CN115931186A - Gradient multilayer flexible piezoresistive sensor and preparation method thereof - Google Patents
Gradient multilayer flexible piezoresistive sensor and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a gradient multilayer flexible piezoresistive sensor and a preparation method thereof, and the gradient multilayer flexible piezoresistive sensor comprises a coplanar metal electrode and a composite material sensitive layer arranged on the coplanar metal electrode, wherein the composite material sensitive layer comprises a plurality of layers of composite material films which are sequentially stacked from top to bottom, the composite material films are made of carbon nano tube polydimethylsiloxane, and the specific gravity of the carbon nano tubes in each composite material film is sequentially decreased from top to bottom; each composite material film between the coplanar metal electrode and the composite material film on the uppermost layer comprises two composite material sheets arranged at intervals to form an arch structure, the two electrodes are formed on the coplanar metal electrode, and the two composite material sheets of the composite material film on the lowermost layer are respectively positioned on the two electrodes of the coplanar metal electrode. The multilayer composite material film has specific gravity gradient, simultaneously realizes the change of resistance, modulus and roughness gradient, has high sensitivity, wide response range and good linearity, and has the characteristics of simple structure, simple and convenient preparation and the like.
Description
Technical Field
The invention relates to the technical field of sensors, in particular to a gradient multilayer flexible piezoresistive sensor and a preparation method thereof.
Background
The flexible wearable pressure sensor has the advantages of biocompatibility, stretchability, transparency, wearability and the like, and has wide application prospects in the fields of electronic skin, intelligent robots, motion sensing and the like. According to different sensing mechanisms, flexible wearable pressure sensors are divided into piezoresistive sensors, capacitance sensors, piezoelectric sensors and friction sensors, wherein piezoresistive sensors are widely concerned and rapidly developed due to the characteristics of simple structure, easiness in preparation and the like.
Most existing flexible piezoresistive sensors tend to exhibit high sensitivity over a small pressure range, but the pressure sensing range is small and the linearity is poor. Therefore, a design strategy of a piezoresistive sensor with high sensitivity, wide sensing range and good linearity is needed.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a gradient multilayer flexible piezoresistive sensor which comprises a multilayer multi-gradient carbon nanotube polydimethylsiloxane composite material, a metal electrode and a polymer protection layer, and the piezoresistive sensor has the advantages of good flexibility, wide measuring range, high sensitivity, good linearity, good piezoresistive repeatability and long service life.
The invention is realized by the following technical scheme:
a gradient multilayer flexible piezoresistive sensor comprises a coplanar metal electrode and a composite material sensitive layer arranged on the coplanar metal electrode, wherein the composite material sensitive layer comprises a plurality of composite material films which are sequentially stacked from top to bottom, the composite material films are made of carbon nano tube polydimethylsiloxane, and the specific gravity of the carbon nano tubes in each composite material film is sequentially decreased from top to bottom;
each composite material film between the coplanar metal electrode 1 and the composite material film on the uppermost layer comprises two spaced composite material sheets, two electrodes are formed on the coplanar metal electrode layer 1, and the two composite material sheets of the composite material film on the lowermost layer are respectively positioned on the two electrodes of the coplanar metal electrode 1.
Preferably, the carbon nanotube polydimethylsiloxane composite layer is one or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes, or a modified conductive polymer doped in polydimethylsiloxane.
Preferably, the number of the composite films in the composite material sensitive layer is 3-10.
Preferably, the composite film has a thickness of 50 to 500 μm, and the composite films of the respective layers have the same thickness.
Preferably, the coplanar metallic electrode 1 comprises a flexible substrate, and two electrodes deposited on one side thereof.
Preferably, the thickness of the electrode is 1 μm to 5 μm.
Preferably, the bottom of the coplanar metal electrode 1 and the top of the uppermost composite film are respectively provided with a polymer protective layer.
Preferably, the specific gravity of the carbon nanotubes in the composite film is 0.5wt% to 10wt%.
