CN111941985B - Flexible strain sensing material and preparation method thereof - Google Patents

Abstract

The invention provides a flexible strain sensing material and a preparation method thereof. Above-mentioned flexible strain sensing material, silver nano wire/anion waterborne polyurethane mix conductive film layer has stronger adhesion, and through the bonding with the anion waterborne polyurethane rete on the flexible substrate layer, has greatly increased the bonding fastness between flexible substrate layer and the silver nano wire, is difficult to drop after repeated friction or deformation, and the durability is good. In addition, the silver nanowires are uniformly dispersed in the silver nanowire/anionic waterborne polyurethane mixed conductive film through prefabricating the silver nanowire/anionic waterborne polyurethane mixed conductive film, and the dispersion is more uniform, so that the conductivity uniformity of the silver nanowire/anionic waterborne polyurethane mixed conductive film is better.

Description

Flexible strain sensing material and preparation method thereof

technical field

The invention relates to the technical field of strain sensing materials, and relates to a flexible strain sensing material and a preparation method thereof.

Background technique

Flexible strain sensing materials have great potential in wearable displays, smart clothing, health monitoring, and other fields. Silver nanowires (AgNWs) are widely used as conductive materials due to their high surface area, low resistance, low mass density, and high stability. Traditional flexible strain sensing materials use silver nanowires to modify textiles, which can impart conductivity to flexible fabrics. Generally, textiles are modified by spraying or dipping. Since silver nanowires mainly exist on the surface of fabric fiber substrates, fabric fibers are closely related to silver nanowires. Lack of adhesion between the threads, resulting in poor durability. During use, the silver nanowires are easy to fall off after repeated friction or deformation. Therefore, more efficient assembly methods are urgently needed to enhance the adhesion between loaded conductive silver nanowires and fiber substrates. In addition, silver nanowires tend to coagulate in aqueous solution, which will affect the conductivity uniformity. These shortcomings also limit the application of silver nanowires in the field of flexible strain sensing materials.

SUMMARY OF THE INVENTION

Based on this, it is necessary to address the lack of adhesion between the fabric fibers and silver nanowires of traditional silver nanowire-modified textiles, resulting in poor durability. During use, after repeated friction or deformation, the silver nanowires are easy to fall off. The invention provides a flexible strain sensing material and a preparation method thereof. Anionic water-based polyurethane (WPU) is used to disperse silver nanowires, and the silver nanowires and the flexible substrate are combined more firmly through the anionic water-based polyurethane.

A flexible strain sensing material proposed by the present invention comprises a flexible substrate layer, an anionic aqueous polyurethane film layer and a silver nanowire/anionic aqueous polyurethane mixed conductive film layer which are laminated in sequence.

On the basis of the above technical solutions, the present invention can also have the following further specific options or optimized options.

In one embodiment, the thickness ratio of the flexible substrate layer, the anionic aqueous polyurethane film layer and the silver nanowire/anionic aqueous polyurethane mixed conductive film layer is (1.5:1)～(3:1 ).

In one embodiment, when the stretching degree of the flexible strain sensing material is 0-60%, the resistance change value of the flexible strain sensing material has an exponential relationship with the stretching degree.

The present invention also provides a preparation method of the above flexible strain sensing material, characterized in that the preparation method comprises the following steps:

The anionic water-based polyurethane film is laminated on the flexible substrate layer by hot pressing;

The silver nanowire/anionic aqueous polyurethane mixed conductive film is pressed on one side of the anionic aqueous polyurethane film of the flexible substrate layer by a hot pressing method.

In one embodiment, the preparation method of the silver nanowire/anionic aqueous polyurethane mixed conductive film includes the following steps:

Mixing silver nanowire water dispersion, anionic water-based polyurethane, foaming agent and foam stabilizer to prepare functional water-based resin foaming agent;

The functional water-based resin foaming agent is placed on a carrier plate after foaming treatment, until the foam is completely eliminated, and then dried at a temperature of 60°C to 80°C for 1.0h to 3.0h to obtain silver nanowires / Anionic water-based polyurethane hybrid conductive film.

In one embodiment, the preparation method of the silver nanowire aqueous dispersion comprises the following steps:

Provide sodium chloride in ethylene glycol solution;

Provide ethylene glycol solution of organic protective agent;

providing a ethylene glycol solution of the silver precursor;

Mixing the ethylene glycol solution of the silver precursor and the ethylene glycol solution of the organic protective agent to obtain a first mixed solution;

Mixing the ethylene glycol solution of the sodium chloride with the first mixed solution to prepare a second mixed solution;

The second mixed solution is reacted at a temperature of 110°C to 150°C for 6h to 10h to obtain a solid-liquid mixture, and the solid-liquid mixture is separated to remove the upper layer solution to obtain silver nanowires;

Dispersing the silver nanowires in deionized water to prepare the silver nanowire aqueous dispersion;

The concentration of silver nanowires in the silver nanowire aqueous dispersion is 1 g/L to 10 g/L.

