Flexible strain sensor and preparation method thereof

Abstract

The present invention provides a flexible strain sensor and a preparation method thereof, the preparation method comprising: preparing a first mixed solution and a second mixed solution with different dispersion forms, and preparing the flexible strain sensor through 3D printing and curing treatment. The preparation method can realize conformal integration and accurate and reliable monitoring of the flexible strain sensor, and the functional characteristics of the flexible strain sensor can be adjusted to a large extent by adjusting the dispersion forms of the first functional filler and the second functional filler, so that the flexible strain sensor has multifunctional characteristics, and the connection part has good tensile resistance, thereby ensuring the reliability of the flexible strain sensor under tensile deformation.

Description

Technical Field

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

[0002] Strain sensors can detect various physiological activities of organisms, including large-scale limb bending and movement, as well as smaller-scale muscle vibrations during breathing, swallowing, and vocalization, blood pressure, and intraocular pressure. Strain sensors can convert physiological movement or weak vibration signals into electrical signals, so they have great application potential in clinical diagnosis, health assessment, health monitoring, virtual electronics, flexible touch screens, flexible electronic skin, and even industrial robots.

[0003] Strain sensors based on materials such as metals or semiconductors are limited in flexibility and stretchability; flexible strain sensors have good biocompatibility, stretchability, transparency, wearability, and continuous detection. However, for monitoring of smaller strains, such as finger movements, eyelid movements, and swallowing movements, the monitoring parts are often complex surfaces or non-developable surfaces with a small overall area. In addition, traditional flexible strain sensor devices require the integration of sensing modules and conductive modules, making it difficult to achieve conformal integration and accurate and reliable monitoring. Summary of the invention

[0004] In view of the above problems, the present invention provides a flexible strain sensor and a preparation method thereof, which can achieve conformal integration and accurate and reliable monitoring of the flexible strain sensor.

[0005] In order to achieve the above object, according to one aspect of the present invention, a method for preparing a flexible strain sensor is provided, the method comprising the following steps:

[0006] Providing a first functional filler, a first polymer material and an aggregation-assisting medium, and adding the first functional filler and the first polymer material into the aggregation-assisting medium to form a first mixed solution;

[0007] Providing a second functional filler, a second polymer material and an auxiliary dispersion medium, and adding the second functional filler and the second polymer material to the auxiliary dispersion medium to form a second mixed solution;

[0008] A substrate is provided, and the first mixed solution and the second mixed solution are respectively printed and cured by 3D printing, so that the first mixed solution forms a first functional part on the surface of the substrate, and the second mixed solution forms a second functional part on the surface of the substrate, and a connecting part is formed at the interface between the first functional part and the second functional part, so as to obtain the flexible strain sensor.

[0009] In one of the embodiments, the elongation at break of the flexible strain sensor is greater than or equal to 100%, and the strain sensitivity coefficient is 10-20.

[0010] In one embodiment, the first functional filler and the second functional filler have the same composition, and when the vibration frequency of the strain signal is 0-1 MHz, the AC impedance of the connecting portion is less than 0.5% of the DC resistance value.

[0011] In one embodiment, the first polymer material and the second polymer material have the same composition, and the Young's modulus of the connecting portion is greater than or equal to 100 MPa.

[0012] In one embodiment, the agglomeration medium includes at least one of benzene, toluene, xylene, tetrahydrofuran, chloroform, and dimethyl sulfoxide;

[0013] And / or, the dispersing aid medium includes at least one of polyvinyl pyrrolidone, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecylamine, Triton, alkyl cellulose, and polyacrylic acid.

[0014] In one embodiment, the first functional filler includes at least one of silver nanowires, copper nanowires, graphene, and carbon black;

[0015] And / or, the second functional filler includes at least one of silver nanowires, copper nanowires, graphene, and carbon black;

[0016] And / or, the first polymer material includes at least one of styrene-butadiene-styrene block copolymer, polydimethylsiloxane, and copolyester (Ecoflex);

[0017] And / or, the second polymer material includes at least one of styrene-butadiene-styrene block copolymer, polydimethylsiloxane, and copolyester (Ecoflex).

[0018] In one embodiment, the mass fraction of the first functional filler in the first functional part is 5%-35%;

[0019] And / or, the mass fraction of the second functional filler in the second functional part is 1%-60%.

[0020] In one embodiment, in the step of adding the first functional filler and the first polymer material into the agglomeration aid medium to form a first mixed solution, a first dispersion is performed using a non-invasive homogenizer.

[0021] In one embodiment, in the step of adding the second functional filler and the second polymer material into the auxiliary dispersion medium to form a second mixed solution, a third roller homogenizer is used for the second dispersion.

[0022] In one embodiment, the pressure value of the 3D printing is 5psi-15psi;

[0023] And / or, the curing treatment includes a heating treatment, and the temperature of the heating treatment is 40°C-80°C.

[0024] According to another aspect of the present invention, there is provided a flexible strain sensor obtained by any of the above-mentioned preparation methods, wherein the flexible strain sensor comprises a first functional portion, a second functional portion and a connecting portion, wherein the connecting portion is arranged between the first functional portion and the second functional portion.

[0025] Compared with the prior art, the preparation method of the present invention has the following beneficial effects:

[0026] First, the first functional filler in the first mixed solution can be in an actively aggregated state through the aid of agglomeration medium, so that the first functional part has a higher strain sensitivity. The second functional filler in the second mixed solution can be in a monodispersed state through the aid of dispersion medium, so that the second functional part has a higher conductivity. The present invention adjusts the dispersion morphology of the first functional filler and the second functional filler to achieve a large degree of adjustment of the functional characteristics of the flexible strain sensor, thereby having multifunctional characteristics.

[0027] Second, since the agglomeration aid is a poor solvent for the first functional filler and the dispersant is a good solvent for the second functional filler, it is difficult to directly fuse the first mixed solution with the second mixed solution. Therefore, during the preparation of the present invention, the agglomeration aid medium and the dispersion medium are volatilized respectively by curing the first mixed solution and the second mixed solution after printing, and the polymer chains in the first polymer material and the polymer chains in the second polymer material are entangled with each other at the interface connection during the curing process to form an interlocking effect. At the same time, the polymer chains in the first polymer material and the polymer chains in the second polymer material will move toward each other, further driving the first functional filler and the second functional filler to approach and penetrate each other at the connection part, thereby reconstructing the interface network of the connection part. In summary, the connection part has good tensile resistance, which ensures the reliability of the flexible strain sensor under tensile deformation.

[0028] In addition, the present invention can obtain a small-sized monitor with a fractal pattern design through 3D printing, and can achieve reliable conformity with complex curved surfaces, thereby achieving accurate measurement of physiological strain signals.

[0029] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of a method for preparing a flexible strain sensor provided in one of the embodiments.

[0031] Figure 2 A schematic diagram of a 3D printing method provided in one embodiment.

[0032] Figure 3 A scanning electron microscope image of a second functional portion in a monodisperse morphology provided for one embodiment.

[0033] Figure 4 A scanning electron microscope image of the first functional portion in an actively aggregated morphology provided for one embodiment.

[0034] Figure 5 An interface impedance test spectrum of the flexible strain sensor connection portion provided in one of the embodiments. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0038] According to one aspect of the present invention, a method for preparing a flexible strain sensor is provided. Figure 1 As shown, Figure 1A schematic diagram of a method for preparing a flexible strain sensor provided in one embodiment of the present invention.

[0039] The preparation method comprises the following steps:

[0040] S1: providing a first functional filler, a first polymer material and an aggregation-assisting medium, and adding the first functional filler and the first polymer material into the aggregation-assisting medium to form a first mixed solution;

[0041] S2: providing a second functional filler, a second polymer material and an auxiliary dispersion medium, and adding the second functional filler and the second polymer material to the auxiliary dispersion medium to form a second mixed solution;

[0042] S3: Provide a substrate, and print and solidify the first mixed solution and the second mixed solution respectively by 3D printing, so that the first mixed solution forms a first functional part on the surface of the substrate, and the second mixed solution forms a second functional part on the surface of the substrate, and a connecting part is formed at the interface between the first functional part and the second functional part, so as to obtain a flexible strain sensor.

[0043] The functional properties of traditional nanocomposites are mainly determined by the properties of nanofillers. Nanocomposites usually adjust the functional properties by adjusting the doping ratio of nanofillers. This adjustment can change the overall conductivity, strain sensitivity, moisture sensitivity, Young's modulus, tensile elongation at break and other physical properties of the composite material. However, adjusting the doping ratio can only achieve regulation of the functional properties within a limited range and cannot achieve a larger adjustment.

[0044] The preparation method of the present invention can make the first functional filler in the first mixed solution actively aggregated by using an agglomeration-assisting medium, so that the first functional part has higher strain sensitivity, and can make the second functional filler in the second mixed solution monodispersed by using an agglomeration-assisting medium, so that the second functional part has higher conductivity. The present invention adjusts the dispersion morphology of the first functional filler and the second functional filler to achieve a large degree of adjustment of the functional characteristics of the flexible strain sensor, thereby having multifunctional characteristics.

[0045] It can be understood that the greater the difference in dispersion morphology between the first functional filler and the second functional filler, the higher the strain sensitivity and the higher the conductivity of the manufactured flexible strain sensor.

[0046] The active agglomeration state referred to in this article means that the first functional filler in the first mixed solution presents multiple stable agglomeration cluster structures under the action of the agglomeration-aiding medium, and the multiple agglomeration cluster structures are diffusely distributed in the first mixed solution. This actively agglomerated cluster structure is different from the whole cluster structure under the action of electrostatic adsorption force.

[0047] When traditional components with different functional characteristics are integrated into a sensor, it is difficult to fuse the interfaces due to the different inherent physicochemical properties (chemical polarity, surface energy, surface charge, work function and energy band, etc.) of the component materials. Even if materials with different physicochemical properties can be fused with each other, the bonding strength and ohmic contact at the connection interface will inevitably be weakened, thus causing interface strength and impedance problems.

[0048] Since the agglomeration agent of the present invention is a poor solvent for the first functional filler, and the dispersant is a good solvent for the second functional filler, it is difficult to directly fuse the first mixed solution with the second mixed solution. Therefore, during the preparation of the present invention, the first mixed solution and the second mixed solution are solidified respectively, and the agglomeration medium and the dispersant medium are volatilized, and the polymer chains in the first polymer material and the polymer chains in the second polymer material are entangled with each other at the interface connection part during the solidification process, forming an interlocking effect. At the same time, the polymer chains in the first polymer material and the polymer chains in the second polymer material will move toward each other, and further drive the first functional filler and the second functional filler to approach and penetrate each other at the connection part, thereby reconstructing the interface network of the connection part. In summary, the connection part has good tensile resistance, which ensures the reliability of the flexible strain sensor under tensile deformation.

[0049] In this preferred embodiment, the elongation at break of the flexible strain sensor is greater than or equal to 100%, and the strain sensitivity coefficient is 10-20.

[0050] Generally, the strain sensitivity coefficient is the degree of change in resistance caused by unit strain, which can be expressed as the ratio of the change ratio of resistance to the strain degree, wherein the strain degree is the length change ratio in the stress loading direction. Preferably, the strain sensitivity coefficient of the flexible strain sensor in this embodiment is 15.

[0051] Specifically, in step S1, the first functional filler includes at least one of silver nanowires, copper nanowires, graphene, and carbon black. The first functional filler has good strain sensitivity in an agglomerated state, and the higher the degree of agglomeration, the better the strain sensitivity, and the more accurate the strain sensitivity performance of the formed first functional part.

[0052] The first polymer material includes at least one of styrene-butadiene-styrene block copolymer, polydimethylsiloxane, and copolyester (Ecoflex).

[0053] The agglomeration medium includes at least one of benzene, toluene, xylene, tetrahydrofuran, chloroform and dimethyl sulfoxide. These agglomeration mediums are poor solvents for the first functional filler and good solvents for the first polymer material. The first functional filler is in a relatively stable active agglomeration state under the action of the agglomeration medium.

[0054] Furthermore, if the mass fraction of the first functional filler in the first functional portion is too high, it will affect the signal monitoring accuracy, strain sensitivity and tensile properties of the formed first functional portion, so the mass fraction of the first functional filler in the first functional portion is 5%-35%.

[0055] Preferably, the mass fraction of the first functional filler in the first functional part is 5%-15%.

[0056] Furthermore, the mass fraction of the first polymer material in the first mixed solution is 0.05 g / mL-0.2 g / mL.

[0057] Furthermore, in the step of adding the first functional filler and the first polymer material to the agglomeration-aiding medium to form a first mixed solution, a first dispersion is performed by a non-invasive homogenizer. In this way, the first functional filler in an actively agglomerated state can be made more uniform and stable in the first mixed solution, and deagglomeration or further agglomeration will not occur, thereby making the performance of the formed first functional part more stable and reliable.

[0058] Specifically, the first dispersion is preferably a two-stage dispersion: the initial dispersion parameter is 100rpm-500rpm, the dispersion times are 1-2 times, each time 5s-15s; 500rpm-1000rpm, the dispersion times are 1-2 times, each time 5s-15s; 1000rpm-2500rpm, the dispersion times are 1-2 times, each time 10s-30s; 2500rpm-3600rpm, the dispersion times are 1-2 times, each time 10s-30s, the above speed is the revolution speed, the rotation speed is 30%-80% of the revolution speed, and remains fixed. The final dispersion parameter is 1000rpm-2000rpm, the dispersion times are 1-2 times, each time 10s-30s; 2000rpm-3600rpm, the dispersion times are 3-6 times, each time 30s-60s. The multi-stage and multi-dispersion can make the agglomerated first functional filler dispersed more evenly in the first polymer material without destroying the agglomerated state.

[0059] Furthermore, in step S2, the second functional filler includes at least one of silver nanowires, copper nanowires, graphene, and carbon black; these functional fillers have good conductivity in a monodisperse state, and the higher the degree of monodispersity, the better the conductivity, and the smaller the resistance of the formed second functional part.

[0060] The second polymer material includes at least one of styrene-butadiene-styrene block copolymer, polydimethylsiloxane, and copolyester (Ecoflex).

[0061] The auxiliary dispersion medium includes at least one of polyvinyl pyrrolidone, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecylamine, Triton, alkyl cellulose, and polyacrylic acid. These auxiliary dispersion mediums are good solvents for the second functional filler and the second polymer material. The second functional filler is in a relatively stable monodisperse state under the action of the auxiliary dispersion medium.

[0062] Considering that if the mass fraction of the second functional filler in the second functional part is too low, it will affect the conductive properties and Young's modulus of the formed second functional part, the mass fraction of the second functional filler in the second functional part is 1%-60%.

[0063] Preferably, the mass fraction of the second functional filler in the second functional part is 30%-50%.

[0064] Furthermore, the mass fraction of the second polymer material in the second mixed solution is 0.05 g / mL-0.2 g / mL.

[0065] It can be understood that in this embodiment, the mass fraction of the first functional filler in the first functional part and the mass fraction of the second functional filler in the second functional part are the same, that is, a large range of performance adjustment is achieved under the same filling mass fraction. In other embodiments, the mass fraction of the first functional filler in the first functional part and the mass fraction of the second functional filler in the second functional part can also be adaptively adjusted according to the morphology of the functional filler or actual use needs, so that the range of performance adjustment can be increased on the original basis.

[0066] Furthermore, in the step of adding the second functional filler and the second polymer material to the auxiliary dispersion medium to form the second mixed solution, a three-roll homogenizer is used for second dispersion. In this way, the second functional filler in a monodispersed state can be made more uniform and stable in the second mixed solution, and microagglomeration or local agglomeration will not occur, thereby making the performance of the formed second functional part more stable and reliable.

[0067] Specifically, the second dispersion is preferably a two-roll pass: first, the distance between the two rollers is adjusted to 10μm-20μm, the distance between the rollers is adjusted to 5μm-15μm, and the rollers are passed 1-4 times; then the distance between the two rollers is adjusted to 5μm-15μm, the distance between the rollers is adjusted to 2μm-10μm, and the rollers are passed 1-3 times. With the distance between the two rollers gradually reduced, multiple roller passes can further improve the monodispersity of the second functional filler.

[0068] It can be understood that the present invention only provides limited examples of the first functional filler and the second functional filler. In addition to the above-mentioned nanofillers with good conductive properties, the first functional filler and the second functional filler can also be nanofillers with other properties, such as nanofillers with magnetic conductivity and thermal conductivity. These nanofillers can all be used to adjust the performance of the flexible strain sensor through the preparation method of the present invention, and are all within the protection scope of the present invention.

[0069] Furthermore, in the preparation method provided by the present invention, the components of the first functional filler and the second functional filler may be the same or different; the components of the first polymer material and the second polymer material may be the same or different.

[0070] In one embodiment, the first functional filler and the second functional filler have the same composition and similar physical and chemical properties, so the first mixed solution and the second mixed solution will have a lower interface impedance at the mixed interface, specifically, when the vibration frequency of the strain signal is 0-1MHz, the AC impedance of the connection part is less than 0.5% of the DC resistance value. The AC impedance value corresponds to the imaginary part in the impedance spectrum, and the DC resistance corresponds to the real part in the impedance spectrum.

[0071] In one embodiment, the first polymer material and the second polymer material have the same composition, so the first mixed solution and the second mixed solution will form a good mixture at the mixing interface, so that the connecting portion has a higher interface connection strength, specifically, the Young's modulus of the connecting portion is greater than or equal to 100 MPa, preferably, the Young's modulus of the connecting portion is greater than or equal to 700 MPa.

[0072] In one embodiment, the first functional filler and the second functional filler have the same composition, and the first polymer material and the second polymer material have the same composition, so the first mixed solution and the second mixed solution not only have a lower interfacial impedance at the mixing interface but also can form a good mix, so that the connection portion will have a lower interfacial impedance and a higher Young's modulus.

[0073] Furthermore, step S3 specifically includes:

[0074] S3.1: Provide a printer nozzle and a substrate, wherein the printer nozzle comprises a first nozzle and a second nozzle;

[0075] S3.2: placing the first mixed solution in the first nozzle and the second mixed solution in the second nozzle, and printing the first mixed solution and the second mixed solution on the surface of the substrate respectively through the printer nozzle; and,

[0076] S3.3: The first mixed solution and the second mixed solution after printing are solidified respectively, so that the first mixed solution after printing forms a first functional part on the surface of the substrate, the second mixed solution after printing forms a second functional part on the surface of the substrate, and a connecting part is formed at the interface between the first functional part and the second functional part, so as to obtain a flexible strain sensor.

[0077] In step S3.1, the printer nozzle can be a pneumatic extrusion type or a screw extrusion type, and the printing pressure of the printer nozzle is 5psi-15psi, and the printing pressure can control the extrusion amount and extrusion speed of the first mixed solution and the second mixed solution.

[0078] In step S3.2, the designed fractal pattern may be printed on the substrate, and the first functional portion and the second functional portion may have specific patterns. Preferably, the material of the substrate includes at least one of glass, silicon wafer, and stainless steel.

[0079] In step S3.3, the curing treatment includes a heating treatment, and the temperature of the heating treatment is 40°C-80°C.

[0080] Under the action of heating treatment, the agglomeration medium in the first mixed solution and the dispersion medium in the second mixed solution will slowly evaporate, and the polymer chains of the first polymer material and the polymer chains of the second polymer material at the interface will entangle with each other to form an interlocking structure. At the same time, the polymer chains of the first polymer material and the second polymer material will move toward each other, further driving the first functional filler and the second functional filler to approach and penetrate each other at the connecting part, thereby reconstructing the interface network of the connecting part and obtaining a flexible strain sensor with a large elongation at break.

[0081] In one embodiment, step S3 further includes:

[0082] S3.4: Transfer the flexible strain sensor to the surface of the medical dressing through the adhesive layer.

[0083] In step S3.4, the adhesive layer may be a water-soluble adhesive tape.

[0084] Specifically, the order of 3D printing is:

[0085] The first mixed solution is printed first, and then the second mixed solution is printed. The mixed solution is then cured by heating to volatilize the agglomeration medium and the dispersion medium, thereby obtaining a first functional part with strain sensitivity and a second functional part with good conductive properties. A connecting part is formed at the interface between the first functional part and the second functional part.

[0086] Small-sized monitors with fractal pattern designs can be quickly obtained through 3D printing, and can be reliably conformed to complex surfaces, thereby achieving accurate measurement of physiological strain signals. The manufacturing pattern can also be customized on demand, and even three-dimensional design can be performed. At the same time, good consistency can be maintained between sensor devices manufactured in multiple batches.

[0087] According to another aspect of the present invention, there is provided a flexible strain sensor prepared by any of the above-mentioned methods, the flexible strain sensor comprising a first functional portion, a second functional portion and a connecting portion, the connecting portion being arranged between the first functional portion and the second functional portion, the elongation at break of the flexible strain sensor being greater than or equal to 100%, and the strain sensitivity coefficient being 10-20.

[0088] Preferably, the strain sensitivity coefficient of the flexible strain sensor is 15.

[0089] Furthermore, the ratio of the strain sensitivity coefficients of the first functional part and the second functional part in the manufactured flexible strain sensor is 3:1-50:1.

[0090] The conductivity ratio of the first functional part to the second functional part is 1:35-1:7000.

[0091] The ratio of Young's modulus of the first functional portion to that of the second functional portion is 2:1-15:1.

[0092] The interface impedance of the connection part is less than 0.5% of the impedance of the flexible strain sensor at a frequency below 1 MHz.

[0093] The Young's modulus of the connecting portion is greater than or equal to 100 MPa. Preferably, the Young's modulus of the connecting portion is greater than or equal to 700 MPa.

[0094] It can be seen that by regulating the dispersion state of the functional filler, a huge performance difference can be generated between the first functional part and the second functional part, thereby greatly adjusting the functional characteristics of the flexible strain sensor; by adjusting the composition of the first functional filler and the second functional filler, the interface impedance of the connecting part can be adjusted; by adjusting the composition of the first polymer material and the second polymer material, the Young's modulus of the connecting part can be adjusted, thus obtaining a flexible strain sensor with multifunctional characteristics, tensile resistance and low interface impedance.

[0095] In addition, it should be noted that all the features and advantages described above for the method for preparing a flexible strain sensor are also applicable to the flexible strain sensor and will not be described in detail here.

[0096] The present invention is described below with reference to specific embodiments, it should be noted that these embodiments are merely illustrative and do not limit the present invention in any way. It is worth mentioning that, where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0097] Embodiment 1:

[0098] (1) The silver nanowires are soaked in a toluene solution and then transferred into a benzene solution of a styrene-butadiene-styrene block copolymer to obtain a first mixed solution.

[0099] The first mixed solution is placed in a non-invasive homogenizer for mixing, and the initial mixing revolution parameters are 500 rpm, the number of dispersions is 1 time, each time for 15 seconds; 1000 rpm, the number of dispersions is 1 time, each time for 15 seconds; 2000 rpm, the number of dispersions is 1 time, each time for 15 seconds; 3000 rpm, the number of dispersions is 1 time, each time for 15 seconds, and the rotation speed is 50% of the revolution speed. The final dispersion parameters are 2000 rpm, the number of dispersions is 2 times, each time for 30 seconds; 3200 rpm, the number of dispersions is 3 times, each time for 30 seconds, and a benzene solution of styrene-butadiene-styrene block copolymer in which silver nanowires are in a stable agglomerated state is obtained.

[0100] The first mixed solution is filled into the first nozzle of the 3D printer.

[0101] (2) The silver nanowires are soaked in a polyvinyl pyrrolidone solution and then transferred into a polyvinyl pyrrolidone solution of styrene-butadiene-styrene block copolymer to obtain a second mixed solution.

[0102] The second mixed solution was placed in a precision three-roll homogenizer for mixing, and the first roller passing parameters were 20 μm between the rollers, 10 μm between the rollers, and 1 roller passing. The second roller passing parameters were 10 μm between the rollers, 5 μm between the rollers, and 2 roller passings, to obtain a polyvinyl pyrrolidone solution of styrene-butadiene-styrene block copolymer in which silver nanowires were in a monodisperse state.

[0103] The second mixed solution is filled into the second nozzle of the 3D printer.

[0104] (3) Then the first nozzle and the second nozzle are installed on a multi-head 3D printer, the working principle of the printer is air pressure extrusion. The pressure is set to 7.5psi. The device is printed on the stainless steel substrate according to the designed fractal pattern.

[0105] The second mixed solution is first printed on a stainless steel substrate, and then the first mixed solution is printed. The mixture is then heated and dried at 70°C to obtain a second functional part with conductive properties, a first functional part with strain-sensitive properties, and a connecting part. The parts are then transferred to a medical dressing using a hydrosol tape to complete the preparation of a flexible physiological strain monitoring device.

[0106] In this embodiment, the mass fraction of silver nanowires in the first functional part is 15%, the mass fraction of silver nanowires in the second functional part is 60%, the mass fraction of styrene-butadiene-styrene block copolymer in the first mixed solution is 0.1 g / mL, and the mass fraction of styrene-butadiene-styrene block copolymer in the second mixed solution is 0.1 g / mL.

[0107] Embodiment 2:

[0108] (1) The copper nanowires are soaked in a dimethyl sulfoxide solution and then transferred into a tetrahydrofuran solution of polydimethylsiloxane to obtain a first mixed solution.

[0109] The first mixed solution is placed in a non-invasive homogenizer for mixing, and the initial mixing revolution parameters are 100 rpm, the dispersion times are 2 times, each time for 10 seconds; 800 rpm, the dispersion times are 2 times, each time for 10 seconds; 1500 rpm, the dispersion times are 1 time, each time for 20 seconds; 3200 rpm, the dispersion times are 1 time, each time for 20 seconds, and the rotation speed is 60% of the revolution speed. The final dispersion parameters are 1800 rpm, the dispersion times are 1 time, each time for 25 seconds; 3000 rpm, the dispersion times are 4 times, each time for 40 seconds, and a tetrahydrofuran solution of polydimethylsiloxane in which copper nanowires are in a stable agglomerated state is obtained.

[0110] The first mixed solution is filled into the first nozzle of the 3D printer.

[0111] (2) The copper nanowires are soaked in a tetrahydrofuran solution, a dispersant alkyl cellulose is added, and then the copper nanowires are transferred into a tetrahydrofuran solution of polydimethylsiloxane to obtain a second mixed solution.

[0112] The second mixed solution was placed in a precision three-roll homogenizer for mixing, and the first roller passing parameters were 15 μm between rollers, 15 μm between rollers, and 2 roller passings. The second roller passing parameters were 15 μm between rollers, 8 μm between rollers, and 1 roller passing, to obtain a sodium dodecyl sulfate solution of polydimethylsiloxane in which copper nanowires were in a monodispersed state.

[0113] The second mixed solution is filled into the second nozzle of the 3D printer.

[0114] (3) Then the first nozzle and the second nozzle are installed on a multi-head 3D printer, the working principle of the printer is air pressure extrusion. The pressure is set to 10 psi. The device is printed on the glass substrate according to the designed fractal pattern.

[0115] The second mixed solution is first printed on a glass substrate, and then the first mixed solution is printed. The mixture is then heated and dried at 60°C to obtain a second functional part with conductive properties, a first functional part with strain-sensitive properties, and a connecting part. The parts are then transferred to a medical dressing using a hydrosol tape to complete the preparation of a flexible physiological strain monitoring device.

[0116] In this embodiment, the mass fraction of copper nanowires in the first functional part is 25%, the mass fraction of copper nanowires in the second functional part is 60%, the mass fraction of polydimethylsiloxane in the first mixed solution is 0.05 g / mL, and the mass fraction of polydimethylsiloxane in the second mixed solution is 0.05 g / mL.

[0117] Embodiment 3:

[0118] (1) Carbon black is impregnated with a chloroform and dimethyl sulfoxide solution, and then transferred into a chloroform and dimethyl sulfoxide solution of polydimethylsiloxane to obtain a first mixed solution.

[0119] The first mixed solution is placed in a non-invasive homogenizer for mixing, and the initial mixing revolution parameters are 500 rpm, the number of dispersions is 1 time, each time for 15 seconds; 500 rpm, the number of dispersions is 2 times, each time for 15 seconds; 1000 rpm, the number of dispersions is 2 times, each time for 30 seconds; 2500 rpm, the number of dispersions is 2 times, each time for 30 seconds, and the rotation speed is 80% of the revolution speed. The final dispersion parameters are 1000 rpm, the number of dispersions is 2 times, each time for 30 seconds; 2000 rpm, the number of dispersions is 6 times, each time for 60 seconds, and a chloroform and dimethyl sulfoxide solution of phenyl polydimethylsiloxane in which carbon black is in a stable agglomerated state is obtained.

[0120] The first mixed solution is filled into the first nozzle of the 3D printer.

[0121] (2) The carbon black is impregnated with an alkyl cellulose and polyacrylic acid solution, and then transferred into an alkyl cellulose and Triton solution of polydimethylsiloxane to obtain a second mixed solution.

[0122] The second mixed solution was placed in a precision three-roll homogenizer for mixing, and the first roller passing parameters were 10 μm between rollers, 5 μm between rollers, and 4 times of passing the rollers. The second roller passing parameters were 5 μm between rollers, 10 μm between rollers, and 1 time of passing the rollers to obtain an alkyl cellulose and triton solution of polydimethylsiloxane in which carbon black was in a monodispersed state.

[0123] The second mixed solution is filled into the second nozzle of the 3D printer.

[0124] (3) Then the first nozzle and the second nozzle are installed on a multi-head 3D printer, the working principle of the printer is air pressure extrusion. The pressure is set to 15psi. The device is printed on the stainless steel substrate according to the designed fractal pattern.

[0125] The second mixed solution is first printed on a stainless steel substrate, and then the first mixed solution is printed. The mixture is then heated and dried at 80°C to obtain a second functional part with conductive properties, a first functional part with strain-sensitive properties, and a connecting part. The parts are then transferred to a medical dressing using a hydrosol tape to complete the preparation of a flexible physiological strain monitoring device.

[0126] In this embodiment, the mass fraction of carbon black in the first functional part is 5%, the mass fraction of carbon black in the second functional part is 25%, the mass fraction of polydimethylsiloxane in the first mixed solution is 0.2 g / mL, and the mass fraction of polydimethylsiloxane in the second mixed solution is 0.2 g / mL.

[0127] Embodiment 4:

[0128] This embodiment is basically the same as Embodiment 1, except that the second functional filler in the second mixed solution is copper nanowires.

[0129] Embodiment 5:

[0130] This embodiment is basically the same as the embodiment 1, except that the second polymer material in the second mixed solution is polydimethylsiloxane.

[0131] Embodiment 6:

[0132] This embodiment is substantially the same as the embodiment 1, except that the mass fraction of the second functional filler in the second functional part is 0.1%.

[0133] Embodiment 7:

[0134] This embodiment is substantially the same as the embodiment 1, except that the mass fraction of the second functional filler in the second functional part is 70%.

[0135] Comparative Example 1:

[0136] This embodiment is basically the same as the embodiment 1, except that: the first mixed solution does not use an agglomeration agent, and the solvent in the first mixed solution is ethanol.

[0137] Comparative Example 2:

[0138] This embodiment is basically the same as Embodiment 1, except that the first mixed solution is not mixed in a non-invasive homogenizer.

[0139] Comparative Example 3:

[0140] This embodiment is substantially the same as the embodiment 1, except that the mass fraction of the first functional filler is 40%, and the mass fraction of the second functional filler is 65%.

[0141] The elongation at break, strain sensitivity coefficient and conductivity of the flexible strain sensors prepared in the above-mentioned Examples 1 to 7 and Comparative Examples 1 to 3 were tested. The test results show that the flexible strain sensors prepared in Examples 1 to 7 of the present invention have high elongation at break, high conductivity and strain sensitivity, and the connecting portion has low interfacial impedance and high Young's modulus; however, since the first mixed solution of Comparative Example 1 does not use an agglomeration aid, the strain sensitivity of the flexible strain sensor is poor, which leads to poor accuracy of signal detection; since the first mixed solution of Comparative Example 2 is not mixed using a non-invasive homogenizer, the first functional filler in the first mixed solution in an actively agglomerated form is unevenly distributed, resulting in large differences in the agglomeration form of the first functional filler, which also leads to poor strain sensitivity of the flexible strain sensor, which leads to poor accuracy of signal detection; the mass fractions of the first functional filler and the second functional filler in Comparative Example 3 are relatively high, which not only affects the signal monitoring accuracy, strain sensitivity and tensile properties of the first functional portion, but also makes the mixing of the connecting portion more difficult, so that the Young's modulus is lower.

[0142] The first functional part and the second functional part of the flexible strain sensor prepared in Example 2 were scanned by SEM electron microscope. The second functional filler in the second functional part was in a monodisperse state. Figure 3 The first functional filler in the first functional part is in an active agglomeration state, as shown in FIG. Figure 4 shown.

[0143] The interface impedance test of the connection part of the flexible strain sensor prepared in Example 2 was performed, and the results were as follows: Figure 5 shown.

[0144] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0145] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a flexible strain sensor, characterized in that: The following steps are involved: Providing a first functional filler, a first polymer material and an agglomeration medium, adding the first functional filler and the first polymer material to the agglomeration medium to form a first mixed solution, wherein the agglomeration agent is a poor solvent for the first functional filler, and the agglomeration medium includes at least one of benzene, toluene, xylene, tetrahydrofuran, chloroform, and dimethyl sulfoxide; Providing a second functional filler, a second polymer material and an auxiliary dispersion medium, adding the second functional filler and the second polymer material to the auxiliary dispersion medium to form a second mixed solution, wherein the auxiliary dispersion agent is a good solvent for the second functional filler, and the auxiliary dispersion medium includes at least one of polyvinyl pyrrolidone, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecylamine, Triton, alkyl cellulose, and polyacrylic acid; A substrate is provided, and the first mixed solution and the second mixed solution are respectively printed and cured by 3D printing, so that the first mixed solution forms a first functional part on the surface of the substrate, and the second mixed solution forms a second functional part on the surface of the substrate, and a connecting part is formed at the interface between the first functional part and the second functional part, to obtain the flexible strain sensor, wherein the curing treatment includes a heating treatment.

2. The method for preparing the flexible strain sensor according to claim 1, characterized in that: The elongation at break of the flexible strain sensor is greater than or equal to 100%, and the strain sensitivity coefficient is 10-20.

3. The method for preparing the flexible strain sensor according to claim 1, characterized in that: The first functional filler and the second functional filler have the same composition, and when the vibration frequency of the strain signal is 0-1 MHz, the AC impedance of the connecting portion is less than 0.5% of the DC resistance value.

4. The method for preparing a flexible strain sensor according to claim 1, characterized in that: The first polymer material and the second polymer material have the same composition, and the Young's modulus of the connecting portion is greater than or equal to 100 MPa.

5. The method for preparing a flexible strain sensor according to claim 1, characterized in that: The first functional filler includes at least one of silver nanowires, copper nanowires, graphene, and carbon black; And / or, the second functional filler includes at least one of silver nanowires, copper nanowires, graphene, and carbon black; And / or, the first polymer material includes at least one of styrene-butadiene-styrene block copolymer, polydimethylsiloxane, and copolyester (Ecoflex); And / or, the second polymer material includes at least one of styrene-butadiene-styrene block copolymer, polydimethylsiloxane, and copolyester (Ecoflex).

6. The method for preparing a flexible strain sensor according to claim 1, characterized in that: The mass fraction of the first functional filler in the first functional part is 5%-35%; And / or, the mass fraction of the second functional filler in the second functional part is 1%-60%.

7. The method for preparing a flexible strain sensor according to claim 1, characterized in that: In the step of adding the first functional filler and the first polymer material into the agglomeration aid medium to form a first mixed solution, a first dispersion is performed by a non-invasive homogenizer.

8. The method for preparing a flexible strain sensor according to claim 1, characterized in that: In the step of adding the second functional filler and the second polymer material into the auxiliary dispersion medium to form a second mixed solution, a third roller homogenizer is used for second dispersion.

9. The method for preparing a flexible strain sensor according to claim 1, characterized in that: The pressure value of the 3D printing is 5psi-15psi; And / or, the temperature of the heating treatment is 40°C-80°C.

10. A flexible strain sensor obtained by the preparation method according to any one of claims 1 to 9, characterized in that: The flexible strain sensor includes a first functional portion, a second functional portion, and a connecting portion, wherein the connecting portion is disposed between the first functional portion and the second functional portion.

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