Flexible stretchable strain sensor and preparation method thereof

Abstract

The invention provides a flexible stretchable strain sensor and a preparation method thereof, the flexible stretchable strain sensor comprises two elastomer substrates, flexible electrodes are arranged on the sides, close to each other, of the two elastomer substrates, and an ionic gel dielectric layer is arranged between the two flexible electrodes; wherein the elastomer substrate is a flexible substrate with controllable modulus. According to the flexible stretchable strain sensor and the preparation method thereof provided by the invention, the problem that an existing strain sensor is difficult to have high sensitivity, high signal-to-noise ratio and high linearity at the same time can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible electronic devices, and more specifically, to a flexible and stretchable strain sensor and a preparation method thereof. Background Art

[0002] With the increase in age-related diseases and the development of technology, more and more medical robots and medical monitoring devices are being used by people. The demand for various robot sensing devices or human motion feedback devices is increasing. The core of these devices lies in obtaining and monitoring real-time human information through internal sensors. However, considering the long-term direct contact between medical devices and the human body, rigid mechanical devices are obviously difficult to meet requirements such as comfort and may even have a negative impact on the human body. However, the advantages of flexible sensors such as being thin, having strong conformal properties, being attachable, and having good biocompatibility are very suitable for applications in medical and health fields such as human physiological information collection and soft robot interaction.

[0003] Human joint rotation, muscle contraction, etc. are important information for recording human movement. Stretchable strain sensors can well adapt to the rotation, stretching, and contraction at joints and muscles, and monitor and feedback on them in real time. Thus, it provides a guiding role for the rehabilitation treatment of various parts. Developing a flexible substrate and sensor with adjustable modulus that can adapt to the deformation of different parts and can well adhere and conform to the human body can capture accurate deformation.

[0004] In addition, in some cases of small muscle deformation or minute deformation caused by breathing and pulse, very high-precision strain sensors are required to capture it. Therefore, strain sensors with high sensitivity, high signal-to-noise ratio, and low resolution are needed to monitor minute deformation. Currently, the commonly used resistive sensors can achieve relatively high sensitivity. However, their resistance usually changes unstably with stretching, resulting in low sensor accuracy. While capacitive sensors have good linearity and stability, they are difficult to achieve high sensitivity and high signal-to-noise ratio.

[0005] Based on the above technical problems, there is an urgent need for a strain sensor with adjustable modulus and high sensitivity, high signal-to-noise ratio, high resolution, and high linearity. Summary of the Invention

[0006] In view of the above problems, the purpose of the present invention is to provide a flexible and stretchable strain sensor and a preparation method thereof to solve the problem that current strain sensors are difficult to simultaneously have high sensitivity, high signal-to-noise ratio, and high linearity.

[0007] The flexible and stretchable strain sensor provided by the present invention includes two elastomeric substrates. On one side of each of the two elastomeric substrates close to each other, a flexible electrode is provided, and an ionic gel dielectric layer is provided between the two flexible electrodes; wherein,

[0008] The elastomeric substrate is a flexible substrate with controllable modulus.

[0009] Furthermore, preferably, the two flexible electrodes are respectively bonded and fixed to the corresponding elastomeric substrates, and the upper and lower sides at both ends of the ionic gel dielectric layer are respectively bonded and fixed to the two flexible electrodes.

[0010] Furthermore, preferably, the elastomeric substrate is a mixed component of magnetic powder particles and a first elastomeric polymer; and

[0011] the modulus of the elastomeric substrate is regulated by the magnetic orientation of the magnetic powder particles.

[0012] Furthermore, preferably, the first elastomeric polymer includes at least one of polyurethane, polyethylene glycol, polyvinyl alcohol, polydimethylsiloxane, ecoflex, and silicone rubber;

[0013] the magnetic powder particles include at least one of strontium ferrite, barium ferrite, iron powder, nickel powder, neodymium iron boron, and alnico.

