Sensitive film, sensitive film assembly, method for manufacturing the same, and resistive strain sensor

Abstract

The application belongs to the field of strain sensors, and particularly relates to a sensitive film, a sensitive film assembly, a preparation method thereof and a resistance strain sensor, and a preparation method of a strain sensitive film, which comprises the following steps: uniformly mixing a polymer prepolymer, a curing agent, a solvent and a one-dimensional conductive material to obtain a mixed solution, spacing two conductive tapes on a substrate, connecting the two conductive tapes with a signal generator, placing the mixed solution on the substrate, and locating the mixed solution between the two conductive tapes, and starting the signal generator, under the action of an electric field, the one-dimensional conductive material is arranged in a direction, and after first curing, a strain sensitive film is obtained, the waveform of the signal generator is a sine wave, the sensitive film has high direction selectivity, can distinguish stretching in different directions, the strain signal is highly directional, and the cross talk that may occur in a traditional flexible strain sensor under a multi-directional force field is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of strain sensor technology, specifically relating to a sensitive membrane, a sensitive membrane assembly and its preparation method, and a resistive strain sensor. Background Technology

[0002] Flexible strain sensors are functional devices that convert mechanical deformations such as tension, bending, or torsion into electrical signal outputs. Compared with traditional rigid strain detection elements, flexible strain sensors have good compliance, stretchability, and the ability to conform to complex curved surfaces. They can achieve stable signal monitoring under large deformation conditions, thus showing broad application prospects in fields such as human motion monitoring, health monitoring, electronic skin, wearable devices, and soft robots. Currently, flexible strain sensors are mainly classified into resistive, capacitive, piezoelectric, triboelectric, and optical types according to their different signal conversion mechanisms. Among them, capacitive strain sensors usually detect strain by changing capacitance due to changes in the distance or effective area between electrodes, but their structure usually relies on multi-layer electrode structures, making device fabrication relatively complex and susceptible to environmental noise. Piezoelectric sensors rely on the charge signal generated by piezoelectric materials when subjected to force. Although the response speed is fast, they can usually only detect dynamic strain and are difficult to achieve continuous monitoring of static strain. Triboelectric sensors rely on the contact-separation between materials to generate electrical signals, and their output signal is closely related to the contact conditions, resulting in relatively low stability. In contrast, resistive flexible strain sensors achieve signal output by causing resistance changes in a conductive network under strain, which results in structural changes. They have advantages such as simple structure, direct signal reading, stable response, and ease of large-area fabrication. Therefore, they have become the most widely researched and applied type of sensor in the field of flexible strain sensing.

[0003] Resistive flexible strain sensors typically employ the introduction of conductive fillers into an elastic polymer matrix to construct a conductive network within the material, enabling effective detection of strain signals while maintaining material flexibility. Although this technology achieves flexible strain detection, current sensors struggle to distinguish strain signals from different directions, leading to signal crosstalk. Particularly in multi-axis deformation or complex force field monitoring applications, the superposition of strain signals from various directions reduces the sensor's orientation recognition capability and measurement accuracy, limiting its application in fields such as electronic skin and multi-dimensional deformation monitoring.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing resistive flexible strain sensors, such as difficulty in distinguishing strain signals in different directions and susceptibility to signal crosstalk. This invention provides a sensitive membrane, a sensitive membrane assembly, a method for preparing the same, and a resistive strain sensor with high directional selectivity, capable of distinguishing tension in different directions, and highly directional strain signals, significantly improving the crosstalk that may occur in traditional flexible strain sensors under multi-directional force fields.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a strain-sensitive membrane, comprising: uniformly mixing a polymer prepolymer, a curing agent, a solvent, and a one-dimensional conductive material to obtain a mixture; spaced two conductive tapes on a substrate; connecting the two conductive tapes to a signal generator; placing the mixture on the substrate, with the mixture positioned between the two conductive tapes; turning on the signal generator; and under the action of an electric field, oriented the one-dimensional conductive material; and performing a first curing to obtain the strain-sensitive membrane, wherein the waveform of the signal generator is a sine wave.

[0007] In some preferred embodiments, the voltage of the sine wave is 10V~20V and the frequency is 80Hz~120Hz. A signal amplifier is connected between the conductive tape and the signal generator, and the amplification factor of the signal amplifier is 80 times~120 times.

[0008] In some preferred embodiments, the concentration of the polymer prepolymer in the mixture is 20wt% to 28wt%, the concentration of the solvent is 65wt% to 75wt%, and the concentration of the one-dimensional conductive material is 1wt% to 3wt%.

