CN117739798A - Preparation method of flexible resistance type strain sensor, prepared flexible resistance type strain sensor and application of flexible resistance type strain sensor - Google Patents
Preparation method of flexible resistance type strain sensor, prepared flexible resistance type strain sensor and application of flexible resistance type strain sensor Download PDFInfo
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Abstract
The invention relates to the technical field of flexible resistance type strain sensors, and aims to provide a preparation method of a flexible resistance type strain sensor, which aims to solve the defects of poor sensitivity and complex preparation process of the flexible sensor and comprises the following steps: s1, dispersing a metal nanowire solution in a polar solvent to obtain a metal nanowire dispersion liquid; s2, modifying the thiol compound metal nanowire dispersion liquid to prepare modified metal nanowire dispersion liquid; s3, diluting the modified metal nanowire dispersion liquid by using a polar solvent, and separating the polar solvent to enable the modified metal nanowire dispersion liquid to deposit a modified metal nanowire conductive network layer on the substrate; s4, casting the elastic polymer on the substrate treated in the step S3, and separating the substrate; s5, connecting leads to two ends of the modified metal nanowire conductive network layer processed in the step S4 respectively, and obtaining the flexible resistance type strain sensor. It is still another object of the present invention to provide a flexible sensor manufactured by the above manufacturing method.
Description
The invention relates to the technical field of flexible resistance type strain sensors, in particular to a preparation method of a flexible resistance type strain sensor, the prepared flexible resistance type strain sensor and application.
Background
With the development of information technology and the wide application in daily life, man-machine interaction becomes more frequent and deeper. In order to realize more convenient man-machine interaction, wearable equipment based on technologies such as gestures, eye movements, face recognition and the like is vigorously developed. The wearable device can be worn on the body to interact with a user, collect biological signals and sense external environment, so that the wearable device has excellent performance in various use environments such as motion detection, medical monitoring and intelligent robots. The flexible strain sensor is used as an important ring in the wearable equipment, and compared with the traditional rigid sensor, the flexible strain sensor is made of flexible materials, is suitable for the change of different postures, and has more comfortable wearing experience; high sensitivity and can respond to small changes and deformations quickly. Therefore, flexible strain sensors have also received extensive attention and development, and have become a research hotspot in recent years.
The flexible resistance strain sensor with the embedded structure has strong working environment adaptability and simple manufacturing process, and consists of three parts, namely a conductive material, a flexible substrate and an electrode. Common conductive materials are three types, metallic conductive materials, carbon materials, and conductive polymers. Metal conductive materials have received great attention as a class of materials with the best conductivity. Compared with metal conductive materials such as gold, copper and the like, the preparation process of the silver nanowire is simpler and has low cost, various methods such as direct synthesis, deposition method, template method, sol-gel method and the like are included, higher temperature and more complex preparation methods are not needed, and the silver nanowire can be prepared on the flexible substrate by using simple and economic methods such as ink-jet printing and the like to form a conductive network. The silver nanowire has excellent oxidation resistance and can not be used for a long timeIs susceptible to oxidation and corrosion. This allows for a longer service life and stability of the silver nanowire flexible strain sensor; silver nanowire conductive networks generally have the property of being highly transparent. This makes them well suited for applications such as displays, touch screens and optoelectronic devices where transparent conductive properties are required; the silver nanowire has excellent flexibility and bendability, can be perfectly combined with a flexible substrate, and is not easy to break or damage; the silver nanowires have very good electrical conductivity and sensitive response to strain, which makes them suitable for measuring small, subtle or dynamically changing strains. Lin et al used silver nanowire/polydimethylsiloxane sensor prepared by screen printing and vacuum filtration in combination, when the deposition density of silver nanowire was 2.0mg/cm 2 When the conductivity reaches 1.07X 104S/cm, the sensitivity is 9-10 [ Nano Research 15 (5): 4590-4598 ].
Sensitivity is the most important performance index of a strain sensor, and high sensitivity enables the sensor to detect minute deformation or strain, adapt to different shapes and curvatures, be light-weighted and thin-type design, and have high accuracy and reliability, etc. Accordingly, how to increase the sensitivity of the silver nanowire strain sensor has become a serious issue in research. In the sensing mechanism of the flexible resistance type strain sensor, the crack expansion mechanism controls the quantity of conductive paths by controlling cracks passing through a conductive network, so that the resistance of the flexible strain sensor is controlled, and the silver nanowire conductive network can generate and expand cracks when being subjected to excessive stress or strain. The generation of cracks is related to the concentration of internal stress of the material, when the stress exceeds the breaking strength of the silver nanowire material, the cracks start to form and expand, the conductive paths of the silver nanowire conductive network are reduced, and the resistance is increased, so that the aim of improving the sensitivity is fulfilled. In addition, when external stress acts on the silver nanowires, relative displacement occurs between the silver nanowires, and slippage also occurs between the silver nanowire layer and the flexible substrate. The relative displacement causes the silver nanowire layer to deform and plastically deform, thereby changing the shape and structure thereof and achieving the effect of changing the sensitivity of the silver nanowire layer. The traditional method for improving the sensitivity integrates multiple aspects of material selection, preparation process, structure optimization and the like, for example, a high-sensitivity metal nano material is selected, a sensor surface microstructure is optimized and the like, and the method is high in cost and complex in manufacturing process.
The performance of the silver nanowire can be improved by introducing an enhancement mechanism so as to meet the requirements of practical application. Liu et al use a low-cost and multifunctional self-assembled monolayer of thiol compound in combination with silver nanowires, which enhances the stability of silver nanowires while maintaining excellent light transmittance and conductivity properties of silver nanowires themselves, achieves stealth design of electrodes and improves the stability of electrodes [ Nano Research 15 (5): 4552-4562 ].
Disclosure of Invention
One of the purposes of the present invention is to overcome at least one of the above drawbacks of the prior art, and to provide a method for manufacturing a flexible resistive strain sensor, which is used to overcome the drawbacks of the prior art, such as poor sensitivity and complex manufacturing process.
The invention aims to provide a preparation method of a flexible resistance strain sensor, which specifically comprises the following steps:
s1, dispersing a first metal nanowire solution in a polar solvent to obtain a first metal nanowire dispersion liquid;
s2, modifying the first metal nanowire dispersion liquid prepared in the step S1 by using a mercaptan compound to prepare a first modified metal nanowire dispersion liquid;
s3, diluting the first modified metal nanowire dispersion liquid prepared in the step S2 by using a polar solvent, and separating the polar solvent to enable the first modified metal nanowire dispersion liquid to deposit a first modified metal nanowire conductive network layer on a first substrate;
S4, casting a first elastic polymer on the first substrate treated in the step S3, and separating the first substrate after curing treatment so as to transfer the first modified metal nanowire conductive network layer to the first elastic polymer;
s5, connecting the two ends of the first modified metal nanowire conductive network layer processed in the step S4 with first leads respectively to obtain the first flexible resistance type strain sensor.
In the present invention, the thiol compound is generally composed of a thiol functional group (-SH) and an organic functional group, wherein the organic functional group is also called "tail group", and the organic functional group of the thiol compound may be any hydrocarbon chain or ring system, which is linked to a sulfur atom, thus developing a series of thiol compounds having a carbon chain or benzene ring as the organic functional group, such as MPTMS, MBI, MBO, MBT, C, C16, C18, PMTA, etc. The thiol functional group of the thiol compound forms a chemical bond with the noble metal surface, and this chemisorption adsorbs thiol molecules to the noble metal surface, forming a stable structure. Among them, the organofunctional group of the thiol compound is usually a carbon chain, a carbocycle or a benzene ring, has hydrophobicity, and a longer chain and a larger ring can provide more hydrophobic regions, thereby further enhancing hydrophobicity. According to the invention, the metal nanowire is modified by adding the thiol compound, and due to the existence of the hydrophobic functional group, when the thiol compound modified metal nanowire is diluted in the polar solvent, the agglomeration phenomenon of the modified metal nanowire is more obvious, the modified metal nanowire is flocculent, and the modified metal nanowire is tightly combined with the flexible substrate, so that the sensitivity coefficient of the prepared flexible resistance type strain sensor is improved, and the application effect of the flexible resistance type strain sensor in the field of human body motion detection is optimized.
