CN114381032A - Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad - Google Patents

Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad Download PDF

Info

Publication number
CN114381032A
CN114381032A CN202210066955.1A CN202210066955A CN114381032A CN 114381032 A CN114381032 A CN 114381032A CN 202210066955 A CN202210066955 A CN 202210066955A CN 114381032 A CN114381032 A CN 114381032A
Authority
CN
China
Prior art keywords
composite material
doping concentration
pdms composite
phase
pdms
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202210066955.1A
Other languages
Chinese (zh)
Inventor
林红
任孟
陈宇岳
张德锁
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Suzhou University
Original Assignee
Suzhou University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Suzhou University filed Critical Suzhou University
Priority to CN202210066955.1A priority Critical patent/CN114381032A/en
Publication of CN114381032A publication Critical patent/CN114381032A/en
Pending legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/36—After-treatment
    • C08J9/40—Impregnation
    • A—HUMAN NECESSITIES
    • A43—FOOTWEAR
    • A43B—CHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
    • A43B17/00—Insoles for insertion, e.g. footbeds or inlays, for attachment to the shoe after the upper has been joined
    • A43B17/14—Insoles for insertion, e.g. footbeds or inlays, for attachment to the shoe after the upper has been joined made of sponge, rubber, or plastic materials
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2383/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen, or carbon only; Derivatives of such polymers
    • C08J2383/04—Polysiloxanes

Abstract

The invention discloses a preparation method of a three-phase PDMS composite material based on a seepage theory, which comprises the following steps: mixing carbon nano tubes, graphene and a proper amount of sugar particles, fully grinding to uniformly mix the particles, adding a proper amount of PDMS and a curing agent, uniformly stirring the mixture, putting the mixture into a tablet press for tabletting and molding, curing the prepared sample, heating in a water bath to accelerate the dissolution of the sugar particles to obtain a three-phase PDMS composite material, explaining the change rule of the dielectric property and the conductive property of the three-phase PDMS composite material under different doping concentrations along with the doping concentrations by combining a percolation theory, and finding out a percolation threshold value to obtain the three-phase PDMS composite material with the maximum sensitivity. The preparation method combines the percolation theory and the in-situ sugar template method, and increases the doping concentration of the conductive material to the percolation threshold value, so that the agglomeration of the filling materials and the interaction between the filling materials and the flexible matrix are reduced, and the dielectric property and the conductive property of the composite material are improved.

