A flexible strain sensor material with high stability of monitoring signal and a preparation method and application thereof

Abstract

The application discloses a flexible strain sensor material with high stability of monitoring signals and a preparation method and application thereof, and the preparation method comprises the following steps: S1, polyvinylpyrrolidone, conductive filler and organic solvent are mixed, the organic solvent is removed by volatilization after being uniformly mixed, and conductive nano filler is obtained; S2, the conductive nano reinforcing filler is mixed with methyl vinyl silicone rubber, nano silicon dioxide, hydroxyl silicone oil, vinyl silicone oil and vulcanizing agent, and mixing is performed to obtain a mixed material; and S3, vulcanization is performed on the mixed material in two stages, the vulcanization temperature in the second stage is 20-30 DEG C higher than that in the first stage, and the flexible strain sensor material is obtained. The flexible strain sensor material with high sensitivity, good mechanical properties and stable monitoring signals is prepared in a high-efficiency, pollution-free and low-cost mode, is suitable for engineering structure health monitoring under size deformation, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rubber materials and strain sensing technology, and particularly relates to a flexible strain sensor material with high stability of monitoring signal and a preparation method and application thereof. BACKGROUND

[0002] During the service process, engineering structures will inevitably be coupled by factors such as load action, environmental corrosion, material aging, fatigue damage, etc., resulting in damage accumulation and resistance attenuation of the structure, which can easily lead to sudden accidents. With the continuous progress of science and technology and the increasing demand for safety in society, engineering structure health monitoring as an important means to ensure the safety of buildings, bridges, aircraft, ships and other structures has become an important research direction in modern engineering technology.

[0003] Earthquake is a natural disaster that seriously threatens human life and property safety, so all countries in the world are working hard to do a good job in engineering earthquake disaster reduction and to improve the seismic fortification level and the seismic capacity of construction projects. The use of seismic mitigation technology and isolation bearings can isolate or consume seismic wave energy, which is the most effective seismic measure at present. Isolation bearing is a device used for building structure isolation, its main function is to reduce the impact of earthquakes on buildings by adding an isolation layer between the foundation and the upper structure of the building. Isolation bearings often work in a high-load environment of "continuous small earthquakes and occasional strong earthquakes", and the bearings are severely damaged and have a short service life. In addition, isolation bearings are mainly made of rubber materials, and the aging and failure of rubber will also accelerate the fatigue and damage of the bearings. It can be said that the service performance of isolation bearings in high-intensity seismic areas directly determines the health status of engineering structures. Therefore, regular detection of isolation bearings is very important to ensure their normal performance. One of the core problems of the structural health monitoring technology of isolation bearings is intelligent sensing technology. The widely used structural health monitoring sensors are mainly made of inorganic non-metallic materials such as fiber Bragg gratings and piezoelectric ceramics. The structure and functional characteristics of rubber isolation bearings determine that the sensing materials must have the characteristics of large deformation, damage resistance, long service life and high sensitivity, and ordinary inorganic non-metallic intelligent materials are not suitable. Therefore, the research and development of new intelligent sensing materials is urgent.

[0004] There are various methods for engineering structure health monitoring, such as sensor monitoring method, acoustic emission monitoring method, non-destructive testing method, image processing monitoring method, data mining and machine learning method, ground monitoring method, ground photogrammetry method, etc. Among the numerous technical means for structural health monitoring, flexible strain sensors have become one of the cores of research due to their high sensitivity, real-time performance, and the ability to effectively reflect the stress state of the structure. Especially in the field of human monitoring and large component monitoring, the application of flexible strain sensors not only provides important support for the maintenance and management of infrastructure, but also provides new ideas for individual health monitoring and industrial safety.

[0005] Common strain sensors include electrical resistance strain gauges, fiber optic grating strain sensors, piezoelectric strain sensors, etc. Traditional strain sensors are susceptible to environmental interference, have low sensitivity, poor stability over a long period of time, poor anti-interference ability, and are difficult to achieve strain monitoring in most structures. In recent years, with the development of material science and nanotechnology, new strain sensors (such as flexible sensors based on carbon nanotubes and conductive polymers) have better sensitivity, response speed, and anti-interference ability, and have gradually been applied in high-precision monitoring fields. Flexible strain sensors output response signals by monitoring changes in electrical properties caused by object deformation. Generally, flexible strain sensors work based on the principle of resistance change. When strain acts on the flexible strain sensor, the geometry of the material changes, such as stretching, which increases the length of the sensor and reduces the cross-sectional area, thereby increasing the resistance; compression is the opposite, and the resistance decreases. The resistance change of the sensor is related to the applied strain in a certain way, and the resistance change is converted into an electrical signal output. This electrical signal can be processed through amplification, filtering, etc. to provide accurate deformation information of the structure.

