Preparation method and application of graphene flexible sensor for identifying stretching direction

Abstract

The invention provides a preparation method and application of a graphene flexible sensor for stretching direction recognition. The method comprises the following steps: step 1, pretreating a substrate material; and 2, preparing the dynamic response flexible sensor based on the graphene material. The invention also relates to an application of the graphene flexible sensor for identifying the stretching direction. The structure prepared by the method is the same whole and is good in stability, and in a two-dimensional plane range, the other two auxiliary strips in the *-shaped structure can expand the measurement range to 0-180 degrees; when the stretching direction measured by using the orthogonal strip is 45 degrees or 135 degrees, whether the stretching direction is 45 degrees or 135 degrees can be determined by combining the two auxiliary strips, and feedback signals of the two auxiliary strips for the two angles are different, so that the stretching direction of the device can be judged in the whole two-dimensional plane, and the application range of the device is expanded.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensing; in particular, it relates to a preparation method and application of a graphene flexible sensor for stretching direction recognition. Background Art

[0002] With the continuous development of wearable devices, the application of flexible electronics is becoming more and more extensive. The basic function of a flexible sensor is to monitor the deformation or minute displacement of an object in real time, convert these strain signals into electrical signals, and then process the signals and feedback information. For a flexible sensor, the information feedback by a single structure is very limited, and judging its stretching direction is a key issue, which is very important for the diversification of the application of flexible sensors. In the existing solutions for judging the stretching direction of flexible devices, whether it is a resistive sensor or a capacitive sensor, a single device structure cannot judge the stretching direction. In addition, for a strain gauge sensor, its measurement method is to paste strain gauges on a flexible material, layout at multiple points, and measure the strain changes at different points. Through the strain responses in different directions, the direction of the applied force can be inferred, but the layout requirements are high, the cost is high, and the strain gauge itself is rigid. Although there is a disclosure of a flexible sensor based on the combination of carbon nanotubes and a flexible material, the orthogonal structure designed by it has limited detection of the stretching direction in a two-dimensional plane (it can only judge the stretching direction within the range of 0 to 90°), and at the same time, the orthogonal structure designed by it is formed by the overlap of two structures, and this structure is prone to sliding, dislocation, etc. during the test process, affecting the measurement accuracy of the device. Based on this, there is an urgent need for a flexible sensor with an expanded detection range. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method and application of a graphene flexible sensor for stretching direction recognition.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a preparation method of a graphene flexible sensor for stretching direction recognition, including the following steps:

[0006] Step 1, pretreatment of the substrate material: Using PDMS as the substrate material, perform oxygen plasma cleaning on the PDMS to remove the hydrophobic groups on the surface, promote the combination with the graphene coating, and cut the substrate material into a PDMS with a "rice" - shaped structure;

[0007] Step 2, preparation of a flexible sensor based on the dynamic response of graphene materials:

[0008] (1) Immerse the PDMS with a "rice" - shaped structure in a polyvinyl alcohol solution, take it out and dry it;

[0009] (2) Immerse it in the graphene slurry again, take it out and dry it, and repeat the process several times until each strip of the "rice" - shaped structure is coated with a graphene conductive coating;

[0010] (3) Then attach copper conductive tapes to all eight ports and lead out silver wires to facilitate the test of electrical properties;

[0011] (4) Encapsulate the device with liquid PDMS and cure it to obtain the final graphene flexible sensor for tensile direction recognition.

[0012] Preferably, in step 1, the thickness of the PDMS is 200 microns.

[0013] Preferably, in step 1, the specification of each strip in the structure is 2mm×16mm.

[0014] Preferably, in step 2, the concentration of the polyvinyl alcohol solution is 0.5wt%.

[0015] Preferably, in step 2, the concentration of the graphene slurry is 0.5wt%.

[0016] Preferably, in step 2, the immersion time of the "rice" - shaped structure PDMS into the graphene slurry is 1 min.

[0017] Preferably, in step 2, the immersion time into the graphene slurry is 1 min.

[0018] The present invention also relates to an application of the graphene flexible sensor for tensile direction recognition. The graphene flexible sensor for tensile direction recognition prepared as described above is used to judge the tensile direction of the device. The specific steps are as follows:

[0019] Step 1, acquisition of device basic data: Take the two orthogonal graphene conductive tapes in the "cross" - shape as the calibration reference in the two - dimensional plane, and the other two graphene conductive tapes as the auxiliary strips for judging the tensile direction; Collect the relevant data of the strain - relative resistance of each of the two orthogonal graphene conductive tapes, fit a quadratic function curve from the data, and obtain the strain - relative resistance change relationship of the entire device in the two - dimensional plane;

[0020] Step 2, judgment of the tensile direction: When the device is stretched in the two - dimensional plane, the relative resistance of the two orthogonal graphene conductive tapes will change. Substitute this change into the quadratic function curve to obtain the magnitude of their respective strains, and calculate the tensile angle using a mathematical model. See the formula:

[0021] tanθ=(ε + ε1) / (ε + ε2) (1)

[0022] θ = tan -1 (ε + ε1) / (ε + ε2) (2)

[0023] ΔR 1，2 / R 1，2 =AΔε 1，2 2 +BΔε 1，2 +C (3)

[0024]

[0025] ε 1,2 =ε·C 1，2 (5)

[0026] θ=tan -1 (1 + C1 / 1 + C2) (6)

[0027] Wherein, θ is the stretching angle, ε is the original length of the device strip, ε1 is the stretching length of the strip in the X-axis direction, ε2 is the stretching length of the strip in the Y-axis direction, A is the coefficient of the quadratic term in the quadratic function obtained by fitting the strain - relative resistance related data of each strip, B is the coefficient of the linear term in the quadratic function obtained by fitting the strain - relative resistance related data of each strip, C is the constant term in the quadratic function obtained by fitting the strain - relative resistance related data of each strip, C1 is the solution obtained by substituting the electric signal value feedback by the strip in the X-axis direction when the device is stretched into the pre-fitted quadratic function curve, C2 is the solution obtained by substituting the electric signal value feedback by the strip in the Y-axis direction when the device is stretched into the pre-fitted quadratic function curve, ΔR 1，2 is the resistance change generated by the orthogonal strips in the X and Y directions when the device is stretched, R 1，2 is the original resistance value of the orthogonal strips in the X and Y directions before being stretched, Δε 1，2 is the stretching ratio of the strips in the X and Y directions obtained by solving the quadratic function, ε 1，2 is the stretching value of the strips in the X and Y directions obtained by solving the quadratic function, C 1，2 are the two solutions obtained by substituting the electric signal values feedback by the strips in the X-axis and Y-axis directions when the device is stretched into the pre-fitted quadratic function curve.

[0028] Principle of the present invention: Prepare a specific substrate structure, then form a graphene conductive coating on the substrate by solution coating method, and then encapsulate the device with polydimethylsiloxane (PDMS);

[0029] Collect the basic data of the device and fit it into a quadratic function curve, calibrate the strain - relative resistance change relationship of the device in the two-dimensional plane. When the device is stretched, determine the strain magnitude according to the measured relative resistance value, and obtain its stretching angle according to the mathematical model.

[0030] The present invention has the following advantages:

[0031] (1) The structure prepared by the method of the present invention is an integral whole with good stability. In the two-dimensional plane range, the other two auxiliary strips in the "rice" - shaped structure can extend the measurement range to 0 - 180°. When the tensile direction measured by the orthogonal strips is 45° or 135°, the two auxiliary strips can be combined to determine whether it is 45° or 135° because the feedback signals of the two auxiliary strips for these two angles are different. Furthermore, the tensile direction of the device can be judged within the entire two - dimensional plane, realizing the expansion of the application range of the device.

[0032] (2) The graphene - based dynamic response flexible sensor prepared by the method of the present invention has a "rice" - shaped structure, making each strip an integral whole with stable structure, and it is not easy to cause structural changes due to the influence of strain, resulting in phenomena that affect the measurement results. Description of the Drawings

[0033] Figure 1 is a schematic structural diagram of the graphene flexible sensor for tensile direction recognition prepared by the present invention;

[0034] Figure 2 is a schematic diagram of the graphene flexible sensor for tensile direction recognition prepared by the present invention in a stretched state;

[0035] Figure 3 is a strain - relative resistance relationship diagram of two orthogonal conductive strips; among them, Figure (a) is the different electrical signal feedbacks shown by the strips in the X and Y directions when the device is stretched in the X - axis direction, and the quadratic function curve diagram after fitting the data collected from the strip in the X - axis direction. Figure (b) is the different electrical signal feedbacks shown by the strips in the X and Y directions when the device is stretched in the Y - axis direction, and the quadratic function curve diagram after fitting the data collected from the strip in the Y - axis direction. Detailed Embodiments

[0036] The present invention will be described in detail below with reference to specific embodiments. It should be noted that the following embodiments are only further descriptions of the present invention, but the protection scope of the present invention is not limited to the following embodiments.

[0037] Embodiment

[0038] This embodiment relates to a preparation method of a graphene flexible sensor for tensile direction recognition, including the following steps:

[0039] Step 1, pretreatment of the substrate material: Using PDMS as the substrate material, PDMS is subjected to oxygen plasma cleaning to remove the hydrophobic groups on the surface, promote the combination with the graphene coating, and cut the substrate material into PDMS with a "rice" - shaped structure;

[0040] Step 2, Preparation of a graphene material-based dynamic response flexible sensor:

[0041] (1) Immerse the PDMS with a "rice" - shaped structure in a polyvinyl alcohol solution, take it out and dry.

[0042] (2) Then immerse it in a graphene slurry, take it out and dry, repeat several times until each strip of the "rice" - shaped structure is coated with a graphene conductive coating.

[0043] (3) Then attach copper conductive tapes to all eight ports and lead out silver wires for convenient electrical property testing.

[0044] (4) Encapsulate the device with liquid PDMS and cure it to obtain the final graphene flexible sensor for tensile direction recognition, as shown in Figure 1 shown.

[0045] Further, in Step 1, the thickness of the PDMS is 200 microns.

[0046] Further, in Step 1, the specification of each strip in the structure is 2mm × 16mm.

[0047] Further, in Step 2, the concentration of the polyvinyl alcohol solution is 0.5wt%.

[0048] Further, in Step 2, the concentration of the graphene slurry is 0.5wt%.

[0049] Further, in Step 2, the immersion time of the "rice" - shaped PDMS structure in the solution is 1 min.

[0050] Further, in Step 2, the immersion time in the graphene slurry is 1 min.

[0051] This embodiment also relates to the application of a graphene flexible sensor for tensile direction recognition. Use the aforementioned prepared graphene flexible sensor for tensile direction recognition to judge the tensile direction of the device. The specific steps are as follows:

[0052] Step 1, Acquisition of device basic data: Take the two orthogonal graphene conductive tapes in a "plus" - shaped as the calibration reference in the two - dimensional plane, and the other two graphene conductive tapes as the auxiliary strips for tensile direction judgment; Collect the relevant data of the strain - relative resistance of each of the two orthogonal graphene conductive tapes, fit a quadratic function curve from the data, and obtain the strain - relative resistance change relationship of the entire device on the two - dimensional plane, as shown in Figure 3 shown; where Figure 3 (a) shows the different electrical signal feedbacks of the strips in the X and Y directions when the device is stretched in the X - axis direction, and the quadratic function curve graph obtained by fitting the data collected from the X - axis direction strip.Figure 3 (b) shows the different electrical signal feedbacks of the strips in the X and Y directions when the device is stretched in the Y-axis direction, as well as the quadratic function curve obtained by fitting the data collected from the strip in the Y-axis direction. It can be seen that Figure 3 two orthogonal strips can calibrate the strain-relative resistance change relationship of the device in the entire two-dimensional plane, so that the strain of the two orthogonal strips can be deduced from the change of the electrical signal obtained in the test.

[0053] Step 2: Judgment of the stretching direction: When the device is stretched in the two-dimensional plane, as shown in Figure 2 the figure, the relative resistance of the two orthogonal graphene conductive strips will change. Substituting this change into the quadratic function curve, the magnitudes of their respective strains are obtained, and the stretching angle is calculated using a mathematical model. See the formula:

[0054] tanθ = (ε + ε1) / (ε + ε2) (1)

[0055] θ = tan -1 (ε + ε1) / (ε + ε2) (2)

[0056] ΔR 1,2 / R 1,2 = AΔε 1，2 2 + BΔε 1，2 + C (3)

[0057]

[0058] ε 1,2 = ε·C 1，2 (5)

[0059] θ = tan -1 (1 + C1 / 1 + C2) (6)

[0060] where θ is the stretching angle, ε is the original length of the device strip, ε1 is the stretching length of the strip in the X-axis direction, ε2 is the stretching length of the strip in the Y-axis direction, A is the coefficient of the quadratic term in the quadratic function obtained by fitting the strain-relative resistance related data of each strip, B is the coefficient of the linear term in the quadratic function obtained by fitting the strain-relative resistance related data of each strip, C is the constant term in the quadratic function obtained by fitting the strain-relative resistance related data of each strip, C1 is the solution obtained by substituting the electrical signal value feedback by the strip in the X-axis direction when the device is stretched into the pre-fitted quadratic function curve, C2 is the solution obtained by substituting the electrical signal value feedback by the strip in the Y-axis direction when the device is stretched into the pre-fitted quadratic function curve, ΔR 1,2 is the resistance change generated by the orthogonal strips in the X and Y directions when the device is stretched, and R1,2 is the original resistance value of the orthogonal strips in the X and Y directions before being stretched, and Δε 1,2 is the stretching ratio of the strips in the X and Y directions obtained by solving the quadratic function, and ε 1,2 is the stretching value of the strips in the X and Y directions obtained by solving the quadratic function, and C 1,2 are the two solutions obtained by substituting the electrical signal values fed back by the strips in the X-axis and Y-axis directions when the device is stretched into the pre-fitted quadratic function curve.

[0061] The structure prepared by the method of the present invention is an integral whole with good stability. In the two-dimensional plane range, the other two auxiliary strips in the "rice" - shaped structure can extend the measurement range to 0 - 180°; when the stretching direction measured by the orthogonal strips is 45° or 135°, the two auxiliary strips can be combined to determine whether it is 45° or 135°, because the feedback signals of the two auxiliary strips for these two angles are different. Furthermore, the stretching direction of the device can be judged within the entire two-dimensional plane, realizing the expansion of the application range of the device.

[0062] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a graphene flexible sensor for stretching direction identification, characterized in that: The following steps are involved: Step 1, pretreatment of the substrate material: using PDMS as the substrate material, cleaning the PDMS with oxygen plasma to remove the hydrophobic groups on the surface, and cutting the substrate material into a PDMS with a "M"-shaped structure; Step 2: Preparation of dynamic response flexible sensor based on graphene material: (1) Immerse the PDMS with a "M" shape into a polyvinyl alcohol solution and take it out to dry; (2) immersing the strips in graphene slurry again, taking them out and drying them, and repeating the cycle several times until each strip of the "M"-shaped structure is coated with a graphene conductive coating; (3) Then attach copper conductive tape to each of the eight ports and lead out silver wires; (4) The device is encapsulated with liquid PDMS and cured to obtain the final graphene flexible sensor for stretching direction recognition.

2. The method for preparing a graphene flexible sensor for stretching direction identification according to claim 1, characterized in that: In step 1, the thickness of the PDMS is 200 microns.

3. The method for preparing a graphene flexible sensor for stretching direction identification according to claim 1, characterized in that: In step 1, the size of each strip in the structure is 2 mm×16 mm.

4. The method for preparing a graphene flexible sensor for stretching direction identification according to claim 1, characterized in that: In step 2, the concentration of the polyvinyl alcohol solution is 0.5 wt %.

5. The method for preparing a graphene flexible sensor for stretching direction identification according to claim 1, characterized in that: In step 2, the concentration of the graphene slurry is 0.5wt%.

6. The method for preparing a graphene flexible sensor for stretching direction identification according to claim 1, characterized in that: In step 2, the PDMS immersion time of the "M"-shaped structure is 1 minute.

7. The method for preparing a graphene flexible sensor for stretching direction identification according to claim 1, characterized in that: In step 2, the immersion time in the graphene slurry is 1 min.

8. An application of a graphene flexible sensor for stretching direction identification, characterized in that: The graphene flexible sensor for stretching direction identification prepared in claim 1 is used to determine the stretching direction of the device, and the specific steps are: Step 1: Collection of basic device data: Two cross-shaped orthogonal graphene conductive strips are used as calibration references for the two-dimensional plane, and the remaining two graphene conductive strips are used as auxiliary strips for determining the stretching direction; the strain-relative resistance related data of the two orthogonal graphene conductive strips are collected, and a quadratic function curve is fitted from the data to obtain the strain-relative resistance change relationship of the entire device on the two-dimensional plane; Step 2: Determine the stretching direction: When the device is stretched in a two-dimensional plane, the relative resistance of the two orthogonal graphene conductive bands will change. This change is brought into the quadratic function curve to obtain the magnitude of each strain, and the stretching angle is calculated using a mathematical model, as shown in the formula: tanθ=(ε+ε1) / (ε+ε2) (1) θ=tan -1 (e+e1) / (e+e2) (2) ΔR 1,2 / R 1,2 =ANo 1,2 2 +BNo 1,2 +C (3) e 1,2 =ε·C 1,2 (5) θ=tan -1 (1+C1 / 1+C2) (6) Wherein, θ is the stretching angle, ε is the original length of the device strip, ε1 is the stretching length of the strip in the X-axis direction, ε2 is the stretching length of the strip in the Y-axis direction, a is the coefficient of the quadratic function obtained by fitting the strain-relative resistance related data of each strip, B is the coefficient of the first power in the quadratic function obtained by fitting the strain-relative resistance related data of each strip, C is the constant term in the quadratic function obtained by fitting the strain-relative resistance related data of each strip, C1 is the solution obtained by substituting the electrical signal value of the strip feedback in the X-axis direction when the device is stretched into the pre-fitted quadratic function curve, C2 is the solution obtained by substituting the electrical signal value of the strip feedback in the Y-axis direction when the device is stretched into the pre-fitted quadratic function curve, ΔR 1,2 is the resistance change of the orthogonal strips in the X and Y directions when the device is stretched, R 1,2 is the original resistance of the orthogonal strips in the X and Y directions when not stretched, Δε 1,2 To solve the quadratic function to obtain the stretch ratio of the X and Y direction strips, ε 1,2 To solve the quadratic function to obtain the stretch value of the strip in the X and Y directions, C 1,2 Two solutions are obtained by substituting the electrical signal values ​​of the strips in the X-axis and Y-axis directions fed back when the device is stretched into the pre-fitted quadratic function curve.

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