[0014] Furthermore, preferably, the ionic gel dielectric layer is an ionic gel dielectric layer; and

[0015] the ionic gel dielectric layer is a mixed component of an ionic liquid and a second elastomeric polymer.

[0016] Furthermore, preferably, the second elastomeric polymer includes at least one of polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl chloride, polymethyl methacrylate, and polyvinylidene fluoride;

[0017] the ions in the ionic liquid include cations and anions; wherein,

[0018] the cations include at least one of methylimidazole, tetraethylammonium, tetrabutylammonium, alkyltributylammonium, alkyltributylphosphonium, pyrrolidinium salt, and quaternary phosphonium salt;

[0019] the anions include at least one of trifluoromethanesulfonic acid, bis(trifluoromethanesulfonyl)imide, tetrafluoroboric acid, hexafluorophosphoric acid, chloride salt, and bromide salt.

[0020] Furthermore, preferably, both ends of the ionic gel dielectric layer are in a parallel plate structure;

[0021] the middle of the ionic gel dielectric layer is in a wavy convex structure.

[0022] Furthermore, preferably, the flexible electrode is a component made of a conductive material;

[0023] The conductive material includes at least one of conductive silver fibers, graphene oxide, gallium-indium liquid metal, multi-walled carbon nanotubes, and silver nanowires.

[0024] On the other hand, the present invention also provides a method for preparing the flexible and stretchable strain sensor as described above, including:

[0025] Preparing the elastomeric substrate based on magnetic powder particles and a first elastomeric polymer;

[0026] Combining two conductive materials on the mutually approaching sides of two said elastomeric substrates respectively to form two said flexible electrodes;

[0027] Composite a preset ionic gel dielectric layer with the two said flexible electrodes to form the flexible and stretchable strain sensor.

[0028] In addition, preferably, the process of presetting the ionic gel dielectric layer includes:

[0029] Preparing a template with a preset wave structure;

[0030] Preparing the ionic gel dielectric layer based on the template.

[0031] Compared with the prior art, the above flexible and stretchable strain sensor and its preparation method according to the present invention have the following beneficial effects:

[0032] The flexible and stretchable strain sensor provided by the present invention can solve the problem that the current strain sensors are difficult to simultaneously have high sensitivity, high signal-to-noise ratio, and high linearity by setting an elastomeric substrate, flexible electrodes, and an ionic gel dielectric layer with controllable modulus; in addition, by using an elastomeric substrate with adjustable modulus, the effect of sharing the common properties with human skin can be achieved, meeting the use requirements in scenarios with different force requirements.

[0033] To achieve the above and related purposes, one or more aspects of the present invention include features that will be described in detail hereinafter and particularly pointed out in the claims. The following description and the accompanying drawings detail certain exemplary aspects of the present invention. However, these aspects merely indicate some of the various ways in which the principles of the present invention can be used. In addition, the present invention is intended to cover all these aspects and their equivalents. Description of the Drawings

[0034] By referring to the following description in conjunction with the accompanying drawings and the content of the claims, and with a more comprehensive understanding of the present invention, other objects and results of the present invention will become more apparent and easier to understand. In the drawings:

[0035] Figure 1 The top view structure of the template provided for the embodiment of the present invention;

[0036] Figure 2 Schematic diagram of the laminated structure of the flexible and stretchable strain sensor provided for the embodiment of the present invention;

[0037] Figure 3 Specific application demonstration diagram of the flexible and stretchable strain sensor provided for the embodiment of the present invention at a human joint;

[0038] Figure 4 Response signal diagram obtained by the flexible and stretchable strain sensor provided for the embodiment of the present invention monitoring finger deformation.

[0039] Reference numerals: elastomeric substrate 1, flexible electrode 2, ionic gel dielectric layer 3:

[0040] In all the drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed implementation manners

[0041] In the following description, for the purpose of illustration, in order to provide a comprehensive understanding of one or more embodiments, many specific details are set forth. However, it is obvious that these embodiments can also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for the purpose of facilitating the description of one or more embodiments.

[0042] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the range.

