A flexible self-powered humidity sensor and preparation method thereof

Abstract

The present invention discloses a flexible self-powered humidity sensor and a preparation method thereof, including the preparation of a porous piezoelectric composite film and the assembly of a self-powered humidity sensor. A mixture of piezoelectric polymers and nanomaterials is subjected to ultrasound, magnetic stirring, spin coating, high-temperature annealing, and low-temperature quenching to obtain a porous piezoelectric composite film; the porous piezoelectric composite film and a micron-pore-shaped flexible electrode are assembled into a sandwich-structured self-powered humidity sensor. The humidity sensor has flexible, porous, hydrophilic and piezoelectric properties and can be self-powered. The voltage response of the sensor shows a good linear relationship and sensitivity with humidity, and the detection range can achieve full coverage. Moreover, the sensor has a simple structure and low cost, and is suitable for large-scale production applications.

Description

Technical Field

[0001] The invention relates to the technical field of humidity sensing, and in particular to a flexible self-powered humidity sensor and a preparation method thereof. Background Art

[0002] Human survival and social activities are closely related to humidity. Traditional humidity sensors are generally divided into resistance type and capacitance type according to output parameters, and often require external power supplies, which limits the use scenarios of the equipment. Moreover, the battery needs to be charged regularly and eventually needs to be replaced, which will cause various energy and environmental problems. With the development of wearable and flexible electronic technologies of smart mobile devices and micro-electromechanical systems, higher requirements are placed on products, and there is an urgent need to develop a flexible self-powered humidity sensor.

[0003] Using electronic devices to collect energy from their surroundings is a better alternative to traditional batteries as a power source. Researchers have proposed various energy harvesting strategies at the mesoscopic, microscopic and nanoscopic levels through energy conversion mechanisms such as electromagnetism, electrostatics, piezoelectricity, triboelectricity and pyroelectricity. Piezoelectric polymers have natural flexibility and durability, are sensitive to small strains, and are easy to manufacture into compact small-size structures for integration into micro-electromechanical systems, so they have broad application prospects. Among them, polyvinylidene fluoride (PVDF) (including derivatives PVDF-TrFE, PVDF-HFP, etc.) has become an outstanding representative due to its advantages such as high flexibility, high electromechanical coupling, good biocompatibility, high optical transparency and wide response range.

[0004] By using the influence of environmental humidity on the piezoelectric properties of PVDF to establish the relationship between humidity and its voltage signal, a self-powered voltage-responsive humidity sensor can be constructed. However, from the perspective of the PVDF material itself, there are problems in three aspects: hydrophilicity, porous structure, and self-powered capability. Therefore, the present invention provides a preparation process for a hydrophilic porous composite membrane with high piezoelectric properties to construct a new type of flexible self-powered voltage-responsive humidity sensor to meet the requirements of humidity sensors for flexibility and self-powered capability. Summary of the invention

[0005] The purpose of the present invention is to solve the needs of humidity sensors for flexibility and self-power supply. Combining the excellent properties of piezoelectric polymers and nanomaterials, a flexible self-powered humidity sensor is prepared by a specific process. The sensor uses a piezoelectric polymer / nanomaterial composite film as a humidity-sensitive material. The humidity-sensitive material itself can be self-powered and can realize true self-powered humidity sensing. It has flexible, porous, hydrophilic and piezoelectric properties, and is low in cost and suitable for large-scale production applications.

[0006] The object of the present invention is achieved through the following technical solutions.

[0007] In one aspect, the present invention provides a method for preparing a flexible self-powered humidity sensor, comprising the following steps:

[0008] (1) Preparation of porous piezoelectric composite film:

[0009] 1-10% of nanomaterials are added to a solvent according to a mass ratio, and ultrasonic dispersion is performed to obtain a nanomaterial dispersion liquid; 90-99% of a piezoelectric polymer is added to the nanomaterial dispersion liquid, and the mixture is stirred and dissolved to obtain a nano piezoelectric polymer solution; the nano piezoelectric polymer solution is spin-coated on a flexible electrode to form a film, and the film is kept warm until it turns completely white; annealing and low-temperature air quenching are performed to obtain a porous piezoelectric composite film attached to the flexible electrode;

[0010] (2) Assembly of self-powered humidity sensor:

[0011] Place the porous piezoelectric composite film attached to the flexible electrode facing upwards, and then place another flexible electrode with micron pores facing downwards. The two flexible electrodes are stacked in an offset manner, and the uncovered parts are led out with wires to obtain a self-powered humidity sensor.

