CN110207585A - A kind of graphene flexible sensor and preparation method thereof - Google Patents

Abstract

A graphene flexible sensor and a preparation method thereof, comprising the following steps: (1) mixing a graphene material with an organic solvent, and obtaining a mixed solution I through ultrasonic vibration treatment; standing the mixed solution I to volatilize the organic solvent to obtain graphite Graphene solution; (2) Add flexible substrate liquid into the graphene solution to obtain mixed solution II; process mixed solution II at room temperature by ultrasonic oscillation to obtain mixed solution III; (3) Add curing agent to mixed solution III, Stir to obtain the mixed solution IV; (4) pour the mixed solution IV into the mold, put it into a vacuum oven to solidify, and obtain the graphene composite material; (5) cool the graphene composite material, and connect the two wires to the graphite two ends of the graphene composite to obtain a graphene flexible sensor. The beneficial effects of the invention are: the invention has both strain and pressure monitoring functions, and has higher sensitivity and wider testing range. The preparation process is simple and the operability is strong.

Description

A kind of graphene flexible sensor and preparation method thereof

technical field

The invention belongs to the technical field of material science, and in particular relates to a graphene flexible sensor and a preparation method thereof.

Background technique

Graphene, as the carbon-based conductive material with the most research potential at present, has good mechanical properties and ultra-high conductivity, and has good compatibility with most flexible substrates. It is very suitable for the preparation of flexible functional composite materials, in which flexible conductive Composite materials mainly use the good mechanical and electrical properties of graphene, combined with the flexibility and tensile properties of flexible substrates to prepare composite materials with good mechanical properties and electrical conductivity. Flexible conductive composites have broad application prospects, such as flexible sensors, aircraft flexible skins, and material structure health monitoring. Among them, the flexible sensor is an important application field. The graphene conductive composite material flexible sensor is based on the piezoresistive effect, and realizes the monitoring of strain and pressure by converting strain or pressure into resistance change. Since traditional flexible sensors generally can only monitor one of the strain or pressure signals, or only have high sensitivity to one of the signals, in the application scenarios of flexible sensors, such as wearable devices and structural health monitoring, etc. It is required to monitor multiple signals such as strain and pressure at the same time. A flexible sensor with both strain and pressure monitoring capabilities will greatly reduce the preparation cost and versatility of the sensor, and will also bring great convenience in signal acquisition.

At present, the main preparation methods of graphene are mechanical method, CVD method and redox method, but all of them have the problems of relatively high cost and unstable product performance.

Contents of the invention

Aiming at the deficiencies in the prior art, the invention provides a graphene flexible sensor and a preparation method thereof. The preparation method has the advantages of simple operation and good repeatability.

A graphene flexible sensor is characterized in that it comprises a graphene composite material and a wire, and the two ends of the graphene composite material are respectively connected to a wire by conductive silver paste;

The electrical conductivity of the graphene flexible sensor is 2×10 ^-5 ~ 2×10 ^-4 S/cm; the strain sensitivity coefficient (Gauge Factor) ≥ 50; the effective stretching range is 0-40%; the pressure sensitivity coefficient ≥ 2.7 ×10 ^-2 kPa ^-1 ; the pressure test range is 0~1000kPa.

A kind of preparation method of graphene flexible sensor is characterized in that, comprises the steps:

(1) mixing the graphene material with an organic solvent, and performing ultrasonic vibration treatment until the graphene material is evenly dispersed in the organic solvent to obtain a mixed solution I; the mixed solution I is left to stand to volatilize the organic solvent to obtain a graphene solution; The ideal effect is that all organic solvents are volatilized; the graphene material is a kind of graphene with high regularity and high carbon-to-oxygen ratio prepared by thermal expansion method, which is prepared by thermal expansion of graphite interlayer compound, compared with common oxidation Graphene and redox graphene have better electrical conductivity, low preparation cost and are more suitable for the preparation of conductive polymers; the graphite intercalation compound graphite intercalation compound (GIC) model is EG Asbury 1395 or 1721, which is Asbury Carbons ( NJ, USA) company.