[0009] In some preferred embodiments, the aspect ratio of the one-dimensional conductive material is 100 to 1000, the length is 1 μm to 5 μm, and the dynamic viscosity of the polymer prepolymer at 25 °C is 3200 mPa·s to 4200 mPa·s.

[0010] In some preferred embodiments, the thickness of the conductive tape is 200μm to 800μm.

[0011] In some preferred embodiments, the one-dimensional conductive material includes at least one of carbon nanotubes, carbon nanofibers, conductive polymer nanofibers, and conductive metal nanowires, wherein the polymer includes at least one of thermoplastic polyurethane, polydimethylsiloxane derivatives, and styrene-ethylene-butene-styrene block copolymers, and the solvent includes at least one of n-hexane, toluene, cyclohexane, tetrahydrofuran, and N,N-dimethylformamide.

[0012] Preferably, the one-dimensional conductive material comprises carboxylated carbon nanotubes.

[0013] In some preferred embodiments, the polymer prepolymer, the curing agent, and the solvent are mixed and stirred evenly to obtain a premixed liquid. A one-dimensional conductive material is added to the premixed liquid, and the mixture is ultrasonically mixed evenly to obtain the final mixture. The mixing and stirring time is 7 min to 13 min, and the ultrasonic power is 10% to 20%. The conductive tape is a copper tape; After the first curing, a precursor strain-sensitive membrane is obtained. A layer of encapsulating liquid is coated on the surface of the precursor strain-sensitive membrane, and a second curing is performed to obtain the strain-sensitive membrane. The encapsulating liquid contains the polymer prepolymer and the curing agent.

[0014] Secondly, the present invention provides a strain-sensitive membrane, which is prepared by the strain-sensitive membrane preparation method described in the first aspect.

[0015] Thirdly, the present invention provides a method for preparing a strain-sensitive membrane assembly, wherein at least two strain-sensitive membranes prepared by the method described in the first aspect or the strain-sensitive membranes described in the second aspect are stacked in different directions to obtain the strain-sensitive membrane assembly.

[0016] Fourthly, the present invention provides a strain-sensitive membrane assembly, which is prepared by the strain-sensitive membrane assembly preparation method described in the third aspect.

[0017] Fifthly, the present invention provides a resistive strain sensor, comprising a sensitive layer and electrodes located on both sides of the sensitive layer, wherein the sensitive layer is any one of the strain-sensitive membrane prepared by the method for preparing the strain-sensitive membrane described in the first aspect, the strain-sensitive membrane described in the second aspect, the strain-sensitive membrane assembly prepared by the method for preparing the strain-sensitive membrane assembly described in the third aspect, and the strain-sensitive membrane assembly described in the fourth aspect.

[0018] The mixture of this invention contains a polymer prepolymer, a curing agent, a solvent, and a one-dimensional conductive material. Two conductive tapes are spaced apart on a substrate and connected to a signal generator. The mixture is placed between the two conductive tapes on the substrate. Under the action of a sinusoidal wave generated by the signal generator, a continuous and stable alternating electric field is formed. The one-dimensional conductive material is subjected to relatively stable polarization and orientation, and the one-dimensional conductive material is uniformly aligned along the electric field direction between the two conductive tapes. Curing is performed under the condition of maintaining the sinusoidal alternating electric field. The polymer is cured, and the oriented alignment structure of the formed one-dimensional conductive material is fixed and locked, resulting in a strain-sensitive film with oriented one-dimensional conductive material and oriented conductive pathways. If the waveform of the signal generator of this invention is a square wave or similar, the electric field change is relatively abrupt, which can easily cause disordered oscillation, local migration, and aggregation of the one-dimensional conductive material, leading to uneven arrangement and disordered overlap of the one-dimensional conductive material. The strain-sensitive membrane prepared by the method of this invention has a one-dimensional conductive material oriented to form a directional conductive path. Because the conductive network is highly regular along the electric field direction, when the strain-sensitive membrane is stretched along this direction, the conductive path experiences microscopic fractures or changes in spacing, resulting in a measurable resistance change and achieving a sensitive response to strain. In the orthogonal direction, since the conductive path does not form an effective connection, the resistance value can exceed 3 MΩ, equivalent to a broken circuit, and it is essentially insensitive to strain in that direction. The strain-sensitive membrane prepared by this invention has high directional selectivity, capable of distinguishing between stretching in different directions, and the strain signal is highly directional, significantly improving the crosstalk that may occur in traditional flexible strain sensors under multi-directional force fields. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the strain-sensitive membrane assembly in Embodiment 1 of the present invention.

[0021] Figure 2 This is a schematic diagram of the directional strain sensing principle of the strain-sensitive membrane assembly in Embodiment 1 of the present invention.

