CN113670484B - Flexible pressure sensor with complementary spiral structure, preparation method and application thereof - Google Patents
Flexible pressure sensor with complementary spiral structure, preparation method and application thereof Download PDFInfo
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- CN113670484B CN113670484B CN202110946607.9A CN202110946607A CN113670484B CN 113670484 B CN113670484 B CN 113670484B CN 202110946607 A CN202110946607 A CN 202110946607A CN 113670484 B CN113670484 B CN 113670484B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- 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
- G01L1/142—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 using capacitors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/12—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in capacitance, i.e. electric circuits therefor
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Abstract
The invention discloses a flexible pressure sensor with a complementary spiral structure, a preparation method and application thereof, and belongs to the technical field of laser micro-nano processing; processing the surface of the graphene oxide/silk fibroin composite film by utilizing laser, wherein oxygen-containing functional groups in the graphene oxide can be removed by the photo-thermal effect of the laser, so that the graphene oxide is reduced and a spiral structure electrode is formed; after the porous adhesive tape is clamped between the pair of electrodes with the complementary spiral structures, the high-performance flexible pressure sensor with the complementary spiral structures is obtained, the detection of double modes of finger bending and finger approaching can be realized, the porous structure of the adhesive tape is beneficial to the large change of capacitance of the sensor during bending, and the accurate detection of finger bending can be realized. Meanwhile, the spiral structure of the electrode increases the area of the edge area of the electrode, is beneficial to expanding more electric fields from the electrode plate area to the outer space, and realizes sensitive detection of finger approach.
Description
Technical Field
The invention belongs to the technical field of laser micro-nano processing, and particularly relates to a flexible pressure sensor with a complementary spiral structure, a preparation method and application thereof.
Background
The flexible capacitive pressure sensor has wide application prospect in the tip application fields of electronic skin, man-machine interaction, wearable health detection and the like. The innovation of capacitive pressure sensors relies mainly on new electrode materials and structures. Graphene is a commonly used electrode material in various flexible electronic devices due to its excellent conductivity, flexibility and mechanical strength. The graphene electrodes prepared by traditional methods for manufacturing the graphene electrodes, such as a chemical stripping method, a chemical vapor deposition method, a dispersion adhesion method and the like, are often required to be attached to special substrates, so that the flexibility of the graphene electrodes is reduced to a greater or lesser extent, and the performance of the sensor is reduced.
In addition, any patterning of the graphene electrode is also a technical challenge for limiting the performance optimization of the capacitive pressure sensor, and at present, high-temperature reduction, chemical reduction, inkjet reduction and the like adopted by people can only realize some simple patterning reduction, and meanwhile, the problems of low resolution, low reduction speed and the like are also caused. In addition, the ductility and mechanical strength of the electrodes also greatly limit the application of graphene electrodes in flexible capacitive pressure sensors.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to solve the problems that: a flexible pressure sensor having a complementary spiral electrode structure is fabricated using laser machining. The laser direct writing technology is utilized to act on the surface of the graphene oxide/silk fibroin composite film formed by suction filtration, and the oxygen-containing functional groups in the graphene oxide can be removed by the photo-thermal effect of the laser, so that the graphene oxide in the graphene oxide/silk fibroin composite film is reduced and forms a spiral structure electrode, and the graphene oxide/silk fibroin composite film has excellent flexibility and ductility, so that the reduced graphene oxide/silk fibroin composite electrode after laser reduction has excellent mechanical properties; and then a porous adhesive tape is clamped between a pair of electrodes with complementary spiral structures, so that the high-performance flexible pressure sensor with the complementary spiral structures is finally obtained, and ultrasensitive detection of two modes of finger bending and finger approaching can be realized. The main detection principle of the sensor is as follows: (1) For contact detection, the formula is given by a parallel plate capacitor(wherein ε) 0 Is vacuum dielectric constant epsilon r For dielectric constant of the dielectric layer, A is the relative area between the two parallel plate electrodes, and d is the relative distance between the two parallel plate electrodes), when an object applies pressure to the sensor, the porous tape is compressed to reduce the relative distance d between the upper and lower plates, and air with relatively smaller dielectric constant in the porous tape is extruded to make dielectric constant epsilon of the dielectric r The capacitance value of the sensor is greatly changed under certain pressure by the combined action of the sensor and the sensor, so that the sensor has higher sensitivity; (2) For non-contact detection, due to fringe field effect of the parallel plate capacitor, the electric field lines in the fringe area can be expanded to the external space, and for the sensor with the ring-plate structure electrode, when the finger approaches, the finger can intercept the fringe electric field lines above the upper electrode, thereby reducing the electric field intensity between the upper electrode and the lower electrode, and finally resulting in reduced capacitance. And a graphene electrode of spiral complementary structure, whichThe electrode structure on the interface can be regarded as superposition of a plurality of ring-disk structure electrodes, the area of the edge area of the electrodes is increased, and the electrode structure contributes to expanding more electric fields from the electrode plate area to the outer space. Thus, when the finger is close, the sensor shows a large capacitance change, and is more sensitive to the approach of the finger.
The invention is realized by the following technical scheme:
the flexible pressure sensor with the complementary spiral structure comprises an upper composite electrode, a lower composite electrode and a dielectric layer, wherein the composite electrode comprises a composite film material 1 and a nano spiral structure 2, the dielectric layer is a porous material 3, and the composite film material 1 is a smooth-surface composite film material formed by mixing graphene oxide solution and silk fibroin solution and suction filtering; the surface of the composite film material 1 is provided with a nano spiral structure 2, the outer surfaces of the composite film material 1 and the nano spiral structure 2 are adhered with a porous material 3, and an upper electrode, a lower electrode and a dielectric layer form a multi-stage micro-nano structure of the composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1.
