CN114479468A

CN114479468A - Preparation method of CNT/PDMS flexible composite material and capacitive pressure sensor

Info

Publication number: CN114479468A
Application number: CN202210066115.5A
Authority: CN
Inventors: 林红; 任孟; 陈宇岳; 张德锁
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2022-01-20
Filing date: 2022-01-20
Publication date: 2022-05-13

Abstract

The invention discloses a preparation method of a CNT/PDMS flexible composite material, which comprises the following steps: fully mixing the CNT modified by a strong acid oxidation method with sugar particles, adding PDMS sponge and a curing agent, fully stirring, tabletting by using a tabletting device, putting the sample into an oven for heating and curing for a certain time, taking out the sample, and putting the sample into water to melt the sugar, thereby preparing the CNT/PDMS flexible composite material. The carbon nano tubes are brought into the PDMS matrix through the sugar particles, the phenomenon of agglomeration among the nano tubes is reduced, the carbon nano tube particles are combined with the polymer matrix and uniformly dispersed in the PDMS, and the PDMS polymer composite material has good sensitivity and durability and ensures stable capacitance response.

Description

Preparation method of CNT/PDMS flexible composite material and capacitive pressure sensor

Technical Field

The invention relates to the technical field of flexible pressure sensors, in particular to a preparation method of a CNT/PDMS flexible composite material and a capacitive pressure sensor.

Background

Carbon nanotubes have excellent mechanical properties, are one of the most rigid materials known, and the tensile strength and elastic modulus of carbon nanotubes are the largest of the currently known materials. From the viewpoint of electrical properties, the carbon nanotube has good electrical conductivity and also has a superconducting property in a low temperature state. From the viewpoint of thermal performance, the thermal conductivity of the carbon nanotubes is also characterized by anisotropy. In addition, the excellent properties of carbon nanotubes include many properties such as adsorption, hydrogen storage, and optics, and it is because of these excellent properties that carbon nanotubes have been the focus of research by researchers in various fields.

In the prior art, a flexible pressure sensor is generally prepared by firstly preparing porous PDMS (polydimethylsiloxane), and then adsorbing a conductive material by an evaporation coating, sputtering or dip coating method, but the sensor prepared by the method has the defects that the conductive material is difficult to permeate into the porous sponge and is easy to fall off from the surface, and particularly, the high sensitivity and stability of the sensor are difficult to obtain under frequent compression operation.

In order to solve the above problems, it is necessary to develop a flexible capacitive pressure sensor having high sensitivity and good stability.

Disclosure of Invention

The invention overcomes the defects of the prior art and provides a preparation method of a CNT/PDMS flexible composite material.

In order to achieve the purpose, the invention adopts the technical scheme that: a preparation method of a CNT/PDMS flexible composite material is characterized by comprising the following steps:

s1, modifying the carbon nano tube by adopting a strong acid oxidation method to obtain an acid-oxidized carbon nano tube;

s2, mixing the carbon nano tube oxidized by the acid with the dispersoid;

s3, adding a curing agent into the PDMS sponge and mixing;

s4, mixing the mixture of S2 and S3, and shaping and curing;

and S5, adding water into the cured sample in the S4, dissolving dispersoids in the sample, and drying to obtain the CNT/PDMS sponge, namely the CNT/PDMS flexible composite material.

In a preferred embodiment of the present invention, the strong acid oxidation modification treatment of carbon nanotubes comprises the following steps:

s11, adding a strong acid solution into the untreated carbon nano tube, and ultrasonically cleaning at room temperature;

s12, performing reflux treatment in a reflux device at the temperature of 50-70 ℃;

s13, evaporating and concentrating the solution after the reflux treatment to form a concentrated solution, and cooling;

s14, centrifuging the concentrated solution in the S13, and removing supernatant to obtain the treated carbon nano tube;

and S15, adding water into the carbon nano tube, performing ultrasonic treatment and centrifugal treatment, repeating for 5-6 times until the solution is neutral, and drying to obtain the acid-oxidized carbon nano tube.

In a preferred embodiment of the present invention, the carbon nanotubes are multi-walled carbon nanotubes.

In a preferred embodiment of the present invention, the doping concentration of the carbon nanotube is 0 to 7 wt%.

In a preferred embodiment of the invention, the dispersoid is a sugar.

