μm, the middle interlayer is a silicone support layer with a thickness of 150 μm, the silicone support layer has a central opening, and a cellulose solid electrolyte membrane is placed in the opening. The cellulose solid electrolyte membrane is divided into two parts: the bottom layer is a large disc with a diameter of 6 mm and a height of 50 μm, and the upper layer is composed of four micro-cylinders with a diameter of 1 mm and a height of 100 μm, providing sensitive deformation. The electrolyte membrane can be prepared into any shape using other molds as needed, all of which fall within the scope of protection of this patent.

[0042] The nickel immersion solution and gold immersion solution used are both from Shenzhen Kesilin Surface Treatment Materials Co., Ltd. The nickel immersion solution model is KS-N110, and the gold immersion solution model is HAU-99.

[0043] Example 1

[0044] Preparation of cellulose solid electrolyte membrane:

[0045] S1. 0.1 g of urea phosphate and 0.6 g of cellulose were added to 5 ml of phosphoric acid and stirred by ultrasonic dispersion for 15 minutes to completely mix and dissolve to obtain a mixed solution 1;

[0046] S2. 2 g of PVA was added to 18 ml of deionized water and heated to melt at 95 ° C; a magnetic stirrer was used to stir at 1000 rpm for 5 minutes to uniformly mix the PVA and water to obtain a PVA solution;

[0047] S3. The mixed solution 1 obtained in step S1 was added dropwise to the PVA solution obtained in step S2 in an amount of 2.17 g, and stirring was maintained during the addition; obtaining an electrolyte solution containing cellulose, ie, a mixed solution 2;

[0048] S4. Pour the mixed solution 2 obtained in step S3 into a mold and dry it in a constant temperature drying oven at 30° C. for 24 hours to obtain a cellulose solid electrolyte membrane.

[0049] Preparation of PI immersion gold electrode:

[0050] (1) Cleaning the PI film by ultrasonic wave, placing the cleaned PI film in a 4M KOH solution for modification to obtain a modified PI film;

[0051] (2) immersing the modified PI film in a 0.05 M nickel sulfate solution at 50° C. to adsorb nickel ions on the surface of the PI film, thereby obtaining a PI film adsorbed with nickel ions;

[0052] (3) placing the PI film adsorbed with nickel ions in a 0.025 M sodium borohydride solution to reduce a nickel seed layer on the surface of the PI film to obtain a reduced PI film;

[0053] (4) The reduced PI film is placed in a nickel precipitation solution at 95°C. A dense nickel layer will grow on the surface of the PI film, and a nickel-treated PI film is obtained;

[0054] (5) Immerse the nickel-treated PI film in a 95°C gold immersion solution. At this time, a uniform and dense gold layer will grow on the surface of the PI film to obtain a PI gold immersion electrode.

[0055] Depend on Figure 1 As can be seen in the figure, the curve shows the relationship between pressure and capacitance. The sensitivity is 0.49 in the 0-2N range, 0.38 in the 2-4N range, and 0.24 in the 4-10N range. The linearity for the corresponding ranges is 1%, 1.1%, and 0.9%. Within the 0-10N range, the sensitivity is 0.3 and the linearity is 2.46%.

[0056] Depend on Figure 2 It can be seen from the response time curve that the response time and recovery time of the sensor are both 380ms.

[0057] Example 2

[0058] Preparation of cellulose solid electrolyte membrane:

[0059] S1. 0.1 g of urea phosphate and 0.4 g of cellulose were added to 5 ml of phosphoric acid and stirred by ultrasonic dispersion for 15 minutes to completely mix and dissolve to obtain a mixed solution 1;

[0060] S2. 2 g of PVA was added to 18 ml of deionized water and heated to melt at 90 ° C; a magnetic stirrer was used to stir at 1000 rpm for 5 minutes to mix the PVA and water to obtain a PVA solution;

[0061] S3. The mixed solution 1 obtained in step S1 was added dropwise to the PVA solution obtained in step S2 in an amount of 2.6 g, and stirring was maintained during the addition; obtaining an electrolyte solution containing cellulose, ie, a mixed solution 2;

[0062] S4. Pour the mixed solution 2 obtained in step S3 into a mold and dry it in a constant temperature drying oven at 35° C. for 36 hours to obtain a cellulose solid electrolyte membrane.

[0063] Preparation of PI immersion gold electrode:

[0064] (1) Cleaning the PI film by ultrasonic wave, placing the cleaned PI film in a 4M KOH solution for modification to obtain a modified PI film;

[0065] (2) immersing the modified PI film in a 0.05 M nickel sulfate solution at 50° C. to adsorb nickel ions on the surface of the PI film, thereby obtaining a PI film adsorbed with nickel ions;

[0066] (3) placing the PI film adsorbed with nickel ions in a 0.025 M sodium borohydride solution to reduce a nickel seed layer on the surface of the PI film to obtain a reduced PI film;

[0067] (4) The reduced PI film is placed in a nickel precipitation solution at 90°C. A dense nickel layer will grow on the surface of the PI film, and a nickel-treated PI film is obtained;

[0068] (5) Immerse the nickel-treated PI film in a 90°C gold immersion solution. At this time, a uniform and dense gold layer will grow on the surface of the PI film to obtain a PI gold immersion electrode.

[0069] Depend on Figure 3 It can be seen that the sensitivity of the curve is 0.28 in the range of 0-2N, 0.38 in the range of 2-4N, and 0.17 in the range of 4-10N. The linearity is 2.7% in the range of 0-2N, 3.2% in the range of 2-4N, and 1.1% in the range of 4-10N.

[0070] Depend on Figure 4It can be seen from the response time curve that the response time and recovery time of the sensor are both 370ms.

