A humidity-sensitive nanofiber film and a method for preparing the same

Abstract

The application discloses a kind of flexible sensor with humidity-sensitive nanofiber film and preparation method thereof.The preparation method includes: S1, wet treatment of nickel halide: after nickel halide powder is ground sufficiently, disperse in solvent, magnetically stir at 60-75 DEG C, obtain the precursor solution of nickel halide, then the precipitate is filtered out by nylon needle filter from the precursor solution, obtain nickel halide dispersion liquid;S2, preparation of spinning solution: take polymer / solvent spinning precursor solution and add to the nickel halide dispersion liquid, magnetically stir under room temperature condition, prepare liquid jet spinning solution;S3, liquid jet spinning preparation humidity-sensitive nanofiber nascent film;S4, humidity-sensitive nanofiber nascent film is placed in oven and heated at 50-65 DEG C for 2.5-3.5h, obtain humidity-sensitive nanofiber film.The method can effectively avoid that humidity-sensitive material is destroyed in the process of use, prolongs the service life of humidity-sensitive film and sensor;The prepared humidity-sensitive film has high reaction sensitivity.

Description

Technical Field

[0001] This invention relates to the field of humidity-sensitive membrane technology, specifically to a humidity-sensitive nanofiber thin film and its preparation method. Background Technology

[0002] Humidity is an essential measurement in agriculture, industrial production, meteorology, and human health. Wearable flexible humidity sensors are in great demand in the fields of the Internet of Things and human-computer interaction, and can be used not only to detect breathing rate but also to measure the humidity of the skin surface.

[0003] Existing flexible humidity sensors mostly consist of a humidity-sensitive film formed by depositing a humidity-sensitive material onto a corresponding flexible substrate, and then supplemented with other electronic components. As the core of the sensor for humidity sensing, the humidity-sensitive film has always been a key research focus in the sensor field.

[0004] Firstly, regarding the construction method, existing humidity-sensitive films are mostly formed by mechanically bonding humidity-sensitive materials onto a substrate material using methods such as spin coating, aerosol deposition, magnetron sputtering, and spraying. Chinese Invention Patent Publication No. CN114894891A constructs an SA / PAN humidity-sensitive film with a double-layer network structure by spin coating a layer of hydrophilic sodium alginate (SA) film onto a polyacrylonitrile (PAN) fiber network using spin coating technology. Chinese Invention Patent Publication No. CN111234275A provides a multilayer humidity-sensitive film and composite humidity-sensitive element based on inorganic material doped polyimide. It uses polyimide as the main component, adds humidity-sensitive inorganic salts to obtain a preliminary composite film, and then coats the film surface with activated carbon powder to obtain the final humidity-sensitive film. Chinese Invention Patent Publication No. CN112924316A uses a spraying method to spray a prepared chitosan and polypyrrole composite humidity-sensitive material onto a substrate to form a humidity-sensitive film. Although this type of humidity-sensitive membrane has excellent humidity response, it is prone to damage and loss during sensor use because the humidity-sensitive material is exposed to the outside and lacks a protection mechanism, resulting in a reduced lifespan for both the membrane and the sensor.

[0005] Secondly, in terms of detection mechanism, most current humidity-sensitive membranes reflect humidity changes through electrical changes in the membrane, such as resistance and capacitance. However, humidity-sensitive membrane materials that combine both electrical and optical response mechanisms for humidity monitoring are still rare.

[0006] Finally, regarding humidity-sensitive materials, as mentioned in the prior art, there are many types and a wide range of materials available for humidity-sensitive membranes, including metal oxides, polymer membranes, and electrolyte materials. However, there are very few literature reports on using nickel halides as the sensing material. Although Chinese invention patent publications CN113916879A and CN111458381A propose using nickel halides as the sensing material and blending them with polyimide to form a solution to prepare a flat sheet humidity-sensitive membrane, the presence of interfacial pores between the sensing material and the organic ligands causes the sensing material to easily detach from the organic substrate, greatly affecting the usability of the membrane. Furthermore, due to the characteristics of flat sheet membranes, their internal pore structure and porosity are difficult to control, thus limiting the membrane's humidity-sensitive properties. Summary of the Invention

[0007] To address the problems existing in the prior art, one objective of this invention is to provide a method for preparing a moisture-sensitive nanofiber film.

