CN111849167A

CN111849167A - Preparation method and application of conductive graphene/polydimethylsiloxane nanocomposite

Info

Publication number: CN111849167A
Application number: CN202010554361.6A
Authority: CN
Inventors: 张小敏
Original assignee: Jinling Institute of Technology
Current assignee: Jinling Institute of Technology
Priority date: 2020-06-17
Filing date: 2020-06-17
Publication date: 2020-10-30

Abstract

The invention discloses a preparation method and application of a conductive graphene/polydimethylsiloxane nano composite material, and belongs to the technical field of composite material preparation. The method comprises the following steps: step 101, mixing and stirring polydimethylsiloxane serving as a base material and a curing agent according to a mass ratio of (8-12): 1 for 18-25 minutes to obtain a dimethyl siloxane polymer; 102, adding a graphene filler into the polymer, and stirring and defoaming for 3-5 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; 103, dispersing the graphene-dimethyl siloxane polymer by ultrasonic waves for 18-25 minutes, and defoaming in a vacuum drying oven to form uniform fluid. The graphene/polydimethylsiloxane composite slurry is prepared by adopting an ultrasonic dispersion and high-speed stirring method, and the electric conductivity of the graphene/polydimethylsiloxane composite material is obtained through hybridization of graphene and a polydimethylsiloxane film.

Description

Preparation method and application of conductive graphene/polydimethylsiloxane nanocomposite

Technical Field

The invention belongs to the technical field of composite material preparation, and particularly relates to a preparation method and application of a conductive graphene/polydimethylsiloxane nano composite material.

Background

Conductive fillers and polymer matrix stretchable conductive materials have attracted considerable attention in recent years due to their use in strain sensors, flexible electrodes, electronic skin, flexible robots, and human motion monitoring systems. One method of constructing a composite strain sensor is to prepare a stretchable conductive material by incorporating conductive fillers, such as metals, graphene, chopped carbon fibers, and carbon nanotubes, including PDMS, silicone rubber, polyethylene terephthalate (PET), epoxy, Thermoplastic Polyurethane (TPU), Polycarbonate (PC), into a suitable elastomeric matrix. In a stretchable conductive material, the conductive filler provides conductivity while the elastic substrate provides the material stretch properties. A strain sensor is made by introducing a high loading (i.e., high percolation threshold) into the elastomeric matrix. High loadings provide dense conductive paths in the elastomeric substrate, resulting in poor mechanical properties, poor heat dissipation, and thus low sensitivity.

Disclosure of Invention

The invention provides a preparation method and application of a conductive graphene/polydimethylsiloxane nanocomposite material to solve the technical problems in the background technology.

The invention is realized by adopting the following technical scheme: a preparation method of a conductive graphene/polydimethylsiloxane nano composite material specifically comprises the following steps:

step 101, mixing and stirring polydimethylsiloxane serving as a base material and a curing agent according to a mass ratio of (8-12): 1 for 18-25 minutes to obtain a dimethyl siloxane polymer;

102, adding a graphene filler into the polymer, and stirring and defoaming for 3-5 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer;

103, dispersing the graphene-dimethyl siloxane polymer by ultrasonic waves for 18-25 minutes, and defoaming in a vacuum drying oven to form uniform fluid.

In a further embodiment, the curing agent is one or more of diethylenetriamine, triethylene tetramine and diethylaminopropylamine.

In a further embodiment, the concentration of graphene in the graphene-dimethylsiloxane polymer is 5-40%.