A preparation method of a gradient multilayer flexible piezoresistive sensor comprises the following steps:
step 5, adding a curing agent into the mixed solution, coating the mixed solution on a mold, and curing to form a composite film;
and 8, packaging the composite material sensitive layer and the coplanar metal electrode to obtain the gradient multilayer flexible piezoresistive sensor.
10. The method for preparing a gradient multilayer flexible piezoresistive sensor according to claim 9, wherein the mass ratio of the polydimethylsiloxane prepolymer to the curing agent in the mixed solution in the step 5 is (5-10): 1.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention provides a gradient multilayer flexible piezoresistive sensor, which comprises a flexible substrate, a coplanar electrode and an arch structure multilayer composite film arranged on the flexible substrate, wherein the specific gravity of carbon nanotubes in the composite film is sequentially reduced from top to bottom by changing the content of the carbon nanotubes in the composite material, so that the resistance, the modulus and the roughness of the composite material are changed, and the gradient change of the resistance, the modulus and the roughness is realized at the same time. By applying voltage on the metal electrode and applying pressure on the flexible piezoresistive device, the CNT/PDMS composite material layer and the layer deform at different pressure stages, and the deformation causes the mutual contact of the carbon nanotubes between the layers and inside the composite material layer, so that more conductive paths are created, the resistance is reduced, the current is increased, and the pressure signal is converted into the current signal to realize the pressure sensing performance. The modulus gradient can effectively regulate and control stress transfer, the soft layer deforms firstly, and the hard layer deforms later, so that the pressure sensing range and the linearity are favorably improved; the conductive gradient can effectively regulate and control the electron transfer in the deformation process, influence the activation sequence of a conductive path and contribute to improving the sensitivity and the linearity. The coarse microstructure among layers in the multilayer structure increases the contact resistance among the layers and improves the initial resistance of the sensitive material on one hand, and is beneficial to causing local stress concentration to cause the obvious change of the contact area among the layers and improve the sensitivity on the other hand; in addition, the multilayer structure can relieve the integral stress concentration of the sensitive material, and the stress is dispersed on each layer, so that the multi-gradient structure and the multilayer structure which are beneficial to improving the linearity and the sensing range have a composite effect on improving the sensitivity, the sensing range and the linearity of the sensor. Finally, the arched structure and the coplanar electrode can effectively regulate and control the current direction, so that the current sequentially passes through the high resistance layer, the low resistance layer and the high resistance layer, and the performance advantage of the gradient multilayer sensitive material is further improved.
Drawings
FIG. 1 is a cross-sectional view of a gradient multilayer flexible piezoresistive sensor according to the present invention;
FIG. 2 is a schematic structural diagram of a gradient multilayer flexible piezoresistive sensor according to the present invention;
FIG. 3 is a graph of resistance of CNT/PDMS composites with different concentrations, with decreasing resistance as the CNT content increases;
FIG. 4 is a plot of the modulus of CNT/PDMS composites at different concentrations, with the composite modulus increasing with increasing CNT content;
FIG. 5 is a graph of roughness of CNT/PDMS composites of different concentrations, with increasing roughness of the composite as the content of CNT increases;
FIG. 6 is a graph of the rate of change of resistance versus stress for a gradient multilayer flexible piezoresistive sensor according to the present invention;
FIG. 7 is a graph of the rate of change of resistance versus stress for a comparative flexible CNT/PDMS single layer piezoresistive sensor;
figure 8 is a graph of the rate of change of resistance versus stress for a comparative flexible CNT/PDMS multilayer piezoresistive sensor.
In the figure, 1, a coplanar metal electrode, 2, a first composite film, 3, a second composite film, 4 and a third composite film.
Detailed Description
The present invention will now be described in further detail with reference to the attached drawings, which are illustrative, but not limiting, of the present invention.