In a preferred embodiment of the present invention, in S5, the dispersoid in the sample is dissolved by a water bath method.

The CNT/PDMS flexible composite material is prepared by the preparation method of the CNT/PDMS flexible composite material, and is characterized in that:

when the doping concentration range of the carbon nano tube is 0-5 wt%, the carbon nano tube particles are uniformly dispersed in the PDMS sponge, the particles are independent from each other, the internal structure is loose, and the Poisson ratio is high;

when the doping concentration range of the carbon nanotube is 5 wt% -7 wt%, the carbon nanotube particles attached to the interior of the PDMS sponge are obviously agglomerated, and the carbon nanotube particles are connected with each other.

A capacitive pressure sensor is prepared by the preparation method of the CNT/PDMS flexible composite material, and is characterized in that: the capacitive pressure sensor is formed by connecting and assembling the CNT/PDMS flexible composite material and a lead.

In a preferred embodiment of the present invention, when the doping concentration of the carbon nanotube ranges from 0 wt% to 7 wt%, the sensitivity value of the capacitive pressure sensor is increased first and then decreased.

In a preferred embodiment of the present invention, the response time of the capacitive flexible sensor with the doped carbon nanotubes having a concentration of 4 to 6 wt% is 0.2 to 0.7s, and the recovery time is 0.3 to 0.9s within a certain pressure range.

The invention solves the defects in the background technology, and has the following beneficial effects:

(1) the invention utilizes an in-situ sugar template method and a tabletting method, and solves the problems that the conductive material is difficult to permeate into the porous sponge and is easy to fall off in the prior art; the carbon nanotubes are brought into the PDMS matrix through the sugar particles, so that the carbon nanotubes are uniformly distributed in the PDMS sponge, the carbon nanotube particles are not closely connected with each other and are not easily separated from the inner surface of the PDMS sponge, the sensitivity and the durability are good, and the stable capacitance response is ensured.

(2) According to the invention, the carbon nano tubes are modified by adopting a strong acid oxidation method, so that the surface energy of the carbon nano tubes is reduced, the phenomenon of agglomeration among the carbon nano tubes is reduced, and the carbon nano tubes are favorably combined with a polymer matrix and uniformly dispersed in the flexible matrix PDMS.

(3) According to the invention, the pure PDMS sponge is doped with the carbon nanotubes with different concentrations to obtain the CNT/PDMS sponge with different sensitivities and stabilities, the spatial arrangement structure of the CNT/PDMS sponge meets the requirements of contact points and surfaces of the carbon nanotubes, and when the CNT/PDMS conductive sponge is compressed, the carbon nanotubes attached to the interior of the PDMS sponge are mutually connected, so that the dielectric constant of the composite material is changed, and the requirements of a stress sensor are met.

(4) Compared with the traditional resistance-type flexible pressure sensor, the CNT/PDMS capacitive flexible sensor has the advantages that the response time and the recovery time are increased along with the increase of pressure; however, the response time and recovery time of the CNT/PDMS capacitive flexible pressure sensor of the present invention are shorter than those of the resistive flexible pressure sensor because the resistive flexible pressure sensor requires a time for connecting conductive materials to each other in addition to a time for compressing and deforming a conductive sponge, and the capacitive flexible pressure sensor is more dependent on a time for changing a distance between electrode plates, i.e., a time for compressing and deforming a sponge, so that the response time and recovery time of the CNT/PDMS capacitive flexible pressure sensor are shorter.

(5) When the doping concentration range of the carbon nano tube is 0-5 wt%, the carbon nano tube particles are uniformly dispersed in PDMS, the particles are independent from each other, the dielectric constant of the composite material is not large when the composite material is not compressed, but after the composite material is compressed, the originally dispersed carbon nano tube particles are connected with each other, so that the dielectric constant of the composite material is rapidly increased, the larger the doping concentration of the carbon nano tube is, the easier the connection between the particles is, the faster the dielectric constant of the composite material is increased, and the sensitivity is higher.

When the doping concentration of the carbon nano tube exceeds 5 wt%, obvious agglomeration phenomenon can occur among particles, so that conductive particles are mutually connected to form a conducting circuit, the dielectric constant of the composite material is larger when the composite material is not compressed, but the dielectric constant of the composite material can not be obviously increased after the composite material is compressed; on the other hand, the mechanical property of the composite material is changed due to the increase of the concentration of the carbon nanotubes, and the higher the concentration of the carbon nanotubes is, the higher the compression modulus and the rigidity of the composite material are, the lower the deformation capability is, and the sensitivity to pressure is reduced.

