A flexible strain material capable of being stretched and compressed simultaneously and a preparation method and application thereof

Abstract

The present invention belongs to the technical field of intelligent devices, specifically a flexible strain material that can be stretched and compressed at the same time, and a preparation method and application. The preparation of the flexible strain material of the present invention includes: dissolving a thermoplastic elastomer in a solvent, and dispersing a conductive substance therein to obtain a dispersion containing a conductive substance; freezing the dispersion into a solid state, and then placing it under negative pressure for freeze drying, and obtaining a foam material with a porous structure after the solvent sublimates; after the porous foam material is cut into a certain shape as required, it is further immersed in a dispersion of a conductive substance, so that the surface is coated with a conductive substance, and a flexible strain material is obtained after drying. The resistance value of the material changes synchronously with the shape, showing good tensile and compression sensing functions, and both have good resilience. It can be used as a flexible strain sensor, with excellent sensing stability, accuracy and efficiency, and has broad application potential in the fields of human motion monitoring and human-computer interaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent devices, and in particular relates to a flexible strain material that can be stretched and compressed simultaneously, and a preparation method and application thereof. Background Art

[0002] The increasing demand for intelligent detection technology and wearable electronic products has set off a wave of development of flexible strain sensors. The working principle of flexible strain sensors is to convert mechanical deformation into electrical signals, such as changes in resistance or capacitance. Flexible strain sensors are easy to deform and have rich structural forms. They have been applied in various emerging intelligent fields such as human activity monitoring, medical diagnosis, human-computer interaction, information encryption, etc.

[0003] According to the direction of force, strain sensors can be simply divided into stretchable and compressive strain sensors. Tensile strain sensing is used to detect mechanical deformation under tension, while compressive strain sensing is preferably used to monitor changes in resistance and gas concentration under external pressure. In recent years, many excellent works have been devoted to optimizing the fabrication techniques of stretchable or compressible strain sensors. Among the various preparation methods of flexible stretchable strain sensors, combining elastic polymer substrates with conductive fillers has attracted widespread attention. Elastic polymers, such as commonly used polydimethylsiloxane (PDMS), thermoplastic polyurethane, poly (styrene-b-ethylene-butylene-b-styrene) (SEBS), have the characteristics of low cost, light weight, and high stretchability. They can be endowed with sensing properties by integrating appropriate conductive fillers while maintaining inherent advantages. For the design of compressible sensors, introducing sufficient compressible space or endowing lateral deformation ability is a common method. Conductive composite films with micro-pyramid array spatial structures, conductive hydrogels, and conductive porous materials such as aerogels and foams are all successful examples.

[0004] In fact, in many complex situations, tensile strain and compressive strain need to be monitored simultaneously. In this case, a single sensor is needed to detect both tension and pressure. However, compared with the many sensors that can be stretched or compressed individually, few sensors can detect both tensile and compressive signals using the same sensing device. If the above-mentioned method of preparing tensile strain sensors based on elastic polymer matrix and conductive filler can be combined with the idea of ​​preparing compressive strain sensors by introducing sufficient compressible space or imparting lateral deformation ability, it is expected to prepare strain sensors that can be stretched and compressed simultaneously. Considering the rapid development of strain sensors in more complex advanced applications, it is of great significance to develop such sensors that can be stretched and compressed simultaneously. Summary of the invention

[0005] The object of the present invention is to provide a flexible strain material that can be stretched and compressed simultaneously and a preparation method and application thereof, so as to improve the application performance of strain sensors and broaden their application scope.

[0006] The flexible strain material capable of being stretched and compressed at the same time of the present invention is a conductive foam material with a porous structure, and its resistance value can change synchronously with the strain, and the strain includes tensile strain and compressive strain; the specific steps of the preparation method thereof are:

[0007] (1) First, a thermoplastic elastomer is dissolved in a solvent, and a conductive material is dispersed therein to obtain a dispersion containing the conductive material; wherein:

[0008] Thermoplastic elastomer and conductive material are calculated by weight as follows: thermoplastic elastomer: 100 parts, conductive material: 0.001-100 parts; preferably conductive material: 1-100 parts;

[0009] (2) freezing the dispersion into a solid state, and then freeze-drying the dispersion under negative pressure, so that a foam material with a porous structure is obtained after the solvent sublimates;

[0010] (3) The porous foam material is cut into a certain shape as required, and then immersed in a dispersion of a conductive substance so that the surface of the porous foam material is coated with the conductive substance; and dried to obtain a flexible strain sensor; wherein the conductive substance dispersion comprises, by weight, 100 parts of solvent, 0.001-10 parts of conductive substance, and 0-10 parts of others; preferably, 1-10 parts of conductive substance and 1-10 parts of others; the others include surfactants and / or dispersants, etc.

