A double-layer nanofiber membrane humidity-responsive actuator and a preparation method and application thereof

Abstract

The application discloses a double-layer nanofiber membrane humidity response actuator and a preparation method and application thereof, and belongs to the technical field of humidity response actuators. The double-layer nanofiber membrane humidity response actuator is a double-layer film structure, comprising a humidity response active layer and a humidity response inert layer. The humidity response active layer is a nanofiber membrane A prepared by electrospinning technology from a hygroscopic polymer material A, and the nanofiber membrane A has an orientation structure. The humidity response inert layer is a nanofiber membrane B prepared by electrospinning technology from a mixture of a hygroscopic polymer material B and a cellulose ether. The double-layer nanofiber membrane humidity response actuator adopts a double-layer nanofiber membrane structure, and the nanofiber membrane has very small bending stiffness. The characteristics make the humidity response actuator have a large driving stroke and a fast response speed. The humidity response inert layer and the humidity response active layer have good binding force, which guarantees excellent cycle stability of the actuator, and the actuator has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of actuator technology, specifically to a humidity-responsive double-layer nanofiber membrane actuator, its preparation method, and its application. Background Technology

[0002] Stimulus-responsive flexible actuators are intelligent actuation devices that convert external stimuli (including light, heat, electricity, magnetic fields, humidity, organic solvents, pH values, etc.) into mechanical motion. Due to their flexibility, small size, and high agility, flexible actuators exhibit great application potential in soft robotics, smart textiles, environmental monitoring, and intelligent sensing during interaction with the environment. The inspiration for humidity response comes from plant movement. The mobility of some plants stems from their unique bilayered heterogeneous structure. When stimulated, the volumes of the two layers change in different ways, achieving actuation and deformation. Taking pine cone seeds as an example, the seeds are tightly wrapped in scales, which consist of a fibrous layer and a hard membrane. The hygroscopic expansion coefficient of the hard membrane layer is much higher than that of the fibrous layer. Therefore, after absorbing moisture, the strain of the two layers becomes mismatched, leading to bending deformation.

[0003] Currently, thin-film humidity-responsive actuators are mainly composed of cast thin films. However, cast thin films typically have a dense structure and lack sufficient channels, making it difficult for water molecules to diffuse rapidly within them, especially during transitions between low and high humidity levels. Furthermore, the relatively high bending stiffness of cast thin films also limits the actuator's response performance to some extent. Fiber-based flexible actuators developed using electrospinning technology, on the other hand, greatly enhance the actuator's moisture exchange capacity with the external environment due to the high specific surface area and porosity of the electrospun nanofiber membrane, thus improving the actuator's humidity response performance. Existing technologies typically use non-hygroscopic dense membranes to achieve strain mismatch after moisture absorption, employing hydrophobic materials as the humidity-responsive inert layer, such as polyimide tape or polyester tape. Due to the difference in hydrophilicity, the bonding force between the two membrane layers is low, and stress during deformation is mainly concentrated at the interface between the two membrane layers, easily leading to interlayer separation and decreased actuator stability. In particular, when the inert layer dense film is combined with the active layer nanofiber film as an actuator, the moisture absorbed by the active layer is not easily diffused from the dense film side. After multiple cycles, moisture is easily accumulated, which will damage the structure of the film and affect the operation of the device. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a humidity-responsive actuator with a double-layer nanofiber membrane, its preparation method, and its application. This humidity-responsive actuator has the advantages of high sensitivity, fast response, large actuation deformation, and excellent stability. The double-layer composite nanofiber membrane humidity-responsive actuator is prepared by electrospinning layer-by-layer deposition. The softness and low stiffness of the nanofiber membrane result in less resistance to the actuator during bending deformation.

[0005] This invention is achieved through the following technical solution:

[0006] The first aspect of this invention provides a dual-layer nanofiber membrane humidity-responsive actuator, wherein the dual-layer nanofiber membrane humidity-responsive actuator has a dual-layer thin film structure, including a humidity-responsive active layer and a humidity-responsive inert layer; the humidity-responsive active layer is a nanofiber membrane A made of a hygroscopic polymer material A by electrospinning technology, and the nanofiber membrane A has an oriented structure; the humidity-responsive inert layer is a nanofiber membrane B made by electrospinning technology after blending a hygroscopic polymer material B and a cellulose ether.

[0007] The humidity-responsive actuator provided by this invention employs a double-layer nanofiber membrane structure. The nanofiber membrane has very low bending stiffness, which enables the humidity-responsive actuator to have a large driving stroke and a fast response speed. The humidity-responsive inert layer prepared by blending hygroscopic polymer materials and cellulose ethers and the humidity-responsive active layer prepared by hygroscopic polymer materials have good bonding force, ensuring the actuator's excellent cycle stability.

[0008] Furthermore, the double-layer thin film structure refers to the composite nanofiber membrane AB obtained by electrospinning and depositing layer by layer.