Description

Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad
Technical Field
The invention relates to the technical field of flexible pressure sensors, in particular to a preparation method of a three-phase PDMS composite material based on a seepage theory and an intelligent foot pad.
Background
The composite material with high dielectric constant plays a great role in storing electric energy, homogenizing electric field and the like, so that the composite material has great application potential in the fields of artificial muscle, coat material assisting in drug release, bioengineering and the like.
Conductors/polymers are currently an effective form of making high dielectric composites. Among them, the multi-walled carbon nanotubes have been widely noticed because of their characteristics such as large aspect ratio, excellent mechanical properties, electrical properties, and heat resistance, so as to prepare various high dielectric constant CNT/polymer composite materials. However, the dispersion of the carbon nanotubes is poor, so that the higher the content of the carbon nanotubes is, the more unfavorable the dispersion of the carbon nanotubes is; in addition, the higher the content of carbon nanotubes, the higher the dielectric loss.
Therefore, it is important to obtain a composite material with low dielectric loss and high dielectric constant under the premise of percolation threshold.
Disclosure of Invention
The invention overcomes the defects of the prior art and provides a preparation method of a three-phase PDMS composite material based on a seepage theory.
In order to achieve the purpose, the invention adopts the technical scheme that: the preparation method of the three-phase PDMS composite material based on the seepage theory is characterized by comprising the following steps:
s1, mixing the carbon nano tube and the graphene with the dispersoid;
s2, adding a curing agent into the PDMS sponge and mixing; adding a mixture of carbon nanotubes, graphene and dispersoids in S1, wherein the doping concentration of the carbon nanotubes and the graphene is 0-3.5 wt%;
s3, shaping and curing the mixture in the S2; adding water into the cured sample, dissolving dispersoids in the sample, and drying to obtain rGO/CNT/PDMS sponge, namely the three-phase PDMS composite material;
and S4, explaining the change rule of the dielectric property and the conductivity of the three-phase PDMS composite material under different doping concentrations along with the doping concentration by combining with a percolation theory, and finding out a percolation threshold value to obtain the three-phase PDMS composite material with the maximum sensitivity.
In a preferred embodiment of the present invention, the doping concentration of the carbon nanotubes and the graphene is 2 to 3 wt%.
In a preferred embodiment of the present invention, when the doping concentration of the carbon nanotube and the graphene reaches the percolation threshold, the dielectric property and the conductivity of the composite material are predicted by a percolation theoretical formula:
ε,∝(Pc-P)-x，P<Pc；
tanθ∝(Pc-P)-r，P<Pc；
σdc∝(P-Pc)t，P>Pc；
wherein ε is a dielectric constant, PcIs the percolation threshold of the filler, P is the content of the filler, tan theta is the dielectric loss and is the direct current conductance; x, r and t are critical indices of dielectric constant, dielectric loss and direct current conductance, respectively.
In a preferred embodiment of the present invention, the carbon nanotubes need to be modified by a strong acid oxidation method before being mixed with graphene, and the method 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 invention, the dispersoid is a sugar.
In a preferred embodiment of the present invention, in S3, the dispersoid in the sample is dissolved by a water bath method.
A three-phase PDMS composite material is prepared by the preparation method of the three-phase PDMS composite material based on the seepage theory:
when the doping concentration range of the three-phase PDMS composite material is 0-2.5 wt%, the carbon nano tubes and the graphene particles are uniformly dispersed in the PDMS sponge, the particles are independent from each other, and the particles are connected more easily and the dielectric constant is increased more quickly after being compressed along with the increase of the doping concentration;
when the doping concentration of the three-phase PDMS composite material is 2.5-3.5 wt%, the carbon nano tube and the graphene particles have obvious agglomeration, the conductive particles are connected with each other to form a conductive circuit, and the dielectric constant is basically kept unchanged after the three-phase PDMS composite material is compressed along with the increase of the doping concentration.
In a preferred embodiment of the present invention, when the doping concentrations of the carbon nanotubes and the graphene do not reach the percolation threshold of the three-phase PDMS composite material, the dc conductance of the three-phase PDMS composite material is inversely proportional to the doping concentration, and the dielectric property is directly proportional to the doping concentration;
when the doping concentration of the carbon nanotube and the graphene is higher than the percolation threshold of the three-phase PDMS composite material, the direct current conductance of the three-phase PDMS composite material is in direct proportion to the doping concentration, and the dielectric property is in inverse proportion to the doping concentration.
An intelligent insole is prepared by the preparation method of the three-phase PDMS composite material based on the seepage theory: the intelligent insole is of a sandwich structure, and the intelligent insole is formed by sequentially and compositely mounting a substrate, an rGO/CNT/PDMS capacitive flexible sensor and an insole, wherein the rGO/CNT/PDMS capacitive flexible sensor is formed by connecting and assembling a prepared three-phase PDMS composite material and a lead.
The invention solves the defects in the background technology, and has the following beneficial effects:
(1) the invention provides a preparation method of a three-phase PDMS composite material, which combines a seepage theory and an in-situ sugar template method to enable a carbon nano tube and graphene to be attached to the inside of a porous PDMS sponge to form the three-phase composite material, and solves the problems that in the prior art, a conductive material is difficult to permeate into the inside of the porous sponge and is easy to fall off.
(2) The invention adopts the seepage theory, and increases the doping concentration of the conductive material to the seepage threshold value, thereby reducing the agglomeration of the filling materials and the interaction between the filling materials and the flexible matrix, and improving the dielectric property and the conductive property of the composite material. In addition, the doping concentration of the carbon nano tube and the graphene is increased to be equal to the percolation threshold value, and the sensitivity of the three-phase PDMS composite material reaches the maximum value.
(3) The sensitivity of the rGO/CNT/PDMS flexible pressure sensor is higher than that of the CNT/PDMS flexible pressure sensor, because dispersed carbon nanotube particles can be better connected to play a role of a bridge due to the addition of the graphene, so that the percolation threshold of the rGO/CNT/PDMS sponge is reduced.
(4) The invention provides an intelligent insole, which is characterized in that a substrate, a capacitive flexible sensor and the insole are assembled to form a sandwich structure, so that the landing mode of a human foot is detected, and the sensor has great application potential in the field of wearable intelligent textiles.
(5) The carbon nano tube is a multi-wall carbon nano tube, and compared with a single-wall carbon nano tube, the multi-wall carbon nano tube has a larger length-diameter ratio, is simple to manufacture and has 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.
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 example of rGO/CNT/PDMS sponge with a doping concentration of 2.5 wt% and its SEM image in cross section according to a first embodiment of the present invention;
FIG. 3 is a graph of the sensitivity of rGO/CNT/PDMS capacitive flexible sensors at different carbon nanotube concentrations for example two of the present invention;
FIG. 4 is a sensitivity fit curve for a flexible pressure sensor with doping concentrations of 0 wt% to 3.5 wt% according to example two of the present invention;
FIG. 5 is a graph of the sensitivity of a sensor according to a second embodiment of the present invention;
FIG. 6 is a graph of the responsiveness and recovery of the rGO/CNT/PDMS flexible pressure sensor of example III of the present invention under three different pressures;
FIG. 7 is a hysteresis curve of a rGO/CNT/PDMS capacitive flexible pressure sensor of example four of the present invention;
FIG. 8 is a graph of the cycle stability test of the rGO/CNT/PDMS flexible pressure sensor of example V of the present invention;
FIG. 9 is a stress-strain curve of rGO/CNT/PDMS composite sponge of example six of the present invention;
fig. 10 is a diagram of a flexible pressure sensor and a detection of a foot landing pattern by the 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 and is divided into a main body and a curing agent, wherein the main body is a siloxane oligomer, the curing agent is a siloxane cross-linking agent, and the two components can generate cross-linking under the 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 graphene are fully mixed with sugar particles, PDMS sponge and a curing agent are added, a tabletting device is used to perform tabletting after fully stirring, then a sample is placed in an oven to be heated and cured for a certain time, and the sample is taken out and placed in water to melt sugar, so as to prepare a three-phase PDMS composite material, and the specific preparation method includes the following steps:
s1, grinding the sugar blocks to form powdery sugar particles, and screening by using a 100-mesh sample separation sieve; mixing the carbon nano tube and the graphene with a proper amount of sugar particles, and fully grinding;
s2, taking a certain amount of pure PDMS sponge, adding a curing agent into the PDMS sponge and fully stirring; adding a mixture of carbon nanotubes, graphene and sugar particles into a mixture of PDMS sponge and a curing agent, and fully stirring, wherein the doping concentration of the carbon nanotubes and the graphene is 0-3.5 wt%;
s3, putting the uniform mixture prepared in the S2 into a tabletting device for tabletting and shaping, and putting the shaped sample into an oven for curing;
s4, taking out the cured sample, putting the sample into a container, adding a proper amount of water to obtain a dissolved sample, and drying the sample to remove the residual water to form rGO/CNT/PDMS sponge, namely the three-phase PDMS 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:
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.
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 nanotubes and graphene is preferably 2.5 wt%, and the rGO/CNT/PDMS sponge with the doping concentration of the carbon nanotubes of 2.5% is prepared by using the above preparation method. This example performed topographical characterization analysis of the prepared and formed rGO/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) rGO/CNT/PDMS sponge SEM analysis
The carbon nano tube and the graphene are 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 rGO/CNT/PDMS sponge, where it can be clearly seen that the surface color of PDMS sponge is black and the surface is rough, which indicates that carbon nanotubes and graphene are successfully combined with PDMS sponge.
The cross-sectional electron microscope test of the real object shows that, as shown in fig. 2 (b) and (c), the carbon nanotubes and graphene on the prepared rGO/CNT/PDMS sponge are clearly seen to be attached to the interior of the PDMS sponge, the carbon nanotubes and graphene are uniformly distributed in the interior in a whole manner, a certain agglomeration phenomenon exists locally, the particles are not closely connected, and therefore the rGO/CNT/PDMS sponge cannot conduct electricity, and therefore the sensor 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 and the graphene after being compressed again, so that the conductivity of the sponge can be correspondingly changed when the sponge is compressed again. When the rGO/CNT/PDMS sponge is compressed, the carbon nanotubes and graphene attached inside the PDMS sponge are extruded by the PDMS sponge to deform, and accordingly the capacitance change rate changes, and the requirement of the stress sensor is met.