Referring to fig. 1 and 2, a gradient multilayer flexible piezoresistive sensor comprises a coplanar metal electrode 1 and a composite material sensitive layer arranged on the coplanar metal electrode 1, wherein the composite material sensitive layer comprises a plurality of composite material films which are sequentially overlapped from top to bottom, the composite material films are made of coplanar carbon nanotube polydimethylsiloxane, and the specific gravity of carbon nanotubes in each composite material film is sequentially decreased from top to bottom;
each composite material film between the coplanar metal electrode 1 and the composite material film on the uppermost layer comprises two composite material sheets arranged at intervals, two electrodes are formed on the coplanar metal electrode layer 1, and the two composite material sheets of the composite material film on the lowermost layer are respectively positioned on the two electrodes of the coplanar metal electrode 1 to form an arch-shaped structure.
The coplanar metal electrode 1 comprises a flexible substrate and two electrodes deposited on one side of the flexible substrate, wherein the flexible substrate is carbon polydimethylsiloxane. The metal electrode is gold, silver, copper, aluminum or platinum.
The carbon nano tube in the carbon nano tube polydimethylsiloxane is one or a mixture of two of a single-wall carbon nano tube and a multi-wall carbon nano tube, or a modified conductive polymer doped in the polydimethylsiloxane.
The number of layers of the composite material film in the sensitive layer is 3-10, preferably 3, the thickness of the composite material film is 50-500 μm, and the composite material films of all the layers are the same.
The bottom of the coplanar metal electrode 1 and the top of the composite film on the uppermost layer are respectively provided with a polymer protective layer for protecting the gradient multilayer flexible piezoresistive sensor, and the polymer protective layers are made of rubber polymers, polyolefin polymers or resin polymers.
The invention provides a gradient multilayer flexible piezoresistive sensor, which comprises a flexible substrate and a plurality of layers of composite material films arranged on the flexible substrate, wherein the specific gravity of carbon nano tubes in the composite material films is sequentially reduced from top to bottom to realize resistance gradient transformation and modulus gradient change, voltage is applied to a metal electrode to apply pressure to a flexible piezoresistive device, the contact area among the plurality of layers of composite material films is changed, so that a current path is increased, the change of external pressure is reflected through the current or resistance change, and a sensitive layer converts a pressure signal into a resistance signal to output to realize the pressure sensing characteristic.
The following is a detailed description of the preparation method of the gradient multilayer flexible piezoresistive sensor provided by the present invention, and the preparation method comprises the following steps:
the organic solvent is at least one of chloroform, isopropanol, THF and N-methyl pyrrolidone.
The method for dispersing the carbon nanotube powder in the organic solvent comprises the following steps:
ultrasonically dispersing carbon nanotube powder and an organic solvent for 3-8h, wherein the concentration of the organic dispersion liquid is 1-3 mg/ml.
specifically, after fully stirring for 3 hours by using a magnetic stirrer, heating the mixed solution to 50-80 ℃ by using a water bath heating mode, continuously stirring for 1-3 hours, and evaporating to remove the organic solvent.
Step 5, adding a curing agent into the mixed solution, coating the mixed solution on a mold, and curing to form a CNT/PDMS composite film;
the curing agent is a mixed solution of a diluent and a polydimethylsiloxane curing agent, and the preparation method comprises the following steps:
weighing the diluent according to a certain proportion, mixing the diluent with the polydimethylsiloxane curing agent, and fully stirring for 3 hours by using a magnetic stirrer;
the diluent is at least one of n-hexane and cyclohexane, and the volume ratio of the diluent to the PDMS is 3:1.
The mass ratio of the polydimethylsiloxane to the polydimethylsiloxane curing agent in the mixed solution is (5-10) to 1.
The curing temperature of the CNT/PDMS composite material is 80-100 ℃, and the curing time is 1-3h.
The mould is plane glass or various types of sand paper.
And 6, repeating the steps 3-5 to prepare a plurality of CNT/PDMS composite films, wherein the specific gravity of the carbon nano tubes in each CNT/PDMS composite material is different.
The specific gravity of the carbon nano-tube in the CNT/PDMS composite film is 0.5wt% -10wt%.