(2) adding a flexible substrate liquid into the graphene solution to obtain a mixed solution II; ultrasonically oscillating the mixed solution II at room temperature; until the graphene is uniformly dispersed to obtain a mixed solution III;

(3) Add a curing agent into the mixed solution III and stir until it is evenly stirred to obtain the mixed solution IV;

(4) Pour the mixed solution IV into the mold and leave it at room temperature until the mixed solution IV is evenly distributed in the mold, put it into a vacuum drying oven to solidify, and obtain a graphene composite material;

(5) The graphene composite material is cooled, and two wires are respectively connected to both ends of the graphene composite material with conductive silver paste to obtain a graphene flexible sensor.

Wherein, the organic solvent is acetone, ethanol, toluene or tetrahydrofuran, which is volatile and safe; the boiling point of the acetone is 56.53°C, the boiling point of ethanol is 78°C, the boiling point of toluene is 110.6°C, and the boiling point of tetrahydrofuran is 66°C.

Wherein, the time of ultrasonic oscillation treatment described in step (1) is 2～6h, is in order to reduce the size of graphene microplate, and the longer the size of graphene microplate is smaller, is conducive to in organic polymer The dispersion is uniform, and the temperature of the ultrasonic vibration treatment can be controlled at a temperature where the organic solvent is not easily volatile.

Among them, the flexible substrate liquid is silicone rubber, polydimethylsiloxane (PDMS), epoxy resin or polyurethane (PU), which is characterized by good flexibility, stretchability and elasticity.

Wherein, the ultrasonic oscillation treatment time in the step (2) is 1 to 4 hours, and the purpose is to disperse the graphene uniformly in the organic solvent.

Wherein, the standing time described in step (4) is 0.5～4h; the curing temperature is 90～140°C, and the curing time is 0.5～2h; the curing time and temperature depend on the type of curing agent, curing The time and temperature will affect the flexibility and mechanical properties of the cured product; the curing agent used is determined according to the type of flexible substrate liquid.

Wherein, the mold described in step (4) is a glass mold.

The beneficial effects of the invention are: the invention has both strain and pressure monitoring functions, and has higher sensitivity and wider testing range. The graphene material that the present invention adopts is prepared by a kind of novel preparation method (Graphene platelets) (references: Zaman I, Kuan HC, Dai J, Kawashima N, Michelmore A, Sovi A, et al.From carbon nanotubes and silicate layers to graphene platelets for polymer nanocomposites.Nanoscale.2012; 4(15):4578-86.), this preparation method realizes the low-cost and high-performance preparation of graphene. The graphene flakes have similar electrical conductivity to single-layer graphene and have good mechanical properties, which are very suitable for the preparation of graphene flexible composite materials. The invention uses the graphene material to prepare a flexible sensor with both strain and pressure monitoring capabilities, and has high sensitivity. The invention is mainly based on the graphene composite material film, adopts the solution blending method, the preparation process is simple, and the operability is strong. The film has the advantages of excellent mechanical properties and high sensing sensitivity, and is suitable for wearable devices or various complex curved surfaces. deformation measurement. The present invention tests the monitoring effect of the flexible sensor on human body motion signals by measuring the pulse, finger bending, foot pressure, etc., and the results show that the flexible sensor can monitor the pulse signal more accurately in the monitoring of the pulse; Changes in plantar pressure during walking were accurately detected in the foot pressure monitoring test. The prepared graphene composite material can not only be applied to flexible sensors, but also can be used as a stretchable conductive substrate, which has a wide range of application prospects.

Description of drawings

Fig. 1 is the electrical conductivity detection schematic diagram of a kind of graphene flexible sensor that flexible substrate liquid is silicone rubber liquid among the present invention;

Fig. 2 is the strain sensitivity detection schematic diagram of a kind of graphene flexible sensor that flexible substrate liquid is silicone rubber liquid among the present invention;

Fig. 3 is the pressure sensitivity detection schematic diagram of a kind of graphene flexible sensor that flexible substrate liquid is silicon rubber liquid among the present invention;

Fig. 4 is the schematic diagram of the monitoring effect of a kind of graphene flexible sensor of the present invention to pulse;

Fig. 5 is a schematic diagram of the monitoring effect of a graphene flexible sensor of the present invention on finger bending;

Fig. 6 is a schematic diagram of the monitoring effect of a kind of graphene flexible sensor of the present invention to sole pressure;

Detailed ways

In order to better explain the present invention and facilitate understanding, the technical solutions and effects of the present invention will be described in detail below through specific implementation manners in conjunction with the accompanying drawings.

