A flexible pressure sensor and preparation and application thereof

Abstract

The present application relates to a kind of sensor for capturing and identifying pressure signal and its preparation and application.The sensor is realized by piezoresistive effect pressure sensing, which is composed of three parts of sensitive layer, electrode, encapsulation layer.Sensitive layer is graphene composite silk fibroin aerogel material, its feature is with ordered three-dimensional porous layered structure, with small density, electrically conductive, compressible-rebound, non-toxic and other characteristics;Electrode is high-conductivity material, and encapsulation layer is flexible scalable polymer material.Benefiting from the excellent piezoresistive change and compression-rebound performance of graphene composite silk fibroin aerogel, the prepared flexible pressure sensor can not only quickly detect pressure and deformation, but also has excellent flexibility and durability.In addition, the preparation method of the sensor is simple, raw material is green and environmentally friendly, detection range is wide, and sensitivity linearity is high.Therefore, the sensor has the potential of large-scale manufacturing, and has broad application prospects in the field of flexible wearable electronic equipment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of flexible pressure sensors, and relates to a flexible pressure sensor and preparation and application thereof. BACKGROUND

[0002] Wearable electronic sensors refer to a kind of devices that can convert external stimuli into electrical signals, including capacitive, piezoelectric, piezoresistive, ionic electronic, etc. Among them, piezoresistive (based on piezoresistive effect) has a wide range of applications in health detection, medical diagnosis, motion capture, speech recognition, human-computer interaction, intelligent robots and other fields due to its simple reading, stable output, mature technology, high linearity and low power consumption. Piezoresistive sensors realize sensing by changing their resistance under applied pressure. The main structure includes a sensitive layer that changes resistance, an electrode layer that captures and transmits electrical signals, and a packaging layer that provides protection. The sensitive layer that realizes signal conversion is the most core structure of the sensor. Since wearable electronic sensors are mainly designed to be installed on the human body, they should not only have high flexibility and stretchability, but also have good sensitivity linearity and can detect a wide range of strains.

[0003] However, the mainstream piezoresistive sensors have a series of shortcomings such as short service life, slow response speed, poor detection limit, poor flexibility, and bulky equipment. Although traditional piezoresistive sensors based on semiconductors and metal foils have high cost-effectiveness, their sensitivity linearity is low and the sensing range is often less than 5%, making the development of piezoresistive flexible pressure sensors challenging. In addition, the sensitive layer structure of most piezoresistive sensors has an irreversible deformation problem, which is prone to collapse in multiple compression cycles, which seriously hinders the application of piezoresistive sensors.

[0004] Therefore, it is necessary and urgent to develop a piezoresistive flexible pressure sensor with high sensitivity linearity, fast response speed, low monitoring limit, wide detection range, long cycle period, good flexibility, and high conductive pressure, to realize efficient and accurate monitoring of various pressure signals including human physiological signals.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] In order to overcome the defects of the above piezoresistive pressure sensors, the first purpose of the present application is to provide a flexible pressure sensor that can adapt to various application scenarios and realize real-time detection and feedback of pressure in different environments, including but not limited to motion capture, speech recognition, health monitoring, and medical diagnosis.

[0007] The second purpose of the present application is to provide a preparation method of the above flexible pressure sensor

[0008] In order to achieve the above-mentioned object of the present application, the technical scheme is as follows:

[0009] A flexible pressure sensor, which comprises a graphene composite silk fibroin aerogel sensitive layer, a high-conductive material electrode layer and a flexible and stretchable polymer material packaging layer; the flexible pressure sensor has a sandwich structure, the high-conductive material electrode layer is placed at both ends of the graphene composite silk fibroin aerogel sensitive layer, and the polymer material packaging layer encapsulates the entire electrode layer and the sensitive layer to protect the flexible pressure sensor from being damaged.

[0010] Further, the graphene composite silk fibroin aerogel is prepared by an alkali-induced hydrothermal method assisted by freeze-drying technology from graphene oxide powder and a silk fibroin solution.

[0011] Still further, the graphene composite silk fibroin aerogel has a highly ordered anisotropic feature; the cross section has a layered concentric circle structure from the outside to the inside, and the longitudinal section has longitudinally distributed lamellas, and there are rich connecting structures between the lamellas.

[0012] Further, the graphene composite silk fibroin aerogel can be customized to the required size and shape by using numerical control cutting technology or laser engraving technology.

[0013] Further, the preparation method of the high-conductive material electrode layer is selected from one of a solid electrode connection method, a vacuum deposition technology and a chemical vapor deposition method.