And 7, sequentially stacking the CNT/PDMS composite films except the CNT/PDMS composite film with the maximum specific gravity according to the specific gravity of the carbon nano tubes from top to bottom, combining the CNT/PDMS composite films through silica gel, cutting the combined multilayer CNT/PDMS composite films into two composite material groups, and combining the CNT/PDMS composite film with the maximum specific gravity of the carbon nano tubes on the top surfaces of the two composite material groups through silica gel to obtain the composite material sensitive layer.
And 8, packaging the composite material sensitive layer and the coplanar metal electrode, and respectively arranging polymer protective layers at the bottom of the coplanar metal electrode 1 and the top of the composite material film on the uppermost layer to obtain the gradient multilayer flexible piezoresistive sensor.
Specifically, the silver colloid is coated on the surface of the electrode, the wide edge of the electrode is aligned with the wide edge of the sensitive layer, the electrode and the sensitive layer can be tightly combined by using the silver colloid, and the electrode and the sensitive layer are vertically attached by using the PU adhesive tape to realize packaging.
The gradient multilayer flexible piezoresistive sensor prepared by the method has the advantages that the carbon nano tubes in the composite material are not mutually overlapped due to the tunneling effect in the single-layer film of the composite material, but the distance is small, so that electrons can penetrate through a potential barrier with certain probability, the interlayer is conductive, and the resistance of the gradient multilayer flexible piezoresistive sensor is related to the distance between the carbon nano tubes; tunneling effect between single-layer films of composite materials. The interlayer spacing of the multilayer structure is too large, electrons cannot pass through the potential barrier, but the interlayer spacing is reduced along with the increase of stress, electrons tunnel at a certain probability to form tunneling current, and a conductive path is formed; piezoresistive effect of the composite material itself. When the CNT/PDMS composite material is stressed, the carbon nanotubes in the composite material are mutually overlapped, so that the resistance of the composite material per se can be changed.
Example 1
A preparation method of a gradient multilayer flexible piezoresistive sensor comprises the following steps:
step 1: coating the prepared PDMS solution on a smooth glass plate in a scraping way, vacuumizing, and then placing on a flat plate heater for heating and curing to obtain a PDMS electrode substrate layer;
and 2, step: etching a symmetrical rectangular pattern with the width of 10mm, the length of 4mm and the distance of 2mm on a polyamide sheet, covering the symmetrical rectangular pattern on the surface of a molded PDMS sheet, and depositing a metal layer on the surface by adopting a magnetron sputtering method, wherein the thickness of the metal layer is 1 mu m to obtain a coplanar electrode layer;
and step 3: weighing a certain amount of carbon nanotube powder according to the preset specific gravity of the composite material, and dispersing the carbon nanotube powder in an organic solvent to obtain stable carbon nanotube dispersion liquid;
and 4, step 4: adding polydimethylsiloxane prepolymer into the carbon nano tube dispersion liquid, fully stirring for 3 hours by using a magnetic stirrer, heating the solution, and continuously stirring for 3 hours to remove the organic solvent;
and 5: weighing the diluent according to a certain proportion, mixing the diluent with the polydimethylsiloxane curing agent, and fully stirring for 3 hours by using a magnetic stirrer;
step 6: adding a diluent/curing agent solution into the carbon nano tube/polydimethylsiloxane prepolymer, coating the mixture on a mould, and placing the mould on a flat heater for curing to form a CNT/PDMS composite material;
the mass ratio of the polydimethylsiloxane prepolymer to the dimethyl siloxane curing agent is 5:1.
and 7: and (3) repeating the step (3) to the step (6) to obtain three CNT/PDMS composite material sheets with different carbon nanotube specific gravities, namely a first composite material film layer 2, a second composite material film layer 3 and a third composite material film layer 4.
And 8: the first composite film and the second composite film were cut into two rectangular sheets each having a width of 10mm and a length of 4mm, and the third composite film was cut into a sheet each having a length and a width of 10 mm. And aligning the wide sides of the first two sheets of the composite material with the wide sides of the second two sheets, aligning and stacking the two wide sides of the third layer of the composite material with the two first and second sheets, and bonding the two wide sides with silica gel to ensure that the three layers of the composite material can be tightly attached to form a sensitive layer, and the specific gravity of the carbon nanotubes in the three layers of the composite material is sequentially reduced.