The application of the conductive graphene/polydimethylsiloxane nanocomposite material prepared by the preparation method in sensor manufacturing specifically comprises the following steps:

Step 401, taking polyethylene terephthalate as a lower substrate;

step 402, spin-coating polydimethylsiloxane on the upper surface of the lower substrate by using a spin-coating method, forming a lower substrate on the upper surface of the lower substrate, and curing;

step 403, fixing a mold on the substrate, injecting the prepared fluid into the mold, heating at 100-120 ℃ for 15-20 minutes, demolding, forming a graphene-dimethyl siloxane polymer interlayer on the lower substrate, and embedding the bottom of the interlayer into the lower substrate;

step 404, bonding the copper electrode on the interlayer by using conductive adhesive;

step 405, taking polyethylene glycol terephthalate as an upper base material, spin-coating polydimethylsiloxane on the lower surface of the lower base material by a spin-coating method, and curing;

step 406, forming an upper substrate on the lower surface of the base material, reversely buckling the interlayer and the lower substrate on the upper base material, and then heating at 80-150 ℃ for 10-25min to form a sensor with an interlayer; one surface of the interlayer adjacent to the upper base material is embedded in the upper base plate.

In a further embodiment, the graphene-dimethylsiloxane polymer interlayer has the structure comprising:

The connecting part is transversely arranged, the vertical section of the connecting part is spindle-shaped, and the front side surface and the rear side surface of the connecting part are sealing layers;

the N support plates are fixed on the outer side wall of the connecting part in parallel at equal intervals; the top end of the sealing layer and the top end of the supporting plate positioned above the connecting part are embedded in the lower substrate;

the bottom of the seal layer and the bottom of the support plate below the connecting portion are embedded in the upper substrate.

In a further embodiment, the thickness of the seal is greater than the thickness of the support plate.

In a further embodiment, the connecting part is provided with a special-shaped through hole in a mirror image manner, so that heat dissipation is facilitated.

The invention has the beneficial effects that: the graphene/polydimethylsiloxane composite slurry is prepared by adopting an ultrasonic dispersion and high-speed stirring method, and the electric conductivity of the graphene/polydimethylsiloxane composite material is obtained through hybridization of graphene and a polydimethylsiloxane film; in addition, the graphene/polydimethylsiloxane conductive composite material is used as an interlayer, a PDMS-GE/PDMS-PDMS flexible strain sensor interlayer structure is prepared, and the structure is a heat dissipation type structure, so that the detection range of small-scale motion signals is enlarged, the structure has good flexibility, good wear resistance and heat dissipation, and can be used for preparing electronic skins, soft robots and human motion monitoring systems.

Drawings

Fig. 1 is a viscosity profile of a conductive graphene/polydimethylsiloxane nanocomposite paste.

Fig. 2 is a viscosity profile of the composite pastes of example 2 and example 5.

Fig. 3 is a resistivity diagram of a conductive graphene/polydimethylsiloxane nano-conductive film.

Fig. 4 is an SEM image of the conductive film.

Fig. 5 is an FTIR spectrum of the composite materials prepared in example 2 and example 6 (a. example 2, b. example 6).

Fig. 6 is a schematic view of the sandwich structure of the sensor of example 10.

Fig. 7 is a front view of the sandwich structure of the sensor of example 10.

Each of fig. 6 to 7 is labeled as: connecting portion 1, seal 2, backup pad 3, heterotypic through-hole 4.

Detailed Description

The invention is further described with reference to the following description of the drawings and specific embodiments.

The inventor finds out through research and reading that: conductive fillers and polymer matrix stretchable conductive materials due to their application in strain sensors, flexible electrodes, electronic skin, flexible robots and human motion monitoring systems, but in stretchable conductive materials, conductive fillers provide conductivity while elastic substrates provide material stretch properties. A strain sensor is made by introducing a high loading (i.e., high percolation threshold) into the elastomeric matrix. High loadings provide dense conductive paths in the elastomeric substrate, resulting in poor mechanical properties, poor heat dissipation, and thus low sensitivity.

Therefore, the invention adopts the methods of ultrasonic dispersion and high-speed stirring to prepare the graphene/polydimethylsiloxane composite slurry for solving the technical problems. The conductive performance of the graphene/polydimethylsiloxane composite material is obtained through hybridization of the graphene and the polydimethylsiloxane film.