[0014] Further, the polymer material packaging layer is selected from one of PDMS, PMMA and PE.

[0015] The present application provides a preparation method of the above-mentioned flexible pressure sensor, and the specific preparation method comprises the following steps.

[0016] (1) A certain mass of graphene oxide powder is dissolved in a proper amount of deionized water, and an ultrasonic and stirring process is performed to obtain a graphene oxide dispersion liquid;

[0017] (2) At 40 DEG C, a certain mass of an alkali inducer, a silk fibroin solution with a certain concentration and a certain mass of glucose are sequentially added to the graphene oxide dispersion liquid, the interval time for each addition is 30 min, the whole process is continuously stirred, and the mass ratio of the solutes in the whole mixed solution should meet the following mass ratio:

[0018] Graphene oxide powder: alkali inducer: glucose = 1:1:4, silk fibroin: graphene oxide powder ≤0.3, and the concentration of graphene oxide in the obtained mixed solution is equal to 4 mg / mL.

[0019] (3), the mixed solution of the above configuration is loaded into a sealed container, the loading amount is 2 / 3 of the sealed container, after sealing is completed, it is placed in an oven at 95 DEG C, and hydrothermal reaction is carried out for 3-6h;

[0020] (4), after the hydrothermal reaction is completed, graphene composite silk fibroin hydrogel is formed in the sealed container, the excess liquid in the sealed container is poured out, then 10% ethanol solution is repeatedly cleaned until the yellow color in the sealed container disappears;

[0021] (5), after cleaning is completed, all the liquid in the sealed container is poured out, and the graphene composite silk fibroin hydrogel is frozen in a refrigerator for 48h, and then freeze-dried in a freeze-drying machine, to obtain graphene composite silk fibroin aerogel;

[0022] (6), the graphene composite silk fibroin aerogel is cut into a certain size and shape by using numerical control cutting technology or laser engraving technology;

[0023] (7), one of solid electrode connection method, vacuum deposition technology, chemical vapor deposition method and magnetron sputtering method is selected, and electrodes are arranged at both ends of the graphene composite silk fibroin aerogel;

[0024] (8), one of PDMS, PMMA and PE materials is selected, and the entire electrode layer and sensitive layer are packaged, and thus a sandwich structure flexible pressure sensor is completed.

[0025] Further, the alkali inducer in step (2) is one of sodium hydroxide, potassium hydroxide and ammonia water;

[0026] Preferably, the alkali inducer is sodium hydroxide.

[0027] Further, the mesh number of the graphene oxide powder in steps (1)-(2) is selected to be 50-1000 mesh;

[0028] Preferably, the mesh number of the graphene oxide powder is selected to be 325 mesh.

[0029] The principle of the application is as follows:

[0030] The sensitive layer of the flexible pressure sensor prepared by the prior art is mostly a flexible polymer elastomer, and the way of converting the pressure signal into an electrical signal by relying on the movement, aggregation and entanglement of the polymer chain segments often has hysteresis, small detection range, low sensitivity, cannot respond to external pressure stimulation in time, cannot detect small stress and strain, and thus cannot realize high-precision measurement in language recognition and pulse detection. The application takes a different approach, and based on the piezoresistive effect principle, uses graphene composite silk fibroin aerogel as a flexible sensitive layer. The graphene composite silk fibroin aerogel has an anisotropic three-dimensionally interconnected porous layered structure, when subjected to external pressure, the aerogel network structure will deform, the contact area between layers will increase, and the resistance will decrease. Due to the presence of graphene, the aerogel sensitive layer has good electrical conductivity, and at the same time, thanks to the highly ordered macrostructure formed by the re-stacking of graphene nanosheets, the aerogel structure is stable, and the compression resilience is good, and the aerogel sensitive layer can be recycled for a long time. Due to the presence of silk fibroin nanofibers, the aerogel sensitive layer has good softness, and even under the action of small external pressure, it can quickly deform, and the resistance decreases rapidly, so the aerogel sensitive layer responds quickly to external pressure stimulation, and can effectively capture and identify small stress and strain. The unique graphene composite silk fibroin aerogel sensitive layer endows the flexible pressure sensor with high sensitivity linearity, fast response speed, low detection limit, large detection range, and at the same time, good recyclability and shape retention, so that it can be widely used in health detection, medical diagnosis, motion capture, language recognition, human-computer interaction, intelligent robots and other fields.