In one embodiment, the ethylene glycol solution of the silver precursor and the ethylene glycol solution of the organic protective agent are mixed by dropwise adding the ethylene glycol solution of the silver precursor to the organic protective agent. in the ethylene glycol solution of the protective agent; the mixing mode of the ethylene glycol solution of the sodium chloride and the first mixed solution is to drop the ethylene glycol solution of the sodium chloride into the first mixed solution middle.

In one embodiment, the molar concentration of the sodium chloride solution in ethylene glycol is 30 μmol/L to 37.5 μmol/L.

In one embodiment, the mass concentration of the ethylene glycol solution of the organic protective agent is 2g/L～10g/L; the mass concentration of the ethylene glycol solution of the silver precursor is 2g/L～10g/L L;

In one embodiment, the mass ratio of the organic protective agent to the silver precursor in the first mixed solution is (1:3)˜(3:1).

In one embodiment, the volume ratio of the sodium chloride ethylene glycol solution to the first mixed solution is 1:100.

In one embodiment, the silver nanowires have an average length of 30 μm˜120 μm.

In one embodiment, in the preparation method of the silver nanowire/anionic aqueous polyurethane mixed conductive film, the concentration of the anionic aqueous polyurethane is 1 g/L to 10 g/L; The dry weight ratio of anionic waterborne polyurethane is (1:9)～(3:7).

In one embodiment, the foaming agent is any one or more of sodium lauryl sulfate, uryl betaine and dodecyl dimethyl benzyl ammonium chloride; the foaming agent is The content of the foaming agent in the functional water-based resin foaming agent is 0.1 g/L to 1.0 g/L.

In one embodiment, the foam stabilizer is any one or more of sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, agar and guar gum; The content in the functional water-based resin foaming agent is 0.1g/L～1.0g/L.

In one embodiment, before the step of laminating the anionic water-based polyurethane film on the flexible substrate layer by hot pressing, the following steps are further included:

The flexible substrate layer was pretreated with acetone.

In one embodiment, the acetone pretreatment is that the flexible substrate layer is placed in a Soxhlet extractor containing acetone, and circulated for 2.0 h to 3.0 h at a temperature of 60° C. to 70° C. The flexible substrate layer is taken out and dried.

In one embodiment, the preparation method of the anionic aqueous polyurethane film comprises the following steps:

The anionic water-based polyurethane with a concentration of 10g/L to 30g/L is placed on a carrier plate, and dried at a temperature of 60°C to 80°C for 1.0h to 2.0h to prepare the anionic waterborne polyurethane film.

In one embodiment, in the step of laminating the anionic water-based polyurethane film on the flexible substrate layer by hot pressing, the hot pressing temperature is 150°C to 170°C, and the hot pressing time is 1.0min to 3.0min ;

In the step of laminating the silver nanowire/anionic aqueous polyurethane mixed conductive film on one side of the anionic aqueous polyurethane film of the flexible substrate layer by hot pressing, the hot pressing temperature is 70°C to 100°C, and the hot pressing The time is 1.0min～2.0min.

For the above flexible strain sensing materials, the silver nanowire/anionic water-based polyurethane mixed conductive film layer has strong adhesion, and by bonding with the anionic water-based polyurethane film layer on the flexible substrate layer, the flexible substrate is greatly increased. The adhesive fastness between the layer and the silver nanowires is not easy to fall off after repeated friction or denaturation, and the durability is good. In addition, by prefabricating silver nanowires/anionic waterborne polyurethane mixed conductive film, silver nanowires are uniformly dispersed in silver nanowires/anionic waterborne polyurethane mixed conductive film, and the dispersion is more uniform, so that silver nanowires/anionic waterborne polyurethane mix The conductivity uniformity of the conductive film is better.

Further, the above-mentioned flexible strain sensing material not only has good electrical conductivity, but also has a large strain range, high sensitivity and good stability through different degrees of stretching.

The preparation method of the flexible strain sensing material has the advantages of simple operation, mild conditions and low cost. The prepared flexible strain sensing material not only has good durability and electrical conductivity, but also has a large strain range, high sensitivity and good stability through different degrees of stretching.

Description of drawings

Fig. 1 is the XRD diffractogram of the silver nanowire/anionic water-based polyurethane mixed conductive film prepared in Examples 1 to 4 of the present invention;

Fig. 2 is the SEM microscopic topography of the silver nanowire/anionic water-based polyurethane mixed conductive film prepared in Example 4 of the present invention;

Fig. 3 is the silver nanowire loading amount-resistivity bar graph of the silver nanowire/anionic aqueous polyurethane mixed conductive film prepared in Examples 1 to 4 of the present invention;

FIG. 4 is a graph of the tensile sensing relationship of the flexible strain sensing materials prepared in Examples 1 to 4 of the present invention;

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

It should be noted that the reaction reagents used in the present invention are all purchased from the market, and the purity is chemically pure or above.

The first major aspect of the present invention provides a flexible strain sensing material, the flexible strain sensing material includes a flexible substrate layer, an anionic aqueous polyurethane film layer, and a silver nanowire/anionic aqueous polyurethane mixed conductive film layer that are stacked in sequence.