[0043] Furthermore, the endpoints and any numerical values disclosed in the ranges herein are not limited to the exact ranges or values, but should be understood to include values close to these ranges or values. Combinations can be formed between the endpoint values of each numerical range, between the endpoint values of each numerical range and individual point values, and between individual point values to form one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0044] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the description of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the description of the present invention are obvious to those skilled in the art. The description and embodiments of this application are only exemplary.

[0045] Figure 2The figure shows a schematic diagram of the laminated structure of the flexible and stretchable strain sensor provided by the embodiments of the present invention. It can be seen from Figure 2 that the flexible and stretchable strain sensor provided by the present invention includes two elastomeric substrates 1 prepared by processes such as reverse molding / spin coating / coating, etc., which are arranged on the outermost layer (the two elastomeric substrates 1 can be exactly the same). On the side where the two elastomeric substrates 1 are close to each other, flexible electrodes 2 with conductive properties are arranged, and an ionic gel dielectric layer 3 is arranged between the two flexible electrodes 2; wherein, the elastomeric substrate 1 is a flexible substrate with controllable modulus.

[0046] It should be noted that the various film layer structures need to be fixedly connected. For example, the two flexible electrodes 2 can be respectively bonded and fixed to the corresponding elastomeric substrates 1, and the upper and lower sides at both ends of the ionic gel dielectric layer 3 can be respectively bonded and fixed to the two flexible electrodes 2.

[0047] To achieve the control of the modulus of the elastomeric substrate 1, the elastomeric substrate 1 can be selected as a mixture of magnetic powder particles and a first elastomeric polymer; specifically, the magnetic powder particles and the first elastomeric polymer are uniformly mixed by mechanical stirring, and the magnetic orientation of the magnetic powder particles is regulated when the polymer is not cured, so as to achieve the purpose of regulating the modulus of the elastomeric substrate 1.

[0048] It can be seen from the above that the flexible and stretchable strain sensor provided by the present invention includes two substrates with adjustable modulus, two layers of parallel plate electrodes attached to the substrates, and a special dielectric layer arranged between the two electrodes; wherein, the substrate is composed of magnetic powder particles and an elastomeric polymer; the magnetic powder particles are uniformly distributed in the elastomeric polymer body, forming a structure similar to reinforced concrete; by adjusting the magnetic orientation of the magnetic powder particles when they are not cured, the arrangement orientation of the magnetic powder can be changed, so as to achieve the effect of regulating the modulus of the substrate.

[0049] Specifically, the first elastomeric polymer can be considered to use, for example, one of polyurethane, polyethylene glycol, polyvinyl alcohol, polydimethylsiloxane, ecoflex (environmentally friendly thermoplastic elastomer), and various silicone rubbers, etc.; the magnetic powder particles can be considered to use, for example, at least one of strontium ferrite, barium ferrite, iron powder, nickel powder, neodymium iron boron, and alnico.

[0050] For the ionic gel dielectric layer 3 and the flexible electrode 2; wherein, the flexible electrode 2 that is in close contact with the elastomeric substrate 1 is stretchable and conductive. The flexible electrode 2 can be firmly bonded to the elastomeric substrate 1 by means of doctor blading or ultrasonic spraying to bond with the first elastomeric polymer; the ionic gel dielectric layer 3 with a special stretchable structure (i.e., a thermoplastic polymer dielectric layer) is sandwiched between the two flexible electrodes 2.

[0051] To achieve the stretchability of the ionic gel dielectric layer 3 and the effect that the entire flexible and stretchable strain sensor can detect external strain, the ionic gel dielectric layer 3 needs to be set as an ionic gel dielectric layer; and this ionic gel dielectric layer is a mixture of an ionic liquid and the second elastomeric polymer.