[0009] Furthermore, the hygroscopic polymer material A and the hygroscopic polymer material B are independently selected from one or more of polyethylene oxide (PEO), polyethylene glycol (PEG), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP).

[0010] Furthermore, the cellulose ether is selected from one or more of hydroxypropyl cellulose (HPC), hydroxymethyl cellulose (HMC), and hydroxyethyl cellulose (HEC).

[0011] Furthermore, the cellulose ether in the nanofiber membrane B has a mass fraction of 50% to 90%.

[0012] Furthermore, the thickness of the humidity-responsive active layer is 20–80 μm, and the thickness of the humidity-responsive inert layer is 30–60 μm, both of which can be controlled by the electrospinning time.

[0013] A second aspect of the present invention provides a method for preparing the humidity-responsive actuator of the bilayer nanofiber membrane described in the first aspect, comprising the following steps:

[0014] S1. Dissolve hygroscopic polymer A in a solvent to obtain spinning solution A; dissolve hygroscopic polymer B and cellulose ether in a solvent to obtain spinning solution B;

[0015] S2. Electrospinning is performed on the spinning solution A described in S1 to obtain a nanofiber membrane A;

[0016] S3. Electrospinning the spinning solution B described in S1 onto the nanofiber membrane A described in S2 to form a nanofiber membrane B, and then drying it to obtain the humidity-responsive actuator of the double-layer nanofiber membrane.

[0017] Furthermore, in S1, the solvent can be deionized water.

[0018] Further, in S1, the concentration of hygroscopic polymer A in spinning solution A is 4-8 wt%, and the total concentration of hygroscopic polymer B and cellulose ether in spinning solution B is 6-10 wt%.

[0019] Furthermore, in S1, the mass ratio of the hygroscopic polymer material B to the cellulose ether is 1:(1-9).

[0020] Furthermore, in S2, the electrospinning process parameters are as follows: spinning voltage is 16-20kV, receiving distance is 22-28cm, micro-pump speed is 0.7-1.0mL / h, and receiving device rotation speed is 800-1500r / min.

[0021] In a specific implementation, a roller is used to collect the nanofiber membrane A.

[0022] Furthermore, in S3, the electrospinning process parameters are as follows: spinning voltage is 16-20kV, receiving distance is 22-28cm, micro-pump speed is 0.7-1.0mL / h, and receiving device rotation speed is 100-1500r / min.

[0023] Further, in S3, nanofiber membrane B (i.e., humidity-responsive inert layer) is deposited on nanofiber membrane A to obtain composite nanofiber membrane AB (i.e., double-layer nanofiber membrane humidity-responsive actuator).

[0024] Furthermore, in S3, the drying temperature is 35–50°C.

[0025] Furthermore, in S3, the drying time is 5 to 12 hours.

[0026] The third aspect of this invention provides an application of the double-layer nanofiber membrane humidity-responsive actuator described in the first aspect in intelligent response, such as its wide application in humidity switches, intelligent sensing, artificial muscles, soft robots, etc.

[0027] The beneficial effects of this invention are:

[0028] 1. The bilayer nanofiber membrane humidity-responsive actuator provided by this invention is prepared using electrospinning technology. Both the humidity-responsive active layer and the humidity-responsive inert layer are electrospun nanofiber membranes. Compared with humidity-responsive actuators where the humidity-responsive inert layer is a cast thin film, the humidity-responsive active material at the interface of the bilayer material has good air permeability on both sides, avoiding the accumulation of water molecules at the interface and thus preventing its impact on device stability. Furthermore, the humidity-responsive inert layer nanofiber membrane has low rigidity, experiences less resistance during deformation, has a larger driving deformation, and responds faster to humidity changes.

[0029] 2. The dual-layer material of the humidity-responsive actuator provided by this invention differs from the conventional assembly strategy of hydrophilic material + hydrophobic material. According to the working principle of dual-layer thin-film actuators, asymmetrical volume changes in the dual-layer material can cause bending deformation. Conventional dual-layer thin-film actuators undergo bending deformation during response, with stress concentrated at the interface of the dual-layer materials. The hydrophilic active layer and the hydrophobic inert layer are difficult to bond firmly, leading to easy separation and affecting the actuator's durability. This application selects a hydrophilic material that does not undergo moisture absorption and expansion as the main component of the humidity-responsive inert layer. This achieves the purpose of bending actuation during moisture absorption while effectively solving the problem of poor bonding between the traditional hydrophobic inert layer and the hydrophilic active layer.

[0030] 3. In preparing the humidity-responsive inert layer electrospun nanofiber membrane, this invention adds a humidity-active layer material to the spinning solution and prepares the composite nanofiber membrane through layer-by-layer deposition, further increasing the bonding force between the humidity-responsive inert layer and the humidity-responsive active layer. Furthermore, during layer-by-layer deposition, because the nanofibers of the humidity-responsive inert layer contain the same or similar materials as the humidity-responsive active layer, when the spinning solution is drawn into nanofibers and deposited onto the collecting roller under electrostatic voltage, the solvent does not completely evaporate. During subsequent evaporation and drying processes, a strong physical connection is formed between the humidity-responsive active layer nanofibers and the humidity-responsive inert layer nanofibers, ensuring the stability of the humidity-responsive actuator structure. Attached Figure Description

[0031] Figure 1 The image shows a surface SEM image of nanofiber membrane A of the humidity-responsive bilayer nanofiber membrane actuator prepared in Example 1.