The flexible strain sensing material, the silver nanowire/anionic water-based polyurethane mixed conductive film layer has strong adhesion, and by bonding with the anionic water-based polyurethane film layer on the flexible substrate layer, the flexible substrate is greatly increased. The adhesive fastness between the layer and the silver nanowires is not easy to fall off after repeated friction or denaturation, and the durability is good. In addition, by prefabricating silver nanowires/anionic waterborne polyurethane mixed conductive film, silver nanowires are uniformly dispersed in silver nanowires/anionic waterborne polyurethane mixed conductive film, and the dispersion is more uniform, so that silver nanowires/anionic waterborne polyurethane mix The conductivity uniformity of the conductive film is better.

In addition, the invention extends the strain sensing material from the solution to the surface of the flexible substrate layer, has the characteristics of good sensitivity and stable electrical conductivity, and improves the application range. The present invention has great potential in the fields of wearable display, smart clothing, health monitoring, etc. in the flexible strain sensing material.

Further, the flexible strain sensing material not only has good electrical conductivity, but also has a large strain range, high sensitivity and good stability through different degrees of stretching.

Wherein, the flexible substrate layer is selected from wearable flexible materials, preferably elastic fabrics. The elastic fabric is selected as the flexible substrate layer because the elastic fabric has good strength, air permeability, wear resistance, light weight, good flexibility and deformability, and is comfortable to wear and soft to the touch.

As an optional embodiment, the thickness ratio of the flexible substrate layer, the anionic water-based polyurethane film layer, and the silver nanowire/anionic water-based polyurethane mixed conductive film layer is (1.5:1)˜(3:1).

As an optional embodiment, when the stretching degree of the flexible strain sensing material is 0-60%, the resistance change value of the flexible strain sensing material is exponentially related to the stretching degree.

The second aspect of the present invention provides a preparation method of the above-mentioned flexible strain sensing material, characterized in that the preparation method includes the following steps:

The anionic water-based polyurethane film is laminated on the flexible substrate layer by hot pressing;

The silver nanowire/anionic aqueous polyurethane mixed conductive film is pressed on one side of the anionic aqueous polyurethane film of the flexible substrate layer by a hot pressing method.

The preparation method of the flexible strain sensing material has the advantages of simple operation, mild conditions and low cost. The prepared flexible strain sensing material not only has good durability and electrical conductivity, but also has a large strain range, high sensitivity and good stability through different degrees of stretching.

As an optional embodiment, the preparation method of the silver nanowire/anionic aqueous polyurethane mixed conductive film comprises the following steps:

Mixing silver nanowire water dispersion, anionic water-based polyurethane, foaming agent and foam stabilizer to prepare functional water-based resin foaming agent;

The functional water-based resin foaming agent is placed on the carrier plate after foaming treatment, until the foam is completely eliminated, and then dried at a temperature of 60 ° C ~ 80 ° C for 1.0 h ~ 3.0 h to obtain silver nanowires/anions. Waterborne polyurethane hybrid conductive film.

Among them, the anionic water-based polyurethane is a carboxylic acid-based water-based polyurethane, and its molecular weight ranges from 2W to 5W.

Optionally, use a foaming machine to foam the functional water-based resin foaming agent, and through the foaming treatment, the silver nanowires can be evenly distributed in the functional water-based resin foaming agent, and can be obtained after drying. The silver nanowire/anionic aqueous polyurethane hybrid conductive film has good conductivity uniformity.

As an optional embodiment, the preparation method of silver nanowire aqueous dispersion comprises the following steps:

Provide sodium chloride in ethylene glycol solution;

Provide ethylene glycol solution of organic protective agent;

providing a ethylene glycol solution of the silver precursor;

Mixing the ethylene glycol solution of the silver precursor and the ethylene glycol solution of the organic protective agent to obtain a first mixed solution;

The ethylene glycol solution of sodium chloride is mixed with the first mixed solution to obtain the second mixed solution;

The second mixed solution is reacted at a temperature of 110°C to 150°C for 6h to 10h to obtain a solid-liquid mixture, and the solid-liquid mixture is separated to remove the upper layer solution to obtain silver nanowires;

Disperse the silver nanowires in deionized water to prepare a silver nanowire aqueous dispersion;

The concentration of silver nanowires in the silver nanowire aqueous dispersion is 1 g/L to 10 g/L.

The preparation method of silver nanowires not only has the characteristics of simplicity, mild reaction conditions, easy control and good repeatability, but also prepares silver nanowires induced by metal chloride, and the average length of the prepared silver nanowires reaches more than 30 μm, and can even be prepared The length of the silver nanowire is about 120 μm, and the length of the prepared silver nanowire is controllable and the size is uniform.

Further optionally, the mixing mode of the ethylene glycol solution of the silver precursor and the ethylene glycol solution of the organic protective agent is to drop the ethylene glycol solution of the silver precursor into the ethylene glycol solution of the organic protective agent; The ethylene glycol solution of sodium and the first mixed solution are mixed by dropping the ethylene glycol solution of sodium chloride into the first mixed solution.