When the nano spiral structure 2 is used for carrying out patterning reduction on the composite film material 1 by laser processing, spiral patterning and a nano pore structure are formed simultaneously when oxygen-containing functional groups in the composite film are removed;
further, the thickness of the composite film material 1 is 50-200 mu m.
Further, the porous material 3 is porous foam tape, porous sponge, ceramic porous material, etc.
Further, the pore diameter of the nano-spiral structure 2 is 500nm-2 μm, the total number of turns of the spiral structure is 3-8, the width of each turn of the spiral structure is 200-300 μm, the spiral width of a unprocessed part is 100-200 μm, and the size of the whole spiral part is 0.3mm-0.8 mm.
A method for preparing a flexible pressure sensor with a complementary spiral structure based on laser processing comprises the following specific steps:
(1) Preparing graphene oxide/silk fibroin mixed solution;
dropwise adding a sodium hydroxide solution into a certain amount of graphene oxide solution to keep the graphene oxide solution neutral, and then mixing the graphene oxide solution with a silk fibroin solution to prepare a graphene oxide/silk fibroin mixed solution;
(2) Preparing a graphene oxide/silk fibroin composite film;
firstly, fixing a microporous filter membrane on a suction filtration device, then wetting the filter membrane with deionized water, and finally dripping a graphene oxide/silk fibroin mixed solution for suction filtration, thereby successfully preparing a graphene oxide/silk fibroin composite film;
(3) Preparing a complementary spiral structure reduced graphene oxide/silk fibroin composite electrode by processing the graphene oxide/silk fibroin composite film by using a laser direct writing method;
cutting the graphene oxide/silk fibroin composite film, fixing the film on a flat substrate, ensuring the surface of the film to be flat, placing the substrate on an optical platform of a laser, and adjusting the relative positions of a laser light source and the surface of the substrate to enable laser to be focused on the surface of the film; inputting a pre-processing pattern and processing parameters at the interface of a laser control program, and then performing laser direct writing to obtain a complementary spiral structure reduced graphene oxide/silk fibroin composite electrode;
(4) Preparing a spiral complementary structure pressure sensor;
cutting the porous adhesive tape, fixing a silver wire on the electrode by using conductive silver adhesive, and finally clamping the porous adhesive tape between two complementary spiral reduced graphene oxide/silk fibroin composite electrodes, thereby obtaining the pressure sensor with a spiral complementary structure.
Further, the specific steps of the preparation in the step (1) are as follows:
15-30mL of graphene oxide solution with the concentration of 5-10mg/mL is put into a beaker with the measuring range of 100mL, then 2-5mL of sodium hydroxide solution with the concentration of 0.05-0.2mol/L is added dropwise, the pH value of the graphene oxide solution is 7, then 2-6mL of silk fibroin solution with the concentration of 30-60mg/mL is added, then the beaker filled with the graphene oxide/silk fibroin mixture is put on a magnetic stirrer for stirring for 10s-1min, and the graphene oxide/silk fibroin mixed solution is obtained after uniform mixing.
Further, the specific synthesis steps of the graphene oxide solution in the step (1) are as follows:
firstly, mixing graphite and sodium nitrate according to the mass ratio of 1:1-1:3 under the ice bath condition of 0-5 ℃, and then adding 90-100mL of concentrated sulfuric acid with the mass fraction of 98%; then adding 5-20g potassium permanganate, stirring for 45-120min at the rotation speed of 500-1000r/min under the ice bath condition of 0-5 ℃; then heating to 35 ℃, maintaining for 120min, adding 80ml of deionized water, heating to 95 ℃, maintaining for 15min, and adding 200ml of deionized water, wherein the water injection time is 35min and 5min respectively; adding 10mL of hydrogen peroxide with volume concentration of 30%, closing heating and stirring for 5-15min, and then closing stirring to naturally settle for 20-30h; pouring out the supernatant after sedimentation, repeatedly diluting the acidic product by using deionized water, centrifuging for 10-20min at the rotating speed of 8000-12000r/min, and repeating for 10-18 times until the pH value of the supernatant is 7; and finally centrifuging the lower product for 10-20min at a rotating speed of 1000-1500r/min, repeating for 3-5 times until no obvious black graphite particles are visible, centrifuging for 15-20min at a rotating speed of 8000-10000r/min, pouring out supernatant, and shaking uniformly to obtain the graphene oxide solution with the concentration of 5-10 mg/mL.
Further, the specific synthesis steps of the silk fibroin solution in the step (1) are as follows:
firstly, adding 6-9g of sodium carbonate powder into 3000-5000mL of deionized water, fully dissolving the sodium carbonate powder by using a glass rod or other stirring devices, and then placing the sodium carbonate powder in a hot table or other heating devices to raise the temperature so that the sodium carbonate solution keeps a boiling state. Cutting the cocoon shell into 1-2cm by scissors or other cutting tool 2 Weighing 8-12g of silkworm pieces by using a tray balance or other weighing instrument, putting the silkworm pieces into a sodium carbonate solution in a boiling state, boiling for 20-50min, and taking out the silkworm pieces. Then preparing a part of boiling sodium carbonate solution with the same concentration by adopting the same method, then putting silk into the freshly prepared sodium carbonate solution, boiling for 20-50min, taking out, and repeatedly soaking into deionized water for 15-25 timesExtruding water, spreading on aluminum foil or other flat substrate, placing in a fume hood or other dry ventilation place for 20-30 hr, and naturally air drying to obtain silk fibroin fiber. Then 2-8g of dry silk fibroin fiber is put into a beaker, 15-25mL of lithium bromide solution with the concentration of 8-10mg/mL is sucked by using a rubber head dropper or other sampling tools, and then the mixture is placed into a vacuum drying oven or other heating devices with the temperature of 50-80 ℃ to be heated for 5-8h, so that dark yellow viscous liquid is obtained. Then pouring the viscous liquid into a dialysis bag with the molecular weight of 10000-18000, clamping the dialysis bag by using a clamp or other clamping tools, then placing the dialysis bag into a beaker filled with deionized water, dialyzing the dialysis bag at the temperature of 0-10 ℃ for 60-80h, replacing the deionized water every 10h, removing salt ions in the solution, centrifuging the dialysis solution for 15-30min at the rotating speed of 6000-12000r/min after the dialysis is finished, and taking supernatant to obtain the silk fibroin solution with the concentration of 30-60 mg/mL.