[0052] Specifically, for the second elastomeric polymer, at least one of the following can be considered: polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl chloride, polymethyl methacrylate, polyvinylidene fluoride; the ionic liquid includes imidazole-based, pyrrolidine-based, quaternary ammonium-based, pyridine-based quaternary phosphonium-based, piperidine, and functionalized ionic liquids; and the ions in the ionic liquid include cations and anions; among them, for the cations, at least one of the following can be considered: methylimidazole, tetraethylammonium, tetrabutylammonium, alkyltributylammonium, alkyltributylphosphonium, pyrrolidinium salts, and quaternary phosphonium salts; for the anions, at least one of the following can be considered: trifluoromethanesulfonic acid, bis(trifluoromethanesulfonyl)imide, tetrafluoroboric acid, hexafluorophosphoric acid, chloride salts, bromide salts. In addition, to improve the detection accuracy, both ends of the ionic gel dielectric layer 3 can be set to have a parallel plate structure; the middle of the ionic gel dielectric layer 3 can be set to have a wavy convex structure, and the wavy convex structure can further improve the movement effect of the ions in the ionic gel, thereby improving the detection accuracy of the flexible and stretchable strain sensor provided by the present invention.

[0053] For the flexible electrode 2, to achieve its conductive performance, the flexible electrode 2 needs to be made of a conductive material, and the conductive material can include at least one of conductive silver fibers, graphene oxide, gallium-indium liquid metal, multi-walled carbon nanotubes, and silver nanowires.

[0054] As can be seen from the above specific embodiments, the flexible and stretchable strain sensor provided by the present invention includes a five-layer stacked structure, and the five-layer stacked structure is arranged in a parallel plate stack. During actual use, when the flexible and stretchable strain sensor provided by the present invention undergoes lateral strain, its overall volume increases with stretching, and it will cause the ionic gel inside its ionic gel dielectric layer 3 to be affected by a normal force, so that the ionic gel ions are squeezed and move towards the flexible electrodes 2 at both ends; and under the action of the normal force, the contact area between the flexible electrode 2 and the ionic gel dielectric layer 3 gradually increases, and this change causes the electric double layer generated between the flexible electrode 2 and the ions in the ionic gel to increase, thereby causing a change in the capacitance of the electric double layer; therefore, the flexible and stretchable strain sensor provided by the present invention can, when a strain change occurs, output a corresponding change in the electrical signal based on the change in the capacitance of the electric double layer, so as to achieve the effect of detecting strain.

[0055] It should be noted that both of the two flexible electrodes 2 need to have certain stretching properties and be able to conduct electricity stably during stretching. To achieve the above effects, a conductive material with stretchability and stable stretching needs to be used to make the flexible electrode 2. At the same time, the flexible electrode 2 is firmly adhered to the elastomeric substrate 1 to improve its stretching stability. Therefore, the flexible electrode 2 needs to be able to adhere tightly to the flexible substrate to form an integral whole.

[0056] To further illustrate the preparation process of the flexible stretchable strain sensor provided by the present invention, the present invention also provides a preparation method for the aforementioned flexible stretchable strain sensor. The preparation method includes:

[0057] Preparing the elastomeric substrate 1 based on magnetic powder particles and a first elastomeric polymer;

[0058] Combining two conductive materials on the mutually adjacent sides of two such elastomeric substrates 1 to form two such conductive materials;

[0059] Compounding a preset ionic gel dielectric layer 3 with the two flexible electrodes 2 to form the flexible stretchable strain sensor.

[0060] Among them, for the preparation of the elastomeric substrate 1 and the conductive material, the actual preparation process is as follows: First, fine magnetic powder particles are blended with the uncured first elastomeric polymer, and then a cured flexible substrate is prepared by coating, spin coating, or the template method to ensure that the electrode material can be smoothly attached; then, an uncured elastomer is obtained on the cured flexible matrix by coating, spin coating, or the template method; finally, the conductive material is laid flat on the uncured elastomer. As the elastomer cures, the electrode material is also tightly adhered to the flexible substrate, thus forming the integral preparation of the elastomeric substrate 1 and the flexible 2. It should be noted that the electrode material needs to have a certain affinity with the flexible substrate to achieve the curing of the elastomer and the tight adhesion between the two.