In the embodiment, the carbon nanotube, the graphene and the PDMS sponge are selected for compounding, and the composite material obtained by doping the inorganic filling material and the organic flexible matrix belongs to a non-uniform system, namely, the filling material is irregularly distributed in the flexible matrix, agglomeration is generated between the filling material to a certain degree, and meanwhile, the dielectric property of the composite material is also influenced by the interaction between the filling material and the flexible matrix. Therefore, an accurate theory is found in the embodiment to explain and predict the change trend of the dielectric property of the composite material, namely the seepage theory.
Percolation theory refers to the fact that when the doping concentration of a conductive material is increased to a certain critical value, the dielectric properties and the conductivity of the composite material are changed accordingly. The seepage theory effectively explains the change rule of the dielectric property and the conductivity of the composite material along with the doping concentration of the conductive material.
When a small amount of conductive material is doped into the composite material, a conductive path cannot be formed inside, and thus the composite material cannot exhibit conductive characteristics; when the doping concentration of the conductive material is continuously increased, the composite material can reach the percolation threshold of the composite material, the conductivity of the composite material is rapidly increased, and the conductive characteristic is further shown; at this time, if the doping concentration of the conductive material is further increased, the conductive path inside the composite material tends to be saturated, so the rate of increase in conductivity starts to be slowed.
When the concentration of the conductive filling material reaches the percolation threshold, namely the doping concentration of the nanotube and the graphene is 2.5 wt%, the dielectric property and the conductive property of the composite material can be predicted through a percolation theoretical formula:
ε’∝(Pc-P)-x，P<Pc；
tanθ∝(Pc-P)-r，P<Pc；
σdc∝(P-Pc)t，P>Pc；
wherein ε is a dielectric constant, PcIs the percolation threshold of the filler, P is the filler content, tan θ is the dielectric loss, and is the DC conductance. x, r and t are critical indices of dielectric constant, dielectric loss and direct current conductance, respectively.
The dielectric properties of the composite material described by percolation theory in this example can be simply explained as: when the doping concentration of the conductive material does not reach the percolation threshold of the composite material, the direct current conductance of the composite material is inversely proportional to the doping concentration of the conductive material, and the dielectric property of the composite material is directly proportional to the doping concentration of the conductive material; when the doping concentration of the conductive material is higher than the percolation threshold of the composite material, the direct current conductance of the composite material is in direct proportion to the doping concentration of the conductive material, and the dielectric property of the composite material is in inverse proportion to the doping concentration of the conductive material.
Example two
In this embodiment, the method for preparing the rGO/CNT/PDMS flexible composite material 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 rGO/CNT/PDMS flexible composite material and a lead, specifically, the prepared rGO/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, so that the capacitive flexible sensor is obtained.
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 embodiment tests the sensitivity of the sensor, and compares the influence of different concentrations of the carbon nanotube and the graphene on the sensitivity of the flexible resistance type pressure sensor. In the method for testing the sensitivity of the sensor in the embodiment, a push-pull meter and an LCR digital bridge are used for testing the rGO/CNT/PDMS capacitive flexible sensor. 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 rGO/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 3.5 wt%, the capacitance change rate of the sensor under the same pressure decreases as the doping concentration of the carbon nanotube and the graphene increases. When the doping concentration of the carbon nano tube and the graphene is increased to 2.5 wt%, the capacitance change rate of the sensor is increased to the maximum value, and then if the doping concentration of the carbon nano tube and the graphene is continuously increased, the capacitance change rate of the sensor is reduced.
The reason is that when the doping concentration range of the carbon nanotubes and the graphene is 0 to 2.5 wt%, the carbon nanotubes and the graphene particles are uniformly dispersed in the 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 nanotubes and the graphene particles are connected with each other, so that the dielectric constant of the composite material is rapidly increased, and the larger the doping concentration of the carbon nanotubes and the graphene is, the easier the connection between the particles is, the faster the dielectric constant of the composite material is increased, and thus the sensitivity is higher. However, when the doping concentration of the carbon nanotubes and the graphene exceeds 2.5 wt%, the particles are significantly agglomerated, so that the conductive particles are connected with each other to form a conductive circuit, and the dielectric constant of the composite material is relatively high when the composite material is not compressed, but the dielectric constant of the composite material is not significantly increased after the composite material is compressed.