In the present invention, both the flexible substrate liquid and the curing agent are commercially available, and the purchased flexible substrate liquid contains the required curing agent for the flexible substrate liquid. When the flexible substrate liquid is silicone rubber liquid, the mass ratio of curing agent to silicone rubber liquid is 1:10.

The organic solvent is used to dilute the flexible substrate liquid, and its added amount varies with the added amount of the flexible substrate liquid.

The addition amount of the flexible substrate liquid determines the volume ratio of the graphene composite material, which will affect the electrical conductivity of the graphene composite material.

The following preferred embodiments further illustrate the technical solution of the present invention, and those skilled in the art should know that the following embodiments are only used to illustrate the present invention, and are not intended to limit the scope of the present invention.

Example 1

A kind of preparation method of graphene flexible sensor, comprises the steps:

(1) Mix the graphene material with the acetone solution, and perform ultrasonic vibration treatment at below 20°C for 2 hours until the graphene material is uniformly dispersed in the acetone solution to obtain the mixed solution I; the mixed solution I is left to stand, and the acetone solution is volatilized for at least amount, to obtain a graphene solution; the ideal effect is that the acetone solution is all volatilized;

(2) Add silicone rubber liquid into the graphene solution, stir evenly, to obtain mixed solution II; perform ultrasonic oscillation treatment on mixed solution II at room temperature for 1 hour, until the graphene is uniformly dispersed, and obtain mixed solution III;

(3) Add a curing agent into the mixed solution III and stir until it is evenly stirred to obtain the mixed solution IV;

(4) Pour the mixed solution IV into a glass mold, and let it stand for 30 minutes at room temperature until the mixed solution IV is evenly distributed in the glass mold, and then put it into a vacuum oven at 100° C. for curing for 30 minutes to obtain a graphene composite material. The conductivity of the graphene/silicone rubber composite material is shown in Figure 1, and its percolation threshold is about 3.5vol%. Generally, a graphene conductive composite material with a graphene volume ratio of about 5vol% is selected to prepare a graphene flexible sensor;

(5) The graphene composite material is taken out, cooled in air, cut to a suitable size, and two wires are respectively connected to both ends of the graphene composite material with conductive silver paste to obtain a graphene flexible sensor.

(6) Paste the graphene flexible sensor on the strongest pulse position of an adult to detect the pulse signal. The result of the signal detection is shown in Figure 4. It can be seen that the waveform of the pulse signal is very regular, which is in line with the pulse signal of an adult human body The frequency, and very similar to the standard pulse waveform, can clearly distinguish the main wave and descending wave of the pulse waveform, so that it can detect whether the arterial blood vessels are normal. As a commonly used medical diagnostic method, pulse has great potential for understanding human health status and predicting diseases, especially in the field of traditional Chinese medicine. Pulse is more important, and the monitoring of pulse signals requires sensors with excellent flexibility and Higher sensitivity. The pulse signal is of great significance for the prediction of human vascular diseases and the assessment of health status, and it is also an important means of diagnosis in traditional Chinese medicine. The graphene flexible sensor prepared by this method has the performance required for monitoring the pulse, and has the ability to monitor the pulse signal. The potential of wearable devices.

Example 2

A kind of preparation method of graphene flexible sensor, comprises the steps:

(1) Mix the graphene material with the ethanol solution, and perform ultrasonic vibration treatment for 3 hours below 20°C until the graphene material is evenly dispersed in the ethanol solution to obtain a mixed solution I; leave the mixed solution I to allow the ethanol solution to volatilize for at least amount, to obtain a graphene solution; the ideal effect is that the ethanol solution is all volatilized;

(2) Add polydimethylsiloxane liquid into the graphene solution, stir evenly to obtain mixed solution II; perform ultrasonic oscillation treatment on mixed solution II at room temperature for 2 hours until the graphene is uniformly dispersed to obtain mixed solution III;

(3) Add a curing agent into the mixed solution III and stir until it is evenly stirred to obtain the mixed solution IV;

(4) Pour the mixed solution IV into a glass mold, and let it stand at room temperature for 1 hour until the mixed solution IV is evenly distributed in the glass mold, and then put it into a vacuum oven at 90° C. for solidification for 1 hour to obtain a graphene composite material;

(5) The graphene composite material is taken out, cooled in air, cut to a suitable size, and two wires are respectively connected to both ends of the graphene composite material with conductive silver paste to obtain a graphene flexible sensor.

(6) Paste the graphene flexible sensor on the finger to identify the finger bending signal. The results of signal monitoring are shown in Figure 5. It can be seen that when the finger is kept straight, the resistance value remains basically stable. When the finger is bent When the finger is bent, the resistance value changes drastically. Since the flexible sensor is stretched when the finger is bent, the resistance value increases sharply. When the finger returns to the straight state, the resistance value returns to the initial value again. The change in the resistance value in the bending state is different.

Example 3

A kind of preparation method of graphene flexible sensor, comprises the steps:

(1) Mix the graphene material with the toluene solution, and perform ultrasonic vibration treatment for 4 hours below 20°C until the graphene material is evenly dispersed in the toluene solution to obtain a mixed solution I; leave the mixed solution I to allow the toluene solution to volatilize for at least amount, to obtain a graphene solution; the ideal effect is that the toluene solution is all volatilized;

(2) adding epoxy resin liquid into the graphene solution, stirring evenly to obtain mixed solution II; ultrasonically oscillating the mixed solution II at room temperature for 3 hours until the graphene is uniformly dispersed to obtain mixed solution III;

(3) Add a curing agent into the mixed solution III and stir until it is evenly stirred to obtain the mixed solution IV;

(4) Pour the mixed solution IV into a glass mould, and let it stand at room temperature for 2 hours until the mixed solution IV is evenly distributed in the glass mold, and then put it into a vacuum oven at 110° C. for curing for 2 hours to obtain a graphene composite material;

(5) The graphene composite material is taken out, cooled in air, cut to a suitable size, and two wires are respectively connected to both ends of the graphene composite material with conductive silver paste to obtain a graphene flexible sensor.

(6) Stick the graphene flexible sensor on the sole of the foot to perform the pressure test on the sole of the foot. The result of signal monitoring is shown in Figure 6. It can be seen that the pressure on the sole of the foot increases rapidly at the moment of landing during walking. The person is an adult male with a weight of about 80kg. When he stands, the pressure generated by the soles of his feet on the ground is about 40kPa. According to the comparison between the measured data at the peak and the resistance change value of the pressure sensor, it proves that the sensor can monitor the pressure. The value corresponds to the sensitivity of the sensor. When the foot is lifted, the pressure decreases instantly, and the resistance value of the sensor quickly returns to the normal value. During the test, the pressure of the sole of the foot was monitored during walking. When the walking speed is about 5 seconds per step, the pressure of the sole of the foot can be seen in the test results. The period of the changing waveform is also about 5 seconds, and the peak value of the resistance change is basically the same, indicating that the sensor has a relatively accurate and rapid monitoring effect on human motion signals, and the sole pressure is the most effective means to test walking or running, which can be measured by the sole of the foot Changes in pressure understand the motion of the human body, so the flexible pressure sensor has great potential for motion detection in wearable devices.

Example 4

A kind of preparation method of graphene flexible sensor, comprises the steps:

(1) Mix the graphene material with the tetrahydrofuran solution, and perform ultrasonic vibration treatment below 20° C. for 6 hours until the graphene material is uniformly dispersed in the tetrahydrofuran solution to obtain a mixed solution I; leave the mixed solution I to allow the tetrahydrofuran solution to volatilize for at least amount, to obtain a graphene solution; the ideal effect is that the tetrahydrofuran solution is all volatilized;

(2) Add polyurethane (PU) liquid into the graphene solution, stir evenly to obtain mixed solution II; perform ultrasonic oscillation treatment on mixed solution II at room temperature for 4 hours until the graphene is uniformly dispersed to obtain mixed solution III ;

(3) Add a curing agent into the mixed solution III and stir until it is evenly stirred to obtain the mixed solution IV;

(4) Pour the mixed solution IV into a glass mold, and let stand at room temperature for 4 hours until the mixed solution IV is evenly distributed in the glass mold, and then put it into a vacuum drying oven at 140° C. for 1 hour to obtain a graphene composite material;

(5) The graphene composite material is taken out, cooled in air, cut to a suitable size, and two wires are respectively connected to both ends of the graphene composite material with conductive silver paste to obtain a graphene flexible sensor.

