A 3D-printed flexible strain sensor with an isolation structure and its fabrication method

Abstract

This invention discloses a 3D-printed flexible strain sensor with an isolated structure and its fabrication method, belonging to the field of sensor technology. The flexible strain sensor is fabricated by 3D printing of flexible polymer filaments with conductive fillers deposited on their surface. The flexible polymer filaments are etched polyurethane filaments; the conductive fillers are carbon nanomaterials. In the 3D-printed flexible strain sensor with an isolated structure, the conductive fillers form a conductive network, and the distribution of the conductive fillers is separated by the flexible polymer, forming several isolated structures. The isolated structures are rhomboid or square. The 3D-printed flexible strain sensor with an isolated structure of this invention has advantages such as customizability, high elasticity, high sensitivity, and high stability. Furthermore, the fabrication process is simple, the conditions are mild, and the equipment requirements are low, making it applicable to fields such as electronic skin and human motion monitoring.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a 3D-printed flexible strain sensor with an isolated structure and its fabrication method. Background Technology

[0002] Strain sensors have broad application prospects in fields such as intelligent robots and wearable electronic devices. With the rapid development of technology, the market demands for strain sensors are increasing, especially in terms of customizability, flexibility, and sensitivity, to meet the specific needs of different application scenarios and enable them to better adapt to complex and changing working environments.

[0003] The complexity of the manufacturing process is a key factor restricting the efficiency and quality of strain sensor fabrication. Traditional strain sensor fabrication methods often involve multiple steps, such as precision machining and strict packaging processes. A mistake in any step may lead to substandard sensor performance or failure. The complexity of the process not only increases the difficulty of fabrication but also increases the manufacturing cost.

[0004] To simplify the preparation method, researchers have conducted in-depth studies. For example, Chinese patent document CN112374490A discloses a three-dimensional porous graphene / polyurethane flexible stress-strain sensor and its preparation method. The method includes: adding graphene oxide to water, ultrasonically dispersing it, adding a reducing agent, mixing it, and obtaining solution A; mixing a surfactant with solution A to obtain solution B; completely immersing a polyurethane sponge in solution B, removing it, performing a reduction reaction, and freeze-drying it to obtain a three-dimensional porous graphene / polyurethane composite material; coating the top and bottom surfaces of the three-dimensional porous graphene / polyurethane composite material with conductive silver paste, bonding copper electrode sheets, and encapsulating it to obtain the sensor. Chinese patent document CN119103960A discloses a method for preparing a strain sensor, including: impregnating spandex fibers in aqueous polyurethane, removing them, and drying them to obtain a flexible substrate layer; impregnating the flexible substrate layer in a mixture of graphene, N-CNTs, and PVP, removing it, and drying it to obtain a core sensitive layer; and encapsulating the core sensitive layer in a thin film to obtain the strain sensor. The aforementioned inventions have the advantage of simple manufacturing processes. Meanwhile, flexible composite material sensors based on carbon nanomaterials, including these inventions, have attracted considerable attention due to their unique properties. However, the conductive network of these flexible composite material sensors is easily damaged under strain, which can easily lead to unstable performance of the strain sensors.

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

[0006] To address the shortcomings of existing technologies, this invention provides a 3D-printed flexible strain sensor with an isolated structure. This flexible strain sensor has advantages such as customizability, high elasticity, high sensitivity, and high stability, and can be applied to fields such as electronic skin and human motion monitoring.

[0007] The specific technical solution adopted is as follows:

[0008] A 3D-printed flexible strain sensor with an isolated structure is prepared by 3D printing from flexible polymer filaments with conductive fillers deposited on their surface.

[0009] In the 3D-printed flexible strain sensor with an isolation structure, conductive filler is constructed to form a conductive network and the distribution of the conductive filler is separated by a flexible polymer to form several isolation structures, wherein the isolation structures are rhomboid or square.

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

[0011] The conductive filler is a carbon nanomaterial.

[0012] This invention utilizes flexible polymer filaments with conductive fillers deposited on the surface of a 3D-printed core-sheath structure. The conductive fillers are selectively distributed at the interfaces of adjacent layers, forming several isolation structures. Compared to strain sensors made of pure polyurethane (TPU), the mechanical properties of this 3D-printed flexible strain sensor with isolation structures are not significantly reduced, exhibiting good stretchability and strength. Furthermore, the conductive fillers effectively construct a conductive network, thereby optimizing the conductivity of the flexible strain sensor and preventing it from suddenly losing conductivity under strain, thus ensuring the stability and reliability of the flexible strain sensor.

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

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

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

[0016] Preferably, the isolation structure is rhomboid. When the corresponding flexible strain sensor is subjected to force, the rhomboid shape causes it to deform along the diagonal direction, resulting in a more uniform stress distribution, reducing stress concentration and local structural damage, minimizing strain-induced damage, and improving its elastic recovery capability under cyclic strain, thus leading to a more stable sensing signal and range.

[0017] This invention also provides a method for fabricating the aforementioned 3D-printed flexible strain sensor with an isolated structure, comprising the following steps:

[0018] (1) Prepare the polyurethane filament to be etched;

[0019] (2) Prepare a mixed solution containing conductive filler and polyurethane, or prepare a mixed solution containing conductive filler, polyurethane and polyvinylpyrrolidone, and use dip coating to form a uniform coating on the surface of the etched polyurethane filament. After drying, a flexible polymer filament with conductive filler deposited on the surface is obtained.

[0020] (3) A flexible polymer filament with conductive filler deposited on the surface of a 3D printed structure is obtained by adjusting the 3D printing parameters to control the size and shape of the isolation structure.

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

[0022] Preferably, 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.

[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, or more preferably 1:1-4. The polyurethane in the mixed solution acts as a binder.

[0024] More preferably, the mixed solution also includes polyvinylpyrrolidone, which acts as a dispersant, and the mass ratio of graphene to polyvinylpyrrolidone 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℃ for 12-36h.

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

[0027] Preferably, the printing path is modeled using CAD. When the isolation structure is square, the printing path is [0°, 90°], meaning that the second layer and the first layer's walking trajectory intersect at an angle α. The first layer's walking trajectory is 0°, and the second layer's walking trajectory is 90°. Odd-numbered layers are parallel to each other, and even-numbered layers are parallel to each other, while there is an angle α between odd-numbered and even-numbered layers. This process is repeated. When the isolation structure is rhomboid, the printing path is [45°, 135°], meaning that the second layer and the first layer's walking trajectory intersect at an angle α. The first layer's walking trajectory is 45°, and the second layer's walking trajectory is 135°. Odd-numbered layers are parallel to each other, and even-numbered layers are parallel to each other, while there is an angle α between odd-numbered and even-numbered layers. This process is repeated.

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

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The flexible polymer filament with graphene deposited on its surface prepared by the method of the present invention exhibits good bonding between the graphene and the polyurethane filament surface. This not only meets the requirements of 3D printing but also achieves good conductivity even with low conductive filler content. When the graphene content is 1.23 wt%, the graphene / thermoplastic polyurethane composite filament reaches the electroosmotic flow threshold, with a conductivity of 7.83 × 10^ -3 The strain sensor exhibits stable sensing performance (S / m). Furthermore, this invention utilizes 3D printing to fabricate a flexible strain sensor with an isolated structure. On one hand, the geometry and size of the isolated structure can be adjusted by modifying the printing parameters, enabling customization of the strain sensor. On the other hand, compared to traditionally fabricated strain sensors, this isolated structure reduces the electroosmotic flow threshold, ensuring its tensile properties and optimizing 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 and good cycle stability under low electroosmotic threshold. Attached Figure Description

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

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

[0034] Figure 3 This is a SEM image of the cross-sectional internal structure of the 3D-printed flexible strain sensor (0.1 mm thick) with an isolated structure obtained in Example 1.

[0035] Figure 4 Static test curves for a flexible strain sensor in a 3D-printed isolation structure.

[0036] Figure 5 Dynamic test curves for flexible strain sensors in 3D-printed isolation structures. Detailed Implementation

[0037] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without mutual conflict.

[0038] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Contents not described in detail in this specification are prior art known to those skilled in the art. Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0039] Example 1

[0040] (1) Add polyurethane filament to N,N-dimethylformamide DMF, let stand at 25°C for 2 min, and use N,N-dimethylformamide to etch polyurethane filament to obtain etched polyurethane filament with a diameter of 1.65 mm ± 0.05 mm.

[0041] (2) Mix 2.5g graphene, 10g polyurethane particles, 0.1g polyvinylpyrrolidone and 100ml DMF evenly, and use ultrasonic dispersion and mechanical stirring to fully dissolve the polyurethane particles and disperse the graphene evenly to prepare a mixed solution for coating.