Preferably, the molar concentration of the ethylene glycol solution of sodium chloride is 30 μmol/L˜37.5 μmol/L.

Preferably, the mass concentration of the ethylene glycol solution of the organic protective agent is 2g/L～10g/L; the mass concentration of the ethylene glycol solution of the silver precursor is 2g/L～10g/L; preferably, the organic protective agent is Polyvinylpyrrolidone.

Preferably, the mass ratio of the organic protective agent to the silver precursor in the first mixed solution is (1:3)˜(3:1).

Preferably, the volume ratio of the ethylene glycol solution of sodium chloride to the first mixed solution is 1:100.

Preferably, the average length of the silver nanowires is 30 μm˜120 μm. More preferably, the average length of the silver nanowires is 80 μm˜120 μm.

As an optional embodiment, in the preparation method of the silver nanowire/anionic water-based polyurethane mixed conductive film, the concentration of the anionic water-based polyurethane is 1 g/L to 10 g/L; the dry weight ratio of the silver nanowires to the anionic water-based polyurethane is ( 1:9)～(9:1); preferably, the dry weight ratio of silver nanowires to anionic aqueous polyurethane is (1:9)～(3:7); more preferably, the ratio of silver nanowires to anionic aqueous polyurethane is The dry weight ratio is (1:9)～(2:8).

Optionally, the foaming agent is any one or more of sodium lauryl sulfate, cinnamyl betaine and dodecyldimethylbenzyl ammonium chloride; The content in the foaming agent is 0.1g/L～1.0g/L.

Optionally, the foam stabilizer is any one or more of sodium alginate, sodium carboxymethylcellulose, polyvinyl alcohol, agar and guar gum; the foam stabilizer in the functional water-based resin foaming agent. The content is 0.1g/L～1.0g/L.

Preferably, before the step of laminating the anionic water-based polyurethane film on the flexible substrate layer by a hot pressing method, the following step is further included: pretreating the flexible substrate layer with acetone.

Wherein, preferably, the acetone pretreatment is to place the flexible substrate layer in a Soxhlet extractor containing acetone, and circulate the backflow for 2.0h to 3.0h at a temperature of 60°C to 70°C, and then take out the flexible substrate layer for drying treatment. .

The silver nanowire/anionic aqueous polyurethane hybrid conductive film is combined with the anionic aqueous polyurethane film of the flexible substrate layer under the action of adhesive force through hot pressing. The amount of adhesion on the surface of the flexible substrate layer enables the silver nanowire/anionic water-based polyurethane mixed conductive film to form a conductive layer on the surface of the flexible substrate layer, which is conducive to the conduction of the flexible substrate and improves the strain sensing capability of the flexible collection.

Preferably, the preparation method of the anionic aqueous polyurethane film comprises the following steps:

The anionic water-based polyurethane with a concentration of 10g/L～30g/L is placed on a carrier plate, and dried at a temperature of 60℃～80℃ for 1.0h～2.0h to prepare an anionic waterborne polyurethane film.

As an optional embodiment, in the step of pressing the anionic water-based polyurethane film on the flexible substrate layer by hot pressing, the hot pressing temperature is 150°C to 170°C, and the hot pressing time is 1.0min to 3.0min;

In the step of laminating the silver nanowire/anionic aqueous polyurethane hybrid conductive film on one side of the anionic aqueous polyurethane film of the flexible substrate layer by hot pressing, the hot pressing temperature is 70℃～100℃, and the hot pressing time is 1.0min ~2.0min.

Example 1

1. Preparation of silver nanowire aqueous dispersion:

The ethylene glycol solution of sodium chloride with molar concentration of 37.5 μmol/L, the ethylene glycol solution of polyvinylpyrrolidone (average molecular weight = 1,300,000) with mass concentration of 6 g/L, and nitric acid with mass concentration of 4 g/L were prepared respectively. Silver in ethylene glycol solution. Add 50 mL of ethylene glycol solution of silver nitrate dropwise to 50 mL of ethylene glycol solution of vinylpyrrolidone to prepare a first mixed solution, and then add 1 mL of ethylene glycol solution of sodium chloride dropwise to the above-mentioned first mixed solution, then The reaction is carried out at 130°C for 6h-10h. The solid-liquid mixture obtained after the reaction was placed in a centrifuge, centrifuged at 4000 rpm for 5 min, the solid was washed 2 to 3 times with absolute ethanol, the upper layer liquid was removed, and the lower layer precipitate, i.e., the silver nanowires, was dispersed in deionized water by ultrasonic for subsequent use. , and the concentration of silver nanowires was controlled to be 3 g/L. After testing, the yield of the obtained silver nanowires was 83.7%, the diameter of the obtained silver nanowires was uniform, and the average length of the silver nanowires was 120 μm. After testing, the length of the silver nanowires in the product ranged from 115 μm to 125 μm. The proportion is 97%.

2. Preparation of functional water-based resin foaming agent:

The above-obtained silver nanowire dispersion is mixed with anionic water-based polyurethane with a concentration of 5 g/L in proportion to make the dry weight ratio of silver nanowires to anionic water-based polyurethane to be silver nanowires:WPU=0.2:9.8, and then an appropriate amount of water is added. The foaming agent and the foaming stabilizer are mixed uniformly to obtain a functional water-based resin foaming agent.

3. Preparation of silver nanowire/anionic water-based polyurethane hybrid conductive film:

The obtained functional water-based resin foaming agent is foamed with a foaming machine and placed in a PTFE carrier plate, waiting for the foam to be eliminated, until the foam is completely ruptured, and the PTFE plate containing the above solution is placed in an oven. Dry in medium, oven temperature is 70 ℃, time is 2.0h. A silver nanowire/anionic aqueous polyurethane mixed conductive film was obtained;

4. Preparation of anionic waterborne polyurethane film:

An anionic water-based polyurethane film with a concentration of 20 g/L was placed on a carrier plate and dried at a temperature of 70°C for 1.5 h to obtain an anionic water-based polyurethane film.

5. Preparation of flexible strain sensing materials:

The above-mentioned anionic water-based polyurethane film was hot-pressed on the elastic fabric pretreated with acetone, the hot-pressing temperature was 160° C., and the hot-pressing time was 2.0 min. Then, the prepared silver nanowire/anionic water-based polyurethane hybrid conductive film was hot-pressed on one side of the anionic water-based polyurethane film of the elastic fabric, the hot-pressing temperature was 85 °C, and the hot-pressing time was 1.5 min, and finally a flexible strain transmission was obtained. Sensitive material.

Among them, in this example, the original fabric needs to be cleaned with acetone: the fabric is put into a Soxhlet extractor containing acetone solution, the temperature is raised to 65°C, and after reflux cleaning for 2.5h, the fabric is transferred to a 60°C oven for drying.

Example 2

The flexible strain sensing material of this embodiment is the same as the preparation method of embodiment 1, except that the dry weight ratio of silver nanowires and anionic waterborne polyurethane in the functional water-based resin foaming agent is silver nanowires:WPU=0.5:9.0.

Example 3

The flexible strain sensing material of this embodiment is the same as the preparation method of embodiment 1, the difference is that the dry weight ratio of silver nanowires and anionic waterborne polyurethane in the functional water-based resin foaming agent is silver nanowires:WPU=1.0:9.0.

Example 4

The flexible strain sensing material of this embodiment is the same as the preparation method of embodiment 1, except that the dry weight ratio of silver nanowires and anionic waterborne polyurethane in the functional water-based resin foaming agent is silver nanowires:WPU=2.0:8.0.

As shown in Figure 1, the silver nanowires/anionic aqueous polyurethane mixed conductive films prepared in Examples 1 to 4 have different ratios of silver nanowires to anionic aqueous polyurethane. Since anionic aqueous polyurethane is an amorphous substance, silver nanowires/anionic aqueous polyurethane Compared with that of silver nanowires, the crystal form of the mixture did not change, and strong diffraction peaks appeared at 2θ=38.2°, 44.38°, 64.54°, and 77.5°.

As shown in Figure 2, it can be seen from the SEM microscopic topography of the silver nanowire/anionic aqueous polyurethane hybrid conductive film prepared in Example 4 that under the adhesion of anionic aqueous polyurethane, the silver nanowires are embedded in the anion Inside the water-based polyurethane film, so that the anionic water-based polyurethane film has conductivity, forming a conductive film. Then, the foaming technology is used to make the silver nanowires evenly dispersed in the anionic aqueous polyurethane solution, so that the conductivity of the conductive film is more uniform.

As shown in Figure 3, the resistivity of the silver nanowires/anionic water-based polyurethane mixed conductive films prepared in Examples 1 to 4 was measured by the four-probe method, and the silver nanowires loaded in the silver nanowires/anionic water-based polyurethane mixed conductive films were obtained. Columnar trend graph of the amount-resistivity change, the resistivity decreases with the increase of the proportion of silver nanowires, when the loading of silver nanowires is 20%, the minimum resistivity measured is ^1.4x10-5 Ω· m.

As shown in Figure 4, a fabric dynamic resistance tester was used to measure the real-time resistance value of the flexible strain sensing materials prepared in Examples 1 to 4 during the dynamic deformation process, and the change curve of the resistance change rate of the fabric with the tensile strain was obtained. With the increase of the proportion of silver nanowires, the larger the strain range of the flexible strain sensing material, the higher the sensitivity. The sensitivity value, ie the slope of the curve, can reach up to 136 during the stretch range of 60-70% strain. In addition, it can be seen from the figure that when the dry weight ratio of silver nanowires and anionic waterborne polyurethane in the functional water-based resin foaming agent is silver nanowires:WPU=2.0:8.0, the stretching degree of the flexible strain sensing material is From 0 to 70%, the resistance change value of the flexible strain sensing material has an exponential relationship with the stretching degree. The prepared flexible strain sensing material greatly enhances the bonding force between the conductive film and the elastic fabric due to hot pressing a layer of adhesive film (anionic water-based polyurethane film) on the elastic fabric substrate, and it is repeatedly stretched for many times (more than 1000 times). ) The test resistance did not change significantly.

Example 5

1. Preparation of silver nanowire aqueous dispersion:

The ethylene glycol solution of sodium chloride with molar concentration of 37.5 μmol/L, the ethylene glycol solution of polyvinylpyrrolidone (average molecular weight = 1,300,000) with mass concentration of 6 g/L, and nitric acid with mass concentration of 4 g/L were prepared respectively. Silver in ethylene glycol solution. Add 50 mL of ethylene glycol solution of silver nitrate dropwise to 50 mL of ethylene glycol solution of vinylpyrrolidone to prepare a first mixed solution, and then add 1 mL of ethylene glycol solution of sodium chloride dropwise to the above-mentioned first mixed solution, then React at 140°C for 6h-10h. The solid-liquid mixture obtained after the reaction was placed in a centrifuge, centrifuged at 4000 rpm for 5 min, the solid was washed 2 to 3 times with absolute ethanol, the upper layer liquid was removed, and the lower layer precipitate, i.e., the silver nanowires, was dispersed in deionized water by ultrasonic for subsequent use. , and the concentration of silver nanowires was controlled to be 3 g/L. After testing, the yield of the obtained silver nanowires was 83.7%, the diameters of the obtained silver nanowires were uniform, and the average length of the silver nanowires was 80 μm. After testing, silver nanowires with a length of 75 μm to 85 μm were found in the product. The proportion is 97%.

2. Preparation of functional water-based resin foaming agent:

The above-obtained silver nanowire dispersion is mixed with anionic water-based polyurethane with a concentration of 5 g/L in proportion to make the dry weight ratio of silver nanowires to anionic water-based polyurethane to be silver nanowires:WPU=0.2:9.8, and then an appropriate amount of water is added. The foaming agent and the foaming stabilizer are mixed uniformly to obtain a functional water-based resin foaming agent.

3. Preparation of silver nanowire/anionic water-based polyurethane hybrid conductive film:

The obtained functional water-based resin foaming agent is foamed with a foaming machine and placed in a PTFE carrier plate, waiting for the foam to be eliminated, until the foam is completely ruptured, and the PTFE plate containing the above solution is placed in an oven. Dry in medium, oven temperature is 70 ℃, time is 2.0h. A silver nanowire/anionic aqueous polyurethane mixed conductive film was obtained;

4. Preparation of anionic waterborne polyurethane film:

An anionic water-based polyurethane film with a concentration of 20 g/L was placed on a carrier plate and dried at a temperature of 70°C for 1.5 h to obtain an anionic water-based polyurethane film.

5. Preparation of flexible strain sensing materials:

The above-mentioned anionic water-based polyurethane film was hot-pressed on the elastic fabric pretreated with acetone, the hot-pressing temperature was 160° C., and the hot-pressing time was 2.0 min. Then, the prepared silver nanowire/anionic water-based polyurethane hybrid conductive film was hot-pressed on one side of the anionic water-based polyurethane film of the elastic fabric, the hot-pressing temperature was 85 °C, and the hot-pressing time was 1.5 min, and finally a flexible strain transmission was obtained. Sensitive material.

Among them, in this example, the original fabric needs to be cleaned with acetone: the fabric is put into a Soxhlet extractor containing acetone solution, the temperature is raised to 65°C, and after reflux cleaning for 2.5h, the fabric is transferred to a 60°C oven for drying.

Example 6

1. Preparation of silver nanowire aqueous dispersion:

The ethylene glycol solution of sodium chloride with molar concentration of 37.5 μmol/L, the ethylene glycol solution of polyvinylpyrrolidone (average molecular weight = 1,300,000) with mass concentration of 6 g/L, and nitric acid with mass concentration of 4 g/L were prepared respectively. Silver in ethylene glycol solution. Add 50 mL of ethylene glycol solution of silver nitrate dropwise to 50 mL of ethylene glycol solution of vinylpyrrolidone to prepare a first mixed solution, and then add 1 mL of ethylene glycol solution of sodium chloride dropwise to the above-mentioned first mixed solution, then React at 150°C for 6h-10h. The solid-liquid mixture obtained after the reaction was placed in a centrifuge, centrifuged at 4000 rpm for 5 min, the solid was washed 2 to 3 times with absolute ethanol, the upper layer liquid was removed, and the lower layer precipitate, i.e., the silver nanowires, was dispersed in deionized water by ultrasonic for subsequent use. , and the concentration of silver nanowires was controlled to be 3 g/L. After testing, the yield of the obtained silver nanowires was 83.7%, the diameter of the obtained silver nanowires was uniform, and the average length of the silver nanowires was 50 μm. After testing, the silver nanowires with a length of 35 μm to 55 μm in the product were detected. The proportion is 97%.

2. Preparation of functional water-based resin foaming agent:

The above-obtained silver nanowire dispersion is mixed with anionic water-based polyurethane with a concentration of 5 g/L in proportion to make the dry weight ratio of silver nanowires to anionic water-based polyurethane to be silver nanowires:WPU=0.2:9.8, and then an appropriate amount of water is added. The foaming agent and the foaming stabilizer are mixed uniformly to obtain a functional water-based resin foaming agent.

3. Preparation of silver nanowire/anionic water-based polyurethane hybrid conductive film:

The obtained functional water-based resin foaming agent is foamed with a foaming machine and placed in a PTFE carrier plate, waiting for the foam to be eliminated, until the foam is completely ruptured, and the PTFE plate containing the above solution is placed in an oven. Dry in medium, oven temperature is 70 ℃, time is 2.0h. A silver nanowire/anionic aqueous polyurethane mixed conductive film was obtained;

4. Preparation of anionic waterborne polyurethane film:

An anionic water-based polyurethane film with a concentration of 20 g/L was placed on a carrier plate and dried at a temperature of 70°C for 1.5 h to obtain an anionic water-based polyurethane film.

5. Preparation of flexible strain sensing materials:

The above-mentioned anionic water-based polyurethane film was hot-pressed on the elastic fabric pretreated with acetone, the hot-pressing temperature was 160° C., and the hot-pressing time was 2.0 min. Then, the prepared silver nanowire/anionic water-based polyurethane hybrid conductive film was hot-pressed on one side of the anionic water-based polyurethane film of the elastic fabric, the hot-pressing temperature was 85 °C, and the hot-pressing time was 1.5 min, and finally a flexible strain transmission was obtained. Sensitive material.

Among them, in this example, the original fabric needs to be cleaned with acetone: the fabric is put into a Soxhlet extractor containing acetone solution, the temperature is raised to 65°C, and after reflux cleaning for 2.5h, the fabric is transferred to a 60°C oven for drying.

Example 7

1. Preparation of silver nanowire aqueous dispersion:

The ethylene glycol solution of sodium chloride with molar concentration of 37.5 μmol/L, the ethylene glycol solution of polyvinylpyrrolidone (average molecular weight = 1,300,000) with mass concentration of 6 g/L, and nitric acid with mass concentration of 4 g/L were prepared respectively. Silver in ethylene glycol solution. Add 50 mL of ethylene glycol solution of silver nitrate dropwise to 50 mL of ethylene glycol solution of vinylpyrrolidone to prepare a first mixed solution, and then add 1 mL of ethylene glycol solution of sodium chloride dropwise to the above-mentioned first mixed solution, then The reaction is carried out under the temperature condition of 170℃ for 6h～10h. The solid-liquid mixture obtained after the reaction was placed in a centrifuge, centrifuged at 4000 rpm for 5 min, the solid was washed 2 to 3 times with absolute ethanol, the upper layer liquid was removed, and the lower layer precipitate, i.e., the silver nanowires, was dispersed in deionized water by ultrasonic for subsequent use. , and the concentration of silver nanowires was controlled to be 3 g/L. After testing, the yield of the obtained silver nanowires was 83.7%, the diameters of the obtained silver nanowires were uniform, and the average length of the silver nanowires was 40 μm. After testing, the silver nanowires with a length of 30 μm to 50 μm in the product were detected. The proportion is 97%.

2. Preparation of functional water-based resin foaming agent:

The above-obtained silver nanowire dispersion is mixed with anionic water-based polyurethane with a concentration of 5 g/L in proportion to make the dry weight ratio of silver nanowires to anionic water-based polyurethane to be silver nanowires:WPU=0.2:9.8, and then an appropriate amount of water is added. The foaming agent and the foaming stabilizer are mixed uniformly to obtain a functional water-based resin foaming agent.

3. Preparation of silver nanowire/anionic water-based polyurethane hybrid conductive film:

The obtained functional water-based resin foaming agent is foamed with a foaming machine and placed in a PTFE carrier plate, waiting for the foam to be eliminated, until the foam is completely ruptured, and the PTFE plate containing the above solution is placed in an oven. Dry in medium, oven temperature is 70 ℃, time is 2.0h. A silver nanowire/anionic aqueous polyurethane mixed conductive film was obtained;

4. Preparation of anionic waterborne polyurethane film:

An anionic water-based polyurethane film with a concentration of 20 g/L was placed on a carrier plate and dried at a temperature of 70°C for 1.5 h to obtain an anionic water-based polyurethane film.

5. Preparation of flexible strain sensing materials:

The above-mentioned anionic water-based polyurethane film was hot-pressed on the elastic fabric pretreated with acetone, the hot-pressing temperature was 160° C., and the hot-pressing time was 2.0 min. Then, the prepared silver nanowire/anionic water-based polyurethane hybrid conductive film was hot-pressed on one side of the anionic water-based polyurethane film of the elastic fabric, the hot-pressing temperature was 85 °C, and the hot-pressing time was 1.5 min, and finally a flexible strain transmission was obtained. Sensitive material.

Among them, in this example, the original fabric needs to be cleaned with acetone: the fabric is put into a Soxhlet extractor containing acetone solution, the temperature is raised to 65°C, and after reflux cleaning for 2.5h, the fabric is transferred to a 60°C oven for drying.

The difference between the flexible strain sensor materials prepared in Examples 4 to 7 is that the average lengths of silver nanowires in the preparation of functional aqueous resin foaming agents are different, which are 120 μm, 80 μm, 50 μm, and 40 μm, respectively.

The resistivity before and after repeated stretching of the flexible strain sensing materials prepared in Examples 4 to 7 was measured by the four-probe method, and the measurement results are shown in Table 1.

Table 1 Resistivity of flexible strain sensing materials before and after repeated stretching

Example number Resistivity of Flexible Strain Sensing Materials Resistivity after repeated stretching (1000 times) Example 4 1.4x10^-5(Ω·m) 4.2x10^-5(Ω·m) Example 5 1.9x10^-5(Ω·m) 5.7x10^-5(Ω·m) Example 6 4.8x10^-5(Ω·m) 1.4x10^-4(Ω·m)

From the test results in Table 1, it can be seen that the longer the average length of the silver nanowires in the flexible strain sensing material, the better the conductivity and durability of the flexible strain sensing material, and the change in conductivity after repeated stretching smaller.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (8)

1. A preparation method of a flexible strain sensing material is characterized by comprising the following steps:

pressing the anionic waterborne polyurethane film on the flexible substrate layer by a hot pressing method;

pressing the silver nanowire/anionic waterborne polyurethane mixed conductive film on one side of the anionic waterborne polyurethane film of the flexible substrate layer by a hot pressing method;

the preparation method of the silver nanowire/anionic waterborne polyurethane mixed conductive film comprises the following steps:

mixing the silver nanowire water dispersion, anionic waterborne polyurethane, a foaming agent and a foam stabilizer to prepare a functional waterborne resin foaming agent;

and placing the functional aqueous resin foaming agent on a carrier plate after foaming treatment until the foam is completely eliminated, and drying the functional aqueous resin foaming agent for 1.0 to 3.0 hours at the temperature of between 60 and 80 ℃ to obtain the silver nanowire/anionic aqueous polyurethane mixed conductive film.

2. The method of preparing a flexible strain sensing material according to claim 1, wherein the method of preparing the aqueous dispersion of silver nanowires comprises the steps of:

providing a glycol solution of sodium chloride;

providing a glycol solution of an organic protectant;

providing a glycol solution of a silver precursor;

mixing the glycol solution of the silver precursor with the glycol solution of the organic protective agent to obtain a first mixed solution;

mixing the ethylene glycol solution of sodium chloride with the first mixed solution to prepare a second mixed solution;

reacting the second mixed solution at the temperature of 110-150 ℃ for 6-10 h to prepare a solid-liquid mixture, and separating the solid-liquid mixture to remove the upper solution to prepare the silver nanowires;

dispersing the silver nanowires in deionized water to prepare the silver nanowire water dispersion;

the concentration of the silver nanowires in the silver nanowire water dispersion liquid is 1 g/L-10 g/L.

3. The method for preparing a flexible strain sensing material according to claim 2, wherein the glycol solution of the silver precursor and the glycol solution of the organic protective agent are mixed in such a manner that the glycol solution of the silver precursor is added dropwise to the glycol solution of the organic protective agent; the mixing mode of the ethylene glycol solution of sodium chloride and the first mixed solution is to drop the ethylene glycol solution of sodium chloride into the first mixed solution.

4. The preparation method of the flexible strain sensing material according to claim 1, wherein in the preparation method of the silver nanowire/anionic waterborne polyurethane mixed conductive film, the concentration of the anionic waterborne polyurethane is 1 g/L-10 g/L; the dry weight ratio of the silver nanowires to the anionic waterborne polyurethane is (1:9) - (3: 7).

5. The method for preparing the flexible strain sensing material according to claim 1, wherein the foaming agent is any one or more of sodium dodecyl sulfate, lauryl betaine and dodecyl dimethyl benzyl ammonium chloride; the content of the foaming agent in the functional aqueous resin foaming agent is 0.1 g/L-1.0 g/L.

6. The preparation method of the flexible strain sensing material according to claim 1, wherein the foam stabilizer is any one or more of sodium alginate, sodium carboxymethylcellulose, polyvinyl alcohol, agar and guar gum; the content of the foam stabilizer in the functional aqueous resin foaming agent is 0.1-1.0 g/L.

7. The method of manufacturing a flexible strain sensing material according to any of claims 1 to 6,

in the step of laminating the anionic waterborne polyurethane film on the flexible substrate layer by a hot pressing method, the hot pressing temperature is 150-170 ℃, and the hot pressing time is 1.0-3.0 min;

and in the step of laminating the silver nanowire/anionic waterborne polyurethane mixed conductive film on one side of the anionic waterborne polyurethane film of the flexible substrate layer by a hot pressing method, the hot pressing temperature is 70-100 ℃, and the hot pressing time is 1.0-2.0 min.

8. A flexible strain sensing material, characterized in that the strain sensing material is prepared by the method for preparing a strain sensing material according to any one of claims 1 to 7.

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