Example 1

Firstly, a preparation method of the conductive graphene/polydimethylsiloxane nano composite material is discussed, and the preparation method specifically comprises the following steps:

step 101, mixing and stirring polydimethylsiloxane serving as a base material and a curing agent according to a mass ratio of 10:1 for 20 minutes to obtain a dimethyl siloxane polymer; the curing agent is diethylenetriamine;

102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 5%;

103, dispersing the graphene-dimethyl siloxane polymer by ultrasonic waves for 20 minutes, and defoaming in a vacuum drying oven to form uniform fluid.

The fluid prepared by the steps is applied to sensor manufacturing, and the method specifically comprises the following steps:

step 401, taking polyethylene terephthalate as a lower substrate;

Step 402, spin-coating polydimethylsiloxane on the upper surface of the lower substrate by adopting a spin-coating method, forming a lower substrate on the upper surface of the lower substrate, and curing at 25 ℃ for 3 hours +200 ℃ for 1 hour;

step 403, fixing a mold on the substrate, injecting the prepared fluid into the mold, heating at 100 ℃ for 20 minutes, demolding, forming a graphene-dimethyl siloxane polymer interlayer on the lower substrate, and embedding the bottom of the interlayer into the lower substrate;

step 404, bonding the copper electrode on an interlayer by using conductive adhesive, wherein the interlayer is a flat laying layer; the fixed mould is a common frame mould;

step 405, taking polyethylene glycol terephthalate as an upper base material, spin-coating polydimethylsiloxane on the lower surface of the lower base material by adopting a spin-coating method, and curing at 25 ℃ for 3 hours +200 ℃ for 1 hour;

step 406, forming an upper substrate on the lower surface of the base material, reversely buckling the interlayer and the lower substrate on the upper base material, and then heating at 100 ℃ for 15min to form a sensor with an interlayer; one surface of the interlayer adjacent to the upper base material is embedded in the upper base plate.

Example 2

The present embodiment is different from embodiment 1 in that: the conductive nanocomposite is polydimethylsiloxane, i.e., does not contain graphene. The other steps were the same as in example 1.

Example 3

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 10%; the other steps were the same as in example 1.

Example 4

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 15%; the other steps were the same as in example 1.

Example 5

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 20%; the other steps were the same as in example 1.

Example 6

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 25%; the other steps were the same as in example 1.

Example 7

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 30%; the other steps were the same as in example 1.

Example 8

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 35%; the other steps were the same as in example 1.

Example 9

The present embodiment is different from embodiment 1 in that: 102, adding a graphene filler into the polymer, and stirring and defoaming for 3 minutes by using a planetary centrifugal mixer to obtain a graphene-dimethyl siloxane polymer; the concentration of the graphene is 40%; the other steps were the same as in example 1.

And (3) carrying out performance detection on the sensors containing different concentrations of graphene.

Firstly, the fluidity of the composite slurry is detected: a rheometer is a device that can subject a sample to dynamic shear strain deformation and then measure the resultant torque that the sample consumes for shear strain. The flow properties of the composite liquid slurries of examples 1 to 9 were tested using the parallel plate method. The shear rate is 1-100 s-1 at 25 ℃. The viscosity is shown in the rheological graph 1. The viscosity of pure PDMS at 25 ℃ is 2.3 pa. The viscosity of the GE/PDMS composite liquid paste exceeded that of pure PDMS. The viscosity of the GE/PDMS composite paste can be improved by adding the graphene filler into the PDMS liquid paste. After the phase body is bonded, the graphene reacts with the PDMS matrix under a high load level, the viscosity is rapidly increased, and a complete crosslinking system is formed.