And step 9: and coating the silver adhesive on the surface of the electrode, aligning the wide edge of the electrode with the wide edge of the sensitive layer, enabling the electrode and the sensitive layer to be tightly combined by using the silver adhesive, and vertically attaching the electrode and the sensitive layer by using a PU (polyurethane) adhesive tape to realize packaging.
Example 2
The difference between the embodiment and the embodiment is in steps 6-8, and the rest steps are the same as follows:
step 6: adding a diluent/curing agent solution into the carbon nano tube/polydimethylsiloxane prepolymer, coating the mixture on a mould, and placing the mould on a flat heater for curing to form a CNT/PDMS composite material;
the mass ratio of the polydimethylsiloxane prepolymer to the dimethyl siloxane curing agent is 8:1.
and 7: repeating the steps 3-6 to obtain 5 CNT/PDMS composite material sheets with different carbon nano tubes in specific gravity;
and 8: the method comprises the following steps of respectively cutting four layers of CNT/PDMS composite materials with sequentially increased specific gravity of carbon nano tubes into two rectangular sheets with the width of 10mm and the length of 4mm, then dividing 8 CNT/PDMS composite materials into two same groups, sequentially stacking the four CNT/PDMS composite materials from bottom to top according to the principle that the specific gravity of the carbon nano tubes is sequentially increased, bonding the four CNT/PDMS composite materials by using silica gel to form a composite material group, and finally bonding the CNT/PDMS composite material with the maximum specific gravity of the carbon nano tubes to the uppermost layer of the two composite material groups to form a composite material sensitive layer.
Example 3
The difference between the embodiment and the embodiment is in steps 6-8, and the rest steps are the same as follows:
step 6: adding a diluent/curing agent solution into the carbon nano tube/polydimethylsiloxane prepolymer, coating the mixture on a mould, and placing the mould on a flat heater for curing to form a CNT/PDMS composite material;
the mass ratio of the polydimethylsiloxane prepolymer to the dimethyl siloxane curing agent is 10:1.
and 7: repeating the steps 3-6 to obtain 10 CNT/PDMS composite material sheets with different carbon nano tubes in specific gravity;
and 8: respectively cutting 8 layers of CNT/PDMS composite materials with sequentially increasing specific gravity of the carbon nano tubes into two rectangular sheets with the width of 10mm and the length of 4mm, then dividing 16 CNT/PDMS composite materials into two groups which are the same, sequentially stacking the 8 CNT/PDMS composite materials from bottom to top according to the principle that the specific gravity of the carbon nano tubes sequentially increases, bonding the CNT/PDMS composite materials with the maximum specific gravity of the carbon nano tubes to the uppermost layer of the two composite material groups to form a composite material sensitive layer.
Example 4
A preparation method of a gradient multilayer flexible piezoresistive sensor comprises the following steps:
s1, preparation of coplanar metal electrode
S1.1, measuring 1g of PDMS prepolymer and 0.1g of curing agent, uniformly stirring, placing for 30min under a vacuum environment of 0.1 to remove air bubbles to obtain a polydimethylsiloxane solution, inverting on a glass plate, standing for 5min for automatic leveling, drying at 80 ℃ for 3h, and peeling to obtain a PDMS film;
s1.2, placing a mask plate on the PDMS film, plating a silver film with the thickness of 5um by utilizing magnetron sputtering, and waiting for a coplanar electrode.
