WO2021013174A1

WO2021013174A1 - Pressure sensor, preparation method and application thereof and wearable smart fabric comprising the same

Info

Publication number: WO2021013174A1
Application number: PCT/CN2020/103502
Authority: WO
Inventors: Jingtang LIU; Minde ZHU; Weijiayakumei NAJIAPAN; Haining LIANG
Original assignee: Xi'an Jiaotong-Liverpool University
Priority date: 2019-07-22
Filing date: 2020-07-22
Publication date: 2021-01-28
Also published as: CN110606981B; CN110606981A

Abstract

Provided herein is a pressure sensor, preparation method and application thereof and a wearable smart fabric comprising the same. The pressure sensor is a graphene-modified polyurethane foam; wherein the graphene has a mass percentage of 0.8-2.5%based on 100%of the total mass of the graphene-modified polyurethane foam. The wearable smart fabric prepared by the sensor provided herein is a completely fabric-based wearable platform and has wide applications.

Description

PRESSURE SENSOR, PREPARATION METHOD AND APPLICATION THEREOF AND WEARABLE SMART FABRIC COMPRISING THE SAME

Technical field

The invention relates to the technical field of sensors, and specifically to a pressure sensor, preparation method and application thereof and a wearable smart fabric comprising the same.

Background

In the past 30 years, the development of smart sensors has attracted great interest because it has huge application prospects in almost all industries such as health, sports and environment. Traditional strain sensors are mainly based on metal and semiconductor materials. They have certain sensitivity, but the materials are often metal based and are usually hard, rigid and uncomfortable to wear for long period of time. Moreover, the materials per se have no transparency, no viscoelasticity and low stretchability and sensitivity, and it is even necessary to embed them in the skin to accurately measure human health and physiological signals, thus limiting the range of applications of strain sensors. For sensors, materials that respond to physical stimuli (such as stretching and pressing) play a crucial role because it is a key part for responding to external factors and converting them into signals.

Compared with the traditional strain sensors, the flexible multi-function strain sensors overcome the shortcoming of the hard material, and have the characteristics of ultra-thin, ultra-light, flexibility, stretchability, high sensitivity and wearability, and exhibit advantages of better biocompatibility and the possibility of continuous detection. In flexible multi-function strain sensors, active materials and flexible substrates are key factors determining sensor performance. The active materials commonly used in currently reported flexible multi-functional strain sensors include nanoparticles, nanowires, carbon nanotubes, graphene and organic materials. Among them, flexible multi-functional strain sensors based on organic materials are the fastest developed, which are simple in preparation process and good in flexibility, with however somewhat limited application range and response time.

Graphene is considered as one of the most promising materials due to its advantageous properties including special thermal (conductivity and stability) , mechanical (flexible and strong) , electrical (high conductivity) properties and good strain factor. In addition, graphene is non-toxic to humans and the environment, and graphene-based sensors are more comfortable to wear and are ideal choice for body-contact sensors.

CN105067159A discloses a capacitive pressure sensor composed of an insulating layer and two substrates comprising electrodes, and the fabrication method thereof, the insulating layer being located between two layers of electrodes, the insulating layer being a porous flexible film, whereby the cost of the capacitive pressure sensor is reduced, but wearability is not really achieved on the base fabric. CN105387927A discloses a novel flexible vibration sensor comprising a three-dimensional graphene and an elastic polymer matrix, the three-dimensional graphene being encapsulated inside the elastic polymer matrix, and three-dimensional graphene is provided with wires at both ends thereof penetrating the elastic polymer. The wires are connected to the three-dimensional graphene by elargol. This patent realizes a wide spectrum, but the concept of the wearable fabric is not realized, and the service life of the sensor is short due to the low adhesion between the graphene and the elastic polymer during use. CN106767374A discloses a preparation method of a flexible multi-functional strain sensor based on a three-dimensional graphene/carbon nanotube network, in which a three-dimensional network of three-dimensional graphene and one-dimensional carbon nanotubes is grown by a two-step chemical vapor deposition method, and the three-dimensional network is combined with an elastic polymer as a flexible substrate through solidification to obtain a flexible wearable multifunctional electronic strain sensor based on a three-dimensional network of graphene and carbon nanotubes. However, its sensitivity is not high enough, and it correlates the sensing to the stretching, which makes it inconvenient to apply.

Therefore, there is a need to provide a truly wearable smart fabric to meet current application requirements of sensors.

Summary

The present invention provides a pressure sensor, preparation method and application thereof and a wearable smart fabric comprising the same. The pressure sensor provided by the invention is a graphene-modified polyurethane foam, on which the graphene loading is high and it has better adhesion to the polyurethane substrate, which can enhance the sensitivity and lifetime of the sensor. Moreover, the wearable smart fabric prepared by the sensor provided herein is a completely fabric-based wearable platform, and has wide applications.

To achieve the purpose of this invention, the present application adopts the following technical solutions:

In a first aspect, the invention provides a pressure sensor which is a graphene-modified polyurethane foam.

Wherein, the graphene has a mass percentage of 0.8-2.5%based on 100%of the total mass of the graphene-modified polyurethane foam, e.g. 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%and the like.

In the graphene-modified polyurethane foam provided by the invention, the graphene loading is high and it has a good adhesion effect on the polyurethane foam. Thus, the pressure sensor provided by the invention is highly sensitive and has a long working life. In addition, graphene is non-toxic to the environment and the human body, which favors its application in wearable smart fabrics.

Preferably, the polyurethane foam has a porosity of 94-96%, e.g. 95%.

In a second aspect, the invention provides a preparation method of the pressure sensor according to the first aspect, which preparation method comprises the following steps:

Treating a polyurethane foam with a graphene oxide solution to obtain a graphene oxide-loaded polyurethane foam; then reducing the graphene oxide to obtain the pressure sensor.

As a preferred technical solution, the preparation method comprises the following steps:

(1) soaking the polyurethane foam in a graphene oxide solution in ethanol, and and air drying, and finally drying at 70-90 ℃ (e.g. 75%, 80%, 85%and the like) ;

(2) reducing the graphene oxide on the dried polyurethane foam by using a reducing agent, then washing and drying to obtain the pressure sensor.

The method comprises soaking the polyurethane foam in a graphene oxide solution in ethanol, wherein ethanol permeates into the polyurethane foam, and the polyurethane foam swells up to a certain extent. The swelling increases the specific surface area of the polyurethane foam and therefore increases the quantity and depth of the graphene oxide entering the polyurethane foam. When the solvent is removed by heating at 70-90 ℃, the polyurethane foam shrinks, resulting in strong adhesion of graphene oxide on the polyurethane foam and better stacking of the graphene oxide inter-layers. The preparation method provided by the invention improves the strength of polyurethane foam and the robustness of the finished pressure sensor, and the finished pressure sensor has higher stability and conductivity.

According to the preparation method provided by the invention, the graphene modified polyurethane foam having robust graphene coating is prepared, and no loose graphene particles would be produced in the preparation method provided by the invention, so that the graphene modified polyurethane foam provided by the invention is resistant to rubbing and washings.

Preferably, the reducing agent includes hydrazine hydrate.

Preferably, a preparation method of the graphene oxide comprises: oxidizing a graphite flake with potassium dichromate in a concentrated sulfuric acid, and then washing and dialyzing to obtain the graphene oxide.

Preferably, the mass ratio of the graphite flake to the oxidant is 1: (2-6) , e.g. 1: 3, 1: 4, 1: 5 and the like.

Preferably, the oxidant includes potassium dichromate or potassium permanganate.

Preferably, the concentrated sulfuric acid used in an amount of 20-50 mL (e.g. 30 mL, 40 mL and the like) of the concentrated sulfuric acid per 1 g of the graphite flake.

Preferably, the oxidant is added to the concentrated sulfuric acid solution in batches. Preferably, the solution temperature is maintained at 0-5 ℃ during the addition of the oxidant.

Preferably, after the oxidant is added, the solution is warmed up to room temperature and then sonicated for 0.5-1 h, e.g. 0.6 h, 0.7 h, 0.8 h, 0.9 hand the like. Preferably, after the sonication is completed, deionized water is added to the reaction system for a reaction at 98 ℃ for 1-2 h, e.g. 2 h, 1.4 h, 1.6 h, 1.8 h and the like.

Preferably, the volume ratio of the deionized water to the concentrated sulfuric acid is (1.5-4) : 1, e.g. 2: 1, 2.5: 1, 3: 1, 3.5: 1 and the like.

Preferably, after the reaction is completed, the unreacted oxidant is removed by using hydrogen peroxide.

Preferably, the washing comprises washing with a hydrochloric acid and a deionized water in sequence, and finally dialyzing with a dialysis bag in deionized water until the pH is neutral.

As a preferred technical solution for the preparation of the graphene oxide, the preparation method is as follows:

adding graphene flakes to a concentrated sulfuric acid in an amount of 50 mL of the concentrated sulfuric acid per 1 g of the graphite flake; keeping the temperature of the reaction solution at 0-5 ℃, adding potassium dichromate in batches with an amount of the potassium dichromate 3 times of the amount of graphene; after the potassium dichromate is added, slowly warming up to room temperature, followed by sonication for 1 h, after the sonication is completed, adding deionized water in a volume ratio of 5: 3 to the concentrated sulfuric acid; slowly warming up to 98 ℃ for a reaction for 1 h, then cooling down to room temperature to complete the reaction. After the reaction is completed, adding hydrogen peroxide to remove the residual potassium dichromate and filtering, then rinsing with 0.5 M hydrochloric acid for at least three times, rinsing with deionized water, finally transferring the product to a dialysis bag immersed in deionized water until the pH of the water is neutral; thus obtaining the graphene oxide.

The present invention can reduce the structural defects of graphene oxide by preparing graphene oxide by the improving Hummer method.

Preferably, the concentration of the graphene oxide in the graphene oxide solution in ethanol is 0.5-2.5 mg/mL, e.g. 0.6 mg/mL, 0.8 mg/mL, 1 mg/mL, 1.4 mg/mL, 1.6 mg/mL, 1.8 mg/mL, 2.0 mg/mL, 2.2 mg/mL, 2.4 mg/mL and the like.

Preferably, the soaking is carried out for 20-30 min, e.g. 22 min, 24 min, 26 min, 28 min, 29 min and the like.

Preferably, the air drying is carried out for at least 4 h, e.g. 4 h, 4.5 h, 4.8 h, 5 h, 6 h, 8 h and the like.

Preferably, the drying in the step (1) is carried out at the temperature of 70-100 ℃, e.g. 75 ℃, 80 ℃, 85 ℃, 90 ℃ and the like, and for a period of 60-120 min, e.g. 70 min, 80 min, 90 min, 100 min, 110 min and the like.

Preferably, the concentration of the hydrazine hydrate in the hydrazine hydrate solution is 5-10%, e.g. 6%, 7%, 5.4%, 8%, 9%and the like.

Preferably, the reduction is carried out at the temperature of 80-95 ℃, e.g. 84 ℃, 88 ℃, 90 ℃, 94 ℃ and the like, and for a period of 3-4 h, e.g. 3.2 h, 3.4 h, 3.6 h, 3.8 h and the like.

Preferably, the drying in the step (2) is carried out at the temperature of 70-100 ℃, e.g. 75 ℃, 80 ℃, 85 ℃, 90 ℃ and the like, and for a period of 4 h or more, e.g. 4 h, 5 h, 10 h, 12 h and the like.

The preparation method provided by the invention can enable the control of the loading amount of graphene, allow the larger load of the graphene on the polyurethane foam, and thus increase the sensitivity of the pressure sensor (graphene modified polyurethane foam) ; meanwhile, the preparation method provided by the invention can achieve excellent adhesion of graphene on the polyurethane foam, thereby increasing the service life of the sensor and avoiding the sensor failure due to the detachment of the graphene from the polyurethane foam during use.

In a third aspect, the invention provides a use of the pressure sensor according to the first aspect in a wearable smart fabric.

Preferably, the fabric comprises a glove, a wristband, a belt, an apron, a trouser, or a knee strap.

A wearable fabric, such as a smart wristband and a smart glove, can be prepared from the sensor provided by the invention, which is a true smart platform based on a textile substrate.

In a fourth aspect, the invention provides a wearable smart fabric based platform comprising the pressure sensor according to the first aspect.

Preferably, the wearable smart fabric further comprises a conversion circuit, a power supply and a substrate.

During the use of the smart wristband provided by the present invention, the pressure sensor is tapped or pressed when necessary, and the pressure sensor receives the signal and converts it into an electrical signal, and the accepted electrical signals are coded by the designed program to finally execute specific commands or functions.

In a fifth aspect, the invention provides a use of the pressure sensor according to the first aspect in a wearable keyboard, a wearable console, a wearable detector or a communication device.

The pressure sensor provided by the invention can also be applied to the fields of a wearable keyboard, a console and the like. The device works in a similar fashion to existing keyboard, hence can be used as man-machine interface control.

As compared to the existing technologies, the present invention has the following beneficial effects:

The pressure sensor provided by the invention is a graphene-modified polyurethane foam, in which the graphene is loaded in a large mount and has better adhesion to the polyurethane, which can enhance the sensitivity and working life of the sensor. Moreover, the wearable smart fabric prepared by the sensor provided herein is a completely fabric-based wearable platform and has wide applications.

Brief Description of the Drawings

Fig. 1 is a schematic structural view of a test component constructed by the present invention;

1-impedance; 2-pressure sensor; 3-tapping; 4-data output.

Fig. 2 is a diagram of the result of a tapping test by the test component.

Fig. 3 is a diagram of the result of a pressing test by the test component.

Fig. 4 is a schematic structural view of a wearable smart wristband provided in Application Example 1.

401-pressure sensor; 402-data connection layer; 403-data reading area; 404-speaker; 405-power supply; 406-LEDs; 407-power connection layer.

Fig. 5 is a schematic view of a wearable smart wristband dial provided by Application Example 1.

Fig. 6 is a schematic view of a wearable smart apron provided in Application Example 2.

Fig. 7 is a schematic view of a wearable smart trouser provided in Application Example 3.

Fig. 8 is a schematic view of a wearable keyboard provided in Application Example 4.

Wherein, 801-microcontroller.

Detailed Description

The technical solution of the invention is further illustrated by the specific embodiments below. Those skilled in the art shall understand that the embodiments are set forth to assist in understanding the present disclosure and should not be regarded as specific limitations to the present disclosure.

Preparation Example 1

A graphene modified polyurethane foam was prepared as follows:

(1) Preparation of a graphene oxide

5g of graphite flakes were added into 150 mL of concentrated sulfuric acid, the temperature of the reaction solution was kept at 0-5 ℃, 15g of potassium dichromate was added in small portions, the resulting mixture was left to warm up to room temperature slowly and then sonicated for 1 h. 250 mL of deionized water was added into the flask and the temperature of the flask was slowly warmed up to 98 ℃ by heating in a water bath, kept at 98 ℃ for another 1 h and allowed to cool down to room temperature. 60 mL of 30%hydrogen peroxide was added slowly to remove the residual oxidizing agent. The resulting product was filtered by pump and rinsed by 0.5 M hydrochloric acid for at least 3 times to remove the residue followed by addition of excess deionizer water. The product was transferred into dialysis bags in a 2000 mL beaker full of deionizer water in order to remove the ions. The water was changed every two hours on the first day and twice every day for six days until the pH was neutral.

(2) Preparation of a graphene modified polyurethane foam

A 2×2×1 cm ³ PU foam (milky white in colour) was immersed into a 1.16 mg/mL GO solution in ethanol for 20 min. The foam was then removed from the solution with excess liquid squeezed out, air dried for at least 4 h. The air-dried GO coated foam was dried in oven at 90 ℃ for at least 60 min. The dried GO coated foam (yellowish brown) was allowed to cool down to room temperature before being transferred into a beaker with hydrazine hydrate solution (5-6%) and heated at 80 ℃for 3 h. During the reduction process the colour of the foam changed from dark yellow to black. After the reduction the sample was washed with plentiful of water, then squeezed and triturated in water to rid of any loosely attached particles. The sample was dried in oven at 90 ℃ for at least 4 h.

Performance testing

The performance test of the pressure sensor provided in the preparation example is as follows:

As shown in Fig. 1, the test component was constructed as including impedance 1, pressure sensor 2 provided in the preparation example 1, with one terminal connected to voltage 3 and another terminal connected to ground and the data output 4, for testing a: tapping; b: pressing.

The test results are shown in Fig. 2 and Fig. 3. The dotted line in Fig. 2 shows the change in resistance depending on tapping pressure, and the broken line in Fig. 3 indicates the change in resistance at the start and end of pressing. As can be seen from the figures, the sensor responds to the pressure, and the response time becomes longer with prolonged pressing; and the sensor provided by the present invention can respond to a slight change in the pressing process, indicating that the response is sensitive.

Application Example 1: On-body communication Wristband for health care (OB-Care)

This example describes the use of an on-body wristband for use as a remote patient assistance system for bed-bound patients.

Fig. 4 & 5 are schematic illustrations of a wearable smart wristband with an array of pressure sensors labeled 401 in accordance with a preferred embodiment of the present invention. The present example comprises a pressure sensor array (401) as softkeys, speaker (404) , and LEDs (406) individually connected via connecting tracks (403) fabricated on layer (402) overlaying the power connection layer (407) . The pressure sensors prepared in Preparation Example 1, also referred as “softkeys” , are designed in different geometric shapes and sizes to allow easy recognition and simple operation for the user. The wearable wristband is connected to a battery powered microcontroller unit with Bluetooth via the connecting tracks.

During operation, the pressure may be applied using a finger or multiple fingers. Activating a sensor or a combination of sensors activates a distinctive function or command. The selective activated softkey generates electrical signals to the microcontroller that send corresponding encoded information to the remote receiving system, such as a computer or a smart device. A feedback loop from the receiving end assures the user that the message is attended to by giving a beeping sound and flashes of LED.

In this example, the wearable smart wristband can be used as a remote patient assistance system with functions described as follow:

Assigned request	Softkeys	Mode of Operation
Medical support	Rectangle	Tapping for 2 seconds
Assistance to use the toilet	Triangle	Tapping for 2 seconds
Assistance for personal hygiene	Circle	Tapping for 2 seconds
Requesting a drink	Square	Tapping for 2 seconds
Emergency	Any two or all 4 softkeys	Pressing for 4 seconds

A bed-bound patient wearing the smart wristband, can request his or her own needs by tapping or pressing the softkeys to send a request message to the remote system, such as a computer or smart device, in the nurses station. The blinking LEDs and the repeating short beeps on the speaker provides the delivery confirmation of the request sent. Request message received confirmation is notified through repeating long beeps on the speaker and long blinks of the LEDs.

Application Example 2

This application example provides a wearable smart apron. Wherein, the wearable platform takes the form of an apron, as shown in Fig. 6, the softkeys are located in the middle section of the apron. The softkeys may be designed to provide an easier reach by the user using any of their two hands.

Application Example 3

This application example provides a wearable smart trouser, as shown in Fig. 7, with the softkeys being located in the in the region depicted in the drawing.

Application Example 4: On-body communication keyboard for human-computer interaction (OB-link)

This application example finds application as a general keyboard that provides all normal functions of a common computer keyboard.

The design comprises 12 softkeys similar to a mobile phone on screen keyboard. There are 8 alphabet-numerical keys and 4 special character keys as shown in figure 8. The operation is also similar to those commonly used on-screen keyboards. Short single tapping activate the first alphabet; short double tapping activate the second alphabet and so on. “→” shows the direction in which data are connected to microcontroller 801.

The present invention is described in the above-described embodiments, but the present invention is not limited to the above process steps, that is, the present invention is not necessarily implemented in accordance with the process steps described above. It will be apparent to those skilled in the art that any modifications of the present disclosure, equivalent substitutions of the materials for the product of the present disclosure, and additions of auxiliary ingredients, selections of the specific means and the like, are all within the protection and disclosure scopes of the present disclosure.

Claims

A pressure sensor, characterized in that the pressure sensor is a graphene-modified fabric materials such as polyurethane foam;

Wherein, the graphene has a mass percentage of 0.8-2.5%based on 100%of the total mass of the graphene-modified polyurethane foam.
The pressure sensor according to claim 1, characterized in that the polyurethane foam has a porosity of 94-96%.
A preparation method of the pressure sensor according to claim 1 or 2, characterized in comprising the following steps:

Treating a polyurethane foam in a graphene oxide solution to obtain a graphene oxide-loaded polyurethane foam; then reducing the graphene oxide to obtain the pressure sensor.
The preparation method according to claim 3, characterized in comprising the following steps:

(1) soaking the polyurethane foam in a graphene oxide solution in a suitable solvent such as water or ethanol, and then air drying, and finally drying in oven at 70-90 ℃;

(2) reducing the graphene oxide on the dried polyurethane foam by using a reducing agent, then washing and drying to obtain the pressure sensor;

preferably, the reducing agent includes hydrazine hydrate.
The preparation method according to claim 3 or 4, characterized in that a preparation method of the graphene oxide comprises: oxidizing a graphite flake with an oxidant in concentrated sulfuric acid, and then washing and dialyzing to obtain the graphene oxide;

preferably, the mass ratio of the graphite flake to the oxidant is 1: (2-6) ;

preferably, the oxidant includes potassium dichromate or potassium permanganate;

preferably, the concentrated sulfuric acid used is 20-50 mL per 1 g of the graphite flake;

preferably, the oxidant is added to the concentrated sulfuric acid solution in batches; preferably, the solution temperature is maintained at 0-5 ℃ during the addition of the oxidant;

preferably, after the oxidant is added, the solution is warmed up to room temperature and then sonicated for 0.5-1h;

preferably, after the sonication is completed, deionized water is added to the reaction system for a reaction at 98 ℃ for 1-2 h;

preferably, the volume ratio of the deionized water to the concentrated sulfuric acid is (1.5-4) : 1;

preferably, after the reaction is completed, the unreacted oxidant is removed by using hydrogen peroxide;

preferably, the washing comprises washing with hydrochloric acid and deionized water in sequence, and finally dialyzing with a dialysis bag in deionized water until the pH is neutral.
The preparation method according to claim 4 or 5, characterized in that the concentration of the graphene oxide in the graphene oxide solution in ethanol is 0.5-2.5 mg/mL;

preferably, the soaking is carried out for 20-30 min;

preferably, the air drying is carried out for at least 4 h;

preferably, the drying in the step (1) is carried out at the temperature of 70-100 ℃, and for a period of 60-120 min.
The preparation method according to any of claims 4-6, characterized in that the concentration of the hydrazine hydrate in the hydrazine hydrate solution is 5-10%;

preferably, the reduction is carried out at the temperature of 80-95 ℃, and for a period of 3-4 h;

preferably, the drying in the step (2) is carried out at the temperature of 70-100 ℃, and for a period of 4 h or more.
A use of the pressure sensor according to claim 1 or 2 to form a wearable smart fabric;

preferably, the fabric comprises a glove, a wristband, a belt, an apron, a trouser, or a knee strap.
A wearable smart fabric, characterized in comprising the pressure sensor according to claim 1 or 2;

preferably, the wearable smart fabric further comprises a conversion circuit, a power supply and a substrate.
A use of the pressure sensor according to claim 1 or 2 in a wearable keyboard, a wearable console, a wearable detector or a wearable communication device.