As shown in FIG. 2, TG curves are shown for uncured pure PDMS and a GE/PDMS composite paste containing 20wt% graphene (example 6). Compared with pure PDMS, the weight loss temperature of 5% of the GE/PDMS slurry is increased by 10 ℃, which shows that the thermal stability of PDMS is improved by adding graphene. This is probably due to the enhanced barrier properties imparted by graphene that prevent oxygen penetration into the resin matrix. As the temperature increased, the samples showed similar pyrolysis behavior during the two weight loss phases. The first phase of rapid weight loss occurs between 320 ℃ and 490 ℃, due to the degradation of the PDMS network. At this stage, these pastes show a similar trend. The second stage weight loss occurs between 510 ℃ and 600 ℃, corresponding to degradation of the char. The graphene filling delays the coal coke pyrolysis of GE/PDMS, and the weight loss rate of the coal coke is lower than that of pure PDMS. Thermal stability analysis of the composite showed that at temperatures below 200 ℃, the thermal decomposition rate of the composite was low with no significant weight loss. Thus, the composite material can be used for thermal sensor interconnects for electronic circuits.

Fig. 3 shows the resistivity of the GE/PDMS conductive film as a function of the graphene filler mass content. The mass content of graphene varies from 5% to 40%. It is possible that the resistivity index of the GE/PDMS conductive film drops beyond the percolation threshold. When the graphene loading is 25 wt%, the resistivity is reduced with the increase of the graphene mass content, and the percolation threshold of 9.4 omega cm is reached. The resistivity values of the mixed graphene samples of 25 wt%, 30 wt%, 35 wt%, and 40 wt% were reduced by 9.4, 7.2, 5.8, and 5 Ω. This indicates that graphene has very high conductivity and provides a mean free path for electron transfer beyond the percolation threshold. The large length-to-diameter ratio of graphene makes it very easy to construct an efficient graphene conductive network in a PDMS matrix, thereby providing a good current conduction path.

The conductivity of the conductive film containing 25wt% of the hybrid graphene filler was found to be higher than the original PDMS, confirming the reinforcing effect of the hybrid filler on the matrix. Rheological analysis of the uncured composite paste showed that the non-newtonian behavior increased with increasing loading of hybrid filler in the PDMS matrix. The optimal content of graphene filler in PDMS is 25 wt%.

An SEM micrograph of the GE/PDMS conductive film is shown in FIG. 4. For the samples of the GE/PDMS conductive films, a pattern is provided. And selecting the graphene filler with the mass fraction of 25% as a representative content, and characterizing the microscopic morphology of the GE/PDMS conductive film. The graphene nanoplatelets are uniformly dispersed between the PDMS. Fig. 4 shows that graphene nanoplatelets are micro-scale planar, only a few layers thick, with some wrinkling, forming a homogeneous hybrid system. This result is a good demonstration of the formation of a three-dimensional conductive network that provides an effective pathway for electron transport.

The chemical structures of cured pure PDMS and GE/PDMS composites containing 25% graphene filler were studied using FTIR spectroscopy (fig. 5). FIG. 5a shows that the strong absorption peak of pure PDMS at 1095cm-1 represents the tensile vibration of siloxane Si-O. The absorption peak at 790cm-1 corresponds to the symmetrical tensile and flexural vibration absorption peak of Si-C, the absorption peak at 1625cm-1 indicates that the tensile vibration of C = C comes from the vinyl group in PDMS. The absorption at 2904cm-1 is the C-H symmetric tensile vibration absorption peak, which is associated with the-CH 3 bond. The absorption peak at 3401cm-1 corresponds to a symmetric tensile vibration. As shown in FIG. 5b, the GE/PDMS composite film showed a weak absorption peak in the spectrum. These absorption peaks decrease with increasing graphene content.

Example 10

This embodiment is different from embodiment 6 in that: the mechanism of the sandwich in step 404 is as follows, including:

the connecting part comprises a connecting part 1 which is transversely arranged, wherein the vertical section of the connecting part is spindle-shaped, and sealing layers 2 are arranged on the front side surface and the rear side surface of the connecting part; the N support plates 3 are fixed on the outer side wall of the connecting part in parallel at equal intervals; the top end of the sealing layer and the top end of the supporting plate positioned above the connecting part are embedded in the lower substrate; n is an integer greater than six; the bottom of the seal layer and the bottom of the support plate below the connecting portion are embedded in the upper substrate. The thickness of the sealing layer is larger than that of the supporting plate. The connecting part is provided with a special-shaped through hole 4 in a mirror image manner, so that heat dissipation is facilitated, as shown in fig. 6 and 7.