[0031] The application has the following beneficial effects:

[0032] (1) A flexible pressure sensor uses graphene composite silk fibroin aerogel as a sensitive layer, the graphene composite silk fibroin aerogel is ultra-light and highly conductive, has an ordered three-dimensionally interconnected porous layered structure, and the flexible pressure sensor based on the graphene composite silk fibroin aerogel can capture and quickly convert pressure signals in time, has the advantages of high sensitivity linearity, fast response speed, low detection limit and wide detection range, and can accurately identify human pulse signals.

[0033] (2) The flexible pressure sensor has good mechanical flexibility and periodic recyclability, can be conformally attached to the surface of the human skin or an object, will not suddenly fail mechanically under long-term work, has very good shape retention and durability, and can be used as a wearable device for a long time.

[0034] (3) The method for preparing the graphene composite silk fibroin aerogel as a sensitive layer is an alkali-induced hydrothermal method assisted by freeze-drying technology, which not only successfully integrates graphene and silk fibroin, but also has the characteristics of simple operation, simple equipment and safety and non-toxicity.

[0035] (4) The raw materials used in the graphene composite silk fibroin aerogel sensitive layer are natural flake graphite and natural renewable silk. These two green raw materials are widely available, inexpensive, and environmentally friendly. Moreover, the graphene composite silk fibroin aerogel contains only graphene and silk fibroin, which are non-toxic to the human body and nature. It can be directly applied to the skin and can be naturally degraded after use. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the specific embodiments or the prior art solutions will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the flexible pressure sensor of the present invention;

[0038] Figure 2 The field emission scanning image of the graphene composite silk fibroin aerogel provided in Example 1 of the present invention;

[0039] Figure 3 This is a durability test diagram of the flexible pressure sensor provided in Embodiment 1 of the present invention;

[0040] Figure 4 The image shows the radial artery pulse wave signal of the human body measured by the flexible pressure sensor provided in Embodiment 1 of the present invention.

[0041] Among them, 3-graphene composite silk fibroin aerogel sensitive layer, 2-highly conductive material electrode layer, and 1-flexible and stretchable polymer material encapsulation layer. Detailed Implementation

[0042] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1

[0044] like Figure 1As shown, a flexible pressure sensor is disclosed. The flexible pressure sensor structure includes: a graphene composite silk fibroin aerogel sensitive layer 3, a highly conductive material electrode layer 2, and a flexible and stretchable polymer material encapsulation layer 1. The flexible pressure sensor has a sandwich structure, with the highly conductive material electrode layer placed at both ends of the graphene composite silk fibroin aerogel sensitive layer. The polymer material encapsulation layer encapsulates the entire electrode layer and sensitive layer to protect the flexible pressure sensor from damage.

[0045] This invention provides a method for fabricating the aforementioned flexible pressure sensor, the specific fabrication method comprising the following steps:

[0046] (1) Weigh a certain amount of 325 mesh graphene oxide powder and dissolve it in an appropriate amount of deionized water. After sonication and stirring, obtain a graphene oxide dispersion.

[0047] (2) At 40℃, a certain mass of sodium hydroxide, a certain concentration of silk fibroin solution, and a certain mass of glucose are added sequentially to the graphene oxide dispersion. The interval between each addition is 30 min. The entire process is continuously stirred. The proportion of each solute in the entire mixed solution should meet the following mass ratio:

[0048] The ratio of graphene oxide powder to sodium hydroxide to glucose is 1:1:4, and the ratio of silk fibroin to graphene oxide powder is 0.20. The concentration of graphene oxide in the resulting mixed solution is 4 mg / mL.

[0049] (3) Fill a sealed container with the above-prepared mixed solution, filling it to 2 / 3 full. After sealing, place it in a 95℃ oven and allow it to react hydrothermally for 3-6 hours.

[0050] (4) After the hydrothermal reaction is completed, a graphene composite silk fibroin hydrogel is formed in a sealed container. Pour off the excess liquid in the sealed container and then wash it repeatedly with 10% ethanol solution until the yellow color in the sealed container disappears.

[0051] (5) After cleaning, pour out all the liquid in the sealed container, freeze it in the refrigerator for 48 hours, and then freeze-dry the graphene composite silk fibroin hydrogel in a freeze dryer to obtain graphene composite silk fibroin aerogel.

[0052] Figure 2 This is a field emission scanning image of the graphene-composite silk fibroin aerogel provided in Example 1 of the present invention.

[0053] From the above Figure 2 It is known that graphene-silk fibroin aerogel has an anisotropic, three-dimensionally interconnected porous layered structure. When subjected to external pressure, the aerogel network structure will deform, the contact area between layers will increase, and the resistance will decrease.