Further, the specific steps of the preparation in the step (2) are as follows:
opening a switch of a suction filtration device, and fixing a purchased water system microporous filter membrane with the aperture of 0.2-0.25 mu m and the diameter of 45-55mm below a suction filtration bottle; 3-5ml of deionized water is sucked by using a rubber head dropper or other sampling tools, the deionized water is dripped on the water-based microporous filter membrane, when the filter membrane is completely wetted by the deionized water, 10-15ml of graphene oxide/silk fibroin mixed solution is sucked by using the rubber head dropper or other sampling tools, then the graphene oxide/silk fibroin mixed solution is dripped on the water-based microporous filter membrane, and after the solution is dripped on the water-based microporous filter membrane for 12-15 hours, the graphene oxide/silk fibroin composite film with the thickness of 50-200 mu m is obtained.
Further, the step of adding the tool body in the step (2) is as follows:
fixing the suction-filtered graphene oxide/silk fibroin composite film on a glass slide by using a 3M adhesive tape, and stripping the graphene oxide/silk fibroin composite film and a water system microporous filter film after completely airing; cutting a rectangle with the size of 5mm by 10mm to 10mm by 20mm by using scissors; fixing the graphene oxide/silk fibroin composite film on a 50 mm/1 mm substrate by using a fixing tool, setting the area of a processing area to be 3 mm/6 mm-8 mm/16 mm, adjusting the distance between a laser head and the film to be 8-12cm, and ensuring the focusing position of laser to be the surface of the film; opening computer control software connected with a laser, adjusting relevant parameters such as line spacing, laser power, processing speed and the like, inputting a pre-processed spiral structure pattern, wherein the area is 3mm x 6mm-8mm x 16mm, adjusting the initial processing position, and ensuring that a processing area is positioned on the graphene oxide/silk fibroin composite film; the complementary spiral structure reduced graphene oxide/silk fibroin composite electrode prepared by a laser direct writing method with the area size of 3 mm-6 mm-8 mm-16 mm is obtained after processing; wherein the aperture of the nanometer spiral structure part is 500nm-2 μm, the total number of turns of the spiral structure is 3-8, the width of each turn of the spiral structure is 200-300 μm, and the spiral width of the unprocessed part is 100-200 μm.
Further, in computer control software connected with the laser, the laser wavelength is 343nm, the laser power parameter is set to 15% -20%, the line spacing is 0.005-0.01mm, the scanning speed is 200-500mm/s, and the processing frequency is 20-40kHz, so that the surface of the graphene oxide forms a complementary spiral structure.
Further, the preparation method of the flexible pressure sensor with the spiral complementary structure in the step (3) comprises the following specific steps:
firstly, cutting a porous adhesive tape with the thickness of 2-3mm into a rectangle with the size of 5mm 10mm-10mm 20mm by using scissors or other cutting tools, fixing a silver wire at the tail end of a reduced graphene oxide/silk fibroin composite electrode with a complementary spiral structure by using conductive silver adhesive, drying the conductive silver adhesive after 5-10min, and finally clamping the porous adhesive tape between two complementary reduced graphene oxide/silk fibroin composite electrodes with the size of 5mm 10mm-10mm 20mm, thereby successfully manufacturing the pressure sensor with the spiral complementary structure.
Another object of the present invention is to provide a laser processing method for preparing a flexible pressure sensor with a complementary spiral structure for finger bending detection, specifically, using a 3M tape or other fixing device to attach the spiral complementary structure pressure sensor to the index finger joint (when the finger is straightened), then connecting the two end wires of the spiral complementary structure pressure sensor to an LCR-6200 digital bridge tester, calibrating the bending angle of the index finger joint by using a protractor, when the index finger joint is straightenedRelative change in capacitance (ΔC/C) of spiral complementary structure pressure sensor when bent at 0 °, 30 °, 60 °, 90 ° 0 ) In the range of 0-0.5; when the spiral complementary structure pressure sensor is bent on a finger, the formula of the parallel plate capacitor is adoptedObtainable (wherein ε) 0 Is vacuum dielectric constant epsilon r For dielectric permittivity, a is the relative area between two parallel plate electrodes, d is the relative distance between two parallel plate electrodes), bending results in a smaller distance between the upper and lower electrodes, resulting in a larger capacitance. In addition, air with smaller dielectric constant is extruded out when the porous double faced adhesive tape is bent, so that the dielectric constant of the dielectric layer is increased, the capacitance is increased, and the air with smaller dielectric constant and the dielectric constant are combined to enable the spiral complementary structure pressure sensor to accurately detect the bending degree of the finger.
A third object of the present invention is to provide an application of laser processing to prepare a flexible pressure sensor with a complementary spiral structure in finger proximity detection, specifically, attaching the spiral complementary structure pressure sensor to a glass slide or other flat substrate using a 3M tape or other fixing device, and then connecting two end wires of the spiral complementary structure pressure sensor to an LCR-6200 digital bridge tester, wherein when the finger is 0-6cm away from the upper electrode surface of the sensor, the capacitance change value (C/C 0 ) 0.86-1.0.
In contrast, the capacitance change (C/C) of the ring-disk structured pressure sensor was measured at a distance of 0-6cm from the upper electrode surface of the sensor using the same method 0 ) 0.9-1.01, indicating that the complementary helix sensor is more sensitive to detection of finger proximity; because of the fringe field effect of the parallel plate capacitor, the electric field lines in the fringe area can be expanded to the external space, and for the sensor with the ring-plate structure electrode, when the finger approaches, the finger can intercept the fringe field lines above the upper electrode, thereby reducing the electric field intensity between the upper electrode and the lower electrode, and finally reducing the capacitance. And the graphene electrode with spiral complementary structure has an electrode structure on the interfaceIt can be seen that the superposition of a plurality of ring-disk structured electrodes increases the area of the edge region of the electrodes, helping to spatially spread more of the electric field outward from the electrode plate region. Thus, when the finger is close, the sensor shows a large capacitance change, and is more sensitive to the approach of the finger.
Compared with the prior art, the invention has the following advantages:
(1) The composite film material 1-nano spiral structure 2 composite electrode with the complementary spiral structure is prepared by adopting laser processing, so that the self-supporting reduced graphene oxide/silk fibroin composite film can be rapidly reduced and finely reduced in any complex patterning;
(2) The graphene oxide solution, the silkworm cocoons and the porous double-sided adhesive are used as raw materials, so that the method has the advantages of easiness in acquisition, low cost, good biocompatibility and the like;
(3) The composite film material 1-nano spiral structure 2 composite electrode prepared by laser processing is characterized in that graphene oxide modifies silk fibroin, so that the composite electrode has excellent flexibility, strong ductility and the like, and has good mechanical tensile property;
(4) The composite film material 1-nano spiral structure 2 composite electrode with the complementary spiral structure prepared by laser processing and the porous material 3 are assembled to obtain the composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1 multi-stage micro-nano structure sensor, and ultrasensitive detection of two modes of object contact (finger bending) and non-contact (finger approaching) can be realized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. Like elements or portions are generally identified by like reference numerals throughout the several figures. In the drawings, elements or portions thereof are not necessarily drawn to scale.
FIG. 1 is a schematic diagram of a device for manufacturing a flexible pressure sensor with a complementary spiral structure based on laser processing according to the present invention;
FIG. 2 is a schematic diagram of a process for preparing a pressure sensor based on laser processing and assembled by a multi-stage micro-nano structure of a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1;
FIG. 3 is a laser scanning confocal microscope image of a part of a composite electrode of a composite film material 1-nano spiral structure 2 in a pressure sensor with a complementary spiral structure based on laser processing;
FIG. 4 is a scanning electron microscope image of a pressure sensor assembled by a multi-stage micro-nano structure of a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1 based on laser processing; wherein, (a) is a scanning electron microscope image of a sensor section formed by a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-multi-stage micro-nano structure of the composite film material 1; (b) Scanning electron microscope images of the composite film material 1 in the composite electrode of the composite film material 1-nano spiral structure 2 in the pressure sensor with the complementary spiral structure; (c) Scanning electron microscope images of the composite electrode of the composite film material 1-nano spiral structure 2 in the pressure sensor with the complementary spiral structure;
FIG. 5 is a graph showing the relative change value of capacitance of a pressure sensor with a complementary spiral structure, which is assembled by a multi-stage micro-nano structure of a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1, based on laser processing;
FIG. 6 is a schematic diagram showing the distribution of electric fields around a sensor when fingers are close to each other, wherein the pressure sensor is assembled by a multi-stage micro-nano structure of a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1 based on laser processing;
fig. 7 is an image of the change of capacitance of a pressure sensor with a complementary spiral structure and a pressure sensor with a ring disk structure, which are assembled by a multi-stage micro-nano structure of a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1, based on laser processing.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Example 1
The flexible pressure sensor with the complementary spiral structure comprises an upper composite electrode, a lower composite electrode and a dielectric layer, wherein the composite electrode comprises a composite film material 1 and a nano spiral structure 2, the dielectric layer is a porous material 3, and the composite film material 1 is a smooth-surface composite film material formed by mixing graphene oxide solution and silk fibroin solution and suction filtering; the surface of the composite film material 1 is provided with a nano spiral structure 2, the outer surfaces of the composite film material 1 and the nano spiral structure 2 are adhered with a porous material 3, and an upper electrode, a lower electrode and a dielectric layer form a multi-stage micro-nano structure of the composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1.
When the nano spiral structure 2 is used for carrying out patterning reduction on the composite film material 1 by laser processing, spiral patterning and a nano pore structure are formed simultaneously when oxygen-containing functional groups in the composite film are removed;
the thickness of the composite film material 1 is 50-200 mu m.
The porous material 3 is porous foam adhesive tape, porous sponge, ceramic porous material, etc.
The aperture of the nano spiral structure 2 is 500nm-2 mu m, the total number of turns of the spiral structure is 3-8, the width of each turn of the spiral structure is 200-300 mu m, the spiral width of a unprocessed part is 100-200 mu m, and the size of the whole spiral part is 0.3mm-0.8 mm.
Example 2
As shown in fig. 1, a method for preparing a flexible pressure sensor with a complementary spiral structure based on laser processing comprises the following specific steps:
(1) Preparing graphene oxide/silk fibroin mixed solution;
20mL of graphene oxide solution with the concentration of 8mg/mL is sucked by using a rubber head dropper and is put into a beaker with the measuring range of 100mL, then 3mL of sodium hydroxide solution with the concentration of 0.05mol/L is added dropwise, so that the pH value of the graphene oxide solution is 7, 2mL of silk fibroin solution with the concentration of 40mg/mL is added, then the beaker with the graphene oxide/silk fibroin mixture is put on a magnetic stirrer and is stirred for 10s-1min, and the graphene oxide/silk fibroin mixed solution is obtained after uniform mixing.
The graphene oxide solution is synthesized by using a Hummer's method, and the specific synthesis steps are as follows: firstly, graphite and sodium nitrate are mixed according to the mass ratio of 1:1, mixing under the ice bath condition of 0 ℃, and adding 90mL of concentrated sulfuric acid with the mass fraction of 98%; 7g of potassium permanganate is added, and stirring is carried out for 60min at the rotation speed of 800r/min under the ice bath condition of 0-5 ℃; then heating to 35 ℃, maintaining for 120min, adding 80ml of deionized water, heating to 95 ℃, maintaining for 15min, and adding 200ml of deionized water, wherein the water injection time is 35min and 5min respectively; adding 10mL of hydrogen peroxide with volume concentration of 30%, closing heating and stirring for 10min, and then closing stirring to naturally settle for 24h; pouring out the supernatant after sedimentation, repeatedly diluting the acidic product by using deionized water, centrifuging for 15min at the rotating speed of 12000r/min, and repeating for 15 times until the pH value of the supernatant is 7; and finally centrifuging the lower product for 10min at a rotating speed of 1000r/min, repeating for 3 times until no macroscopic black graphite particles exist, centrifuging for 15min at a rotating speed of 8000r/min, pouring out supernatant, and shaking uniformly to obtain the graphene oxide solution with the concentration of 8 mg/mL.
The specific preparation steps of the silk fibroin solution used are as follows: first, 8g of sodium carbonate powder was added to 5000mL of deionized water, and the mixture was sufficiently dissolved by stirring with a glass rod, and then placed on a hot table to raise the temperature so that the sodium carbonate solution remained in a boiling state. Then the cocoon shell is sheared into the area of 1cm by using scissors 2 10g of silkworm flakes are weighed by a tray balance, put into a sodium carbonate solution in a boiling state, boiled for 30min, and taken out. Then prepare a portion again by the same methodBoiling sodium carbonate solution with the same concentration, putting silk into the newly prepared sodium carbonate solution, boiling for 30min, taking out, repeatedly soaking in deionized water for 20 times, extruding out water, spreading on aluminum foil, placing in a fume hood for 24h, and naturally airing to obtain the silk fibroin fiber. Then, 6g of the dried silk fibroin fiber was put into a beaker, 20mL of a lithium bromide solution with a concentration of 9mg/mL was sucked up by using a rubber head dropper, and then the mixture was placed into a vacuum drying oven at 70 ℃ and heated for 5 hours, to obtain a dark yellow viscous liquid. Then pouring the viscous liquid into a dialysis bag with the molecular weight of 14000, clamping the dialysis bag by using a clamp, then placing the dialysis bag into a beaker filled with deionized water, dialyzing at 4 ℃ for 72 hours, replacing the deionized water every 10 hours, removing salt ions in the solution, centrifuging for 20 minutes at the rotating speed of 10000r/min after the dialysis is finished, and taking the supernatant as the silk fibroin solution with the concentration of 40 mg/mL.
(2) Preparing a graphene oxide/silk fibroin composite film;
selecting and clamping a water system (mixed cellulose) microporous filter membrane with a flat surface and a diameter of 50mm and a pore diameter of 0.22 mu m by using tweezers, opening an oilless diaphragm type vacuum pump, fixing the filter membrane on a funnel base, covering a filter cup, and fixing by using an aluminum clamp; 3ml of deionized water is sucked by using a rubber head dropper with the capacity of 5ml and is completely dripped on the water system microporous filter membrane, and when the filter membrane is in a completely wetted state, 12ml of graphene oxide/silk fibroin mixed solution is sucked by using the rubber head dropper with the capacity of 5ml and is dripped on the water system microporous filter membrane. And waiting for 12 hours to obtain the graphene oxide/silk fibroin composite film formed by the composite film material 1 with the thickness of 100 mu m.
(3) Preparing a complementary spiral structure reduced graphene oxide/silk fibroin composite electrode by processing a graphene oxide/silk fibroin composite film formed by the composite film material 1 by a laser direct writing method;
the ultraviolet laser with the laser wavelength of 343nm has high adjustability of laser power, line spacing, scanning speed and processing frequency; fixing the suction-filtered graphene oxide/silk fibroin composite film on a glass slide by using a 3M adhesive tape, and manually stripping the graphene oxide/silk fibroin composite film and the microporous filter film after completely airing; cutting a rectangle with the size of 8mm by 16mm by using scissors; fixing the graphene oxide/silk fibroin composite film on a 50 mm/1 mm substrate by using a 3M adhesive tape, wherein the area of a set processing area is 6 mm/12 mm; when the distance between the laser head and the film is regulated to be 10cm, focusing the laser on the surface of the film; opening computer control software connected with a laser, setting laser power to be 20%, line spacing to be 0.01, scanning speed to be 500mm/s, processing frequency to be 40Hz, inputting a pre-processed spiral structure pattern, adjusting an initial processing position, and ensuring that a processing area is positioned on the graphene oxide/silk fibroin composite film; and (3) after processing, obtaining the complementary spiral structure reduced graphene oxide/silk fibroin composite electrode formed by the composite film material 1-nano spiral structure 2 prepared by a laser direct writing method with the area size of 6mm x 12 mm. Wherein the pore diameter of the nano spiral structure part is 1 mu m, the total number of turns of the spiral structure is 6 turns, the width of each turn of the spiral structure is 250 mu m, and the spiral width of a unprocessed part is 125 mu m.