The conductivity of the sensors of different sandwich structures was tested: in order to evaluate the application of the composite conductive film, a composite conductive film circuit was fabricated using a metal wire and a red LED lamp. During the test, the LED lamp is found to be lighted under the condition that the external voltage is 3V, and the phenomenon indicates that the composite conductive film has good conductivity.

The performance test was performed on the sensors of different interlayers prepared in example 6 and example 10. Example 10 the resistive response of the sensor under cyclic tensile strain, the profiled sandwich sensor was pre-stretched and released at 10% strain. The resistance of the film was monitored in real time as the peak strain of the continuous triangular wave increased from 1% to 10%. Common sandwich GE/PDMS sensors exhibit a weak non-monotonic resistance response to tensile strains below 4%. Under strain loading, the resistance decreases first. When the tensile strain was increased from 5% to 9%, the resistance change value was sharply increased due to crack formation between the graphene nanofillers and breakage of the conductive network during the stretching. As the strain increases further above 9%, the resistance of the strain sensor film begins to increase due to the reduction of the graphene joints. For the special-shaped sensor, because the internal structure of the special-shaped sensor leaves enough elastic space for strain, under the strain loading, the resistance can be continuously reduced until the tensile strain is increased from 1% to 8.5%, and the reason is analyzed, the special-shaped structure of the interlayer gives the strain space, the graphene and the filler in the material cannot be really pulled, and the damage to the material is buffered by using a mechanical structure. In order to research the potential application of the sensor in human health monitoring, a weak finger muscle movement detection method based on the sensor is provided. A retractable sensor is used to detect specific movements of the finger muscles at different bending angles. The sensor membrane was tested by moving the finger muscle at different angles. The motion of bending the finger muscle at 0-80 degrees and 80-0 degrees under 5% strain is measured for the sensor with the common interlayer, a change curve of relative resistance along with strain is drawn, and the output signal of the sensor has good stability; the sensor with the special-shaped interlayer measures the motion of bending of finger muscles at 0-120 degrees and 120-0 degrees under 5% strain, and the output signal of the sensor has good stability. The result shows that the sandwich strain sensor is a promising strain sensor of a human body motion monitoring system.

Claims

1. A preparation method of a conductive graphene/polydimethylsiloxane nano composite material is characterized by comprising the following steps:

2. The method for preparing the conductive graphene/polydimethylsiloxane nanocomposite material according to claim 1, wherein the curing agent is one or more of diethylenetriamine, triethylenetetramine and diethylaminopropylamine.

3. The method for preparing a conductive graphene/polydimethylsiloxane nanocomposite material according to claim 1, wherein the concentration of graphene in the graphene-dimethylsiloxane polymer is 5-40%.

4. Use of the conductive graphene/polydimethylsiloxane nanocomposite material prepared by the preparation method according to any one of claims 1 to 3 in sensor manufacturing, wherein the sensor manufacturing method specifically comprises the following steps:

Step 401, taking polyethylene terephthalate as a lower substrate;

5. Use of the conductive graphene/polydimethylsiloxane nanocomposite material of claim 4 in sensor fabrication, wherein the graphene-dimethylsiloxane polymer interlayer has the structure comprising:

the N support plates are fixed on the outer side wall of the connecting part in parallel at equal intervals; the top end of the sealing layer and the top end of the supporting plate positioned above the connecting part are embedded in the lower substrate; n is an integer greater than six;

6. Use of the conductive graphene/polydimethylsiloxane nanocomposite material of claim 5 in sensor fabrication, wherein the thickness of the seal layer is greater than the thickness of the support plate.

7. The application of the conductive graphene/polydimethylsiloxane nanocomposite material in sensor manufacturing according to claim 5, wherein the connecting portion is provided with special-shaped through holes in a mirror image manner, so that heat dissipation is facilitated.