[0012] For the above technical solution, the present invention has a further preferred solution:

[0013] The solvent is a mixed solvent consisting of any one of DMF, DMSO, NMP and DMAc and acetone, and the concentration of the dispersion is 2-20 mg / mL.

[0014] The nanomaterial is any one or a mixture of more than one of carbon dots, carbon nanotubes, graphene, ZnO, TiO2, NiO, SiO2, Mg(OH)2 and Al2O3.

[0015] The piezoelectric polymer is any one of PVDF and its derivatives PVDF-TrFE and PVDF-HFP.

[0016] In the step (1), the ultrasonic time is 10 to 30 minutes, and the magnetic stirring time is 1 to 4 hours.

[0017] In the step (1), the spin coating speed is 500 to 2000 rpm and the time is 30 to 90 seconds.

[0018] In the step (1), the insulation temperature is 20 to 40° C. and the insulation time is 5 to 30 minutes.

[0019] In the step (1), the annealing temperature is 120-140° C. and the annealing time is 1-4 hours.

[0020] In the step (1), the air quenching temperature is -30 to 20°C and the time is 10 to 30 minutes.

[0021] Another aspect of the present invention provides a flexible self-powered humidity sensor prepared by the method.

[0022] The present invention adopts the above technical solution, which has the following beneficial effects:

[0023] 1. The incorporation of nanomaterials in the present invention significantly improves the hydrophilicity, porous structure and self-powered ability of the piezoelectric polymer, so that the hygroscopic material of the sensor can be self-powered without the need for a power source.

[0024] 2. The sensor in the present invention is voltage-responsive, and the voltage and humidity show a good linear relationship (R 2 >0.96), the sensitivity is not less than 12mV / %RH, and the detection range can be fully covered.

[0025] 3. The preparation process of the present invention does not involve any large-scale instruments and equipment, and the preparation process is simple. The sensor has a simple structure, is flexible, porous, hydrophilic and piezoelectric, and has low cost, and is suitable for large-scale production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute an improper limitation of the present invention. In the drawings:

[0027] Figure 1 is a schematic diagram of the structure of a flexible self-powered humidity sensor in an embodiment of the present invention;

[0028] Figure 2 is the SEM morphology of the composite film in the embodiment of the present invention;

[0029] Figure 3 is a pressure-voltage response curve of the sensor in an embodiment of the present invention;

[0030] Figure 4 is the humidity-voltage response curve of the sensor in the embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0032] The present invention provides a method for preparing a flexible self-powered humidity sensor, comprising the following steps:

[0033] (1) Preparation of porous piezoelectric film:

[0034] The porous piezoelectric film is composed of 90-99% piezoelectric polymer and 1-10% nanomaterial in a mass ratio. First, 1-10% nanomaterial is added to a solvent, the concentration of the dispersion is 2-20 mg / mL, and the solvent in the mixed solution is a mixed solvent composed of any one of DMF, DMSO, NMP and DMAc and acetone; ultrasonic dispersion is uniform, and the ultrasonic time is 10-30 minutes; 90-99% piezoelectric polymer is added to the dispersion, and magnetic stirring is used to dissolve, and the magnetic stirring time is 1-4 hours; take an appropriate amount of solution, drop it on the flexible electrode, and form a film by spin coating; the spin coating speed is 500-2000rpm, and the time is 30-90s. Then keep the temperature at 20-40°C for 5-30 minutes until the film turns completely white; then anneal at 120-140°C for 1-4 hours, and then perform low-temperature air quenching at -30-20°C for 10-30 minutes to obtain a porous piezoelectric film attached to the flexible electrode.

[0035] The piezoelectric polymer is any one of PVDF and its derivatives (PVDF-TrFE, PVDF-HFP, etc.).