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 introduced below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts;

FIG. 1 is a SEM image of a pure PDMS sponge and its cross section according to one embodiment of the present invention;

FIG. 2 is an SEM image of an embodiment of a CNT/PDMS sponge with a carbon nanotube doping concentration of 5% according to a first embodiment of the present invention;

FIG. 3 is a graph of the sensitivity of a CNT/PDMS capacitive flexible sensor with different carbon nanotube concentrations according to a second embodiment of the present invention;

FIG. 4 is a sensitivity fit curve of a flexible pressure sensor with a doping concentration of 0 wt% to 7 wt% in example two of the present invention;

FIG. 5 is a sensitivity curve of a sensor according to a second embodiment of the present invention;

FIG. 6 is a graph of the response and recovery of a CNT/PDMS flexible pressure sensor under three different pressures according to a third embodiment of the present invention;

FIG. 7 is a hysteresis curve of a CNT/PDMS capacitive flexible pressure sensor according to a fourth embodiment of the present invention;

FIG. 8 is a graph of the cycling stability of a CNT/PDMS flexible pressure sensor according to a fifth embodiment of the present invention;

FIG. 9 is a stress-strain curve of a CNT/PDMS composite sponge according to example six of the present invention;

fig. 10 is a diagram of a CNT/PDMS based capacitive array flexible pressure sensor according to a seventh embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example one

The flexible base material selected in the embodiment is polydimethylsiloxane PDMS, which is taken as a typical silicone rubber material and has a silicon-oxygen bond (Si-O) with a spiral structure, all side groups are methyl, and the bond angle of the PDMS silicon-oxygen bond is large, so that the PDMS silicon-oxygen bond is easy to rotate, and good flexibility is generated. PDMS is a thermosetting material which is divided into a main body and a curing agent, wherein the main body is siloxane oligomer, the curing agent is a siloxane cross-linking agent, and the two components can be cross-linked under a heating condition. Because a plurality of reaction sites exist between the main body of the PDMS and the curing agent, the PDMS can be cured and formed under the action of heat after being fully mixed.

In this embodiment, PDMS is used to replace water, carbon nanotube CNT and sugar particles are fully mixed, PDMS sponge and a curing agent are added, a tabletting device is used for tabletting after fully stirring, then a sample is placed in an oven for heating and curing for a certain time, the sample is taken out and placed in water to melt sugar, and thus the CNT/PDMS flexible composite material is prepared, and the specific preparation method includes the following steps:

s2, grinding the sugar blocks into powdery sugar particles, and sieving; mixing the sieved sugar particles with the carbon nano tubes oxidized by acid;

s3, weighing the modified carbon nano tubes according to a certain proportion, adding a proper amount of screened sugar particles, and grinding to fully mix the carbon nano tubes and the sugar particles;

s4, taking a certain amount of pure PDMS sponge, adding a curing agent into the PDMS sponge, and fully stirring; adding the mixture of the carbon nano tube and the sugar particles into the mixture of the PDMS sponge and the curing agent, and fully stirring, wherein the doping concentration of the carbon nano tube is 0-7 wt%;

s5, shaping and curing the uniform mixture prepared in the S4;

s6, taking out the cured sample, putting the sample into a container, adding a proper amount of water to obtain a sample after dissolution, and drying the sample to remove the residual water to form a CNT/PDMS sponge, namely the CNT/PDMS flexible composite material.

The carbon nanotubes are twisted with each other due to the large length-diameter ratio of the carbon nanotubes, and the carbon nanotubes are agglomerated due to the large surface energy, which is not favorable for the dispersion of particles, and the dispersibility and conductivity of the carbon nanotubes are reduced. In order to improve the dispersibility and conductivity of the carbon nanotubes, the surface of the carbon nanotubes needs to be modified to reduce the surface energy thereof, so that the carbon nanotubes can be better combined with the polymer matrix and uniformly dispersed in the flexible matrix PDMS.