[0022] Figure 3 This is a micrograph of the strain-sensitive membrane in Embodiment 1 of the present invention.

[0023] Figure 4 This is a first resistance waveform curve of the strain-sensitive membrane assembly in Embodiment 1 of the present invention.

[0024] Figure 5This is a second resistance waveform curve of the strain-sensitive membrane assembly in Embodiment 1 of the present invention.

[0025] Figure 6 This is a micrograph of the strain-sensitive membrane in Example 7 of the present invention. Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The inventors of this invention have discovered that existing resistive flexible strain sensors have difficulty distinguishing strain signals from different directions and are prone to signal crosstalk.

[0028] In this first aspect, the present invention provides a method for preparing a strain-sensitive membrane, comprising: mixing a polymer prepolymer, a curing agent, a solvent, and a one-dimensional conductive material uniformly to obtain a mixture; placing two conductive tapes spaced apart on a substrate; connecting the two conductive tapes to a signal generator; placing the mixture on the substrate, with the mixture positioned between the two conductive tapes; turning on the signal generator; and under the action of an electric field, oriented the one-dimensional conductive material; and performing a first curing to obtain the strain-sensitive membrane, wherein the waveform of the signal generator is a sine wave.

[0029] The mixture of the present invention contains a polymer prepolymer, a curing agent, a solvent, and a one-dimensional conductive material. Two conductive tapes are spaced apart on a substrate and connected to a signal generator. The mixture is placed between the two conductive tapes on the substrate. Under the action of a sinusoidal wave generated by the signal generator, an electric field with a continuous, smooth, and periodically changing electric field intensity is formed. The one-dimensional conductive material is subjected to relatively continuous polarization and orientation torque, which restricts the continuous migration of the one-dimensional conductive material to one side of the conductive tape and the local deposition near the conductive tape. The one-dimensional conductive material undergoes periodic polarization, rotation, and limited migration. The one-dimensional conductive material is uniformly arranged along the electric field direction between the two conductive tapes, forming a relatively uniform, consistent, and continuous directional conductive network inside the mixture. Curing is performed under the condition of maintaining a sinusoidal alternating electric field. The polymer is cured, and the directional arrangement structure of the formed one-dimensional conductive material is fixed and locked, resulting in a strain-sensitive film with directional conductive pathways and directional arrangement of one-dimensional conductive material. If a square wave or similar wave is used in this invention, the electric field switches rapidly between high and low levels, and the electric field strength changes abruptly at the rising and falling edges. Consequently, the polarization force and orientation torque experienced by the one-dimensional conductive material change discontinuously, which can easily disturb the motion state of the one-dimensional conductive material, causing it to accelerate instantaneously, oscillate repeatedly, and migrate unstablely. This may also exacerbate charge accumulation, local enrichment, and agglomeration of the one-dimensional conductive material near the conductive tape. In a mixed system with a certain viscosity formed by polymers, solvents, and one-dimensional conductive materials, the one-dimensional conductive material is difficult to respond to the abrupt changes in the square wave electric field in a timely and stable manner, and is prone to forming bent, crossed, or disordered overlapping conductive structures. The strain-sensitive membrane prepared by the method of this invention has a one-dimensional conductive material oriented to form a directional conductive path. Because the conductive network is highly regular along the electric field direction, when the strain-sensitive membrane is stretched along this direction, the conductive path experiences microscopic fractures or changes in spacing, resulting in a measurable resistance change and achieving a sensitive response to strain. In the orthogonal direction, since the conductive path does not form an effective connection, the resistance value can exceed 3 MΩ, equivalent to a broken circuit, and it is essentially insensitive to strain in that direction. The strain-sensitive membrane prepared by this invention has high directional selectivity, capable of distinguishing between stretching in different directions. The strain signal is highly directional, significantly improving the crosstalk that may occur in traditional flexible strain sensors under multi-directional force fields. Understandably, the length of the conductive tape is equivalent to the width of the strain-sensitive membrane, the spacing between two conductive tapes is equivalent to the length of the strain-sensitive membrane, and the thickness of the conductive tape is equivalent to the thickness of the strain-sensitive membrane.