[0071] Example 3 Preparation of Cellulose Solid Electrolyte Membrane

[0072] S1. 0.1 g of urea phosphate and 0.2 g of cellulose were added to 5 ml of phosphoric acid and stirred by ultrasonic dispersion for 15 minutes to completely mix and dissolve to obtain a mixed solution 1;

[0073] S2. 2 g of PVA was added to 18 ml of deionized water and heated to melt at 90 ° C; a magnetic stirrer was used to stir at 1000 rpm for 5 minutes to mix the PVA and water to obtain a PVA solution;

[0074] S3. The mixed solution 1 obtained in step S1 was added dropwise to the PVA solution obtained in step S2 in an amount of 2.0 g, and stirring was maintained during the addition; obtaining an electrolyte solution containing cellulose, ie, a mixed solution 2;

[0075] S4. Pour the mixed solution 2 obtained in step S3 into a mold and dry it in a constant temperature drying oven at 35° C. for 48 hours to obtain a cellulose solid electrolyte membrane.

[0076] Preparation of PI immersion gold electrode:

[0077] (1) Cleaning the PI film by ultrasonic wave, placing the cleaned PI film in a 4M KOH solution for modification to obtain a modified PI film;

[0078] (2) immersing the modified PI film in a 0.05 M nickel sulfate solution at 45° C. to adsorb nickel ions on the surface of the PI film, thereby obtaining a PI film adsorbed with nickel ions;

[0079] (3) placing the PI film adsorbed with nickel ions in a 0.025 M sodium borohydride solution to reduce a nickel seed layer on the surface of the PI film to obtain a reduced PI film;

[0080] (4) The reduced PI film is placed in a nickel precipitation solution at 90°C. A dense nickel layer will grow on the surface of the PI film, and a nickel-treated PI film is obtained;

[0081] (5) Immerse the nickel-treated PI film in a 90°C gold immersion solution. At this time, a uniform and dense gold layer will grow on the surface of the PI film to obtain a PI gold immersion electrode.

[0082] Depend on Figure 5It can be seen that the sensitivity of the curve is 0.72 in the range of 0-2N, 0.48 in the range of 2-4N, and 0.37 in the range of 4-10N. The linearity is 4.62% in the range of 0-2N, 2.93% in the range of 2-4N, and 1.71% in the range of 4-10N.

[0083] Depend on Figure 6 It can be seen from the response time curve that the response time and recovery time of the sensor are both 380ms.

[0084] In summary, the flexible pressure sensor made of cellulose solid electrolyte membrane has a fast response, accurate and stable sensing, and is an excellent flexible pressure sensor.

Claims

1. A flexible pressure sensor based on cellulose solid electrolyte membrane, characterized in that: A cellulose solid electrolyte membrane and PI immersion gold electrode using a phosphoric acid and urea phosphate dissolution system were used; The preparation steps of the cellulose solid electrolyte membrane are: S1. Urea phosphate and cellulose were added to phosphoric acid and completely mixed and dissolved by ultrasonication to obtain a mixed solution 1; S2. PVA was added to deionized water, heated to melt at 90-95°C, and the PVA and water were mixed uniformly by stirring to obtain a PVA solution; S3. The mixed solution obtained in step S1 1 was added dropwise to the PVA solution obtained in step S2, and stirring was maintained during the addition; Obtaining an electrolyte solution in which cellulose is dissolved, namely, mixed solution 2; the mass ratio of the mixed solution 1 added dropwise to the PVA solution is 1:10 to 1.3:10; S4. The mixed solution 2 obtained in step S3 is poured into a mold and dried in a constant temperature drying oven at 30 to 35 ° C for 24 to 48 hours to obtain a cellulose solid electrolyte membrane; The steps for preparing the PI immersion gold electrode are as follows: (1) Cleaning the PI film by ultrasonic wave, placing the cleaned PI film in KOH solution for modification, and obtaining a modified PI film; (2) immersing the modified PI film in a nickel sulfate solution at 45-50° C. to adsorb nickel ions on the surface of the PI film, thereby obtaining a PI film adsorbed with nickel ions; (3) placing the PI film adsorbed with nickel ions in a sodium borohydride solution to reduce a nickel seed layer on the surface of the PI film to obtain a reduced PI film; (4) placing the reduced PI film in a nickel precipitation solution at 85-90°C, a dense nickel layer will grow on the surface of the PI film to obtain a nickel-treated PI film; (5) Immerse the nickel-treated PI film in a gold immersion solution at 85-90°C. At this time, a uniform and dense gold layer will grow on the surface of the PI film to obtain a PI gold immersion electrode.

2. A flexible pressure sensor based on cellulose solid electrolyte membrane according to claim 1, characterized in that: After being dried in a mold, the cellulose solid electrolyte membrane has micro-columnar protrusions on its surface.

3. The flexible pressure sensor based on cellulose solid electrolyte membrane according to claim 1, characterized in that: In the step S1, the concentration of phosphoric acid is 85 wt %, and the mass ratio of urea phosphate, cellulose and phosphoric acid solution is 1:2 to 6:1.

74.

4. The flexible pressure sensor based on cellulose solid electrolyte membrane according to claim 1, characterized in that: The mass ratio of the amount of the mixed solution 1 added dropwise to the PVA solution in step S3 is 1:

10.

5. A flexible pressure sensor based on a cellulose solid electrolyte membrane according to claim 1, characterized in that: The concentration of the KOH solution in step (1) is 4M, the concentration of the nickel sulfate solution in step (2) is 0.05M, and the concentration of the sodium borohydride solution in step (3) is 0.025M. The nickel precipitation solution and the gold precipitation solution are produced by Shenzhen Keslin Surface Treatment Materials Co., Ltd., and the nickel precipitation solution model is KS-N110, and the gold precipitation solution model is HAU-99.

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