[0032] Figure 2The image shows a surface SEM image of the nanofiber membrane B of the humidity-responsive bilayer nanofiber membrane actuator prepared in Example 1.

[0033] Figure 3 The image shows a surface SEM image of the nanofiber membrane B of the humidity-responsive bilayer nanofiber membrane actuator prepared in Example 2.

[0034] Figure 4 The figures show the hydrophilicity test results of nanofiber membranes A and B of the bilayer nanofiber membrane humidity-responsive actuators prepared in Examples 1 and 2, respectively; where (a) is nanofiber membrane A of Example 1, (b) is nanofiber membrane B of Example 1, and (c) is nanofiber membrane B of Example 2.

[0035] Figure 5 Image showing the water contact angle of the nanofiber membrane B of the humidity-responsive actuator prepared in Comparative Example 3.

[0036] Figure 6 This is a schematic diagram of a method for measuring the bending angle of a humidity-responsive actuator.

[0037] Figure 7 The graph shows the response performance data of the humidity-responsive actuators prepared in Examples 1-3 and Comparative Examples 1-2 as the bending actuation changes over time when the ambient humidity changes from 40% to 90%.

[0038] Figure 8 Images of the bending deformation and corresponding curvature of the humidity-responsive actuators prepared in Examples 1-3 and Comparative Examples 1-2 under different constant humidity conditions.

[0039] Figure 9 The graph shows the bending curvature data of the humidity-responsive actuators prepared in Examples 1-3 and Comparative Examples 1-2 under different constant humidity conditions.

[0040] Figure 10 The graph shows the results of cyclic stability tests conducted on the humidity-responsive actuator prepared in Comparative Example 1, switching between 18.3% and 95.0% humidity environments.

[0041] Figure 11 The graph shows the results of the cyclic stability test of the bilayer nanofiber membrane humidity-responsive actuator prepared in Example 2, switching between 18.3% and 95.0% humidity environments.

[0042] Figure 12 The graph shows the results of cyclic stability tests conducted on the humidity-responsive actuator prepared in Comparative Example 3, switching between 18.3% and 95.0% humidity environments.

[0043] Figure 13This is a schematic diagram illustrating the application of the bilayer nanofiber membrane humidity-responsive actuator prepared in Example 2 as a humidity switch.

[0044] Figure 14 This is a schematic diagram illustrating the application of the bilayer nanofiber membrane humidity-responsive actuator prepared in Example 2 as a responsive driving force mechanism in artificial muscle. Detailed Implementation

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0048] Example 1

[0049] A method for fabricating a humidity-responsive actuator using a bilayer nanofiber membrane includes the following steps:

[0050] S1. Dissolve polyethylene oxide (PEO) in deionized water and stir thoroughly to obtain spinning solution A with a PEO concentration of 6 wt%; dissolve PEO and hydroxypropyl cellulose (HPC) in deionized water at a mass ratio of 1:1 and stir thoroughly to obtain spinning solution B with a total PEO and HPC concentration of 8 wt%.

[0051] S2. Add spinning solution A to the extrusion syringe of the electrospinning machine. Set the electrospinning process parameters as follows: spinning voltage of 18kV, receiving distance of 24cm, micro-pump speed of 0.8mL / h, and receiving device speed of 1200r / min. Perform electrospinning to deposit nanofibers onto the release paper of the collecting roller. Control the spinning time to obtain a nanofiber membrane A with a thickness of 25μm.

[0052] S3. Electrospinning solution B is performed on nanofiber membrane A. The spinning solution B is added to the extrusion syringe of the electrospinning machine. The electrospinning process parameters are set as follows: spinning voltage is 18kV, receiving distance is 26cm, micro-pump speed is 0.8mL / h, and receiving device speed is 1200r / min. Electrospinning is performed, and the spinning time is controlled to produce a nanofiber membrane B with a thickness of 35μm (the mass fraction of HPC in nanofiber membrane B is 50%). A composite nanofiber membrane AB is obtained by layer-by-layer deposition. The composite nanofiber membrane AB is removed from the collecting roller and dried in an oven at 40℃ for 8h. It is then cut into 5*20mm rectangular double-layer nanofiber membrane humidity-responsive actuators along the fiber orientation direction.

[0053] Example 2

[0054] A method for preparing a humidity-responsive actuator for a double-layer nanofiber membrane is basically the same as that in Example 1, except that: in S1, PEO and HPC are dissolved in deionized water at a mass ratio of 1:3 and stirred thoroughly to obtain a spinning solution B with a total concentration of 8wt% of PEO and HPC, that is, the mass fraction of HPC in nanofiber membrane B in S3 is 75%.