[0006] However, shoulder peak effect often occurs in the output resistance / response signal of flexible strain sensors. Shoulder peak effect refers to the irregular distortion or sudden inflection point in the resistance change curve of the flexible strain sensor when it is deformed. It is usually manifested as a slow or stagnant change in resistance within a certain strain range, which leads to unstable sensor output response signals, thereby affecting the judgment of the damage degree of the structure. This phenomenon is mainly caused by the instability of the contact network between the conductive fillers in the flexible strain sensor. As the strain increases, the conductive network may be restructured or disconnected, leading to discontinuous or nonlinear signal response. Shoulder peak effect limits the accuracy and stability of flexible strain sensors within the monitoring range, hindering their application in high-precision strain measurement. In addition, shoulder peak effect can also cause aging effect of the sensor during long-term use, further affecting its reliability and repeatability. Therefore, solving shoulder peak effect is the key to improving the monitoring stability of flexible strain sensors, and new materials and optimized design are urgently needed to improve the response characteristics of flexible strain sensors. SUMMARY

[0007] The application aims to provide a flexible strain sensor material with high stability of monitoring signals and a preparation method and application thereof.

[0008] In order to achieve the above-mentioned purposes, the application adopts the technical scheme of:

[0009] The first aspect of the application provides a preparation method of a flexible strain sensor material with high stability of monitoring signals, comprising the following steps:

[0010] S1, preparing conductive nano-reinforced fillers

[0011] The polyvinylpyrrolidone, the conductive filler and the organic solvent are mixed, and after being uniformly mixed, the organic solvent is removed by heating and volatilization to obtain the conductive nano filler.

[0012] The mass ratio of the polyvinylpyrrolidone and the conductive filler is 0-1.0:0.1-0.4.

[0013] S2, preparing conductive nano-rubber composite material

[0014] The conductive nano-reinforced fillers prepared in step S1, methyl vinyl silicone rubber, nano-silicon dioxide, hydroxyl silicone oil, vinyl silicone oil and vulcanizing agent are mixed according to the mass ratio of 18-26:500-700:100-140:30-42:0-80:10-14, and mixing is carried out to obtain a mixture.

[0015] S3, vulcanization

[0016] The mixture obtained in step S2 is vulcanized in two stages, and the vulcanization temperature in the second stage is 20-30 DEG C higher than that in the first stage to obtain the flexible strain sensor material.

[0017] Preferably, the organic solvent is ethyl acetate or tetrahydrofuran or acetone.

[0018] The conductive filler is selected from multi-walled carbon nanotubes or conductive carbon black or graphene.

[0019] The vinyl silicone oil is end-vinyl silicone oil, and the end-vinyl silicone oil is selected from one or two of end-vinyl polydimethylsiloxane (Vi-PDMS) and end-vinyl polymethylvinylsiloxane (Vi-PMVS) mixed in any ratio.

[0020] The vulcanizing agent is selected from one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate and dibenzoyl peroxide.

[0021] The mass-volume ratio of polyvinylpyrrolidone, conductive filler and organic solvent in step S1 is 0.2-1.0 g: 0.1-0.4 g: 100-1200 ml or 0.2-0.8 g: 0.18-0.3 g: 200-1000 ml;

[0022] The polyvinylpyrrolidone, conductive filler and organic solvent are mixed and ultrasonically stirred to mix uniformly, and the organic solvent is removed by heating and volatilization to obtain a conductive nano filler; the ultrasonic stirring conditions are ultrasonic frequency of 100-150 Hz, stirring rate of 450-600 rpm, and ultrasonic stirring mixing for 2-4 h;

[0023] Preferably, magnetic stirring is performed before ultrasonic stirring, and the magnetic stirring conditions are stirring at a stirring rate of 450-600 rpm for 30-60 min;

[0024] The organic solvent is tetrahydrofuran, and the tetrahydrofuran is removed by heating to 50-70°C to obtain a conductive nano filler.