In this embodiment, a strong acid oxidation method is used to remove metal catalyst and other impurities on the surface of the carbon nanotube, thereby enhancing the conductivity and purification. Specifically, the strong acid oxidation modification treatment of the carbon nanotube comprises the following steps:

and S15, adding water into the carbon nano tube, performing ultrasonic treatment and centrifugal treatment, repeating for 5-6 times until the solution is neutral, and drying to obtain the acid-oxidized carbon nano tube. The carbon nanotubes in this embodiment are preferably multi-walled carbon nanotubes. Compared with single-wall carbon nanotubes, the multi-wall carbon nanotubes have larger length-diameter ratio, simple manufacture and lower preparation cost. The length-diameter ratio of the multi-walled carbon nanotube is related to the purity, the higher the purity is, the larger the length-diameter ratio is, the easier the mutual lapping of the inner parts is, and a better conductive network can be formed in the composite material even if a small amount of multi-walled carbon nanotubes are added. In addition, the dielectric constant of the composite material is also greatly improved after the conductive particles are added.

In this embodiment, the doping concentration of the carbon nanotube is preferably 5 wt%, and the CNT/PDMS sponge having the doping concentration of the carbon nanotube of 5% is prepared by using the above preparation method. This example performed a topographical characterization analysis of the prepared CNT/PDMS sponge, comparing SEM images of pure PDMS sponge and CNT/PDMS sponge.

(1) SEM analysis of pure PDMS sponge

In order to explore the internal condition of pure PDMS sponge, the material was scanned by electron microscopy. The appearance of the pure PDMS sponge is shown in figure 1, the pure PDMS sponge has a white surface color, a plurality of pore structures are arranged inside the pure PDMS sponge, the surface of the pure PDMS sponge is smooth, and no impurity particles are attached to the pure PDMS sponge.

(2) CNT/PDMS sponge SEM analysis

The carbon nano tube is uniformly doped in the PDMS sponge, which is an important link for manufacturing the flexible conductive sponge. Fig. 2 (a) is a physical diagram of the CNT/PDMS sponge, in which it can be clearly seen that the surface color of the PDMS sponge is light black and the surface is rough, which indicates that the carbon nanotubes are successfully combined with the PDMS sponge.

The sectional electron microscope test of the material object shows that, as shown in fig. 3 (b) and (c), the carbon nanotubes on the prepared CNT/PDMS sponge are clearly attached to the interior of the PDMS sponge, the carbon nanotubes are uniformly distributed in the interior in a whole manner, a certain agglomeration phenomenon exists locally, the carbon nanotube particles are not tightly connected, and therefore the CNT/PDMS sponge cannot conduct electricity, and therefore the CNT/PDMS sponge can be used as a capacitive flexible sensor.

The spatial arrangement structure meets the requirement that the sponge can cause contact points and surfaces of the carbon nanotubes after being compressed again, so that the conductivity of the sponge can be correspondingly changed when the sponge is compressed again. When the CNT/PDMS sponge is compressed, the carbon nanotubes attached to the interior of the PDMS sponge are extruded by the PDMS sponge to be deformed, and then the capacitance change rate is changed, so that the requirement of the stress sensor is met.

Example two

In this embodiment, a method for preparing a CNT/PDMS flexible composite material as in the first embodiment is adopted, and a capacitive flexible sensor is prepared and formed. The capacitive flexible sensor is formed by connecting and assembling a CNT/PDMS flexible composite material and a lead, specifically, the prepared CNT/PDMS flexible composite material is placed on a workbench, conductive adhesive tapes are attached to the upper surface and the lower surface of a conductive sponge, and tested electrodes are led out to obtain the capacitive flexible sensor.

The sensitivity refers to the sensitivity of the sensor to external pressure when the sensor is stimulated by the external pressure, and is mainly determined by the slope of the curve of the delta R/R0. The sensitivity of the sensor is tested by the embodiment, and the influence of different carbon nano tube concentrations on the sensitivity of the flexible resistance type pressure sensor is compared. In the method for testing the sensitivity of the sensor in the embodiment, the CNT/PDMS capacitive flexible sensor is tested by using a push-pull meter and an LCR digital bridge. The capacitive flexible sensor is placed on the platform of the test rig and connected to an LCR digital bridge, then different pressures are applied to the sensor, and data are collected and recorded.

As shown in fig. 3, the sensitivity curves of the CNT/PDMS capacitive flexible sensor at different carbon nanotube concentrations in this example are shown.

As can be seen from fig. 3, when the doping concentration of the carbon nanotube ranges from 0 wt% to 7 wt%, the capacitance change rate of the sensor under the same pressure decreases as the doping concentration of the carbon nanotube increases. When the doping concentration of the carbon nanotubes is increased to 5 wt%, the capacitance change rate of the sensor increases to a maximum value, and then if the doping concentration of the carbon nanotubes is increased, the capacitance change rate of the sensor decreases.

The reason for this is because when the doping concentration of the carbon nanotubes is in the range of 0 wt% to 5 wt%, the carbon nanotube particles are uniformly dispersed in the PDMS, the particles are independent from each other, and the dielectric constant of the composite material is not large when not compressed, but when compressed, the originally dispersed carbon nanotube particles are connected to each other, resulting in a rapid increase in the dielectric constant of the composite material, and the higher the doping concentration of the carbon nanotubes is, the easier the connection between the particles is, and the faster the dielectric constant of the composite material is increased, thus having higher sensitivity.

When the doping concentration of the carbon nano tube exceeds 5 wt%, obvious agglomeration phenomenon can occur among particles, so that the conductive particles are mutually connected to form a conducting circuit, the dielectric constant of the composite material is larger when the composite material is not compressed, but the dielectric constant of the composite material can not be obviously increased after the composite material is compressed; on the other hand, the mechanical property of the composite material is changed due to the increase of the concentration of the carbon nanotubes, and the higher the concentration of the carbon nanotubes is, the higher the compression modulus and the rigidity of the composite material are, the lower the deformation capability is, and the sensitivity to pressure is reduced.

In the embodiment, sensitivity fitting is carried out on 8 CNT/PDMS flexible pressure sensors with different doping concentrations within the pressure ranges of 0-0.5 kPa, 1-2.5 kPa and 3.0-4.5 kPa to obtain corresponding sensitivity values. The fitting result is shown in fig. 4, wherein (a) - (h) are sensitivity fitting curves of the flexible pressure sensor with the doping concentration of 0 wt% -7 wt%; FIG. 5 shows the sensitivity curve of the sensor; the sensitivity values in the range of 0 to 0.5kPa are shown in Table 1.

Table 10-0.5 kPa pressure range sensitivity values of different carbon nanotube doping concentrations

It can be seen from (a) to (f) of fig. 4 that the sensitivity of the composite material increases with the doping concentration of the carbon nanotube when the doping concentration of the carbon nanotube ranges from 0 wt% to 5 wt%, and reaches a maximum value of 23.107kPa when the doping concentration is 5 wt%^-1。

As the doping concentration of the carbon nanotubes continues to increase, the sensitivity of the composite gradually begins to decrease. By comparing the sensitivity in the pressure ranges of 0-0.5 kPa, 1-2.5 kPa and 3.0-4.5 kPa, the sensitivity of the composite material is found to decrease with increasing pressure.

The reason is that when no pressure is applied to the sponge, the carbon nanotube particles are uniformly dispersed in the PDMS sponge, and the particles are not connected to each other, so that the dielectric constant of the composite material is not large, and the internal structure is relatively loose, and has a relatively large poisson ratio, so that the conductive sponge can be greatly deformed when a relatively small pressure is applied, and the originally dispersed carbon nanotubes are connected to each other, and the dielectric constant of the composite material is rapidly increased, so that the composite material has a relatively high sensitivity. However, as the pressure is increased, the poisson ratio of the conductive sponge is reduced, and when a larger pressure is applied, only a small deformation occurs, most of the carbon nanotube particles in the sponge are connected with each other, the dielectric constant of the composite material is increased slowly, and therefore the sensitivity is gradually reduced.

EXAMPLE III

The sensitivity of the CNT/PDMS capacitive flexible sensor is the maximum when the doping concentration of the carbon nano tube is 5 wt% obtained from the first embodiment and the second embodiment. In the embodiment, the response time of the flexible pressure sensor is tested by adopting a weight and an electrochemical workstation, the sensor and the electrochemical workstation form a series circuit, then an i-t test program is selected from the programs of the electrochemical workstation, the weight is placed on the flexible pressure sensor, and the response time of the flexible pressure sensor to the weight is recorded.