In addition, in order to improve the sensitivity of the strain sensor, the prior art is generally realized by selecting a conductive material with high sensitivity or optimizing the microstructure of the sensor surface, and the like, and has the defects of high cost, complex manufacturing process and the like. In this regard, the thiol compound is used for directly modifying the metal nanowire, so that the performances such as the sensitivity of the metal nanowire conductive network layer can be improved, the manufacturing process of the high-sensitivity strain sensor is greatly simplified, and the thiol compound is low in cost, so that the manufacturing cost of the strain sensor is reduced.
The second object of the present invention is to provide another method for manufacturing a flexible resistive strain sensor, which specifically comprises the following steps:
s01, dispersing a second metal nanowire solution in a polar solvent to obtain a second metal nanowire dispersion liquid;
s02, modifying the second metal nanowire dispersion liquid prepared in the step S01 by adopting a mercaptan compound to prepare a second modified metal nanowire dispersion liquid;
s03, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent for a plurality of times, and separating the polar solvent to enable the second metal nanowire dispersion liquid to be deposited on a second substrate, wherein a layer of unmodified metal nanowire conductive network layer is deposited each time; or, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with a polar solvent for a plurality of times, and separating the polar solvent to enable the second modified metal nanowire dispersion liquid to be deposited on the second substrate, wherein a second modified metal nanowire conductive network layer is deposited each time; wherein, a plurality of layers of unmodified metal nanowire conductive network layers and a plurality of layers of second modified metal nanowire conductive network layers are alternately stacked to construct a composite metal nanowire conductive network layer on the second substrate;
S04, casting a second elastic polymer on the second substrate treated in the step S03, and separating the second substrate after curing treatment so as to transfer the composite metal nanowire conductive network layer to the second elastic polymer;
s05, connecting second leads to two ends of the composite metal nanowire conductive network layer processed in the step S04 respectively, and manufacturing the second flexible resistance type strain sensor.
The flexible resistance type strain sensor with the single-layer modified metal nanowire network layer structure has higher sensitivity compared with the flexible resistance type strain sensor with the single-layer unmodified metal nanowire network layer.
Compared with an unmodified silver nanowire network layer which is uniformly distributed, in the modified metal nanowire network layer, the metal nanowires are agglomerated and distributed in flocculent form, so that when the flexible resistance type strain sensor with the single-layer modified metal nanowire network layer structure is stretched, the crack of the conductive network layer is compared with that of the flexible resistance type strain sensor with the single-layer modified metal nanowire network layer structureThe crack of the flexible resistance type strain sensor of the nanowire network layer is deeper, thicker and thinner, and the conductive path is fewer than that of a single-layer unmodified silver nanowire network layer with shallower, thinner and denser cracks, so that the flexible resistance type strain sensor with the single-layer modified metal nanowire network layer structure has higher resistance change rate, namely higher sensitivity, under the same stretching degree. However, compared with a single-layer unmodified metal nanowire network layer, after the single-layer modified metal nanowire network layer is stretched to a certain extent, the crack in the network layer is too large, so that the conductive path is completely disconnected, the working range of the single-layer modified metal nanowire network layer is lower than that of the single-layer unmodified metal nanowire network layer, and the single-layer modified metal nanowire network layer is poor in recovery performance and poor in stability. Based on the above, the invention designs a multi-layer structure of double layers, interlayers, four layers and the like, wherein the double layers, the interlayers, the four layers and the like are alternately stacked between the unmodified metal nanowire network layer and the modified metal nanowire network layer. Taking a double-layer structure of stacking an unmodified metal nanowire network layer and a modified metal nanowire network layer as an example, two different metal nanowire network layers form a parallel structure, and a resistance parallel formula is adopted The unmodified metal nanowire network layer with lower sensitivity and initial resistance plays a main role in the total resistance, the initial resistance and sensitivity of the modified metal nanowire network layer are higher, the reciprocal of the larger resistance generated after stretching is smaller, the effect is smaller in the total resistance, and the stability and the working range of the flexible resistance type strain sensor are increased. And when the stretching degree is too large, the cracks of the modified metal wire network layer are too large, and after the conductive network fails, the unmodified metal wire network layer can continue to work, which means that a plurality of modified metal nanowire blocks are connected in parallel on the unmodified metal wire network layer, thereby increasing the working range, multi-layer mechanisms such as interlayers, four layers and the like, and the like.
The third object of the present invention is to provide a flexible resistive strain sensor based on the preparation method, which includes the first modified metal nanowire conductive network layer, the first elastic polymer substrate layer and the first lead, wherein the first modified metal nanowire conductive network layer is embedded into the surface of the first elastic polymer substrate layer, two first leads are provided, and the two first leads are respectively connected with two ends of the first modified metal nanowire conductive network layer; or the flexible resistance type strain sensor comprises the composite metal nanowire conductive network layer, the second elastic polymer substrate layer and the second lead, wherein the composite metal nanowire conductive network layer is embedded into the surface of the second elastic polymer substrate layer, two second leads are arranged, and the two second leads are respectively connected with two ends of the composite metal nanowire conductive network layer.
The fourth object of the invention is to provide a flexible resistance type strain sensor manufactured by the manufacturing method or application of the flexible resistance type strain sensor in human body motion detection.
Compared with the prior art, the invention has the beneficial effects that:
(1) The flexible resistance strain sensor prepared by the method has higher sensitivity, simple process and greatly reduced preparation cost;
(2) The flexible resistance type strain sensor prepared by the invention has good performance and can meet the requirements of human motion detection.
Drawings
Fig. 1 is a schematic structural diagram of a flexible resistive strain sensor according to the present invention, wherein fig. 1a is a schematic structural diagram of a flexible resistive strain sensor according to an embodiment of the present invention, and fig. 1b is a schematic structural diagram of a silver nanowire conductive network layer modified by a thiol compound and having a cluster structure with uneven distribution.
Fig. 2 is a microscopic image of a modified silver nanowire layer and an unmodified silver nanowire layer according to the present invention, wherein fig. 2a is a microscopic image of a modified silver nanowire layer having a cluster structure according to an embodiment of the present invention, and fig. 2b is a microscopic image of an unmodified silver nanowire layer uniformly distributed.
Fig. 3 is a schematic view of a modified silver nanowire layer and an unmodified silver nanowire layer according to the present invention, wherein fig. 3a is a schematic view of an unmodified silver nanowire layer uniformly distributed, and fig. 2b is a schematic view of a modified silver nanowire layer having a cluster structure.
Fig. 4 is a low magnification micro image of a modified silver nanowire and an unmodified silver nanowire photographed by a drop coating method, wherein fig. 4a is a micro image of an unmodified silver nanowire, and fig. 4b is a micro image of a modified silver nanowire.
Fig. 5 is a high magnification micro image of a modified silver nanowire and an unmodified silver nanowire photographed by a drop coating method, wherein fig. 5a is a microscopic image of an unmodified silver nanowire, and fig. 5b is a microscopic image of a modified silver nanowire.
Fig. 6 is an optical image of the modified silver nanowires of the present invention after being transferred onto an elastic substrate, wherein fig. 6a and 6b are both optical images of the modified silver nanowires of one embodiment of the present invention transferred onto an elastic substrate by spin coating.
Fig. 7 is a microscopic image of a strain sensor based on an unmodified silver nanowire conductive network layer and a strain sensor based on a modified silver nanowire conductive network layer, wherein fig. 7a is a strain sensor surface based on an uniformly distributed unmodified silver nanowire conductive network layer, and fig. 7b is a strain sensor surface of a modified silver nanowire conductive network layer having a cluster structure modified based on a thiol compound in one of the embodiments of the present invention.