[0025] In step S2, the mass ratio of conductive nano-reinforced filler, methyl vinyl silicone rubber, nano-silica, hydroxyl silicone oil, vinyl silicone oil and vulcanizing agent is 18-26: 500-700: 100-140: 30-42: 40-80: 10-14 or 20-24: 550-650: 110-130: 33-39: 60-80: 11-13;

[0026] The mixing temperature is 40-60°C, the roll gap is 0.5-1 mm, the rate is 20-35 rpm, and the mixing process is 40-60 min.

[0027] In step S3, the vulcanization temperature of the first stage vulcanization is 150-170°C, the time is 10-20 min, and the pressure is 10-20 MPa, preferably the vulcanization temperature is 160-170°C, the time is 10-15 min, and the pressure is 10-15 MPa;

[0028] Subsequently, the second stage vulcanization treatment is performed, and the vulcanization temperature is 180-200°C and the time is 2-4 h.

[0029] Preferably, in step S3, the first stage vulcanization is performed on a flat plate vulcanizer, and the second stage vulcanization is performed in an oven.

[0030] In the above preparation method,

[0031] The vinyl content in the methyl vinyl silicone rubber is 0.16%, and the molecular weight is 7.2 x 10 5 g / mol;

[0032] The multi-walled carbon nanotube is 20-30 mu m in length, 6-8 nm in diameter, and 500-500 m in specific surface area 2 / g.

[0033] The nano-silica is 7-40 nm in particle size and 200 m in specific surface area 2 / g.

[0034] The vinyl silicone oil is 8000±1000 Pa·s in viscosity and 0.1-1.2 wt% in vinyl content.

[0035] The hydroxyl silicone oil is 7-9% in hydroxyl content and 25-30 Pa·s in viscosity.

[0036] The second aspect of the present application provides a flexible strain sensor material prepared by the preparation method of any one of the above.

[0037] The third aspect of the present application provides the application of the above flexible strain sensor material in the preparation of a flexible strain sensor.

[0038] In the application technical scheme, the flexible strain sensor material is prepared into a flexible sensor for engineering structure health monitoring or human motion monitoring.

[0039] The present application has the following beneficial effects:

[0040] (1) Compared with traditional commercial conductive fillers, the conductive nano-reinforced filler in the present application is self-assembled from multi-walled carbon nanotubes modified by non-ionic compound polyvinylpyrrolidone with a suitable ratio, which can form a stable adsorption layer on the surface of multi-walled carbon nanotubes through its hydrophilicity and flexibility of the polymer chain, thereby effectively reducing the aggregation phenomenon between multi-walled carbon nanotubes. At the same time, during ultrasonic stirring, ultrasonic waves propagate in the liquid, producing periodic high and low pressure fluctuations, forming cavitation bubbles. When the bubbles collapse rapidly in the liquid, local high temperature and high pressure are generated, producing strong shear force and shock wave, which can effectively break and disperse the multi-walled carbon nanotube agglomerates. This self-assembly strategy not only significantly improves the dispersion uniformity of the conductive nano-reinforced filler in the rubber matrix, but also promotes the reconstruction and stability of the conductive network inside the material, thereby endowing the composite material with excellent deformation adaptability and conductive performance. This method effectively optimizes the microstructure of the composite material and enhances its comprehensive performance, laying a solid foundation for the development of high-performance functional materials.

[0041] (2) The self-assembled conductive nano-reinforced filler and the end-vinyl silicone oil are introduced into the methyl vinyl silicone rubber, the reaction sites on the molecular chains of the methyl vinyl silicone rubber are increased, the crosslinking points between the molecular chains are increased, the free chains in the methyl vinyl silicone rubber are converted into the crosslinked chains to form the highly constrained regions, and the conductive crosslinked network structure in the methyl vinyl silicone rubber is enhanced. When the conductive network is reconstructed, the movement of the conductive nano-reinforced filler attached to the molecular chains of the methyl vinyl silicone rubber is limited, the twist or the sudden inflection point generated by the conductive nano-reinforced filler on the molecular chains of the methyl vinyl silicone rubber during strain unloading is eliminated, the interface bonding interaction between the conductive nano-reinforced filler and the molecular chains of the methyl vinyl silicone rubber is enhanced, the shoulder peak effect is eliminated, and the stability of the output response signal of the flexible strain sensor in the monitoring process is improved.

[0042] The flexible strain sensor material with high sensitivity, good mechanical properties and stable monitoring signal is prepared in a high-efficiency, pollution-free and low-cost manner, is suitable for engineering structure health monitoring under size deformation, and provides a material with wide application prospect for the development of the field of structure health monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The process flow chart of the preparation method of the present application is shown.

