CN115449264A

CN115449264A - Conductive ink and preparation method and application thereof

Info

Publication number: CN115449264A
Application number: CN202211016304.8A
Authority: CN
Inventors: 吴鑫; 陈曦玥; 杨汝雪
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2022-08-24
Filing date: 2022-08-24
Publication date: 2022-12-09

Abstract

The invention provides conductive ink and a preparation method and application thereof, and relates to the technical field of sensors. The preparation method of the conductive ink comprises the following steps: s1, using graphite plates as an anode and a counter electrode, and immersing in deionized water for electrolysis to obtain nano graphite water dispersion liquid; and S2, mixing silver paste with the nano graphite water dispersion liquid to obtain a mixed liquid, and performing ultrasonic dispersion on the mixed liquid to obtain the conductive ink. The invention develops the conductive ink which is prepared by mixing nano graphite water dispersion liquid obtained by electrolysis and silver paste, the conductive ink is printed on the surface of a flexible substrate in an ink-jet printing mode to obtain the flexible electrode, and the prepared flexible mechanical sensor has excellent electric conductivity, high sensitivity and high repeatable electric response.

Description

Conductive ink and preparation method and application thereof

Technical Field

The invention relates to the technical field of sensors, in particular to conductive ink and a preparation method and application thereof.

Background

Flexible electronics is a technique for attaching inorganic/organic devices to flexible substrates to form circuits. At present, flexible wearable electronic devices have the potential of wide application in the fields of wearable equipment, energy storage materials, artificial skin, intelligent motion detection sensors and the like. The advent of smart wearable devices has put higher demands on matching sensing of mechanical deformations (bending folds, twists, stretches, etc.) of the respective mechanical sensors. Traditional mechanical sensors made of metal or semiconductor can only sense less than 5% of stress, and cannot be worn due to inherent rigidity, and flexible strain sensors have good flexibility, light weight and good fit with skin, and have the potential of developing intelligent wearable health monitoring equipment. These flexible mechanical sensors achieve transmission by converting external stimuli such as stress, pressure, humidity and temperature into electrical signals such as current, voltage, resistance change, etc.

The ink-jet printing is a processing technology for forming a specified electrode structure by high-precision controllable printing and ejecting of ink from a needle head in a piezoelectric driving mode and the like, and has the advantages of high precision, low cost, simple processing procedure, room-temperature working, high flexibility and the like. The preparation of electrodes for mechanical sensors by ink-jet printing has been widely used.

Generally, inks used for inkjet printing are mainly conductive active materials such as graphene, metal nanoparticles, carbon nanotubes, and the like. However, the cost of the carbon nanotube and silver nanoparticle ink is too high, and the application is limited; graphene ink is poor in conductivity and is not suitable for sophisticated logic circuits due to its zero band gap characteristic.

Chinese patent application CN 104277592A discloses a graphene-based aqueous ink and an application of the same in inkjet printing of a transparent patterned conductive electrode, wherein the graphene-based aqueous ink is a composite of graphene, graphene oxide and silver nanoparticles prepared by a liquid phase stripping method. However, the patterned conductive electrode made of the ink is not a flexible electrode, and has poor performance of conducting electrical signals under the action of repeated bending and stress.

Therefore, it is desirable to provide a conductive ink that can be used to prepare electrodes for flexible mechanical sensors.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide the conductive ink, the preparation method and the application thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

the conductive ink is prepared by the following preparation method:

s1, using graphite plates as an anode and a counter electrode, immersing in deionized water for electrolysis, and obtaining nano graphite water dispersion liquid after ultrasonic treatment and centrifugation of electrolyte;

and S2, mixing silver paste with the nano graphite water dispersion liquid to obtain a mixed liquid, and performing ultrasonic dispersion on the mixed liquid to obtain the conductive ink.

According to the invention, the nano graphite water dispersion liquid and the silver paste are used as raw materials of the conductive ink, and the prepared conductive ink has excellent conductive sensitivity and high repeated response performance.

The nano graphite water dispersion liquid subjected to electrolytic treatment contains graphene, graphene oxide and nano carbon particles, wherein the graphene is uniformly distributed in the nano graphite water dispersion liquid in a two-dimensional lamellar structure. After the silver paste and the nano graphite water dispersion liquid are mixed, the two-dimensional graphene sheets are inserted into silver nanoparticles in the silver paste to form a tightly connected conductive network, so that the conductive ink has excellent conductive sensitivity.

Due to the specificity of the graphene and the silver nanoparticles and the specific combination mode of the graphene and the silver nanoparticles, the formed conductive ink is subjected to ink-jet printing to form a flexible electrode, and the flexible electrode is attached to a flexible substrate to generate a conductive network with high repetitive response. When the mechanical sensor is stressed, the flexible electrode can generate microcracks, and when the stress is released, the sizes of the microcracks are reduced and the flexible electrode is restored to the initial state. The formation and recovery of the microcracks is a reversible process and thus the conductive ink of the present invention has a high repetitive responsiveness.

Preferably, the purity of the graphite plate is more than or equal to 99%.

Preferably, the current of the electrolytic treatment is constant current 15-30 mA, the temperature is 20-30 ℃, and the time is 7-14 days.

By the electrolysis treatment method, the nano-graphite water dispersion with good dispersibility and proper concentration can be prepared.

The silver paste contains silver nanoparticles.

Preferably, the average particle size of the silver nanoparticles in the silver paste is 80-600 nm.

More preferably, the average particle size of the silver nanoparticles in the silver paste is 100-300 nm.

The silver nanoparticles in the silver paste are not suitable for being too large in particle size, poor in dispersibility when the particle size is too large, and easy to agglomerate, so that a spray head of an ink-jet printer is blocked, the printability of the prepared conductive ink is poor, and the combinability of the conductive ink and two-dimensional graphene sheets is also poor.

Preferably, the concentration of graphene in the nano graphite water dispersion liquid is 15-30 mg/ml, and the concentration of silver nanoparticles in the silver paste is 30-40 mg/ml.

Preferably, in the step S2, the volume ratio of the nano graphite water dispersion liquid to the silver paste is 1: 4-10.

The inventor researches and discovers that the content of the graphene and the silver nanoparticles is in a proper range, and the conductive ink can achieve good conductive performance and printability.

According to the invention, the concentration of graphene in the nano graphite water dispersion liquid and the concentration of silver nanoparticles in the silver paste are adjusted, and the volume ratio of the nano graphite water dispersion liquid to the silver paste is controlled, so that the contents of effective components of graphene and silver nanoparticles in the conductive ink are controlled. When the concentration and the volume ratio are within the range, the viscosity of the mixed solution is 7-8 cp, and the ink prepared by ultrasonic dispersion is suitable for ink-jet printing; and the concentration of the graphene and the silver nanoparticles is matched, and the graphene and the silver nanoparticles can be effectively combined to form a conductive network, so that the conductivity of the ink is strong.

The invention also discloses conductive ink prepared by the preparation method.

The invention also protects the application of the conductive ink as an electrode material in the preparation of a flexible mechanical sensor.

The invention also discloses a flexible mechanical sensor, which is prepared by the following method:

and adding the conductive ink into an ink-jet printer, printing a flexible electrode on the surface of the flexible substrate by ink-jet printing, and heating to obtain the flexible mechanical sensor.

The conductive ink is used as ink for ink-jet printing, and the flexible electrode is printed on the surface of the flexible substrate, so that the flexible mechanical sensor is prepared. When the flexible mechanical sensor is stressed, the applied stress enables the flexible substrate to deform, microcracks can be generated in the flexible electrode printed on the surface of the flexible substrate, and the microcracks can change the resistance, so that sensitive electric conduction is generated; when the strain is increased, the number and the size of micro cracks are increased, and the micro cracks are uniformly propagated on the whole flexible film, so that the electric signal conduction accuracy is high; when the stress is released, the size of the microcrack is reduced, the flexible electrode is recovered to be almost the same as the original relaxed state, and the repeated responsiveness of the flexible mechanical sensor is high when the flexible mechanical sensor conducts an electric signal.

Preferably, the flexible substrate is at least one of Polyimide (PI), thermoplastic polyurethane elastomer (TPU), polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), and Polyethylene (PE).

Preferably, the heating treatment is carried out at 130-150 ℃ for 30-60 min.

The solvent in the conductive ink is removed by a heating treatment.

Compared with the prior art, the invention has the beneficial effects that:

the invention develops the conductive ink which is prepared by mixing nano graphite water dispersion liquid obtained by electrolysis and silver paste, the conductive ink is printed on the surface of a flexible substrate in an ink-jet printing mode to obtain the flexible electrode, and the prepared flexible mechanical sensor has excellent electric conductivity, high sensitivity and high repeatable electric response.

Drawings

FIG. 1 is a graph of resistance change of a flexible mechanical sensor prepared in example 1 under a single strain;

FIG. 2 is a graph showing the resistance change of the flexible mechanical sensor prepared in example 1 under the continuous tapping action of the index finger;

FIG. 3 is a graph of resistance change of the flexible mechanical sensor prepared in example 1 under different bending angles of a finger;

fig. 4 is a graph of 100 identical stress cycles for a flexible mechanical sensor prepared in example 1.

Fig. 5 is a GF plot of the 10% uniaxial tensile response of the flexible mechanical sensor prepared in example 1.

Detailed Description

For better illustrating the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to specific examples and drawings, but the examples are not intended to limit the present invention in any way. The reagents, methods and apparatus employed in the present invention are conventional in the art, except as otherwise indicated. Unless otherwise indicated, reagents and materials used in the present invention are commercially available.

Example 1

The embodiment provides conductive ink and a flexible mechanical sensor.

The conductive ink is prepared by the following method:

s1, using graphite plates (the purity is more than or equal to 99%) as an anode and a counter electrode, soaking the two electrodes in deionized water, and carrying out electrolytic treatment under the conditions of constant current of 20mA and 25 ℃ for 7 days; ultrasonically dispersing the electrolyte, centrifuging and filtering to remove large-particle substances to obtain nano graphite water dispersion liquid;

after the nano graphite water dispersion liquid is concentrated, the concentration of graphene is 20mg/ml;

s2, mixing silver paste (silver paste-1, the concentration of silver nanoparticles is 30mg/ml, and the average particle size is 100 nm) with the nano graphite water dispersion liquid, wherein the volume ratio of the nano graphite water dispersion liquid to the silver paste is 1: 5, so as to obtain a mixed liquid, wherein the viscosity of the mixed liquid is 7cp; and ultrasonically dispersing the mixed solution for 20min to obtain the conductive ink.

The flexible mechanical sensor is prepared by the following method:

adding the conductive ink into an ink-jet printer (Broadjet DP500 ink-jet printer), taking PET as a flexible substrate, and carrying out ink-jet printing on the surface of the PET to obtain a flexible electrode; and heating at 150 ℃ for 30min, and removing the solvent to obtain the flexible mechanical sensor.

Example 2

The embodiment provides conductive ink and a flexible mechanical sensor.

The preparation method of the conductive ink is different from that of the embodiment 1 in that:

silver paste-1 is replaced by silver paste-2, the concentration of silver nanoparticles is A, and the average particle size is 300nm.

The flexible mechanical sensor of the present example was prepared in the same manner as in example 1, wherein the conductive ink prepared in example 2 was used as the ink.

Example 3

The embodiment provides a conductive ink and a flexible mechanical sensor.

silver paste-1 is replaced by silver paste-3, the concentration of silver nanoparticles is A, and the average particle size is 600nm.

The flexible mechanical sensor of the present example was prepared in the same manner as in example 1, wherein the conductive ink prepared in example 3 was used as the ink.

Example 4

The embodiment provides conductive ink and a flexible mechanical sensor.

and (3) after the nano graphite water dispersion liquid is concentrated, controlling the concentration of the graphene to be 15mg/ml.

The flexible mechanical sensor of the present example was prepared in the same manner as in example 1, wherein the conductive ink prepared in example 4 was used as the ink.

Example 5

The embodiment provides conductive ink and a flexible mechanical sensor.

and after the nano graphite water dispersion liquid is concentrated, controlling the concentration of the graphene to be 30mg/ml.

The flexible mechanical sensor of the present example was prepared in the same manner as in example 1, wherein the conductive ink prepared in example 5 was used as the ink.

Example 6

The embodiment provides conductive ink and a flexible mechanical sensor.

the concentration of silver nanoparticles in the silver paste is 35mg/ml, and the volume ratio of the nano graphite water dispersion liquid to the silver paste is 1: 10; a mixed solution having a viscosity of 8cp was obtained.

The flexible mechanical sensor of the present example was prepared in the same manner as in example 1, wherein the conductive ink prepared in example 6 was used as the ink.

Example 7

The embodiment provides conductive ink and a flexible mechanical sensor.

The conductive ink of this example was prepared in the same manner as in example 1.

The preparation method of the flexible mechanical sensor is different from that of the embodiment 1 in that: PDMS is used as a flexible substrate.

Comparative example 1

The present comparative example provides a conductive ink and a mechanical sensor.

The conductive ink is nano-graphite water dispersion liquid, and the nano-graphite water dispersion liquid is prepared by the following method: graphite plates (the purity is more than or equal to 99%) are used as an anode and a counter electrode, the two electrodes are immersed in deionized water for electrolytic treatment, and the electrolytic treatment conditions are constant current of 20mA and 25 ℃, and the electrolysis is carried out for 7 days; ultrasonically dispersing the electrolyte, centrifuging and filtering to remove large particle substances to obtain nano graphite water dispersion liquid; the concentration of graphene in the nano graphite water dispersion liquid after concentration is 40mg/ml.

The mechanical sensor was prepared in the same manner as in example 1, using the conductive ink prepared in comparative example 1.

Comparative example 2

The conductive ink was the aqueous dispersion of nano-graphite prepared in example 1, and the concentration of graphene was 20mg/ml.

The mechanical sensor was prepared in the same manner as in example 1, wherein the ink used was the conductive ink prepared in comparative example 2.

Comparative example 3

The conductive ink is prepared by the following method:

dispersing graphene particles prepared by a liquid phase stripping method in water to obtain a dispersion liquid A, wherein the concentration of graphene is 20mg/ml; dispersing silver nanoparticles in water to obtain a dispersion liquid B, wherein the concentration of the silver nanoparticles is 30mg/ml;

and mixing the dispersion liquid A and the dispersion liquid B in a volume ratio of 1: 5 to obtain the conductive ink.

The mechanical sensor was prepared in the same manner as in example 1, wherein the ink used was the conductive ink prepared in comparative example 3.

Performance test

The performance of the mechanical sensor obtained in the above examples and comparative examples is characterized, and the specific test items and test methods are as follows:

(1) And (3) testing the sensitivity: calibrating the sensitivity of the sensor by using a Guage Factor;

wherein

Is the relative resistance change,. Epsilon.is the strain, R and R ₀ Resistance under load and original condition, respectively; the higher the GF is, the more sensitive the sensor is;

(2) Repeated response performance: using a mechanical testing platform and a binomial step electrode controller to give 100 times of uniaxial tension of the same strain to the mechanical sensor, and calculating the relative resistance change rate (delta R/R) of the sensor at the 100 th time ₀ ) Retention rate as compared to first time；

(3) And (3) testing the resistance change under the action of single strain: measuring a resistance change diagram of the mechanical sensor under different strains by adopting a mechanical platform and a binomial step electrode controller, clamping the mechanical sensor on the mechanical platform, controlling the mechanical platform by a computer to stretch the mechanical sensor in a single shaft, and measuring the resistance change by using a precision resistance/capacitance measuring instrument;

(4) And (3) testing the resistance change under the continuous knocking action of the forefinger: horizontally placing the mechanical sensor, quickly and lightly knocking the interdigital electrode part of the sensor by an index finger, and measuring resistance change by using a precision resistance/capacitance measuring instrument;

(5) And (3) testing the resistance change of the fingers under the action of different bending angles: the mechanical sensor is attached to a finger, the finger is bent at different angles, and the resistance change is measured using a precision resistance/capacitance measuring instrument.

The resistance change curve of the flexible mechanical sensor prepared in example 1 under the action of single strain is shown in FIG. 1, wherein the horizontal axis represents strain, and the vertical axis represents the relative resistance change rate (Δ R/R) under different strain conditions ₀ ). It can be seen that the mechanical sensor of example 1 increases the relative resistance change from 0 to 1100% when the strain increases from 0 to 10% under the action of uniaxial tension.

FIG. 2 is a graph showing the resistance change of the flexible mechanical sensor prepared in example 1 under the continuous tapping action of the index finger, wherein the relative resistance change of the flexible mechanical sensor is between 0 and 25 percent along with the tapping of the index finger. Fig. 3 is a resistance change curve diagram of the flexible mechanical sensor prepared in example 1 under different bending angles of the finger, and the relative resistance change of the flexible mechanical sensor is between 45% and 50%. It can be seen that the flexible mechanical sensor of the invention has high sensitivity and can respond to stress quickly.

Fig. 4 shows 100 identical stress cycles of the flexible mechanical sensor prepared in example 1. As can be seen from the figure, the repeated responsiveness is good, and the durability of the sensor is good.

Fig. 5 is a GF plot of the 10% uniaxial tensile response of the flexible mechanical sensor prepared in example 1. GF can reach 131.7, indicating high sensitivity of the sensor.

The mechanical sensors prepared in each example and comparative example were subjected to sensitivity (condition 10% uniaxial tensile response) and repeated response performance tests, and the results are shown in table 1.

TABLE 1

	Sensitivity (GF)	Repeated response Property (%)
			Example 1	131.7	99.8
Example 2	128.9	99.5
			Example 3	126.4	99.3
Example 4	129.5	99.6
			Example 5	128.1	99.6
Example 6	130.9	99.7
			Example 7	130.2	99.7
Comparative example 1	115.2	86.2
			Comparative example 2	107.6	85.3
Comparative example 3	86.4	82.1

According to the test results in table 1, the mechanical sensors prepared in the embodiments of the present application all have excellent sensitivity and repeated response performance.

The conductive inks of comparative example 1 and comparative example 2 do not contain silver nanoparticles, the conductivity of the graphene ink alone is poor, and the sensitivity of the prepared mechanical sensor is low. In the comparative example 3, the granular graphene prepared by the liquid phase stripping method is used for dispersing, the morphology of the granular graphene prepared by the liquid phase stripping method is not uniform enough, so that the ink-jet printing effect of the conductive ink is poor, the binding force between the silver nanoparticles in the silver paste and the granular graphene is poor, and the sensitivity of the prepared mechanical sensor is low.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of conductive ink is characterized by comprising the following steps:

s1, using a graphite plate as an anode and a counter electrode, immersing in deionized water for electrolysis, and obtaining nano-graphite water dispersion liquid after ultrasonic treatment and centrifugation of electrolyte;

2. The method for preparing the conductive ink according to claim 1, wherein the purity of the graphite plate is not less than 99%.

3. The method for preparing the conductive ink according to claim 1, wherein the current of the electrolytic treatment is a constant current of 15 to 30mA, the temperature is 20 to 30 ℃, and the time is 7 to 14 days.

4. The method for preparing the conductive ink according to claim 1, wherein the average particle size of the silver nanoparticles in the silver paste is 80-600 nm.

5. The method for preparing the conductive ink according to claim 1, wherein the nano graphite aqueous dispersion contains graphene, and the concentration of the graphene is 15-30 mg/ml; the concentration of silver nano particles in the silver paste is 30-40 mg/ml.

6. The method for preparing the conductive ink according to claim 5, wherein in the step S2, the volume ratio of the nano graphite water dispersion liquid to the silver paste is 1: 4-10.

7. A conductive ink produced by the production method according to any one of claims 1 to 6.

8. Use of the conductive ink of claim 7 as an electrode material in the preparation of flexible mechanical sensors.

9. A flexible mechanical sensor is characterized by being prepared by the following method:

the conductive ink of claim 7 is added to an ink-jet printer, a flexible electrode is printed on the surface of a flexible substrate, and after heating treatment, the flexible mechanical sensor is obtained.

10. The flexible mechanical sensor according to claim 9, wherein the flexible substrate is at least one of PI, TPU, PDMS, PET, PE.