[0011] The flexible strain material of the present invention is a material whose resistance value changes when the strain changes and whose resistance value recovers when the strain recovers. The strain of the present invention can be either tensile strain or compressive strain.

[0012] In the present invention, the solvent is a substance that can dissolve the thermoplastic elastomer used and can sublime under negative pressure in a solid state. The solvent can be specifically selected from cyclohexane, tert-butyl alcohol, glacial acetic acid, dimethyl sulfoxide, water, etc.

[0013] In the present invention, the thermoplastic elastomer refers to an elastomeric substance that has good mechanical properties and can be melt-processed based on physical cross-linking, mainly including one or more of polystyrene elastomers (such as SBS, SEBS, SIS, etc.), polyolefin elastomers (such as OBC, etc.), polyurethane elastomers, etc.

[0014] In the present invention, the conductive material is one or more of carbon black, carbon nanotubes, graphene, metal nanoparticles or nanowires, two-dimensional transition metal carbides, nitrides or carbonitrides (Mxenes) and the like.

[0015] In the present invention, the freeze drying is to create a low temperature environment by liquid nitrogen or other means, firstly freeze the mixture of the solvent and the conductive composite into a solid state, and then place the solid state in a negative pressure environment to allow the solvent to sublime to achieve drying; at the same time, the solvent sublimates to form a foam material with a porous structure.

[0016] The porous conductive foam material of the present invention is cut into a desired shape or size by any method, and then immersed in a solvent dispersion of various conductive substances, and then dried to obtain the porous conductive foam material. The conductive substance here can be one or more of the aforementioned conductive substances, and the solvent for preparing the conductive substance dispersion is not limited to the aforementioned solvent for preparing the thermoplastic solution.

[0017] The flexible strain material prepared by the present invention that can be stretched and compressed at the same time has abundant variable holes, has good elongation at break as a whole, and can be sensed under high strain. The stretchability of the thermoplastic elastomer and the deformation of the holes give the foam material the property of stretchability, and the deformation of its holes also makes the material compressible. These two characteristics make this material useful as a flexible strain sensor.

[0018] The flexible strain sensor of the present invention has good conductivity and flexibility, and can be bent, twisted, curled, and cut arbitrarily, and has good customizability. Therefore, it can be used to monitor human body movements, and can also encrypt and transmit human body signals by changing the frequency and amplitude of stretching and compression to achieve human-computer interaction.

[0019] The present invention has the following technical characteristics and functional advantages

[0020] (1) The raw materials used in the present invention are common commercial products and conductive materials, which are cheap, readily available, non-toxic and harmless; the preparation method of the flexible strain sensor proposed in the present invention is green, environmentally friendly, simple and easy to operate;

[0021] (2) The raw material thermoplastic elastomer used in the present invention has the characteristics of being highly stretchable and having excellent elastic recovery properties after deformation;

[0022] (3) The flexible strain material provided by the present invention has abundant variable pores and good elongation at break as a whole, and can be sensed under high strain;

[0023] (4) The flexible strain sensor provided by the present invention has good flexibility and can be arbitrarily bent, twisted, curled, and cut, and has good customizability;

[0024] (5) The flexible strain sensor provided by the present invention has the properties of stretchability of the thermoplastic elastomer and deformation of the pores, which endow the foam material with stretchable properties. The deformation of the pores also enables the material to be compressed, so that it has the properties of being both stretchable and compressible, and has a wide strain sensing range and good resilience.

[0025] (6) The flexible strain sensor provided by the present invention can be used to monitor human body movements based on its stretchability and compressibility. It can also encrypt and transmit human body signals by changing the frequency and amplitude of stretching and compression to achieve human-computer interaction. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below through specific examples, but the protection scope is not limited to the following examples, which are exemplary rather than restrictive.

[0027] Example 1

[0028] 1 g of CNTs was dispersed in 100 ml of cyclohexane and ultrasonicated for 3 h to make the dispersion uniform. Then 8 g of thermoplastic elastomer poly(styrene-b-ethylene-butylene-b-styrene) (SEBS) was added to the above dispersion and stirred for 2 h until SEBS was completely dissolved to obtain a premixed solution. The above mixed solution was poured into a special mold with a high thermal conductivity aluminum plate as the bottom and a low thermal conductivity glass plate as the wall, and then the mold was placed in a container filled with liquid nitrogen to freeze the solution into ice cubes. The height of the aluminum plate was the same as the level of liquid nitrogen. After freeze-drying the ice cubes for 48 hours, a lightweight precursor SEBS / CNTs porous foam material was obtained.