[0042] (3) Using the 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 of the mixed solution on the surface of the polyurethane filament. It is then further dried in a vacuum oven at 80°C for 24 hours to remove the solvent, resulting in a flexible polymer filament with graphene deposited on its surface; its optical image is shown below. Figure 1 As shown, the flexible polymer filament with graphene deposited on its surface has a core-sheath structure, with the graphene located in the outermost layer. Figure 2According to TGA testing, the graphene content in the flexible polymer filament with graphene deposited on its surface is 1.23 wt%. This flexible polymer filament with graphene deposited on its surface reaches the electroosmotic flow threshold, with a conductivity of 7.83 × 10^6. -3 S / m;

[0043] (4) 3D printing is performed on a flexible polymer filament with graphene deposited on the surface. The 3D printing path is [0°, 90°], that is, the second layer and the first layer have an intersection angle α. The first layer has a 0° walking path and the second layer has a 90° walking path. Odd layers are parallel to each other and even layers are parallel to each other. There is an angle α between odd and even layers. The printing is repeated in this way. 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 kept at 0.05mm, 0.1mm, 0.2mm and 0.3mm respectively, resulting in four types of 3D printed flexible strain sensors with square isolation structures.

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

[0045] Example 2

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

[0047] Example 3

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

[0049] Example 4

[0050] The difference between this embodiment and embodiment 1 is that the 3D printing path in step (4) is [45°, 135°], that is, the second layer and the first layer have an intersection angle α, the first layer has a 45° walking trajectory, the second layer has a 135° walking trajectory, 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 so on, printing 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 kept at 0.05mm, 0.1mm, 0.2mm, and 0.3mm respectively, to obtain four kinds of 3D printed isolation structure flexible strain sensors.

[0051] In this flexible strain sensor, the distribution of conductive filler is separated by a flexible polymer to form several isolation structures, which are rhomboid in shape.

[0052] Sample Analysis

[0053] The performance of the fabricated 3D-printed flexible strain sensor with an isolation structure was tested; details are shown below:

[0054] Static testing: Slowly varying forces were applied to the flexible strain sensors (graphene addition 3.5 g, layer thickness 0.1 mm) with square and rhomboid isolation structures prepared in the examples, and the resistance changes of the sensors were recorded. The resistance changes were compared with the initial resistance to analyze the sensor's sensitivity, strain, linearity, and other performance characteristics; based on... Figure 4 The test results show that the flexible strain sensor with a rhomboid isolation structure has a wider strain range and still has excellent sensing performance under 40% deformation. The square isolation structure has relatively high sensitivity, with a change of ΔR / R0 of 15 under 1% deformation.

[0055] Dynamic testing: A cyclically varying force was applied to a flexible strain sensor with a rhomboid isolation structure (graphene addition 3.5g, layer thickness 0.1mm) to simulate actual working conditions. The sensor's dynamic response was recorded, and its performance parameters such as response speed, stability, and sensitivity were analyzed. Figure 5 The test results demonstrate that the graphene and polyurethane filament surfaces in the rhombic isolation structure flexible strain sensor have good bonding force, and the strain-induced damage is small at 20% strain. After 100 cycles at 20% strain, the rhombic isolation structure flexible strain sensor exhibits excellent stability.

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

Claims

1. A 3D-printed flexible strain sensor with an isolated structure, characterized in that, It is prepared by 3D printing from flexible polymer filaments with conductive fillers deposited on their surface; In the 3D-printed flexible strain sensor with an isolation structure, conductive filler is constructed to form a conductive network and the distribution of the conductive filler is separated by a flexible polymer to form several isolation structures. The shape of the isolation structure can be controlled by adjusting the 3D printing path. The isolation structure is rhomboid or square. The flexible polymer filament is an etched polyurethane filament; The conductive filler is a carbon nanomaterial.

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

3. The 3D-printed flexible strain sensor with an isolated structure according to claim 1, characterized in that, The flexible polymer filament is a... N,N - Polyurethane filaments etched with dimethylformamide.

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

5. The method for fabricating a 3D-printed flexible strain sensor with an isolated structure according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of etched polyurethane filaments; (2) Prepare a mixed solution containing conductive filler and polyurethane, or prepare a mixed solution containing conductive filler, polyurethane and polyvinylpyrrolidone, and use dip coating to form a uniform coating on the surface of the etched polyurethane filament. After drying, a flexible polymer filament with conductive filler deposited on the surface is obtained. (3) A flexible polymer filament with conductive filler deposited on the surface of a 3D printed structure is obtained by adjusting the 3D printing parameters to control the size and shape of the isolation structure.

6. The method for fabricating a 3D-printed flexible strain sensor with an isolated structure according to claim 5, characterized in that, In step (1), the etching temperature is 20-35℃ and the etching time is 30s-2min.

7. The method for fabricating a 3D-printed flexible strain sensor with an isolated structure 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 fabricating a 3D-printed flexible strain sensor with an isolated structure 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 fabricating a 3D-printed flexible strain sensor with an isolated structure according to claim 8, characterized in that, The mixed solution also includes polyvinylpyrrolidone, and the mass ratio of graphene to polyvinylpyrrolidone is 1:0.01-0.

5.

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

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