(4) Preparing a flexible pressure sensor with a spiral complementary structure;
cutting a porous adhesive tape with the thickness of 2.65mm (the thickness is obtained by a cross-section scanning electron microscope image of a device in fig. 4 (a)) into a rectangle with the size of 6mm x 12mm by using scissors, fixing silver wires with the diameter of 0.1mm at two ends of a reduced graphene oxide/silk fibroin composite electrode with a complementary spiral structure by using conductive silver adhesive, drying the conductive silver adhesive after 5min, and finally clamping the porous adhesive tape between two spiral complementary graphene electrodes with the size of 6mm x 12mm, thereby successfully preparing the pressure sensor with the complementary spiral structure, wherein the pressure sensor is assembled by a multi-stage micro-nano structure of a composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1.
Fig. 1 and fig. 2 are schematic views of a device structure and a preparation flow of the present invention, respectively, and it can be seen from the figures that the operation process is simple, and a complex and tedious processing process is avoided;
fig. 3 and fig. 4 show the surface morphology of the reduced graphene oxide/silk fibroin composite electrode and the microstructure of the whole device structure, which are formed by the patterned composite film material 1-nano spiral structure 2 in the spiral complementary structure pressure sensor; the thickness of the complementary spiral structure pressure sensor assembled by the composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-multi-stage micro-nano structure of the composite film material 1 is 2.65mm.
Example 3
The embodiment provides an application of a flexible pressure sensor with a complementary spiral structure in finger bending detection based on laser processing, which comprises the following specific steps:
firstly, a 3M adhesive tape is used for attaching a spiral complementary structure pressure sensor to an index finger joint (the finger is attached when straightened), then two ends of the spiral complementary structure pressure sensor are connected to an LCR-6200 digital bridge tester through wires, a protractor is used for calibrating the bending angle of the index finger joint, and when the finger joint bends 0 DEG, 30 DEG, 60 DEG and 90 DEG, the relative change of capacitance (delta C/C) of the spiral complementary structure pressure sensor 0 ) 0, 0.21, 0.33, 0.48, respectively; when the finger is bent, the parallel plate capacitorIt can be obtained that the distance d between the upper electrode and the lower electrode is reduced during bending, and air with smaller dielectric constant is extruded out of the porous double-sided adhesive tape, so that the dielectric constant epsilon of the dielectric layer r The pressure sensor with the complementary spiral structure can accurately detect the bending degree of the finger due to the combined action of the pressure sensor and the complementary spiral structure;
FIG. 5 shows the relationship of the relative capacitance change of the sensor with the change of the bending angle of the finger when the spiral complementary structure pressure sensor assembled by the composite film material 1-nano spiral structure 2-porous material 3-nano spiral structure 2-composite film material 1 is attached to the finger joint, wherein the greater the bending degree of the finger is, the greater the change value of the capacitance is;
example 4
The embodiment provides an application of the flexible pressure sensor with the complementary spiral structure in finger proximity detection based on laser processing,the method comprises the following specific steps: the spiral complementary structure pressure sensor is attached to a glass slide by using a 3M adhesive tape, then two end wires of the spiral complementary structure pressure sensor are connected to an LCR-6200 digital bridge tester, and when the distance between a finger and the upper surface of the sensor is 6cm, 4cm, 2cm and 0.1cm respectively, the change value (C/C 0 ) 0.99, 0.98, 0.93, 0.86, respectively. By contrast, the ring-disk structure pressure sensor was measured using the same method, and the change value (C/C 0 ) 1.01, 0.99, 0.95, 0.9, respectively, as compared to the results shown in fig. 6, the complementary spiral sensor is therefore more sensitive to finger proximity detection; based on fringe field effects of the parallel plate capacitor, the electric field lines in the fringe area are spread to the outside space, as shown in fig. 6, for the sensor of the ring-plate structure electrode, when the finger approaches, the finger intercepts the fringe field lines above the upper electrode, thereby reducing the electric field intensity between the upper and lower electrodes, and the charge stored in the capacitor is reduced, eventually resulting in a reduction in the capacitance. The electrode structure on the interface of the spiral complementary structure reduced graphene oxide/silk fibroin composite electrode can be regarded as superposition of a plurality of ring-disk structure electrodes, the area of the edge area of the electrode is increased, and more electric fields can be expanded from the electrode plate area to the outer space. Thus, when the finger is close, the sensor shows a large capacitance change, and is more sensitive to the approach of the finger.
FIG. 6 is a schematic diagram showing the distribution of the fringe electric fields around the finger and the sensor when the finger is approaching over the sensor;
FIG. 7 is a schematic diagram showing the change of capacitance values of two different electrode structures (a composite film material 1-nano spiral structure 2 electrode structure and a ring disk electrode structure) according to the vertical distance between a finger and the upper surface of the sensor when the finger is close to the upper surface of the sensor, wherein the sensor of the composite film material 1-nano spiral structure 2 electrode structure is more sensitive to the proximity of the finger and the fringe electric field of the sensor is more diffused to the outer space;
the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.