[0029] Sample strips with a size of 30×5×2 mm were cut from the SEBS / CNTs porous foam material and immersed in 100 ml of CNTs aqueous dispersion containing 1 g of CNTs for 2 h to coat the CNTs surface. After rinsing and drying these strips in a vacuum oven, the foamed flexible strain material was obtained, which was recorded as SEBS / CNTs@CNT.

[0030] G=(R0-R) / R0 (R0 is the resistance in the initial state, R is the resistance when stretched or compressed to a certain strain) represents the sensing characteristics of the sensor (the larger the G value, the more sensitive the sensor), then the G value of the porous foam sensor above reaches 18.5 and 1.75 when stretched to 150% and compressed to 25%, respectively. The sensor has excellent tensile and compressibility, and can be twisted, bent, folded, and curled arbitrarily, and can be restored to its original shape. It can also be cut into any shape and has the ability to be customized.

[0031] Example 2

[0032] The other conditions are the same as in Example 1. The sample strips cut from the SEBS / CNTs porous foam material are immersed in 100 ml of CNTs aqueous dispersion for 2 hours. In addition to 1 g of CNTs, the aqueous dispersion also contains 3 g of surfactant sodium dodecyl sulfate to coat the CNTs surface. After rinsing and drying these strips in a vacuum oven, the foam flexible strain material SEBS / CNTs@CNT is obtained.

[0033] The prepared porous foam sensor has a G value of 20.0 and 1.82 when stretched to 150% and compressed to 25%, respectively. The sensor has excellent tensile and compressibility, and can be arbitrarily twisted, bent, folded, and curled, and can be restored to its original shape. It can also be cut into any shape and has customizable capabilities.

[0034] Example 3

[0035] The other conditions are the same as in Example 2. 2 g of CNTs were dispersed in 100 ml of cyclohexane and ultrasonicated for 3 h to make the dispersion uniform. Then 6 g of the original thermoplastic elastomer SEBS was added to the above dispersion and stirred for 2 h until the SEBS was completely dissolved to obtain a premixed solution. The premixed solution was subjected to directional freezing, freeze drying, surface coating and other steps to finally obtain the foamed flexible strain material SEBS / CNTs@CNT.

[0036] The foam sensor can be stretched to 250% and compressed to 30%. The G values ​​of stretching and compressing sensing in the above strain range are 21.5 and 1.55 respectively. The sensor has excellent tensile and compressibility, and can be twisted, bent, folded, and curled arbitrarily, and can be restored to its original shape. It can also be cut into any shape and has customizable capabilities.

[0037] Example 4

[0038] The other parts are the same as in Example 2, but the size of the sample strip cut from the freeze-dried SEBS / CNTs porous foam material is 30×5×5 mm. After soaking in the surface and further coating CNTs and drying, the foam flexible strain material SEBS / CNTs@CNT is obtained, which can be stretched to 250% and compressed to 50%. The G values ​​of the tensile and compressive sensors in the above strain range are 21.5 and 1.8 respectively. The sensor has excellent tensile and compressive properties, can be twisted, bent, folded, and curled arbitrarily, and can be restored to the original shape. It can also be cut into any shape and has the ability to be customized.

[0039] Example 5

[0040] The other steps are the same as those in Example 2, but the conductive material dispersion liquid used for coating is a dispersion liquid of 100 ml ethanol and 0.5 g high-temperature thermally reduced graphene oxide.

[0041] The prepared porous foam sensing material has a G value of 17.7 and 1.48 when stretched to 150% and compressed to 25%, respectively. The sensor has excellent tensile and compressibility, and can be arbitrarily twisted, bent, folded, and curled, and can be restored to its original shape. It can also be cut into any shape and has customizable capabilities.

[0042] Example 6

[0043] The other conditions are the same as those in Example 2. 5 g of high temperature thermally reduced graphite oxide is dispersed in 100 ml of cyclohexane and ultrasonically treated for 3 h to make the dispersion uniform. Then 6 g of original thermoplastic elastomer SEBS is added to the above dispersion and stirred for 2 hours until TPU is completely dissolved to obtain a premixed solution. The premixed solution is subjected to directional freezing and freeze drying to obtain a precursor porous foam.

[0044] Sample strips with a size of 30×5×1 mm were cut from the above porous foam and immersed in 100 ml of an aqueous dispersion of CNTs for 2 hours, wherein the aqueous dispersion contained 2 g of CNTs and 3 g of sodium dodecyl sulfate to surface coat the CNTs. After rinsing and drying these strips in a vacuum oven, a porous foam flexible sensor was obtained.