[0036] Among them, the nanomaterial is any one or more mixtures of carbon dots, carbon nanotubes, graphene, ZnO, TiO2, NiO, SiO2, Mg(OH)2 and Al2O3.

[0037] (2) Assembly of self-powered humidity sensor:

[0038] Place the porous piezoelectric film attached to the flexible electrode upwards, and then take another flexible electrode with micron pores downwards and cover its upper surface with an offset. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0039] The flexible self-powered humidity sensor of the present invention is composed of a porous piezoelectric film and a flexible electrode with micron pores. The wire is fixed to the flexible electrode lead by a conductive silver paste. The schematic diagram of the structure is shown in FIG. Figure 1 .

[0040] The preparation method of the present invention is further described in detail below through specific examples.

[0041] Embodiment 1:

[0042] (1) Preparation of porous piezoelectric film:

[0043] Add 2% ZnO by mass into a mixed solvent of DMF and acetone (volume ratio of 5:5), and disperse it evenly by ultrasonic treatment for 10 minutes to obtain a dispersion with a concentration of 4 mg / mL; weigh 98% PVDF and add it to the dispersion, and stir it magnetically for 2 hours to completely dissolve it; take 50uL of the solution, drop it on the PEN-ITO flexible electrode, and form a film by spin coating at a speed of 1000rpm for 60s; keep it warm at 25℃ for 10 minutes until the film turns completely white; anneal at 130℃ for 1 hour, and then air quench it at 4℃ to obtain a porous piezoelectric film.

[0044] (2) Assembly of self-powered humidity sensor:

[0045] The porous piezoelectric film attached to the PEN-ITO flexible electrode is placed upwards, and then another PEN-ITO flexible electrode with micron pores is placed downwards and staggered to cover its upper surface. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0046] Figure 2 The SEM morphology of the piezoelectric composite film in Example 1 is shown, indicating that the composite film is a porous structure with a pore size in the range of 1-3 μm and a thickness of about 10 μm.

[0047] Figure 3 The pressure-voltage response curve of the sensor under different humidity in Example 1 is shown. When the applied external force increases from 0N to 5N, the voltage response signal of the sensor gradually increases.

[0048] Figure 4 The middle line (1) shows the humidity-voltage response curve of the sensor when the external force is 3N in Example 1. As the humidity increases, the voltage response signal at the same pressure gradually weakens and shows a good linear relationship (R 2 =0.982), and the sensitivity is 12.5mV / %RH.

[0049] Embodiment 2:

[0050] (1) Preparation of porous piezoelectric film:

[0051] 5% of graphene was added to a mixed solvent of DMSO and acetone (volume ratio of 8:2), and ultrasonicated for 20 minutes to disperse it evenly to obtain a dispersion with a concentration of 10 mg / mL; 95% of PVDF-TrFE was weighed and added to the dispersion, and magnetically stirred for 4 hours to completely dissolve it; 50uL of the solution was taken and dropped on the PEN-ITO flexible electrode, and a film was formed by spin coating at a speed of 1500rpm for 40s; the film was kept at 20℃ for 20 minutes until it turned completely white; it was annealed at 120℃ for 2 hours, and then air quenched at -20℃ to obtain a porous piezoelectric film.

[0052] (2) Assembly of self-powered humidity sensor:

[0053] The porous piezoelectric film attached to the PEN-ITO flexible electrode is placed upwards, and then another PEN-ITO flexible electrode with micron pores is placed downwards and staggered to cover its upper surface. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0054] Figure 4 The middle line (2) shows the humidity-voltage response curve of the sensor when the external force is 3N in Example 2. As the humidity increases, the voltage response signal at the same pressure gradually weakens and shows a good linear relationship (R 2 =0.997), and the sensitivity is 16.4mV / %RH.

[0055] Embodiment 3:

[0056] (1) Preparation of porous piezoelectric film:

[0057] 8% carbon nanotubes by mass were added to a mixed solvent of NMP and acetone (volume ratio of 3:7), and ultrasonicated for 20 minutes to make them evenly dispersed to obtain a dispersion with a concentration of 16 mg / mL; 92% PVDF-HFP was weighed and added to the dispersion, and magnetically stirred for 3 hours to make it completely dissolved; 50uL of the solution was taken and dropped on the PEN-ITO flexible electrode, and a film was formed by spin coating at a speed of 500rpm for 90s; the film was kept at 35℃ for 15min until it turned completely white; it was annealed at 140℃ for 1.5h, and then air quenched at 10℃ to obtain a porous piezoelectric film.