[0030] In some preferred embodiments, the voltage of the sine wave is 10V~20V, the frequency is 80Hz~120Hz, and a signal amplifier is connected between the conductive tape and the signal generator, with the signal amplifier having an amplification factor of 80x~120x. In this preferred embodiment, assuming the waveform of the signal generator is a sine wave, a voltage of not less than 10V is more conducive to the one-dimensional conductive material overcoming the viscous resistance of the polymer mixture to rotate, migrate, and overlap, and to forming a directional conductive path extending along the electric field direction. A voltage of not more than 20V is more conducive to avoiding excessively fast migration of the one-dimensional conductive material, leading to enrichment and aggregation near the electrode or in local areas, thus balancing orientation efficiency and uniformity of arrangement, while reducing phenomena such as localized heating of the mixture, uneven solvent evaporation, and abnormal discharge between electrodes. The frequency of the sine wave is no less than 80Hz, allowing the electric field direction to change periodically at a certain speed. This is more conducive to reducing the continuous migration of conductive materials to one side of the electrode, electrode polarization, and local deposition phenomena. The one-dimensional conductive material mainly exhibits periodic polarization and orientation movement, improving the uniformity of the conductive material distribution within the mixture. The frequency is no higher than 120Hz, giving the one-dimensional conductive material sufficient time to respond to the electric field changes in each cycle, which is more conducive to promoting the effective rotation of the one-dimensional conductive material, increasing the average orientation torque on the one-dimensional conductive material, and directional alignment of the one-dimensional conductive material. The amplification factor of the signal amplifier is no less than 80 times, which is more conducive to the orientation of the one-dimensional conductive material, promoting the formation of a directional conductive network, and shortening the orientation time. The amplification factor is no higher than 120 times, which is more conducive to maintaining the stability and repeatability of the electric field action process, reducing the risk of rapid aggregation of one-dimensional conductive materials, local instability of the mixture, abnormal solvent evaporation, and inter-electrode discharge. More preferably, the voltage of the sine wave is 13V~18V, the frequency is 90Hz~110Hz, and the amplification factor of the signal amplifier is 90 times~110 times. This is more conducive to obtaining a strain-sensitive membrane with a more continuous conductive path along the electric field direction and fewer conductive paths in the orthogonal direction, thereby improving the electrical anisotropy, directional selectivity, signal consistency and anti-crosstalk capability of the strain-sensitive membrane.

[0031] In some preferred embodiments, the concentration of the polymer prepolymer in the mixture is 20wt%~28wt%, the concentration of the solvent is 65wt%~75wt%, and the concentration of the one-dimensional conductive material is 1wt%~3wt%. In this preferred embodiment, the voltage based on the sinusoidal wave is 10V~20V, the frequency is 80Hz~120Hz, the amplification factor is 80x~120x, and the concentration of the polymer prepolymer is not less than 20wt%, which is more conducive to forming a continuous and complete polymer matrix during the first curing process, stabilizing and locking the already formed directional conductive network. The concentration is not higher than 28wt%, which is more conducive to reducing the resistance to rotation and migration of the one-dimensional conductive material under the action of the electric field. The sinusoidal alternating electric field effectively drives the one-dimensional conductive material to align along the direction of the electric field, avoiding local agglomeration, uneven arrangement, and inconsistent film thickness of the one-dimensional conductive material. The concentration of one-dimensional conductive material is not less than 1 wt%, which is more conducive to the formation of continuous directional conductive pathways, reducing initial resistance, and improving signal stability and response sensitivity. The concentration is not higher than 3 wt%, which is more conducive to the full rotation and alignment of one-dimensional conductive material under the action of sinusoidal alternating electric field, avoiding the agglomeration of one-dimensional conductive material and the formation of disordered conductive pathways, reducing the formation of orthogonal conductive pathways, and improving the electrical anisotropy and directional selectivity of strain-sensitive film. More preferably, the concentration of polymer prepolymer is 22 wt%~26 wt%, the concentration of solvent is 69 wt%~73 wt%, and the concentration of one-dimensional conductive material is 1.5 wt%~2.5 wt%, which is more conducive to the full rotation, migration and overlap of one-dimensional conductive material before polymer curing, and timely fixation by polymer matrix after the formation of stable directional structure, improving the uniformity and continuity of one-dimensional conductive material arrangement, avoiding local agglomeration and the formation of disordered conductive pathways, and improving the resistance response of strain-sensitive film along the orientation direction and the signal discrimination ability between different directions.

