CN114777965A - Flexible capacitive pressure sensor and preparation method thereof - Google Patents
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- G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
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- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
- A61B2562/02—Details of sensors specially adapted for in-vivo measurements
- A61B2562/0247—Pressure sensors
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Abstract
The invention discloses a flexible capacitive pressure sensor and a preparation method thereof, and relates to the technical field of sensing devices, wherein the flexible capacitive pressure sensor sequentially comprises the following components from bottom to top: the flexible electrode comprises a first flexible electrode, a first flexible medium layer and a second flexible electrode, wherein the first flexible electrode and the second flexible electrode respectively comprise a flexible substrate with a wrinkled surface and metal nanowires dispersed on the wrinkled surface. Because the flexible electrode comprises the flexible substrate with the wrinkled surface, and the metal nanowires are dispersed on the wrinkled surface of the flexible substrate, even if the flexible electrode is stretched, the wrinkles are unfolded, and the density of the metal nanowires dispersed on the wrinkled surface can still keep good conductive performance of the flexible electrode, so that the sensitivity of the sensor can be basically unchanged.
Description
Technical Field
The invention relates to the technical field of sensing devices, in particular to a flexible capacitive pressure sensor and a preparation method thereof.
Background
With the rapid development of artificial intelligence and internet of things technology, the flexible pressure sensor has received extensive attention from the scientific research and industrial fields as a key component in wearable electronic equipment for motion monitoring, health monitoring, medical diagnosis, tactile perception and the like. The flexible capacitive pressure sensor has the advantages of high sensitivity, high response speed, low hysteresis and the like, and has wide application prospect.
However, such sensors also have a lot of practical problems in practical application. For example, when the flexible capacitive pressure sensor is applied to human health monitoring or touch sensing, because human skin has a certain extensibility, the current flexible capacitive pressure sensor is difficult to extend together with human skin, and thus the monitoring result is erroneous. The individual flexible capacitive pressure sensors are, however, to some extent coextensive with the human skin and can be monitored. However, after extension, the sensitivity rapidly decreases, which also causes test errors.
Disclosure of Invention
The invention provides a flexible capacitive pressure sensor which has good ductility and can keep the sensitivity basically unchanged after being extended.
The invention provides a flexible capacitive pressure sensor, which sequentially comprises the following components from bottom to top: the flexible electrode comprises a first flexible electrode, a first flexible medium layer and a second flexible electrode, wherein the first flexible electrode and the second flexible electrode respectively comprise a flexible substrate with a corrugated surface and metal nanowires dispersed on the corrugated surface.
Further, the flexible capacitive pressure sensor further comprises a second flexible dielectric layer covering the wrinkled surface with the metal nanowires.
Optionally, the second flexible dielectric layer is made of polydimethylsiloxane.
Optionally, the flexible substrate and the first flexible dielectric layer are both made of polydimethylsiloxane.
Optionally, the metal nanowires are copper nanowires.
The invention provides a preparation method of a flexible capacitive pressure sensor, which comprises the following steps: (1) preparing a flexible electrode comprising a flexible substrate having a wrinkled surface and metal nanowires dispersed on the wrinkled surface; (2) preparing a first flexible medium layer; (3) and encapsulating the first flexible medium layer between the two flexible electrodes, and leading out an electrode lead from the flexible electrode.
Further, the step (1) includes: (a) stretching the substrate material, and then placing the substrate material in an ultraviolet ozone environment for irradiation; (b) cleaning the base material still in a stretched state, and then drying; (c) uniformly dispersing the metal nanowires in a liquid organic matter to form a nanowire organic liquid, then spraying the nanowire organic liquid on the surface of the dried substrate material, and air-drying; (d) removing organic matters coated around the metal nanowires on the sprayed substrate material; (e) curing the base material; (f) releasing the stretched substrate material to a natural state to form the flexible substrate having the wrinkled surface on which the metal nanowires are dispersed.
Optionally, between the step (d) and the step (e), further comprising: (g) forming a first dielectric material solution; (h) and spin-coating the first medium material solution on the metal nano wire to form a second flexible medium layer.
Optionally, the second flexible dielectric layer is made of polydimethylsiloxane.
Further, the step (2) comprises: (A) forming a second dielectric material solution; (B) spin coating the second medium material solution on a substrate with a smooth surface; (C) solidifying the second medium material solution on the substrate to form the first flexible medium layer; (D) and peeling the first flexible medium layer from the substrate.
Optionally, the flexible substrate and the first flexible dielectric layer are both made of polydimethylsiloxane.
Optionally, the metal nanowire is a copper nanowire.
In the flexible capacitive pressure sensor and the preparation method thereof provided by the invention, as the flexible electrode in the flexible capacitive pressure sensor comprises the flexible substrate with the wrinkled surface, and the metal nanowires are dispersed on the wrinkled surface of the flexible substrate, even if the flexible electrode is stretched, the wrinkles are unfolded, and the density of the metal nanowires dispersed on the wrinkled surface can still keep the good conductivity of the flexible electrode, the sensitivity of the sensor can be ensured to be basically unchanged, in addition, the wrinkles of the flexible substrate can reduce the stretching stress, and the stretching is more convenient, so that the sensor has better ductility. In addition, the preparation method has the advantages of no pollution, low equipment cost, simple process, low cost, large-area large-scale production, high stability and wide application prospect.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is an exploded perspective view of a flexible capacitive pressure sensor according to an embodiment of the present invention;
fig. 2 is a schematic cross-sectional structural diagram of a flexible capacitive pressure sensor according to an embodiment of the present invention;
fig. 3 is a schematic perspective view and a partial microscopic image of a flexible electrode in a flexible capacitive pressure sensor according to an embodiment of the present invention;
fig. 4 is a schematic cross-sectional structural view of a flexible electrode in a flexible capacitive pressure sensor according to an embodiment of the present invention;
fig. 5 is a schematic diagram illustrating a relationship between an elongation and a sensitivity of a flexible capacitive pressure sensor according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
In order to make the technical scheme of the invention more clear, the following detailed description of the embodiments of the invention is made with reference to the accompanying drawings.
An embodiment of the present invention provides a flexible capacitive pressure sensor, as shown in fig. 1 to 3, the flexible capacitive pressure sensor in the embodiment sequentially includes, from bottom to top: the flexible display device comprises a first flexible electrode 11, a first flexible medium layer 12 and a second flexible electrode 13, wherein the first flexible electrode 11 and the second flexible electrode 13 each comprise a flexible substrate A with a wrinkled surface and metal nanowires B dispersed on the wrinkled surface.
In the flexible capacitive pressure sensor provided by the embodiment of the invention, the flexible electrodes (11,13) comprise the flexible substrate A with the wrinkled surface, and the metal nanowires B are dispersed on the wrinkled surface of the flexible substrate A, so that even if the flexible electrodes are stretched, the wrinkles are unfolded, and the density of the metal nanowires B dispersed on the wrinkled surface can still keep the good conductivity of the flexible electrodes, thereby ensuring that the sensitivity of the sensor is basically unchanged.
The flexible capacitive pressure sensor provided by the embodiment of the invention can also include a second flexible medium layer 42 covering the wrinkled surface with the metal nanowires 41, that is, the second flexible medium layer 42 is formed on the wrinkled surface of the flexible substrate 43 and covers the metal nanowires 41, as shown in fig. 4.
As known to those skilled in the art, the metal nanowires 41 are bonded to the flexible substrate 43 by van der waals force, and are particularly easy to fall off, and the metal nanowires are easy to be oxidized and fail, so that the metal nanowires can be prevented from falling off during use and can also be prevented from being oxidized and failing by forming the second flexible dielectric layer 42.
In the above embodiment, the second flexible dielectric layer may be made of PDMS (Polydimethylsiloxane), which has physiological inertia, good chemical stability, electrical insulation, weather resistance, good hydrophobicity, and high shear resistance, and can be used at-50 ℃ to 200 ℃ for a long time.
In addition, the flexible substrate and the first flexible medium layer can be both made of PDMS.
The metal nanowires in the above embodiments can be copper nanowires, which have good conductivity, but are particularly easy to be oxidized to lose conductivity, and the second flexible dielectric layer covers the surface of the copper nanowires to prevent oxidation.
The embodiment of the invention also provides a preparation method of the flexible capacitive pressure sensor, which comprises the following steps.
(1) Flexible electrodes, as shown in fig. 1 to 4 (a first flexible electrode 11 and a second flexible electrode 13), were prepared, including a flexible substrate a having a wrinkled surface and metal nanowires B dispersed on the wrinkled surface. The flexible substrate A can be prepared by adopting PDMS material.
(2) The first flexible dielectric layer 12 is made of PDMS material.
(3) The first flexible dielectric layer 12 is encapsulated between the two flexible electrodes (11,13) and electrode leads (C and D in fig. 3) are led out from the flexible electrodes.