[0058] (2) Assembly of self-powered humidity sensor:

[0059] The porous piezoelectric film attached to the PEN-ITO flexible electrode is placed upwards, and then another PEN-ITO flexible electrode with micron pores is placed downwards and staggered to cover its upper surface. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0060] Figure 4 The middle line (3) shows the humidity-voltage response curve of the sensor when the external force is 3N in Example 3. As the humidity increases, the voltage response signal at the same pressure gradually weakens and shows a good linear relationship (R 2 =0.997), and the sensitivity is 14.8mV / %RH.

[0061] Embodiment 4:

[0062] (1) Preparation of porous piezoelectric film:

[0063] A mixture of TiO2 and NiO with a mass ratio of 10% was added to a mixed solvent of DMAc and acetone (volume ratio of 4:6), and ultrasonicated for 30 minutes to make it evenly dispersed to obtain a dispersion with a concentration of 20 mg / mL; 90% of PVDF-TrFE was weighed and added to the dispersion, and magnetically stirred for 3 hours to make it completely dissolved; 50uL of the solution was taken and dropped on the PEN-ITO flexible electrode, and a film was formed by spin coating at a speed of 2000rpm for 30s; the film was kept warm at 40℃ for 5min until it turned completely white; annealed at 135℃ for 2h, and then air quenched at -10℃ to obtain a porous piezoelectric film.

[0064] (2) Assembly of self-powered humidity sensor:

[0065] The porous piezoelectric film attached to the PEN-ITO flexible electrode is placed upwards, and then another PEN-ITO flexible electrode with micron pores is placed downwards and staggered to cover its upper surface. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0066] Figure 4 The middle line (4) shows the humidity-voltage response curve of the sensor when the external force is 3N in Example 4. As the humidity increases, the voltage response signal at the same pressure gradually weakens and shows a good linear relationship (R 2 =0.992), and the sensitivity is 23.9mV / %RH.

[0067] Embodiment 5:

[0068] (1) Preparation of porous piezoelectric film:

[0069] 1% Mg(OH)2 was added to a mixed solvent of DMF and acetone (volume ratio of 6:4), and ultrasonicated for 15 minutes to disperse it evenly to obtain a dispersion with a concentration of 2 mg / mL; 99% PVDF was weighed and added to the dispersion, and magnetically stirred for 2.5 hours to completely dissolve it; 50uL of the solution was taken and dropped on the PEN-ITO flexible electrode, and a film was formed by spin coating at a speed of 1800rpm for 70 seconds; the film was kept warm at 20℃ for 15 minutes until it turned completely white; it was annealed at 135℃ for 3 hours, and then air quenched at -30℃ to obtain a porous piezoelectric film.

[0070] (2) Assembly of self-powered humidity sensor:

[0071] The porous piezoelectric film attached to the PEN-ITO flexible electrode is placed upwards, and then another PEN-ITO flexible electrode with micron pores is placed downwards and staggered to cover its upper surface. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0072] Figure 4 The middle line (5) shows the humidity-voltage response curve of the sensor when the external force is 3N in Example 5. As the humidity increases, the voltage response signal at the same pressure gradually weakens and shows a good linear relationship (R 2 =0.971), and the sensitivity is 16.2mV / %RH.

[0073] Embodiment 6:

[0074] (1) Preparation of porous piezoelectric film:

[0075] A mixture of Al2O3 and SiO2 with a mass ratio of 6% was added to a mixed solvent of DMF and acetone (volume ratio of 6:4), and ultrasonicated for 20 minutes to make it evenly dispersed to obtain a dispersion with a concentration of 12 mg / mL; 94% PVDF-TrFE was weighed and added to the dispersion, and magnetically stirred for 3 hours to completely dissolve it; 50uL of the solution was taken and dropped on the PEN-ITO flexible electrode, and a film was formed by spin coating at a speed of 800rpm for 50s; the film was kept warm at 35℃ for 30min until it turned completely white; annealed at 125℃ for 2h, and then air quenched at 20℃ to obtain a porous piezoelectric film.

[0076] (2) Assembly of self-powered humidity sensor:

[0077] The porous piezoelectric film attached to the PEN-ITO flexible electrode is placed upwards, and then another PEN-ITO flexible electrode with micron pores is placed downwards and staggered to cover its upper surface. The uncovered parts of the two flexible electrodes are used as leads, and the wires are fixed to the flexible electrode leads through conductive silver paste to obtain a self-powered humidity sensor.

[0078] Figure 4 The middle line (6) shows the humidity-voltage response curve of the sensor when the external force is 3N in Example 6. As the humidity increases, the voltage response signal at the same pressure gradually weakens and shows a good linear relationship (R 2 =0.969), and the sensitivity is 12.7mV / %RH.

[0079] It can be seen from the above embodiments and experimental results that the humidity-sensitive material of the flexible self-powered humidity sensor prepared by the method of the present invention is a porous piezoelectric polymer / nanomaterial composite film with a pore size in the range of 1-3 μm, and the nanomaterial is evenly distributed in the piezoelectric polymer; the humidity-sensitive material of the humidity sensor can be self-powered without the need for a power supply; the sensor is voltage-responsive; the sensor exhibits different piezoelectric properties under different humidity environments, and as the humidity increases, the voltage signal of the sensor gradually decreases, showing a good linear relationship (R 2 >0.96), the sensitivity is not less than 12mV / %RH, and the detection range can be fully covered.

[0080] It can be seen from this that the method of the present invention is a method for preparing a flexible self-powered humidity sensor, which has a simple process, low cost, and is suitable for large-scale production applications.

[0081] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A method for preparing a flexible self-powered humidity sensor, characterized in that The following steps are involved: (1) Preparation of porous piezoelectric composite membrane: 1-10% of nanomaterials are added to the solvent according to the mass ratio, and ultrasonic dispersion is performed to obtain a nanomaterial dispersion liquid; 90-99% of piezoelectric polymers are added to the nanomaterial dispersion liquid, and stirred to dissolve to obtain a nano piezoelectric polymer solution; the nano piezoelectric polymer solution is spin-coated on a flexible electrode to form a film, and the film is kept at 20-40°C for 5-30 minutes until the film turns completely white; annealing is performed at 120-140°C for 1-4 hours, and low-temperature air quenching is performed at a temperature of -30-20°C for 10-30 minutes to obtain a porous piezoelectric composite film attached to the flexible electrode with a pore size of 1-3 μm; The piezoelectric polymer is any one of PVDF and its derivatives PVDF-TrFE and PVDF-HFP; The nanomaterial is any one or a mixture of more than one of carbon dots, carbon nanotubes, graphene, ZnO, TiO2, NiO, SiO2, Mg(OH)2 and Al2O3; (2) Assembly of self-powered humidity sensor: Place the porous piezoelectric composite film attached to the flexible electrode facing upwards, and then place another flexible electrode with micron pores facing downwards. The two flexible electrodes are stacked in an offset manner, and the uncovered parts are led out with wires to obtain a self-powered humidity sensor.

2. The method for preparing a flexible self-powered humidity sensor according to claim 1, characterized in that: The solvent is a mixed solvent consisting of any one of DMF, DMSO, NMP and DMAc and acetone, and the concentration of the dispersion is 2-20 mg / mL.

3. The method for preparing a flexible self-powered humidity sensor according to claim 1, characterized in that: In the step (1), the ultrasonic time is 10 to 30 minutes, and the magnetic stirring time is 1 to 4 hours.

4. The method for preparing a flexible self-powered humidity sensor according to claim 1, characterized in that: In the step (1), the spin coating speed is 500-2000 rpm and the time is 30-90 s.

5. A flexible self-powered humidity sensor prepared by the method according to any one of claims 1 to 4, characterized in that: The humidity sensor is voltage-responsive, and the voltage and humidity show a linear relationship R 2 >0.96, sensitivity not less than 12mV / %RH.

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