In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.
Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.
Claims (6)
1. The flexible pressure sensor with the complementary spiral structure is characterized by comprising an upper composite electrode, a lower composite electrode and a dielectric layer, wherein the composite electrode comprises a composite film material (1) and a nano spiral structure (2), the dielectric layer is a porous material (3), and the composite film material (1) is a surface smooth composite film material formed by mixing and suction filtering graphene oxide solution and silk fibroin solution; the surface of the composite film material (1) is provided with a nano spiral structure (2), the outer surfaces of the composite film material (1) and the nano spiral structure (2) are adhered with a porous material (3), and the upper electrode, the lower electrode and the dielectric layer form a multi-stage micro-nano structure of the composite film material (1) -the nano spiral structure (2) -the porous material (3) -the nano spiral structure (2) -the composite film material (1);
the thickness of the composite film material (1) is 50-200 mu m, the aperture of the nano spiral structure (2) is 500nm-2 mu m, the total number of turns of the spiral structure is 3-8 turns, the width of each turn of the spiral structure is 200-300 mu m, the spiral width of a unprocessed part is 100-200 mu m, and the size of the whole spiral part is 0.3mm x 0.8mm; the porous material (3) is porous foam adhesive tape, porous sponge or ceramic porous material;
the flexible pressure sensor with the complementary spiral structure is prepared by the following steps:
(1) Preparing graphene oxide/silk fibroin mixed solution;
15-30mL of graphene oxide solution with the concentration of 5-10mg/mL is put into a beaker with the measuring range of 100mL, then 2-5mL of sodium hydroxide solution with the concentration of 0.05-0.2mol/L is added dropwise, the PH value of the graphene oxide solution is 7, then 2-6mL of silk fibroin solution with the concentration of 30-60mg/mL is added, then the beaker filled with the graphene oxide/silk fibroin mixture is put on a magnetic stirrer to be stirred for 10s-1min, and the graphene oxide/silk fibroin mixed solution is obtained after uniform mixing;
the specific synthesis steps of the graphene oxide solution are as follows:
firstly, graphite and sodium nitrate are mixed according to the mass ratio of 1:1-1:3 mixing under the ice bath condition of 0-5 ℃, and then adding 90-100mL of concentrated sulfuric acid with the mass fraction of 98%; then adding 5-20g potassium permanganate, stirring for 45-120min at the rotation speed of 500-1000r/min under the ice bath condition of 0-5 ℃; then heating to 35 ℃, maintaining for 120min, adding 80ml of deionized water, heating to 95 ℃, maintaining for 15min, and adding 200ml of deionized water, wherein the water injection time is 35min and 5min respectively; adding 10mL of hydrogen peroxide with volume concentration of 30%, closing heating and stirring for 5-15min, and then closing stirring to naturally settle for 20-30h; pouring out the supernatant after sedimentation, repeatedly diluting the acidic product by using deionized water, centrifuging for 10-20min at the rotating speed of 8000-12000r/min, and repeating for 10-18 times until the pH value of the supernatant is 7; finally centrifuging the lower product at a rotating speed of 1000-1500r/min for 10-20min, repeating for 3-5 times until no obvious black graphite particles are visible, centrifuging at a rotating speed of 8000-10000r/min for 15-20min, pouring out supernatant, and shaking uniformly to obtain graphene oxide solution with a concentration of 5-10 mg/mL;
the specific synthesis steps of the silk fibroin solution are as follows:
firstly, adding 6-9g of sodium carbonate powder into 3000-5000mL of deionized water, using a glass rod or other stirring device to dissolve the sodium carbonate powder sufficiently, and then placing the solution in a heat table or other heating device to raise the temperature so that the sodium carbonate solution keeps boilingA state; cutting the cocoon shell into 1-2cm by scissors or other cutting tool 2 Weighing 8-12g of silkworm pieces by using a tray balance or other weighing instrument, putting the silkworm pieces into sodium carbonate solution in a boiling state, boiling for 20-50min, and taking out the silkworm pieces; then preparing a part of boiling sodium carbonate solution with the same concentration by adopting the same method, then putting silk into the freshly prepared sodium carbonate solution, boiling for 20-50min, taking out, repeatedly soaking in deionized water for 15-25 times, extruding out water, spreading the water on an aluminum foil or other flat substrates, placing the aluminum foil or other flat substrates in a fume hood or other dry ventilation place for 20-30h, and naturally airing to obtain silk fibroin fibers; then 2-8g of dry silk fibroin fibers are put into a beaker, 15-25mL of lithium bromide solution with the concentration of 8-10mg/mL is sucked by using a rubber head dropper or other sampling tools, and then the mixture is placed into a vacuum drying oven or other heating devices with the temperature of 50-80 ℃ to be heated for 5-8 hours, so that dark yellow viscous liquid is obtained; then pouring the viscous liquid into a dialysis bag with the molecular weight of 10000-18000, clamping the dialysis bag by using a clamp or other clamping tools, then placing the dialysis bag into a beaker filled with deionized water, dialyzing the dialysis bag at 0-10 ℃ for 60-80h, replacing the deionized water every 10h, removing salt ions in the solution, centrifuging the dialysis solution for 15-30min at the rotating speed of 6000-12000r/min after the dialysis is finished, and taking supernatant to obtain a silk fibroin solution with the concentration of 30-60 mg/mL;
(2) Preparing a graphene oxide/silk fibroin composite film;
firstly, fixing a microporous filter membrane on a suction filtration device, then wetting the filter membrane with deionized water, and finally dripping a graphene oxide/silk fibroin mixed solution for suction filtration, thereby successfully preparing a graphene oxide/silk fibroin composite film;
(3) Preparing a complementary spiral structure reduced graphene oxide/silk fibroin composite electrode by processing the graphene oxide/silk fibroin composite film by using a laser direct writing method;
cutting the graphene oxide/silk fibroin composite film, fixing the film on a flat substrate, ensuring the surface of the film to be flat, placing the substrate on an optical platform of a laser, and adjusting the relative positions of a laser light source and the surface of the substrate to enable laser to be focused on the surface of the film; inputting a pre-processing pattern and processing parameters at the interface of a laser control program, and then performing laser direct writing to obtain a complementary spiral structure reduced graphene oxide/silk fibroin composite electrode;
(4) Preparing a spiral complementary structure pressure sensor;
cutting the porous adhesive tape, fixing a silver wire on the electrode by using conductive silver adhesive, and finally clamping the porous adhesive tape between two complementary spiral reduced graphene oxide/silk fibroin composite electrodes, thereby obtaining the pressure sensor with a spiral complementary structure.