[0055] Example 3

[0056] A method for preparing a humidity-responsive actuator for a double-layer nanofiber membrane is basically the same as that in Example 1, except that: in S1, PEO and HPC are dissolved in deionized water at a mass ratio of 3:1 and stirred thoroughly to obtain a spinning solution B with a total concentration of 8wt% of PEO and HPC, that is, the mass fraction of HPC in nanofiber membrane B in S3 is 25%.

[0057] Example 4

[0058] A method for fabricating a humidity-responsive actuator using a bilayer nanofiber membrane includes the following steps:

[0059] S1. Dissolve PEO in deionized water and stir thoroughly to obtain spinning solution A with a PEO concentration of 8 wt%; dissolve PEO and HPC in deionized water at a mass ratio of 1:9 and stir thoroughly to obtain spinning solution B with a total PEO and HPC concentration of 6 wt%.

[0060] S2. Add spinning solution A into the extrusion syringe of the electrospinning machine. Set the electrospinning process parameters as follows: spinning voltage of 20kV, receiving distance of 22cm, micro-pump speed of 0.7mL / h, and receiving device speed of 1500r / min. Perform electrospinning to deposit nanofibers onto the release paper of the collecting roller. Control the spinning time to obtain a nanofiber membrane A with a thickness of 80μm.

[0061] S3. Electrospinning solution B is performed on nanofiber membrane A. The spinning solution B is added to the extrusion syringe of the electrospinning machine. The electrospinning process parameters are set as follows: spinning voltage is 20kV, receiving distance is 22cm, micro-pump speed is 1.0mL / h, and receiving device speed is 100r / min. Electrospinning is performed, and the spinning time is controlled to produce a nanofiber membrane B with a thickness of 60μm (the mass fraction of HPC in nanofiber membrane B is 90%). A composite nanofiber membrane AB is obtained by layer-by-layer deposition. The composite nanofiber membrane AB is removed from the collecting roller and dried in an oven at 50℃ for 5h. It is then cut into 5*20mm rectangular double-layer nanofiber membrane humidity-responsive actuators along the fiber orientation direction.

[0062] Example 5

[0063] A method for fabricating a humidity-responsive actuator using a bilayer nanofiber membrane includes the following steps:

[0064] S1. Dissolve PEO in deionized water and stir thoroughly to obtain spinning solution A with a PEO concentration of 4 wt%; dissolve PEO and HPC in deionized water at a mass ratio of 1:6 and stir thoroughly to obtain spinning solution B with a total PEO and HPC concentration of 10 wt%.

[0065] S2. Add spinning solution A to the extrusion syringe of the electrospinning machine. Set the electrospinning process parameters as follows: spinning voltage of 16kV, receiving distance of 28cm, micro-pump speed of 1.0mL / h, and receiving device speed of 800r / min. Perform electrospinning to deposit nanofibers onto the release paper of the collecting roller. Control the spinning time to obtain a nanofiber membrane A with a thickness of 20μm.

[0066] S3. Electrospinning solution B is performed on nanofiber membrane A. The spinning solution B is added to the extrusion syringe of the electrospinning machine. The electrospinning process parameters are set as follows: spinning voltage is 16kV, receiving distance is 28cm, micro-pump speed is 0.7mL / h, and receiving device speed is 1500r / min. Electrospinning is performed, and the spinning time is controlled to produce a nanofiber membrane B with a thickness of 30μm (the mass fraction of HPC in nanofiber membrane B is about 85%). A composite nanofiber membrane AB is obtained by layer-by-layer deposition. The composite nanofiber membrane AB is removed from the collecting roller and dried in an oven at 35℃ for 12h. It is then cut into 5*20mm rectangular double-layer nanofiber membrane humidity-responsive actuators along the fiber orientation direction.

[0067] Example 6

[0068] A method for fabricating a humidity-responsive actuator using a bilayer nanofiber membrane includes the following steps:

[0069] S1. Dissolve polyvinyl alcohol (PVA) in deionized water and stir thoroughly to obtain spinning solution A with a PVA concentration of 8 wt%; dissolve PVA and hydroxyethyl cellulose (HEC) in deionized water at a mass ratio of 1:4 and stir thoroughly to obtain spinning solution B with a total PVA and HEC concentration of 9 wt%.

[0070] S2. Add spinning solution A to the extrusion syringe of the electrospinning machine. Set the electrospinning process parameters as follows: spinning voltage of 19kV, receiving distance of 26cm, micro-pump speed of 0.8mL / h, and receiving device speed of 1000r / min. Perform electrospinning to deposit nanofibers onto the release paper of the collecting roller. Control the spinning time to obtain a nanofiber membrane A with a thickness of 50μm.