[0054] (6) Use CNC cutting technology to cut graphene composite silk fibroin aerogel into a certain size and shape;

[0055] (7) Use conductive silver paste to bond and fix copper foil to both ends of graphene composite silk fibroin aerogel;

[0056] (8) The entire electrode layer and the sensitive layer are encapsulated by wrapping with porous and breathable PE tape, thus completing the fabrication of a flexible pressure sensor with a sandwich structure.

[0057] The sensing performance of a flexible pressure sensor was obtained by measuring the electrical signal change under pressure using an electrochemical workstation. The pressure sensor exhibits a sensitivity linearity exceeding 0.99, a response time of 0.5 s, a mechanical detection limit of 0.35 kPa, and rapid response and recovery within a strain range of 0-60%. The flexible pressure sensor did not exhibit sudden mechanical failure under more than 12,000 cyclic loading-unloading tests, demonstrating its ability to operate continuously and stably for extended periods. The electrical signal change under cyclic testing is shown in the figure below. Figure 3 As shown.

[0058] Figure 4 The image shows the radial artery pulse wave signal of the human body measured by the flexible pressure sensor provided in Embodiment 1 of the present invention.

[0059] From the above Figure 4 It is known that the flexible pressure sensor can monitor the radial artery pulse wave signal of the human body.

[0060] Comparative Example 1

[0061] (1) Weigh a certain amount of 325 mesh graphene oxide powder and dissolve it in an appropriate amount of deionized water. After sonication and stirring, obtain a graphene oxide dispersion.

[0062] (2) At 40℃, a certain concentration of silk fibroin solution and a certain mass of glucose are added sequentially to the graphene oxide dispersion. The interval between each addition is 30 min. The mixture is stirred continuously throughout the process. The proportion of each solute in the entire mixed solution should meet the following mass ratio:

[0063] The ratio of graphene oxide powder to glucose is 1:4, and the ratio of silk fibroin to graphene oxide powder is 0.20. The concentration of graphene oxide in the resulting mixed solution is 4 mg / mL.

[0064] Due to the lack of alkali induction, graphene oxide and silk fibroin agglomerate severely under strong electrostatic attraction, resulting in a large amount of precipitate in the solution, making subsequent experiments impossible.

[0065] Comparative Example 2

[0066] (1) Weigh a certain amount of 325 mesh graphene oxide powder and dissolve it in an appropriate amount of deionized water. After sonication and stirring, obtain a graphene oxide dispersion.

[0067] (2) At 40℃, a certain mass of sodium hydroxide, a certain concentration of silk fibroin solution, and a certain mass of hydrazine hydrate are added sequentially to the graphene oxide dispersion. The interval between each addition is 30 min. The entire process is continuously stirred. The proportion of each solute in the entire mixed solution should meet the following mass ratio:

[0068] The ratio of graphene oxide powder to sodium hydroxide to hydrazine hydrate is 1:1, and the ratio of silk fibroin to graphene oxide powder is 0.20. The concentration of graphene oxide in the resulting mixed solution is 4 mg / mL.

[0069] In a hydrothermal environment where hydrazine hydrate is used as a reducing agent, it is difficult to successfully form a structurally stable hydrogel, making it impossible to conduct subsequent experiments.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 above is that:

[0072] In step (2), at 40°C, a certain mass of sodium hydroxide and a certain mass of glucose are added sequentially to the graphene oxide dispersion, with an interval of 30 minutes between each addition. The entire process is continuously stirred, and the proportion of each solute in the entire mixed solution should meet the following mass ratios:

[0073] The ratio of graphene oxide powder to sodium hydroxide to glucose is 1:1:4, and the concentration of graphene oxide in the resulting mixed solution is 4 mg / mL.

[0074] Due to the lack of silk fibroin, the resulting sensor has poor flexibility and cannot monitor pulse signals.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Example 1 above is that:

[0077] In step (2), at 40°C, a certain mass of sodium hydroxide, a certain concentration of silk fibroin solution, and a certain mass of ascorbic acid are added sequentially to the graphene oxide dispersion. The interval between each addition is 30 minutes. The entire process is continuously stirred. The proportion of each solute in the entire mixed solution should meet the following mass ratio:

[0078] The ratio of graphene oxide powder to sodium hydroxide to ascorbic acid is 1:1:2, and the ratio of silk fibroin to graphene oxide powder is 0.20. The concentration of graphene oxide in the resulting mixed solution is 4 mg / mL.

[0079] Due to the acid-base neutralization reaction between ascorbic acid and sodium hydroxide, the resulting aerogel structure is disordered and collapses under 500 load-unload tests.