In this embodiment, the capacitive flexible sensor with the highest sensitivity doped carbon nanotube concentration of 5 wt% is selected for the response and recovery tests, the response time and the recovery time are measured when the pressure is 1kPa, 2.5kPa and 5kPa, and the test result is shown in fig. 6, in which fig. 6(a) - (c) show the response and recovery curves of the CNT/PDMS capacitive flexible sensor under the action of 1kPa, 2.5kPa and 5kPa, respectively.

When the applied pressure is 1kPa, the response time of the sensor is 0.2s, and the recovery time is 0.3 s; when the applied pressure is 2.5kPa, the response time of the sensor is 0.5s, and the recovery time is 0.7 s; when the applied pressure was 5kPa, the response time of the sensor was 0.7s and the recovery time was 0.9 s. The results show that the greater the applied pressure, the longer the response time and recovery time of the flexible pressure sensor, since as the pressure continues to increase, the greater the degree of deformation of the conductive sponge when compressed, and the corresponding longer the response time and recovery time.

In contrast to the response time of resistive flexible pressure sensors, their response time and recovery time both increase with increasing pressure. However, the response time and recovery time of the CNT/PDMS capacitive flexible sensor in this embodiment are shorter than those of the resistive flexible pressure sensor because the resistive flexible pressure sensor requires a time for the conductive material to be connected to each other in addition to the time for the conductive sponge to be compressed and deformed, and the capacitive flexible pressure sensor is more dependent on the time for the distance between the electrode plates to change, i.e., the time for the sponge to be compressed and deformed, so the response time and recovery time of the capacitive flexible pressure sensor are shorter.

Example four

In this embodiment, the hysteresis stability of the CNT/PDMS capacitive flexible sensor prepared in the above embodiments is tested, and fig. 7 shows a hysteresis curve of the CNT/PDMS capacitive flexible sensor.

The hysteresis in this embodiment refers to the degree of coincidence of the two sensitivity curves after the flexible pressure sensor is subjected to pressure and pressure is removed, that is, whether the flexible pressure sensor can return to the original state after pressure is removed, and the stability of the sensor is shown.

In this embodiment, a push-pull meter and an LCR digital bridge are used to test the CNT/PDMS capacitive flexible sensor, and the change in resistance after applying pressure is compared with the change in resistance after removing pressure to verify the hysteresis of the sensor.

As can be seen in fig. 7, the CNT/PDMS sensor has little hysteresis, and the two curves substantially coincide, indicating that the sensor recovers well without being damaged after the pressure is removed.

EXAMPLE five

In order to further verify the cycling stability performance of the CNT/PDMS capacitive flexible sensor under different compression deformation amounts, the CNT/PDMS sponge with the highest sensitivity in the above embodiments was selected for the stability test.

In the embodiment, the electrochemical workstation and the universal material testing machine are adopted to test the circulation stability performance of the flexible pressure sensor. Specifically, a conductive sponge sample is placed on a universal material testing machine, the sample is connected and assembled into a flexible pressure sensor through a conductive adhesive tape and a lead and is connected with an LCR digital bridge, and cycle data of 200 times of compression of the CNT/PDMS capacitive flexible sensor is tested.

A cyclic compression stability experiment in which the amount of deformation is 30% and the number of compression times is 200 was performed using a sensor in which the doping concentration of the carbon nanotube is 5 wt%, and the change rates of capacitance in which the amount of compression deformation is 10%, 20%, and 30% were compared, and the test results are shown in fig. 8, in which fig. 8(a) is a cyclic stability test graph in which compression is 200 times, and (b) is a resistance change rate comparison graph in which the amounts of deformation are different.

It can be seen from the figure that the wave troughs and wave crests of the cyclic curve almost form two parallel straight lines in the 200 times of repeated compression, which shows that the flexible sensor has better repeatability, and the resistance change rate gradually increases along with the increase of the deformation quantity.

EXAMPLE six

In this example, the CNT/PDMS sponge with the highest sensitivity in the above examples was selected to perform a cyclic compression type stress-strain experiment, a universal material testing machine was used, and stress-strain curves after 300 times and 500 times of compression were selected for comparison, and fig. 9 is a stress-strain curve diagram of the CNT/PDMS composite sponge.