(6) Carry out the strain response test on the graphene flexible sensor, Fig. 2 is the test result, the test result shows that the resistance of the graphene flexible sensor increases linearly with the strain increase, and it can be seen from the small picture of Fig. 2 that the graphene flexible sensor The sensor has high sensitivity to strain. In the strain range of 0-5%, the sensitivity coefficient (gauge factor) can reach up to about 100, and the average sensitivity coefficient is also as high as 50 in the strain range of 5% to 30%. Then the graphene flexible sensor is subjected to a pressure response test. The pressure test range is 0-1000kPa. The signal monitoring results are shown in Figure 3. It can be seen that with the increase of pressure, the resistance value decreases continuously. This is due to the piezoresistive The effect results in a change in resistance generated by a change in the conductive network inside the graphene flexible sensor. It is more obvious that when the pressure is relatively small, the resistance change is relatively large, especially when the pressure range is 0-10kPa, the resistance change is obvious. In this pressure range, the sensitivity coefficient of the sensor is about 2.7×10 ^-2 kPa ^-1 ; at 100 In the pressure range of ~1000kPa, the sensitivity coefficient of the sensor is about 1.5×10 ^-4 kPa ^-1 , and generally speaking, it shows relatively good sensitivity in the range of 0 ~ 1000kPa.

Claims (9)

1. a kind of graphene flexible sensor, which is characterized in that including graphene composite material and conducting wire, the graphene is compound The both ends of material connect a conducting wire by conductive silver paste respectively.

2. a kind of graphene flexible sensor according to claim 1, which is characterized in that the graphene flexible sensor Electric conductivity be 2 × 10^-5~2 × 10^-4S/cm；Ga(u)ge factor (Gauge Factor) >=50；Effective range of stretch is 0~40%；Pressure sensitivity coefficient of the sensor >=2.7 × 10^-2kPa^-1；Pressure test range is 0~1000kPa.

3. a kind of preparation method of graphene flexible sensor described in claim 1, which comprises the steps of:

(1) grapheme material is mixed with organic solvent, carries out sonic oscillation processing, until grapheme material has been dispersed in In solvent, mixed solution I is obtained；Mixed solution I is stood, organic solvent is made to volatilize, obtains graphene solution；

(2) flexible parent metal liquid is added in graphene solution, obtains mixed solution II；Mixed solution II is carried out at room temperature Sonic oscillation processing；Until graphene dispersion is uniform, mixed solution III is obtained；

(3) curing agent is added in mixed solution III, is stirred, until stirring evenly, obtain mixed solution IV；

(4) mixed solution IV is poured into mold, is stood at room temperature, until mixed solution IV is uniformly distributed in a mold, put Enter in vacuum oven and solidified, obtains graphene composite material；

(5) graphene composite material is subjected to cooling treatment, it is compound that two conducting wires are connected to graphene with conductive silver paste The both ends of material obtain graphene flexible sensor.

4. a kind of preparation method of graphene flexible sensor according to claim 3, which is characterized in that in step (1) The organic solvent is acetone, ethyl alcohol, toluene or tetrahydrofuran.

5. a kind of preparation method of graphene flexible sensor according to claim 3, which is characterized in that in step (1) The time of the sonic oscillation processing is 2~6h.

6. a kind of preparation method of graphene flexible sensor according to claim 3, which is characterized in that in step (2) The flexible parent metal liquid is silicon rubber, dimethyl silicone polymer (PDMS), epoxy resin or polyurethanes (PU).

7. a kind of preparation method of graphene flexible sensor according to claim 3, which is characterized in that in step (2) The time of the sonic oscillation processing is 1~4h.

8. a kind of preparation method of graphene flexible sensor according to claim 3, which is characterized in that in step (4) The time of the standing is 0.5~4h；The cured temperature is 90~140 DEG C, and the cured time is 0.5~2h.

9. a kind of preparation method of graphene flexible sensor according to claim 3, which is characterized in that in step (4) The mold is glass mold.