[0008] Another object of the present invention is to provide a moisture-sensitive nanofiber film prepared by the above method.

[0009] Therefore, the present invention adopts the following technical solution:

[0010] A method for preparing a humidity-sensitive nanofiber thin film includes the following steps:

[0011] S1, Wet processing of nickel halide: 0.5-1.5 mmol of nickel halide powder is thoroughly ground and dispersed in 2-3 mL of solvent. The mixture is magnetically stirred at 60-75℃ for 12-36 h to obtain a nickel halide precursor solution. The precursor solution is then filtered through a nylon needle filter to remove the precipitate, resulting in a nickel halide dispersion. The nickel halide is a binary compound composed of nickel and halogen atoms, selected from NiCl2, NiBr2, and NiI2. The solvent is DMAC, DMF, or water. The pore size of the nylon needle filter membrane is ≤0.45 μm.

[0012] S2, Preparation of spinning solution: Prepare a 10%-20wt% polymer / solvent spinning precursor solution; add 10-20g of the polymer / solvent spinning precursor solution to the nickel halide dispersion obtained in step S1, and magnetically stir at room temperature for 8-15h to obtain the liquid-jet spinning solution. Wherein: the polymer is a white or colorless hydrophilic or hydrophobic organic polymer suitable for liquid-jet spinning, such as thermoplastic polyurethane (TPU), PAN, or polyvinyl alcohol (PVA); the solvent is an organic or inorganic colorless solvent such as DMAC, DMF, or water.

[0013] S3, Preparation of wet-sensitive nanofiber nascent membrane by liquid-jet spinning: Using the liquid-jet spinning solution obtained in step S2, a wet-sensitive nanofiber nascent membrane is prepared by liquid-jet spinning method.

[0014] S4, Preparation of moisture-sensitive nanofiber membrane: The nascent moisture-sensitive nanofiber membrane is placed in an oven and heated at 50-65℃ for 2.5-3.5h to obtain the moisture-sensitive nanofiber thin film.

[0015] Preferably, in step S1, the nickel halide powder and 0.5-1.5 mmol of modifier powder are thoroughly ground and dispersed in a solvent to prepare the precursor solution and the nickel halide dispersion, wherein the modifier is perfluorooctyl iodide (CF3(CF2)7I), tetrabutylammonium iodide (TBAI), or tetramethylammonium iodide (C4H). 12 IN), PVA, or SiO2. Modifiers are used to hydrophilically modify moisture-sensitive nanofiber membranes.

[0016] Preferably, the modifier is tetramethylammonium iodide, and the dosage is 1 mmol.

[0017] Preferably, in step S1, the solvent is DMAC and the nickel halide is NiI2.

[0018] Preferably, in step S1, the magnetic stirring time is 24 hours.

[0019] Preferably, in step S2, the polymer is PAN, and the polymer mass fraction in the polymer / solvent spinning precursor solution is 12%.

[0020] In step S2, the solvent is preferably DMAC.

[0021] The present invention also protects a moisture-sensitive nanofiber film prepared by the above preparation method.

[0022] This invention uses a polymer nanofiber membrane as the supporting matrix and nickel halide as the moisture-sensitive material, employing a liquid-jet spinning process to fabricate a moisture-sensitive nanofiber film with a three-dimensional stacked porous structure. This moisture-sensitive film can be applied in humidity sensors, respiratory depth detectors in the medical field, moisture-sensitive anti-counterfeiting labels, food packaging, and other fields.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The humidity-sensitive membrane of the present invention uses nickel halide as the sensitive material, which has excellent humidity-sensitive properties. It adopts liquid-jet spinning process, which is simple and efficient in production.

[0025] 2. This invention applies nickel halide as a sensitive material to the field of humidity sensors, achieving good results in humidity detection. It can simultaneously reflect humidity changes through changes in the color and resistance of the humidity-sensitive nanofiber film.

[0026] 3. In the moisture-sensitive nanofiber membrane of the present invention, the moisture-sensitive material and the substrate material are an integral whole. The moisture-sensitive material is bound inside the substrate material as part of the spinning solution, which avoids its loss during membrane use and extends the service life of the moisture-sensitive membrane.