In the flexible capacitive pressure sensor prepared by the preparation method of the flexible capacitive pressure sensor provided by the embodiment of the invention, the flexible electrode comprises the flexible substrate with the wrinkled surface, and the metal nanowires are dispersed on the wrinkled surface of the flexible substrate, so that even if the flexible electrode is stretched, the wrinkles are unfolded, and the density of the metal nanowires dispersed on the wrinkled surface can still keep the good conductivity of the flexible electrode, thereby ensuring that the sensitivity of the sensor is basically unchanged.
Wherein, the step (1) is used for preparing the flexible electrode and comprises the following steps.
(a) After stretching the base material, the base material is placed in an ultraviolet ozone environment for irradiation.
(b) The base material still in the stretched state is washed and then dried.
(c) And uniformly dispersing the metal nanowires in a liquid organic matter to form a nanowire organic liquid, then spraying the nanowire organic liquid on the surface of the dried substrate material, and air-drying.
(d) And removing the organic matter coated around the metal nano wire on the sprayed substrate material.
(e) The base material is cured.
(f) Releasing the stretched substrate material to a natural state to form a flexible substrate having a wrinkled surface on which the metal nanowires are dispersed.
In addition, the method can further comprise the following steps between the step (d) and the step (e) for forming a second flexible medium layer on the metal nanowires, preventing the metal nanowires from falling off, and preventing the metal oxidation phenomenon from occurring.
(g) A first dielectric material solution is formed.
(h) The solution of the first dielectric material is spin coated on the metal nanowires to form a second flexible dielectric layer (42 in fig. 4).
The second flexible dielectric layer may be made of PDMS.
In addition, the step (2) for preparing the first flexible medium layer may include the following steps.
(A) A second dielectric material solution is formed.
(B) The second dielectric material solution is spin coated on a substrate having a smooth surface.
(C) And curing the second medium material solution on the substrate to form the first flexible medium layer.
(D) And peeling the first flexible medium layer from the substrate.
In the above embodiments, the metal nanowires may be copper nanowires.
Therefore, the preparation method has the advantages of no pollution, low equipment cost, simple process, low cost, large-area large-scale production, high stability and wide application prospect. The flexible capacitive pressure sensor prepared by the method has the advantages of excellent performance, low cost, simple process and high repeatability.
Three specific examples of the preparation method are given below, and the sensitivity variation of each example when the pressure test is carried out in different stretching ranges is given.
Example 1
1. After the base material (PDMS) was stretched by 100%, it was left to be irradiated in an ultraviolet ozone environment for 60 minutes.
2. And ultrasonically cleaning the base material in the stretching state for 5 minutes by adopting acetone, absolute ethyl alcohol and deionized water, and then drying.
3. And uniformly dispersing the copper nanowires in isopropanol, transferring the copper nanowires into a spray bottle, aligning the spray bottle to the surface of the dried substrate material, spraying for 15 times, and naturally drying in the air.
4. And horizontally placing the sprayed substrate material into glacial acetic acid for 20 seconds, taking out the substrate material, and then placing the substrate material into a blast oven for drying at 80 ℃, so as to remove organic matters coated around the copper nanowires.
5. A first dielectric material (PDMS) is dissolved in n-hexane to prepare a diluted PDMS solution, and the ratio of PDMS to n-hexane is 1: 20.
6. The diluted PDMS solution was spin coated on copper nanowires at 2000 rpm and cured at 50 ℃ for 10 hours.
7. Releasing the stretched substrate material to a natural state to form a flexible substrate having a wrinkled surface on which the copper nanowires are dispersed.
8. Mixing the PDMS prepolymer solution and a curing agent into a viscous solution according to a certain volume ratio of 5:1, defoaming, and adding a certain amount of deionized water according to a ratio of 1:5 to the PDMS solution. Stirring at 600r/min for 20min on a magnetic stirrer to form a second medium material solution.
9. And (3) spin-coating the stirred second medium material solution on a quartz plate (substrate) with a smooth surface at the speed of 500r/min for 5 minutes, curing at 100 ℃ for 1 hour to form a PDMS porous medium layer, namely a first flexible medium layer, and stripping the PDMS porous medium layer from the quartz.
10. And (4) encapsulating the PDMS porous dielectric layer in the flexible electrode prepared after the step (7) in a sandwich structure mode, and respectively leading out electrode leads from the upper layer of flexible electrode and the lower layer of flexible electrode to obtain the flexible capacitive pressure sensor.
And (4) a pressure test result: the prepared flexible capacitive pressure sensor can be used for carrying out pressure test within the stretching range of 0-210%, and the sensitivity of the flexible capacitive pressure sensor is kept unchanged within the stretching range of 0-70%.
Example 2
1. After stretching the base material (PDMS) by 200%, the substrate was placed in an ultraviolet ozone environment and irradiated for 5 minutes.
