CN111043950A

CN111043950A - Flexible strain sensor based on MXenes/high-molecular conductive fiber composite membrane and preparation method thereof

Info

Publication number: CN111043950A
Application number: CN201911331884.8A
Authority: CN
Inventors: 贾志欣; 李彰杰; 张文强; 陈勇军; 贾德民
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2019-12-21
Filing date: 2019-12-21
Publication date: 2020-04-21

Abstract

The invention discloses a flexible strain sensor based on an MXenes/high-molecular conductive fiber composite membrane and a preparation method thereof. The invention adopts an electrostatic spinning method to prepare a polymer fiber membrane, then the obtained polymer fiber membrane is immersed in a dispersion liquid of transition metal carbide MXenes for ultrasonic treatment, taken out and dried to obtain the MXenes/polymer conductive fiber composite membrane. And connecting a lead fixing unit and a lead at two ends of the MXenes/macromolecule conductive fiber composite film to obtain the flexible strain sensor based on the MXenes/macromolecule conductive fiber composite film. The flexible strain sensor has the advantages of low raw material cost, excellent product performance, simple process operation, wide strain test range, high sensitivity and the like, and has important application prospects in the fields of flexible wearable equipment, human body-imitated electronic skin, intelligent robots, internet of things, health monitoring and the like.

Description

Flexible strain sensor based on MXenes/high-molecular conductive fiber composite membrane and preparation method thereof

Technical Field

The invention relates to the field of strain sensors, in particular to a flexible strain sensor based on an MXenes/high-molecular conductive fiber composite membrane and a preparation method thereof.

Background

In recent years, flexible strain sensors have received much attention due to their great potential in the fields of electronic skin, robotics, motion detection, and the like. Conventional strain sensors based on metal or semiconductor materials have narrow strain ranges (typically less than 5%) and high stiffness, which cannot meet the requirements of intelligent wearable devices. Therefore, it is highly desirable to develop a flexible strain sensor having excellent sensitivity and high stretchability to meet the increasing demand.

At present, the mainstream way of a flexible strain sensor is to convert the deformation of the sensor into the change of the resistance value in the stretching process. It is common practice to incorporate conductive nanomaterials (e.g., carbon black, graphene, carbon nanotubes, etc.) into elastomeric polymers as flexible, stretchable substrates as sensing active materials. By this approach, flexible sensors with a more controllable sensing range compared to conventional sensors have been achieved. However, the interaction between the conductive nanomaterial (such as carbon black, graphene, carbon nanotube, etc.) and the elastic polymer substrate that is commonly used at present is usually weak, and in order to implement a flexible sensor with low resistance and high sensitivity, the amount of the conductive nanomaterial needs to be increased, which causes a problem in cost. It remains a challenge to prepare flexible sensors with a large sensing range and high sensitivity while reducing the amount of expensive conductive nanomaterials.

MXenes is a two-dimensional layered transition metal carbide of the formula M_n+1X_nAnd n is 1, 2 or 3(M is an early transition metal element, and X is a carbon element or a nitrogen element). MXenes can be obtained by selective etching away the A layer from the MAX phase (M, X, n here is the same as above, A is a group IIIA element or a group IVA element). MXenes has conductivity comparable to that of graphene, and a hydrophilic surface, so that the MXenes has a great application prospect in the field of strain sensing.

Disclosure of Invention

The invention aims to provide a flexible strain sensor based on an MXenes/macromolecule conductive fiber composite membrane and a preparation method thereof, aiming at the problems of complex preparation process, high cost, weak interaction force between a conductive nano material and a flexible base material and the like of the conventional flexible sensor.

The purpose of the invention is realized by the following technical scheme.

A preparation method of a flexible strain sensor based on an MXenes/high polymer conductive fiber composite membrane comprises the following steps:

(1) dissolving a high polymer material in a solvent to obtain a high polymer spinning solution;

(2) performing electrostatic spinning on the high-molecular spinning solution obtained in the step (1) to obtain a high-molecular fiber membrane;

(3) cutting the polymer fiber membrane obtained in the step (2) into a required size, immersing the polymer fiber membrane into the MXenes nanosheet layer dispersion liquid obtained in the step (1) for ultrasonic treatment, taking out and drying to obtain an MXenes/polymer conductive fiber composite membrane;

(4) and (4) connecting two ends of the MXenes/polymer conductive fiber composite membrane obtained in the step (3) with a conductor fixing unit and a conductor to obtain the flexible strain sensor based on the MXenes/polymer conductive fiber composite membrane.

Preferably, the polymer material in step (1) is at least one of polyester, polyamide, polyvinyl alcohol, polyacrylonitrile, polypropylene, polyvinyl chloride, or polyurethane; further preferred is at least one of thermoplastic polyurethane and polyacrylonitrile.

Preferably, the solvent in step (1) is at least one of acetone, N-dimethylformamide, N-methylpyrrolidone and tetrahydrofuran; further preferred is N, N-dimethylformamide.

Preferably, the mass fraction of the solute in the polymer solvent in the step (1) is 10-15 wt%.

Preferably, the electrostatic spinning process conditions in step (2) are as follows: the temperature is room temperature, the humidity is 50% -70%, the voltage is 20-30kV, the distance between the syringe needle and the receiving plate is 10-15cm, the receiving plate is one of aluminum foil or tin foil, the sample injection speed is 0.5-2ml/h, and the spinning time is 6-8 h.

Preferably, the polymer fiber membrane in the step (2) has a network structure; the thickness of the polymer fiber membrane is 100-300 mu m.

Preferably, the diameter of a single fiber of the polymer fiber membrane in the step (2) is 100-2000 nm.

Preferably, the MXenes nanosheets of step (3)Is Ti₃C₂，Ti₂C，Ti₄C₃，V₃C₂，V₂One or more of C, more preferably Ti₃C₂。

Preferably, the liquid phase of the MXenes nanosheet dispersion liquid in step (3) is at least one of deionized water, ethanol, N-dimethylformamide and tetrahydrofuran; preferably deionized water.

Preferably, the concentration of the MXenes nanosheet dispersion of step (3) is 0.5-3 mg/mL.

Preferably, the time for the ultrasound in the step (3) is 30-120 minutes; the ultrasonic temperature is controlled at 10-40 ℃.

Preferably, the drying in the step (3) is vacuum drying; the drying time is 30-120 min; the drying temperature is 40-70 ℃.

Preferably, the lead fixing unit in the step (4) is at least one of silver paste, two-component epoxy paste or inorganic material conductive paste, and is further preferably silver paste; the lead is connected with the measuring instrument and fixed on the conducting layer through the lead fixing unit.

The flexible strain sensor based on the MXenes/macromolecule conductive fiber composite membrane prepared by any one of the methods has the stretching degree of more than 70% and the sensitivity of 25.52.

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

1. the sensing range is wide: the flexible strain sensor of the invention can detect and distinguish 0.1% -70% strain.

2. The response time is short: the response time of the flexible strain sensor of the invention to the transient strain of 0.1% is as low as 140.6 ms.

3. And (4) multiple functions: the flexible strain sensor can be applied to detection of various activities such as human joint movement, pulse vibration, vocal cord vibration and the like.

4. The acting force between the conductive nano material and the flexible substrate is strong: the hydrogen bond formed by the active group on the surface of the MXene nanosheet layer and the functional group on the used polymer molecular chain is utilized, so that the interaction force between the MXene nanosheet layer and the flexible substrate is effectively improved, and the surface resistance of the MXene/polymer conductive fiber composite membrane is remarkably reduced.

5. Save raw materials, practice thrift the cost: the invention adopts the dip-coating method to prepare the flexible strain sensor, the dip-coating liquid can be repeatedly used, and the conductive nano material is generally expensive, so the cost for preparing the flexible strain sensor is obviously reduced.

Drawings

Fig. 1 is a schematic diagram of a preparation process of a flexible strain sensor based on an MXenes/polymer conductive fiber composite film according to the present invention.

Fig. 2 is a scanning electron microscope image of the surface of the MXenes/polymeric conductive fiber composite film prepared in example 1.

Fig. 3 is a time versus relative resistance plot for 3 cycles at 1%, 2%, 3%, 4%, and 5% tensile strain for the flexible strain sensors prepared in example 1.

Fig. 4 is a time versus resistance plot for each of 3 cycles at 50%, 60%, 70% tensile strain for the flexible strain sensor prepared in example 1.

Fig. 5 is a scanning electron microscope image of the surface of the MXenes/polymeric conductive fiber composite film prepared in example 2.

Fig. 6 is a graph of time versus resistance for 3 cycles at 1%, 2%, 3%, 4%, and 5% tensile strain for the strain sensors obtained in example 2.

Fig. 7 is a graph of time versus resistance for 3 cycles at 60%, 70%, 80% tensile strain for the strain sensor obtained in example 2.

Fig. 8 is a scanning electron microscope image of the surface of the MXenes/polymeric conductive fiber composite film prepared in example 3.

Fig. 9 is a graph of time versus resistance for 3 cycles at 1%, 2%, 3%, 4%, and 5% tensile strain for the strain sensors obtained in example 3.

Fig. 10 is a plot of time versus resistance for 3 cycles at 50%, 60%, 70% tensile strain for the strain sensors obtained in example 3.

FIG. 11 shows the surface resistance of MXenes/polymer conductive fiber composite membrane obtained after MXenes nanosheet layer dispersion liquid is repeatedly used for multiple times from 1 time to 7 times

Detailed Description

Specific embodiments of the present invention will be further described below with reference to the following examples and drawings, but the present invention is not limited thereto.

Example 1

(1) Preparing a high-molecular spinning solution: adding 2.40g of TPU and 0.13g of TPU into 15ml of N, N-dimethylformamide, and magnetically stirring at normal temperature until the TPU and the N, N-dimethylformamide are fully dissolved to obtain the uniform high-molecular spinning solution.

(2) Preparing a polymer fiber membrane: performing electrostatic spinning on the high-molecular spinning solution prepared in the step (1), wherein electrostatic spinning parameters are as follows: the temperature is room temperature, the humidity is 60%, the voltage is 25kV, the distance between the syringe needle and the receiving plate is 10cm, the receiving plate is an aluminum foil, the sample injection speed is 1ml/h, and the spinning time is 8 h. Finally obtaining the polymer fiber membrane with the diameter of a single fiber of 300nm and the thickness of 200 mu m.

(3) Preparing an MXenes/macromolecule conductive fiber composite membrane: 0.5g of Ti₃C₂Adding the nanosheet layer into 50g of deionized water, and carrying out ultrasonic treatment for 30min to obtain MXenes nanosheet layer dispersion liquid with the mass fraction of 1 wt%; and (3) placing the polymer fiber membrane obtained in the step (2) into the MXenes nanosheet layer dispersion liquid for ultrasonic treatment for 60min, taking out, and vacuum-drying at 50 ℃ for 90min to obtain the MXenes/polymer conductive fiber composite membrane.

(4) Preparing a flexible strain sensor based on an MXenes/high-molecular conductive fiber composite membrane: and (4) fixing the wires at two ends of the MXenes/polymer conductive fiber composite membrane obtained in the step (3) through silver colloid, so as to obtain the flexible strain sensor based on the MXenes/polymer conductive fiber composite membrane.

Example 2

(1) Preparing a high-molecular spinning solution: 2.3g of TPU and 0.23g of PAN are added into 15ml of N, N-dimethylformamide and are magnetically stirred at normal temperature until the materials are fully dissolved, thus obtaining the uniform macromolecular spinning solution.

(2) Preparing a polymer fiber membrane: performing electrostatic spinning on the high-molecular spinning solution prepared in the step (1), wherein electrostatic spinning parameters are as follows: the temperature is room temperature, the humidity is 60%, the voltage is 25kV, the distance between the syringe needle and the receiving plate is 10cm, the receiving plate is an aluminum foil, the sample injection speed is 1ml/h, and the spinning time is 8 h.

Example 3

(1) Preparing a high-molecular spinning solution: 2.02g of TPU and 0.51g of PAN are added into 15ml of N, N-dimethylformamide and are magnetically stirred at normal temperature until the materials are fully dissolved, thus obtaining the uniform macromolecular spinning solution.

(2) Preparing a polymer fiber membrane: performing electrostatic spinning on the high-molecular spinning solution prepared in the step (1), wherein electrostatic spinning parameters are as follows: the temperature is room temperature, the humidity is 60%, the voltage is 25kV, the distance between the syringe needle and the receiving plate is 12cm, the receiving plate is an aluminum foil, the sample injection speed is 1ml/h, and the spinning time is 8 h.

Fig. 1 is a schematic diagram of a preparation process of a flexible strain sensor based on an MXenes/polymer conductive fiber composite film according to the present invention. As can be seen from FIG. 1, the sensor has the advantages of simple preparation method, low production cost and convenience for large-scale production.

Fig. 2 is a scanning electron microscope image of the surface of the MXenes/polymeric conductive fiber composite film prepared in example 1. As can be seen from fig. 2, the MXenes nanosheet layer is well bonded to the polymer fiber, and the MXenes nanosheet layer is well attached to the polymer fiber.

FIG. 3 is a graph of time versus resistance for 3 cycles at 1%, 2%, 3%, 4%, and 5% tensile strain for the strain sensors obtained in example 1. The results indicate that the strain sensor can detect and distinguish very small tensile strains.

FIG. 4 is a graph of time versus resistance for 3 cycles at 50%, 60%, 70% tensile strain for the strain sensors obtained in example 1. This indicates that the strain sensor prepared by the present invention can work in a large strain range.

Fig. 5 is a scanning electron microscope image of the surface of the MXenes/polymeric conductive fiber composite film prepared in example 2. As can be seen from fig. 5, the MXenes nanosheet layer wraps the polymer fibers like silk, which indicates that there is a strong interaction force between the MXenes nanosheet layer and the polymer fibers.

FIG. 6 is a graph of time versus resistance for 3 cycles at 1%, 2%, 3%, 4%, and 5% tensile strain for the strain sensors obtained in example 2. The results also indicate that the strain sensor can detect and distinguish very small tensile strains.

Fig. 7 is a graph of time versus resistance for 3 cycles at 60%, 70%, 80% tensile strain for the strain sensor obtained in example 2. This indicates that the sensing range of the strain sensor prepared by the present invention can reach 80%.

FIG. 9 is a graph of time versus resistance for 3 cycles at 1%, 2%, 3%, 4%, and 5% tensile strain for the strain sensors obtained in example 3. The results also indicate that the strain sensor can detect and distinguish very small tensile strains.

Fig. 10 is a graph of time versus resistance for 3 cycles of the strain sensor obtained in example 3 at 50%, 60%, 70% tensile strain. The results also show that the strain sensor prepared by the invention can work in a large strain range.

Fig. 11 shows the surface resistance of the MXenes/polymer conductive fiber composite film obtained after the MXenes nanosheet dispersion obtained in example 2 is used repeatedly for a plurality of times, from 1 time to 7 times; as can be seen from fig. 8, the surface resistance of the MXenes/polymer conductive fiber composite film obtained by dip-coating the MXenes nanosheet dispersion for the 7 th time is still an order of magnitude higher than that of the conductive fiber composite film obtained by dip-coating the MXenes/polymer conductive fiber composite film for the 1 st time, and still does not exceed 200 Ω/sqr. This is also the benefit of the strong interaction force between the MXenes nanosheets and the polymer fiber membrane obtained in example 1. Based on the method, the consumption of expensive conductive nano materials is greatly saved, and further the cost is saved.

TABLE 1

Strain of	1％	2％	3％	4％	5％	50％	60％	70％
									Coefficient of sensitivity	25.52	13.94	12.42	13.22	14.74	8.16	8.27	8.41

Table 1 shows the sensitivity coefficients (GF) of the strain sensor obtained in example 1 under different tensile strains, and it can be seen that the strain sensor prepared according to the present invention has higher sensitivity under both small strain and large strain.

TABLE 2

Strain of	1％	2％	3％	4％	5％	60％	70％	80％
									Coefficient of sensitivity	7.01	6.33	5.59	4.91	4.50	4.89	8.37	9.69

Table 2 shows the sensitivity coefficients of the strain sensors obtained in example 2 at different tensile strains. It can be seen that the strain sensor prepared by the invention has higher sensitivity under small strain and large strain.

TABLE 3

Strain of	1％	2％	3％	4％	5％	50％	60％	70％
									Coefficient of sensitivity	5.69	3.16	2.91	2.74	2.84	1.82	1.79	6.81

Table 3 shows the sensitivity coefficients of the strain sensors obtained in example 3 at different tensile strains. It can be seen that the strain sensor prepared by the invention has higher sensitivity under small strain and large strain.

In conclusion, the flexible strain sensor based on the MXenes/polymer conductive fiber composite membrane prepared by the invention solves the problem of weak interaction force between the conductive nano material and the flexible substrate in the existing scheme, and by adjusting the components of the polymer fiber membrane, the interaction force between the MXenes nanosheet layer and the polymer fiber membrane is effectively improved, and the utilization rate of the expensive conductive nano material is improved. The flexible strain sensor has a wide sensing range, short response time, multiple functions, raw material saving and cost saving, so the flexible strain sensor has great potential in the aspects of electronic skin, biomedical monitoring and motion detection.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A preparation method of a flexible strain sensor based on an MXenes/macromolecule conductive fiber composite membrane is characterized by comprising the following steps:

(3) immersing the polymer fiber film obtained in the step (2) into MXenes nanosheet layer dispersion liquid for ultrasonic treatment, taking out and drying to obtain an MXenes/polymer conductive fiber composite film;

2. The preparation method according to claim 1, wherein the polymer material in step (1) is at least one of polyester, polyamide, polyvinyl alcohol, polyacrylonitrile, polypropylene, polyvinyl chloride and polyurethane; the solvent is at least one of acetone, N-dimethylformamide, N-methylpyrrolidone and tetrahydrofuran.

3. The preparation method according to claim 1, wherein the electrostatic spinning process conditions of step (2) comprise: the temperature is room temperature, the humidity is 50% -70%, the voltage is 20-30kV, the distance between the syringe needle and the receiving plate is 10-15cm, and the receiving plate is one of aluminum foil or tin foil; the spinning time is 6-8 h.

4. The production method according to claim 1, wherein the polymer fiber membrane of step (2) has a network structure; the thickness of the polymer fiber membrane is 100-300 mu m; the single fiber diameter of the polymer fiber membrane is 100-2000 nm.

5. The method according to claim 1, wherein MXenes of the formula M in step (3)_n+ ₁X_nWherein n is 1, 2 and 3, M is an early transition metal element, and X is one or two of carbon and nitrogen; the MXenes is Ti₃C₂，Ti₂C，Ti₄C₃，V₃C₂And V₂C, one or more of C.

6. The method of claim 1, wherein: the liquid phase of the MXenes nanosheet layer dispersion liquid in the step (3) is at least one of deionized water, ethanol, N-dimethylformamide and tetrahydrofuran; the concentration of the dispersion is 0.5-3 mg/mL.

7. The method of claim 1, wherein: the ultrasonic treatment time in the step (3) is 30-120 minutes; the ultrasonic temperature is controlled to be 10-40 ℃.

8. The method of claim 1, wherein: the drying in the step (3) is vacuum drying; the drying time is 30-120 min; the drying temperature is 40-70 ℃.

9. The method of claim 1, wherein: the lead fixing unit in the step (4) is at least one of silver adhesive, double-component epoxy adhesive and inorganic material conductive adhesive; the lead is connected with the measuring instrument and fixed on the conducting layer through the lead fixing unit.

10. Flexible strain sensor based on MXenes/polymer conductive fiber composite membrane prepared by the method of any one of claims 1-9.