[0032] In some preferred embodiments, the aspect ratio of the one-dimensional conductive material is 100–1000, the length is 1 μm–5 μm, and the dynamic viscosity of the polymer prepolymer at 25 °C is 3200 mPa·s–4200 mPa·s. In this preferred embodiment, an aspect ratio of not less than 100 has several advantages. First, it results in more significant geometric anisotropy and polarization anisotropy, increasing the orientation torque under the aforementioned sinusoidal alternating electric field. This facilitates the one-dimensional conductive material overcoming the viscous resistance of the mixture and rotating along the electric field direction, promoting the directional alignment of the one-dimensional conductive material. Second, it facilitates the overlapping of adjacent one-dimensional conductive materials, forming conductive pathways extending along the electric field direction. An aspect ratio not exceeding 1000 further prevents the one-dimensional conductive materials from entangled during mixing, increasing the viscosity of the mixture and limiting the independent rotation and migration of the one-dimensional conductive material under the alternating electric field, thus preventing the formation of local aggregates or disordered conductive pathways. The length of the one-dimensional conductive material is not less than 1 μm. Under the aforementioned sinusoidal alternating electric field, the polarization response and orientation torque of the one-dimensional conductive material are more significant, and the probability of the one-dimensional conductive materials contacting or overlapping each other is greater. This is more conducive to forming continuous directional conductive pathways within the aforementioned concentration range of the one-dimensional conductive material, reducing initial resistance, and improving strain response sensitivity and stability. The length is not greater than 5 μm. On the one hand, this is more conducive to avoiding the one-dimensional conductive materials from entanglement, bending, and agglomeration during mixing, reducing the spatial and viscous resistance encountered by the one-dimensional conductive materials when rotating in the polymer mixture, and promoting the independent adjustment of orientation of the one-dimensional conductive materials under the aforementioned sinusoidal alternating electric field. On the other hand, it is more conducive to avoiding the disordered cross-connection of one-dimensional conductive materials with multiple adjacent one-dimensional conductive materials at the same time, forming undesirable conductive pathways in the orthogonal direction. The dynamic viscosity of the polymer prepolymer at 25 °C is not less than 3200. The mixed system formed by the polymer and solvent has more suitable viscosity and suspension stability, which is more conducive to avoiding rapid sedimentation, excessive migration or local enrichment of one-dimensional conductive materials near the conductive tape under the action of electric field and the first curing process, forming a directional conductive network. The value is no higher than 4200 mPa·s, which is more conducive to the full rotation, migration and overlap of one-dimensional conductive materials with an aspect ratio of 100 to 1000 and a length of 1 μm to 5 μm under the aforementioned conditions of sinusoidal voltage of 10 V to 20 V, frequency of 80 Hz to 120 Hz and signal amplifier amplification factor of 80 to 120 times, forming a directional continuous conductive network.

[0033] In some preferred embodiments, the thickness of the conductive tape is 200 μm to 800 μm. In this preferred embodiment, a thickness of not less than 200 μm is more conducive to forming a continuous and stable directional conductive path, dispersing the stress on the strain-sensitive film, and improving the tensile strength of the strain-sensitive film. A thickness of not more than 800 μm is more conducive to improving the uniformity of the electric field, viscous resistance, and orientation degree of the one-dimensional conductive material, and preventing defects such as bubbles, pores, and uneven curing in the sensitive film. More preferably, a thickness of 400 μm to 600 μm of conductive tape is more conducive to balancing the uniformity of electric field orientation, the mechanical strength of the film layer, and the strain transfer efficiency.

[0034] This invention does not limit the type of polymer. Any elastic polymer material with good flexibility and stretchability that can form a stable composite structure with conductive fillers can be used as the polymer of this invention. It also does not limit the type of one-dimensional conductive material. Any one-dimensional conductive nanomaterial that can be oriented and form a conductive path under the action of an external electric field can be used as a one-dimensional conductive material.

[0035] In some preferred embodiments, the one-dimensional conductive material includes at least one of carbon nanotubes, carbon nanofibers, conductive polymer nanofibers, and conductive metal nanowires. The polymer includes at least one of thermoplastic polyurethane, polyurethane elastomer, polydimethylsiloxane derivative, and styrene-ethylene-butene-styrene block copolymer. The solvent includes at least one of n-hexane, toluene, cyclohexane, tetrahydrofuran, and N,N-dimethylformamide. More preferably, when the polymer is PDMS, SEBS, etc., the solvent includes at least one of n-hexane, toluene, and cyclohexane; when the polymer is TPU, PU, ​​etc., the solvent includes tetrahydrofuran and / or N,N-dimethylformamide. In this preferred embodiment, using the above-mentioned solvents provides a suitable dielectric environment for the one-dimensional conductive material to polarize, rotate, migrate, and overlap under the action of a sinusoidal alternating electric field, allowing the one-dimensional conductive material to overcome viscous resistance and form a directional conductive path along the electric field direction. Conductive metal nanowires include, for example, silver nanowires, gold nanowires, and copper nanowires.

[0036] Preferably, the one-dimensional conductive material comprises carboxylated carbon nanotubes. This preferred embodiment facilitates the directional alignment of the one-dimensional conductive material.