2. And ultrasonically cleaning the base material in the stretching state for 10 minutes by adopting acetone, absolute ethyl alcohol and deionized water, and then drying.
3. And uniformly dispersing the copper nanowires in isopropanol, transferring the mixture into a spray bottle, aligning the spray bottle to the surface of the dried substrate material, spraying for 25 times, and naturally drying.
4. And horizontally placing the sprayed substrate material into glacial acetic acid for 40 seconds, taking out the substrate material, placing the substrate material into a blast oven for drying at 50 ℃, and removing organic matters coated around the copper nanowires.
5. Dissolving a first dielectric material (PDMS) in n-hexane to prepare a diluted PDMS solution, wherein the ratio of the PDMS to the n-hexane is 1: 100.
6. The diluted PDMS solution was spin coated on copper nanowires at 500 rpm and cured at 100 ℃ for 1 hour.
7. Releasing the stretched substrate material to a natural state to form a flexible substrate having a wrinkled surface, the copper nanowires being dispersed on the wrinkled surface.
8. Mixing PDMS prepolymer solution and curing agent into viscous solution at a certain volume ratio of 15:1, defoaming, and adding a certain amount of deionized water at a ratio of 1:2 to PDMS solution. Stirring the mixture on a magnetic stirrer at 2000r/min for 5min to form a second medium material solution.
9. And (3) spin-coating the stirred second medium material solution on a quartz plate (substrate) with a smooth surface at the speed of 3000r/min for 1 minute, curing at 50 ℃ for 10 hours to form a PDMS porous medium layer, namely a first flexible medium layer, and stripping the PDMS porous medium layer from the quartz.
10. And (4) encapsulating the PDMS porous medium layer in the flexible electrode prepared after the step (7) in a sandwich structure manner, and respectively leading out electrode leads from the upper and lower flexible electrodes to obtain the flexible capacitive pressure sensor.
And (4) a pressure test result: the prepared flexible capacitive pressure sensor can be used for carrying out pressure test within the stretching range of 0-200%, and the sensitivity of the flexible capacitive pressure sensor is kept unchanged within the stretching range of 0-80%.
Example 3
1. After the base material (PDMS) was stretched by 150%, it was left to be irradiated in an ultraviolet ozone environment for 10 minutes.
2. And ultrasonically cleaning the base material in the stretching state for 20 minutes by adopting acetone, absolute ethyl alcohol and deionized water, and then drying.
3. And uniformly dispersing the copper nanowires in isopropanol, transferring the mixture into a spray bottle, aligning the spray bottle to the surface of the dried substrate material, spraying for 20 times, and naturally drying.
4. And horizontally placing the sprayed substrate material into glacial acetic acid for 40 seconds, taking out the substrate material, placing the substrate material into a blast oven for drying at 60 ℃, and removing organic matters coated around the copper nanowires.
5. A first dielectric material (PDMS) is dissolved in n-hexane to prepare a diluted PDMS solution, and the ratio of PDMS to n-hexane is 1: 100.
6. The diluted PDMS solution was spin coated on copper nanowires at 1000 rpm and cured at 80 ℃ for 3 hours.
7. Releasing the stretched substrate material to a natural state to form a flexible substrate having a wrinkled surface, the copper nanowires being dispersed on the wrinkled surface.
8. Mixing the PDMS prepolymer solution and a curing agent into a viscous solution according to a certain volume ratio of 10:1, defoaming, and adding a certain amount of deionized water according to a ratio of 1:3 to the PDMS solution. Stirring the mixture on a magnetic stirrer at 1000r/min for 8min to form a second medium material solution.
9. And (3) spin-coating the stirred second medium material solution on a quartz plate (substrate) with a smooth surface at the speed of 2000r/min for 1 minute, curing for 3 hours at the temperature of 80 ℃ to form a PDMS porous medium layer, namely a first flexible medium layer, and stripping the PDMS porous medium layer from the quartz.
10. And (4) encapsulating the PDMS porous medium layer in the flexible electrode prepared after the step (7) in a sandwich structure manner, and respectively leading out electrode leads from the upper and lower flexible electrodes to obtain the flexible capacitive pressure sensor.
And (4) a pressure test result: the prepared flexible capacitive pressure sensor can be used for pressure testing in a stretching range of 0-200%, and the sensitivity of the flexible capacitive pressure sensor is kept unchanged in a stretching range of 0-80%.