[0061] It should be further noted that for the preparation of the ionic gel dielectric layer 3, a template with a special stretchable structure (for example, a template with a preset wavy structure) needs to be prepared in advance, and then the flexible electrode 2 is prepared based on this template. Among them, for the production of the template, it needs to be prepared by photocuring 3D printing. The preparation process is as follows: Transfer the high-temperature resistant resin to the 3D printer cartridge and print according to the set parameters; rinse the printed part obtained after printing; put the printed part into the curing box and cure it to form a template with a special stretchable structure.

[0062] Further, the preparation process of the ionic gel medium layer 3 containing the ionic gel is as follows: First, a thermoplastic elastomer polymer (i.e., the second elastomer polymer) and an ionic liquid are dissolved in an organic solvent in a certain proportion, and then the two are made compatible by heating and blending to obtain a mixed solution; finally, the mixed solution is made into an ionic gel by the template method and the ionic gel medium layer 3 is obtained through heat treatment at a certain temperature. Specifically, for the thermoplastic elastomer polymer, at least one of the following can be considered: polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl chloride, polymethyl methacrylate, polyvinylidene fluoride; for the ionic liquid, the following can be selected: imidazole-based, pyrrolidine-based, quaternary ammonium-based, pyridine-based quaternary phosphonium-based, piperidine, and functionalized ionic liquids. The ionic liquid includes a cation and an anion; wherein, the cation includes at least one of methylimidazole, tetraethylammonium, tetrabutylammonium, alkyltributylammonium, alkyltributylphosphonium, pyrrolidinium salt, and quaternary phosphonium salt; the anion includes at least one of trifluoromethanesulfonic acid, bis(trifluoromethanesulfonyl)imide, tetrafluoroboric acid, hexafluorophosphoric acid, chloride salt, and bromide salt.

[0063] It should be noted that the optimal thickness of the ionic gel medium layer 3 includes 200μm, 300μm, 400μm, 500μm, 600μm, and the ionic gel medium layer 3 and the elastomeric substrate 1 preferably have the same thickness. The wave structure height of the ionic gel medium layer 3 is preferably 0.6 - 1.8mm; the distance between each wave in the medium layer wave structure is preferably 0 - 1mm; the angle of each wave in the medium layer wave structure is preferably 60 - 180°; the optimal mass percentages of the ionic liquid in the ionic gel include 5wt%, 10wt%, 15wt%, 20wt%.

[0064] The following further illustrates the specific preparation process and working principle of the flexible and stretchable strain sensor provided by the present invention by way of examples.

[0065] Practical Example 1:

[0066] The structure of the flexible and stretchable strain sensor provided by this embodiment is as Figure 2 shown, including a modulus-adjustable elastomeric substrate 1, a flexible electrode 2, and an ionic gel medium layer 3. Among them, the elastomeric substrate 1 is specifically prepared by mechanically stirring and mixing Ecoflex and neodymium iron boron particles, and through the template method, the external magnetic orientation is adjusted when the elastomer is not cured to change the orientation of the magnetic powder particles inside the polymer, so as to achieve the effect of modulus adjustment.

[0067] The preparation material of the flexible electrode 2 is a liquid metal, the component of which is a gallium indium alloy with a ratio of 3:1, and it is prepared by scraping on a metal mask plate.

[0068] The ionic gel dielectric layer 3 is specifically prepared by using plastic polyurethane, N-N dimethylformamide and acetone, and a mixture of N-N dimethylformamide and acetone; specifically, the preparation process of the ionic gel in the ionic gel dielectric layer 3 includes: first, uniformly dissolve thermoplastic polyurethane and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in a mixed solvent of N-N dimethylformamide and acetone under the conditions of 60 °C and 800 r / min. Then, the prepared solution is cast and coated in a template with a special stretchable structure (such as a stretchable wave structure) (the template structure is as Figure 1 shown), and then it is placed in a vacuum oven, evacuated and heated at 80 °C for twelve hours until the solvent is completely volatilized, and the prepared ionic gel can be obtained.