[0044] Figure 2 The actual picture of the flexible strain sensor material prepared in Example 5 is shown.

[0045] Figure 3 The SEM micro-morphology diagram of the flexible strain sensor materials of Comparative Example 1 and Example 5 is shown.

[0046] Figure 4 The output monitoring signal comparison diagram of the flexible strain sensor materials of Comparative Example 1 and Example 5 is shown.

[0047] Figure 5 The output response signal of the flexible strain sensor material of Example 5 for monitoring the seismic isolation bearing is shown.

[0048] Figure 6 The response signal of the flexible strain sensor material of Example 5 for monitoring the human body is shown. DETAILED DESCRIPTION

[0049] The present application is further described below in combination with examples, but is not limited by the examples.

[0050] The experimental methods in the following examples are all conventional methods, unless otherwise specified.

[0051] Examples

[0052] The raw materials are:

[0053] Nonionic compound polyvinylpyrrolidone (PVP), multi-walled carbon nanotubes (MWCNT), tetrahydrofuran (THF), methyl vinyl silicone rubber (VMQ), nanosilica, hydroxyl silicone oil (PDMS), vinyl-terminated polymethylvinylsiloxane (Vi-PMVS), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (vulcanizing agent bis-25).

[0054] The vinyl content in the methyl vinyl silicone rubber is 0.16%, and the molecular weight is 7.2*10 5 g / mol;

[0055] The multi-walled carbon nanotubes have a length of 20-30μm, a diameter of 6-8nm, and a specific surface area of 500-500m 2 / g;

[0056] The nanosilica has a particle size of 7-40nm and a specific surface area of 200m 2 / g;

[0057] The Vi-PMVS has a viscosity of 8000Pa·s and a vinyl content of 0.15wt%;

[0058] The hydroxyl silicone oil has a hydroxyl content of 7-9% and a viscosity of 25-30Pa·s;

[0059] The 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is of analytical purity.

[0060] The preparation method of the flexible strain sensor material of the present application (the process flow chart is shown in Figure 1 The following steps are performed:

[0061] S1, preparing conductive nano-reinforced filler

[0062] The nonionic compound polyvinylpyrrolidone (PVP) is mixed with multi-walled carbon nanotubes (MWCNT) and tetrahydrofuran (THF), and stirred at room temperature by a magnetic stirrer at a stirring rate of 550rpm for 60min to obtain a conductive nano-filler suspension. Then, the beaker containing the conductive filler suspension is placed in an ultrasonic cleaning instrument, a stirrer is installed above the beaker, the stirring head is inserted into the beaker, the ultrasonic frequency is set to 100Hz, the temperature is set to 25℃, the stirring rate of the stirrer is set to 550rpm, and ultrasonic stirring is performed for 3h. After the end, the temperature is increased to 50℃ to remove the tetrahydrofuran, and a conductive nano-filler (light black powder) is obtained.

[0063] This process can form a stable adsorption layer on the surface of multi-walled carbon nanotubes by the hydrophilicity and flexibility of the high molecular chain of non-ionic compound polyvinylpyrrolidone, thereby effectively reducing the aggregation phenomenon between multi-walled carbon nanotubes. Further, it can be uniformly dispersed in methyl vinyl silicone rubber in the next step. The obtained conductive nano-reinforced filler is a black light powder, which can be uniformly mixed with methyl vinyl silicone rubber in a two-roll open mill in the subsequent preparation process.

[0064] S2, preparing a conductive nano-rubber composite material

[0065] The conductive nano-reinforced filler prepared in step S1 is uniformly mixed with methyl vinyl silicone rubber (VMQ), nano-silica, hydroxyl silicone oil (PDMS), Vi-PMVS, 2,5-dimethyl-2,5-di(tert-butyl peroxy) hexane (vulcanizing agent double-25) in a two-roll open mill, wherein the mixing temperature is 50°C, the roll distance is 1mm, the speed is 25rpm, and the mixing process is 50min. A non-vulcanized conductive nano-rubber composite material is obtained.

[0066] This process uniformly disperses the filler in methyl vinyl silicone rubber to form a three-dimensional tunneling conductive network through the shear force generated by the two-roll open mill. At the same time, the number of reaction sites on the molecular chain of methyl vinyl silicone rubber is increased, resulting in an increase in the crosslinking points between the molecular chains. The free chains inside the methyl vinyl silicone rubber are converted into crosslinked chains to form a highly constrained region, enhancing the conductive crosslinked network structure inside the methyl vinyl silicone rubber, and enabling it to have signal acquisition capability for monitoring under size deformation.