[0045] The foam sensor can be stretched to 500% and compressed to 20%, with G values ​​reaching 15.8 and 1.42 respectively. It exhibits better tensile strain sensing properties. The sensor has excellent tensile and compressible properties, and can be twisted, bent, folded, and curled arbitrarily, and can be restored to its original shape. It can also be cut into any shape and has customizable capabilities.

[0046] Example 7

[0047] The rest is the same as in Example 2, except that SEBS is replaced with thermoplastic polyurethane (TPU) to prepare a foam sensor with a size of 30×5×1 mm, which is denoted as TPU / CNTs@CNT.

[0048] The foam sensor can be stretched to 500% and compressed to 10% within the strain range, with G values ​​reaching 15.5 and 1.52 respectively. It exhibits better tensile strain sensing properties. The sensor has excellent tensile and compressible properties, and can be twisted, bent, folded, and curled arbitrarily, and can be restored to its original shape. It can also be cut into any shape and has customizable capabilities. It exhibits good tensile strain properties.

[0049] Example 8

[0050] The rest is the same as in Example 2, except that SEBS is replaced with ethylene-octene multi-block copolymer (OBC), and sample strips with a size of 30×5×3 mm are prepared. After the same surface coating steps, a foam sensor is obtained, which is denoted as OBC / CNTs@CNT.

[0051] The foam sensor can be stretched to 200% and compressed to 45% within the strain range, with G values ​​reaching 16.0 and 1.55 respectively. It exhibits good stretchable and compressible strain characteristics. The sensor has excellent tensile and compressible properties, and can be twisted, bent, folded, and curled arbitrarily, and can be restored to its original shape. It can also be cut into any shape and has customizable capabilities.

[0052] The prepared stretchable and compressible flexible porous foam sensor is fixed on the joints of the human body, such as fingers, wrists, knees, or fixed on certain parts of the human body, such as the soles of the feet. Through repeated stretching, bending or compression movements, the resistance of the foam sensor will change periodically, thereby realizing the monitoring of human movement.

Claims

1. A method for preparing a flexible strain material that can be stretched and compressed simultaneously, characterized in that: The flexible strain material is a conductive foam material with a porous structure, and its resistance value can change synchronously with the strain, and the strain includes tensile strain and compressive strain. The specific steps of the preparation method are: (1) First, a thermoplastic elastomer is dissolved in a solvent, and a conductive material is dispersed therein to obtain a dispersion containing the conductive material; wherein: The thermoplastic elastomer and the conductive material are calculated by weight: 100 parts of the thermoplastic elastomer and 0.001-100 parts of the conductive material; (2) freezing the dispersion into a solid state, and then freeze-drying the dispersion under negative pressure, so that a foam material with a porous structure is obtained after the solvent sublimates; (3) The porous foam material is cut into a certain shape as required, and then immersed in a dispersion of a conductive substance so that the surface of the porous foam material is coated with the conductive substance; and dried to obtain a flexible strain material; the conductive substance dispersion comprises, by weight, 100 parts of solvent; 0.001-10 parts of conductive substance; and 0-10 parts of others; the others are surfactants and / or dispersants.

2. The preparation method according to claim 1, characterized in that: The solvent is a substance that can dissolve the thermoplastic elastomer used and can sublime in a negative pressure environment in a solid state. The solvent is selected from cyclohexane, tert-butyl alcohol, glacial acetic acid, dimethyl sulfoxide and water.

3. The preparation method according to claim 2, characterized in that: The thermoplastic elastomer is selected from one or more of polystyrene elastomers, polyolefin elastomers and polyurethane elastomers.

4. The preparation method according to claim 3, characterized in that: The thermoplastic elastomer is selected from SBS, SEBS, SIS and OBC.

5. The preparation method according to claim 3, characterized in that: The conductive material is selected from one or more of carbon black, carbon nanotubes, graphene, metal nanoparticles or nanowires, two-dimensional transition metal carbides, nitrides or carbonitrides.

6. The preparation method according to claim 3, characterized in that: The freeze drying is to create a low temperature environment by liquid nitrogen or other means, firstly freeze the mixture of the solvent and the conductive compound into a solid state, and then place the solid state in a negative pressure environment to allow the solvent to sublime to achieve drying; at the same time, the solvent sublimates to form a foam material with a porous structure.

7. A flexible strain material capable of being stretched and compressed simultaneously obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the flexible strain material capable of being stretched and compressed simultaneously as claimed in claim 7 as a flexible sensor.