Fig. 5 shows the amount of elongation of the flexible capacitive pressure sensor as a function of sensitivity, with the horizontal axis representing the amount of elongation in percent and the vertical axis representing sensitivity. The S1 curve is a curve showing the change in sensitivity of the pressure sensor with respect to the change in elongation when the pressure applied thereto is 6kPa or less, and the S0 curve is a curve showing the change in sensitivity of the pressure sensor with respect to the change in elongation when the pressure applied thereto is greater than 6 kPa.
For a flexible capacitive pressure sensor, with a fixed amount of extension, a pressure of 6kPa is an approximate sensitivity trend demarcation point, and when the pressure is less than 6kPa, the sensitivity of the pressure sensor increases faster with increasing pressure, and when the pressure is greater than 6kPa, the sensitivity of the pressure sensor increases slower with increasing pressure.
The S1 curve shows the sensitivity delay of the pressure sensor when the pressure is below 6kPaThe curve is changed by long amount change, so that the sensitivity change range of the curve is lower than that of the S0 curve, when the applied pressure is fixed, as can be seen from figure 5, the sensitivity is basically not reduced when the extension amount is changed from 0-80%; the S0 curve is a curve showing the change of the sensitivity of the pressure sensor with the change of the elongation when the applied pressure is more than 6kPa, and when the applied pressure is fixed and the elongation is changed from 0 to 80%, the sensitivity is reduced by about 0.04kPa-1The amount of change is also very small.
Therefore, the flexible capacitive pressure sensor provided by the embodiment of the invention has the advantages that the sensitivity cannot be greatly reduced along with the change of the elongation when the pressure is small, the sensitivity cannot be greatly reduced along with the change of the elongation when the pressure is large, the sensitivity and the ductility are good, and the flexible capacitive pressure sensor is suitable for the field of human health monitoring or touch perception.
In the embodiments of the present invention, PDMS may be used for the flexible substrate, the first flexible medium layer, and the second flexible medium layer, and other dielectric materials with ductility known to those skilled in the art may also be used.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (12)
1. The utility model provides a flexible capacitive pressure sensor which characterized in that, by supreme down include in proper order: the flexible electrode comprises a first flexible electrode, a first flexible medium layer and a second flexible electrode, wherein the first flexible electrode and the second flexible electrode respectively comprise a flexible substrate with a corrugated surface and metal nanowires dispersed on the corrugated surface.
2. The flexible capacitive pressure sensor of claim 1, further comprising a second flexible dielectric layer overlying the wrinkled surface with the metal nanowires.
3. The flexible capacitive pressure sensor of claim 2, wherein the second flexible dielectric layer is made of polydimethylsiloxane.
4. The flexible capacitive pressure sensor according to any one of claims 1 to 3, wherein the flexible substrate and the first flexible dielectric layer are both made of polydimethylsiloxane.
5. The flexible capacitive pressure sensor according to any of claims 1 to 3, wherein the metal nanowires are copper nanowires.
6. A method for preparing a flexible capacitive pressure sensor is characterized by comprising the following steps:
(1) preparing a flexible electrode comprising a flexible substrate having a wrinkled surface and metal nanowires dispersed on the wrinkled surface;
(2) preparing a first flexible medium layer;
(3) and encapsulating the first flexible medium layer between the two flexible electrodes, and leading out an electrode lead from the flexible electrode.
7. The method of claim 6, wherein step (1) comprises:
(a) stretching the substrate material, and then placing the substrate material in an ultraviolet ozone environment for irradiation;
(b) cleaning the base material still in a stretched state, and then drying;
(c) uniformly dispersing the metal nanowires in a liquid organic matter to form a nanowire organic liquid, then spraying the nanowire organic liquid on the surface of the dried substrate material, and air-drying;
(d) removing organic matters coated around the metal nanowires on the sprayed substrate material;
(e) curing the base material;
(f) releasing the stretched substrate material to a natural state to form the flexible substrate having the wrinkled surface on which the metal nanowires are dispersed.
8. The method of claim 7, further comprising, between step (d) and step (e):
(g) forming a first dielectric material solution;
(h) and spin-coating the first medium material solution on the metal nano wire to form a second flexible medium layer.
9. The method of claim 10, wherein the second flexible dielectric layer is made of polydimethylsiloxane.
10. The method of claim 6, wherein step (2) comprises:
(A) forming a second dielectric material solution;
(B) spin coating the second medium material solution on a substrate with a smooth surface;
(C) solidifying the second medium material solution on the substrate to form the first flexible medium layer;
(D) and peeling the first flexible medium layer from the substrate.
11. The method according to any one of claims 6 to 10, wherein the flexible substrate and the first flexible medium layer are both made of polydimethylsiloxane.
12. The method according to any one of claims 6 to 10, wherein the metal nanowires are copper nanowires.
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