[0037] In some preferred embodiments, the polymer prepolymer, the curing agent, and the solvent are mixed and stirred evenly to obtain a premixed liquid. A one-dimensional conductive material is added to the premixed liquid, and the mixture is ultrasonically mixed evenly to obtain the final mixture. The mixing and stirring time is 7 min to 13 min, and the ultrasonic power is 10% to 20%. The conductive tape is a copper tape; After the first curing, a precursor strain-sensitive membrane is obtained. A layer of encapsulating liquid is coated on the surface of the precursor strain-sensitive membrane, and a second curing is performed to obtain the strain-sensitive membrane. The encapsulating liquid contains the polymer prepolymer and the curing agent.

[0038] In this preferred embodiment, a mixture of polymer prepolymer and curing agent is coated onto the surface of the precursor strain-sensitive membrane, and a second curing is performed to encapsulate the strain-sensitive membrane, thereby preventing the influence of the external environment.

[0039] Secondly, the present invention provides a strain-sensitive membrane, which is prepared using the strain-sensitive membrane preparation method described in the first aspect. The strain-sensitive membrane of the present invention exhibits high directional selectivity, capable of distinguishing between tension in different directions, and the strain signal is highly directional, significantly improving the crosstalk that may occur in traditional flexible strain sensors under multi-directional force fields.

[0040] Thirdly, the present invention provides a method for preparing a strain-sensitive membrane assembly, wherein at least two strain-sensitive membranes prepared by the method described in the first aspect or the strain-sensitive membranes described in the second aspect are stacked crosswise in different directions to obtain the strain-sensitive membrane assembly. The structure and strain sensing principle of the strain-sensitive membrane assembly are referenced below. Figure 1 and Figure 2 The resistance of the strain-sensitive membrane in each direction is monitored separately. When strain is applied in a certain direction, the resistance of the strain-sensitive membrane in that direction changes, while the resistance of the strain-sensitive membrane in other directions remains almost unchanged. Based on the resistance detection results, the direction of strain can be effectively identified. In some preferred embodiments, two strain-sensitive membranes are orthogonally stacked to form a cross shape, which can detect the force components along the X and Y axes. Understandably, at least two strain-sensitive membranes can be cross-stacked in different directions, coated with a mixture of polymer prepolymer and curing agent, and then cured for encapsulation.

[0041] Fourthly, the present invention provides a strain-sensitive membrane assembly, which is prepared using the strain-sensitive membrane assembly preparation method described in the third aspect. The strain-sensitive membrane assembly of the present invention performs resistance monitoring on the strain-sensitive membrane in each direction, and can effectively identify the direction of strain based on the resistance detection results.

[0042] Fifthly, the present invention provides a resistive strain sensor, comprising a sensitive layer and electrodes located on both sides of the sensitive layer, wherein the sensitive layer is any one of the strain-sensitive membrane prepared by the method for preparing the strain-sensitive membrane described in the first aspect, the strain-sensitive membrane described in the second aspect, the strain-sensitive membrane assembly prepared by the method for preparing the strain-sensitive membrane assembly described in the third aspect, and the strain-sensitive membrane assembly described in the fourth aspect.

[0043] The present invention will be further described in detail below with reference to specific embodiments.

[0044] Example 1 A method for preparing a strain-sensitive membrane, comprising the following steps: Step 1: Mix PDMS prepolymer, curing agent, and n-hexane until homogeneous to obtain a premixed solution. The mixing time is 10 minutes. Add carboxylated CNTs to the premixed solution and ultrasonically mix until homogeneous to obtain a final mixture. The ultrasonic power is 15%. The aspect ratio of the carboxylated CNTs is 100–1000, and the length is approximately 1 μm–5 μm. The dynamic viscosity of the PDMS prepolymer at 25 °C is approximately 3700 mPa·s. The mass of the PDMS prepolymer in the mixture is 5 g, the mass of the curing agent is 0.5 g, the mass of n-hexane is 15 g, and the mass of carboxylated carbon nanotubes is 0.418 g. Two copper adhesive tapes are attached alternately to a pre-prepared acrylic substrate. Wires are led out from the copper adhesive tapes and connected to a signal generator. The thickness of the conductive tapes is 500 μm. Step 2: Drop the mixture from Step 1 between the copper tape electrodes on the substrate, and simultaneously turn on the signal generator. Under the action of the electric field, the carboxylated CNTs are oriented and aligned. The waveform of the signal generator is a sine wave with a voltage of 15V and a frequency of 100Hz. A signal amplifier is connected between the conductive tape and the signal generator, and the amplification factor of the signal amplifier is 100 times. Step 3: After the first curing, the strain-sensitive membrane is obtained.

[0045] A strain-sensitive membrane, prepared using the aforementioned method, comprises an array of carbon nanotubes oriented in the same direction. See attached microstructure. Figure 3 .