Fig. 8 is a schematic diagram of a preparation flow of a single-layer modified silver nanowire flexible resistive strain sensor in embodiment 1 of the present invention.
FIG. 9 is a graph showing the change in resistance with the change in strain of the MPTMS modified silver nanowire flexible resistance strain sensor of example 1; in FIG. 9a, the solid line is an unmodified silver nanowire, the dotted line is MPTMS concentration 1x10 -3 mol/L modified silver nanowires; MPTMS concentration in FIG. 9b is 0.5X10 -3 mol/L, MPTMS concentration of 1.5x10 in FIG. 9c -3 mol/L。
FIG. 10 is a graph showing the resistance/strain curve of the flexible resistive strain sensor prepared in example 3, wherein FIG. 10c is a cross-sectional view of the flexible resistive strain sensor with double-layered silver nanowires prepared in example 3, wherein the composite metal nanowire conductive network layer is a non-modified silver nanowire conductive network from top to bottomA layer-modified silver nanowire conductive network layer; FIGS. 10a and 10b are graphs of the resistance/strain of the dual-layer silver nanowire flexible resistive strain sensor of different silver nanowire concentrations prepared in example 3; in FIG. 10a, the modified silver nanowire layer concentration was 0.08mg/cm 2 By superposing a layer of 0.8mg/cm concentration on the modified silver nanowire layer 2 Forming a double-layer structure on the unmodified silver nanowire layer; in FIG. 9b, the modified silver nanowire layer concentration was 0.12mg/cm 2 By superposing a layer of 1.2mg/cm concentration on the modified silver nanowire layer 2 The unmodified silver nanowire layer of (2) forms a double-layer structure.
FIG. 11 is a graph of resistance/strain of the flexible resistive strain sensor prepared in example 4, wherein FIG. 11b is a cross-sectional view of the three-layer silver nanowire flexible resistive strain sensor prepared in example 4, wherein the composite metal nanowire conductive network layer is a modified silver nanowire conductive network layer-a non-modified silver nanowire conductive network layer-a modified silver nanowire conductive network layer from top to bottom; FIG. 11a is a graph of resistance/strain of a three-layer silver nanolayer flexible resistive strain sensor prepared in example 4.
Fig. 12 is a resistance/strain graph of the flexible resistive strain sensor prepared in example 5, wherein fig. 12b is a cross-sectional view of the flexible resistive strain sensor of the four-layer silver nanowire prepared in example 5, wherein the composite metal nanowire conductive network layer is a non-modified silver nanowire conductive network layer-a modified silver nanowire conductive network layer from top to bottom; fig. 12a is a graph of the resistance/strain curve of the flexible resistive strain sensor of the four-layer silver nanowires prepared in example 5.
FIG. 13 is a graph showing the resistance/strain curve of the flexible resistive strain sensor prepared in example 6, wherein FIG. 13a is a graph showing the characteristics of a single-layer modified silver nanowire (silver nanowire concentration of 0.8 mg/cm) prepared in example 6 2 ) A resistance/strain graph of a flexible resistive strain sensor; FIG. 13b is a four-layer silver nanowire (two-layer silver nanowire concentration of 0.4 mg/cm) obtained in example 6 2 The concentration of the unmodified silver nanowire and the two-layer silver nanowire is 0.04mg/cm 2 A thiol compound modified silver nanowire).
FIG. 14 is a graph showing the resistance/time of the flexible resistive strain sensor prepared in example 7, wherein FIG. 14a is a graph showing the characteristics of a single-layer modified silver nanowire (silver nanowire concentration of 1.2 mg/cm) prepared in example 7 2 ) A resistance/time graph of a flexible resistive strain sensor; FIG. 14b is a four-layer silver nanowire (two-layer silver nanowire concentration of 0.4 mg/cm) obtained in example 7 2 The concentration of the unmodified silver nanowire and the two-layer silver nanowire is 0.04mg/cm 2 A thiol compound modified silver nanowire).
FIG. 15 is a schematic diagram of a flexible resistive strain sensor with a single modified metal nanowire conductive network layer according to the present invention.
FIG. 16 is a schematic diagram of a flexible resistive strain sensor with a composite metal nanowire conductive network layer according to the present invention.
FIG. 17 is a flowchart illustrating a process for fabricating a flexible resistive strain sensor in accordance with some embodiments of the present invention.
FIG. 18 is a second flowchart of a process for manufacturing a flexible resistive strain sensor according to some embodiments of the present invention.
Reference numerals: a first elastic polymer base layer 1, a first modified metal nanowire conductive network layer 2, a first lead 3, a second elastic polymer base layer 01, a composite metal nanowire conductive network layer 02 and a second lead 03.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the invention. For better illustration of the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the actual product dimensions; it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
As shown in fig. 17, a first object of the present invention is to provide a method for manufacturing a flexible resistive strain sensor, which includes the following steps:
s1, dispersing a first metal nanowire solution in a polar solvent to obtain a first metal nanowire dispersion liquid;
S2, modifying the first metal nanowire dispersion liquid prepared in the step S1 by using a mercaptan compound to prepare a first modified metal nanowire dispersion liquid;
s3, diluting the first modified metal nanowire dispersion liquid prepared in the step S2 by using a polar solvent, and separating the polar solvent to enable the first modified metal nanowire dispersion liquid to deposit a first modified metal nanowire conductive network layer on a first substrate;
s4, casting a first elastic polymer on the first substrate treated in the step S3, and separating the first substrate after curing treatment so as to transfer the first modified metal nanowire conductive network layer to the first elastic polymer;
s5, connecting the two ends of the first modified metal nanowire conductive network layer processed in the step S4 with first leads respectively to obtain the first flexible resistance type strain sensor.
In the present invention, the thiol compound is generally composed of a thiol functional group (-SH) and an organic functional group, wherein the organic functional group is also called "tail group", and the organic functional group of the thiol compound may be any hydrocarbon chain or ring system, which is linked to a sulfur atom, thus developing a series of thiol compounds having a carbon chain or benzene ring as the organic functional group, such as MPTMS, MBI, MBO, MBT, C, C16, C18, PMTA, etc. The thiol functional group of the thiol compound forms a chemical bond with the noble metal surface, and this chemisorption adsorbs thiol molecules to the noble metal surface, forming a stable structure. Among them, the organofunctional group of the thiol compound is usually a carbon chain, a carbocycle or a benzene ring, has hydrophobicity, and a longer chain and a larger ring can provide more hydrophobic regions, thereby further enhancing hydrophobicity. According to the invention, the metal nanowire is modified by adding the thiol compound, and due to the existence of the hydrophobic functional group, when the thiol compound modified metal nanowire is diluted in the polar solvent, the agglomeration phenomenon of the modified metal nanowire is more obvious, the modified metal nanowire is flocculent, and the modified metal nanowire is tightly combined with the flexible substrate, so that the sensitivity coefficient of the prepared flexible resistance type strain sensor is improved, and the application effect of the flexible resistance type strain sensor in the field of human body motion detection is optimized. In addition, compared with the prior art, the sensitivity performance of the strain sensor is improved by selecting high-sensitivity conductive materials or optimizing the surface microstructure of the sensor, and the like, the invention can improve the sensitivity and other performances of the conductive network layer of the metal nanowire by directly modifying the metal nanowire by using the thiol compound, thereby greatly simplifying the manufacturing process of the high-sensitivity strain sensor, and the thiol compound has low cost and can reduce the manufacturing cost of the strain sensor.
In the specific implementation, in step S1, the first metal nanowire solution is one or more of a gold nanowire solution, a silver nanowire solution, and a copper nanowire solution, and more preferably, the first metal nanowire solution is a silver nanowire solution, where the silver nanowire solution is preferably made of silver nanowires with diameters of 10-90 nm.
In step S1 and step S3, in order to obtain a better dispersing effect, the polar solvent is one or more of absolute ethanol, isopropanol, acetone, sunflower alcohol and hexanol.
In step S2, the thiol compound is a compound having the following structure: a hydrophilic structural unit or functional group with a hydrophobic group or carbon-nitrogen chemical bond at one end, and a hydrophobic hydrocarbon chain or cyclic organic group such as methyl, methoxy, butyl, benzene ring, trifluoromethyl, propylene and the like connected to a sulfur atom at the other end; preferably, the mercaptan compound is one or more of dodecyl mercaptan (C12), hexadecyl mercaptan (C16), octadecyl mercaptan (C18), trimethoxy silane (MPTMS), mercaptobenzothiazole (MBT), mercaptobenzimidazole (MBI), mercaptobenzoxazole (MBO), and mercaptophenyl tetrazole (PMTA), wherein the optimal addition concentration of the mercaptan compound is 0.1X10 × -3 mol/L-5×10 -3 mol/L, more preferably, trimethoxysilane (MPTMS) is used as the thiol compound; in order to achieve a better modifying effect, the volume ratio of the first metal nanowire solution to the thiol compound solution is 1000: (0.1-6.25).
In the step S3, the method for separating the metal nanowires from the polar solvent comprises dripping, spin coating, spraying, screen printing and suction filtration; the substrate can specifically select any one of filter paper, glass, plastic and silicon wafer; the first elastic polymer is any one or more of Polydimethylsiloxane (PDMS), polydimethylsiloxane Polyurethane (PU), polypropylene (PP), ecoFlex, dragon Skin, styrene-butadiene-styrene copolymer (SBS) and SEBS.
In step S4, it is preferable to use a heat curing method for curing.
As shown in fig. 18, a second object of the present invention is to provide another method for manufacturing a flexible resistive strain sensor, which includes the following steps:
s01, dispersing a second metal nanowire solution in a polar solvent to obtain a second metal nanowire dispersion liquid;
s02, modifying the second metal nanowire dispersion liquid prepared in the step S01 by adopting a mercaptan compound to prepare a second modified metal nanowire dispersion liquid;
S03, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent for a plurality of times, and separating the polar solvent to enable the second metal nanowire dispersion liquid to be deposited on a second substrate, wherein a layer of unmodified metal nanowire conductive network layer is deposited each time; or, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with a polar solvent for a plurality of times, and separating the polar solvent to enable the second modified metal nanowire dispersion liquid to be deposited on the second substrate, wherein a second modified metal nanowire conductive network layer is deposited each time; wherein, a plurality of layers of unmodified metal nanowire conductive network layers and a plurality of layers of second modified metal nanowire conductive network layers are alternately stacked to construct a composite metal nanowire conductive network layer on the second substrate;
s04, casting a second elastic polymer on the second substrate treated in the step S03, and separating the second substrate after curing treatment so as to transfer the composite metal nanowire conductive network layer to the second elastic polymer;
s05, connecting second leads to two ends of the composite metal nanowire conductive network layer processed in the step S04 respectively, and manufacturing the second flexible resistance type strain sensor.
In the preferred implementation, in the step S01, the second metal nanowire solution is one or more of a gold nanowire solution, a silver nanowire solution and a copper nanowire solution, and more preferably, the second metal nanowire solution is a silver nanowire solution, wherein the silver nanowire solution is preferably prepared by silver nanowires with diameters of 10-90 nm.
In step S01 and step S03, the polar solvent is one or more of absolute ethanol, isopropanol, acetone, sunflower alcohol and hexanol.
In step S02, the thiol compound is a compound having the following structure: a hydrophilic structural unit or functional group with a hydrophobic group or carbon-nitrogen chemical bond at one end, and a hydrophobic hydrocarbon chain or cyclic organic group such as methyl, methoxy, butyl, benzene ring, trifluoromethyl, propylene and the like connected to a sulfur atom at the other end; preferably, the mercaptan compound is one or more of dodecyl mercaptan (C12), hexadecyl mercaptan (C16), octadecyl mercaptan (C18), trimethoxy silane (MPTMS), mercaptobenzothiazole (MBT), mercaptobenzimidazole (MBI), mercaptobenzoxazole (MBO), and mercaptophenyl tetrazole (PMTA), wherein the optimal addition concentration of the mercaptan compound is 0.1X10 × -3 mol/L-5×10 -3 mol/L, more preferably, trimethoxysilane (MPTMS) is used as the thiol compound; in order to achieve a better modifying effect, the volume ratio of the second metal nanowire solution to the thiol compound solution is 1000: (0.1-6.25).
In step S03, the method for separating the metal nanowires from the polar solvent includes dropping, spin coating, spray coating, screen printing, and suction filtration; the substrate can specifically select any one of filter paper, glass, plastic and silicon wafer; the second elastic polymer is any one or more of Polydimethylsiloxane (PDMS), polydimethylsiloxane Polyurethane (PU), polypropylene (PP), ecoFlex, dragon Skin, styrene-butadiene-styrene copolymer (SBS) and SEBS.
In step S04, a heat curing method is preferably used for curing.
In a specific implementation, the composite metal nanowire conductive network layer constructed in the step S03 is required to at least include one unmodified metal nanowire conductive network layer and one modified metal nanowire conductive network layer, and when the composite metal nanowire conductive network layer has more than two metal nanowire layers, the unmodified metal nanowire conductive network layer and the modified metal nanowire conductive network layer are required to be deposited in an alternately stacked manner, so that two adjacent metal nanowire layers necessarily consist of one unmodified metal nanowire conductive network layer and one modified metal nanowire conductive network layer.
In specific implementation, step S03 includes, but is not limited to, the following ways:
s031, firstly, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer A on the second substrate, then uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer A on the unmodified metal nanowire conductive network layer A, and then constructing a composite metal nanowire conductive network layer A on the second substrate; or,
s032, firstly, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with a polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer B on the second substrate, then, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with the polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer B on the second modified metal nanowire conductive network layer B, and then, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer C on the unmodified metal nanowire conductive network layer B, and further, constructing a composite metal nanowire conductive network layer B on the second substrate; or,
S033, firstly, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer C on the second substrate, secondly, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer D on the unmodified metal nanowire conductive network layer C, secondly, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with the polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer D on the second modified metal nanowire conductive network layer D, secondly, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer E on the unmodified metal nanowire conductive network layer D, and further constructing a composite metal nanowire conductive network layer C on the second substrate.
As shown in fig. 15, a third object of the present invention is to provide a flexible resistive strain sensor manufactured by the above manufacturing method, which includes the first modified metal nanowire conductive network layer 2, the first elastic polymer substrate layer 1, and the first lead 3, wherein the first modified metal nanowire conductive network layer 2 is embedded in the surface of the first elastic polymer substrate layer 1, the first lead 3 has two first leads 3, and the two first leads 3 are respectively connected to two ends of the first modified metal nanowire conductive network layer 2;
Alternatively, as shown in fig. 16, the flexible resistive strain sensor includes the composite metal nanowire conductive network layer 02, the second elastic polymer substrate layer 01 and the second lead 03, where the composite metal nanowire conductive network layer 01 is embedded in the surface of the second elastic polymer substrate layer 01, and two second leads 03 are respectively connected to two ends of the composite metal nanowire conductive network layer 02.
In a specific implementation, the composite metal nanowire conductive network layer at least comprises an unmodified metal nanowire conductive network layer and a modified metal nanowire conductive network layer, and when the composite metal nanowire conductive network layer is provided with more than two metal nanowire layers, the unmodified metal nanowire conductive network layer and the modified metal nanowire conductive network layer are required to be deposited in an alternate stacking mode, so that two adjacent metal nanowire layers are necessarily in a structure of the unmodified metal nanowire conductive network layer and the modified metal nanowire conductive network layer.
The present invention will be further specifically described with reference to the following examples.
Example 1
The preparation process of the flexible resistance strain sensor of this embodiment is shown in fig. 8, in which a pipette is used to measure 15000 μl of absolute ethyl alcohol and 3000 μl of silver nanowire solution with a concentration of 8mg/mL and a diameter of 90nm are sequentially added into the same sample bottle, and a mixer is used for 5min, and the mixture is uniformly mixed, so that the silver nanowires are completely dispersed, and a silver nanowire dispersion with a concentration of 1.33mg/mL is prepared.
Dividing the silver nanowire dispersion into four parts, respectively adding 0.6 mu L, 1.25 mu L and 2.5 mu L of MPTMS solution, and uniformly mixing for 5min by using a uniformly mixer to obtain three parts of MPTMS modified silver nanowire dispersion with different concentrations, wherein the MPTMS concentrations are respectively 0.5 multiplied by 10 -3 mol/L、1×10 -3 mol/L、2×10 -3 mol/L, and one part of unmodified silver nanowire dispersion. The concentration of silver nanowires in the four dispersions was 1.33mg/mL.
And cutting the silica gel mold by using a laser cutting machine, wherein the whole silica gel mold is a circular sheet with the diameter of 7cm, and two rectangles with the diameter of 4 multiplied by 28mm are hollowed out in the middle to obtain the silica gel film suction filtration template.
And (3) using a vacuum suction filter, sequentially placing filter paper and a suction filtration template on the filter element, covering a filter cup and clamping. Taking the MPTMS concentration as 1×10 -3 3000 mu L of modified silver nanowire dispersion liquid with mol/L and 10mL of absolute ethyl alcohol are mixed and stirredPouring the mixture into a filter bowl after uniform dispersion, and carrying out suction filtration to obtain filter paper loaded with two rectangular modified silver nanowire conductive network layers with the concentration of 1.2mg/cm, wherein the two rectangular modified silver nanowire conductive network layers are 4 multiplied by 28mm 2 . And storing the rest modified silver nanowire dispersion liquid in a refrigerator.
PDMS10g was taken and mixed with curing agent 10: 1g of curing agent is added in the mass ratio of 1, and the mixture is stirred for 10min by a glass rod and placed in a vacuum drying oven, and defoaming is carried out for 20min until PDMS has no bubbles.
Casting the defoamed PDMS on filter paper loaded with a modified silver nanowire layer, wherein the thickness of the PDMS is 1.5-2mm; the whole was transferred to a hot plate and heated at 80℃for 2h until the PDMS was cured.
After heating, the modified silver nanowire conductive layer is stably combined with PDMS, and the modified silver nanowire layer is completely transferred to the PDMS. Tearing off filter paper, cutting PDMS loaded with the modified silver nanowire layer to a corresponding size, and connecting electrodes at two ends of the modified silver nanowire to obtain the flexible resistance strain sensor, as shown in fig. 1 (a).
The same procedure was followed to prepare a flexible resistive strain sensor based on unmodified silver nanowires with a MPTMS concentration of 0.5X10 -3 mol/L、2×10 -3 A mol/L modified silver nanowire strain sensor. Fig. 2b is a microscopic image of an original silver nanowire layer, silver nanowires are uniformly distributed and have dense conductive networks, and compared with the microscopic image of the modified silver nanowire layer in fig. 2a, the modified silver nanowires are obviously flocculent and have sparse conductive networks.
The samples were tested using a tensile platform and a digital source meter, as shown in fig. 9a, the flexible resistive strain sensor based on the modified silver nanowires has a remarkable effect of improving sensitivity, and the concentration of MPTMS is 1×10 -3 The sensitivity (GF) of the sensor prepared with the modified silver nanowire of mol/L was 94, which is three times higher than that of the unmodified silver nanowire (gf=28).
As shown in fig. 9a, 9b, 9c, as the concentration of MPTMS increases, the sensitivity of the flexible resistive strain sensor based on the modified silver nanowires also increases. MPTMS concentrations were 0.5X10 respectively -3 mol/L、1×10 -3 mol/L、2×10 -3 mol/L, preparedThe sensor sensitivity (GF) was 40, 94, 214, respectively.
The conductive network layer modified by thiol compound from the strain sensor surface of the modified silver nanowire conductive network layer with cluster structure modified by thiol compound in fig. 7b and the strain sensor surface of the unmodified silver nanowire conductive network layer based on uniform distribution in fig. 7a has fewer, deeper and wider cracks, and denser, shallower and narrower cracks of the unmodified silver nanowire layer due to the aggregation structure of silver nano-particles.
Example 2
The preparation process of this example refers to example 1, referring to FIG. 8, a pipette is used to measure 1.5mL of absolute ethyl alcohol, 3000. Mu.L of silver nanowire solution with the concentration of 8mg/mL and the diameter of 90nm is added into the same sample bottle successively, a mixer is used for 5min, and the mixture is uniformly mixed, so that the silver nanowires are completely dispersed, and silver nanowire dispersion with the concentration of 1.33mg/mL is prepared.
The silver nanowire dispersion liquid is divided into three parts, 1.25 mu L of a tri-methoxypropyl trimethyl silane solution (MPTMS), 1.25 mu L of a dodecanethiol (NDM) solution and 1 mu L of di-Mercaptobenzothiazole (MBT) are respectively taken and uniformly mixed by using a mixer for 5min, and three parts of silver nanowire dispersion liquid modified by different thiol compounds are obtained. Wherein the MPTMS, NDM, MBT concentration is 1x10 -3 mol/L。
And cutting the silica gel mold by using a laser cutting machine, wherein the whole silica gel mold is a circular sheet with the diameter of 7cm, and two rectangles with the diameter of 4 multiplied by 28mm are hollowed out in the middle to obtain the silica gel film suction filtration template.
And (3) using a vacuum suction filter, sequentially placing filter paper and a suction filtration template on the filter element, covering a filter cup and clamping. Taking 3000 mu L of MPTMS modified silver nanowire dispersion liquid, mixing and stirring with 10mL of absolute ethyl alcohol, pouring into a filter bowl after uniform dispersion, and carrying out suction filtration to obtain filter paper loaded with two rectangular modified silver nanowire conductive network layers with the concentration of 4 multiplied by 28mm, wherein the concentration of the modified silver nanowire is 1.2mg/cm 2 . And storing the rest modified silver nanowire dispersion liquid in a refrigerator.
PDMS10g was taken and mixed with curing agent 10: 1g of curing agent is added in the mass ratio of 1, and the mixture is stirred for 10min by a glass rod and placed in a vacuum drying oven, and defoaming is carried out for 20min until PDMS has no bubbles.
Casting the defoamed PDMS on filter paper loaded with a modified silver nanowire layer, wherein the thickness of the PDMS is 1.5-2mm; the whole was transferred to a hot plate and heated at 80℃for 2h until the PDMS was cured.
After heating, the modified silver nanowire layer is stably combined with PDMS, and the modified silver nanowire layer is completely transferred to the PDMS. Tearing filter paper, cutting PDMS loaded with the modified silver nanowire layer to a corresponding size, and connecting electrodes at two ends of the modified silver nanowire to obtain the MPTMS modified silver nanowire-based flexible resistance strain sensor.
And repeating the steps to respectively prepare the flexible resistance type strain sensor based on the NDM modified silver nanowire and the flexible resistance type strain sensor based on the MBT modified silver nanowire. Three different thiol compound-modified strain sensors were measured using a tensile bench and a digital source meter, respectively, as shown in Table 1, with silver nanowire layer concentrations of 1.2mg/cm 2 And the concentration of thiol compound is 1x10 -3 mol/L, the initial resistance of the strain sensor using the 3-methoxypropyl trimethylsilane modified silver nanowire is 6.2 omega, and sensitivity GF=93; the strain sensor using the dodecanethiol modified silver nanowire has an initial resistance of 4.4 Ω and a sensitivity gf=62; the strain sensor using the 2-mercaptobenzothiazole modified silver nanowire had an initial resistance of 5.9 Ω and a sensitivity gf=78.
TABLE 1 initial resistance and sensitivity of Flexible resistive Strain sensor based on different thiol Compound modified silver nanowires prepared in example 2 of the present invention
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Example 3
20mL of absolute ethyl alcohol and 4000 mu L of silver nanowire solution with the concentration of 8mg/mL and the diameter of 90nm are measured by using a pipette, sequentially added into the same sample bottle, and uniformly mixed by using a uniformly mixing instrument for 5min, so that silver nanowires are completely dispersed, and silver nanowire dispersion with the concentration of 1.33mg/mL is prepared.
Then the silver nanowire dispersion liquid is divided into two parts, 2.5 mu L of MPTMS solution is added into one part of the silver nanowire dispersion liquid, and the silver nanowire dispersion liquid modified by MPTMS is obtained by uniformly mixing for 5min by using a uniformly mixing instrument, wherein the concentration of the MPTMS is 1 multiplied by 10 -3 mol/L。
And cutting the silica gel mold by using a laser cutting machine, wherein the whole silica gel mold is a circular sheet with the diameter of 7cm, and two rectangles with the diameter of 4 multiplied by 28mm are hollowed out in the middle to obtain the silica gel film suction filtration template.
And (3) using a vacuum suction filter, sequentially placing filter paper and a suction filtration template on the filter element, covering a filter cup and clamping. Taking 3000 mu L of the original silver nanowire dispersion liquid, mixing and stirring with 10mL of absolute ethyl alcohol, pouring into a filter bowl after uniform dispersion, and carrying out suction filtration to obtain filter paper loaded with two rectangular unmodified silver nanowire conductive network layers with the thickness of 4 multiplied by 28mm, wherein the concentration of the unmodified silver nanowire is 1.2mg/cm 2 . The remaining silver nanowire dispersion was stored in a refrigerator.
Standing after suction filtration, collecting 300 μl of the modified silver nanowire dispersion, mixing with 10mL of absolute ethanol, stirring, dispersing uniformly, pouring into a filter bowl, suction filtering, and covering an unmodified silver nanowire conductive network layer with a modified silver nanowire conductive network layer, wherein the concentration of silver nanowire is 0.12mg/cm 2 。
PDMS10g was taken and mixed with curing agent 10: 1g of curing agent is added in the mass ratio of 1, and the mixture is stirred for 10min by a glass rod and placed in a vacuum drying oven, and defoaming is carried out for 20min until PDMS has no bubbles.
Casting the defoamed PDMS on filter paper subjected to suction filtration, wherein the thickness of the PDMS is 1.5-2mm; the whole was transferred to a hot plate and heated at 80℃for 2h until the PDMS was cured.
After heating, the modified silver nanowire is stably combined with PDMS, and the modified silver nanowire layer is completely transferred to the PDMS. Tearing filter paper, cutting PDMS loaded with the modified silver nanowire layer to a corresponding size, and connecting electrodes at two ends of the modified silver nanowire to obtain the double-layer silver nanowire flexible resistance strain sensor.
According to the same procedure, 2000. Mu.L of the original silver nanowire dispersion was taken with 200Preparation of mu L of modified silver nanowire Dispersion with silver nanowire layer concentration of 0.8mg/cm 2 +0.08mg/cm 2 A double silver nanowire layer flexible resistance type strain sensor.
The structure of the prepared double-layer embedded flexible resistance type strain sensor is shown in fig. 10 c. The silver nano sensing layer consists of a layer of uniformly distributed unmodified silver nanowire conductive network layer and a layer of non-uniformly distributed silver nanowire conductive network layer with a cluster structure modified by thiol compound, which are seamlessly and vertically stacked, embedded into an elastic polymer substrate, and the double-layer flexible resistance strain sensor prepared by using a stretching platform and a digital source meter test has the resistance change along with the strain as shown in fig. 10, wherein fig. 10a shows that: the concentration of the unmodified silver nanowire layer is 0.8mg/cm 2 The concentration of the superimposed modified silver nanowire layer is 0.08mg/cm 2 Flexible resistive strain sensor sensitivity gf=145; fig. 10b shows: the concentration of the unmodified silver nanowire layer is 1.2mg/cm 2 The concentration of the superimposed modified silver nanowire layer is 0.12mg/cm 2 Flexible resistive strain sensor sensitivity gf=60.
Example 4
Using a pipette to measure 20000 mu L of absolute ethyl alcohol and 4000 mu L of silver nanowire solution with the concentration of 8mg/mL and the diameter of 90nm, sequentially adding the solution into the same sample bottle, using a mixing instrument for 5min, and uniformly mixing to ensure that the silver nanowires are completely dispersed, thus preparing silver nanowire dispersion with the concentration of 1.33 mg/mL.
Then the silver nanowire dispersion liquid is divided into two parts, 2.5 mu L of MPTMS solution is added into one part of the silver nanowire dispersion liquid, and the silver nanowire dispersion liquid modified by MPTMS is obtained by uniformly mixing for 5min by using a uniformly mixing instrument, wherein the concentration of the MPTMS is 1 multiplied by 10 -3 mol/L。
And cutting the silica gel mold by using a laser cutting machine, wherein the whole silica gel mold is a circular sheet with the diameter of 7cm, and two rectangles with the diameter of 4 multiplied by 28mm are hollowed out in the middle to obtain the silica gel film suction filtration template.
And (3) using a vacuum suction filter, sequentially placing filter paper and a suction filtration template on the filter element, covering a filter cup and clamping. Taking 300 mu L of the modified silver nanowire dispersion liquid, mixing and stirring with 10mL of absolute ethyl alcohol, uniformly dispersing, and pouring into a filter In the cup, suction filtering to obtain filter paper loaded with two rectangular modified silver nanowire conductive network layers with the thickness of 4 multiplied by 28mm, wherein the concentration of the modified silver nanowire is 0.12mg/cm 2 . The remaining silver nanowire dispersion was stored in a refrigerator.
After the suction filtration is finished, 3000 mu L of the unmodified silver nanowire dispersion liquid is taken and mixed with 10mL of absolute ethyl alcohol, the mixture is poured into a filter bowl after being uniformly dispersed, the filter bowl is subjected to suction filtration, a layer of unmodified silver nanowire conductive network layer is covered on the modified silver nanowire conductive network layer to serve as an intermediate layer, and the concentration of silver nanowires in the unmodified silver nanowire conductive network layer is 1.2mg/cm 2 。
Repeating the above steps to obtain 300 μl of modified silver nanowire dispersion, mixing with 10mL of absolute ethanol, stirring, dispersing uniformly, pouring into a filter bowl, suction filtering, covering a layer of modified silver nanowire conductive network layer above the intermediate layer formed by the unmodified silver nanowire conductive network layer, wherein the concentration of silver nanowire in the modified silver nanowire conductive network layer is 0.12mg/cm 2 。
PDMS10g was taken and mixed with curing agent 10: 1g of curing agent is added in the mass ratio of 1, and the mixture is stirred for 10min by a glass rod and placed in a vacuum drying oven, and defoaming is carried out for 20min until PDMS has no bubbles.
Casting the defoamed PDMS on filter paper subjected to suction filtration, wherein the thickness of the PDMS is 1.5-2mm; the whole was transferred to a hot plate and heated at 80℃for 2h until the PDMS was cured.
After heating, the modified silver nanowire is stably combined with PDMS, and the silver nanowire sensing layer is completely transferred to the PDMS. Tearing filter paper, cutting PDMS loaded with a modified silver nanowire layer to a corresponding size, connecting electrodes at two ends of the modified silver nanowire, and preparing the three-layer silver nanowire flexible resistance type strain sensor, wherein the silver nanowire sensing network layer is formed by seamlessly and vertically stacking three silver nanowire conductive network layers, which are not uniformly distributed and have a cluster structure and are modified by two thiol compounds, in a staggered manner, and are embedded into an elastic polymer substrate, as shown in figure 11 b.
The sensor was measured using a tensile stage and a digital source meter, the resistance varied with strain as shown in fig. 11a, and the sensitivity gf=78.
Example 5
And measuring 10mL of absolute ethyl alcohol with a pipette, sequentially adding 4000 mu L of silver nanowire solution with the concentration of 8mg/mL and the diameter of 90nm into the same sample bottle, using a mixing instrument for 5min, and uniformly mixing to ensure that the silver nanowires are completely dispersed, thereby preparing silver nanowire dispersion with the concentration of 1.33 mg/mL.
Then the silver nanowire dispersion liquid is divided into two parts, 2.5 mu L of MPTMS solution is added into one part of the silver nanowire dispersion liquid, and the silver nanowire dispersion liquid modified by MPTMS is obtained by uniformly mixing for 5min by using a uniformly mixing instrument, wherein the concentration of the MPTMS is 1 multiplied by 10 -3 mol/L。
And cutting the silica gel mold by using a laser cutting machine, wherein the whole silica gel mold is a circular sheet with the diameter of 7cm, and two rectangles with the diameter of 4 multiplied by 28mm are hollowed out in the middle to obtain the silica gel film suction filtration template.
And (3) using a vacuum suction filter, sequentially placing filter paper and a suction filtration template on the filter element, covering a filter cup and clamping. Firstly taking 1000 mu L of the unmodified silver nanowire dispersion liquid, mixing and stirring with 10mL of absolute ethyl alcohol, pouring into a filter cup after uniform dispersion, and carrying out suction filtration to obtain filter paper loaded with two rectangular unmodified silver nanowire conductive network layers with the thickness of 4 multiplied by 28mm, wherein the concentration of the unmodified silver nanowire is 0.4mg/cm 2 . The remaining silver nanowire dispersion was stored in a refrigerator.
Standing after suction filtration, mixing 100 μl of the modified silver nanowire dispersion with 10mL of absolute ethanol, stirring, dispersing uniformly, pouring into a filter bowl, suction filtering, covering an unmodified silver nanowire conductive network layer with a modified silver nanowire conductive network layer having silver nanowire concentration of 0.04mg/cm 2 。
Repeating the above steps, mixing 1000 μl of unmodified silver nanowire dispersion with 10mL of absolute ethanol, stirring, dispersing, filtering in a filter bowl, and covering with an unmodified silver nanowire conductive network layer (silver nanowire concentration of 0.4 mg/cm) 2 )。
Repeating the above steps, collecting 100 μl of modified silver nanowire dispersion, mixing with 10mL of absolute ethanol, stirring, and dispersingPouring into a filter bowl, suction filtering, and covering with a modified silver nanowire conductive network layer (silver nanowire concentration is 0.04 mg/cm) 2 )。
PDMS10g was taken and mixed with curing agent 10: 1g of curing agent is added in the mass ratio of 1, and the mixture is stirred for 10min by a glass rod and placed in a vacuum drying oven, and defoaming is carried out for 20min until PDMS has no bubbles.
Casting the defoamed PDMS on filter paper subjected to suction filtration, wherein the thickness of the PDMS is 1.5-2mm; the whole was transferred to a hot plate and heated at 80℃for 2h until the PDMS was cured.
After heating, the modified silver nanowire is stably combined with PDMS, and the silver nanowire sensing layer is completely transferred to the PDMS. Tearing filter paper, cutting PDMS loaded with modified silver nanowire layers to corresponding sizes, connecting electrodes at two ends of the modified silver nanowires, and preparing a four-layer silver nanowire flexible resistance type strain sensor, as shown in fig. 12b, wherein the silver nanowire sensing network layer is formed by vertically stacking four layers of non-uniformly distributed silver nanowire conductive network layers with clustered structures, which are modified by two layers of thiol compounds, and two layers of non-modified uniformly distributed silver nanowire conductive network layers in a seamless and staggered manner, and is embedded into an elastic polymer substrate.
The sensor was measured using a tensile stage and a digital source meter, the resistance varied with strain as shown in fig. 12a, and the sensitivity gf=133.
The invention provides a method for improving the sensitivity of a silver-based nano flexible resistance type strain sensor, which adopts an easily obtained thiol compound to modify silver nanowires, has simple manufacturing process, and particularly has controllable process cost when using MPTMS with low cost as a modifier, and the manufactured flexible resistance type strain sensor has excellent sensitivity. In addition, the silver nanowire conductive material and the elastic polymer have good tensile properties, and can be used for preparing sensors with different shapes and sizes according to specific requirements, so that the silver nanowire conductive material is convenient to apply and high in environment adaptability.
Example 6
This example was used to prepare a monolayer modified silver nanowire (silver nanowire concentration of 0.8 mg/cm) by the preparation method of example 1 2 ) Strain sensor, parameterFour layers of silver nanowires (two-layer silver nanowire concentration of 0.4 mg/cm) were prepared according to the preparation method of example 5 2 The concentration of the unmodified silver nanowire and the two-layer silver nanowire is 0.04mg/cm 2 Thiol compound modified silver nanowires), and the other parameters are consistent except for the concentration of the nanowires in the process of preparing the 2 sensors.
The two strain sensors of this embodiment were tested, and as shown in fig. 13a and 13b, the ultimate elongation of the single-layer modified silver nanowire strain sensor according to the working requirements of this embodiment is 50% -60%, while the ultimate elongation of the four-layer silver nanowire strain sensor according to the working requirements of this embodiment exceeds 100%, and it is apparent that the working range of the four-layer silver nanowire strain sensor is significantly better than that of the single-layer modified silver nanowire strain sensor, and in this embodiment, the concentration of the modified silver nanowire contained in the single-layer modified silver nanowire strain sensor is 0.8mg/cm 2 10 times the total concentration of modified silver nanowires (0.08 mg/cm) in a four-layer silver nanowire strain sensor 2 ) Therefore, the tensile property of the flexible resistance type strain sensor based on the composite metal nanowire conductive network layer (formed by alternately stacking a plurality of layers of modified metal nanowires and a plurality of layers of non-modified metal nanowires) is remarkably improved, and the working range of the flexible resistance type strain sensor can be greatly expanded.
In the invention, taking a double-layer structure of stacking an unmodified metal nanowire network layer and a modified metal nanowire network layer as an example, two different metal nanowire network layers form a parallel structure, and a resistance parallel formula is adopted In the parallel structure, the unmodified metal wire network layer with lower sensitivity and initial resistance plays a main role in the total resistance, the initial resistance and sensitivity of the modified silver nanowire network layer are higher, the reciprocal of the larger resistance generated after stretching is smaller, the effect in the total resistance is smaller, and the stability and the working range of the flexible resistance type strain sensor are increased. And when the stretching amount exceeds the working range of the modified metal nanowire layer,after the conductive network fails, the non-modified metal network layer can continue to work, which is equivalent to connecting a plurality of modified metal nanowire network blocks in parallel on the non-modified metal network layer, thereby increasing the working range, multi-layer mechanisms such as interlayers, four layers and the like, and the like.
Example 7
This example was used to prepare monolayer modified silver nanowires (silver nanowire concentration of 1.2 mg/cm) by the preparation method of example 1 2 ) Strain sensor, four-layered silver nanowire (two-layered silver nanowire concentration of 0.4 mg/cm) was prepared by referring to the preparation method of example 5 2 The concentration of the unmodified silver nanowire and the two-layer silver nanowire is 0.04mg/cm 2 Thiol compound modified silver nanowires), and the other parameters are consistent except for the concentration of the nanowires in the process of preparing the 2 sensors.
The two strain sensors of the embodiment are tested, and as shown in fig. 14a and 14b, the single-layer modified silver nanowire strain sensor of the embodiment has unstable tensile resistance after repeated tensile-recovery test for more than 100 seconds; in the four-layer silver nanowire strain sensor of the embodiment, it is obvious that the four-layer silver nanowire strain sensor still maintains stable resistance change after repeated tensile-recovery tests for more than 16000s, and has excellent resistance stability. In addition, in the present example, the single-layer modified silver nanowire strain sensor contained a modified silver nanowire concentration of 1.2mg/cm 2 15 times the total concentration of modified silver nanowires (0.08 mg/cm) in a four-layer silver nanowire strain sensor 2 ) Therefore, the stability of the flexible resistance type strain sensor based on the composite metal nanowire conductive network layer (formed by alternately stacking a plurality of layers of modified metal nanowires and a plurality of layers of non-modified metal nanowires) is remarkably improved, the working range of the flexible resistance type strain sensor can be greatly prolonged, and the service life of the flexible resistance type strain sensor is prolonged. This is because the single-layer modified metal nanowire network layer, after being stretched to a certain extent, has too large cracks in the network layer, which can lead to complete disconnection of the conductive path and recovery thereof, compared with the single-layer unmodified metal nanowire network layer Poor performance and macroscopically poor stability. Based on the structure, the invention designs a multi-layer structure of double layers, interlayers, four layers and the like, wherein the double layers, interlayers and the four layers are alternately stacked with the modified metal nanowire network layer, when the stretching degree is too large, the crack of the modified metal nanowire network layer is too large, and after the conductive network fails, the unmodified metal nanowire network layer can continue to work, which is equal to connecting a plurality of modified metal wire blocks in parallel on the unmodified metal nanowire network layer, thereby enhancing the stretching resistance, further improving the stability of the flexible resistance type strain sensor, and simultaneously increasing the working range.
It should be understood that the foregoing examples of the present invention are merely illustrative of the present invention and are not intended to limit the present invention to the specific embodiments thereof. Any modification, equivalent replacement, improvement, etc. that comes within the spirit and principle of the claims of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. The preparation method of the flexible resistance type strain sensor is characterized by comprising the following steps of:
s1, dispersing a first metal nanowire solution in a polar solvent to obtain a first metal nanowire dispersion liquid;
S2, modifying the first metal nanowire dispersion liquid prepared in the step S1 by using a mercaptan compound to prepare a first modified metal nanowire dispersion liquid;
s3, diluting the first modified metal nanowire dispersion liquid prepared in the step S2 by using a polar solvent, and separating the polar solvent to enable the first modified metal nanowire dispersion liquid to deposit a first modified metal nanowire conductive network layer on a first substrate;
s4, casting a first elastic polymer on the first substrate treated in the step S3, and separating the first substrate after curing treatment so as to transfer the first modified metal nanowire conductive network layer to the first elastic polymer;
s5, connecting the two ends of the first modified metal nanowire conductive network layer processed in the step S4 with first leads respectively to obtain the first flexible resistance type strain sensor.
2. The preparation method of the flexible resistance type strain sensor is characterized by comprising the following steps of:
s01, dispersing a second metal nanowire solution in a polar solvent to obtain a second metal nanowire dispersion liquid;
s02, modifying the second metal nanowire dispersion liquid prepared in the step S01 by using a mercaptan compound to prepare a second modified metal nanowire dispersion liquid;
S03, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent for a plurality of times, and separating the polar solvent to enable the second metal nanowire dispersion liquid to be deposited on a second substrate, wherein a layer of unmodified metal nanowire conductive network layer is deposited each time; or, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with a polar solvent for a plurality of times, and separating the polar solvent to enable the second modified metal nanowire dispersion liquid to be deposited on the second substrate, wherein a second modified metal nanowire conductive network layer is deposited each time; wherein, a plurality of layers of unmodified metal nanowire conductive network layers and a plurality of layers of second modified metal nanowire conductive network layers are alternately stacked to construct a composite metal nanowire conductive network layer on the second substrate;
s04, casting a second elastic polymer on the second substrate treated in the step S03, and separating the second substrate after curing treatment so as to transfer the composite metal nanowire conductive network layer to the second elastic polymer;
s05, connecting second leads to two ends of the composite metal nanowire conductive network layer processed in the step S04 respectively, and manufacturing the second flexible resistance type strain sensor.
3. The method for manufacturing a flexible resistive strain sensor according to claim 2, wherein in step S03, the specific method for constructing the composite metal nanowire conductive network layer on the second substrate is as follows:
firstly, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer A on the second substrate, and then uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer A on the unmodified metal nanowire conductive network layer A, and further constructing a composite metal nanowire conductive network layer A on the second substrate; or,
firstly, uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with a polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer B on the second substrate, then uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with the polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer B on the second modified metal nanowire conductive network layer B, and then uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer C on the unmodified metal nanowire conductive network layer B, and further constructing a composite metal nanowire conductive network layer B on the second substrate; or,
Firstly, uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with a polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer C on the second substrate, then uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer D on the unmodified metal nanowire conductive network layer C, then uniformly mixing the second metal nanowire dispersion liquid prepared in the step S01 with the polar solvent, separating the polar solvent, depositing a layer of unmodified metal nanowire conductive network layer D on the second modified metal nanowire conductive network layer D, and then, after uniformly mixing the second modified metal nanowire dispersion liquid prepared in the step S02 with the polar solvent, separating the polar solvent, depositing a layer of second modified metal nanowire conductive network layer E on the unmodified metal nanowire conductive network layer D, and further constructing a composite metal nanowire conductive network layer C on the second substrate.
4. A method of manufacturing a flexible resistive strain sensor according to any of claims 1 to 3 wherein the thiol compound is one or more of dodecyl mercaptan, hexadecyl mercaptan, octadecyl mercaptan, trimethoxy silane, mercaptobenzothiazole, mercaptobenzimidazole, mercaptobenzoxazole, mercaptophenyl tetrazole; and/or the concentration of the thiol compound is 0.1X10 -3 mol/L-5×10 -3 mol/L。
5. A method of manufacturing a flexible resistive strain sensor as in any of claims 1-3 wherein the polar solvent is one or more of absolute ethanol, isopropanol, acetone, decanol, hexanol.
6. A method of manufacturing a flexible resistive strain sensor according to any of claims 1 to 3 wherein the volume ratio of the first metal nanowire solution to the thiol compound solution is 1000: (0.1-6.25); and/or the volume ratio of the second metal nanowire solution to the thiol compound solution is 1000: (0.1-6.25).
7. A method of manufacturing a flexible resistive strain sensor according to any of claims 1 to 3 wherein the first metal nanowire solution is one or a combination of more of a gold nanowire solution, a silver nanowire solution, a copper nanowire solution, and/or the metal nanowires in the first metal nanowire solution have a diameter of 10-90nm; and/or the second metal nanowire solution is one or a combination of more of gold nanowire solution, silver nanowire solution and copper nanowire solution, and/or the diameter of the metal nanowire in the second metal nanowire solution is 10-90nm.
8. A method of manufacturing a flexible resistive strain sensor according to any of claims 1 to 3 wherein the first elastomeric polymer is one or more of PDMS, PU, PP, ecoFlex, dragon Skin, SBS, SEBS; and/or the second elastic polymer is one or more of PDMS, PU, PP, ecoFlex, dragon Skin, SBS and SEBS.
9. A flexible resistive strain sensor manufactured by the manufacturing method according to any one of claims 1 to 3 and 5, comprising the first modified metal nanowire conductive network layer, the first elastic polymer substrate layer and the first lead wire, wherein the first modified metal nanowire conductive network layer is embedded in the surface of the first elastic polymer substrate layer, two first lead wires are provided, and the two first lead wires are respectively connected with two ends of the first modified metal nanowire conductive network layer; or the composite metal nanowire conductive network layer, the second elastic polymer substrate layer and the second lead are included, the composite metal nanowire conductive network layer is embedded into the surface of the second elastic polymer substrate layer, two second leads are arranged, and the two second leads are respectively connected with two ends of the composite metal nanowire conductive network layer.
10. Use of a flexible resistive strain sensor manufactured according to the manufacturing method of any one of claims 1-3, 5 or of a flexible resistive strain sensor according to claim 9 for human motion detection.
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