In summary, the sensitivity of the rGO/CNT/PDMS flexible pressure sensor is higher than that of the CNT/PDMS flexible pressure sensor, because due to the addition of the graphene, the dispersed carbon nanotube particles can be better connected to play a role of a "bridge", so that the percolation threshold of the rGO/CNT/PDMS sponge is reduced.
In the embodiment, sensitivity fitting is carried out on the rGO/CNT/PDMS flexible pressure sensors with 8 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% -3.5 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 3.
Table 30-0.5 kPa of sensitivity values for different graphene and carbon nanotube doping concentrations
Figure BDA0003480626700000111
From the figure, it can be seen that when the doping concentration of the carbon nanotubes and the graphene is in the range of 0-3.5 wt%, the sensitivity of the composite material increases with the increase of the doping concentration of the carbon nanotubes and the graphene, and when the doping concentration is 2.5 wt%, the sensitivity reaches the maximum value, which is 31.324 kPa-1. As the concentration of carbon nanotubes and graphene 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.
EXAMPLE III
The first embodiment and the second embodiment show that the sensitivity of the rGO/CNT/PDMS capacitive flexible sensor is the maximum when the doping concentration of the carbon nano tube and the graphene is 5 wt%. 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 2.5 wt% is selected to perform the responsiveness and recovery tests, the response time and the recovery time are measured when the pressure is 1kPa, 2.5kPa and 5kPa, and the test results are shown in fig. 6, where fig. 6(a) - (c) show the responsiveness and recovery curves of the rGO/CNT/PDMS capacitive flexible sensor under the actions 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. Experimental results show that the response time and recovery time of the flexible pressure sensor are longer the greater the applied pressure, because the greater the degree of deformation of the conductive sponge when compressed, the longer the response time and recovery time, respectively, as the pressure continues to increase.
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 rGO/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 the time for the conductive material to connect with each other in addition to the time for the conductive sponge to deform under compression, 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 deform under compression, 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 rGO/CNT/PDMS capacitive flexible sensor prepared in the above embodiment was tested, and fig. 7 shows the hysteresis curve of the rGO/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 the embodiment, a push-pull meter and an LCR digital bridge are adopted to test the rGO/CNT/PDMS capacitive flexible sensor, and the change of the resistance value after pressure is applied is compared with the change of the resistance value after pressure is removed to verify the hysteresis of the sensor.
As can be seen in fig. 7, the rGO/CNT/PDMS sensor has very little hysteresis, and the two curves substantially coincide, indicating that the sensor recovers well without being destroyed after the pressure is removed.
EXAMPLE five
In order to further verify the cycling stability performance of the rGO/CNT/PDMS capacitive flexible sensor under different compression deformation amounts, the rGO/CNT/PDMS sponge with the highest sensitivity in the above embodiments was selected for stability testing.
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 rGO/CNT/PDMS capacitive flexible sensor is tested.
A cyclic compression stability test with a deformation amount of 30% and a compression number of 200 times was performed using a sensor with a doping concentration of 2.5 wt% of carbon nanotubes and graphene, and the capacitance change rates with compression deformation amounts of 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 with compression of 200 times, and (b) is a resistance change rate comparison graph with different deformation amounts.
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 embodiment, the rGO/CNT/PDMS sponge with the highest sensitivity in the above embodiments is selected to perform a cyclic compression type stress-strain experiment, a universal material testing machine is used, and stress-strain curves after compression for 300 times and 500 times are selected for comparison, and fig. 9 is a stress-strain curve graph of the rGO/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 2.5 wt%, the flexible resistance type pressure sensor has the maximum sensitivity, faster responsiveness, good hysteresis, good repetition stability and good resilience.
In this embodiment, an intelligent insole capable of detecting sole pressure is designed, as shown in fig. 10. The prepared rGO/CNT/PDMS capacitive flexible sensor is arranged on a substrate, the insole is placed on the upper layer to form the intelligent insole with a sandwich structure, and a lead is connected to detect the pressure distribution of the sole. As shown in FIG. 10, three typical phases of normal walking are shown, namely heel strike, ball strike and forefoot strike, and the corresponding 3D histogram shows the pressure distribution for these three phases. The results show that the foot landing modes are different, and the corresponding pressure distributions are also different.
The intelligent insole prepared in the embodiment shows the successful combination of the flexible pressure sensor and the wearable textile, and shows that the flexible pressure sensor has a huge application prospect in the field of wearable intelligent textiles. The intelligent insole can help people to correctly walk or run by detecting the foot landing modes of different people by detecting the pressure distribution of soles of different people when walking or running.
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 (10)

