Self-curling spiral strain sensor and preparation method thereof

Abstract

The invention belongs to the technical field of three-dimensional micro-nano manufacturing and sensing, and discloses a self-curling spiral strain sensor and a preparation method thereof, and the method comprises the steps: preparing a patterned graphene conductive film in situ on a top-layer high-molecular polymer film of a flexible film substrate through a laser processing mode; cutting the flexible thin film substrate with the graphene conductive thin film into strip-shaped structures; the swelling effect of the bottom-layer high-molecular polymer film of the flexible film substrate is greater than that of the top-layer high-molecular polymer film, so that the strip-shaped flexible film substrate is subjected to swelling deformation in a solvent, and the self-curling spiral strain sensor can be obtained. The preparation of the flexible spiral structure is realized by utilizing a swelling mechanism, the in-situ preparation of the graphene conductive film is realized by adopting a laser-induced graphene processing mode, the preparation of a multi-level spiral functional structure can be realized by adjusting characteristic parameters, and strain sensors with different sensitivities and working ranges are obtained.

Description

Technical Field

[0001] The present invention belongs to the field of three-dimensional micro-nano manufacturing and sensing technology, and specifically relates to a self-curling spiral strain sensor and a preparation method thereof. Background Art

[0002] The principle of resistance change caused by strain-induced length / shape deformation of materials has been widely used in sensor manufacturing. Traditional commercial thin-film resistive strain gauges can amplify resistance changes by sputtering thin metal serpentine lines on polyimide films. However, this strain design has high manufacturing costs and the thin metal lines are prone to failure after repeated bending, making it unsuitable for deformation monitoring of the human body and complex 3D surfaces.

[0003] At present, as an important component of wearable electronic devices, flexible strain sensors have attracted widespread attention due to their good stretchability and broad application prospects in the fields of electronic skin, medical monitoring, human-computer interaction, artificial intelligence, etc. Among them, high sensitivity and wide working range are the key parameters of high-quality strain sensors, but due to structural and conductivity limitations, it is difficult to achieve these two characteristics on the same sensor at the same time.

[0004] Self-curling technology is a three-dimensional micro-nano self-assembly technology that uses internal gradient stress or external force to drive a two-dimensional film into a three-dimensional configuration. It has become a hot spot in the current frontier research of science and technology because of its compatibility with typical planar micro-nano manufacturing processes, the ability to realize multi-level three-dimensional micro-nano structure manufacturing, and the ability to selectively carry or integrate multiple functional materials. Developing a new self-curling forming manufacturing process with simple process, low cost, and high safety can overcome the problems and shortcomings of the existing technology, such as complex process, high price, and low safety, and realize the preparation of three-dimensional spiral functional structures, which can provide a new preparation process and new device structure for flexible strain sensors, and further obtain high sensitivity and a wide working range. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a self-curling spiral strain sensor and a preparation method thereof, through which a strain sensor with high sensitivity and a wide working range can be obtained.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a self-curling spiral strain sensor comprises the following steps: Prepare a flexible film substrate, wherein the flexible film substrate comprises a top polymer film and a bottom polymer film, wherein the swelling effect of the bottom polymer film is greater than that of the top polymer film; A patterned graphene conductive film is in-situ prepared on the top polymer film by laser processing to obtain a flexible film substrate with the graphene conductive film; Cutting the flexible film substrate with the graphene conductive film into strip structures to obtain a strip-shaped flexible film substrate; The strip-shaped flexible film substrate is swelled and deformed in a solvent to obtain the self-curling spiral strain sensor.

[0007] Preferably, the top polymer film is a polyimide film.

[0008] Preferably, the preparation process of the polyimide film includes: The polyimide precursor liquid is spin-coated on the front side of the silicon wafer, and a thermal imidization and stripping process is performed by a gradient heating method to obtain a polyimide film.

[0009] Preferably, the bottom polymer film is a polyvinyl chloride / acrylic adhesive composite film.

[0010] Preferably, the polyimide film is arranged on the surface of the polyvinyl chloride layer in the polyvinyl chloride / acrylic adhesive composite film.

[0011] Preferably, the polyimide film and the polyvinyl chloride / acrylic adhesive composite film are hot-pressed to form the flexible film substrate.

[0012] Preferably, the solvent is acetone.

[0013] Preferably, the strip-shaped flexible film substrate is in the shape of a parallelogram with an internal angle not equal to 90°.

[0014] Preferably, the strip-shaped flexible film substrate contains a complete patterned graphene conductive film unit.

[0015] The present invention also provides a self-curling spiral strain sensor, which is prepared by the preparation method of the present invention as described above.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: In the preparation method of the self-curling spiral strain sensor of the present invention, since the swelling effect of the bottom polymer film is greater than the swelling effect of the top polymer film, after the strip flexible film substrate is placed in the solvent, the bottom polymer film will cause the plane strip flexible film substrate to swell unevenly and generate internal stress under the action of the solvent, thereby inducing the strip flexible film substrate to deform unevenly, and finally obtain a self-curling spiral strain sensor. Since the stress sensor of the present invention is spiral, it has good deformation ability, is suitable for deformation monitoring of the human body and complex 3D surfaces, and has higher conformity with the corresponding surface. In the present invention, the patterned graphene conductive film is prepared in situ by laser processing, so the graphene conductive film is a component of the strain sensor itself, and its coordinated deformation ability with other parts of the flexible film substrate is better, it is not easy to deform and fail, and the conductivity is high, so the sensitivity of the self-curling spiral strain sensor of the present invention is high. Due to the characteristics of the above-mentioned preparation method of the present invention, the preparation of multi-level spiral functional structures can be realized, and then strain sensors with different sensitivities and working ranges can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the preparation process of the self-curling spiral strain sensor in an embodiment of the present invention; Figure 2 The schematic diagram of the self-curling spiral strain sensor of the present invention is formed; In the figure: 1-Polyimide film, a polymer film without swelling effect on the top layer; 2-Polyvinyl chloride / acrylic composite film, a polymer film with swelling effect on the bottom layer; 3-Laser-induced graphene conductive film; 4-Laser, θ is the inner angle of the flexible film substrate ( θ ≠90 o ), F is the internal stress induced by swelling. DETAILED DESCRIPTION

[0018] Hereinafter, the specific embodiments of the present application will be described in detail with reference to the accompanying drawings. According to these detailed descriptions, those skilled in the art can clearly understand the present application and can implement the present application. Without violating the principles of the present application, the features in the various embodiments can be combined to obtain new implementations, or certain features in certain embodiments can be replaced to obtain other preferred implementations.

[0019] The main ideas and principles used in the technical solution of the present invention are as follows: Swelling is a phenomenon in which the volume of a polymer expands in a solvent, which is caused by the diffusion of the solution molecules inside. Under the action of the solvent, the asymmetry of the microstructure of the polymer film will cause uneven swelling, and internal stress will be generated inside, thereby inducing bending or twisting deformation, etc. In addition, in order to prepare graphene electrodes, the present invention adopts a laser processing method, so that a patterned graphene conductive film can be prepared in situ.

[0020] For details, see Figure 1 The method for preparing the self-curling spiral strain sensor of the present invention comprises the following steps: Prepare a flexible film substrate, wherein the flexible film substrate comprises a top polymer film and a bottom polymer film, wherein the swelling effect of the bottom polymer film is greater than that of the top polymer film; A patterned graphene conductive film is in-situ prepared on the top polymer film by laser processing to obtain a flexible film substrate with the graphene conductive film; Cutting the flexible film substrate with the graphene conductive film into strip structures to obtain a strip-shaped flexible film substrate; The strip-shaped flexible film substrate is swelled and deformed in a solvent. Since the swelling effect of the bottom polymer film is greater than that of the top polymer film, during the swelling and deformation, the strip-shaped flexible film substrate will swell and deform with the top polymer film as the inner surface and the bottom polymer film as the outer surface, thereby obtaining the self-curling spiral strain sensor.

[0021] In the above scheme of the present invention, the top polymer film can also be a polymer film without swelling effect, and the bottom polymer film can be a polymer film with swelling effect. In this case, the swelling effect of the bottom polymer film is greater than that of the top polymer film.

[0022] In the above scheme of the present invention, by controlling the aspect ratio, inner angle of the strip flexible film substrate, the material and thickness of the top polymer film and the bottom polymer film, and the type of solvent and conducting multiple groups of experiments, a self-curling spiral strain sensor with a preset shape can be obtained.

[0023] The present invention further illustrates the above scheme by taking the top polymer film using a polyimide film and the bottom polymer film using a polyvinyl chloride / acrylic adhesive composite film as an example.

[0024] The self-curling spiral strain sensor of this embodiment mainly includes a double-layer flexible film substrate for achieving self-curling and a laser-induced graphene conductive film.

[0025] Specifically, the flexible film substrate for achieving self-curling comprises a top polymer film polyimide film 1 having no swelling effect and a bottom polymer film polyvinyl chloride / acrylic adhesive composite film 2 having swelling effect, and the top polymer film polyimide film 1 having no swelling effect and the bottom polymer film polyvinyl chloride / acrylic adhesive composite film 2 having swelling effect are integrated and manufactured by hot pressing to obtain a flexible film substrate. Under the action of the solvent acetone, the bottom polymer film polyvinyl chloride / acrylic adhesive composite film 2 having swelling effect can swell, and internal stress is generated inside the bottom polymer film polyvinyl chloride / acrylic adhesive composite film 2 having swelling effect. By adjusting the internal angle of the strip-shaped flexible film substrate, the flexible film substrate can be induced to self-curl and deform into a spiral structure. Among them, laser-induced graphene conductive film is produced by utilizing laser processing, wherein laser is irradiated on the polyimide film on the flexible film substrate, and the production is induced under certain processing power and scanning rate. The in-situ preparation of patterned graphene conductive film by laser-induced polyimide film is a mature technology and is not specifically limited in the present invention.

[0026] It can be seen from the above scheme that the present invention utilizes the swelling mechanism to realize the preparation of a flexible spiral structure, with a simple process and low cost; the laser-induced graphene processing method is used to realize the in-situ preparation of a graphene conductive film, with a simple manufacturing process and large-area manufacturing; by adjusting the characteristic parameters, the preparation of a multi-level spiral functional structure can be realized, and strain sensors with different sensitivities and working ranges can be obtained.

[0027] Exemplarily, the method for preparing the self-curling spiral strain sensor of the above embodiment comprises the following steps: Step 1, preparing a polyimide film by spin coating: spin coating a polyimide precursor solution on the front side of a silicon wafer, performing thermal imidization and stripping processes by a gradient heating method, and obtaining a polyimide film having a thickness of 30 μm; Step 2: hot pressing the polyimide film obtained in step 1 and a commercial polyvinyl chloride / acrylic adhesive composite film (thickness of 100 microns) to form a polyimide film on the top layer and the polyvinyl chloride / acrylic adhesive composite film on the bottom layer; the polyimide film is arranged on the surface of the polyvinyl chloride layer in the polyvinyl chloride / acrylic adhesive composite film; Step 3: Prepare graphene conductive film by laser processing: Set laser processing parameters (including power and scanning rate), where the power is set to 4.5 W and the rate is 10 cm s -1, applying laser to the surface of the top polyimide film in step 2 to achieve in-situ preparation of graphene, and forming a patterned graphene conductive film on the top polyimide film; Step 4: Cut the flexible film substrate with the laser-induced graphene conductive film in step 3 into long strips, and then place it in an acetone solvent. The long strip flexible film substrate swells and deforms under the induction of acetone to form a self-curling spiral strain sensor.

[0028] The shape of the long strip of flexible film substrate is specifically the inner angle θ ≠90 o The parallelogram can realize the processing of strain sensors with different characteristic sizes by adjusting the main body size (such as thickness and aspect ratio) of the long flexible film substrate.

[0029] In this embodiment, the flexible film substrate after hot pressing is subjected to the action of the solvent acetone, when the internal stress F in the bottom polymer film polyvinyl chloride / acrylic adhesive composite film 2 with swelling effect is large enough, such as Figure 2 As shown, when the internal angle of the plane film θ ≠90 o When released, the flexible film curls and deforms into a spiral structure, thus realizing the preparation of a spiral strain sensor.

[0030] In this embodiment, when the interior angle θ =30°, the main technical indicators that the self-curling spiral strain sensor can achieve are as follows: Piezoresistive strain sensing: Sensitivity factor 100, measurement range 150% It can be seen from the above scheme that the technical solution of the present invention has the following characteristics: ① The three-dimensional spiral configuration is prepared based on the swelling mechanism, which abandons the preparation and selective etching process of the etching layer in the existing self-curling process, simplifies the preparation process, improves operational safety, and can further reduce processing costs.

[0031] ② Laser processing is used to in-situ induce a graphene conductive film on the top layer of the substrate. The production process is simple and can be manufactured on a large scale.

[0032] ③The preparation of multi-level spiral functional structures was realized, and strain sensors with different sensitivities and working ranges were obtained.

[0033] The realization of the above new ideas and methods can provide new preparation processes and new device structures for flexible strain sensors, further obtain high sensitivity and wide working range, and have broad application prospects in the development of flexible electronic devices and the construction of on-chip laboratories.

[0034] The above is only one embodiment of the present invention, not all or the only embodiment. Any equivalent changes made by ordinary technicians in this field in the face of the technical solution of the present invention after reading the specification of the present invention are covered by the claims of the present invention.

Claims

1. A method for preparing a self-curling spiral strain sensor, characterized in that: The process includes the following: Prepare a flexible film substrate, wherein the flexible film substrate comprises a top polymer film and a bottom polymer film, wherein the swelling effect of the bottom polymer film is greater than that of the top polymer film; A patterned graphene conductive film is in-situ prepared on the top polymer film by laser processing to obtain a flexible film substrate with the graphene conductive film; Cutting the flexible film substrate with the graphene conductive film into strip structures to obtain a strip-shaped flexible film substrate; The strip-shaped flexible film substrate is swelled and deformed in a solvent to obtain the self-curling spiral strain sensor.

2. The method for preparing a self-curling spiral strain sensor according to claim 1, characterized in that: The top polymer film is a polyimide film.

3. The method for preparing a self-curling spiral strain sensor according to claim 2, characterized in that: The preparation process of the polyimide film comprises: The polyimide precursor liquid is spin-coated on the front side of the silicon wafer, and a thermal imidization and stripping process is performed by a gradient heating method to obtain a polyimide film.

4. The method for preparing a self-curling spiral strain sensor according to claim 2, characterized in that: The bottom polymer film is a polyvinyl chloride / acrylic adhesive composite film.

5. The method for preparing a self-curling spiral strain sensor according to claim 4, characterized in that: The polyimide film is arranged on the surface of the polyvinyl chloride layer in the polyvinyl chloride / acrylic adhesive composite film.

6. The method for preparing a self-curling spiral strain sensor according to claim 4, characterized in that: The polyimide film and the polyvinyl chloride / acrylic adhesive composite film are hot-pressed to form the flexible film substrate.

7. The method for preparing a self-curling spiral strain sensor according to claim 4, characterized in that: The solvent used is acetone.

8. The method for preparing a self-curling spiral strain sensor according to claim 1, characterized in that: The strip-shaped flexible film substrate is in the shape of a parallelogram with an internal angle not equal to 90°.

9. The method for preparing a self-winding spiral strain sensor according to claim 1, characterized in that: The strip-shaped flexible film substrate contains complete patterned graphene conductive film units.

10. A self-curling spiral strain sensor, characterized in that: The self-curling spiral strain sensor is manufactured by the method for preparing a self-curling spiral strain sensor according to any one of claims 1 to 9.

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