[0027] 4. The humidity-sensitive material used in this invention is suitable for low-humidity or even ultra-low-humidity environments, exhibits significant resistance response, and has a wide humidity detection range.

[0028] 5. The flexible sensor humidity-sensitive nanofiber membrane of the present invention has a three-dimensional stacked porous structure. The nanofiber material provides a channel for water molecules to enter, increasing the chance of its binding with the humidity-sensitive material, and has higher sensitivity than the humidity-sensitive membrane with ordinary structure.

[0029] 6. The moisture-sensitive membrane material of the present invention has a simple preparation process, high production efficiency, is green and environmentally friendly, and has a wide range of applications.

[0030] 7. The humidity sensor prepared using the humidity-sensitive nanofiber film of the present invention is a flexible sensor that can be bent and is suitable for humidity detection in various fields such as human body and environment. Moreover, the humidity-sensitive element in the sensor is a unified whole and has a long service life. Attached Figure Description

[0031] Figure 1 This is a flowchart of a preparation method according to an embodiment of the present invention;

[0032] Figure 2 This is a graph showing the optical color-changing properties of the humidity-sensitive nanofiber membrane prepared in Example 2 under different humidity conditions;

[0033] Figure 3 The resistance variation of the humidity-sensitive nanofiber membrane material prepared in Example 2 under different humidity conditions is shown in the graph.

[0034] Figure 4 The cyclic stability diagram of the resistance of the humidity-sensitive nanofiber membrane material prepared in Example 2 under different humidity conditions;

[0035] Figure 5 The instantaneous stability diagram of the resistance of the humidity-sensitive nanofiber membrane material prepared in Example 2 under different humidity conditions is shown. Detailed Implementation

[0036] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0037] Example 1

[0038] See Figure 1 The present invention discloses a method for preparing a moisture-sensitive nanofiber thin film, comprising the following steps:

[0039] S1, wet processing of nickel halides:

[0040] 1 mmol of nickel iodide powder was thoroughly ground and dispersed in 2.5 mL of DMAC solvent. Then, it was heated at 60 °C and magnetically controlled for 15 h to obtain a nickel iodide precursor solution. The precursor solution was then filtered through a nylon needle filter to remove the precipitate, resulting in a nickel iodide dispersion.

[0041] S2, Preparation of spinning solution:

[0042] Prepare a PAN / DMAC spinning precursor solution with a mass fraction of 12%; take 10g of the spinning precursor solution and add it to the nickel iodide dispersion in step S1, and stir magnetically for 8h at room temperature to obtain the liquid-jet spinning solution.

[0043] S3, Liquid-jet spinning preparation of moisture-sensitive nanofiber primary membranes:

[0044] Using the liquid-jet spinning solution described in S2, a moisture-sensitive nanofiber nascent membrane was prepared by liquid-jet spinning method.

[0045] S4, Preparation of moisture-sensitive nanofiber membrane:

[0046] The above-mentioned moisture-sensitive nanofiber nascent membrane was placed in a 50°C oven and heated for 3.5 hours to obtain the moisture-sensitive nanofiber thin film.

[0047] Test results show that the humidity-sensitive nanofiber has a humidity range of 10%-95%RH, and its color transitions from dark red to light orange-yellow as humidity increases. Furthermore, its electrical performance exhibits cyclic stability up to 20 cycles. Its sensitivity is as high as 1.5 MΩ / %RH. When the humidity-sensitive nanofiber membrane was placed in different humidity environments for 60 minutes, its resistance was measured every 5 minutes, revealing good instantaneous stability within 60 minutes.

[0048] Example 2

[0049] A method for preparing a humidity-sensitive nanofiber thin film includes the following steps:

[0050] S1, wet processing of nickel halides:

[0051] 1 mmol of nickel iodide powder and 1 mmol of tetramethylammonium iodide powder were thoroughly ground and dispersed in 2.5 mL of LDMAC solvent. The mixture was then magnetically stirred at 68 °C for 18 h to obtain a nickel iodide precursor solution. The precursor solution was then filtered through a nylon needle filter to remove the precipitate, resulting in a nickel iodide dispersion.

[0052] S2, Preparation of spinning solution:

[0053] A PAN / DMAC spinning precursor solution with a mass fraction of 12% was prepared. 10 g of this spinning precursor solution was added to the nickel iodide dispersion in S1, and the mixture was magnetically stirred at room temperature for 8 h to obtain the liquid-jet spinning solution.

[0054] S3, Liquid-jet spinning preparation of moisture-sensitive nanofiber primary membranes:

[0055] Using the liquid-jet spinning solution described in S2, a moisture-sensitive nanofiber nascent membrane was prepared by liquid-jet spinning method.

[0056] S4, Preparation of moisture-sensitive nanofiber membrane:

[0057] The above-mentioned moisture-sensitive nanofiber nascent membrane was placed in an oven at 55°C and heated for 3 hours to obtain the moisture-sensitive nanofiber membrane.

[0058] The optical color-changing properties of the humidity-sensitive nanofiber membrane prepared in this embodiment under different humidity conditions are shown in the figure. Figure 2 .Depend on Figure 2 It is known that the humidity-sensitive nanofiber membrane has excellent optical color-changing properties and is highly sensitive to changes in humidity. The color change is obvious in both low and high humidity environments, and the humidity measurement range can reach 10% RH-90% RH.

[0059] Figure 3 The figure shows the resistance variation of the humidity-sensitive nanofiber membrane material prepared in Example 2 under different humidity conditions. As shown in the figure, the resistance of the humidity-sensitive nanofiber membrane changes significantly within the humidity range of 55-90% RH, indicating high humidity sensitivity.

[0060] Figure 4 The figure shows the cyclic stability of the resistance of the humidity-sensitive nanofiber membrane material prepared in Example 2 under different humidity conditions. As can be seen from the figure, the humidity-sensitive nanofiber membrane exhibits good cyclic stability within the 55-90% RH humidity range, demonstrating that the humidity-sensitive membrane has excellent recyclability.

[0061] Figure 5 The figure shows the instantaneous stability of the resistance of the humidity-sensitive nanofiber membrane material prepared in Example 2 under different humidity conditions. As shown in the figure, the humidity-sensitive nanofiber membrane material exhibits good instantaneous stability under different humidity conditions within the humidity range of 55-90% RH, which provides a basis for the accuracy of its humidity measurement.

[0062] Example 3

[0063] A method for preparing a humidity-sensitive nanofiber thin film includes the following steps:

[0064] S1, wet processing of nickel halides:

[0065] 1 mmol of nickel bromide powder and 1.5 mmol of tetramethylammonium iodide powder were thoroughly ground and dispersed in 2.5 mL of LDMF solvent. The mixture was then magnetically stirred at 65 °C for 24 h to obtain a nickel iodide precursor solution. The precursor solution was then filtered through a nylon needle filter to remove the precipitate, resulting in a nickel iodide dispersion.

[0066] S2, Preparation of spinning solution:

[0067] A 15% (w / w) TPU / DMF spinning precursor solution was prepared. 15g of this spinning precursor solution was added to the nickel iodide dispersion in S1, and the mixture was magnetically stirred for 10h at room temperature to obtain the liquid-jet spinning solution.

[0068] S3, Liquid-jet spinning preparation of wet-sensitive nanofiber primary membranes:

[0069] Using the liquid-jet spinning solution described in S2, a moisture-sensitive nanofiber nascent membrane was prepared by liquid-jet spinning method.

[0070] S4, Preparation of moisture-sensitive nanofiber membrane:

[0071] The above-mentioned moisture-sensitive nanofiber nascent membrane was heated in a 60°C oven for 2.5 hours to obtain the moisture-sensitive nanofiber membrane.

[0072] Testing revealed that the nickel bromide nanofiber membrane exhibited excellent humidity-sensitive properties within a humidity range of 11%-75% RH. The membrane's color and impedance were clearly defined; specifically, at low humidity (11%-24% RH), the membrane was grayish-green, gradually shifting towards yellowish-green and light yellow under high humidity conditions. The membrane resistance showed a clear linear change, with a sensitivity of approximately 2.3 MΩ / %RH. Its resistance exhibited good stability within 60 minutes, and the humidity-sensitive membrane demonstrated high cyclic stability, up to 7 cycles.

