阅读说明：本技术 一种基于复合温敏水凝胶的柔性温度传感器及其制备方法 (Flexible temperature sensor based on composite temperature-sensitive hydrogel and preparation method thereof ) 是由 吴俊� 李颖慧 段升顺 于 2020-05-08 设计创作，主要内容包括：本发明公开了一种基于复合温敏水凝胶的柔性温度传感器及其制备方法,所述传感器包括导热层、导电层和电极,导电层分别与导热层、电极相连,导热层、导电层均由PNIPAM/MXene复合材料制成,所述导热层中的MXene浓度高于导电层中的MXene浓度。所述方法包含以下步骤：将重结晶后的NIPAM与BIS加入去离子水形成单体溶液；滴加MXene溶液,使其含量为0.3～1.2mg/mL；加入APS和TEMED溶液,搅拌均匀后超声震荡；在低温无氧环境中,先后进行交联反应,分别生成含高浓度MXene的导热层和含低浓度MXene的导电层；在导电层的两端固定导电金属线。本发明通过调整复合凝胶上、下层导电填充材料浓度,可以对30～42℃做出快速逻辑判断响应,适用于人体监测等,制备过程简单,成本低,易于批量生产。(The invention discloses a flexible temperature sensor based on composite temperature-sensitive hydrogel and a preparation method thereof, wherein the sensor comprises a heat conduction layer, a conducting layer and an electrode, the conducting layer is respectively connected with the heat conduction layer and the electrode, the heat conduction layer and the conducting layer are both made of PNIPAM/MXene composite materials, and the MXene concentration in the heat conduction layer is higher than that in the conducting layer.)

1. A flexible temperature sensor based on composite temperature-sensitive hydrogel is characterized in that: the conductive layer (2) is connected with the heat conduction layer (1) and the electrode (3) respectively, the heat conduction layer (1) and the conductive layer (2) are made of PNIPAM/MXene composite materials, and the concentration of MXene in the heat conduction layer (1) is higher than that of MXene in the conductive layer (2).

2. The flexible temperature sensor based on the composite temperature-sensitive hydrogel of claim 1, wherein: in the PNIPAM/MXene composite material, MXene is uniformly dispersed in PNIPAM temperature-sensitive hydrogel.

3. The flexible temperature sensor based on composite temperature-sensitive hydrogel of claim 1, wherein the concentration of MXene in the heat conducting layer (1) is 0.7mg/m L-1.2 mg/m L, and the concentration is 106-159 mg/m L.

4. The flexible temperature sensor based on composite temperature-sensitive hydrogel of claim 1, wherein the concentration of MXene in the conductive layer (2) is 0.3mg/m L-0.5 mg/m L, and the concentration is 106-159 mg/m L.

5. The flexible temperature sensor based on the composite temperature-sensitive hydrogel of claim 1, wherein: the electrode (3) is a copper electrode, a platinum electrode or a silver electrode.

6. The flexible temperature sensor based on the composite temperature-sensitive hydrogel of claim 1, wherein: the thickness of the heat conduction layer (1) is smaller than that of the conductive layer (2).

7. A preparation method of a flexible temperature sensor based on composite temperature-sensitive hydrogel is characterized by comprising the following steps:

transferring the recrystallized NIPAM and a crosslinking agent BIS into a beaker, and adding deionized water to form a monomer solution;

slowly dripping the MXene solution into the solution to enable the MXene content in the mixed solution to reach 0.3-1.2 mg/m L;

adding 10-30 u L of APS solution with the mass fraction of 10% -20% into the mixed solution obtained in the step two, adding 10-20 u L of TEMED solution, stirring uniformly, and then carrying out ultrasonic oscillation treatment for 3-5 minutes;

respectively carrying out cross-linking reaction on the mixed solution containing different MXene concentrations in a low-temperature oxygen-free environment to generate a heat conduction layer (1) and a conductive layer (2), wherein the MXene concentration in the heat conduction layer (1) is higher than that in the conductive layer (2);

and step five, fixing conductive metal wires as electrodes (3) at two ends of the conductive layer (2) of the composite hydrogel obtained in the step four respectively.

8. The preparation method of the flexible temperature sensor based on the composite temperature-sensitive hydrogel according to claim 7, which is characterized in that: in the first step, the mass ratio of NIPAM to BIS is 27-29: 1.

9. The preparation method of the flexible temperature sensor based on the composite temperature-sensitive hydrogel, according to the claim 7, is characterized in that in the step one, 1-2 g of NIPAM and 40-80 m L of n-hexane are mixed, the mixed liquid is stirred and completely dissolved at 50-60 ℃, then placed in a refrigerator at-7-4 ℃ for standing for 2-3 hours until crystals are completely separated out, the crystal solution mixture is subjected to suction filtration to obtain NIPAM powder without completely removing the stabilizer, and the operation is repeated for 2-3 times to obtain pure NIPAM powder without the stabilizer.

10. The preparation method of the flexible temperature sensor based on the composite temperature-sensitive hydrogel according to claim 7, which is characterized in that: the fourth step specifically comprises:

(1) slowly pouring the mixed solution with MXene concentration of 0.7-1.2 mg/m L into a mold, slowly placing one end of a glass sheet in contact with the mold until the glass sheet is tightly combined with the liquid, pressing a weight on the glass sheet to ensure that no bubble remains in the liquid below the glass sheet, placing the glass sheet in a low-temperature environment at-7 to-4 ℃, storing the glass sheet for 12-24 hours, and taking out the glass sheet;

(2) putting the composite hydrogel into another mold, continuously and slowly pouring a mixed solution with MXene concentration of 0.3-0.5 mg/m L, slowly putting one end of a glass sheet into contact with the mold until the glass sheet is tightly combined with the liquid, pressing a weight on the glass sheet to ensure that no bubble remains in the liquid below the glass sheet, putting the glass sheet into a low-temperature environment at-7 to-4 ℃, preserving the glass sheet for 12-24 hours and then taking the glass sheet out;

(3) and (3) flushing the composite hydrogel under flowing deionized water for 2-3 hours.

Technical Field

The invention relates to the field of sensors, in particular to a flexible temperature sensor based on composite temperature-sensitive hydrogel and a preparation method thereof.

Background

Wearable sensors are one of the important working elements in the fields of flexible electronic systems, artificial skin, etc., which enable personalized medical detection such as fine temperature detection and long-term monitoring. Temperature sensing is one of the main sensing devices, and is divided into continuous temperature monitoring and logic output type temperature sensing. The logic output type temperature sensor outputs signals after exceeding a set temperature range.

According to the working principle of the temperature sensor, the temperature sensor mainly comprises contact temperature sensing and non-contact temperature sensing. The non-contact sensing is mainly based on the blackbody radiation law and is mainly applied to temperature distribution monitoring and transient temperature acquisition. However, such sensors are easily affected by the surface state and microstructure of the object to be measured, and therefore, the accuracy is relatively poor compared with the touch sensors.

The contact sensor mainly comprises a bimetallic thermometer, a glass liquid thermometer, a pressure type thermometer, a resistance thermometer and the like. The metal temperature sensor has obvious heat effect, high sensitivity, high stability and high integration level, and may be used widely in traditional miniature electronic system.

However, in a flexible electronic system, it is often difficult to directly connect a solid-state hard electronic device to a flexible circuit substrate, and a critical temperature sensing chip and the like exist in the form of an element island. Component connection stability in flexible electronic circuits is therefore an important solution. On the other hand, for sensing devices such as metal materials which are greatly affected by temperature, the temperature drift phenomenon is easily generated, and the phenomenon needs to be solved by additionally carrying out logic processing and program control, so that the integration difficulty and the design difficulty of the flexible circuit are further increased.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention aims to provide the flexible temperature sensor based on the composite temperature-sensitive hydrogel, which has better connection stability and is not easily influenced by temperature drift, and the invention also aims to provide the preparation method of the flexible temperature sensor based on the composite temperature-sensitive hydrogel, which has lower integration cost.

The technical scheme is as follows: the flexible temperature sensor based on the composite temperature-sensitive hydrogel comprises a heat conduction layer, a conducting layer and an electrode, wherein the conducting layer is respectively connected with the heat conduction layer and the electrode, the heat conduction layer and the conducting layer are both made of PNIPAM/MXene composite materials, and the concentration of MXene in the heat conduction layer is higher than that of MXene in the conducting layer.

In the PNIPAM/MXene composite material, MXene is uniformly dispersed in PNIPAM temperature-sensitive hydrogel to form a uniform electric conduction and heat conduction network, the concentration of MXene in the heat conduction layer is 0.7mg/m L-1.2 mg/m L and 106-159 mg/m L, and the concentration of MXene in the electric conduction layer is 0.3mg/m L-0.5 mg/m L and 106-159 mg/m L.

The electrodes are preferably copper electrodes with the specification of awg 20-awg 24, platinum electrodes with the diameter of 0.6-0.85 mm or silver electrodes, and the influence of electron thermal motion caused by high conductivity of the lower layer is avoided. The thickness of the heat conducting layer is smaller than that of the electric conducting layer.

The preparation method of the flexible temperature sensor based on the composite temperature-sensitive hydrogel comprises the following steps:

transferring the recrystallized NIPAM and a crosslinking agent BIS into a beaker, wherein the mass ratio of the NIPAM to the BIS is 27-29: 1, and adding 4-6 m L deionized water to form a monomer solution;

slowly dripping the MXene solution into the solution to enable the MXene content in the monomer solution to reach 0.3-1.2 mg/m L;

adding 10-30 u L of APS solution with the mass fraction of 10% -20% into the mixed solution obtained in the step two, adding 10-20 u L of TEMED solution, stirring uniformly, and then carrying out ultrasonic oscillation treatment for 3-5 minutes;

respectively carrying out cross-linking reaction on the mixed solution containing different MXene concentrations in a low-temperature oxygen-free environment to generate a heat conduction layer and a conductive layer, wherein the MXene concentration in the heat conduction layer is higher than that in the conductive layer;

and fifthly, fixing conductive metal wires as leading-out electrodes at two ends of the conductive layer of the composite hydrogel obtained in the fourth step, wherein the conductive metal wires are copper wires, platinum wires or silver wires.

The recrystallization in the first step is that 1-2 g of NIPAM and 40-80 m L of n-hexane are mixed, the mixed liquid is stirred to be completely dissolved at 50-60 ℃, then the mixed liquid is placed in a refrigerator at minus 4-minus 7 ℃ to stand for 2-3 hours until crystals are completely separated out, the crystal solution mixture is subjected to suction filtration to obtain NIPAM powder without completely removing the stabilizer, the operation is repeated for 2-3 times to obtain pure NIPAM powder without the stabilizer, and the obtained pure NIPAM powder without the stabilizer is stored in the refrigerator at minus 4-7 ℃ and is sealed for storage.

Wherein, the fourth step specifically comprises:

(1) slowly pouring a mixed solution with MXene concentration of 0.7-1.2 mg/m L into a mold, slowly placing one end of a glass sheet in contact with the mold until the glass sheet is tightly combined with liquid, pressing a weight on the glass sheet to ensure that no bubble remains in the liquid below the glass sheet, constructing an anaerobic environment for the crosslinking reaction of gel, placing the glass sheet in a low-temperature environment of-7 to-4 ℃, storing the glass sheet for 12-24 hours, and taking out the glass sheet;

(2) placing the composite hydrogel into another mold, continuously and slowly pouring a mixed solution with MXene concentration of 0.3-0.5 mg/m L, contacting one end of a glass sheet with the mold, slowly placing the glass sheet down until the glass sheet is tightly combined with liquid, pressing a weight on the glass sheet to ensure that no bubble remains in the liquid below, constructing an oxygen-free environment for the crosslinking reaction of the gel, placing the glass sheet in a low-temperature environment at-7-4 ℃, storing the glass sheet for 12-24 hours, and taking out the glass sheet;

(3) and (3) flushing the composite hydrogel under flowing deionized water for 2-3 hours.

The working principle is as follows: the temperature is increased to be higher than the hydrogel phase transition point, so that the resistance of the PNIPAM/MXene composite hydrogel material is turned within the range of 30-42 ℃, and the temperature judgment and the circuit logic signal output are realized. The specific working modes are as follows:

(1) when the contact temperature of the object to be detected is lower than the phase transition temperature of the composite hydrogel: the logic output type flexible temperature sensor has no signal output and no alarm prompt. The heat conducting layer rapidly transfers heat upwards into the conducting layer, at the moment, the conducting layer is still in a hydrophilic swelling state due to the fact that the temperature is lower than the lowest phase transition temperature of the temperature-sensitive hydrogel PNIPAM, the three-dimensional network expands, and the MXene conducting filler is in the three-dimensional conducting network which is uniformly distributed in the hydrogel. The resistance of the composite hydrogel is slightly reduced under the influence of electron and ion thermal motion. The micro integrated chip maintains a no-signal output state by judging the resistance variation trend.

(2) When the contact temperature of the object to be detected is increased and is higher than the hydrogel phase transition temperature: the logic output type flexible temperature sensor has signal output and alarm prompt. The heat conducting layer rapidly transfers heat upwards into the electric conducting layer, at the moment, the temperature crosses the lowest phase transition temperature of the temperature-sensitive hydrogel PNIPAM, the temperature-sensitive hydrogel is subjected to phase transition and is in a hydrophobic state, the three-dimensional network exploration shows that the MXene conductive filler is in a two-dimensional conductive path state in the hydrogel, and the resistance of the composite hydrogel is changed from descending to ascending through an inflection point. The micro integrated chip outputs signals by judging the variation trend of the resistance and the existence of the inflection point.

Has the advantages that: compared with the prior art, the invention has the following remarkable characteristics:

1. the concentration of the conductive filling materials on the upper layer and the lower layer of the composite gel is adjusted, so that the rapid logical judgment response can be made at 30-42 ℃, the composite gel is suitable for human body monitoring and the like, the preparation process is simple, the cost is low, and the mass production is easy;

2. through the layered design, the heat conducting layer at the bottom layer keeps the contact surface heated uniformly, and the heat can be quickly and upwards transferred into the composite hydrogel; the conducting layer on the upper layer reduces the influence of electron thermal motion on the temperature sensitivity of the composite hydrogel resistor, and simultaneously keeps the quick response of the hydrogel to the temperature;

3. the temperature-sensitive hydrogel PNIPAM has the characteristic of fixing the lowest phase transition temperature, and the lowest phase transition temperature is not influenced by the external environment temperature, so that compared with the traditional MXene sensing device, the temperature sensing device based on the composite temperature-sensitive hydrogel phase transition principle cannot generate the temperature drift phenomenon.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a back-end circuit design of the present invention.

Detailed Description

Referring to fig. 1, the logic output type temperature sensor based on the composite temperature-sensitive hydrogel comprises three parts, namely a bottom heat conduction layer 1, an upper conductive layer 2 and an electrode 3, wherein the heat conduction layer 1 is composed of high-concentration MXene (the concentration is 0.7mg/m L-1.2 mg/m L) and common PNIPAM temperature-sensitive hydrogel, the lower-concentration and middle-concentration and low-concentration conductive layer 2 in the upper layer is composed of low-concentration and middle-concentration MXene (the concentration is 0.3mg/m L-0.5 mg/m L) and common PNIPAM temperature-sensitive hydrogel, the MXene concentration in the heat conduction layer 1 is higher and the thickness is thinner, the purpose is to enable the gel to be heated uniformly on a contact surface to be detected, and to be capable of rapidly transferring heat to the interior of the composite gel of the heat conduction layer 2, the MXene concentration in the conductive layer 2 is lower and the thickness is larger than that of the heat conduction layer 1, the purpose is capable of rapidly responding to the temperature, and simultaneously reducing the influence of the electronic thermal motion caused by the high-density of the high-induced electrode 3 brought by.

Referring to fig. 2, the rear-end hardware circuit design principle realizes the judgment of temperature and the output of circuit logic signals by the turning of the composite hydrogel resistance caused by the temperature rise above the lowest phase transition temperature of the hydrogel. After the switch is closed, the specific working mode is as follows:

(1) when the contact temperature of the object to be measured is lower than the phase transition temperature of the composite hydrogel

At the moment, the logic output type flexible temperature sensor has no signal output and no alarm prompt. The bottom heat conduction layer 1 rapidly transfers heat upwards into the upper conductive layer 2, at the moment, the conductive layer 2 is still in a hydrophilic swelling state due to the temperature lower than the lowest phase transition temperature of the temperature-sensitive hydrogel PNIPAM, the three-dimensional network expands, and MXene conductive filler is in a three-dimensional conductive network uniformly distributed in the hydrogel. The resistance of the composite hydrogel is slightly reduced under the influence of electron and ion thermal motion. The micro integrated chip maintains a no-signal output state by judging the resistance variation trend.

(2) When the contact temperature of the object to be measured is increased and is higher than the hydrogel phase transition temperature

At the moment, the logic output type flexible temperature sensor has signal output and alarm prompt. The bottom heat conduction layer 1 quickly transfers heat upwards into the upper conductive layer 2, at the moment, the temperature-sensitive hydrogel is in a hydrophobic state due to the fact that the temperature exceeds the lowest phase change temperature of the temperature-sensitive hydrogel PNIPAM, the MXene conductive filler is in a two-dimensional conductive path state in the hydrogel, and the resistance of the composite hydrogel is changed from descending to ascending through an inflection point. The micro integrated chip outputs signals by judging the variation trend of the resistance and the existence of the inflection point.

And (2) recrystallizing the hydrogel monomer, namely mixing 1-2 g of NIPAM with 40-80 m L of n-hexane, magnetically stirring the mixed liquid at 50-60 ℃, completely dissolving the mixed liquid, placing the mixed liquid in a refrigerator at-4 to-7 ℃ for standing for 2-3 hours until crystals are completely separated out, performing suction filtration on the crystal solution mixture by using a Buchner funnel to obtain NIPAM powder without completely removing the stabilizer, repeating the operation for 2-3 times on the substance to obtain pure NIPAM powder without the stabilizer, storing the obtained pure NIPAM powder without the stabilizer in the refrigerator at-4 to-7 ℃, and sealing and storing for later use.

The method comprises the following steps that a PTFE hydrophobic material is selected as a template of a mould, a first mould with the length of 2cm, the width of 2cm and the thickness of 1mm is obtained after laser engraving, and a cuboid with the length of 1cm, the width of 1cm and the thickness of 1mm is engraved in the center of the first mould; a second die with the length of 2cm, the width of 2cm and the thickness of 1 mm; and stacking the first mold and the second mold up and down to be tightly attached to form a first module. Obtaining a third die with the length of 2cm, the width of 2cm and the thickness of 4mm by laser engraving, and engraving a cuboid with the length of 1cm, the width of 1cm and the thickness of 4mm in the center of the third die 3; a fourth die with the length of 2cm, the width of 2cm and the thickness of 1 mm; and stacking the third mold and the fourth mold up and down to be tightly attached to form a second module.

The remaining raw materials used in the following examples were purchased directly.