[0046] A method for preparing a strain-sensitive membrane module involves cutting the strain-sensitive membrane prepared by the aforementioned method into three strips and stacking them in a cross shape. A layer of PDMS containing a curing agent is coated onto the cross-shaped membrane module, and the module is placed in an oven for curing to obtain a strain-sensitive membrane module. The cut shape is 3 mm long and 0.5 mm wide, and the thickness of the scraper is set to 300 μm.

[0047] A strain-sensitive membrane module, the structure and directional strain sensing principle are described in [reference needed]. Figure 1 and Figure 2 Three strain-sensitive membranes are stacked in a cross-shaped pattern, each containing an array of carbon nanotubes oriented in the same direction. The three membranes are connected to carbon fiber wires via conductive silver paste. Resistance monitoring is performed on each membrane under a 15% cyclic tensile strain applied along the x-axis. The resistance waveforms of the strain-sensitive membranes along the x-axis are shown below. Figure 4 The resistance waveform curve of the strain-sensitive membrane in the y-axis direction can be found in [reference needed]. Figure 5When strain is applied in the x-axis direction, the resistance of the strain-sensitive membrane in the x-axis direction changes linearly, while the resistance of the strain-sensitive membrane in the y-axis direction remains almost unchanged. Based on the resistance detection results, the direction of strain can be effectively identified.

[0048] Example 2 The preparation method was carried out in accordance with Example 1, except that the thickness of the conductive tape in step one was 180 μm.

[0049] Example 3 The preparation method was carried out in accordance with Example 1, except that in step one, the dynamic viscosity of the PDMS prepolymer used at 25 °C was about 5000 mPa·s.

[0050] Example 4 The preparation method was carried out according to Example 1, except that in step one, the length of the carboxylated CNT was approximately 8 μm.

[0051] Example 5 The preparation method was carried out according to Example 1, except that in step one, the mass of the PDMS prepolymer in the mixture was 7 g.

[0052] Example 6 The preparation method was carried out in accordance with Example 1, except that in step one, the mass of carboxylated carbon nanotubes was 0.15 g.

[0053] Example 7 The preparation method was carried out according to Example 1, except that in step two, the voltage of the sine wave was 5 V. See [link to microstructure description]. Figure 6 .

[0054] Example 8 The preparation method was carried out in accordance with Example 1, except that in step two, the frequency of the sine wave was 150 Hz.

[0055] Example 9 The preparation method is the same as in Example 1, except that in step two, the amplification factor of the signal amplifier is 150 times.

[0056] Comparative Example 1 The preparation method is the same as in Example 1, except that in step two, the waveform of the signal generator is a square wave.

[0057] The strain direction selectivity of the strain-sensitive membranes in the above embodiments and comparative examples was characterized, and the characterization results are shown in Table 1. Tensile strain of 15% was applied to the strain-sensitive membrane along both the x-axis and y-axis directions. The relative resistance change rate (ΔR / R0)x of the strain-sensitive membrane when a 15% tensile strain was applied along the x-axis and the relative resistance change rate (ΔR / R0)y of the strain-sensitive membrane when a 15% tensile strain was applied along the y-axis were measured. The ratio of (ΔR / R0)x to (ΔR / R0)y was calculated to obtain the strain direction selectivity coefficient SD. A larger SD indicates a stronger strain response along the x-axis relative to the strain response along the y-axis, and better strain direction selectivity of the strain-sensitive membrane.

[0058] Table 1

[0059] Comparing Examples 1 and 2, the thickness of the conductive tape is not less than 200 μm. The one-dimensional conductive material exhibits better orientation in the X-axis direction, forming a continuous and stable directional conductive path. It has a stronger strain response in the X-axis direction and a weaker strain response in the Y-axis direction, which is more conducive to improving strain direction selectivity and reducing crosstalk between different directions. Comparing Examples 1 and 3, the dynamic viscosity of the polymer prepolymer at 25 °C is not higher than 4200 mPa·s, which is more conducive to the directional alignment of the one-dimensional conductive material, improving strain direction selectivity and reducing crosstalk between different directions. Comparing Examples 1 and 4, the length of the one-dimensional conductive material is not higher than 5 μm. The concentration of the polymer prepolymer in the mixture is not greater than 28 wt%, which is more conducive to the directional alignment of the one-dimensional conductive material, improving strain direction selectivity and reducing crosstalk between different directions. Comparing Examples 1 and 5, the concentration of the conductive material in the mixture is not less than 1 wt%, which is more conducive to reducing initial resistance and improving response sensitivity. Comparing Examples 1 and 7, the voltage of the sine wave is not less than 10 V, which is more conducive to the directional alignment of the one-dimensional conductive material, improving strain direction selectivity and reducing crosstalk between different directions. Comparing Examples 1 and 8, the frequency of the sine wave is not higher than 120 Hz, which is more conducive to the directional alignment of the one-dimensional conductive material, improving strain direction selectivity and reducing crosstalk between different directions. Comparing Examples 1 and 9, the amplification factor of the signal amplifier is not higher than 120 times, which is more conducive to improving strain direction selectivity and reducing crosstalk between different directions.