[0073] Example 4

[0074] A method for preparing a humidity-sensitive nanofiber thin film includes the following steps:

[0075] S1, wet processing of nickel halides:

[0076] 1 mmol of nickel chloride powder and 1 mmol of perfluorooctyl iodide powder were thoroughly ground and dispersed in 2.5 mL of LDMF solvent. The mixture was then magnetically stirred at 70 °C for 12 h to obtain a nickel iodide precursor solution. The precursor solution was then filtered through a nylon needle filter to remove the precipitate, resulting in a nickel iodide dispersion.

[0077] S2, Preparation of spinning solution:

[0078] A PVDF / DMF spinning precursor solution with a mass fraction of 15% was prepared. 18g of this spinning precursor solution was added to the nickel iodide dispersion in S1, and the mixture was magnetically stirred for 15h at room temperature to obtain the liquid-jet spinning solution.

[0079] S3, Liquid-jet spinning preparation of moisture-sensitive nanofiber primary membranes:

[0080] Using the liquid-jet spinning solution described in S2, a moisture-sensitive nanofiber nascent membrane was prepared by liquid-jet spinning method.

[0081] S4, Preparation of moisture-sensitive nanofiber membrane:

[0082] The above-mentioned moisture-sensitive nanofiber nascent membrane was heated in a 65°C oven for 2 hours to obtain the moisture-sensitive nanofiber membrane.

[0083] The nickel chloride thin film prepared by the above method has a humidity-sensitive range of 11%-80%. As the humidity decreases, its color changes from bright grass green to light green. The humidity-sensitive resistance changes significantly with humidity, with a sensitivity of 3.2 MΩ / %RH. In terms of stability, the film has an instantaneous stability of 40 minutes and a cycle stability of 15 cycles.

Claims

1. A method for preparing a humidity-sensitive nanofiber thin film, comprising the following steps: S1, Wet processing of nickel halide: 0.5-1.5 mmol of nickel halide powder is thoroughly ground and dispersed in 2-3 mL of solvent. The mixture is magnetically stirred at 60-75℃ for 12-36 h to obtain a nickel halide precursor solution. The precursor solution is then filtered through a nylon needle filter to remove the precipitate, yielding a nickel halide dispersion. Wherein: The nickel halide is a binary compound composed of nickel atoms and halogen atoms, selected from one of NiCl2, NiBr2 and NiI2; The solvent is DMAC, DMF, or water; The nylon needle filter S2, Preparation of spinning solution: Prepare a polymer / solvent spinning precursor solution with a concentration of 10-20 wt%; add 10-20 g of the polymer / solvent spinning precursor solution to the nickel halide dispersion obtained in step S1, and magnetically stir at room temperature for 8-15 h to obtain a liquid-jet spinning solution, wherein: the polymer is a white or colorless hydrophobic or hydrophilic organic polymer suitable for liquid-jet spinning; the solvent is the same as the solvent in S1. S3, Preparation of wet-sensitive nanofiber nascent membrane by liquid-jet spinning: Using the liquid-jet spinning solution obtained in step S2, a wet-sensitive nanofiber nascent membrane is prepared by liquid-jet spinning method. S4, Preparation of moisture-sensitive nanofiber membrane: The nascent moisture-sensitive nanofiber membrane is placed in an oven and heated at 50-65℃ for 2.5-3.5h to obtain the moisture-sensitive nanofiber thin film.

2. The preparation method according to claim 1, characterized in that: In step S1, the nickel halide powder and 0.5-1.5 mmol of modifier powder are thoroughly ground and dispersed in a solvent to prepare the precursor liquid and the nickel halide dispersion. The modifier is perfluorooctyl iodide, tetrabutylammonium iodide, tetramethylammonium iodide, PVA or SiO2.

3. The preparation method according to claim 2, characterized in that: The modifier is tetramethylammonium iodide, and the dosage is 1 mmol.

4. The preparation method according to claim 1, characterized in that: In step S1, the solvent is DMAC; the nickel halide is NiI2.

5. The preparation method according to claim 1, characterized in that: In step S1, the magnetic stirring time is 24 hours.

6. The preparation method according to claim 1, characterized in that: In step S2, the polymer is TPU, PAN, or PVDF.

7. The preparation method according to claim 6, characterized in that: The polymer is PAN, and the mass fraction of PAN in the polymer / solvent spinning precursor solution is 12%.

8. The preparation method according to claim 1, characterized in that: In step S2, the solvent is DMAC.

9. A moisture-sensitive nanofiber film prepared by any one of claims 1-8.

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