阅读说明：本技术 一种用作可穿戴应变传感器的石墨烯二维网格结构及其制备方法 (Graphene two-dimensional grid structure used as wearable strain sensor and preparation method thereof ) 是由 杨金山 董绍明 游潇 丁玉生 高乐 于 2020-12-29 设计创作，主要内容包括：本发明涉及一种用作可穿戴应变传感器的石墨烯二维网格结构及其制备方法。所述石墨烯二维网格结构的制备方法包括：将石墨烯同分散剂加入至溶剂中,均匀分散得到稳定的石墨烯悬浮液；向石墨烯悬浮液中加入聚二甲基硅氧烷PDMS主剂,蒸发部分溶剂,得到石墨烯分散液；向石墨烯分散液中加入PDMS固化剂,得到石墨烯打印浆料；以及利用3D打印机在基底上堆积石墨烯打印浆料制备二维网格结构；再经固化得到石墨烯二维网格结构。(The invention relates to a graphene two-dimensional grid structure used as a wearable strain sensor and a preparation method thereof. The preparation method of the graphene two-dimensional grid structure comprises the following steps: adding graphene and a dispersing agent into a solvent, and uniformly dispersing to obtain a stable graphene suspension; adding a polydimethylsiloxane PDMS (polydimethylsiloxane) main agent into the graphene suspension, and evaporating part of the solvent to obtain a graphene dispersion liquid; adding a PDMS curing agent into the graphene dispersion liquid to obtain graphene printing slurry; stacking graphene printing slurry on the substrate by using a 3D printer to prepare a two-dimensional grid structure; and curing to obtain the graphene two-dimensional grid structure.)

1. a preparation method of a graphene two-dimensional grid structure is characterized by comprising the following steps:

adding graphene and a dispersing agent into a solvent, and uniformly dispersing to obtain a stable graphene suspension; adding a polydimethylsiloxane PDMS (polydimethylsiloxane) main agent into the graphene suspension, and evaporating part of the solvent to obtain a graphene dispersion liquid; adding a PDMS curing agent into the graphene dispersion liquid to obtain graphene printing slurry; stacking graphene printing slurry on the substrate by using a 3D printer to prepare a two-dimensional grid structure; and curing to obtain the graphene two-dimensional grid structure.

2. The preparation method according to claim 1, wherein when preparing the graphene dispersion liquid, heating and evaporating part of the solvent, wherein the heating temperature is 70-90 ℃, the mass fraction of the evaporated solvent in the total amount of the solvent is 85-95 wt%, and the mass fraction of graphene in the graphene dispersion liquid is 3.7-6.2 wt%.

3. The method according to claim 1 or 2, wherein the graphene has a thickness of 5 to 10nm and a width of 20 to 50 μm.

4. The preparation method according to any one of claims 1 to 3, wherein the dispersant is at least one selected from polyvinylpyrrolidone, polyvinyl butyral and methyl violet, and the mass ratio of the dispersant to graphene is 1:2 to 1: 50.

5. The preparation method according to any one of claims 1 to 4, wherein the solvent is at least one selected from absolute ethyl alcohol, deionized water and acetone, and the mass ratio of the graphene to the solvent is 1: 100-1: 200.

6. The preparation method according to claims 1 to 5, wherein the dispersion is ultrasonic dispersion, the power is 100-500W, and the time is 1-3 hours.

7. The preparation method according to any one of claims 1 to 6, wherein the mass ratio of the graphene to the main agent of polydimethylsiloxane PDMS is 1: 5-1: 10; the mass ratio of the polydimethylsiloxane to the PDMS curing agent is 5: 1-15: 1.

8. The method for preparing according to any one of claims 1 to 7, wherein the parameters of the 3D printing process include: the air pressure borne by the printing nozzle is 0-0.6 MPa, the moving speed of the printing nozzle is 1-30 mm/s, the diameter of the printing nozzle is 0.1-0.6 mm, the spacing of monofilaments in a layer is 0.1-5 mm, and the included angle between the warp direction and the weft direction of the grid is 0-90 degrees.

9. The method according to any one of claims 1 to 8, wherein the curing temperature is 80 to 150 ℃ and the curing time is 0.5 to 2 hours.

10. A graphene two-dimensional lattice structure prepared by the preparation method according to any one of claims 1 to 9, wherein the graphene two-dimensional lattice has intersection points of warp and weft directions which are connected and overlapped with each other.

11. The graphene two-dimensional grid structure according to claim 10, wherein the graphene two-dimensional grid structure has a maximum tensile strain of up to 113% and a sensitivity coefficient of up to 256 at 20% strain.

12. Use of a graphene two-dimensional grid structure according to claim 10 or 11 in a wearable strain sensor.

Technical Field

The invention relates to a graphene two-dimensional grid structure capable of being used as a wearable strain sensor and prepared by a direct extrusion type 3D printing method and a preparation method thereof, belonging to the macro application of graphene in the field of flexible sensors.

Background

Wearable electronic products are becoming common necessities in modern human life, and have attracted great attention in application fields from intelligent skins to scalable sensors and the like through interaction and integration of people and external information. High-performance flexible wearable sensors represented by flexible electronic skins play an important role in realizing intelligent and sensitive functions of flexible electronic products. In recent years, carbon-based nano materials are widely applied to the field of flexible wearable sensors due to unique structures and novel functions of the carbon-based nano materials. Particularly, the graphene has the advantages of high electron mobility, excellent electric conduction and thermal conductivity, unique mechanical property, easiness in functional modification and the like, realizes reasonable design of micro-morphology and macro-topology structure, and has important significance in developing and popularizing a novel flexible sensor based on a nano material. In practical applications, graphene-based wearable sensors generally need to have good flexibility and stretchability, and a variety of structures and material compositions, and can be stably attached to the surface of an irregular or rigid object, and also can be attached to the skin of a human, so that graphene planar grids with precise two-dimensional configurations are receiving wide attention in current research. The graphene two-dimensional grid can provide a current conduction path which is connected with each other macroscopically, has a penetrating electronic transmission channel microscopically, has obvious advantages in the transmission process of strain signals and response signals, and has potential application prospects in the fields of robots, handheld consumer electronics, monitors, medical health monitoring equipment and the like.

In the current research, the preparation method of the graphene two-dimensional grid structure mainly comprises a monofilament weaving method and a template method. The monofilament weaving method is to weave the prepared fiber or monofilament transversely and longitudinally in a crossed manner to obtain a grid structure, and the grid structure obtained by the method is actually uncontrollable and cannot realize efficient and repeatable preparation; when the strain is applied, random deformation and dislocation are easy to occur, and the electrical response signal generates irregular fluctuation. More importantly, the structure obtained by weaving is not an accurate two-dimensional structure actually, the cross point of the structure in the transverse direction and the longitudinal direction has obvious up-and-down fluctuation, and the unbalanced surface makes the structure difficult to be stably attached to a flexible surface, and finally, the sensitivity and the accuracy of the structure serving as a wearable sensor are low; the template method is to use a nickel grid or an ice grid as an initial template structure, to realize the coating of graphene by using a deposition technology or an in-situ growth process, and to finally remove the template to obtain a similar graphene grid structure. This process can repeat the etching of the template to obtain a graphene mesh with a precise planar structure, but the graphene sheet layer and the microstructure are easily damaged during the etching of the template, which finally results in the collapse or deformation of the mesh structure. In addition, the attachment and growth process of graphene on the template are difficult to control, and uneven performance distribution of the net structure is easily caused. Therefore, how to realize efficient and controllable preparation of the graphene grid with an accurate two-dimensional structure and excellent structural stability has important significance for improving the response sensitivity and accuracy of the graphene grid.

Disclosure of Invention

In view of the above problems, the present invention provides a graphene two-dimensional grid structure used as a wearable strain sensor and a preparation method thereof, so as to realize macroscopic application of graphene and optimize structural stability and response sensitivity when the graphene is used as a flexible wearable sensor.

In a first aspect, the present invention provides a method for preparing a graphene two-dimensional grid structure, including: adding graphene and a dispersing agent into a solvent, and uniformly dispersing to obtain a stable graphene suspension; adding a polydimethylsiloxane PDMS (polydimethylsiloxane) main agent into the graphene suspension, and evaporating part of the solvent to obtain a graphene dispersion liquid; adding a PDMS curing agent into the graphene dispersion liquid to obtain graphene printing slurry; and stacking graphene printing slurry on the substrate by using a 3D printer, and curing to obtain the graphene two-dimensional grid structure.

The graphene two-dimensional grid structure capable of being used as a wearable strain sensor is prepared by using a direct extrusion type 3D printing technology. Microscopically, the graphene sheet layers are uniformly dispersed in the PDMS, so that irreversible stacking and agglomeration of graphene can not occur, and meanwhile, the highly-crystallized PDMS substrate ensures that the grid structure has excellent flexibility and stretchability, so that the basic requirement of the grid structure applied to a wearable sensor is met; on the other hand, during the extrusion of the printing paste, the graphene sheet layers are subjected to shear force to generate directional deflection, and a microscopic three-dimensional network state distributed in parallel to the axial direction is formed. When the microcosmic interconnected conductive network is deformed and released, the contact points are disconnected and reconnected, so that a conductive path is changed, and the resistance of the graphene two-dimensional grid correspondingly fluctuates; macroscopically, the 3D printing technology is taken as a typical additive manufacturing technology, has the characteristics of simplicity, rapidness, individuation design and the like, and can be used for preparing a planar mesh structure with a complete and clear structure, self-support and a controllable shape by stacking slurry according to a path set by a program. More importantly, the movement path of the printing nozzles in series ensures that there is no repetitive stacking of this stacking pattern by stacking the slurry at the desired spots on the substrate using 3D printing in a programmable path. Therefore, the prepared grid structure has accurate two-dimensional characteristics, has overlapped warp-wise and weft-wise intersection points which are connected with each other, does not have continuous up-and-down fluctuation, and is the biggest characteristic which is different from the traditional woven grid structure. The precise two-dimensional grid structure can be easily attached to a flexible surface or a rigid irregular surface, and can keep the structure stable without generating redundant interface resistance when deformed, so that stable and efficient current transfer and electrical response can be realized.

Preferably, when the graphene dispersion liquid is prepared, heating and evaporating part of the solvent, wherein the heating temperature is 70-90 ℃, the evaporation capacity of the solvent accounts for 85-95 wt% of the total mass of the solvent, and the mass fraction of the graphene in the graphene dispersion liquid is 3.7-6.2 wt%.

When the evaporation solvent is too little, the viscosity of the printing paste is low, and finally, the printed grid structure cannot realize self-support and is difficult to form; when the evaporation solvent is excessive, the viscosity of the printing paste is too high, and graphene may be re-agglomerated in the paste, which may cause instability of the paste extrusion process and non-uniformity of electrical properties of the grid structure.

Preferably, the thickness of the raw material graphene is 5-10 nm, and the width is 20-50 μm.

Preferably, the dispersant is at least one of polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB) and Methyl Violet (MV), preferably polyvinylpyrrolidone (PVP).

Preferably, the mass ratio of the dispersing agent to the graphene is 1: 2-1: 50. When the mass ratio is less than 1:2, the viscosity of the printing paste is too high, so that the paste extrusion process is difficult to stably control; when the mass ratio is greater than 1:50, the graphene cannot be stably and uniformly dispersed, so that the electrical properties of the grid structure are not uniform.

Preferably, the solvent is at least one of absolute ethyl alcohol, deionized water and acetone.

Preferably, the mass ratio of the graphene to the solvent is 1: 100-1: 200. The addition amount of the solvent is properly increased, and the graphene is uniformly dispersed. The uniform dispersion of graphene in the printing paste ensures that the paste has the typical rheological characteristics suitable for 3D printing.

Preferably, the dispersion process is ultrasonic dispersion, the power of the ultrasonic process is 100-500W, and the time is 1-3 hours. The graphene is more uniformly dispersed by properly improving the ultrasonic power and prolonging the ultrasonic time.

Preferably, the mass ratio of the graphene to the polydimethylsiloxane PDMS is 1: 5-1: 10. By properly selecting the mass ratio of graphene to PDMS, the 3D printing paste can be smoothly extruded to realize the structural self-supporting property. Too much PDMS addition amount may cause too high viscosity of the printing paste to be extruded, and too low PDMS addition amount may cause difficulty in excellent flexibility and stretchability of the printed structure.

Preferably, the mass ratio of the polydimethylsiloxane PDMS main agent to the corresponding curing agent is 5: 1-15: 1, and preferably 10: 1.

Preferably, the parameters of the printing process include: the air pressure borne by the printing nozzle is 0-0.6 MPa, the moving speed of the printing nozzle is 1-30 mm/s, the diameter of the printing nozzle is 0.1-0.6 mm, the spacing of monofilaments in a layer is 0.1-5 mm, and the included angle between the warp direction and the weft direction of the grid is 0-90 degrees.

The graphene/PDMS two-dimensional grid obtained through 3D printing is only printed on the substrate, the warp-wise and weft-wise junction points are connected with each other and well combined, and the graphene two-dimensional grid is guaranteed to have excellent flexibility, stretchability and accurate two-dimensional characteristics.

Preferably, the curing temperature is 80-150 ℃ and the curing time is 0.5-2 hours.

The 3D printing technology has the characteristics of simplicity, rapidness and free design. According to the invention, the graphene grid structure with complete and clear structure, self-supporting property and accurate two-dimensional characteristic can be prepared by performing model slicing treatment on the planar grid structure to set the corresponding slurry accumulation path and regulating and controlling printing parameters such as air pressure and moving speed of the printing nozzle.

In a second aspect, a graphene two-dimensional grid structure prepared by the preparation method is provided, and the graphene two-dimensional grid structure is characterized in that the graphene two-dimensional grid structure is provided with connecting points which are connected and overlapped with each other in a warp direction and a weft direction.

The graphene two-dimensional grid structure can freely design the filling density and the filling angle of the internal monofilaments according to actual requirements, and meanwhile, the graphene nano sheets can be assembled to form a directional three-dimensional network structure in a microscopic mode, so that the graphene two-dimensional grid structure has excellent flexibility and stretchability and has sensitive electrical response.

Preferably, the maximum tensile strain of the graphene two-dimensional grid structure can reach 113%, and the sensitivity coefficient under 20% strain can reach 256.

In a third aspect, the invention provides an application of the graphene two-dimensional grid structure in a wearable strain sensor. The graphene two-dimensional grid structure prepared by the invention can be easily attached to a flexible surface or a rigid irregular surface, generates real-time stable electrical response to strain, and can be applied to wearable strain sensors. Meanwhile, the graphene two-dimensional grid is provided with the warp-wise and weft-wise cross joints which are mutually connected and overlapped, and the structural integrity can be kept when the graphene two-dimensional grid is subjected to strain, so that no obvious interface resistance exists, the resistance change of the graphene two-dimensional grid is mainly controlled by tiny resistance between graphene layers, and efficient current transfer and resistance response can be realized.

Drawings

Fig. 1 shows a schematic flow chart of 3D printing preparation of a graphene two-dimensional grid structure.

Fig. 2 shows the optical photographs of the graphene two-dimensional grids with different filling angles in the warp and weft directions prepared in example 2 and examples 9 to 11.

Fig. 3 shows a scanning electron image of the surface of the graphene two-dimensional grid prepared in example 2.

Fig. 4 shows a variation trend of the resistance of the graphene two-dimensional grid prepared in example 2 during horizontal stretching.

Fig. 5 shows the relative resistance change values of the graphene two-dimensional grids prepared in examples 1 to 12 and comparative examples 1 and 2 at a horizontal tensile strain of 20%.

Detailed Description

The following detailed description of the present invention will be made in conjunction with the accompanying drawings and examples. It is to be understood that the following drawings and examples are illustrative of the invention and are not to be construed as limiting the invention.

In the method, graphene is uniformly dispersed by taking graphene as a raw material, polyvinylpyrrolidone (PVP) as a dispersing agent, Polydimethylsiloxane (PDMS) as a thickening agent and absolute ethyl alcohol as a solvent in an ultrasonic mode to obtain a graphene suspension; evaporating in water bath to remove the solvent, adding PDMS curing agent, and stirring to obtain printable slurry with high concentration; parameters such as a filling interval, a filling angle and a thickness of the two-dimensional grid structure are set, and parameters such as a nozzle diameter and a moving speed used for 3D printing are adjusted to realize preparation of the graphene two-dimensional grid structure; and finally obtaining the graphene two-dimensional grid structure which has excellent flexibility and stretchability and is high in sensitivity and can be used for wearable strain sensors through curing.

The following exemplarily illustrates a method for preparing a graphene two-dimensional lattice structure, as shown in fig. 1.

Adding graphene and a dispersant polyvinylpyrrolidone (PVP) into a solvent (such as absolute ethyl alcohol, deionized water, acetone and the like), and uniformly mixing the graphene and the dispersant PVP in an ultrasonic mode to obtain a stably dispersed graphene suspension. Next, a polydimethylsiloxane PDMS base was added to the suspension, and uniformly dispersed again by ultrasonic oscillation. The power range in the ultrasonic process can be 100-500W, the time range can be 1-3 hours, the ultrasonic power is properly increased, the ultrasonic time is prolonged, the graphene can be dispersed more uniformly, and the excellent rheological behavior of the printing paste is ensured. In a preferred embodiment, the mass ratio of the dispersing agent to the graphene can be 1: 2-1: 50, and a proper amount of the dispersing agent can ensure that the electrical properties of the graphene are not affected and the graphene is uniformly and stably dispersed. The mass ratio of the graphene to the solvent can be 1: 100-1: 200, and the addition amount of the solvent is properly increased, so that the graphene is uniformly dispersed.

Heating the graphene suspension liquid in a water bath until most of the solvent in the graphene suspension liquid is volatilized, and obtaining the high-concentration graphene dispersion liquid. Wherein the evaporation capacity of the solvent accounts for 85-95 wt% of the total amount of the solvent, the temperature range in the heating process can be 70-90 ℃, and the mass fraction of the graphene in the dispersion liquid is preferably ensured to be 3.7-6.2 wt%. And adding a curing agent corresponding to polydimethylsiloxane PDMS into the graphene suspension, and stirring for a long time to finally obtain paste graphene/PDMS printing slurry.

And transferring the printing slurry into a printing pipe, designing a two-dimensional grid structure by using three-dimensional drawing software, and guiding the two-dimensional grid structure into a 3D printer, wherein the slurry is stacked according to a path set by the path to obtain a grid with accurate two-dimensional characteristics. Specifically, parameters such as a filling interval, a filling angle and a thickness of the two-dimensional grid structure are set, and parameters such as a nozzle diameter and a moving speed used for 3D printing are adjusted to achieve preparation of the graphene two-dimensional grid structure. Wherein, the parameters of printing mainly include: the air pressure borne by the printing nozzle is 0-0.6 MPa, the moving speed of the printing nozzle is 1-30 mm/s, the diameter of the printing nozzle is 0.1-0.6 m, the spacing of monofilaments in the layer is 0.1-5 mm, and the included angle between the warp direction and the weft direction of the grid is 0-90 degrees. Preferably, the pressure and the moving speed of the printing nozzle are matched to obtain the two-dimensional grid with stable structure.

And (3) placing the printed sample in an oven for high-temperature curing to finally obtain the graphene two-dimensional grid structure with excellent flexibility and stretchability for the wearable sensor. Wherein the temperature in the curing process is 80-150 ℃ and the time is 0.5-2 hours.

In the disclosure, the maximum tensile strain of the graphene two-dimensional grid structure can reach 113% as measured by a stress-strain test of a universal testing machine. When the graphene grid is subjected to stretching-releasing circulation for 100 times under the strain of 20%, the stress retention rate is close to 100%, and the stress attenuation phenomenon is not found, so that the prepared graphene two-dimensional grid has excellent flexibility and stretchability; the graphene two-dimensional grid shows good electrical response sensitivity in the stretching process, the resistance value of the graphene two-dimensional grid is positively correlated with the stretching deformation, and the sensitivity coefficient of the graphene two-dimensional grid can reach 256 by utilizing a two-probe method of a digital multimeter; in multiple stretching-releasing cycles, the maximum value and the minimum value of the relative resistance change value of the graphene two-dimensional grid can be kept stable, and the resistance value of the graphene two-dimensional grid can return to the initial value with the same change trend after strain release.

The graphene two-dimensional grid prepared by the invention macroscopically has the cross points of the warp direction and the weft direction which are connected with each other, and can keep the structure stable when being strained, so that stable electrical response can be realized. Meanwhile, the highly flat structure ensures that the adhesive can be easily attached to the surface of a human body or the surface of a rigid irregular object, and has a wide application range; microscopically, the graphene sheet layers form a conductive current transmission path, and the resistance change of the graphene sheet layers is caused by disconnection of contact points of the graphene conductive network or reduction of contact area, so that efficient current transmission and resistance response can be realized, the basic requirements of the flexible wearable sensor are met, and the graphene sheet layers have important significance for promoting macroscopic application of graphene.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1

A preparation method of a graphene planar network structure comprises the following specific steps:

(1) 0.6g of graphene (thickness 5nm, width 50um) and 0.012g of polyvinylpyrrolidone PVP were added to 80ml of absolute ethanol to ensure a graphene to dispersant mass ratio of 50: 1. Carrying out ultrasonic dispersion on the graphene oxide suspension for 2 hours under the power of 200W to obtain a uniformly dispersed graphene suspension; 6g of polydimethylsiloxane PDMS base were added to the suspension and again subjected to ultrasonic dispersion for 2 hours at a power of 200W. And then heating the obtained suspension at the temperature of 80 ℃ to remove most of the solvent anhydrous ethanol, wherein the evaporation capacity of the solvent accounts for 90 wt% of the total mass of the solvent, and the mass fraction of graphene in the obtained graphene dispersion liquid is 4.6 wt%. And finally, adding 0.6g of PDMS curing agent into the graphene dispersion liquid, and magnetically stirring for 2 hours to finally obtain the graphene/PDMS printing paste.

(2) And transferring the printing paste to a printing pipe, and introducing a two-dimensional grid structure model designed by three-dimensional drawing software at a computer control end, wherein the size of the two-dimensional grid structure model is 20mm multiplied by 0.3 mm. And then gradually stacking slurry according to a path set by a program and printing to obtain the graphene two-dimensional grid with the same size. The air pressure used in the printing process is 0.4MPa, the moving speed is 15mm/s, the diameter of the nozzle is 0.3mm, the spacing of monofilaments in the layer is 1.5mm, and the included angle of the longitude and the latitude of the grid is 90 degrees.

(3) And (3) curing the printed sample in an oven at 150 ℃ for 1 hour to obtain the graphene two-dimensional grid structure with excellent flexibility and stretchability.

Example 2

Example 2 differs from example 1 only in that: 0.02g of dispersant polyvinylpyrrolidone PVP is added in the step (1) to ensure that the mass ratio of the graphene to the dispersant is 30: 1.

Example 3

Example 3 differs from example 1 only in that: 0.03g of dispersant polyvinylpyrrolidone PVP is added in the step (1) to ensure that the mass ratio of the graphene to the dispersant is 20: 1.

Example 4

Example 4 differs from example 1 only in that: 0.06g of dispersant polyvinylpyrrolidone PVP is added in the step (1) to ensure that the mass ratio of the graphene to the dispersant is 10: 1.

Example 5

Example 5 differs from example 1 only in that: 0.12g of dispersant polyvinylpyrrolidone PVP is added in the step (1) to ensure that the mass ratio of the graphene to the dispersant is 5: 1.

Example 6

Example 6 differs from example 1 only in that: 0.3g of dispersant polyvinylpyrrolidone PVP is added in the step (1) to ensure that the mass ratio of the graphene to the dispersant is 2: 1.

Example 7

Example 7 differs from example 2 only in that: in the step (2), the size of the two-dimensional grid structure edited by the three-dimensional drawing software is introduced into the computer control end and is 20mm multiplied by 0.4 mm; the nozzle diameter for 3D printing was 0.4 mm.

Example 8

Example 8 differs from example 2 only in that: in the step (2), the size of the two-dimensional grid structure edited by the three-dimensional drawing software is introduced into the computer control end and is 20mm multiplied by 0.5 mm; the nozzle diameter for 3D printing was 0.5 mm.

Example 9

Example 9 differs from example 2 only in that: and (3) forming a warp-weft included angle of the two-dimensional grid structure printed in the step (2) to be 60 degrees.

Example 10

Example 10 differs from example 2 only in that: and (3) forming a warp-weft included angle of 45 degrees for the two-dimensional grid structure printed in the step (2).

Example 11

Example 11 differs from example 2 only in that: and (3) the included angle of the longitude and latitude directions of the two-dimensional grid structure printed in the step (2) is 30 degrees.

Example 12

Example 12 differs from example 2 only in that: and (3) forming a warp-weft included angle of 0 degree for the two-dimensional grid structure printed in the step (2).

Comparative example 1

Comparative example 1 differs from example 2 only in that: in the step (1), the evaporation amount of the solvent accounts for 70 wt% of the total amount of the solvent, and the mass fraction of graphene in the graphene dispersion liquid is 2.4 wt%.

Comparative example 2

Comparative example 1 differs from example 2 only in that: in the step (1), the mass fraction of the evaporation amount of the solvent in the total amount of the solvent is 98 wt%, and the mass fraction of graphene in the graphene dispersion liquid is 7.6 wt%.

Fig. 2 shows the optical photographs of the graphene two-dimensional grids with different filling angles in the warp and weft directions prepared in example 2 and examples 9 to 11. The graph shows that the graphene grid prepared by 3D printing has excellent structural integrity and accurate periodic arrangement, and the graphene slurry system has excellent self-supporting performance and good stability in the 3D printing process. The two-dimensional grids with different filling included angles in the longitude and latitude directions can be efficiently obtained by adjusting the printing model, and the response sensitivity of the two-dimensional grids can be accurately regulated and controlled to meet different application requirements.

Fig. 3 shows a scanning electron image of the surface of the graphene two-dimensional grid prepared in example 2. It can be seen from (a) in fig. 3 that the printed lattice structure achieves precise two-dimensional characteristics with overlapping warp and weft junctions connected to each other without significant misalignment and structural mismatching. Fig. 3 (b) shows a corner image of graphene grid junctions, which remains rounded without excess slurry buildup. The accurate two-dimensional structure ensures the stability and the transmission efficiency of current transfer, and obviously improves the electrical response sensitivity of the graphene grid in strain.

Fig. 4 shows a variation tendency of the resistance of the graphene two-dimensional grid prepared in example 2 during horizontal stretching. As can be seen from the figure, as the tensile strain increases, the relative resistance change of the graphene two-dimensional grid gradually increases. Analysis shows that the breaking of microscopic contact points of the graphene conductive network and the reduction of contact areas in the stretching process cause the fluctuation of a conductive path, so that the resistance of the graphene two-dimensional grid changes.

Fig. 5 shows the relative resistance change values of the graphene two-dimensional grids prepared in examples 1 to 12 and comparative examples 1 and 2 at a horizontal tensile strain of 20%. For embodiments 1-6 (PVP content gradually increased), the maximum tensile strain of the graphene mesh was gradually reduced, because PVP formed a layer of hard shell on the surface of the graphene monofilament, which ensured higher mechanical strength of the mesh, while also attenuated its flexibility and stretchability. This causes microcracks to be generated on the surface of the graphene grid during the stretching process, so that the stress of the graphene grid is attenuated to a certain extent, and finally the relative resistance change value of the graphene grid is reduced. This result is also consistent with the stress retention and the relative resistance change retention after 100 stretch-release cycles at 20% strain. For example 7 and example 8, the thickness of the printed graphene two-dimensional grid may be controlled by the diameter of the printing nozzle. This change in thickness does not affect the mechanical strength and electrical response sensitivity of the graphene mesh, has a relative resistance change value close to that of example 2, and generally has more excellent flexibility for thinner structures and can be more easily attached to the surface of an object. Examples 9-12 are graphene two-dimensional grids with different fill angles in warp and weft directions. When the grid is stretched, different angles can correspond to different conductive path variation amounts, so that different relative resistance variation values can be obtained. The printing paste in comparative example 1 has low viscosity, so that the self-supporting performance and structural strength of the printed two-dimensional grid are weak, and the structure is easy to break when the printing paste is stretched, so that the microscopic graphene conductive paths are disconnected to the greatest extent under the strain of 20%, and therefore, more remarkable relative resistance change is generated. The printing paste of comparative example 2 has too high a viscosity to easily cause local agglomeration of graphene, and causes instability of the paste extrusion process and non-uniformity of electrical response, which may exhibit fluctuating relative resistance changes during the stretch release cycle.

Table 1 shows the maximum tensile strain, stress retention (100 stretch-release cycles under 20% strain), relative resistance change retention (100 stretch-release cycles under 20% strain) and sensitivity coefficient (20% strain) of the graphene two-dimensional grids obtained in examples 1 to 12 and comparative examples 1 to 2.

Table 1: