A flexible strain sensor and its preparation method

Abstract

The present invention provides a flexible strain sensor and its preparation method. The sensor comprises a polymer substrate composed of a P(MEA-co-BA) copolymer, with an AgNW network embedded on the surface. A parallel conductive pattern is formed by pre-stretching and dispensing printing technology, and a chemical reduction gold plating layer is covered to improve stability. The preparation method includes preparing the polymer substrate, pre-stretching, dispensing printing of the conductive pattern, chemical reduction gold plating, and connecting the gold-plated PI film for conductivity. This design effectively solves the reliability and controllability issues of traditional crack-type strain sensors, achieving sensing performance with high sensitivity, a wide strain range, and excellent stability, and is suitable for multiple fields such as human-computer interaction.

Description

Technical Field

[0001] The present invention relates to a flexible sensor, and in particular to a flexible strain sensor and a preparation method thereof. Background Art

[0002] Flexible strain sensors, based on flexible polymers, are stretchable and bendable, allowing them to conform to human skin. They are widely used in various human-computer interaction applications, such as virtual reality (VR), sign language recognition, robotic control, and rehabilitation equipment. Accurately capturing and quantifying subtle deformation signals from the human body surface presents numerous performance challenges for flexible strain sensors, including sensitivity, detection limit, stability, and repeatability. These challenges require ensuring accurate and precise measurement of minute strains at the wearer's location. Highly sensitive and robust flexible strain sensors hold significant market value and research significance in diverse fields, including daily life, healthcare, and industrial production.

[0003] Currently, the mainstream design for highly sensitive strain sensing is a resistive strain sensor based on a crack sensing mechanism. Its structure generally consists of two parts: a stretchable, bendable, flexible polymer substrate that serves as a support, possessing sufficient mechanical strength and flexibility to meet basic wearable requirements; and a conductive material film layer that performs a sensing function, which feeds back changes in strain as changes in the layer's resistance, thereby achieving strain sensing. Crack-type strain sensors introduce micro- / nanocracks into the conductive active layer by bending and stretching the flexible polymer matrix. When the device is strained, these micro- / nanochannel cracks result in a steep resistance response, quantifying the strain as a resistance change to establish a correspondence between mechanical and electrical quantities, thus achieving highly sensitive strain sensing.

[0004] Although the sensitivity of crack-type strain sensors has been significantly improved, they face the problems of crack recoverability and poor reliability. Since the crack formation process is random and uncontrollable, the consistency and repeatability of the preparation process are difficult to guarantee, which poses a challenge to the reliability in long-term use environments. New structural designs are needed to balance the electrical sensitivity and mechanical durability of flexible strain sensors.

[0005] It should be noted that the information disclosed in the above background technology section is only used to understand the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0006] The main purpose of the present invention is to overcome the defects existing in the above-mentioned background technology and provide a flexible strain sensor and a preparation method thereof.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A flexible strain sensor, comprising:

[0009] A polymer substrate, wherein the polymer substrate is composed of a copolymer of 2-methoxyethyl 2-acrylate (MEA) and 2-butyl acrylate (BA), P(MEA-co-BA), and a silver nanowire (AgNWs) network is embedded on the surface;

[0010] A conductive pattern, wherein the conductive pattern is printed on a pre-stretched polymer substrate by dispensing to form a parallel pattern structure;

[0011] a chemical reduction gold plating layer covering the conductive pattern to improve contact resistance and enhance sensor stability;

[0012] A gold-plated polyimide (PI) film is connected to the conductive pattern as a conductor for transmitting electrical signals.

[0013] Further:

[0014] After pre-stretching and retraction, the spacing between adjacent printed patterns is no more than 20 μm, the length of the parallel lines is 1-3 mm, and the number of parallel lines is 25-60.

[0015] A method for preparing a flexible strain sensor comprises the following steps:

[0016] S1, preparing a polymer substrate composed of a copolymer of 2-methoxyethyl acrylate (MEA) and 2-butyl acrylate (BA), P(MEA-co-BA), and embedding a silver nanowire (AgNWs) network on the surface;

[0017] S2. pre-stretching the polymer substrate to a predetermined extent and fixing it;

[0018] S3, printing a conductive pattern on a pre-stretched polymer substrate by dispensing to form a parallel patterned structure;

[0019] S4, performing chemical reduction gold plating on the conductive pattern to improve contact resistance and enhance sensor stability;

[0020] S5. Connect the conductive pattern to the gold-plated polyimide (PI) film to form a conductive connection for transmitting electrical signals.

[0021] Furthermore, step S1 includes preparing a glass interlayer coated with silver nanowires (AgNWs), specifically comprising:

[0022] Add silver nanowire (AgNWs) ethanol dispersion dropwise onto a glass slide and evenly soak the entire surface of the slide; place the treated slide on a horizontal heating plate and heat dry for later use;

[0023] Another glass slide was placed in an oxygen plasma cleaning machine to treat the surface, and then a dextran (molecular weight 40,000) aqueous solution was spin-coated and heated to evaporate the residual water to form a water-soluble sacrificial layer.

[0024] Furthermore, in step S1, the preparation of the polymer substrate specifically includes:

[0025] 2-Methoxyethyl acrylate (MEA) and 2-butyl acrylate (BA) were mixed at a molar ratio of 1:1;

[0026] Add 0.1% polyethylene glycol diacrylate (PEGDA) relative to the total molar amount of MEA and BA;

[0027] 1% of 1-hydroxycyclohexylphenyl ketone (photoinitiator 184) was added relative to the total molar amount of MEA and BA;

[0028] 0.1–2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added as an ionic liquid to enhance the conductivity of the polymer;

[0029] The resulting mixture was injected into a glass slide sandwich coated with an AgNWs layer and photopolymerized by ultraviolet light.

[0030] Furthermore, in step S2 , the polymer substrate is pre-stretched to a length of 140%-200%.

[0031] Furthermore, in step S3, the conductive ink used for dispensing printing includes the following components: hydroxyl-terminated polydimethylsiloxane PDMS-OH; octamethylcyclotetrasiloxane D4; crosslinking agent 3-(2,3-epoxypropyloxy)propyltrimethoxysilane (GPTMS); silver flake powder; and dibutyltin dilaurate (DBTDL) as a catalyst.

[0032] Furthermore, in step S3, the length of the parallel lines printed by the dispensing glue is 1-3 mm, the horizontal arrangement period is 0.85 mm, the number of parallel lines is 25-60, the dispensing glue printing height is 0.2-0.4 mm, and the printing speed is 20-30 mm / min to ensure that adjacent patterns can contact after pre-stretching and release, and are heated at 70°C for more than 30 minutes after printing to cure; the spacing between adjacent printed patterns after pre-stretching and retraction is not greater than 20 μm.

[0033] Furthermore, in step S4, the gold plating solution used in the chemical reduction gold plating contains HAuCl4, Na2S2O3 and Na2SO3.

[0034] Furthermore, in step S4, the sample is immersed in the solution and reacted at 70° C. for 2 hours.

[0035] The present invention has the following beneficial effects:

[0036] The present invention proposes a flexible strain sensor and a preparation method thereof. A pattern-type strain sensor is constructed based on a pre-stretching-dispensing printed conductive pattern, and highly sensitive strain sensing is achieved by utilizing the contact and separation of the conductive path during stretching and retraction. This sensing mechanism does not involve the destruction and reconstruction of the conductive path, and can effectively solve the problem of poor reliability of crack-type strain sensing. It has demonstrated stable and reliable sensing performance in cyclic tests.

[0037] In order to solve the problems of insufficient controllability and poor sensing stability in the preparation of crack-type flexible strain sensors, the preparation method of the present invention prepares a pattern-type flexible strain sensor by pre-stretching and dispensing a conductive pattern. A parallel conductive pattern similar to micro / nanocracks is printed on a pre-stretched polymer substrate, effectively converting uncontrollable micro / nanocracks into gaps between adjacent conductive paths. The contact and separation of the conductive paths during stretching and retraction are used to achieve highly sensitive strain sensing. This sensing mechanism does not involve the random generation of cracks and the unstable recovery of the conductive path, and can effectively solve the problems of poor reliability and uncontrollable preparation of crack-type strain sensors.

[0038] The present invention prints parallel conductive patterns on a pre-stretched polymer substrate by dispensing glue, and obtains a patterned flexible strain sensor after release. The prepared strain sensor has excellent sensing performance with high sensitivity, wide strain range and excellent stability.

[0039] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Flowchart of a method for preparing a flexible strain sensor according to an embodiment of the present invention.

[0041] Figure 2 This is a schematic structural diagram of a polymer film with an AgNWs network embedded on its surface prepared by a sandwich method according to an embodiment of the present invention.

[0042] Figure 3 This is a sample image after pre-stretching, fixed, and glue-dispensing printing according to an embodiment of the present invention.

[0043] Figure 4 This is a sample image stored on release paper after chemical reduction gold plating according to an embodiment of the present invention.

[0044] Figure 5 This is a microscopic morphology diagram of the flexible strain sensor according to an embodiment of the present invention.

[0045] Figure 6 Graph showing the strain response curve and cyclic stability test data of the flexible strain sensor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope of the present invention and its application.

[0047] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for both fixing and coupling or communication.

[0048] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0049] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0050] See Figures 1 to 5 An embodiment of the present invention provides a flexible strain sensor, comprising: a polymer substrate 1, the polymer substrate 1 being composed of a copolymer P(MEA-co-BA) of 2-methoxyethyl acrylate (MEA) and 2-butyl acrylate (BA), and having a silver nanowire (AgNWs) network embedded on its surface; a conductive pattern 2, the conductive pattern 2 being printed on the pre-stretched polymer substrate 1 by dispensing to form a parallel pattern structure; a chemical reduction gold-plated layer 3 covering the conductive pattern 2 to improve contact resistance and enhance sensor stability; and a gold-plated polyimide (PI) film 4, connected to the conductive pattern 2 as a wire for transmitting electrical signals.

[0051] In a preferred embodiment, after pre-stretching and retraction, the spacing between adjacent printed patterns is no more than 20 μm, the length of the parallel lines is 1-3 mm, and the number of parallel lines is 25-60.

[0052] See Figures 1 to 5 The present invention also provides a method for preparing a flexible strain sensor, comprising the following steps:

[0053] Step S1, preparing a polymer substrate 1, which is composed of a copolymer P(MEA-co-BA) of 2-methoxyethyl acrylate (MEA) and 2-butyl acrylate (BA), and embedding a silver nanowire (AgNWs) network on the surface;

[0054] Step S2: pre-stretching the polymer substrate 1 to a predetermined extent and fixing it;

[0055] Step S3: printing the conductive pattern 2 on the pre-stretched polymer substrate 1 by dispensing to form a parallel pattern structure;

[0056] Step S4: performing chemical reduction gold plating on the conductive pattern 2 to improve contact resistance and enhance sensor stability;

[0057] Step S5: Connect the conductive pattern to the gold-plated polyimide (PI) film 4 to form a conductive connection for transmitting electrical signals.

[0058] The present invention provides a flexible strain sensor with high sensitivity, high stability and strong controllability and a preparation method thereof. The sensor uses P(MEA-co-BA) copolymer as the base material, and a silver nanowire network is embedded on the surface. A parallel conductive pattern is formed by pre-stretching and dispensing printing technology, which is effectively converted into a controllable pattern path, replacing the uncontrollable crack-type path in the traditional crack-type strain sensor. This design not only improves the controllability and consistency of the sensor preparation, but also improves the contact resistance and enhances the stability of the sensor through chemical reduction gold plating technology. In addition, while maintaining high sensitivity, the sensor of the present invention also achieves sensing over a wide strain range, breaking through the limitation that the conductive circuit of the traditional crack-type sensor is easily destroyed within a small strain range, thereby showing stable and reliable sensing performance in the cycle test, meeting the needs of multiple fields such as daily life, medical health, and industrial production for highly sensitive and robust flexible strain sensors.

[0059] Specific embodiments of the present invention are further described below.

[0060] In an embodiment of the present invention, a patterned flexible strain sensor is obtained by dispensing and printing a parallel conductive pattern on a pre-stretched polymer substrate. The preparation process of the flexible strain sensor includes several important steps, such as transferring the AgNWs layer, pre-stretching fixation and dispensing printing, and chemical reduction gold plating. The prepared strain sensor has excellent sensing performance with high sensitivity, wide strain range and excellent stability.

[0061] The process of preparing flexible strain sensor is as follows Figure 1 The specific steps are as follows:

[0062] ① Drop coating of AgNWs layer on glass substrate

[0063] A glass slide was used as the glass substrate. The slide was first placed in an oxygen plasma cleaner for about 3 minutes, and then 1 ml of 5 mg / ml silver nanowire (AgNWs) ethanol dispersion was added to each slide to evenly soak the entire surface of the slide. The slide was then placed on a horizontal heating plate and heated at 60°C for drying.

[0064] ②Polymer transfer AgNWs layer

[0065] The AgNWs layer on the glass slide was transferred to the polymer surface by sandwich photopolymerization, e.g. Figure 2 As shown, one of the two glass slides used as the interlayer is obtained from step ①. The other slide is coated with a water-soluble sacrificial layer to facilitate subsequent peeling. After the slide is placed in an oxygen plasma cleaner for approximately 3 minutes, an approximately 8% aqueous solution of dextran (molecular weight 40,000) is spin-coated at 500 rpm for 5 seconds, then accelerated to 1500 rpm for 20 seconds. Residual moisture is evaporated by heating. Polymer monomer is injected into the interlayer between the two parallel glass slides using a syringe and photopolymerization is initiated. The thickness of the interlayer is determined by the thickness of the 3M double-sided tape. Considering the mechanical strength requirements of the polymer, the thickness should not be less than 0.25 mm.

[0066] The polymer used was a copolymer of 2-methoxyethyl acrylate (MEA) and 2-butyl acrylate (BA), P(MEA-co-BA). The adhesiveness and tensile resilience of the flexible polymer substrate were utilized for subsequent pre-stretching and dispensing printing. MEA and BA were mixed at a molar ratio of 1:1, and 0.1% of polyethylene glycol diacrylate (PEGDA, average molecular weight 400) and 1% of 1-hydroxycyclohexylphenyl ketone (photoinitiator 184) were added relative to the total molar amount. 0.1-2M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was also added and dissolved. After mixing, the mixture was injected into a glass slide interlayer and exposed to UV light for 1 hour. After removal, the edges were pried open underwater to dissolve the dextran to achieve peeling, resulting in a P(MEA-co-BA) polymer film with an embedded AgNWs network on the surface. LiTFSI is added as an ionic liquid, so that the obtained P(MEA-co-BA) polymer acts as an ionic conductor and still has conductivity under large strain conditions.

[0067] ③Pre-stretching and fixing of polymer substrate

[0068] Use scissors to cut off the 3M double-sided tape around the P(MEA-co-BA) polymer film, as well as the part of the film near the injection port where polymerization was incomplete due to monomer evaporation. After the P(MEA-co-BA) polymer film with AgNWs embedded on its surface was stretched horizontally to 140%-200% of its length, the back side of the P(MEA-co-BA) (the side without AgNWs) was fixed to a glass slide using the adhesive properties of the polymer film itself. A water-soluble sacrificial layer was attached to the surface of the glass slide as described in step ② to facilitate subsequent separation.

[0069] ④Glue printing

[0070] The electrode pattern was printed using a high-viscosity dispensing printer. The printing ink was the PDMS-OH / Ag conductive ink configured in this scheme. This is because the commercial conductive silver paste has poor bonding strength with the polymer film, which causes the conductive pattern to separate from the polymer and fall off when the polymer substrate is released from the pre-stretched state to its original length. The conductive ink was prepared as follows: 0.3g of hydroxyl-terminated polydimethylsiloxane PDMS-OH (average molecular weight 110,000), 0.7ml of octamethylcyclotetrasiloxane D4, and 19μl of the crosslinker 3-(2,3-epoxypropyloxy)propyltrimethoxysilane (GPTMS) were mixed evenly under magnetic stirring. 3.9g of silver microflake powder with an average particle size of 2μm was added and magnetic stirring was performed for 24h to mix evenly. Finally, 1μl of dibutyltin dilaurate (DBTDL) was added as a catalyst. After mixing for 3 minutes, the mixture was poured into a dispensing tube as PDMS-OH / Ag conductive ink for printing. The designed parallel pattern was printed on the pre-stretched P(MEA-co-BA) substrate using a high-viscosity dispensing printer V-One. The dispensing needle was 27G (inner diameter 0.21mm, outer diameter 0.4mm), the parallel line length was 1-3mm, the horizontal arrangement period was 0.85mm, the number of parallel lines was 25-60, the dispensing print height was 0.2-0.4mm, and the printing speed was 20-30mm / min. It can be adjusted according to the final use requirements of the strain sensor. The thickness of the dispensing tip needs to match the parameters such as the printing cycle. The interval between adjacent patterns should be minimized as much as possible to ensure that adjacent patterns can contact after the pre-stretching is released. After printing, it was heated at 70℃ for more than 30 minutes to cure. The obtained sample is as follows Figure 3 shown.