[0080] Example 2

[0081] The difference between this embodiment and Embodiment 1 above is that:

[0082] In step (2), the ratio of silk fibroin to graphene oxide powder is 0.10.

[0083] Example 3

[0084] The difference between this embodiment and Embodiment 1 above is that:

[0085] In step (6), laser engraving technology is used to cut the graphene composite silk fibroin aerogel into a certain size and shape.

[0086] Example 4

[0087] The difference between this embodiment and Embodiment 1 above is that:

[0088] In step (7), the ITO / PET conductive film is directly bonded and fixed to both ends of the graphene composite silk fibroin aerogel.

[0089] Example 5

[0090] The difference between this embodiment and Embodiment 1 above is that:

[0091] In step (7), the graphene composite silk fibroin aerogel with the electrodes already fixed is first placed in a custom mold. Then, PDMS with added curing agent is poured into the mold. Finally, the PDMS is cured in an environment of 60-80℃ to achieve encapsulation of the entire electrode layer and the sensitive layer. The ratio of curing agent to PDMS should meet the following requirements:

[0092] Curing agent: PDMS = 1:10.

[0093] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A flexible pressure sensor, characterized by: The flexible pressure sensor comprises a graphene composite silk fibroin aerogel sensitive layer, a high-conductive material electrode layer and a flexible and stretchable polymer material packaging layer; the flexible pressure sensor has a sandwich structure, the high-conductive material electrode layer is arranged at two ends of the graphene composite silk fibroin aerogel sensitive layer, and the polymer material packaging layer is used to package the high-conductive material electrode layer and the graphene composite silk fibroin aerogel sensitive layer, so as to protect the flexible pressure sensor from being damaged; The specific preparation method of the flexible pressure sensor comprises the following steps: (1) a certain mass of graphene oxide powder is weighed and dissolved in a proper amount of deionized water, and then ultrasonic and stirring are performed to obtain a graphene oxide dispersion solution; (2) at 20-40℃, a certain mass of alkali inducer, a silk fibroin solution with a certain concentration and a certain mass of glucose are sequentially added into the graphene oxide dispersion solution, and the whole process is continuously stirred, and the mass ratio of each solute in the obtained mixed solution meets the following mass ratio: the mass ratio of the alkali inducer to the graphene oxide powder is 0.5-1.5, the mass ratio of the silk fibroin to the graphene oxide powder is 0.1-0.5, and the mass ratio of the glucose to the graphene oxide powder is 2-6; (3) the mixed solution is loaded into a sealed container, and the loading amount is 1 / 2 to 3 / 4 of the sealed container, then after the sealing is completed, the sealed container is placed in an oven at 90-100℃, and hydrothermal reaction is performed for 3-6h; (4) after the hydrothermal reaction is completed, graphene composite silk fibroin hydrogel is formed in the sealed container, the excess liquid in the sealed container is poured out, and then the sealed container is repeatedly cleaned with 10% ethanol solution until the yellow color disappears; (5) after the cleaning is completed, all the liquid in the sealed container is poured out, the graphene composite silk fibroin hydrogel is completely frozen at low temperature, and then the graphene composite silk fibroin hydrogel is freeze-dried in a freeze dryer to obtain graphene composite silk fibroin aerogel; (6) the graphene composite silk fibroin aerogel is cut into a certain size and shape by using numerical control cutting technology or laser engraving technology; (7) one of solid electrode connection method, vacuum deposition technology, chemical vapor deposition method and magnetron sputtering method is selected to arrange electrodes at two ends of the graphene composite silk fibroin aerogel; (8) one of PDMS, PMMA and PE materials is selected to package the whole high-conductive material electrode layer and the graphene composite silk fibroin aerogel sensitive layer, and thus a flexible pressure sensor with a sandwich structure is prepared; the alkali inducer in step (2) is sodium hydroxide; the mesh number of the graphene oxide powder is 325; the graphene composite silk fibroin aerogel is prepared by alkali-induced hydrothermal method and freeze-drying technology from graphene oxide powder and a silk fibroin solution; the graphene composite silk fibroin aerogel has highly ordered anisotropic characteristics; the cross section has a layered concentric circular structure from outside to inside, and the longitudinal section has longitudinally distributed lamellas, and there are rich connection structures between the lamellas; the graphene composite silk fibroin aerogel is customized into a required size and shape by using numerical control cutting technology or laser engraving technology; The preparation method of the high-conductivity material electrode layer is selected from one of solid-state electrode connection, vacuum deposition technology, chemical vapor deposition, and magnetron sputtering. The polymer material packaging layer is selected from one of PDMS, PMMA, and PE.

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