[0060] Compared with Comparative Example 1, the waveform of the signal generator is a sine wave, which can form a network of oriented conductive materials.

[0061] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a strain-sensitive membrane, characterized in that, include: A polymer prepolymer, curing agent, solvent, and one-dimensional conductive material are mixed evenly to obtain a mixture. Two conductive tapes are placed at intervals on a substrate. The two conductive tapes are connected to a signal generator. The mixture is placed on the substrate, with the mixture located between the two conductive tapes. The signal generator is turned on. Under the action of an electric field, the one-dimensional conductive material is oriented and aligned. After the first curing, the strain-sensitive film is obtained. The waveform of the signal generator is a sine wave.

2. The method for preparing the strain-sensitive membrane according to claim 1, characterized in that, The voltage of the sine wave is 10V~20V and the frequency is 80Hz~120Hz. A signal amplifier is connected between the conductive tape and the signal generator, and the amplification factor of the signal amplifier is 80 times~120 times.

3. The method for preparing the strain-sensitive membrane according to claim 1 or 2, characterized in that, The concentration of the polymer prepolymer in the mixture is 20wt%~28wt%, the concentration of the solvent is 65wt%~75wt%, and the concentration of the one-dimensional conductive material is 1wt%~3wt%.

4. The method for preparing the strain-sensitive membrane according to claim 1 or 2, characterized in that, The aspect ratio of the one-dimensional conductive material is 100 to 1000, and the length is 1 μm to 5 μm. The dynamic viscosity of the polymer prepolymer at 25 °C is 3200 mPa·s to 4200 mPa·s.

5. The method for preparing the strain-sensitive membrane according to claim 1 or 2, characterized in that, The thickness of the conductive tape is 200μm~800μm.

6. The method for preparing the strain-sensitive membrane according to claim 1, characterized in that, The one-dimensional conductive material includes at least one of carbon nanotubes, carbon nanofibers, conductive polymer nanofibers, and conductive metal nanowires. The polymer includes at least one of thermoplastic polyurethane, polydimethylsiloxane derivatives, and styrene-ethylene-butene-styrene block copolymers. The solvent includes at least one of n-hexane, toluene, cyclohexane, tetrahydrofuran, and N,N-dimethylformamide.

7. The method for preparing the strain-sensitive membrane according to claim 6, characterized in that, The one-dimensional conductive material includes carboxylated carbon nanotubes.

8. The method for preparing the strain-sensitive membrane according to claim 1, characterized in that, The polymer prepolymer, the curing agent, and the solvent are mixed and stirred evenly to obtain a premixed liquid. A one-dimensional conductive material is added to the premixed liquid, and the mixture is ultrasonically mixed evenly to obtain the final mixture. The mixing and stirring time is 7 min to 13 min, and the ultrasonic power is 10% to 20%. The conductive tape is a copper tape; After the first curing, a precursor strain-sensitive membrane is obtained. A layer of encapsulating liquid is coated on the surface of the precursor strain-sensitive membrane, and a second curing is performed to obtain the strain-sensitive membrane. The encapsulating liquid contains the polymer prepolymer and the curing agent.

9. A strain-sensitive membrane, characterized in that, The strain-sensitive membrane was prepared using the method described in any one of claims 1 to 8.

10. A method for preparing a strain-sensitive membrane module, characterized in that, The strain-sensitive membrane assembly is obtained by cross-stacking strain-sensitive membranes prepared by the preparation method of at least two strain-sensitive membranes according to any one of claims 1 to 8 or strain-sensitive membranes according to claim 9 in different directions.

11. A strain-sensitive membrane assembly, characterized in that, It was prepared using the method described in claim 10.

12. A resistive strain sensor, characterized in that, The device includes a sensitive layer and electrodes located on both sides of the sensitive layer. The sensitive layer is any one of the strain-sensitive membrane prepared by the method of preparing the strain-sensitive membrane according to any one of claims 1 to 8, the strain-sensitive membrane according to claim 9, the strain-sensitive membrane assembly prepared by the method of preparing the strain-sensitive membrane assembly according to claim 10, and the strain-sensitive membrane assembly according to claim 11.

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