[0071] ⑤Chemical reduction gold plating

[0072] The printed sample is separated from the glass slide by dissolving the sacrificial layer underwater. After separation, the redundant part without printed pattern is cut off and immersed in gold plating solution for displacement gold plating to improve the contact resistance of adjacent patterns after retraction and improve the stability of the strain sensor. The gold plating solution is an aqueous solution containing 1mM HAuCl4, 8.4mM Na2S2O3 and 8.4mM Na2SO3. After dissolving Na2S2O3 and Na2SO3 in water, high concentration of HAuCl4 is added while stirring. After preparation, the sample is immersed in the solution at 70℃ for 2h, taken out and rinsed with plenty of water. Since the polymer substrate of the sensor has pressure-sensitive adhesive properties, its adhesive properties help it adhere to the skin. It is stored on release paper for easy access. Figure 4 shown.

[0073] ⑥Packaging molding

[0074] The commercial gold-plated polyimide (PI) film cut out was attached to both sides of the printed pattern as a conductor to obtain the final flexible strain sensor. Its microscopic morphology is as follows: Figure 5 As shown, after pre-stretching and retraction, the distance between adjacent printed patterns is less than 20 μm. Due to the dense AgNWs network on the surface of the P(MEA-co-BA) polymer film, the retracted printed pattern can achieve stable electrical contact. From the enlarged SEM image, it can be seen that there is silver microflake powder added to the printing ink on the pattern surface, and the gaps between adjacent patterns can be seen with embedded AgNWs network on the bottom surface of the P(MEA-co-BA) film.

[0075] The sensing performance of strain sensors is as follows Figure 6 As shown in the figure, it includes strain response curve and cyclic stability test, where GF = (ΔR / R0) / ε, which is the relative change ΔR of sensor resistance, divided by the initial resistance R0 when the strain is zero, and then divided by the strain ε, corresponding to the slope value in the response curve, characterizes the sensitivity of the sensor. It can be seen that the strain sensor has very high sensitivity in a small strain range, and at the same time, it shows excellent electrical / mechanical stability in 2500 stretch-recovery cycle tests.

[0076] In summary, the present invention provides a flexible strain sensor and a method for manufacturing the same. Compared with conventional technologies, the main advantages of the flexible strain sensor of the present invention are:

[0077] ① Controllable preparation. Compared to traditional crack-type strain sensors, which have a random and uncontrollable crack formation process, ensuring consistency and repeatability in the preparation process is difficult. This experimental scheme, based on a pre-stretching-dispensing printing method, transforms the uncontrollable crack-type path in the strain sensing mechanism into a controllable patterned path. During the preparation process, the pre-stretching ratio of the polymer substrate and the length, interval, period, and range of the dispensing printing pattern can be adjusted, making the strain sensor preparation process highly controllable.

[0078] Secondly, the stability of sensing performance. Although crack-type strain sensors offer significant improvements in sensitivity, they can generate new cracks during the stretching and retraction process. Furthermore, the retraction and contact of micro- and nanocracks during stretch recovery are uncontrollable, resulting in unstable sensing performance. The initial resistance of the device often drifts upward with increasing stretching cycles. This experimental scheme transforms crack generation and recovery into the contact and separation of adjacent printed patterns, and additionally introduces a chemical reduction gold plating method to improve the contact resistance of adjacent patterns. Because crack generation and recovery are not involved, the stability of sensing performance is improved.

[0079] ③ Balancing the sensing range and sensitivity. To improve sensor sensitivity, crack-type strain sensors are often designed to completely destroy the conductive circuit within a relatively small strain range, thereby increasing the generation of micro- / nanocracks and sensitivity. This limits their sensing range. This experimental scheme, based on a retracted pattern fabricated by pre-stretching and dispensing printing, a surface-embedded AgNW network, and an underlying ionic conductor P(MEA-co-BA), further expands the sensing range while maintaining sensor sensitivity.

[0080] The above description further details the present invention in conjunction with specific / preferred embodiments, and the specific implementation of the present invention should not be construed as being limited to these descriptions. Persons skilled in the art will appreciate that, without departing from the spirit of the present invention, they may make various substitutions or modifications to the described embodiments, and these substitutions or modifications should be considered to fall within the scope of protection of the present invention. Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "preferred embodiments," "examples," "specific examples," or "some examples" indicates that the specific features, structures, materials, or characteristics described in conjunction with such embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Persons skilled in the art may combine and assemble the different embodiments or examples described in this specification, as well as features of different embodiments or examples, without conflicting opinions. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications may be made herein without departing from the scope of protection of the patent application.