[0071] S3. Electrospinning solution B is performed on nanofiber membrane A. The spinning solution B is added to the extrusion syringe of the electrospinning machine. The electrospinning process parameters are set as follows: spinning voltage is 18kV, receiving distance is 25cm, micro-pump speed is 0.8mL / h, and receiving device speed is 500r / min. Electrospinning is performed, and the spinning time is controlled to produce a nanofiber membrane B with a thickness of 40μm (the mass fraction of HEC in nanofiber membrane B is 80%). A composite nanofiber membrane AB is obtained by layer-by-layer deposition. The composite nanofiber membrane AB is removed from the collecting roller and dried in an oven at 40℃ for 8h. It is then cut into 5*13mm rectangular double-layer nanofiber membrane humidity-responsive actuators along the fiber orientation direction.

[0072] Example 7

[0073] A method for fabricating a humidity-responsive actuator using a bilayer nanofiber membrane includes the following steps:

[0074] S1. Dissolve polyvinylpyrrolidone (PVP) in deionized water and stir thoroughly to obtain spinning solution A with a PVP concentration of 7 wt%; dissolve PVP and hydroxymethyl cellulose (HMC) in deionized water at a mass ratio of 1:5 and stir thoroughly to obtain spinning solution B with a total PVP and HMC concentration of 8 wt%.

[0075] S2. Add spinning solution A to the extrusion syringe of the electrospinning machine. Set the electrospinning process parameters as follows: spinning voltage of 18kV, receiving distance of 26cm, micro-pump speed of 0.9mL / h, and receiving device speed of 1200r / min. Perform electrospinning to deposit nanofibers onto the release paper of the collecting roller. Control the spinning time to obtain a nanofiber membrane A with a thickness of 45μm.

[0076] S3. Electrospinning solution B is performed on nanofiber membrane A. The spinning solution B is added to the extrusion syringe of the electrospinning machine. The electrospinning process parameters are set as follows: spinning voltage of 20kV, receiving distance of 24cm, micro-pump speed of 0.8mL / h, and receiving device speed of 600r / min. Electrospinning is performed, and the spinning time is controlled to produce a nanofiber membrane B with a thickness of 45μm (the mass fraction of HMC in nanofiber membrane B is about 83%). A composite nanofiber membrane AB is obtained by layer-by-layer deposition. The composite nanofiber membrane AB is removed from the collecting roller and dried in an oven at 40℃ for 8h. It is then cut into 5*13mm rectangular double-layer nanofiber membrane humidity-responsive actuators along the fiber orientation direction.

[0077] Comparative Example 1

[0078] A method for preparing a humidity-responsive actuator (PEO nanofiber membrane + PI thin film tape) includes the following steps:

[0079] S1. Dissolve PEO in deionized water and stir thoroughly to obtain spinning solution A with a PEO concentration of 6 wt%.

[0080] S2. Add spinning solution A to the extrusion syringe of the electrospinning machine. Set the electrospinning process parameters as follows: spinning voltage of 18kV, receiving distance of 24cm, micro-pump speed of 0.8mL / h, and receiving device speed of 1200r / min. Perform electrospinning to deposit nanofibers onto the release paper of the collecting roller. Control the spinning time to obtain a nanofiber membrane A with a thickness of 25μm. Remove the nanofiber membrane A from the roller and dry it in an oven at 40℃ for 8h.

[0081] S3. Using a 35μm thick polyimide (PI) film tape, attach the adhesive side of the PI film tape to the nanofiber membrane A, peel the nanofiber membrane A from the release paper, roll it to obtain a double-layer composite film, and cut it into a 5*20mm rectangular humidity-responsive actuator along the fiber orientation direction.

[0082] Comparative Example 2

[0083] A method for preparing a humidity-responsive actuator (PEO nanofiber membrane + PVP nanofiber membrane) is basically the same as that in Example 1, except that in S1, polyvinylpyrrolidone (PVP) is dissolved in deionized water and stirred thoroughly to obtain a spinning solution B with a PVP concentration of 8 wt%.

[0084] Comparative Example 3

[0085] A method for preparing a humidity-responsive actuator (PEO nanofiber membrane + PVDF nanofiber membrane) is basically the same as that in Example 1, except that in S1, polyvinylidene fluoride (PVDF) is dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and acetone (mass ratio 4:1) and stirred thoroughly to obtain a spinning solution B with a PVDF concentration of 10 wt%.

[0086] Test Example 1

[0087] The microstructure of the humidity-responsive active layer (nanofiber membrane A) and humidity-responsive inert layer (nanofiber membrane B) of the bilayer nanofiber membrane humidity-responsive actuators prepared in Examples 1 and 2 were observed and analyzed.

[0088] Figure 1 This is a scanning electron microscope (SEM) image of the surface of nanofiber membrane A of the humidity-responsive bilayer nanofiber membrane actuator prepared in Example 1. Figure 1 As can be seen, since the collecting drum rotates at 1200 r / min, most fibers have a good orientation, which will be beneficial to stress transmission during fiber deformation, ensuring response sensitivity and improving response driving force.

[0089] Figure 2 This is a surface SEM image of the nanofiber membrane B of the humidity-responsive bilayer nanofiber membrane actuator prepared in Example 1. Figure 2 As can be seen, PEO and HPC can be co-spun to produce nanoscale fiber membranes, wherein the mass fraction of HPC in nanofiber membrane B is 50%.

