CN113831565B

CN113831565B - High-transparency recyclable flexible multifunctional electronic skin and preparation method and application thereof

Info

Publication number: CN113831565B
Application number: CN202111228470.XA
Authority: CN
Inventors: 朱雨田; 常晓华; 陈良仁
Original assignee: Hangzhou Normal University
Current assignee: Hangzhou Normal University
Priority date: 2021-10-21
Filing date: 2021-10-21
Publication date: 2023-09-29
Anticipated expiration: 2041-10-21
Also published as: CN113831565A

Abstract

The invention discloses a high-transparency recyclable multifunctional electronic skin and a preparation method and application thereof. Adding citric acid and a silver source into polyvinyl alcohol, heating and blending, then pouring the mixture into a mold after ultrasonic treatment, carrying out in-situ reduction reaction to obtain silver nano particles, and volatilizing a solvent to obtain the polyvinyl alcohol/citric acid/silver nano particle conductive composite film. And taking out the film, and applying copper electrodes at two ends to prepare the high-transparency recyclable multifunctional electronic skin material. According to the invention, the mechanical property and the electrical conductivity of the electronic skin are regulated by changing the feeding ratio of the polyvinyl alcohol, the citric acid and the silver source, so that the electronic skin can respond to the change of temperature, humidity and external acting force, has multifunctionality and multiple responsiveness, and has excellent repeatability and stability in response behavior. By utilizing the water solubility and biodegradability of the bio-based material, the electronic skin film can be directly hydrolyzed, and the hydrolyzed solution can be re-cast and assembled, so that the obtained regenerated electronic skin has equivalent performance.

Description

High-transparency recyclable flexible multifunctional electronic skin and preparation method and application thereof

Technical Field

The invention belongs to the technical field of high polymer materials and flexible electronics, and particularly relates to a high-transparency recyclable flexible multifunctional electronic skin material, and a preparation method and application thereof.

Background

With the development of science and technology, human beings are stepping into the intelligent era. Flexible electronic devices based on artificial intelligence technology are receiving great attention due to their great application prospects in emerging fields such as wearable electronic devices and electronic skin. The electronic skin has human skin characteristics (such as stretchability, elasticity and the like), can convert perceived external stimuli such as tension, pressure, temperature, humidity and the like into visual/measurable electric signals, and has important application in the fields of human-computer interaction, health monitoring, soft robots and the like. At present, electronic skin sensing mechanical deformation has been reported, and related technologies tend to mature, but less researches on temperature sensing and humidity sensing are performed, which limits further development of electronic skin. In addition, the conventional electronic skin sensor is obtained by compounding a conductive material and a flexible substrate. Common flexible matrix materials include polydimethylsiloxane, thermoplastic polyurethane, rubber, and the like. However, the wide use of the electronic skin sensor based on the synthetic polymer material can generate a large amount of undegradable electronic garbage, which is easy to cause resource waste and environmental pollution, and is not in compliance with the requirement of green sustainable development of the current society, thereby severely restricting the application of the electronic skin in the fields of flexible electronic devices and the like. Therefore, the natural polymer material with a plurality of advantages such as wide sources, excellent biocompatibility, biodegradability and the like is reasonably processed and designed, and the novel green flexible sensing device is prepared and has important significance for promoting the development of electronic skin.

Polyvinyl alcohol (PVA) has attracted much attention as an environment-friendly material which is abundant in nature and has biodegradability and biocompatibility. In recent years, researchers have prepared PVA-based electronic skin sensors by incorporating different conductive materials, such as metals, alloys, liquid metals, ions, semiconductors, and carbon nanomaterials, into the PVA matrix. Among the above conductive materials, carbon-based materials are widely used due to their excellent electrical conductivity, heat permeability and mechanical properties. However, the use of carbon-based materials reduces the transparency of the sensor, making it difficult to meet the needs of people for sensor visualization applications. In addition, the PVA material has poor flexibility and low elasticity, so that the detection range of the strain sensor is limited; the high viscosity and low fluidity of the polymer material often cause the problems of uneven distribution, agglomeration and the like when the conductive filler is doped in the substrate material, and how to realize the uniform dispersion of the conductive filler in the polymer matrix is also a great challenge.