S2, preparing the CNT/PDMS composite conductive film:
s2.1, weighing 30mg of multi-walled carbon nanotubes, mixing the multi-walled carbon nanotubes with 60ml of isopropanol, magnetically stirring for 1 hour, then ultrasonically dispersing for 4-6 hours to obtain carbon nanotube dispersion liquid with better dispersibility, then adding 1g of dimethyl siloxane prepolymer, magnetically stirring for 3 hours, and then stirring and evaporating for 3 hours at 80 ℃ to remove the isopropanol to obtain a CNT/dimethyl siloxane prepolymer solution;
s2.2, weighing 0.1g of polydimethylsiloxane curing agent, mixing with 5ml of n-hexane, and magnetically stirring for 3 hours;
s2.3, mixing and stirring the CNT/polydimethylsiloxane prepolymer solution and the normal hexane/polydimethylsiloxane curing agent solution, coating the mixture on a 100 x 100mm glass template, and curing for 3 hours at 80 ℃ to obtain a 3wt% CNT/PDMS composite material;
s2.4, weighing 50mg of multi-walled carbon nanotubes and mixing with 100ml of isopropanol, and repeating the steps S2.1-S2.3 to obtain the 5wt% CNT/PDMS composite material;
s2.5, weighing 70mg of multi-walled carbon nanotubes, mixing with 140ml of isopropanol, and repeating the steps S2.1-S2.3 to obtain a 7wt% CNT/PDMS composite;
s2.5, respectively cutting the CNT/PDMS composite materials prepared in the step S2.3 and the step S2.4 into two rectangular sheets with the width of 10mm and the length of 4mm, and cutting the CNT/PDMS composite material prepared in the step S2.5 into sheets with the length and the width of 10 mm. And aligning the wide sides of the two sheets of the composite material obtained in the step S2.3 with the wide sides of the two sheets obtained in the step S2.4 respectively, aligning and stacking the two wide sides of the composite material obtained in the step S2.5 with the two sheets of the first sheet and the second sheet respectively, and bonding the two wide sides with silica gel to ensure that the three layers of the composite material sheets can be tightly attached to form the sensitive layer.
S3, preparing a flexible piezoresistive sensing device:
and (3) tightly combining the copper electrodes on two sides of the multilayer composite film by utilizing silver adhesive to prepare the multilayer piezoresistive sensor with the gradient of resistance, modulus and roughness, and packaging the multilayer piezoresistive sensor by using a PU (polyurethane) adhesive tape to prepare the composite flexible piezoresistive sensor based on the gradient multilayer structure.
And S4, connecting wires at two ends of the electrode, testing the manufactured sensor by using a micro-force compression table, and showing the change relation of the resistance change rate along with the strain in fig. 6.
Comparative example 1
A preparation method of a single-layer piezoresistive sensor comprises the following steps:
s1, preparation of coplanar metal electrode
S1.1, measuring 1g of PDMS prepolymer and 0.1g of curing agent, uniformly stirring, placing for 30min under a vacuum environment of 0.1 to remove air bubbles to obtain a polydimethylsiloxane solution, inverting on a glass plate, standing for 5min for automatic leveling, drying at 80 ℃ for 3h, and stripping to obtain a PDMS film;
s1.2, placing a mask plate on the PDMS film, plating a silver film with the thickness of 5um by utilizing magnetron sputtering, and waiting for a coplanar electrode.
S2, preparing the CNT/PDMS composite conductive film:
s2.1, weighing 30mg of multi-walled carbon nanotube and 60ml of isopropanol, mixing the multi-walled carbon nanotube with the isopropanol by magnetic stirring for 1 hour, then carrying out ultrasonic dispersion for 4-6 hours to obtain a carbon nanotube dispersion liquid with better dispersibility, then adding 1g of dimethyl siloxane prepolymer, stirring the mixture by magnetic stirring for 3 hours, and then stirring and evaporating the mixture for 3 hours at 80 ℃ to remove the isopropanol to obtain a CNT/dimethyl polysiloxane prepolymer solution;
s2.2, weighing 0.1g of polydimethylsiloxane curing agent, mixing with 5ml of n-hexane, and magnetically stirring for 3 hours;
s2.3, mixing and stirring the CNT/polydimethylsiloxane prepolymer solution and the normal hexane/polydimethylsiloxane curing agent solution, coating the mixture on a 100 x 100mm glass template, and curing for 3 hours at 80 ℃ to obtain a 3wt% CNT/PDMS composite material;
s2.4, cutting the CNT/PDMS composite material prepared by the S2.3 into a sheet with the length and the width of 10 mm.