[0069] Finally, the flexible electrode 2 and the dielectric layer are attached and bonded by hot pressing, and the flexible stretchable strain sensor provided in this embodiment can be obtained. The pictures and usage examples of the obtained sensor are as Figure 3 shown. This flexible stretchable strain sensor can sense the deformation at the human joint and output a capacitance signal as Figure 4 shown. It can be seen from Figure 4 that the degree of deformation at the human joint (such as the finger bending degree, e.g., 30°, 60°, 90°) can be sensed through the input capacitance signal.

[0070] As described above by way of example with reference to Figures 1 to 4 the flexible stretchable strain sensor according to the present invention and its preparation method. However, those skilled in the art should understand that various improvements can be made to the above-mentioned flexible stretchable strain sensor according to the present invention and its preparation method without departing from the content of the present invention. Therefore, the protection scope of the present invention should be determined by the content of the appended claims.

Claims

1. A flexible stretchable strain sensor, characterized in that: It comprises two elastomer substrates, flexible electrodes are arranged on the sides of the two elastomer substrates close to each other, and an ion gel medium layer is arranged between the two flexible electrodes; wherein, The elastomeric substrate is a flexible substrate with controllable modulus.

2. The flexible stretchable strain sensor according to claim 1, characterized in that: The two flexible electrodes are respectively bonded and fixed to the corresponding elastic substrates, and the upper and lower sides of both ends of the ion gel medium layer are respectively bonded and fixed to the two flexible electrodes.

3. The flexible stretchable strain sensor according to claim 2, characterized in that: The elastomer substrate is a mixed product of magnetic powder particles and a first elastomer polymer; and The modulus of the elastomeric substrate is controlled by the magnetic orientation of the magnetic powder particles.

4. The flexible stretchable strain sensor according to claim 3, characterized in that: The first elastomeric polymer comprises at least one of polyurethane, polyethylene glycol, polyvinyl alcohol, polydimethylsiloxane, ecoflex and silicone rubber; The magnetic powder particles include at least one of strontium ferrite, barium ferrite, iron powder, nickel powder, neodymium iron boron, and aluminum nickel cobalt.

5. The flexible stretchable strain sensor according to claim 2, characterized in that: The ion gel medium layer is a mixed product of ionic liquid and a second elastic polymer.

6. The flexible stretchable strain sensor according to claim 5, characterized in that: The second elastomeric polymer comprises at least one of polyurethane, thermoplastic polyurethane, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl chloride, polymethyl methacrylate, and polyvinylidene fluoride; The ions in the ionic liquid include cations and anions; wherein, The cation includes at least one of methylimidazole, tetraethylammonium, tetrabutylammonium, alkyltributylammonium, alkyltributyphosphonium, pyrrolidinium salt and quaternary phosphonium salt; The anion includes at least one of trifluoromethanesulfonic acid, bistrifluoromethanesulfonimide, tetrafluoroboric acid, hexafluorophosphoric acid, chloride salt, and bromide salt.

7. The flexible stretchable strain sensor according to claim 2, characterized in that: The two ends of the ion gel medium layer are parallel plate structures; The middle of the ion gel medium layer is a wave convex structure.

8. The flexible stretchable strain sensor according to claim 2, characterized in that: The flexible electrode is made of conductive material; The conductive material includes at least one of conductive silver fiber, graphene oxide, gallium indium liquid metal, multi-walled carbon nanotube and silver nanowire.

9. A method for preparing a flexible stretchable strain sensor according to any one of claims 1 to 8, characterized in that: include: Prepare the elastomeric substrate based on magnetic powder particles and a first elastomeric polymer; Combining two conductive materials on the mutually adjacent sides of the two elastic substrates respectively to form the two flexible electrodes; The preset ion gel medium layer is compounded with the two flexible electrodes to form the flexible stretchable strain sensor.

10. A method for preparing a flexible stretchable strain sensor as claimed in claim 9, characterized in that: The process of presetting the ion gel medium layer includes: preparing a template with a preset wave structure; The ion gel medium layer is prepared based on the template.

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