1. The preparation method of the three-phase PDMS composite material based on the seepage theory is characterized by comprising the following steps:
s1, mixing the carbon nano tube and the graphene with the dispersoid;
s2, adding a curing agent into the PDMS sponge and mixing; adding a mixture of carbon nanotubes, graphene and dispersoids in S1, wherein the doping concentration of the carbon nanotubes and the graphene is 0-3.5 wt%;
s3, shaping and curing the mixture in the S2; adding water into the cured sample, dissolving dispersoids in the sample, and drying to obtain rGO/CNT/PDMS sponge, namely the three-phase PDMS composite material;
and S4, explaining the change rule of the dielectric property and the conductivity of the three-phase PDMS composite material under different doping concentrations along with the doping concentration by combining with a percolation theory, and finding out a percolation threshold value to obtain the three-phase PDMS composite material with the maximum sensitivity.
2. The method for preparing a three-phase PDMS composite based on percolation theory as claimed in claim 1, wherein: the doping concentration of the carbon nano tube and the graphene is 2-3 wt%.
3. The method for preparing a three-phase PDMS composite based on percolation theory as claimed in claim 1, wherein: when the doping concentration of the carbon nano tube and the graphene reaches a percolation threshold value, predicting the dielectric property and the conductivity of the composite material by a percolation theoretical formula:
ε’∝(Pc-P)-x，P<Pc；
tanθ∝(Pc-P)-r，P<Pc；
σdc∝(P-Pc)t，P>Pc；
wherein ε is a dielectric constant, PcIs the percolation threshold of the filler, P is the content of the filler, tan theta is the dielectric loss and is the direct current conductance; x, r and t are critical indices of dielectric constant, dielectric loss and direct current conductance, respectively.
4. The method for preparing a three-phase PDMS composite based on percolation theory as claimed in claim 1, wherein: before the carbon nano tube is mixed with graphene, a strong acid oxidation method is adopted for modification treatment, and the method 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.
5. The method for preparing a three-phase PDMS composite based on percolation theory as claimed in claim 1, wherein: the carbon nano-tube is a multi-wall carbon nano-tube.
6. The method for preparing a three-phase PDMS composite based on percolation theory as claimed in claim 1, wherein: the dispersoid is sugar.
7. The method for preparing a three-phase PDMS composite based on percolation theory as claimed in claim 1, wherein: in S3, the dispersoid in the sample is dissolved by a water bath method.
8. A three-phase PDMS composite fabricated using the method of fabricating a three-phase PDMS composite based on percolation theory according to any one of claims 1-7, wherein:
when the doping concentration range of the three-phase PDMS composite material is 0-2.5 wt%, the carbon nano tubes and the graphene particles are uniformly dispersed in the PDMS sponge, the particles are independent from each other, and the particles are connected more easily and the dielectric constant is increased more quickly after being compressed along with the increase of the doping concentration;
when the doping concentration of the three-phase PDMS composite material is 2.5-3.5 wt%, the carbon nano tube and the graphene particles have obvious agglomeration, the conductive particles are connected with each other to form a conductive circuit, and the dielectric constant is basically kept unchanged after the three-phase PDMS composite material is compressed along with the increase of the doping concentration.
9. A three-phase PDMS composite according to claim 8, characterized in that: when the doping concentration of the carbon nano tube and the graphene does not reach the percolation threshold of the three-phase PDMS composite material, the direct current conductance of the three-phase PDMS composite material is inversely proportional to the doping concentration, and the dielectric property is directly proportional to the doping concentration;
when the doping concentration of the carbon nanotube and the graphene is higher than the percolation threshold of the three-phase PDMS composite material, the direct current conductance of the three-phase PDMS composite material is in direct proportion to the doping concentration, and the dielectric property is in inverse proportion to the doping concentration.
10. An intelligent insole, which is made by the method for preparing the three-phase PDMS composite material based on the percolation theory as claimed in any one of claims 1 to 7, and is characterized in that: the intelligent insole is of a sandwich structure, and the intelligent insole is formed by sequentially and compositely mounting a substrate, an rGO/CNT/PDMS capacitive flexible sensor and an insole, wherein the rGO/CNT/PDMS capacitive flexible sensor is formed by connecting and assembling a prepared three-phase PDMS composite material and a lead.
CN202210066955.1A 2022-01-20 2022-01-20 Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad Pending CN114381032A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202210066955.1A CN114381032A (en) 2022-01-20 2022-01-20 Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202210066955.1A CN114381032A (en) 2022-01-20 2022-01-20 Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad

Publications (1)

Publication Number Publication Date
CN114381032A true CN114381032A (en) 2022-04-22

Family

ID=81204516

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202210066955.1A Pending CN114381032A (en) 2022-01-20 2022-01-20 Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad

Country Status (1)

Country Link
CN (1) CN114381032A (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103073891A (en) * 2013-01-15 2013-05-01 华东理工大学 Preparation method of high-conductivity flexible conductive composite material
CN107057362A (en) * 2017-05-16 2017-08-18 华蓥市高科德电子科技有限公司 A kind of highly conductive soft foam material and preparation method thereof
WO2019129387A1 (en) * 2018-01-01 2019-07-04 Rhodia Operations Structured composites useful as low force sensors
CN113372609A (en) * 2021-06-24 2021-09-10 中南大学 Porous flexible GNP/PDMS composite material, preparation method thereof and application thereof in strain sensor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103073891A (en) * 2013-01-15 2013-05-01 华东理工大学 Preparation method of high-conductivity flexible conductive composite material
CN107057362A (en) * 2017-05-16 2017-08-18 华蓥市高科德电子科技有限公司 A kind of highly conductive soft foam material and preparation method thereof
WO2019129387A1 (en) * 2018-01-01 2019-07-04 Rhodia Operations Structured composites useful as low force sensors
CN113372609A (en) * 2021-06-24 2021-09-10 中南大学 Porous flexible GNP/PDMS composite material, preparation method thereof and application thereof in strain sensor

Similar Documents

Publication Publication Date Title
CN107525832B (en) A kind of preparation method of the flexible fiber sensor electrode of silver nanowires modification
CN106052544A (en) Flexible wearable strain sensor and preparation method thereof
CN101855276B (en) Process for the preparation of a conductive polymer composition
Yang et al. Highly stretchable and sensitive conductive rubber composites with tunable piezoresistivity for motion detection and flexible electrodes
CN111253751B (en) Carbon nanotube polydimethylsiloxane composite material and preparation method and application thereof
Zhang et al. Facile one-step preparation of laminated PDMS based flexible strain sensors with high conductivity and sensitivity via filler sedimentation
CN109932105A (en) Capacitance type pressure sensor and preparation method thereof
KR20150024490A (en) Thermally healable and reshapable conductive hydrogel composite
Chen et al. Piezoresistive anisotropy in conductive silicon rubber/multi-walled carbon nanotube/nickel particle composites via alignment of nickel particles
KR102452956B1 (en) Thermally healable and reshapable conductive hydrogel composite
Zhang et al. Conductive graphene/polydimethylsiloxane nanocomposites for flexible strain sensors
Zhao et al. Globally reinforced mechanical, electrical, and thermal properties of nonlinear conductivity composites by surface treatment of varistor microspheres
CN110306354A (en) A kind of preparation method of the stretchable strain transducer of high heat conductance
CN112697034A (en) Flexible strain sensor made of graphene composite material and preparation method of flexible strain sensor
Song et al. Vertically aligned carbon nanotubes/graphene/cellulose nanofiber networks for enhancing electrical conductivity and piezoresistivity of silicone rubber composites
Huang et al. Regenerated silk fibroin-modified soft graphene aerogels for supercapacitive stress sensors
Shar et al. 3D Printable One‐Part Carbon Nanotube‐Elastomer Ink for Health Monitoring Applications
CN106832718A (en) A kind of conducting polymer composite graphite alkene material and preparation method thereof
CN114381032A (en) Three-phase PDMS composite material preparation method based on seepage theory and intelligent foot pad
Tan et al. Highly sensitive and extremely durable wearable e-textiles of graphene/carbon nanotube hybrid for cardiorespiratory monitoring
CN103467986A (en) Nano titanium carbide/polyimide composite material modified by small organic molecules
CN114479468A (en) Preparation method of CNT/PDMS flexible composite material and capacitive pressure sensor
Wei et al. 3D printable and stretchable PVA‐PAAm dual network hydrogel with conductivities for wearable sensors
CN108891108B (en) High-drive-strain electro-drive elastomer and preparation method thereof
CN108511110B (en) Preparation method of printable nanocomposite elastic conductor, conductive paste and electronic fabric

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination