3D printing isolation structure flexible strain sensor and preparation method thereof

Abstract

The invention discloses a 3D printing isolation structure flexible strain sensor and a preparation method thereof, and belongs to the technical field of sensors, the flexible strain sensor is prepared from a flexible polymer wire with a conductive filler deposited on the surface through 3D printing; the flexible polymer wire material is an etched polyurethane wire material; the conductive filler is a carbon nanomaterial; in the 3D printing isolation structure flexible strain sensor, the conductive filler is constructed to form a conductive network, the distribution of the conductive filler is separated by the flexible polymer, a plurality of isolation structures are formed, and the isolation structures are rhombus-shaped or square-shaped. The flexible strain sensor with the 3D printing isolation structure has the advantages of customizability, high elasticity, high sensitivity, high stability and the like, the preparation process is simple, the condition is mild, the equipment requirement is low, and the flexible strain sensor can be applied to the fields of electronic skin, human motion monitoring and the like.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a 3D printed isolation structure flexible strain sensor and a preparation method thereof. Background Art

[0002] Strain sensors have broad application prospects in the fields of intelligent robots, wearable electronic devices, etc. With the rapid development of science and technology, the market requirements for strain sensors are increasing, especially in terms of customizability, elasticity and sensitivity, to meet the specific needs of different application scenarios, so that they can better adapt to complex and changing working environments.

[0003] Process complexity is a key factor restricting the efficiency and quality of strain sensor preparation. Traditional strain sensor preparation methods often involve multiple steps, such as precision machining, strict packaging technology, etc. A mistake in one link may cause the sensor performance to fail or even fail. Process complexity not only increases the difficulty of preparation, but also increases the preparation cost.

[0004] In order to simplify the preparation method, researchers have conducted in-depth research. For example, a Chinese patent document with publication number CN112374490A discloses a three-dimensional porous graphene / polyurethane flexible stress and strain sensor and a preparation method thereof, which includes: adding graphene oxide to water, ultrasonically dispersing, adding a reducing agent, and mixing to obtain solution A; mixing a surfactant with solution A to obtain solution B; completely immersing the polyurethane sponge in solution B, taking it out and performing a reduction reaction, and freeze-drying to obtain a three-dimensional porous graphene / polyurethane composite material; coating the upper and lower surfaces of the three-dimensional porous graphene / polyurethane composite material with conductive silver paste, bonding copper sheet electrodes, and encapsulating to obtain a sensor; a Chinese patent document with publication number CN119103960A discloses a preparation method for a strain sensor, including: dipping spandex fiber into water-based polyurethane, removing it from the water, and drying it to obtain a flexible substrate layer; dipping the flexible substrate layer into a mixed solution of graphene, N-CNTs and PVP, and then removing it from the water to dry it to obtain a core sensitive layer; and encapsulating the core sensitive layer with a thin film to obtain a strain sensor. The above invention has the advantage of simple manufacturing process. At the same time, flexible composite material sensors based on carbon nanomaterials, including the above invention, have attracted much attention due to their unique properties. However, the conductive network of such flexible composite material sensors is easily destroyed under the action of strain, which can easily lead to unstable performance of strain sensors.

[0005] Therefore, there is an urgent need to develop a new strain sensor with good stability, customizability, high elasticity and high sensitivity and its preparation method. Summary of the invention

[0006] In order to solve the deficiencies in the prior art, the present invention provides a 3D printed isolation structure flexible strain sensor, which has the advantages of customizability, high elasticity, high sensitivity and high stability, and can be applied to electronic skin, human motion monitoring and other fields.

[0007] The specific technical solutions adopted are as follows:

[0008] A 3D printed isolation structure flexible strain sensor, which is prepared by 3D printing from a flexible polymer filament with a conductive filler deposited on the surface;

[0009] In the 3D printed isolation structure flexible strain sensor, the conductive filler forms a conductive network and the distribution of the conductive filler is separated by the flexible polymer to form a plurality of isolation structures, and the isolation structure is a diamond or square;

[0010] The flexible polymer filament is an etched polyurethane filament;

[0011] The conductive filler is carbon nanomaterial.

[0012] The present invention deposits a flexible polymer filament with conductive filler on the surface of the 3D printed core-sheath structure, so that the conductive filler is selectively distributed at the interface of adjacent layers to form a plurality of isolation structures. Compared with the strain sensor prepared from pure polyurethane TPU, the mechanical properties of the 3D printed isolation structure flexible strain sensor are not significantly reduced, and the sensor has good stretchability and strength. In addition, the conductive filler effectively constructs a conductive network, thereby optimizing the conductive performance of the flexible strain sensor, so that the flexible strain sensor will not suddenly lose its conductive performance when subjected to strain, thereby ensuring the stability and reliability of the flexible strain sensor.

[0013] Preferably, the diameter of the flexible polymer filament is 1.5-2 mm, further 1.65 mm (±0.05 mm); and the carbon nanomaterial is graphene.

[0014] Furthermore, the flexible polymer filament with conductive filler deposited on the surface has a core-sheath structure, the core layer is an etched polyurethane filament, the sheath layer is graphene, and the loading amount of graphene is 1wt%-6wt%, more preferably 2.88wt%.

[0015] Specifically, the flexible polymer filament is a polyurethane filament etched by N,N-dimethylformamide. Surface etching can enhance the interaction between graphene and polyurethane filament.

[0016] Preferably, the isolation structure is in a diamond shape. When the corresponding flexible strain sensor is subjected to stress, the diamond shape causes it to deform along the diagonal direction, resulting in a more uniform stress distribution, reduced stress concentration and local structural damage, less damage caused by strain, better elastic recovery under cyclic strain, and more stable sensing signals and range.

[0017] The present invention also provides a method for preparing the 3D printed isolation structure flexible strain sensor, comprising the following steps:

[0018] (1) preparing etched polyurethane filaments;

[0019] (2) preparing a mixed solution containing a conductive filler and polyurethane, or preparing a mixed solution containing a conductive filler, polyurethane and polyvinyl pyrrolidone, and using a dip coating method to form a uniform coating on the surface of the etched polyurethane wire with the mixed solution, and after drying, obtaining a flexible polymer wire with a conductive filler deposited on the surface;

[0020] (3) A flexible polymer filament with conductive filler deposited on the 3D printing surface is used to adjust the 3D printing parameters and then adjust the size and shape of the isolation structure to obtain the 3D printed isolation structure flexible strain sensor.

[0021] Preferably, in step (1), the etching temperature is 20-35° C., and the etching time is 30 s-2 min.

[0022] Preferably, in step (2), the solid content of the mixed solution is 10wt%-15wt%; and the solvent of the mixed solution is N,N-dimethylformamide or N,N-dimethylacetamide.

[0023] Preferably, in step (2), the conductive filler in the mixed solution is graphene, and the mass ratio of graphene to polyurethane is 1:0.5-15, further 1:1-4, and the polyurethane in the mixed solution acts as a binder.

[0024] Further preferably, the mixed solution also includes polyvinyl pyrrolidone, which plays a dispersing role, and the mass ratio of graphene to polyvinyl pyrrolidone is 1:0.01-0.5.

[0025] Preferably, in step (2), the drying method is vacuum drying, and the drying parameters are further preferably 80° C., 12-36 h.

[0026] In step (3), the shape of the isolation structure is regulated by adjusting the 3D printing path, and the size of the isolation structure is regulated by adjusting the printing layer thickness;

[0027] Preferably, the printing path is modeled using CAD; when the isolation structure is a square, the printing path is [0°, 90°], that is, there is an intersection angle α between the walking trajectories of the second layer and the first layer, the walking trajectory of the first layer is 0°, the walking trajectory of the second layer is 90°, the odd layers are parallel to each other, the even layers are parallel to each other, and there is an angle α between the odd layers and the even layers, and printing is performed alternately and reciprocatingly; when the isolation structure is a diamond, the printing path is [45°, 135°], that is, there is an intersection angle α between the walking trajectories of the second layer and the first layer, the walking trajectory of the first layer is 45°, the walking trajectory of the second layer is 135°, the odd layers are parallel to each other, the even layers are parallel to each other, and there is an angle α between the odd layers and the even layers, and printing is performed alternately and reciprocatingly.

[0028] Preferably, the printing layer thickness is 0.05-0.3 mm, further 0.05 mm, 0.1 mm, 0.2 mm or 0.3 mm.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The flexible polymer filaments with graphene deposited on the surface prepared by the method of the present invention have good bonding force with the surface of the polyurethane filaments, which not only meets the requirements of 3D printing, but also can obtain good conductivity at a low content of conductive filler. When the graphene content is 1.23wt%, the graphene / thermoplastic polyurethane composite filaments reaches the electroosmotic threshold, and the conductivity is 7.83×10^ -3 S / m, with stable sensing performance; further, the present invention prepares an isolated structure flexible strain sensor through 3D printing. On the one hand, the geometric shape and size of the isolation structure can be adjusted by adjusting the printing parameters to achieve customization of the strain sensor. On the other hand, compared with the traditionally prepared strain sensor, the setting of this isolation structure reduces its electroosmosis threshold, ensures its stretchability, and optimizes the sensing performance of the flexible strain sensor.

[0031] (2) The 3D printed isolation structure flexible strain sensor prepared by the present invention has the advantages of sensing capability under low electroosmotic threshold and good cyclic stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is an optical picture of the flexible polymer filament with graphene deposited on the surface in Example 1.

[0033] Figure 2 This is a SEM image of the flexible polymer filament with graphene deposited on the surface prepared in Example 1.

[0034] Figure 3 This is a SEM image of the cross-sectional internal structure of the 3D printed isolation structure flexible strain sensor (layer thickness 0.1 mm) prepared in Example 1.

[0035] Figure 4 This is the static test curve of the 3D printed isolation structure flexible strain sensor.

[0036] Figure 5 This is a dynamic test curve diagram of the 3D printed isolation structure flexible strain sensor. DETAILED DESCRIPTION

[0037] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the following is a detailed description through specific embodiments. In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0038] The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. The contents not described in detail in this specification belong to the prior art known to professionals in the field. The experimental materials used in the following examples, unless otherwise specified, can be purchased from conventional biochemical reagent companies.

[0039] Example 1

[0040] (1) adding the polyurethane filament to N,N-dimethylformamide (DMF), standing at 25° C. for 2 min, and etching the polyurethane filament with N,N-dimethylformamide to obtain an etched polyurethane filament having a diameter of 1.65 mm±0.05 mm;

[0041] (2) 2.5 g of graphene, 10 g of polyurethane particles, 0.1 g of polyvinyl pyrrolidone and 100 ml of DMF were mixed uniformly, and the polyurethane particles were fully dissolved and the graphene was uniformly dispersed by ultrasonic dispersion and mechanical stirring to prepare a mixed solution for coating;

[0042] (3) Using a dip coating method, the etched polyurethane filament is immersed in the mixed solution obtained in step (2), and then pulled out at a constant speed to form a uniform coating on the surface of the polyurethane filament. The mixed solution is further dried in a vacuum oven at 80° C. for 24 hours to remove the solvent, thereby obtaining a flexible polymer filament with graphene deposited on the surface. The optical image thereof is shown in FIG. Figure 1 As shown, the flexible polymer filament with graphene deposited on the surface has a core-sheath structure, with graphene located in the outermost layer ( Figure 2), the TGA test showed that the graphene content in the flexible polymer filament with graphene deposited on the surface was 1.23wt%; the flexible polymer filament with graphene deposited on the surface reached the electroosmotic threshold, and the conductivity was 7.83×10^ -3 S / m;

[0043] (4) A flexible polymer filament with graphene deposited on the 3D printing surface, the 3D printing path is [0°, 90°], that is, there is an intersection angle α between the second layer and the first layer, the first layer walking trajectory is 0°, the second layer walking trajectory is 90°, the odd layers are parallel to each other, the even layers are parallel to each other, and there is an angle α between the odd layers and the even layers, and the printing is repeated alternately; the printing layer thickness is set to 0.05mm, 0.1mm, 0.2mm, and 0.3mm, that is, the printing thickness of each layer is maintained at 0.05mm, 0.1mm, 0.2mm, and 0.3mm, respectively, to obtain four 3D printed isolation structure flexible strain sensors with square isolation structures.

[0044] The cross-sectional internal structure SEM image of a representative 3D printed isolation structure flexible strain sensor (layer thickness 0.1 mm) is shown below: Figure 3 As shown, the distribution of conductive fillers in the flexible strain sensor is separated by a flexible polymer.

[0045] Example 2

[0046] The only difference between this embodiment and embodiment 1 is that, when preparing the mixed solution for coating in step (2), the amount of graphene added is 3.5 g, and the graphene content in the obtained flexible polymer filament with graphene deposited on the surface is 2.88 wt%; the other processes and parameters are the same as those in embodiment 1, and a 3D printed isolation structure flexible strain sensor is prepared.

[0047] Example 3

[0048] The only difference between this embodiment and embodiment 1 is that, in step (2) when preparing the mixed solution for coating, the amount of graphene added is 6.5 g, and the graphene content in the obtained flexible polymer filament with graphene deposited on the surface is 6.7 wt%; the other processes and parameters are the same as those in embodiment 1, and a 3D printed isolation structure flexible strain sensor is prepared.

[0049] Example 4

[0050] The only difference between this embodiment and embodiment 1 is that the 3D printing path in step (4) is [45°, 135°], that is, there is an intersection angle α between the walking trajectories of the second layer and the first layer, the walking trajectory of the first layer is 45°, and the walking trajectory of the second layer is 135°, the odd-numbered layers are parallel to each other, the even-numbered layers are parallel to each other, and there is an angle α between the odd-numbered layers and the even-numbered layers, and printing is repeated alternately; the printing layer thickness is set to 0.05mm, 0.1mm, 0.2mm, and 0.3mm, respectively, that is, the printing thickness of each layer is maintained at 0.05mm, 0.1mm, 0.2mm, and 0.3mm, respectively, to obtain four types of 3D printed isolation structure flexible strain sensors.

[0051] The distribution of the conductive filler in the flexible strain sensor is separated by the flexible polymer to form a plurality of isolation structures, wherein the isolation structures are in a rhombus shape.

[0052] Sample analysis

[0053] The performance test of the prepared 3D printed isolation structure flexible strain sensor is carried out; the details are as follows:

[0054] Static test: Apply slowly changing force to the flexible strain sensors with square and diamond isolation structures (graphene addition amount 3.5g, layer thickness 0.1mm) prepared in the embodiment, and record the resistance change of the sensor. Compare the resistance change with the initial resistance, and analyze the sensitivity, strain, linearity and other performance of the sensor; Figure 4 The test results show that the flexible strain sensor with diamond isolation structure has a wide strain range and still has excellent sensing performance under 40% deformation. The sensitivity of the square isolation structure is relatively high, and the change of △R / R0 reaches 15 under 1% deformation.

[0055] Dynamic test: Apply cyclically changing force to the flexible strain sensor with diamond-shaped isolation structure (graphene addition amount 3.5g, layer thickness 0.1mm) to simulate the actual working state. Record the dynamic response of the sensor and analyze its performance parameters such as response speed, stability, sensitivity, etc. Figure 5 The test results prove that the graphene in the diamond isolation structure flexible strain sensor has good bonding strength with the surface of the polyurethane filament, and the damage caused by the strain is small under 20% strain; after 100 cycles under 20% strain, the diamond isolation structure flexible strain sensor shows excellent stability.

[0056] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A 3D printed isolation structure flexible strain sensor, characterized in that: It is prepared by 3D printing from flexible polymer filaments with conductive fillers deposited on the surface; In the 3D printed isolation structure flexible strain sensor, the conductive filler forms a conductive network and the distribution of the conductive filler is separated by the flexible polymer to form a plurality of isolation structures, and the isolation structure is a diamond or square; The flexible polymer filament is an etched polyurethane filament; The conductive filler is carbon nanomaterial.

2. The 3D printed isolation structure flexible strain sensor according to claim 1, characterized in that: The diameter of the flexible polymer filament is 1.5-2 mm, and the carbon nanomaterial is graphene.

3. The 3D printed isolation structure flexible strain sensor according to claim 1, characterized in that: The flexible polymer filaments are polyurethane filaments etched by N,N-dimethylformamide.

4. The 3D printed isolation structure flexible strain sensor according to claim 2, characterized in that: The flexible polymer filament with conductive filler deposited on the surface has a core-sheath structure, the core layer is an etched polyurethane filament, the sheath layer is graphene, and the loading amount of the graphene is 1wt%-6wt%.

5. The method for preparing a 3D printed isolation structure flexible strain sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) preparing etched polyurethane filaments; (2) preparing a mixed solution containing a conductive filler and polyurethane, or preparing a mixed solution containing a conductive filler, polyurethane and polyvinyl pyrrolidone, and using a dip coating method to form a uniform coating on the surface of the etched polyurethane wire with the mixed solution, and after drying, obtaining a flexible polymer wire with a conductive filler deposited on the surface; (3) A flexible polymer filament with conductive filler deposited on the 3D printing surface is used to adjust the 3D printing parameters and then adjust the size and shape of the isolation structure to obtain the 3D printed isolation structure flexible strain sensor.

6. The method for preparing a 3D printed isolation structure flexible strain sensor according to claim 5, characterized in that: In step (1), the etching temperature is 20-35° C., and the etching time is 30 s-2 min.

7. The method for preparing a 3D printed isolation structure flexible strain sensor according to claim 5, characterized in that: In step (2), the solid content of the mixed solution is 10wt%-15wt%; the solvent of the mixed solution is N,N-dimethylformamide or N,N-dimethylacetamide.

8. The method for preparing a 3D printed isolation structure flexible strain sensor according to claim 5, characterized in that: In step (2), the conductive filler in the mixed solution is graphene, and the mass ratio of graphene to polyurethane is 1:0.5-15.

9. The method for preparing a 3D printed isolation structure flexible strain sensor according to claim 8, characterized in that: The mixed solution also includes polyvinyl pyrrolidone, and the mass ratio of graphene to polyvinyl pyrrolidone is 1:0.01-0.

5.

10. The method for preparing a 3D printed isolation structure flexible strain sensor according to claim 5, characterized in that: In step (3), the shape of the isolation structure is regulated by adjusting the 3D printing path, and the size of the isolation structure is regulated by adjusting the layer thickness.

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