A flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, a preparation method thereof, and applications thereof

Abstract

A flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film, a preparation method thereof, and an application thereof in temperature sensing belong to the technical field of temperature sensing. The flexible temperature sensor has a planar layered structure and is composed of an upper electrode layer, a middle double-layer hydrogel temperature-sensitive film, and a lower electrode layer; wherein, the double-layer hydrogel temperature-sensitive film is composed of a polyvinyl alcohol hydrogel film and a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, and the sensor can be obtained by laminating the upper electrode layer, the middle hydrogel temperature-sensitive film, and the lower electrode layer together. By changing the thickness of the hydrogel film and the ion concentration contained therein, the transport process of ions in the hydrogel film is regulated to achieve high-precision temperature sensing; the prepared sensor has high sensitivity, high resolution, and good cyclic stability, providing the possibility for high-precision monitoring of body temperature, and having good application prospects in the fields of human health monitoring and electronic skin.

Description

Technical Field

[0001] The present invention belongs to the technical field of temperature sensing, and particularly relates to a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film, a preparation method thereof, and an application thereof in temperature sensing. Background Art

[0002] Among various physiological indexes of the human body, body temperature is an important parameter reflecting the health status of the human body. The relative stability of body temperature is a necessary condition to ensure the normal progress of basic life activities such as human metabolism. Excessively high body temperature is usually caused by virus or bacterial infection, and is often accompanied by inflammation of functional organs such as the lungs or respiratory tract; while low body temperature means a relatively low basal metabolic rate of the human body, and often indicates some basic metabolic diseases such as hypothyroidism and anemia. Therefore, the monitoring of body temperature is crucial for evaluating the quality of various life activities of the human body. However, due to the narrow change range of body temperature, very small body temperature fluctuations can reflect changes in the health status of the human body, which puts forward higher requirements for the accuracy of temperature sensors.

[0003] With the continuous increase in people's attention to their own health, resistive flexible temperature sensors have been widely reported due to their advantages such as simple structure and easy integration. The sensitive materials usually used for resistive flexible temperature sensors are mainly divided into electronically conductive composite materials and ionically conductive composite materials. Electronically conductive composite materials are usually composed of metal or semiconductor particles dispersed in a flexible polymer elastomer, and often have problems such as poor uniformity and flexibility; while ionically conductive composite materials have good flexibility and stability and have been widely used in the preparation of flexible sensors, but the flexible temperature sensors based on ionically conductive composite materials have problems such as low response and long response and recovery times. Therefore, in order to meet the need for body temperature monitoring, it is of great significance to design a highly sensitive flexible temperature sensor. Summary of the Invention

[0004] Aiming at the existing problems, the purpose of the present invention is to design a hydrogel film with a double-layer structure by utilizing the regulation effect of temperature on ion migration movement, and then provide an ionic temperature sensor with good temperature sensing function, a preparation method thereof, and an application thereof by regulating the ion concentration and its transmission path, so as to achieve highly sensitive detection in the near-body temperature range and solve the deficiencies of existing temperature sensors in body temperature monitoring.

[0005] A flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film according to the present invention has a planar layered structure, which is composed of an upper electrode layer of flexible polyethylene terephthalate (PET) printed with a conductive material, a middle double-layer hydrogel temperature-sensitive film, and a lower electrode layer of flexible polyethylene terephthalate (PET) printed with a conductive material; wherein, the double-layer hydrogel temperature-sensitive film is composed of a polyvinyl alcohol hydrogel film and a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film. By bonding the upper electrode layer, the middle hydrogel temperature-sensitive film, and the lower electrode layer together, a flexible temperature sensor with a layered structure can be obtained. When the temperature changes, the current passing through the double-layer hydrogel temperature-sensitive film will change. By measuring the current value, the response of the sensor can be calculated, so as to obtain the corresponding relationship between the sensor response and the current temperature and establish a temperature detection model. In actual application, the response of the sensor is measured, and the current temperature can be obtained through this temperature detection model to realize the detection of temperature. The response (S) of the device is defined as: S = I T / I 0 , where I T is the device current at temperature T, and I 0 is the device current at 10 °C.

[0006] A preparation method of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film according to the present invention comprises the following steps:

[0007] (1) Add 0.5 - 1.0 g of polyvinyl alcohol powder (molecular weight 63,800 - 114,400) to 10 mL of deionized water, and stir at 85 - 95 °C for 3 - 5 h to obtain a polyvinyl alcohol solution;

[0008] (2) Add 0.1 - 1.0 g of glycerol to the polyvinyl alcohol solution obtained in step (1), and stir at 85 - 95 °C for 3 - 5 h to obtain a polyvinyl alcohol hydrogel precursor solution;

[0009] (3) Repeat step (1) to obtain a polyvinyl alcohol solution; add 0.1 - 1.0 g of glycerol and 1.0 - 4.0 g of sodium polystyrene sulfonate (molecular weight 70,000 - 80,000) to this polyvinyl alcohol solution, and stir at 85 - 95 °C for 3 - 5 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution;

[0010] (4) Ultrasonically clean and dry two polyethylene terephthalate substrates (with dimensions of 2 cm * 2 cm and a thickness of 240 - 300 μm) with ethanol and deionized water in sequence;

[0011] (5) The conductive silver paste (with a conductivity higher than 1×10 5(S / cm) were printed on two polyethylene terephthalate substrates by screen printing method respectively as the upper electrode layer and the lower electrode layer;

[0012] (6) Cool the polyvinyl alcohol hydrogel precursor solution obtained in step (2) to room temperature and let it stand for 10 - 15 h. Take 0.5 - 1.0 mL of this solution and drop - coat it on the lower electrode layer obtained in step (5). Place it in a fume hood and let it stand for 5 - 10 h to obtain a polyvinyl alcohol hydrogel film on the surface of the lower electrode layer, with a thickness of 80 - 300 μm;

[0013] (7) Cool the sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution obtained in step (3) to room temperature and let it stand for 10 - 15 h. Take 0.5 - 1.0 mL of this solution and drop - coat it on the upper electrode layer obtained in step (5). Place it in a fume hood and let it stand for 5 - 10 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the surface of the upper electrode layer, with a thickness of 50 - 200 μm;

[0014] (8) Press - fit the two hydrogel films obtained in step (6) and step (7) to prepare a flexible temperature sensor based on a bilayer hydrogel temperature - sensitive film. The structure is polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer and polyethylene terephthalate substrate. The thickness of the obtained sensor is 0.7 - 1.0 mm.

[0015] The advantages of the present invention are as follows:

[0016] 1) In the present invention, the preparation process of the hydrogel film is simple and does not involve the polymerization process of polymers. And the solvent is water, which is green, pollution - free and low - cost, suitable for mass production;

[0017] 2) The hydrogel - based temperature sensor with a layered structure in the present invention does not require complex preparation processes. It is prepared only by simple drop - coating and then press - fitting, suitable for large - scale industrial production, and has good flexibility;

[0018] 3) The I - V curve of the double - layer hydrogel - type temperature sensor prepared in the present invention shows non - Ohmic characteristics, which proves the ion transport phenomenon between layers; and its resistance changes significantly with temperature, having good temperature - sensing characteristics;

[0019] 4) Based on the temperature-dependent characteristics of the ionic mobility of the hydrogel, a hydrogel film-type temperature sensor with a layered structure is constructed. By changing the thickness of the hydrogel film and the ionic concentration contained therein, the transport process of ions in the hydrogel film is regulated. Based on the temperature-dependent characteristics of the ionic transport process, high-precision temperature sensing is achieved, and a temperature change of 0.03 °C can be resolved, which provides the possibility for high-precision monitoring of body temperature and has good application prospects in the field of human health monitoring and the field of electronic skin. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the flexible temperature sensor prepared by the present invention.

[0021] The names of each part are: the flexible polyethylene terephthalate (PET) upper electrode layer 1 printed with a conductive material and the flexible polyethylene terephthalate (PET) lower electrode layer 6 printed with a conductive material, the conductive copper wires 2 and 5 attached to the upper and lower electrode layers, the sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film 3 drop-coated on the surface of the upper electrode layer, and the polyvinyl alcohol hydrogel film 4 drop-coated on the surface of the lower electrode layer.

[0022] Figure 2 It is the Fourier transform infrared spectrum of the polyvinyl alcohol-sodium polystyrene sulfonate / polyvinyl alcohol double-layer hydrogel temperature-sensitive film in Example 3.

[0023] Figure 3 It is the I-V characteristic curve of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3.

[0024] Figure 4 It is the current change curve of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3 at different temperatures.

[0025] Figure 5 It is the response curve of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3 to different temperatures.

[0026] Figure 6 It is the current change curve with temperature of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3 in the near-body temperature range (25 °C to 45 °C).

[0027] Figure 7 It is the dynamic response curve of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3 to a very small temperature change (~0.03 °C).

[0028] Figure 8 It is the repeatability curve of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3 for a 20 °C temperature change (T 0= 25 °C, T = 45 °C).

[0029] Figure 9 is the response and recovery curve of the flexible temperature sensor based on the double-layer hydrogel temperature-sensitive film in Example 3 for a 20 °C temperature change (T 0 = 25 °C, T = 45 °C). Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0031] Example 1

[0032] (1) Add 0.5 g of polyvinyl alcohol powder (molecular weight about 67000) to 10 mL of deionized water, and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution;

[0033] (2) Add 1.0 g of glycerol to the polyvinyl alcohol solution obtained in step (1), and continue to stir at 90 °C for 4 h to obtain a polyvinyl alcohol hydrogel precursor solution;

[0034] (3) Repeat step (1) to obtain a polyvinyl alcohol solution; add 1.0 g of glycerol and 4.0 g of sodium polystyrene sulfonate (molecular weight about 80000) to this polyvinyl alcohol solution, and stir at 90 °C for 4 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution;

[0035] (4) Use two pieces of polyethylene terephthalate as substrates, with a size of 2 cm * 2 cm and a thickness of 290 μm. Ultrasonically clean the substrates with ethanol and deionized water in sequence and dry them;

[0036] (5) Print conductive silver paste on the two polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer;

[0037] (6) Cool the solution obtained in step (2) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop-coat it on the lower electrode layer of the polyethylene terephthalate substrate obtained in step (5), and let it stand in a fume hood for 8 h to obtain a polyvinyl alcohol hydrogel film with a thickness of 100 μm on the surface of the lower electrode layer;

[0038] (7) Cool the mixed solution obtained in step (3) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop-coat it on the upper electrode layer of the polyethylene terephthalate substrate obtained in step (5), and let it stand in a fume hood for 8 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film with a thickness of 80 μm on the surface of the upper electrode;

[0039] (8) Press the two layers of hydrogel films obtained in steps (6) and (7) together to prepare a flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer, and polyethylene terephthalate substrate. The thickness of the obtained sensor is 0.8 mm.

[0040] Example 2

[0041] (1) Add 1.0 g of polyvinyl alcohol powder (molecular weight about 67,000) to 10 mL of deionized water and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0042] (2) Add 1.0 g of glycerol to the polyvinyl alcohol solution obtained in step (1) and continue to stir at 90 °C for 4 h to obtain a polyvinyl alcohol hydrogel precursor solution.

[0043] (3) Add 0.5 g of polyvinyl alcohol powder (molecular weight about 67,000) to 10 mL of deionized water and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0044] (4) Add 1.0 g of glycerol and 4.0 g of sodium polystyrene sulfonate (molecular weight about 80,000) to the polyvinyl alcohol solution obtained in step (3) and stir at 90 °C for 4 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution.

[0045] (5) Use two pieces of polyethylene terephthalate as substrates, with dimensions of 2 cm * 2 cm and a thickness of 290 μm. Ultrasonically clean the substrates with ethanol and deionized water in sequence and then dry them.

[0046] (6) Print conductive silver paste on the two pieces of polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer.

[0047] (7) Cool the solution obtained in step (2) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop-coat it on the lower electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a polyvinyl alcohol hydrogel film on the lower electrode surface, with a thickness of 200 μm.

[0048] (8) Cool the mixed solution obtained in step (4) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop-coat it on the upper electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the upper electrode surface, with a thickness of 80 μm.

[0049] (9) Press the two-layer hydrogel films obtained in steps (7) and (8) together to prepare a flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer, and polyethylene terephthalate substrate. The resulting sensor has a thickness of 0.9 mm.

[0050] Example 3

[0051] (1) Add 1.0 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0052] (2) Add 0.1 g of glycerol to the polyvinyl alcohol solution obtained in step (1) and continue to stir at 90 °C for 4 h to obtain a polyvinyl alcohol hydrogel precursor solution.

[0053] (3) Add 0.5 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0054] (4) Add 1.0 g of glycerol and 4.0 g of sodium polystyrene sulfonate (molecular weight of about 80,000) to the polyvinyl alcohol solution obtained in step (3) and stir at 90 °C for 4 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution.

[0055] (5) Use two pieces of polyethylene terephthalate as substrates, with dimensions of 2 cm * 2 cm and a thickness of 290 μm. Ultrasonically clean the substrates with ethanol and deionized water in sequence and then dry them.

[0056] (6) Print conductive silver paste on the two pieces of polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer.

[0057] (7) Cool the solution obtained in step (2) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop-coat it on the lower electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a polyvinyl alcohol hydrogel film on the lower electrode surface with a thickness of 180 μm.

[0058] (8) Cool the mixed solution obtained in step (4) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop-coat it on the upper electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the upper electrode surface with a thickness of 80 μm.

[0059] (9) Press the two layers of hydrogel films obtained in steps (7) and (8) together to prepare a flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer, and polyethylene terephthalate substrate. The resulting sensor has a thickness of 0.9 mm.

[0060] Example 4

[0061] (1) Add 1.0 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water, and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0062] (2) Add 0.1 g of glycerol to the polyvinyl alcohol solution obtained in step (1), and continue to stir at 90 °C for 4 h to obtain a polyvinyl alcohol hydrogel precursor solution.

[0063] (3) Add 0.5 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water, and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0064] (4) Add 1.0 g of glycerol and 4.0 g of sodium polystyrene sulfonate (molecular weight of about 80,000) to the polyvinyl alcohol solution obtained in step (3), and stir at 90 °C for 4 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution.

[0065] (5) Use two pieces of polyethylene terephthalate as substrates, with a size of 2 cm * 2 cm and a thickness of 290 μm. Ultrasonically clean the substrates with ethanol and deionized water in sequence and dry them.

[0066] (6) Print conductive silver paste on the two polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer.

[0067] (7) Cool the solution obtained in step (2) to room temperature and let it stand for 12 h. Take 1.0 mL of this solution and drop it on the lower electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a polyvinyl alcohol hydrogel film on the lower electrode surface, with a thickness of 290 μm.

[0068] (8) Cool the mixed solution obtained in step (4) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop it on the upper electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the upper electrode surface, with a thickness of 80 μm.

[0069] (9) Press the two layers of hydrogel films obtained in steps (7) and (8) together to prepare a flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer, and polyethylene terephthalate substrate. The resulting sensor has a thickness of 1.0 mm.

[0070] Example 5

[0071] (1) Add 1.0 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0072] (2) Add 0.1 g of glycerol to the polyvinyl alcohol solution obtained in step (1) and continue to stir at 90 °C for 4 h to obtain a polyvinyl alcohol hydrogel precursor solution.

[0073] (3) Add 0.5 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0074] (4) Add 1.0 g of glycerol and 4.0 g of sodium polystyrene sulfonate (molecular weight of about 80,000) to the polyvinyl alcohol solution obtained in step (3) and stir at 90 °C for 4 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution.

[0075] (5) Use two pieces of polyethylene terephthalate as substrates, with dimensions of 2 cm * 2 cm and a thickness of 290 μm. Ultrasonically clean the substrates with ethanol and deionized water in sequence and dry them.

[0076] (6) Print conductive silver paste on the two pieces of polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer.

[0077] (7) Cool the solution obtained in step (2) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop it on the lower electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a polyvinyl alcohol hydrogel film on the lower electrode surface, with a thickness of 180 μm.

[0078] (8) Cool the mixed solution obtained in step (4) to room temperature and let it stand for 12 h. Take 1.0 mL of this solution and drop it on the upper electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the upper electrode surface, with a thickness of 200 μm.

[0079] (9) Press the two layers of hydrogel films obtained in steps (7) and (8) together to prepare a flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer, and polyethylene terephthalate substrate. The thickness of the obtained sensor is 1.0 mm.

[0080] Example 6

[0081] (1) Add 1.0 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water, and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0082] (2) Add 0.1 g of glycerol to the polyvinyl alcohol solution obtained in step (1), and continue to stir at 90 °C for 4 h to obtain a polyvinyl alcohol hydrogel precursor solution.

[0083] (3) Add 0.5 g of polyvinyl alcohol powder (molecular weight of about 67,000) to 10 mL of deionized water, and stir at 90 °C for 4 h to obtain a polyvinyl alcohol solution.

[0084] (4) Add 1.0 g of glycerol and 2.0 g of sodium polystyrene sulfonate (molecular weight of about 80,000) to the polyvinyl alcohol solution obtained in step (3), and stir at 90 °C for 4 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution.

[0085] (5) Use two pieces of polyethylene terephthalate as substrates, with a size of 2 cm * 2 cm and a thickness of 290 μm. Ultrasonically clean the substrates with ethanol and deionized water in sequence and then dry them.

[0086] (6) Print conductive silver paste on the two pieces of polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer.

[0087] (7) Cool the solution obtained in step (2) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop it on the lower electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a polyvinyl alcohol hydrogel film on the lower electrode surface, with a thickness of 180 μm.

[0088] (8) Cool the mixed solution obtained in step (4) to room temperature and let it stand for 12 h. Take 0.6 mL of this solution and drop it on the upper electrode layer of the polyethylene terephthalate substrate obtained in step (6), and let it stand in a fume hood for 8 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the upper electrode surface, with a thickness of 60 μm.

[0089] (9) Press the two-layer hydrogel films obtained in steps (7) and (8) to prepare a flexible temperature sensor based on a bilayer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer and polyethylene terephthalate substrate. The thickness of the obtained sensor is 0.7 mm.

[0090] The Fourier transform infrared spectrum of the polyvinyl alcohol-sodium polystyrene sulfonate / polyvinyl alcohol bilayer hydrogel temperature-sensitive film prepared in Example 3 is as Figure 2 shown. The vibration absorption peaks of the polyvinyl alcohol-sodium polystyrene sulfonate / polyvinyl alcohol composite material are all caused by the chemical bonds contained in the polyvinyl alcohol or sodium polystyrene sulfonate molecules, and no new chemical bonds are found, indicating that no chemical reaction occurs to produce new substances during the process of introducing sodium polystyrene sulfonate into the polyvinyl alcohol film.

[0091] The I-V characteristics of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 are as Figure 3 shown. It can be observed that when positive and negative voltages are applied, the current of the device is not completely symmetric, indicating that the sensor is a non-Ohmic device. And after the applied negative voltage exceeds a certain value, the current shows saturation because at this time, due to the external electric field, Na + moves towards the electrode in the sodium polystyrene sulfonate / polyvinyl alcohol film, accumulating positive charges at the electrode. On the contrary, negative charges accumulate at the electrode of the polyvinyl alcohol film, forming a built-in electric field opposite to the external electric field. When the built-in electric field reaches equilibrium with the external electric field, the current reaches equilibrium, that is, the current shows saturation. This phenomenon is not observed when a positive voltage is applied, which verifies the intermembrane migration behavior of ions in the hydrogel film.

[0092] The dynamic current change curves of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 at different temperatures are as Figure 4 shown. It can be seen that due to the significant influence of temperature on the ion migration rate, when the temperature increases from 10 °C to 60 °C, the current value of the sensor shows an obvious change spanning two orders of magnitude.

[0093] The temperature response curve of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 is as Figure 5 shown. When the temperature increases by 50 °C, the current value of the sensor increases to 215 times the original value.

[0094] The current change curve with temperature of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 in the near-body temperature range (25 °C - 45 °C) is as Figure 6As shown, it can be seen that the sensor current changes significantly with temperature. When the temperature increases by 20 °C, the sensor current value increases to 7 times the original value, and within this temperature range, the current changes almost linearly with temperature.

[0095] The dynamic response curve of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 for extremely small temperature changes (~0.03 °C) is shown in Figure 7 . It can be seen that for a temperature change of approximately 0.03 °C, the current value of the device changes significantly, indicating that the sensor based on the layered hydrogel film has the ability to resolve small temperature changes and is suitable for measuring human body temperature.

[0096] The response repeatability curve of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 in the near-body temperature range (25 °C to 45 °C) is shown in Figure 8 . The sensor based on the layered hydrogel film shows a stable repeated response during multiple heating and cooling cycles, indicating that the temperature response of the sensor has good repeatability.

[0097] The response and recovery transient curve of the temperature sensor based on the bilayer hydrogel temperature-sensitive film prepared in Example 3 in the near-body temperature range (25 °C to 45 °C) is shown in Figure 9 . It can be seen that the sensor has fast response and recovery characteristics for a temperature change of 20 °C.

Claims

1. A preparation method of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film, the steps are as follows: (1) Add 0.5 - 1.0 g of polyvinyl alcohol powder to 10 mL of deionized water and stir to obtain a polyvinyl alcohol solution; (2) Add 0.1 - 1.0 g of glycerol to the polyvinyl alcohol solution obtained in step (1) and stir to obtain a polyvinyl alcohol hydrogel precursor solution; (3) Repeat step (1) to obtain a polyvinyl alcohol solution; add 0.1 - 1.0 g of glycerol and 1.0 - 4.0 g of sodium polystyrene sulfonate to this polyvinyl alcohol solution and stir to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution; (4) Ultrasonically clean and dry two polyethylene terephthalate substrates with ethanol and deionized water in sequence; (5) Print conductive silver paste on the two polyethylene terephthalate substrates by screen printing method as the upper electrode layer and the lower electrode layer; (6) Cool the polyvinyl alcohol hydrogel precursor solution obtained in step (2) to room temperature and let it stand for 10 - 15 h. Take 0.5 - 1.0 mL of this solution and drop-coat it on the lower electrode layer obtained in step (5), and let it stand in a fume hood for 5 - 10 h to obtain a polyvinyl alcohol hydrogel film on the surface of the lower electrode layer, with a thickness of 80 - 300 μm; (7) Cool the sodium polystyrene sulfonate / polyvinyl alcohol hydrogel precursor solution obtained in step (3) to room temperature and let it stand for 10 - 15 h. Take 0.5 - 1.0 mL of this solution and drop-coat it on the upper electrode layer obtained in step (5), and let it stand in a fume hood for 5 - 10 h to obtain a sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film on the surface of the upper electrode layer, with a thickness of 50 - 200 μm; (8) Press the two hydrogel films obtained in step (6) and step (7) together to prepare a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film, with a structure of polyethylene terephthalate substrate, upper electrode layer, sodium polystyrene sulfonate / polyvinyl alcohol hydrogel film, polyvinyl alcohol hydrogel film, lower electrode layer and polyethylene terephthalate substrate.

2. A preparation method of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film as described in claim 1, characterized in that: The molecular weight of the polyvinyl alcohol powder is 63800 - 114400, and the molecular weight of the sodium polystyrene sulfonate is 70000 - 80000.

3. A preparation method of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film as described in claim 1, characterized in that: Stir at 85 - 95 °C for 3 - 5 h.

4. A preparation method of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film as described in claim 1, characterized in that: The size of the polyethylene terephthalate substrate is 2 cm * 2 cm, and the thickness is 240 - 300 μm.

5. A preparation method of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film as described in claim 1, characterized in that: The thickness of the sensor is 0.7 - 1.0 mm.

6. A flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film, characterized in that: It is prepared by the method according to any one of claims 1 to 5.

7. Use of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film according to claim 6 in temperature sensing.

8. Use of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film according to claim 7 in temperature sensing, characterized in that: It is used to detect human body temperature.

9. Use of a flexible temperature sensor based on a double-layer hydrogel temperature-sensitive film according to claim 7 in temperature sensing, characterized in that: It is used for electronic skin.

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