[0067] S3, vulcanization

[0068] S3.1, first stage vulcanization:

[0069] The conductive nano-rubber composite material of step S2 is placed in a flat plate vulcanizing instrument for vulcanization under the conditions of a temperature of 160°C, a pressure of 15MPa, and a time of 15min, to obtain a first stage vulcanization product.

[0070] The first stage vulcanization decomposes 2,5-dimethyl-2,5-di(tert-butyl peroxy) hexane into free radicals under high temperature conditions. These free radicals excite the rupture of the vinyl double bonds in the methyl vinyl silicone rubber, and further generate new free radicals. The free radicals promote crosslinking reactions of the rubber molecular chains, and finally form a network with a highly crosslinked structure. Through this reaction, a blocky conductive nano-rubber composite material is successfully prepared.

[0071] S3.2, second stage vulcanization:

[0072] The conductive nanometer rubber composite material after the first stage vulcanization is placed into a blast drying oven, and second stage vulcanization is carried out at a temperature of 180 DEG C for 3h, that is, a flexible strain sensor material is obtained.

[0073] The second stage vulcanization further optimizes the crosslinking structure through a free radical initiated crosslinking reaction under high temperature conditions, thereby significantly enhancing the mechanical properties, high temperature resistance, elasticity and chemical stability of the flexible strain sensor, and improving the overall performance thereof.

[0074] In the process of the present application, the vulcanization of the mixture is carried out in two stages, the first stage vulcanization is mainly to vulcanize the conductive mixture into a shape and form a crosslinking network inside. The second stage vulcanization is mainly to improve the crosslinking density of the first stage vulcanization, so that the mechanical properties and aging resistance of the composite material are improved.

[0075] According to the above method, the conductive nanometer rubber composite materials of Examples 1-5 are prepared, and the specific raw material ratios of each example are shown in Table 1:

[0076] Table 1

[0077]

[0078] Comparative Example 1 (same filler as in the present invention, different process)

[0079] The same raw materials and amounts as in Example 5 of the present application are used, but the preparation process uses the process in the prior art, that is, the methyl vinyl silicone rubber, multi-walled carbon nanotubes, polyvinylpyrrolidone, nanometer silicon dioxide, hydroxyl silicone oil, Vi-PMVS, 2,5-dimethyl-2,5-di(tert-butyl peroxy) hexane are directly placed into a mixing mill for mixing, the temperature is set to 70 DEG C, the speed is 80 rpm, the roll gap is 1mm, and the time is 40 min. Subsequently, it is placed into a flat vulcanization instrument for vulcanization molding under a pressure of 10 MPa, a temperature of 170 DEG C and a time of 10 min, that is, it is obtained.

[0080] Comparative Example 2 (different filler than in the present invention, same process)

[0081] Different fillers are used in the present application, specifically, the fillers include 100 parts of methyl vinyl silicone rubber, 10 parts of commercial graphene, 300ml of acetone, 10 parts of nanometer silicon dioxide and 2 parts of di-tert-butyl peroxide (DTBP) by weight. The flexible strain sensor is prepared by the preparation process of the present application.

[0082] Specifically, the process includes: stirring graphene and tetrahydrofuran in a magnetic stirrer at room temperature at 550 rpm for 1 h to obtain a conductive filler suspension. Then the conductive filler suspension is placed in an ultrasonic cleaner, and ultrasonic stirring is carried out at an ultrasonic frequency of 100 Hz, a temperature of 25°C, and an ultrasonic stirring rate of 550 rpm for 3 h. Then the temperature is raised to 50°C to remove tetrahydrofuran, and a conductive nano filler is obtained. The methyl vinyl silicone rubber is placed in a two-roll open mill, and then the conductive nano filler, silica, and di-t-butyl peroxide are uniformly mixed at a temperature of 50°C, a roll gap of 1 mm, a speed of 25 rpm, and a time of 50 min to obtain an unvulcanized conductive nano mixture. The unvulcanized conductive nano mixture is placed in a flat vulcanizing instrument for first-stage vulcanization at a temperature of 160°C, a pressure of 15 MPa, and a time of 15 min to obtain a vulcanized conductive nano mixture. Finally, the conductive nano mixture is placed in an oven for second-stage vulcanization at 180°C for 3 h to obtain a flexible strain sensor.

[0083] Performance test

[0084] The performance of the prepared flexible strain sensor material is detected.