As can be seen from fig. 9, the stress-strain curves after 300 times and 500 times of compression are substantially overlapped, which indicates that the flexible composite sponge can be restored to the original size after multiple times of compression, and has better resilience performance.

EXAMPLE seven

The first embodiment and the sixth embodiment show that when the doping concentration of the carbon nanotube is 5 wt%, the flexible resistance type pressure sensor has the maximum sensitivity, quick response, good hysteresis, good repetition stability and good resilience.

This example prepares a capacitive flexible array sensor device in order to show the potential application of the flexible CNT/PDMS sponge prepared above. The device is based on the principle of parallel capacitive plates, and the sensing elements are in an array structure formed by upper and lower crossed electrodes, as shown in (a) of fig. 10. The conductive adhesive tapes are designed into electrodes of an upper electrode plate and a lower electrode plate, the lower electrode plate is assumed to have m electrodes, the upper electrode plate has n electrodes, and the upper electrode plate and the lower electrode plate are vertically distributed in space to form m multiplied by n capacitor units. In order to study the working condition of the sensor, a 10 × 10 capacitive flexible array pressure sensor was fabricated, and the pressure distribution of the sensor can be known by testing the capacitance of each sensing unit as shown in fig. 10 (b). As shown in fig. 10 (c), the capacitance response of each sensing unit on the sensor can reflect the pressure change in the area, and the distribution of the pressure test is realized by collecting the capacitance value of each capacitance unit of the sensor.

The mortar, the reaction vessel and three weights of different masses were placed on the sensor array as shown in fig. 10 (d), (e) and (f). The capacitance change values of 100 sensing units in the sensor are detected, and the shape of the placed object can be clearly distinguished by the capacitance change values. Meanwhile, different capacitance changes are generated at corresponding positions, and large capacitance changes can be observed at positions bearing large weights. The reason for this is that, since the object causes compression deformation on the sponge dielectric layer, the distance between the upper and lower electrodes at the corresponding position is reduced, resulting in an increase in capacitance at the corresponding position. Heavier objects result in a shorter distance between the two electrodes, resulting in a larger capacitive response. The result shows that the capacitive array sensor can not only measure the weight of the placed object, but also identify and display the shape and the position of the object, and has great application potential on electronic skins and flexible robots.

In light of the foregoing description of the preferred embodiment of the present invention, it is to be understood that various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A preparation method of a CNT/PDMS flexible composite material is characterized by comprising the following steps:

s2, mixing the carbon nano tube oxidized by the acid with the dispersoid;

s3, adding a curing agent into the PDMS sponge and mixing;

s4, mixing the mixture of S2 and S3, and shaping and curing;

2. The method of claim 1, wherein the CNT/PDMS flexible composite is prepared by the following steps: the strong acid oxidation method modification treatment of the carbon nano tube comprises the following steps:

3. The method of claim 1, wherein the CNT/PDMS flexible composite is prepared by the following steps: the carbon nano-tube is a multi-wall carbon nano-tube.

4. The method of claim 1, wherein the CNT/PDMS flexible composite is prepared by the following steps: the doping concentration of the carbon nano tube is 0-7 wt%.

5. The method of claim 1, wherein the CNT/PDMS flexible composite is prepared by the following steps: the dispersoid is sugar.

6. The method of claim 1, wherein the CNT/PDMS flexible composite is prepared by the following steps: in S5, the dispersoid in the sample is dissolved by a water bath method.

7. A CNT/PDMS flexible composite material prepared by the method for preparing the CNT/PDMS flexible composite material according to any one of claims 1 to 6, wherein the method comprises the following steps:

8. A capacitive pressure sensor, made by a method for preparing a CNT/PDMS flexible composite material according to any one of claims 1-7, characterized in that: the capacitive pressure sensor is formed by connecting and assembling the CNT/PDMS flexible composite material and a lead.

9. The method of claim 8, wherein the CNT/PDMS flexible composite is prepared by the following steps: when the doping concentration range of the carbon nano tube is 0 wt% -7 wt%, the sensitivity value of the capacitance type pressure sensor is increased firstly and then reduced.

10. The method of claim 9, wherein the CNT/PDMS flexible composite is prepared by: in a certain pressure range, the response time of the capacitive flexible sensor with the concentration of the doped carbon nano tube of 4-6 wt% is 0.2-0.7 s, and the recovery time is 0.3-0.9 s.