S3, preparing a flexible piezoresistive sensing device: and tightly combining copper electrodes on two sides of the composite membrane by using silver colloid to prepare a 3wt% single-layer piezoresistive sensor, and packaging by using a PU (polyurethane) adhesive tape to prepare the single-layer flexible piezoresistive sensor.
And S4, connecting wires at two ends of the electrode, testing the manufactured sensor by using a micro-force compression table, and showing the change relation of the resistance change rate along with the strain in fig. 7.
Comparative example 2
A method for preparing a gradient-free multilayer piezoresistive sensor comprises the following steps:
s1, preparation of coplanar metal electrode
S1.1, measuring 1g of PDMS prepolymer and 0.1g of curing agent, uniformly stirring, placing for 30min under a vacuum environment of 0.1 to remove bubbles to obtain a polydimethylsiloxane solution, inverting the polydimethylsiloxane solution on a glass plate, standing for 5min for automatic leveling, drying for 3h at 80 ℃, and stripping to obtain a PDMS film;
s1.2, placing a mask plate on the PDMS film, plating a silver film with the thickness of 5um by utilizing magnetron sputtering, and waiting for a coplanar electrode.
S2, preparing the CNT/PDMS composite conductive film:
s2.1, weighing 30mg of multi-walled carbon nanotube and 60ml of isopropanol, mixing the multi-walled carbon nanotube with the isopropanol by magnetic stirring for 1 hour, then carrying out ultrasonic dispersion for 4-6 hours to obtain a carbon nanotube dispersion liquid with better dispersibility, then adding 1g of dimethyl siloxane prepolymer, stirring the mixture by magnetic stirring for 3 hours, and then stirring and evaporating the mixture for 3 hours at 80 ℃ to remove the isopropanol to obtain a CNT/dimethyl polysiloxane prepolymer solution;
s2.2, weighing 0.1g of polydimethylsiloxane curing agent and 5ml of n-hexane, mixing, and magnetically stirring for 3 hours;
s2.3, mixing and stirring the CNT/polydimethylsiloxane prepolymer solution and the normal hexane/polydimethylsiloxane curing agent solution, coating the mixture on a 100 x 100mm glass template, and curing for 3 hours at 80 ℃ to obtain a CNT/PDMS composite material with the percentage of 3 wt%;
s2.4, cutting the CNT/PDMS composite material prepared by the S2.3 into four rectangular sheets with the width of 10mm and the length of 4 mm;
s2.5, cutting the CNT/PDMS composite material prepared in the step S2.3 into a sheet with the length and the width of 10 mm;
and S2.6, taking two of the composite material sheets prepared in the step S2.4 as a first layer and the rest two sheets as a second layer, aligning the wide sides of the first layer sheet with the wide sides of the two sheets of the second layer respectively, aligning and stacking the two wide sides of the composite material sheet prepared in the step S2.5 with the two first and second sheets respectively, and bonding the two wide sides with silica gel to ensure that the three composite material sheets can be tightly bonded to form a sensitive layer.
S3, preparing a flexible piezoresistive sensing device: and (3) tightly combining copper electrodes on two sides of the composite membrane by utilizing silver colloid to prepare the resistance and modulus gradient multilayer piezoresistive sensor, and packaging the piezoresistive sensor by utilizing a PU (polyurethane) adhesive tape to prepare the composite flexible piezoresistive sensor based on the gradient-free multilayer structure.
And S4, connecting wires at two ends of the electrode, testing the manufactured sensor by using a micro-force compression table, and showing the change relation of the resistance change rate along with the strain in fig. 8.