[0085] (1) Volume conductivity: The volume conductivity of the conductive nano rubber material is tested according to the GT / T 1692-2008 standard. First, the sample is cut into a standard sample with a size of 40 mm x 100 mm x 1 mm (the surface is cleaned with anhydrous ethanol), and the resistance value of the sample under no strain is measured using a Keysight 34465A digital multimeter. The average resistance value within 1 s of the digital multimeter is collected, and each group of test strips is 3, and the average value is taken. The volume conductivity formula is defined as:

[0086]

[0087] In formula (1), σ is the volume conductivity (S / m), ρ is the volume resistivity of the material (Ω·m), R is the volume resistance (Ω), L is the length of the sample (m), and S is the cross-sectional area (m 2 ).

[0088] (2) Sensitivity test: The two ends of the conductive nano rubber material are clamped on an electronic universal testing machine, a wire is taken, one end of the wire is connected to the conductive nano rubber material, the other end of the wire is connected to a digital multimeter, the strain is set through the universal testing machine, and the maximum resistance value is transmitted to the computer through the digital multimeter after a single tensile cycle. Then the sensitivity is calculated according to formula (2) through the resistance and strain.

[0089] Sensitivity calculation method: formula (2) is used to evaluate the sensitivity of the composite material:

[0090] GF = (AR / R0) / ε Equation (2)

[0091] In Equation (2), ε is the strain. ΔR / R0, ΔR = R-R0, where R0 is the initial resistance and R is the test resistance.

[0092] (3) Test method of resistance / strain response signal: The conductive nanorubber material was cut into a strip of 40 mm x 40 mm x 1 mm, the sample was fixed on an electronic universal testing machine to perform a cyclic loading-unloading test, and a digital multimeter was used to record the resistance / strain response signal change.

[0093] (4) Test method of mechanical properties: According to GB / T528-2009, the mechanical properties of the dumbbell-shaped standard conductive nanorubber material sample were measured using an electronic universal testing machine (DDL10), and the tensile rate was 200 mm / min- 1 , and the average value of 3 groups of experimental data was taken.

[0094] The performance test results are shown in Table 2.

[0095] Table 2: Performance results of flexible strain sensor material

[0096]

[0097] Figure 2 A physical map of the flexible strain sensor material prepared for Example 5.

[0098] From the various examples and comparative examples, it can be seen that the volume conductivity of each example of the present application is significantly reduced compared to Comparative Example 1. Especially for Example 5 which uses the same filler, the volume conductivity is reduced more significantly compared to Comparative Example 1, indicating that the process of the present application can maximize the reduction of volume conductivity.

[0099] Each example can achieve good sensitivity, and compared to Comparative Example 1 or Comparative Example 2 which uses different fillers and different preparation methods from the present application, the sensitivity of each example is improved to varying degrees.

[0100] By comparing the SEM micro-morphology graphs of Comparative Example 1 and Example 5 Figure 3 , it can be seen that the conductive filler of Comparative Example 1 has a serious agglomeration phenomenon in the rubber matrix, which hinders the continuity of the conductive filler in the rubber matrix. The self-assembled conductive filler of Example 5 has good dispersibility in the rubber matrix, which is an important factor for obtaining low volume conductivity, high sensitivity, good mechanical properties, and stable resistance / strain response signal.

[0101] The tensile strength and elongation at break are mainly related to the dispersibility of the conductive nanofiller in the matrix. Comparative Example 1 uses the same raw materials as the examples but a different process. Since all the raw materials are mixed at one time, the dispersibility of the conductive filler is poor during the mixing process with the rubber matrix, and therefore no well-dispersed conductive rubber nanocomposite is formed. Comparative Example 2 does not modify the commercial graphene by self-assembly, and its dispersibility in the rubber matrix is also poor. Comparative Example 1 or Comparative Example 2 does not have self-assembled conductive nanofillers, and the tensile strength and elongation at break of the final composite material are low. The tensile strength and elongation at break of Example 5 using the filler ratio and process of the application are significantly improved.

[0102] Comparison of the output monitoring signals of the flexible strain sensors of Comparative Example 1 and Example 5: The flexible strain sensor materials prepared in Comparative Example 1 and Example 5 were respectively cut into strips of 40 mm x 40 mm x 1 mm, and the samples were fixed on an electronic universal testing machine for cyclic loading-unloading tests, and the resistance / strain response signal changes were recorded with a digital multimeter. From Figure 4 It can be seen that: the monitoring signal graph of the material of Comparative Example 1 shows a sudden increase in resistance (called shoulder peak effect); while the monitoring signal graph of the material of Example 5 is continuous and reflects a stable monitoring signal, and no shoulder peak effect occurs. Example 5 combines self-assembled conductive fillers with Vi-PMVS, increasing the reaction sites on the rubber matrix molecular chain, resulting in an increase in crosslinking points between molecular chains, and the free chains inside the rubber are converted into crosslinked chains to form a highly constrained region, enhancing the conductive crosslinked network structure inside the rubber matrix. When the conductive network is reconstructed, it limits the movement of the self-assembled conductive filler attached to the rubber molecular chain, reduces the resistance surge generated by the self-assembled conductive filler on the molecular chain during strain unloading, enhances the interfacial bonding interaction between the self-assembled conductive filler and the rubber molecular chain, and eliminates the shoulder peak effect.

[0103] By the method of the application, in combination with the specific non-ionic compound polyvinylpyrrolidone and the mass ratio of multi-walled carbon nanotube conductive nano-reinforced filler and methyl vinyl silicone rubber, a flexible strain sensor with low volume conductivity, high sensitivity, and good mechanical properties can be produced. Moreover, the innovative raw material ratio of the application eliminates the shoulder peak effect in the monitoring signal (the smaller the resistance / strain response hysteresis rate (%) value in Table 2, the weaker the influence of the shoulder peak effect on the stability of the signal), making it have a stable monitoring signal, which is more conducive to real-time structural health monitoring of the size deformation of the structure. At the same time, the flexible strain sensor can overcome the defects of traditional strain sensors such as brittleness, low sensitivity, and narrow monitoring range. The output monitoring signal during the monitoring process is perfectly coordinated with the deformation of the measured structure, and the health status of the measured engineering structure is obtained in real time.

[0104] Application Example 1

[0105] The flexible strain sensor material prepared in Example 5 is cut into a block of 40mm x 10mm x 1mm, and is pasted on a high-damping isolation rubber bearing in the laboratory of the research team by using a special glue for silicone rubber. One end of the wire is pasted with the sensor material, and the other end is combined with a digital multimeter. When the high-damping rubber bearing deforms, it drives the sensor to deform, which causes the resistance to change. The real-time resistance / strain response signal is output on the computer, so as to evaluate the deformation degree of the high-damping rubber bearing, and to achieve the monitoring of the high-damping isolation rubber bearing. When the rubber bearing deforms greatly under certain experimental conditions, it drives the sensor to deform greatly, which causes the resistance / response signal to change significantly, indicating that the rubber bearing is damaged or aged.

[0106] The entire experiment is carried out on a compression-shear machine, and the working conditions are frequency: 0.03-0.12Hz, deformation displacement: 30-80mm, pressure: 15MPa-30MPa. The deformation direction is bidirectional shear deformation. As shown in Table 1, with the deformation of the high-damping rubber bearing, the sensors can capture and stably output the resistance / strain response signal with high sensitivity, and the detection results are accurate and reliable. Figure 5

[0107] At present, most of the isolation bearings on the market are rubber bearings. The flexible strain sensor material prepared by the present application has a rubber base, which can solve the compatibility problem with the rubber isolation bearing. At the same time, the flexible strain sensor has high sensitivity, and the resistance / strain response signal output by the deformation of the isolation bearing is stable. In addition, the excellent deformation capacity can realize perfect coordinated deformation with the isolation bearing. Moreover, since the isolation bearing is often in a harsh environment, compared with the traditional strain sensor which is fragile, low in sensitivity, poor in aging resistance and cannot be used for real-time monitoring of the isolation bearing under large deformation, the flexible strain sensor material of the present application is especially suitable for real-time monitoring of the structural health of the isolation bearing. The sensor of the present application is used for real-time monitoring of the isolation bearing, which does not need to disassemble each bearing and bring it back to the laboratory for detection, greatly saving manpower, material resources and detection cost.

[0108] Application Example 2

[0109] The flexible strain sensor material prepared in Example 5 is cut into a block of 40mm x 10mm x 1mm, and is pasted on a high-damping isolation rubber bearing in the laboratory of the research team by using a special glue for silicone rubber. One end of the wire is pasted with the sensor material, and the other end is combined with a digital multimeter. When the high-damping rubber bearing deforms, it drives the sensor to deform, which causes the resistance to change. The real-time resistance / strain response signal is output on the computer, so as to evaluate the deformation degree of the high-damping rubber bearing, and to achieve the monitoring of the high-damping isolation rubber bearing. When the rubber bearing deforms greatly under certain experimental conditions, it drives the sensor to deform greatly, which causes the resistance / response signal to change significantly, indicating that the rubber bearing is damaged or aged.​Figure 6 ), the detection result is accurate and reliable.

Claims

1. A method for preparing a flexible strain sensor material for monitoring signal high stability, characterized in that, Comprising the following steps: S1, preparing conductive nano-reinforced filler Take polyvinyl pyrrolidone, conductive filler multi-walled carbon nanotubes, organic solvent mixture, mix well, remove organic solvent by heating and volatilization, obtain conductive nano filler; Wherein, the mass ratio of polyvinyl pyrrolidone and conductive filler is 0.2-0.8:0.18-0.3; S2, preparation of conductive nanometer rubber composite material Take the conductive nano-reinforced filler prepared in step S1 and methyl vinyl silicone rubber, nano-silicon dioxide, hydroxyl silicone oil, vinyl silicone oil, curing agent according to the mass ratio of 18-26:500-700:100-140:30-42:40-80:10-14, mixing, mixing, getting mixed material; S3, vulcanization: Take the mixed material prepared in step S2, vulcanization is carried out in two stages, the vulcanization temperature of the first stage vulcanization is 150-170℃, the vulcanization temperature of the second stage vulcanization is 20-30℃ higher than that of the first stage vulcanization, and the flexible strain sensor material is obtained.

2. The preparation method of claim 1, wherein: The organic solvent is ethyl acetate or tetrahydrofuran or acetone; The curing agent is selected from one or more of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate and dibenzoyl peroxide.

3. The method of claim 1, wherein: In step S1, The mass volume ratio of polyvinyl pyrrolidone, conductive filler and organic solvent is 0.2-0.8g:0.18-0.3g:200-1000ml; Take polyvinyl pyrrolidone, conductive filler, organic solvent mixture, ultrasonic stirring mixing, remove organic solvent by heating and volatilization, obtain conductive nano filler; The condition of ultrasonic stirring is that the ultrasonic frequency is 100-150Hz, the stirring rate is 450-600rpm, and the ultrasonic stirring mixing time is 2-4h.

4. The method of claim 3, wherein: In step S1, Magnetic stirring is carried out before ultrasonic stirring, and the magnetic stirring condition is that the stirring rate is 450-600rpm and the stirring time is 30-60min; The organic solvent is tetrahydrofuran, and the tetrahydrofuran is removed by heating to 50-70℃ to obtain the conductive nano filler.

5. The method of claim 1, wherein: In step S2, the mass ratio of conductive nano-reinforced filler, methyl vinyl silicone rubber, nano-silicon dioxide, hydroxyl silicone oil, vinyl silicone oil and curing agent is 20-24:550-650:110-130:33-39:60-80:11-13; The mixing temperature is 40-60℃, the roll gap is 0.5-1mm, the speed is 20-35rpm, and the mixing process is 40-60min.

6. The method of claim 1, wherein: In step S3, The vulcanization temperature of the first stage vulcanization is 150-170℃, the time is 10-20min, and the pressure is 10-20MPa; Then the second stage vulcanization treatment is carried out, the vulcanization temperature is 180-200℃, and the time is 2-4h.

7. The preparation method of claim 6, wherein: In step S3, the first stage vulcanization is carried out on a flat plate vulcanizer, and the second stage vulcanization is carried out in an oven.

8. The preparation method of claim 1, wherein: The methylvinyl silicone rubber has a vinyl content of 0.16%, a molecular weight of 7.2 x 10 5 g / mol; The multi-walled carbon nanotube has a length of 20-30 μm, a diameter of 6-8 nm, and a specific surface area of 500 m 2 / g; The nano-silica has a particle size of 7-40 nm, a specific surface area of 200 m 2 / g; The viscosity of the end-vinyl polydimethylsiloxane is 8000±1000 Pa·s, and the vinyl content is 0.1-1.2 wt %. The hydroxyl content of the hydroxyl silicone oil is 7-9 %, and the viscosity is 25-30 Pa·s.

9. A flexible strain sensor material, characterized by: The flexible strain sensor material is prepared by the preparation method in any one of claims 1 to 8.

10. Use of the flexible strain sensor material in claim 9 in the preparation of a flexible strain sensor.

11. Use according to claim 10, characterized in that: The flexible strain sensor material is prepared into a flexible sensor for engineering structure health monitoring or human motion monitoring.

Images