Flexible temperature sensor based on PVA and preparation method thereof

Abstract

The invention relates to a PVA-based flexible temperature sensor and a preparation method thereof. The preparation method comprises the following steps: S1, preparing a water-soluble polymer conductive microsphere dispersion liquid; s2, preparing a hydrophobic modified emulsion; s3, preparation of a film-forming liquid: dissolving PVA to obtain a PVA aqueous solution, adding the dispersion liquid, and stirring to obtain the film-forming liquid; and S4, sensor forming: pouring the film forming liquid into a film forming mold to form a liquid film, drying until the water content is lower than 30% to obtain a semi-dry film, pouring the emulsion into the mold, fully soaking, pouring out excess emulsion, performing illumination to initiate in-situ polymerization, fully polymerizing, drying to obtain a sensor film, and fixing conductive electrodes at two ends to obtain the sensor. According to the invention, the water-soluble polymer conductive microspheres are used as a conductive medium, so that the nano metal which can be better dispersed and has a conductive effect after film formation can be stably combined on the surface of the polymer core, and is not easy to agglomerate and stable in performance; the PVA film layer can be modified by the hydrophobic modified emulsion, so that the flexible temperature sensor can keep stable temperature-sensitive characteristics in different humidity environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensors, and in particular relates to a PVA-based flexible temperature sensor and a preparation method thereof. Background Art

[0002] Temperature sensors are sensors that can sense temperature and convert it into usable output signals. Traditionally, they can be divided into two categories: thermal resistors and thermocouples according to the characteristics of sensor materials and electronic components. With the promotion of wearable electronic products and the expansion of electronic product application fields, traditional hard material temperature sensors can no longer meet the needs of technical applications, and flexible temperature sensors that can be bent, stretched or compressed are needed.

[0003] Some current flexible temperature sensors are usually prepared based on two-dimensional or one-dimensional new materials with strong conductivity such as graphene, carbon nanotubes and MXene. The preparation cost is often relatively high, and the mechanical strength of the flexible temperature sensors is usually poor. In addition, some researchers have tried to use PVA as a substrate, and improve the conductivity and thermosensitivity of PVA by in-situ reduction to generate silver nanoparticles and disperse them in PVA film materials. They have initially obtained a flexible temperature sensor that combines organic and inorganic materials and has temperature-sensitive properties at room temperature. However, due to the poor dispersion of silver nanoparticles in PVA film materials, easy agglomeration and oxidation, the performance stability of the flexible temperature sensor is poor. At the same time, the temperature sensor is also sensitive to humidity, so the environmental humidity interference is large during use, affecting the use of its temperature-sensitive properties. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a PVA-based flexible temperature sensor and a preparation method thereof, so as to overcome the above-mentioned deficiencies existing in the prior art.

[0005] The technical solution of the present invention to solve the above technical problem is as follows: a method for preparing a flexible temperature sensor based on PVA, which comprises the following steps:

[0006] S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water and ultrasonically dispersing the dispersion;

[0007] S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 8-12 parts of butyl acrylate, 2-4 parts of hexafluorobutyl acrylate, 0.2-0.5 parts of an iodinated compound initiator, 0.4-0.8 parts of an emulsifier and 25-40 parts of distilled water were mixed and stirred to obtain an emulsion;

[0008] S3 film-forming solution preparation: PVA was added to distilled water, heated and stirred to fully dissolve the PVA aqueous solution, and then the dispersion obtained in S1 was added to the PVA aqueous solution, and the film-forming solution was obtained after stirring;

[0009] S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. Then pour the emulsion prepared in S2 into the film-forming mold. After sufficient soaking, pour out the excess emulsion. Then, illuminate the film material in the film-forming mold to induce in-situ polymerization. After sufficient polymerization, dry it to obtain a sensor film. Fix conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

[0010] On the basis of the above technical solutions, the present invention can also have the following further specific options.