The invention prepares the polyvinyl alcohol/citric acid/silver nano particles (PVA/CA/AgNPs) electronic skin material by using in-situ reduction and solution casting methods, and assembles the material to obtain the electronic skin sensor, thereby developing a preparation method of the high-transparency recyclable multifunctional electronic skin material with excellent performance, simple process and low cost. The AgNPs not only have good conductivity and antibacterial property, but also realize uniform dispersion of the AgNPs in the composite film through strong interaction with PVA and CA, and improve the comprehensive performance of the PVA/CA/AgNPs conductive composite film. The high-transparency and flexible electronic skin sensor can be used for detecting strain, temperature and humidity stimulus, and has high sensitivity, good stability and repeatability of sensing. Meanwhile, the polymer has good biocompatibility and biodegradability, so that the recycling property of the electronic skin material can be realized, and the polymer has important significance for the development of green flexible electrons in the future.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a preparation method of a high-transparency recyclable flexible multifunctional electronic skin material, and the prepared electronic skin sensor has excellent mechanical property, high sensitivity, good stability and multifunctional sensing performance on strain, temperature and humidity.

In order to solve the technical problems, the invention adopts the following solutions:

the preparation method of the high-transparency recyclable flexible multifunctional electronic skin material, which is soluble in water, comprises the following steps:

step (1), adding polyvinyl alcohol (PVA) into deionized water, heating and stirring to obtain a polymer solution;

preferably, the heating temperature in the step (1) is 80-100 ℃;

preferably, the concentration of the polyvinyl alcohol solution in the step (1) is 8-20wt%;

step (2), adding the citric acid solution into the polymer solution in the step (1), and heating and stirring to uniformly mix the citric acid solution and the polymer solution to obtain a first mixed solution; wherein the mass ratio of the citric acid CA to the polyvinyl alcohol is 0.2-0.5: 1, a step of;

preferably, the heating temperature in the step (2) is 40-60 ℃, and the stirring time is 0.5-1 h;

preferably, the concentration of the citric acid solution in the step (2) is 10-23 wt%;

step (3), adding a silver source into the first mixed solution in the step (2), and heating and stirring to obtain a second mixed solution; wherein the mass ratio of the silver source to the polyvinyl alcohol is 0.02-0.5: 1, a step of;

preferably, the heating temperature in the step (3) is 40-60 ℃, and the stirring time is 1.5-3 h;

preferably, the silver source in the step (3) is one of silver nitrate or silver acetate;

step (4), pouring the second mixed solution obtained in the step (3) into a mould after ultrasonic treatment, putting the mould into a constant temperature and humidity box to perform in-situ reduction reaction to generate silver nano particles, and drying to obtain a conductive composite film of polyvinyl alcohol/citric acid/silver nano particles (PVA/CA/AgNPs);

preferably, the ultrasonic time in the step (4) is 20-40 min; the temperature of the constant temperature and humidity box is 35-55 ℃, the relative humidity is 50-65%, and the drying time is 6-12 h;

preferably, the thickness of the conductive composite film is 0.12 to 0.3mm.

And (5) taking the conductive composite film out of the die, cutting the conductive composite film into a strip shape, and pasting copper electrodes at two ends of the conductive composite film to prepare the electronic skin material.

The electronic skin material prepared by the invention has recycling property, the conductive composite film in the step (4) is redissolved in water, the mass of the water is 8-20 times that of the electronic skin material, the film is cast again according to the method of the step (4), the electronic skin sensor is assembled and prepared, and the remolded electronic skin sensor can still be used for monitoring the sensing performance of strain, temperature and humidity.

Another object of the present invention is to provide an electronic skin material, which is prepared by the above method.

It is a further object of the present invention to provide an electronic skin sensor employing the above electronic skin material, wherein the electronic skin sensor is a strain, temperature or humidity sensor.

Preferably, the electronic skin sensor is a humidity sensor.

Compared with the prior art, the invention has the following advantages:

(1) The invention adopts silver source and reducer citric acid with proper proportion to realize the uniform dispersion of AgNPs: if the amount of the silver source is too large, the silver nano particles are agglomerated and distributed unevenly; if the amount is too small, the conductivity of the composite film decreases, and the conductivity decreases.

(2) The invention adopts an in-situ reduction method to prepare the high-transparency recyclable flexible multifunctional electronic skin, has simple preparation method, low cost and high feasibility, and is easy to realize industrial production; because the electronic skin material is soluble in water, the electronic skin sensor can be assembled and prepared again by re-casting the film after re-dissolving in water, thereby realizing recycling.

(3) The conductive composite film prepared by the invention has response behaviors to strain, temperature and humidity stimulus, and the multifunctional characteristics of the conductive composite film can be used for monitoring human body movement, sensing external environment temperature change and human body skin humidity change, and is used for personal health management.

(4) The water solubility and the biodegradability of the citric acid and the polymer matrix realize the recycling property of the electronic skin material, and provide a new idea for efficiently developing the high-value utilization of green flexible electronic and bio-based high polymer materials.

Drawings

FIGS. 1 (a) - (b) are scanning electron micrographs of comparative example 3 and example 3, respectively.

Fig. 2 is an assembled schematic view of an electronic skin sensor.

Fig. 3 is a graph showing the relative resistance change under stretching in example 2.

Fig. 4 is a graph showing the relative resistance change with temperature in example 2.

FIG. 5 is a plot of the resistance response of example 3 at alternating relative humidity levels between 50% and 90%.

Fig. 6 shows the strain sensing performance of example 2 before and after hydrolysis.

Detailed Description

The following examples will provide those skilled in the art with a more complete understanding of the present invention and are not intended to limit the invention in any way. As described above, in view of the shortcomings of the prior art, the present inventors have long studied and practiced in a large number, and have proposed the technical solution of the present invention, which mainly depends on at least: (1) The silver source and the reducing agent citric acid with proper proportions are adopted to realize the uniform dispersion of AgNPs: if the amount of the silver source is too large, the silver nano particles are agglomerated and distributed unevenly; if too little, the conductivity of the composite film is reduced, and the conductivity is reduced; (2) The high-transparency recyclable flexible multifunctional electronic skin is prepared by adopting an in-situ reduction method, the preparation method is simple, the cost is low, the feasibility is high, and the industrial production is easy to realize; (3) The conductive composite film has a response behavior to strain, temperature and humidity stimuli; (4) The electronic skin material can be dissolved in water, and the electronic skin sensor can be assembled and prepared again by re-casting the film after re-dissolving in water, so that the recycling is realized;

the present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.

The invention relates to a high-transparency recyclable flexible multifunctional electronic skin material, which is soluble in water, and the preparation method comprises the following steps:

preferably, the heating temperature in the step (1) is 80-100 ℃;

preferably, the thickness of the conductive composite film is 0.12 to 0.3mm.

And (5) taking the conductive composite film out of the die, cutting the conductive composite film into a strip shape, and attaching copper electrodes to the two ends of the conductive composite film to prepare the electronic skin sensor.

The electronic skin sensor is assembled by applying copper sheets to two ends of the electronic skin material, wherein the electronic skin sensor is a strain, temperature or humidity sensor.

The following description of the present invention is further provided with reference to several preferred embodiments, but the experimental conditions and setting parameters should not be construed as limiting the basic technical scheme of the present invention. And the scope of the present invention is not limited to the following examples.

Examples 1 to 6

In examples 1 to 6, polyvinyl alcohol of a certain mass was dissolved in deionized water according to the data in table 1, and a polyvinyl alcohol solution was obtained after heating and stirring; preparing a citric acid solution, and adding the citric acid solution into a polyvinyl alcohol solution to obtain a first mixed solution of polyvinyl alcohol and citric acid; and adding a silver source into the polyvinyl alcohol/citric acid first mixed solution, and heating and stirring to obtain a second mixed solution. And (3) after ultrasonic treatment, pouring the second mixed solution into a mould, and placing the mould into a constant temperature and humidity box with constant temperature and humidity to perform in-situ reduction reaction to generate silver nano particles, wherein the reaction time is 6-12h. And (3) volatilizing the solvent to obtain the polyvinyl alcohol/citric acid/silver nanoparticle (PVA/CA/AgNPs) conductive composite film. And taking the film out of the die, cutting the film into strips with the length of 30mm multiplied by 6mm, and applying copper electrodes on two sides of the strips to assemble the multifunctional electronic skin sensor. The raw material feed ratio, heating temperature, stirring time, reduction reaction temperature, humidity and reaction time in the preparation of the PVA/CA/AgNPs conductive composite film are shown in Table 1.

In comparative examples 1 to 3, a first mixed solution was prepared according to the above method without adding a silver nitrate solution using polyvinyl alcohol and citric acid as raw materials, and was dried in a constant temperature and humidity cabinet at constant temperature and humidity to prepare a polymer composite film.

Table 1: the reaction parameters (raw material feed ratio, heating temperature, stirring time, reduction reaction temperature, humidity and reaction time) of examples 1 to 6 and comparative examples 1 to 3

The conductivity of the samples of the present invention was calculated using the formula σ=l/RS, where L, S and R represent the length, cross-sectional area, and resistance of the samples to be measured, respectively, and the results are shown in table 2. Comparative examples 1 to 3 contained no conductive component and had no conductivity. Examples 1-3 the conductivity of the PVA/CA/AgNPs conductive composite film was enhanced with increasing the amount of citric acid. Similarly, examples 4 to 6 showed an increase in the amount of silver nitrate, and the conductive properties of the composite film were enhanced mainly due to the increase in the amount of silver nanoparticles generated by the in-situ reduction reaction, and the formation of more conductive paths, and the conductivity of the composite film was increased.

FIG. 1 (a) (b) is a scanning electron microscope image of the microstructure of comparative example 3 and example 3. As can be seen from the figure, the cross section of example 3 is distributed with a large number of silver nano particles with uniform size, the size is 10-15 nm, which indicates that the PVA/CA/AgNPs conductive composite film is successfully prepared, and the silver nano particles are uniformly dispersed. The transparency of the PVA/CA/AgNPs conductive composite film was characterized by an ultraviolet-visible spectrometer. As shown in Table 2, the prepared PVA/CA/AgNPs conductive composite film has high transparency, the light transmittance is 87% or more, and the requirements of transparency of electronic skin can be met.

Table 2: thickness, conductivity and transmittance of examples 1 to 6 and comparative examples 1 to 3

According to the mode of figure 2, the PVA/CA/AgNPs conductive composite film is assembled into an electronic skin material, namely, the composite film is cut into rectangular sample strips, silver paste is brushed at two ends of the sample strips, then the sample strips are wrapped by copper sheets, and then copper wires are connected to the copper sheets. The electronic skin material is subjected to sensing performance test of strain, temperature and humidity, and the resistance change of the electronic skin under different external stimuli is recorded in real time by using a digital multimeter.

And the universal testing machine and the digital multimeter are combined to realize the real-time strain sensing performance test of the PVA/CA/AgNPs multifunctional electronic skin. Fig. 3 is a graph showing the change in resistance at 150% strain for example 2. As the strain increases from 0 to 150%, the conductive pathways within the electronic skin are correspondingly broken and the electrical resistance increases. As the external force is removed, the electronic skin returns to its original shape, the internal conductive path returns accordingly, and the resistance drops sharply, returning to its original state. From this, it is known that the prepared electronic skin can respond in real time to the strain. The resistance change is basically consistent after 10 times of cyclic stretching under the strain, which shows that the prepared multifunctional electronic skin has good stability and repeatability. Experimental results prove that the PVA/CA/AgNPs-based multifunctional electronic skin has good application function in the aspect of real-time sensing of strain.

And the real-time temperature sensing performance test of the PVA/CA/AgNPs multifunctional electronic skin is realized by using the combination of the heat table and the digital multimeter. As shown in fig. 4, the relative resistance change of example 2 decreased as the temperature increased from 30 ℃ to 40 ℃, showing a significant negative temperature effect, i.e., increased temperature, decreased resistance, and enhanced conductivity of the film. Experimental results prove that the PVA/CA/AgNPs-based multifunctional electronic skin can monitor the change of the environmental temperature in real time.

And the real-time humidity sensing performance test of the PVA/CA/AgNPs multifunctional electronic skin is realized by using a constant temperature and humidity box and a digital multimeter. As shown in fig. 5, when the relative humidity was reduced from 90% to 50%, the resistance of example 3 was increased, i.e., the conductivity of the film was decreased. When the relative humidity was recovered from 50% to 90%, the resistance of example 3 was reduced and the conductivity of the film was recovered to the original state. This is because of the hydrophilic nature of citric acid and polyvinyl alcohol, which has good hygroscopicity. When the ambient humidity is increased, the surface of the PVA/CA/AgNPs electronic skin adsorbs a large amount of water molecules to form more conductive paths, so that the conductivity is improved, and the relative resistance change is reduced; conversely, the ambient humidity decreases, the conductive path decreases, and the resistance increases. The electronic skin is repeatedly circulated for 3 times, and the relative resistance change is almost unchanged, so that the prepared electronic skin not only can monitor the environmental humidity change, but also has good circulation stability.

The water-solubility and biodegradability of polyvinyl alcohol and citric acid make the prepared multifunctional electronic skin material recyclable. As shown in fig. 6, example 2 still maintains good sensing performance before and after hydrolysis, and the resistance change is almost the same. The result shows that the PVA/CA/AgNPs-based multifunctional electronic skin material has recycling property, reduces the generation of electronic garbage and promotes the development of green flexible electronic skin.

Finally, it should be noted that the above list is only specific embodiments of the present invention. Obviously, the invention is not limited to the above embodiments, but many variations are possible. All modifications directly derived or suggested to one skilled in the art from the present disclosure should be considered as being within the scope of the present invention.

Claims

1. A preparation method of a high-transparency recyclable flexible multifunctional electronic skin material is characterized by comprising the following steps of:

step (1), adding polyvinyl alcohol PVA into deionized water, heating and stirring to obtain a polymer solution;

step (4), pouring the second mixed solution obtained in the step (3) into a mould after ultrasonic treatment, putting the mould into a constant temperature and humidity box for in-situ reduction reaction to generate silver nano particles, and drying to obtain the conductive composite film of polyvinyl alcohol/citric acid/silver nano particles PVA/CA/AgNPs; the conductive composite film has a response behavior to strain, temperature and humidity stimuli;

2. The method for preparing the high-transparency recyclable flexible multifunctional electronic skin material, which is characterized in that the heating temperature in the step (1) is 80-100 ℃; the heating temperature of the step (2) is 40-60 ℃, and the stirring time is 0.5-1 h; the heating temperature of the step (3) is 40-60 ℃, and the stirring time is 1.5-3 h.

3. The method for preparing the high-transparency recyclable flexible multifunctional electronic skin material is characterized in that the concentration of the polyvinyl alcohol solution in the step (1) is 8wt% -20 wt%; the concentration of the citric acid solution in the step (2) is 10wt% -23 wt%.

4. The method for preparing the high-transparency recyclable flexible multifunctional electronic skin material according to claim 1, wherein the silver source in the step (3) is one of silver nitrate or silver acetate.

5. The method for preparing the high-transparency recyclable flexible multifunctional electronic skin material is characterized in that the ultrasonic time in the step (4) is 20-40 min; the temperature of the constant temperature and humidity box is 35-55 ℃, the relative humidity is 50-65%, and the drying time is 6-12h.

6. An electronic skin material prepared by the method of any one of claims 1-5.

7. The electronic skin material of claim 6, wherein the conductive composite film has a thickness of 0.12-0.3 mm.

8. An electronic skin material according to claim 7, characterized in that it is obtained by dissolution-casting, redissolved in water, then poured into a mould after ultrasound, and dried in a constant temperature and humidity box, and the recast film is obtained to obtain a conductive composite film of polyvinyl alcohol/citric acid/silver nanoparticles PVA/CA/AgNPs; wherein the mass of the water is 8-20 times of the mass of the electronic skin material.

9. An electronic skin sensor characterized in that an electronic skin material according to claim 7 is used.

10. Use of an electronic skin sensor according to claim 9 in a strain, temperature or humidity sensor.