The comparison of the data of the devices in the examples and the comparative examples is as follows:
| linear detection Range/KPa | S/KPa -1 | |
| Example 4 | 0.003-120 | 14.93 |
| Comparative example 1 | 0.5-18 | 2.03 |
| Comparative example 2 | 0.04-80 | 5.16 |
In the table: s represents sensitivity, and the sensitivity calculation formula is as follows:
in conclusion, by comparing comparative example 1 and comparative example 2, it can be found that the sensitivity, measurement range and linearity values of the multilayer structure are higher than those of the single-layer structure;
by comparing example 4 with comparative example 2, it can be found that the sensitivity, measurement range and linearity values of the gradient multilayer structure are higher than those of the gradient-free multilayer structure, and the scheme has better comprehensive performance.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A gradient multilayer flexible piezoresistive sensor is characterized by comprising coplanar metal electrodes and composite material sensitive layers arranged on the coplanar metal electrodes, wherein the composite material sensitive layers comprise multilayer composite material films which are sequentially stacked from top to bottom, the composite material films are made of carbon nano tube polydimethylsiloxane, and the specific gravity of the carbon nano tubes in each composite material film is sequentially decreased from top to bottom;
each composite material film between the coplanar metal electrode and the composite material film on the uppermost layer comprises two spaced composite material sheets, two electrodes are formed on the coplanar metal electrode layer, and the two composite material sheets of the composite material film on the lowermost layer are respectively positioned on the two electrodes of the coplanar metal electrode.
2. The gradient multilayer flexible piezoresistive sensor according to claim 1, wherein the carbon nanotube polydimethylsiloxane composite layer is one or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes, or a modified conductive polymer doped in polydimethylsiloxane.
3. The gradient multilayer flexible piezoresistive sensor according to claim 1, wherein the number of layers of composite material in said composite sensitive layer is 3-10.
4. The gradient multilayer flexible piezoresistive sensor according to claim 1, wherein the thickness of the composite film is between 50 μm and 500 μm, and the thickness of the composite film is the same for each layer.
5. The gradient multilayer flexible piezoresistive sensor according to claim 1, wherein said coplanar metal electrodes comprise a flexible substrate, and two electrodes deposited on one side of the flexible substrate.
6. The gradient multilayer flexible piezoresistive sensor according to claim 1, wherein said electrodes have a thickness of between 1 μm and 5 μm.
7. The gradient multilayer flexible piezoresistive sensor according to claim 1, wherein the bottom of the coplanar metal electrodes 1 and the top of the uppermost composite film are provided with a polymer protective layer, respectively.
8. The gradient, multilayer, flexible piezoresistive sensor according to claim 1, wherein the specific gravity of said carbon nanotubes in said composite film is between 0.5wt% and 10wt%.
9. A method of fabricating a gradient multilayer flexible piezoresistive sensor according to any of the claims 1-8, comprising the steps of:
step 1, uniformly coating liquid carbon polydimethylsiloxane on a mould, and curing to form a flexible substrate;
step 2, depositing on the flexible substrate to form two electrodes to obtain a coplanar metal electrode;
step 3, dispersing the carbon nano tube powder in an organic solvent to obtain a carbon nano tube dispersion liquid;
step 4, adding a polydimethylsiloxane prepolymer into the carbon nano tube dispersion liquid, fully stirring, and removing the organic solvent to obtain a mixed solution of the carbon nano tube polydimethylsiloxane prepolymer;
step 5, adding a curing agent into the mixed solution, coating the mixed solution on a mold, and curing to form a composite material film;
step 6, repeating the steps 3-5 to prepare a plurality of composite films with different carbon nano tubes;
step 7, stacking and combining the composite material films from bottom to top in sequence according to the principle of increasing the specific gravity of the carbon nano tubes, cutting the combined multilayer CNT/PDMS composite material films into two composite material groups, and combining the CNT/PDMS composite material film with the largest specific gravity of the carbon nano tubes on the top surfaces of the two composite material groups to obtain a composite material sensitive layer;
and 8, packaging the composite material sensitive layer and the coplanar metal electrode to obtain the gradient multilayer flexible piezoresistive sensor.
10. The method for manufacturing the gradient multilayer flexible piezoresistive sensor according to claim 9, wherein the mass ratio of the polydimethylsiloxane prepolymer to the curing agent in the mixed solution in the step 5 is (5-10): 1.
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| CN117030079B (en) * | 2023-10-09 | 2024-02-23 | 之江实验室 | Wide-range flexible pressure sensor and preparation method thereof |
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