2. A flexible pressure sensor having a complementary spiral structure as claimed in claim 1, wherein the specific steps of preparation in step (2) are:
opening a switch of a suction filtration device, and fixing a purchased water system microporous filter membrane with the aperture of 0.2-0.25 mu m and the diameter of 45-55mm below a suction filtration bottle; 3-5ml of deionized water is sucked by using a rubber head dropper or other sampling tools, the deionized water is dripped on the water-based microporous filter membrane, when the filter membrane is completely wetted by the deionized water, 10-15ml of graphene oxide/silk fibroin mixed solution is sucked by using the rubber head dropper or other sampling tools, then the graphene oxide/silk fibroin mixed solution is dripped on the water-based microporous filter membrane, and after the solution is dripped on the water-based microporous filter membrane for 12-15 hours, the graphene oxide/silk fibroin composite film with the thickness of 50-200 mu m is obtained.
3. The flexible pressure sensor with complementary spiral structure of claim 1, wherein the tool body adding step in step (2) is as follows:
fixing the suction-filtered graphene oxide/silk fibroin composite film on a glass slide by using a 3M adhesive tape, and stripping the graphene oxide/silk fibroin composite film and a water system microporous filter film after completely airing; cutting a rectangle with the size of 5mm by 10mm to 10mm by 20mm by using scissors; fixing the graphene oxide/silk fibroin composite film on a 50 mm/1 mm substrate by using a fixing tool, setting the area of a processing area to be 3 mm/6 mm-8 mm/16 mm, adjusting the distance between a laser head and the film to be 8-12cm, and ensuring the focusing position of laser to be the surface of the film; opening computer control software connected with a laser, adjusting relevant parameters such as line spacing, laser power, processing speed and the like, inputting a pre-processed spiral structure pattern, wherein the area is 3mm x 6mm-8mm x 16mm, adjusting the initial processing position, and ensuring that a processing area is positioned on the graphene oxide/silk fibroin composite film; the complementary spiral structure reduced graphene oxide/silk fibroin composite electrode prepared by a laser direct writing method with the area size of 3 mm-6 mm-8 mm-16 mm is obtained after processing; wherein the aperture of the nanometer spiral structure part is 500nm-2 mu m, the total number of turns of the spiral structure is 3-8, the width of each turn of the spiral structure is 200-300 mu m, and the spiral width of the unprocessed part is 100-200 mu m; in computer control software connected with a laser, the wavelength of the laser is 343nm, the laser power parameter is set to 15% -20%, the line spacing is 0.005-0.01mm, the scanning speed is 200-500mm/s, and the processing frequency is 20-40kHz, so that the surface of the graphene oxide forms a complementary spiral structure.
4. A flexible pressure sensor with a complementary spiral structure according to claim 1, wherein the specific steps of preparing the flexible pressure sensor with the spiral complementary structure in the step (3) are as follows:
firstly, cutting a porous adhesive tape with the thickness of 2-3mm into a rectangle with the size of 5mm 10mm-10mm 20mm by using scissors or other cutting tools, fixing a silver wire at the tail end of a reduced graphene oxide/silk fibroin composite electrode with a complementary spiral structure by using conductive silver adhesive, drying the conductive silver adhesive after 5-10min, and finally clamping the porous adhesive tape between two complementary reduced graphene oxide/silk fibroin composite electrodes with the size of 5mm 10mm-10mm 20mm, thereby successfully manufacturing the pressure sensor with the spiral complementary structure.
5. Use of a flexible pressure sensor with complementary spiral structure according to claim 1, in finger bending detection, in particular using 3M tape or other fixing means to attach the spiral complementary structure pressure sensor at the index finger joint, then connecting the two wires of the spiral complementary structure pressure sensor to LCR-6200 digital bridge tester, calibrating the bending angle at the index finger joint using a protractor, the relative variation of the capacitance of the spiral complementary structure pressure sensor being in the range of 0-0.5 when the index finger joint bends 0 °, 30 °, 60 °, 90 °.
6. Use of a flexible pressure sensor with a complementary spiral structure for finger proximity detection according to claim 1, in particular using 3M tape or other fastening means to attach the spiral complementary structure pressure sensor to a glass slide or other flat substrate, and then connecting the two wires of the spiral complementary structure pressure sensor to an LCR-6200 digital bridge tester, wherein the capacitance of the spiral complementary structure pressure sensor changes by 0.86-1.0 when the finger is 0-6cm from the upper electrode surface of the sensor.
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