[0011] Specifically, the water-soluble polymer conductive microspheres in S1 are sulfonated polystyrene-polyaniline composite microspheres with nano-copper, nano-silver or nano-gold loaded on the surface.

[0012] Specifically, the usage ratio of water-soluble polymer conductive microspheres to distilled water in S1 is 10-25 mg:1 mL.

[0013] Specifically, the iodinated compound initiator in S2 is 2-iodo-2-methylpropionitrile.

[0014] Specifically, the emulsifier in S2 is sodium dioctyl sulfosuccinate.

[0015] Specifically, the concentration of PVA in the PVA aqueous solution in S3 is 10-15wt%.

[0016] Specifically, the volume ratio of the PVA aqueous solution and the dispersion in S3 when mixed is 1:0.3-0.5.

[0017] Specifically, the thickness of the liquid film in S4 is 0.5-1 mm, and the thickness of the semi-dry film is 0.1-0.3 mm.

[0018] Specifically, in S4, after the conductive electrode is fixed, a flexible packaging film is attached to both sides of the sensor film for packaging, and the flexible packaging film is a PI film, a PET film or a PDMS film.

[0019] The present invention also provides a PVA-based flexible temperature sensor, which is prepared by the above method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) Water-soluble polymer conductive microspheres are used as conductive media, and conductive nano-metals are loaded on their surfaces. The conductive microspheres themselves have certain water solubility and can be well dispersed in water. At the same time, they have a polymer core, so they can be better dispersed when mixed with PVA aqueous solution, and the conductive nano-metals can be relatively stably combined with the surface of the polymer core after film formation, and are not easy to agglomerate. In addition, during the in-situ polymerization of the hydrophobic modified emulsion, the polymer conductive microspheres dispersed in the PVA film layer will be consolidated and coated to a certain extent again, ensuring that the conductivity and thermal sensitivity of the obtained sensor film are more stable.

[0022] 2) The hydrophobic modified emulsion can modify the PVA film layer, which is originally hygroscopic and moisture-sensitive, to ensure that it is insensitive to the humidity in the environment and to ensure that the flexible temperature sensor maintains stable temperature-sensitive properties in different humidity environments.

[0023] 3) The hydrophobic modified emulsion penetrates into the semi-dry film and then induces in-situ polymerization under light, which not only makes the sensor film hydrophobic, but also forms a hydrophobic component copolymerized by butyl acrylate and hexafluorobutyl acrylate interspersed in the PVA film layer and on the surface, thereby improving the comprehensive performance of the sensor film, such as weather resistance and mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of a method for preparing a PVA-based flexible temperature sensor provided by the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the PVA flexible temperature sensor after packaging prepared by the present invention.

[0026] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0027] 1. Sensor film; 2. Conductive electrode; 3. Flexible packaging film. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0029] like Figure 1 As shown, the present invention provides a method for preparing a flexible temperature sensor based on PVA, which comprises the following steps:

[0030] S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water and ultrasonically dispersing the dispersion;

[0031] S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 8-12 parts of butyl acrylate, 2-4 parts of hexafluorobutyl acrylate, 0.2-0.5 parts of an iodinated compound initiator, 0.4-0.8 parts of an emulsifier and 25-40 parts of distilled water were mixed and stirred to obtain an emulsion;

[0032] S3 film-forming solution preparation: PVA was added to distilled water, heated and stirred to fully dissolve the PVA aqueous solution, and then the dispersion obtained in S1 was added to the PVA aqueous solution, and the film-forming solution was obtained after stirring;

[0033] S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. Then pour the emulsion prepared in S2 into the film-forming mold. After sufficient soaking, pour out the excess emulsion. Then, illuminate the film material in the film-forming mold to induce in-situ polymerization. After sufficient polymerization, dry it to obtain a sensor film. Fix conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

[0034] It should be noted that if Figure 2 As shown, after the conductive electrodes 2 are fixed at both ends of the sensor film 1 in step S4, a flexible packaging film 3 can be attached to the front and back sides of the sensor film 1 for packaging. The flexible packaging film is a PI film, a PET film or a PDMS film. After packaging, the PVA-based flexible temperature sensor has a further enhanced ability to resist environmental humidity interference and better durability. The processing temperature range of the polyvinyl alcohol (PVA) of the present invention is between 120 and 140°C.

[0035] To avoid redundant description, the raw materials used in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods in the art unless otherwise specified.

[0036] The water-soluble polymer conductive microspheres used in the following examples are all sulfonated polystyrene-polyaniline-nanosilver composite microspheres, which have sulfonated polystyrene as the core and polyaniline as the shell. The nanosilver is relatively evenly dispersed and bonded to the surface of the polyaniline shell. The particle size of the composite microspheres is about 1.5 μm. The preparation process of the composite microspheres refers to Example 1 of the existing patent technology CN105315565A. The selected PVA is preferably a raw material with an average molecular weight of 60,000-100,000. When the light is used to initiate the in-situ polymerization, a red light or near-infrared laser with a wavelength of 680-780 nm is used, and the light intensity is 40-60 mW / cm 2 , the lighting time is controlled at more than 30h.

[0037] Example 1

[0038] A method for preparing a PVA-based flexible temperature sensor comprises the following steps:

[0039] S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water, ultrasonically dispersing to obtain a dispersion, the amount ratio of water-soluble polymer conductive microspheres to distilled water is 16 mg: 1 mL;

[0040] S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 10 parts of butyl acrylate, 3 parts of hexafluorobutyl acrylate, 0.4 parts of 2-iodo-2-methylpropionitrile, 0.6 parts of sodium diisooctyl sulfosuccinate and 32 parts of distilled water were mixed and stirred to obtain an emulsion;

[0041] S3. Preparation of membrane-forming solution: PVA was added to distilled water, heated and stirred to fully dissolve to obtain a PVA aqueous solution, wherein the concentration of PVA in the PVA aqueous solution was 13 wt %, and then the dispersion prepared in S1 was added to the PVA aqueous solution, wherein the volume ratio of the PVA aqueous solution to the dispersion was 1:0.4, and the membrane-forming solution was obtained after stirring;

[0042] S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. The thickness of the liquid film is 0.8 mm, and the thickness of the semi-dry film is about 0.2 mm. Then pour the emulsion prepared in S2 into the film-forming mold, soak it fully (soak for more than 2 hours), pour out the excess emulsion, and then illuminate the film material in the film-forming mold to induce in-situ polymerization, maintain the relative humidity of the environment at more than 85%, and after sufficient polymerization, dry it to obtain a sensor film, use conductive glue to fix the copper conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

[0043] Example 2

[0044] A method for preparing a PVA-based flexible temperature sensor comprises the following steps:

[0045] S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water, ultrasonically dispersing to obtain a dispersion, the amount ratio of water-soluble polymer conductive microspheres to distilled water is 10 mg: 1 mL;

[0046] S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 8 parts of butyl acrylate, 2 parts of hexafluorobutyl acrylate, 0.2 parts of 2-iodo-2-methylpropionitrile, 0.4 parts of sodium diisooctyl sulfosuccinate and 25 parts of distilled water were mixed and stirred thoroughly to obtain an emulsion;

[0047] S3. Preparation of membrane-forming solution: PVA was added to distilled water, heated and stirred to fully dissolve to obtain a PVA aqueous solution, wherein the concentration of PVA in the PVA aqueous solution was 10 wt %, and then the dispersion prepared in S1 was added to the PVA aqueous solution, wherein the volume ratio of the PVA aqueous solution to the dispersion was 1:0.5, and the membrane-forming solution was obtained after stirring;

[0048] S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. The thickness of the liquid film is 0.5 mm, and the thickness of the semi-dry film is about 0.1 mm. Then pour the emulsion prepared in S2 into the film-forming mold, soak it fully (soak for more than 2 hours), pour out the excess emulsion, and then perform light-induced in-situ polymerization on the film material in the film-forming mold, maintain the relative humidity of the environment at more than 85%, and after sufficient polymerization, dry it to obtain a sensor film, use conductive glue to fix the copper conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

[0049] Example 3

[0050] A method for preparing a PVA-based flexible temperature sensor comprises the following steps:

[0051] S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water, ultrasonically dispersing to obtain a dispersion, the amount ratio of water-soluble polymer conductive microspheres to distilled water is 20 mg: 1 mL;

[0052] S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 9 parts of butyl acrylate, 3 parts of hexafluorobutyl acrylate, 0.4 parts of 2-iodo-2-methylpropionitrile, 0.5 parts of sodium diisooctyl sulfosuccinate and 28 parts of distilled water were mixed and stirred thoroughly to obtain an emulsion;

[0053] S3. Preparation of membrane-forming solution: PVA was added to distilled water, heated and stirred to fully dissolve to obtain a PVA aqueous solution, wherein the concentration of PVA in the PVA aqueous solution was 12 wt %, and then the dispersion prepared in S1 was added to the PVA aqueous solution, wherein the volume ratio of the PVA aqueous solution to the dispersion was 1:0.4, and the membrane-forming solution was obtained after stirring;

[0054] S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. The thickness of the liquid film is 0.7mm, and the thickness of the semi-dry film is about 0.2mm. Then pour the emulsion prepared in S2 into the film-forming mold, soak it fully (soak for more than 2h), pour out the excess emulsion, and then perform light-induced in-situ polymerization on the film material in the film-forming mold, maintain the relative humidity of the environment above 85%, and after sufficient polymerization, dry it to obtain a sensor film, fix copper conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

[0055] Example 4

[0056] A method for preparing a PVA-based flexible temperature sensor comprises the following steps:

[0057] S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water, ultrasonically dispersing to obtain a dispersion, the amount ratio of water-soluble polymer conductive microspheres to distilled water is 25 mg: 1 mL;

[0058] S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 12 parts of butyl acrylate, 4 parts of hexafluorobutyl acrylate, 0.5 parts of 2-iodo-2-methylpropionitrile, 0.8 parts of sodium diisooctyl sulfosuccinate and 40 parts of distilled water were mixed and stirred to obtain an emulsion;

[0059] S3. Preparation of membrane-forming solution: PVA was added to distilled water, heated and stirred to fully dissolve to obtain a PVA aqueous solution, wherein the concentration of PVA in the PVA aqueous solution was 15 wt %, and then the dispersion prepared in S1 was added to the PVA aqueous solution, wherein the volume ratio of the PVA aqueous solution to the dispersion was 1:0.3, and the membrane-forming solution was obtained after stirring;

[0060] S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. The thickness of the liquid film is 1 mm, and the thickness of the semi-dry film is about 0.3 mm. Then pour the emulsion prepared in S2 into the film-forming mold, soak it fully (soak for more than 2 hours), pour out the excess emulsion, and then perform light-induced in-situ polymerization on the film material in the film-forming mold, maintain the relative humidity of the environment above 85%, and after sufficient polymerization, dry it to obtain a sensor film, fix copper conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

[0061] Comparative Example 1

[0062] Compared with Example 1, in the preparation of the PVA-based flexible temperature sensor, the comparative example lacks the S2 step, and the S4 step does not include the steps of emulsion immersion and photopolymerization of the semi-dry film, but the liquid film is directly dried to obtain the sensor film.

[0063] Comparative Example 2

[0064] Compared with Example 1, in this comparative example, when preparing the PVA-based flexible temperature sensor, hexafluorobutyl acrylate was not added during the preparation of the hydrophobically modified emulsion in step S2.

[0065] The PVA-based flexible temperature sensors obtained in Examples 1 to 4 and Comparative Examples 1 to 2 were tested for electrical conductivity, temperature sensitivity and humidity sensitivity. In each example or comparative example, a plurality of corresponding flexible temperature sensors were repeatedly prepared and the average value was taken. The results showed that at room temperature of 25°C and relative humidity of 80%, the flexible temperature sensors obtained in Examples 1 to 4 and Comparative Examples 1 to 2 had electrical conductivity. The electrical conductivity of the flexible temperature sensors corresponding to Examples 1 to 4 was between 0.015-0.034 S / cm, and the electrical conductivity of the flexible temperature sensors corresponding to Comparative Examples 1 to 2 was between 0.063-0.0 75S / cm, that is, comparative examples 1 and 2 are affected by the relative humidity of the environment, and the conductivity of the sensor is significantly enhanced; in addition, at a constant relative humidity of 80%, as the temperature rises from 25°C to 40°C, the flexible temperature sensors corresponding to each embodiment and comparative example all show obvious temperature-sensitive characteristics, and the conductivity increases significantly; at a constant temperature of 25°C, the relative humidity gradually increases from 40% to 80%, and the conductivity of the flexible temperature sensors corresponding to embodiments 1 to 4 does not change significantly, and has no humidity-sensitive characteristics, while the conductivity of the flexible temperature sensors corresponding to comparative examples 1 and 2 increases significantly, especially the increase in comparative example 1 is more obvious. The flexible temperature sensors corresponding to each embodiment and comparative example can be bent freely and have good flexibility. The flexible temperature sensors corresponding to embodiments 1 to 4 are significantly stronger than comparative example 1 in their ability to resist tensile damage.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a flexible temperature sensor based on PVA, characterized in that: The steps include: S1. Preparation of water-soluble polymer conductive microsphere dispersion: adding water-soluble polymer conductive microspheres to distilled water and ultrasonically dispersing the dispersion; S2. Preparation of a hydrophobically modified emulsion: In parts by weight, 8-12 parts of butyl acrylate, 2-4 parts of hexafluorobutyl acrylate, 0.2-0.5 parts of an iodinated compound initiator, 0.4-0.8 parts of an emulsifier and 25-40 parts of distilled water were mixed and stirred to obtain an emulsion; S3 film-forming solution preparation: PVA was added to distilled water, heated and stirred to fully dissolve the PVA aqueous solution, and then the dispersion obtained in S1 was added to the PVA aqueous solution, and the film-forming solution was obtained after stirring; S4. Sensor molding: pour the film-forming liquid into the film-forming mold to form a liquid film, and dry it until the water content of the liquid film is less than 30% to form a semi-dry film. Then pour the emulsion prepared in S2 into the film-forming mold. After sufficient soaking, pour out the excess emulsion. Then, illuminate the film material in the film-forming mold to induce in-situ polymerization. After sufficient polymerization, dry it to obtain a sensor film. Fix conductive electrodes at both ends of the sensor film to obtain a PVA-based flexible temperature sensor.

2. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: The water-soluble polymer conductive microspheres in S1 are sulfonated polystyrene-polyaniline composite microspheres with nano-copper, nano-silver or nano-gold loaded on the surface.

3. The method for preparing a PVA-based flexible temperature sensor according to claim 2, characterized in that: The usage ratio of water-soluble polymer conductive microspheres to distilled water in S1 is 10-25 mg:1 mL.

4. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: The iodinated compound initiator in S2 is 2-iodo-2-methylpropionitrile.

5. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: The emulsifier in S2 is sodium dioctyl sulfosuccinate.

6. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: The concentration of PVA in the PVA aqueous solution in S3 is 10-15 wt %.

7. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: The volume ratio of the PVA aqueous solution and the dispersion in S3 when mixed is 1:0.3-0.

5.

8. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: The thickness of the liquid film in S4 is 0.5-1mm, and the thickness of the semi-dry film is 0.1-0.3mm.

9. The method for preparing a PVA-based flexible temperature sensor according to claim 1, characterized in that: In S4, after the conductive electrode is fixed, a flexible packaging film is attached to both sides of the sensor film for packaging, and the flexible packaging film is a PI film, a PET film or a PDMS film.

10. A flexible temperature sensor based on PVA, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

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