[0090] Figure 3 This is a surface SEM image of nanofiber membrane B in the humidity-responsive bilayer nanofiber membrane actuator prepared in Example 2. At this point, the mass fraction of HPC in nanofiber membrane B has increased to 75%. Figure 3 As can be seen, with the increase of HPC ratio, the adhesion of the spinning solution increases, and the number of interconnection points between the fibers in the prepared fiber membrane increases. This is beneficial to increase the interaction force between fibers and improve the bonding stability with the humidity-responsive active layer.

[0091] Test Example 2

[0092] The hydrophilicity of the humidity-responsive active layer (nanofiber membrane A) and humidity-responsive inert layer (nanofiber membrane B) of the humidity-responsive actuators prepared in Examples 1, 2 and 3 was tested and analyzed.

[0093] Figure 4The figures show the hydrophilicity test results of nanofiber membranes A and B for the humidity-responsive bilayer nanofiber membrane actuators prepared in Examples 1 and 2, respectively; where (a) is nanofiber membrane A of Example 1, (b) is nanofiber membrane B of Example 1, and (c) is nanofiber membrane B of Example 2. Figure 4 As can be seen, nanofiber membrane A prepared by PEO has good hydrophilicity, and water droplets completely spread and permeate within 10 seconds on the surface of the fiber membrane. The hydrophilicity of nanofiber membrane B prepared by mixing HPC and PEO is reduced, and the higher the HPC content, the greater the decrease in hydrophilicity. However, it can still completely spread and wet within 60 seconds, indicating that the humidity-responsive inert layer side also has good hydrophilicity, ensuring the adsorption, diffusion and transfer of water molecules.

[0094] Figure 5 The image shows the water contact angle of the nanofiber membrane B of the humidity-responsive actuator prepared in Comparative Example 3. This humidity-responsive actuator has a double-layer composite nanofiber membrane, which ensures the diffusion and transfer of water molecules on both sides of the actuator. At the same time, the PVDF nanofiber membrane does not absorb moisture and expand, and the water contact angle reaches 135 degrees, providing the difference in humidity response between the two films on both sides of the humidity-responsive actuator.

[0095] Test Example 3

[0096] The response performance of a humidity-responsive actuator is quantitatively characterized by the degree of bending of the rectangular strip-type humidity-responsive actuator, such as... Figure 6 As shown, when the rectangular strip is perpendicular to the horizontal plane, it is recorded as 0°. The angle of the arc formed on the right side is recorded as a negative angle, and vice versa, the angle of the arc formed on the left side is recorded as a positive angle. The bending angle can be obtained from the angle between the tangents at both ends of the arc. Then, the curvature K of the arc can be calculated using the formula: K=(θ×π) / (180°×L), where θ is the bending angle and L is the length of the humidity-responsive actuator. This method allows for comparison of the response performance of humidity-responsive actuators of different lengths.

[0097] Figure 7 The graphs show the response performance data of the humidity-responsive actuators prepared in Examples 1-3 and Comparative Examples 1-2 as the ambient humidity changes from 40% to 90% over time. The influence of different humidity-responsive inert layers on the response performance of the humidity-responsive actuators was compared and analyzed, including PI film tape (Comparative Example 1), hygroscopic polymer material PVP nanofiber membrane (Comparative Example 2), nanofiber membrane B with a 25% HPC mass fraction (Example 3), nanofiber membrane B with a 50% HPC mass fraction (Example 1), and nanofiber membrane B with a 75% HPC mass fraction (Example 2). Figure 7As can be seen, in Comparative Example 1, a humidity-responsive actuator using PI film tape as the humidity-responsive inert layer exhibits a low degree of deformation (curvature change) due to the non-hygroscopic expansion of the PI film tape. This is because the active layer responds to humidity changes, leading to stress mismatch in the double-layer film and resulting in bending actuation. However, the deformation degree of bending actuation (curvature change) is not high, mainly because the rigidity of the dense PI film limits its deformation. In Comparative Example 2, a humidity-responsive actuator using a hygroscopic polymer PVP nanofiber membrane as the humidity-responsive inert layer exhibits very small deformation. This is mainly because both nanofiber membrane materials are humidity-active materials with hygroscopic expansion properties, which cancel each other out, thus preventing stress mismatch and bending actuation. The slight deformation of this composite nanofiber membrane mainly stems from the slight differences in the expansion coefficients of the different materials. When a composite nanofiber membrane prepared by mixing PEO and HPC is used as a humidity-responsive inert layer, when the HPC content is too low (25%, Example 3), since the moisture-absorbing and expanding material PEO is the main component, the difference in the degree of absorption and expansion between the two nanofiber membranes is not significant. Therefore, the resulting actuation bending is not very high, but it still exceeds the bending change degree when using PI film tape as a humidity-responsive inert layer. When the HPC content increases, the degree of expansion change of the humidity-responsive inert layer decreases significantly. This is reflected in the significant increase in the actuation response change amplitude of Example 1 (HPC mass fraction of 50%) and Example 2 (HPC mass fraction of 75%), especially the maximum driving stroke of the humidity-responsive actuator of the composite nanofiber membrane in Example 2 reaching 6.39 cm. -1 The response speed reaches 0.42cm. -1 ·s -1 Compared with actuators using PI film tape as a humidity-responsive inert layer, the maximum driving stroke is increased by 83.1% and the response speed is increased by 7.6%. This is due to the low rigidity of the humidity-responsive inert layer in Example 2, which results in less resistance during response deformation and greater driving deformation. At the same time, water molecules can be exchanged on both sides of the membrane, thus responding to humidity changes more quickly.

[0098] Figure 8 Images of the bending deformation and corresponding curvature of the humidity-responsive actuators prepared in Examples 1-3 and Comparative Examples 1-2 under different constant humidity conditions are shown. Figure 8As can be seen, the humidity-responsive actuator prepared in Comparative Example 1 exhibits a large reverse bending curvature under low humidity, while the humidity-responsive actuator of the present invention with a bilayer nanofiber membrane is more likely to obtain a positive bending curvature. This is because during the preparation process of Comparative Example 1, the solvent was not completely evaporated when the humidity-responsive active layer was formed by electrospinning and was removed in the subsequent drying process. At this time, the nanofiber membrane was bound by the receiving release paper, so there was shrinkage stress within the fiber membrane. After the actuator was assembled with the PI film tape on the release paper, it would bend towards the humidity-responsive layer. In contrast, the humidity-responsive actuator of the present invention, prepared by layer-by-layer deposition, shows that both layers of electrospun nanofiber membrane shrink after drying. Therefore, the state of the bilayer nanofiber membrane does not change significantly after being removed from the release paper, making it easier to prepare a humidity-responsive actuator with stable structure and performance.

[0099] Figure 9 The graph shows the bending curvature data of the humidity-responsive actuators prepared in Examples 1-3 and Comparative Examples 1-2 under different constant humidity conditions. Figure 8 Correspondingly. From Figure 9 As can be seen, the curvature changes of Comparative Examples 1-2 and Example 3 under different humidity levels are significantly smaller than those of Example 1 and Example 2, which also demonstrates that the bilayer nanofiber membrane humidity-responsive actuator constructed with a composite nanofiber membrane with a certain HPC doping has better humidity response performance.

[0100] Test Example 4

[0101] The humidity-responsive actuators prepared in Example 2, Comparative Example 1, and Comparative Example 3 were subjected to cyclic stability tests in switching environments of 18.3% and 95.0% humidity.

[0102] Figure 10 The graph shows the cyclic stability test results of the humidity-responsive actuator prepared in Comparative Example 1, switching between 18.3% and 95.0% humidity environments. Figure 10As can be seen, in the first five cycles, the curvature of the humidity-responsive actuator gradually shifts downwards, meaning that both the initial and final states of the actuator's response shrink towards the humidity-responsive active layer (PEO). This is because the PEO active layer is an electrospun nanofiber membrane. During preparation, when the fibers are deposited on the release paper, the solvent does not completely evaporate. During subsequent drying, the solvent evaporates, causing the fiber membrane to shrink. After assembly into a device, during cyclic testing, with the adsorption and desorption of water molecules, especially in high-humidity environments, a large number of water molecules exist in the fibers. This causes the polymer molecular chains to move, gradually releasing the stress within the fibers, resulting in a shift towards the humidity-responsive active layer. In subsequent cycles, the curvature of the humidity-responsive bending gradually decreases, and the driving stroke of the actuator gradually diminishes. This is because the PI film tape is hydrophobic and impermeable; after moisture absorption cycles, water molecules easily accumulate at the interface between the two membranes, leading to damage to the fiber structure and a certain degree of separation between the two membranes, thus reducing the actuation performance.

[0103] Figure 11 The graph shows the cyclic stability test results of the bilayer nanofiber membrane humidity-responsive actuator prepared in Example 2, switching between 18.3% and 95.0% humidity environments. Figure 11 As can be seen, the humidity-responsive actuator prepared in Example 2, which exhibits superior actuation performance, demonstrates excellent stability. This is because the bilayer nanofiber membrane is obtained through layer-by-layer deposition, resulting in a strong bonding force between the two layers. Furthermore, the addition of PEO to the humidity-responsive inert layer enhances its affinity with the active nanofiber membrane. Simultaneously, during water molecule adsorption and desorption, the exchange of water molecules between both sides and the environment is ensured, improving the response performance and structural stability of the humidity-responsive actuator. Additionally, during the drying process after electrospinning, both nanofiber membranes experience shrinkage stress, which is gradually released during cycling and remains balanced on both sides, canceling each other out. Therefore, the phenomenon of deflection towards the humidity-responsive active layer, as seen in Comparative Example 1, does not occur.

[0104] Figure 12 The graph shows the cyclic stability test results of the humidity-responsive actuator prepared in Comparative Example 3, switching between 18.3% and 95.0% humidity environments. Figure 12As can be seen from the data, Comparative Example 3 uses a hydrophobic PVDF nanofiber membrane as a humidity-responsive inert layer. A composite nanofiber membrane humidity-responsive actuator was also obtained through layer-by-layer deposition, and this actuator also exhibits a good range of humidity-responsive curvature changes. However, after cycling, the curvature change range gradually decreases, and after three cycles, it loses its responsiveness to humidity changes. This is because the hydrophilic PEO nanofiber membrane and the hydrophobic PVDF nanofiber membrane have a large difference in hydrophilicity and hydrophobicity, resulting in weak bonding between the two membranes. When one side absorbs and expands, it detaches from the non-hygroscopic fibers on the other side, leading to the separation of the two nanofiber membranes and thus gradually losing its actuation response performance.

[0105] The response performance of the bilayer nanofiber membrane humidity-responsive actuators prepared in Examples 4-7 is similar to that in Example 2, and they also have good cycle stability.

[0106] Application Example 1

[0107] The humidity-responsive actuator of the bilayer nanofiber membrane prepared in Example 2 was installed in a circuit switch, such as... Figure 13 As shown, when the humidity is low, the circuit is open, and the indicator light is off. When the ambient humidity rises, the actuator bends and deforms, thereby driving the switch to close, the circuit is closed, and the indicator light illuminates. Simultaneously, when the ambient humidity drops again, the actuator returns to its original state, thus disconnecting the circuit again, and the indicator light goes out. Therefore, the double-layer nanofiber membrane humidity-responsive actuator provided by this invention has broad applications in humidity monitoring and early warning, humidity control, industrial production, and agriculture.

[0108] Application Example 2

[0109] The humidity-responsive actuator of the bilayer nanofiber membrane prepared in Example 2 was applied as a responsive driving force mechanism to artificial muscles, such as... Figure 14 As shown, when the ambient humidity rises, the nanofiber membrane on the humidity-responsive active layer absorbs moisture and expands, bending towards the humidity-responsive inert layer, thereby driving it to lift a certain object. When the humidity drops, it returns to its initial state. Therefore, the double-layer nanofiber membrane humidity-responsive actuator provided by this invention can be used as an artificial muscle module that interacts with the environment, a flexible soft manipulator, etc., and applied to actuated soft robots in special environments.

[0110] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A humidity-responsive actuator with a double-layer nanofiber membrane, characterized in that, The dual-layer nanofiber membrane humidity-responsive actuator has a dual-layer thin film structure, including a humidity-responsive active layer and a humidity-responsive inert layer; the thickness of the humidity-responsive active layer is 20~80 μm, and the thickness of the humidity-responsive inert layer is 30~60 μm. The humidity-responsive active layer is a nanofiber membrane A made of hygroscopic polymer material A using electrospinning technology. The nanofiber membrane A has an oriented structure. The electrospinning process parameters are as follows: the hygroscopic polymer material A is dissolved in a solvent to obtain spinning solution A, the concentration of hygroscopic polymer material A in the spinning solution A is 4~8 wt%; the spinning voltage is 16~20 kV; the receiving distance is 22~28 cm; the micro-pump speed is 0.7~1.0 mL / h; and the receiving device rotation speed is 800~1500 r / min. The humidity-responsive inert layer is a nanofiber membrane B made by electrospinning a blend of hygroscopic polymer material B and cellulose ether. The hygroscopic polymer material A and hygroscopic polymer material B are independently selected from one or more of polyethylene oxide, polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone. The mass fraction of cellulose ether in the nanofiber membrane B is 50%–90%. The electrospinning process parameters are as follows: hygroscopic polymer material B and cellulose ether are dissolved in a solvent to obtain spinning solution B, the total concentration of hygroscopic polymer material B and cellulose ether in spinning solution B is 6–10 wt%; the spinning voltage is 16–20 kV, the receiving distance is 22–28 cm, the micropump speed is 0.7–1.0 mL / h, and the receiving device rotation speed is 100–1500 r / min.

2. The humidity-responsive actuator with a double-layer nanofiber membrane according to claim 1, characterized in that, The cellulose ether is selected from one or more of hydroxypropyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose.

3. A method for preparing a humidity-responsive actuator with a bilayer nanofiber membrane as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Dissolve hygroscopic polymer A in a solvent to obtain spinning solution A; dissolve hygroscopic polymer B and cellulose ether in a solvent to obtain spinning solution B; S2. Electrospinning is performed on the spinning solution A described in S1 to obtain a nanofiber membrane A; S3. Electrospinning the spinning solution B described in S1 onto the nanofiber membrane A described in S2 to form a nanofiber membrane B, and then drying it to obtain the humidity-responsive actuator of the double-layer nanofiber membrane.

4. The application of the bilayer nanofiber membrane humidity-responsive actuator according to any one of claims 1 to 2 in intelligent response.

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