Claims

1. A flexible strain sensor, characterized in that: include: A polymer substrate, wherein the polymer substrate is composed of a copolymer P(MEA-co-BA) of 2-methoxyethyl acrylate MEA and 2-butyl acrylate BA, and a silver nanowire AgNWs network is embedded on the surface; A conductive pattern is printed on a pre-stretched polymer substrate by dispensing conductive ink to form a parallel pattern structure; the conductive ink comprises the following components: hydroxyl-terminated polydimethylsiloxane (PDMS-OH); octamethylcyclotetrasiloxane (D4); a crosslinker (3-(2,3-epoxypropyloxy)propyltrimethoxysilane (GPTMS); silver flake powder; and dibutyltin dilaurate (DBTDL) as a catalyst. a chemical reduction gold plating layer covering the conductive pattern to improve contact resistance and enhance sensor stability; The gold-plated polyimide PI film is connected to the conductive pattern as a conductor for transmitting electrical signals.

2. The flexible strain sensor according to claim 1, wherein: After pre-stretching and retraction, the spacing between adjacent printed patterns is no more than 20 μm, the length of parallel lines is 1–3 mm, and the number of parallel lines is 25–60.

3. A method for preparing a flexible strain sensor, characterized in that: The following steps are involved: S1, prepare a polymer substrate composed of a copolymer of 2-methoxyethyl acrylate MEA and 2-butyl acrylate BA (P(MEA-co-BA)), and embed a silver nanowire AgNWs network on the surface; S2. pre-stretching the polymer substrate to a predetermined extent and fixing it; S3. A conductive pattern is printed on a pre-stretched polymer substrate by dispensing to form a parallel patterned structure. The conductive ink used for dispensing includes the following components: hydroxyl-terminated polydimethylsiloxane (PDMS-OH); octamethylcyclotetrasiloxane (D4); a crosslinker (3-(2,3-epoxypropyloxy)propyltrimethoxysilane (GPTMS); silver flake powder; and dibutyltin dilaurate (DBTDL) as a catalyst. S4, performing chemical reduction gold plating on the conductive pattern to improve contact resistance and enhance sensor stability; S5. Connect the conductive pattern to the gold-plated polyimide PI film to form a conductive connection for transmitting electrical signals.

4. The method for preparing a flexible strain sensor according to claim 3, wherein: Step S1 includes preparing a glass interlayer coated with silver nanowires AgNWs, specifically comprising: Add silver nanowires (AgNWs) ethanol dispersion dropwise onto a glass slide and evenly wet the entire surface of the slide. Place the treated slide on a horizontal heating plate and heat dry for later use. After the surface of another glass slide was treated in an oxygen plasma cleaner, a dextran aqueous solution was spin-coated and the residual water was evaporated by heating to form a water-soluble sacrificial layer.

5. The method for preparing a flexible strain sensor according to claim 4, wherein: The molecular weight of the dextran is 40,000.

6. The method for preparing a flexible strain sensor according to claim 3 or 4, wherein: In step S1, the preparation of the polymer substrate specifically includes: 2-Methoxyethyl 2-acrylate MEA and 2-butyl 2-acrylate BA were mixed in a molar ratio of 1:1; Add 0.1% polyethylene glycol diacrylate PEGDA relative to the total molar amount of MEA and BA; Add 1% of 1-hydroxycyclohexylphenyl ketone relative to the total molar amount of MEA and BA; 0.1–2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added as an ionic liquid to enhance the conductivity of the polymer; The resulting mixture was injected into a glass slide sandwich coated with an AgNWs layer and photopolymerized by ultraviolet light.

7. The method for preparing a flexible strain sensor according to any one of claims 3 to 4, characterized in that: In step S2 , the polymer substrate is pre-stretched to a length of 140%–200%.

8. The method for preparing a flexible strain sensor according to any one of claims 3 to 4, wherein: In step S3, the length of the parallel lines printed by dispensing glue is 1-3 mm, the horizontal arrangement period is 0.85 mm, the number of parallel lines is 25-60, the height of dispensing glue is 0.2-0.4 mm, and the printing speed is 20-30 mm / min to ensure that adjacent patterns can contact after pre-stretching and release. After printing, heat at 70°C for more than 30 minutes to solidify; after pre-stretching and retraction, the spacing between adjacent printed patterns is no more than 20 μm.

9. The method for preparing a flexible strain sensor according to any one of claims 3 to 4, characterized in that: In step S4, the gold plating solution used in the chemical reduction gold plating contains HAuCl4, Na2S2O3 and Na2SO3.

10. The method for preparing a flexible strain sensor according to claim 9, wherein: In step S4, the sample is immersed in the solution and reacted at 70° C. for 2 hours.

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