Temperature and humidity responsive driver and method of making same

Abstract

This invention provides a temperature and humidity responsive actuator and its preparation method. The actuator is a double-layer electrospun film actuator, composed of a sequentially electrospun polyacrylonitrile (PAN) fiber layer and a poly(N-isopropylacrylamide) (PNIPAM) fiber layer. This invention introduces electrospinning technology into the preparation of the actuator, selecting temperature-inert polyacrylonitrile (PAN) and temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) as the polymers for sequential electrospinning. Through a simple preparation process, an actuator with good temperature and humidity responsiveness can be efficiently prepared, and the prepared actuator exhibits high sensitivity, fast temperature and humidity response speed, and stable performance.

Description

Technical Field

[0001] This invention relates to the field of stimulus-responsive deformable materials technology, specifically to a temperature and humidity responsive actuator and its preparation method. Background Technology

[0002] Polymer-based stimulus-responsive materials have long attracted attention due to their ability to translate chemical or physical stimuli into observable changes. Hydrogels, in particular, have become a focus of research due to their excellent biocompatibility. Hydrogel-based films, assemblies, microgels, and nanogels have been designed to respond to various stimuli and are widely used in tissue engineering, artificial muscles, and actuators. Among stimulus-responsive hydrogel actuators, thermoresponsive actuators are of particular interest because temperature is the most suitable stimulus for working with living cells, which can withstand temperatures ranging from 4 to 37°C. For hydrogels, the swelling and deswelling processes during differential expansion are greatly limited by the diffusion rate of the solution within the gel network, resulting in consistently slow actuation speeds for hydrogel actuators. Therefore, fabricating fast-responding hydrogel actuators remains a significant challenge.

[0003] In nature, plants possess the ability to convert stimuli from their environment into mechanical movements. For example, sunlight alters auxin distribution, leading to phototropism in seedlings and humidity-responsive flowering and closing in morning glories. Humidity is a ubiquitous stimulus in the air, and converting it into other forms of energy would be of great significance, such as developing humidity-responsive actuators. Typically, humidity-responsive materials contain typical hydrophilic groups, such as hydroxyl, amide, carboxyl, or pyrrole groups, which readily interact with water molecules, causing macroscopic deformation.

[0004] Therefore, it is necessary to prepare a hydrogel actuator that can rapidly respond to temperature and humidity. Through long-term experimental research, our team has developed a temperature and humidity responsive actuator by introducing electrospinning technology into the preparation of hydrogels. We selected temperature-inert polyacrylonitrile (PAN) and temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) as the polymers for sequential electrospinning. Since the electrospun PAN / PNIPAM bilayer film has a larger specific surface area than the bulk gel, it enhances the exchange rate between the solution and the gel, improving the hydrogel's response speed. Simultaneously, the PNIPAM molecular chain is rich in hydrophilic amide groups. Under a humidity gradient, the anisotropic adsorption of water vapor leads to a difference in expansion on both sides of the film, forming internal stress that triggers the humidity-responsive drive of the electrospun film. This can act as a humidity-responsive switch, endowing the bilayer film with humidity-responsive driving properties. Thus, an actuator that can rapidly respond to temperature is prepared and can be used as a switch in humid environments, achieving dual responsiveness to both temperature and humidity. Summary of the Invention

[0005] The purpose of this invention is to provide a driver that responds to humidity and temperature.

[0006] Another object of the present invention is to provide a method for preparing a humidity and temperature responsive actuator.

[0007] This invention is achieved through the following technical solution:

[0008] The present invention provides a temperature and humidity responsive actuator, wherein the actuator is a double-layer electrospun film actuator, which is composed of a sequentially electrospun polyacrylonitrile fiber layer and a poly(N-isopropylacrylamide) fiber layer;

[0009] The polyacrylonitrile fiber layer is prepared by stirring and electrospinning using polyacrylonitrile as raw material and N,N-dimethylformamide as solvent. The poly(N-isopropylacrylamide) fiber layer is prepared by stirring, electrospinning and curing using poly(N-isopropylacrylamide), 2-ethyl-4-methylimidazolium and octaglycidyl polyhedral oligomeric silsesquioxane as raw materials and N,N-dimethylformamide and tetrahydrofuran as solvent.

[0010] The diameter of the polyacrylonitrile fiber layer in this invention is 205-300 nm; the diameter of the poly(N-isopropylacrylamide) fiber layer is 560-870 nm.

[0011] The method for preparing the temperature and humidity responsive actuator of the present invention includes the following steps:

[0012] (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to a certain mass ratio. Dissolve it in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A.

[0013] (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B.

[0014] (3) Adjust the settings of the electrospinning instrument and electrospin the deposits onto the tin foil covering the surface of the roller;

[0015] (4) First, electrospin the mixed solution B, and then replace the mixed solution B with the mixed solution A for electrospinning, that is, continue to electrospin a layer of poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film; then put it in the oven for curing to obtain a double-layer electrospun fiber film driver.

[0016] The mass ratio described in step (1) of the present invention is: poly(N-isopropylacrylamide): octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazolium = 100:15:0.3.

[0017] The volume ratio of dimethylformamide to tetrahydrofuran in step (1) of the present invention is: dimethylformamide: tetrahydrofuran = 1:1.

[0018] The N,N-dimethylformamide mentioned in step (2) of the present invention can also be selected as N,N-dimethylacetamide.

[0019] The parameters set in step (3) of the present invention are as follows: voltage 18-20 kV, receiving distance 13-15 cm, feeding rate 1.0-1.2 mL / h, and receiver rotation speed 25-30 r / min.

[0020] Preferably, the parameter settings in step (3) of the present invention are: voltage 20 kV, receiving distance 15 cm, feeding rate 1.2 mL / h, and receiver rotation speed 30 r / min.

[0021] The curing conditions described in step (4) of the present invention are: curing temperature 150-170℃, curing time 3-5 h.

[0022] Preferably, the curing conditions in step (4) of the present invention are: curing temperature 160°C and curing time 4 h.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention combines temperature-inert PAN with temperature-sensitive PNIPAM using electrospinning technology. The spun fibers have diameters of 205-300 nm and 560-870 nm, respectively, which greatly increases the specific surface area and porosity of the hydrogel, thereby achieving rapid temperature-responsive actuation (3 s) and recovery (5 s) behavior. In contrast, the braking of traditional bulk hydrogel materials often takes tens of minutes, solving the problem of slow actuator braking speed. At the same time, since the PNIPAM molecular chain is rich in hydrophilic amide groups, under a humidity gradient, the anisotropic adsorption of water vapor will cause the expansion difference on both sides of the film, forming internal stress that triggers the humidity-responsive drive of the electrospun film, which can be used as a humidity-responsive switch.

[0025] 2. The preparation process of the method of the present invention is simple and efficient, and the prepared actuator has high sensitivity, fast temperature and humidity response speed and stable performance.

[0026] 3. This invention, through infrared spectroscopy testing, reveals that: using PNIPAM and Ope POSS as raw materials, under the conditions of EMI as a catalyst and heating, the epoxy groups on Ope POSS undergo an epoxy ring-opening reaction with the active hydrogen on the secondary amine of the PNIPAM molecular chain. One Ope POSS contains 8 epoxy groups, and the PNIPAM molecular chain contains secondary amine groups with multiple functionalities. Thus, a cross-linked system is formed after the reaction, avoiding the complex chemical modification process of PNIPAM or its monomers before electrospinning, which is necessary for further cross-linking after spinning in traditional PNIPAM electrospun films. After reacting at 160 °C for 4 h, the characteristic peak of the epoxy groups in the Cured Ope POSS / PNIPAM mixture disappeared, confirming the ring-opening reaction of the epoxy groups in Ope POSS, thereby determining the formation of the cross-linked structure.

[0027] 4. This invention, through solubility testing of cured PNIPAM electrospun membranes, reveals the following: Uncured PNIPAM electrospun fibers exhibit a linear molecular structure. When placed in water at 20°C, they swell and rapidly dissolve, forming a clear, transparent solution. At 40°C, above their LCST, a phase transition is observed, with the solution's transparency rapidly decreasing to a pale white. Cured PNIPAM membranes swell in water at 20°C, forming a transparent gel film, but do not dissolve. When the temperature rises to 40°C, above their LCST, PNIPAM molecules undergo a phase transition, with molecular chain contraction causing a macroscopic volume reduction in the fiber membrane. This further confirms the formation of a three-dimensional cross-linked insoluble network through an epoxy ring-opening reaction between PNIPAM and Ope POSS molecules. Thus, the cured PNIPAM electrospun membrane remains stable in water and successfully completes the temperature-responsive phase transition behavior, laying the foundation for rapid response-driven implementation.

[0028] 5. The present invention obtained the following results through the expansion rate test of the electrospun membrane in water: PAN electrospun membrane has no temperature response, and its size does not change significantly with temperature changes, and is the same as the initial sample. Its expansion rate is -0.17% (20℃) and 0% (40℃); due to the temperature sensitivity of PNIPAM, its electrospun membrane absorbs water and expands at 20℃ (less than LCST=31℃), and shrinks when the temperature rises to 40℃ (greater than LCST). Its expansion rate is 9.17% (20℃) and -48.33% (40℃).

[0029] 6. This invention utilizes the humidity-responsive behavior of electrospun membranes to achieve the following: PNIPAM molecular chains contain a large number of hydrophilic amide groups, which can interact with gaseous water molecules, enabling the PNIPAM electrospun membrane to rapidly adsorb and desorb water vapor; when the electrospun membrane adsorbs water vapor, it expands, and when it desorbs, it contracts, and the amount of adsorbed water vapor increases with increasing humidity. Therefore, the higher the humidity, the more water vapor is adsorbed, and the greater the expansion rate; if there is a humidity gradient distribution in the air, the PNIPAM membrane placed therein will form an expansion rate distribution structure consistent with the humidity gradient in the thickness direction, resulting in expansion mismatch and triggering bending actuation behavior.

[0030] 7. This invention utilizes the temperature response of electrospun membranes to drive the following behavior: When the double-layer actuator is placed in water at 20°C, it expands because the temperature is lower than the LCST temperature of PNIPAM (31°C), while the PAN fiber layer does not respond to temperature changes. The tightly bonded double-layer electrospun membranes experience an expansion mismatch, generating internal stress that activates the rapid bending behavior of the double-layer membrane towards the PAN layer (t=5 s). When placed in water at 40°C, it contracts because the temperature is higher than the LCST temperature of PNIPAM, while the PAN fiber layer does not change volume when the temperature changes. The tightly bonded double-layer electrospun membranes establish a new expansion mismatch, generating internal stress that triggers the rapid bending of the double-layer membrane in the opposite direction (t=3 s).

[0031] 8. The electrospun double-layer film actuator prepared by this invention can be used as a humidity-responsive switch under a humidity gradient and has the ability to perform work. In the future, it can be considered as an energy conversion device. Humidity is everywhere in the air. If we can realize the conversion of humidity in the air into other forms of energy for storage in an era where new energy sources are urgently needed, it will be very meaningful. Attached Figure Description

[0032] Figure 1 : Schematic diagram of the braking process of the temperature and humidity response actuator based on PNIPAM / PAN double-layer electrospun film (a is the temperature response mechanism diagram, b is the humidity response mechanism diagram).

[0033] Figure 2 Images and corresponding SEM images of electrospun PAN and PNIPAM films before and after curing at 160℃ (Figures a and b show the morphology of the electrospun PAN film before curing; Figures c and d show the morphology of the electrospun PAN film after curing; Figures e and f show the morphology of the electrospun PNIPAM film before curing; Figures g and h show the morphology of the electrospun PNIPAM film after curing; the scale bar in Figures a, c, e, and g is 10 mm, and the scale bar in Figures b, d, f, and h is 5 μm).

[0034] Figure 3Photographs of the electrospun PNIPAM / PAN bilayer film before and after curing at 160℃, and SEM images of its cross-section after the reaction (where, Figure a is the SEM image of the cross-section before curing; Figures b, c, d, and e are the SEM images of the cross-section after curing; the scale bars in Figures a and b are 10 mm, in d is 5 μm, and in c and e is 2 μm).

[0035] Figure 4 Schematic diagram of PNIPAM curing reaction;

[0036] Figure 5 Infrared spectra of Ope POSS, PNIPAM, non-cured PNIPAM mixture, and Cured PNIPAM mixture;

[0037] Figure 6 Infrared spectra of PAN before and after treatment at 160 °C for 4 h;

[0038] Figure 7 Solubility test results of PNIPAM film in water at 20℃ and 40℃ before and after curing reaction;

[0039] Figure 8 The driving process of the PNIPAM / PAN bilayer membrane's response to humidity;

[0040] Figure 9 Example diagram of a light switch responding to humidity using a PNIPAM / PAN double-layer film (where the light is off for 0~3 s and 10~11 s, and on for 4~9 s).

[0041] Figure 10 : Expansion and contraction graphs of PAN and PNIPAM membranes in water at 20 °C and 40 °C (all scales are 5 mm);

[0042] Figure 11 : Expansion rate of PNIPAM and PAN membranes in water at 20 °C and 40 °C;

[0043] Figure 12 : Response behavior of electrospun PNIPAM / PAN bilayer membrane to temperature (where the bilayer membrane in water at 20 ℃ completes actuation within 5s, and the bilayer membrane in water at 40 ℃ completes actuation within 3s). Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0045] Example 1: Method for fabricating a humidity and temperature responsive actuator

[0046] (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to the mass ratio (N-isopropylacrylamide: octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazole = 100:15:0.3. Dissolve the polymer in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A.

[0047] (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B.

[0048] (3) Adjust the voltage of the electrospinning instrument to 20 kV, the receiving distance to 15 cm, the pushing rate to 1.2 mL / h, and the receiver rotation speed to 30 r / min. Electrospinning deposits are made on the tin foil covering the surface of the roller.

[0049] (4) First, electrospin the polyacrylonitrile solution for 20 min, then replace the solution with a poly(N-isopropylacrylamide) solution and electrospin for 60 min, that is, continue to electrospin a poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film; then put it into an oven at 160℃ for 4 h to cure, and obtain a double-layer electrospun fiber film actuator.

[0050] Example 2: Method for fabricating a humidity and temperature responsive actuator

[0051] (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to the mass ratio (N-isopropylacrylamide: octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazole = 100:15:0.3. Dissolve the polymer in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A.

[0052] (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B.

[0053] (3) Adjust the voltage of the electrospinning instrument to 18 kV, the receiving distance to 13 cm, the pushing rate to 1.0 mL / h, and the receiver rotation speed to 25 r / min. Electrospinning deposits are made on the tin foil covering the surface of the roller.

[0054] (4) First, electrospin the polyacrylonitrile solution for 20 min, then replace the solution with a poly(N-isopropylacrylamide) solution and electrospin for 60 min, that is, continue to electrospin a poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film; then put it into an oven at 150℃ for 3 h to cure, and obtain a double-layer electrospun fiber film actuator.

[0055] Example 3: Method for fabricating a humidity and temperature responsive actuator

[0056] (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to the mass ratio (N-isopropylacrylamide: octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazole = 100:15:0.3. Dissolve the polymer in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A.

[0057] (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B.

[0058] (3) Adjust the voltage of the electrospinning instrument to 19 kV, the receiving distance to 14 cm, the pushing rate to 1.1 mL / h, and the receiver rotation speed to 27 r / min. Electrospinning deposits are made on the tin foil covering the surface of the roller.

[0059] (4) First, electrospin the polyacrylonitrile solution for 20 min, then replace the solution with a poly(N-isopropylacrylamide) solution and electrospin for 60 min, that is, continue to electrospin a poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film; then put it into an oven at 170℃ for 5 h to cure, and obtain a double-layer electrospun fiber film actuator.

[0060] Example 4: Method for fabricating a humidity and temperature responsive actuator

[0061] (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to the mass ratio (N-isopropylacrylamide: octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazole = 100:15:0.3. Dissolve the polymer in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A.

[0062] (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B.

[0063] (3) Adjust the voltage of the electrospinning instrument to 20 kV, the receiving distance to 14 cm, the pushing rate to 1.0 mL / h, and the receiver rotation speed to 30 r / min. Electrospinning deposits are made on the tin foil covering the surface of the roller.

[0064] (4) First, electrospin the polyacrylonitrile solution for 20 min, then replace the solution with a poly(N-isopropylacrylamide) solution and electrospin for 60 min, that is, continue to electrospin a poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film; then put it into an oven at 155℃ for 3.5 h to cure, and obtain a double-layer electrospun fiber film actuator.

[0065] Example 5: Method for fabricating a humidity and temperature responsive actuator

[0066] (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to the mass ratio (N-isopropylacrylamide: octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazole = 100:15:0.3. Dissolve the polymer in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A.

[0067] (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B.

[0068] (3) Adjust the voltage of the electrospinning instrument to 20 kV, the receiving distance to 15 cm, the pushing rate to 1.1 mL / h, and the receiver rotation speed to 25 r / min. Electrospinning deposits are made on the tin foil covering the surface of the roller.

[0069] (4) First, electrospin the polyacrylonitrile solution for 20 min, then replace the solution with a poly(N-isopropylacrylamide) solution and electrospin for 60 min, that is, continue to electrospin a poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film; then put it into an oven at 165℃ for 4.5 h to cure, and obtain a double-layer electrospun fiber film actuator.

[0070] To further verify the feasibility of the present invention, the inventors conducted a series of experiments, the steps of which are as follows:

[0071] I. Experimental Section of the Actuator Based on Temperature and Humidity Response

[0072] 1. Main raw materials and reagents

[0073] The specifications of the main raw materials and reagents used in the experiment are shown in Table 1.

[0074] .

[0075] 2. Main instruments and equipment

[0076] The main instruments and equipment used in the experiment are shown in Table 2.

[0077] .

[0078] 3. Testing and Characterization

[0079] 3.1 Fourier Transmission Infrared Spectroscopy (FT-IR)

[0080] The Fourier transform infrared spectrometer (Thermo Scientific Nicolet iS10) is used to test the structure of raw materials and mixtures before and after the curing reaction, scanning wavelengths from 400 to 4000 cm⁻¹. -1 The resolution is 4 cm. -1 The number of scans was 32.

[0081] 3.2 Scanning Electron Microscopy (SEM)

[0082] The microstructure of the electrospun fiber membranes prepared in the experiment was analyzed using a Nova Nano SEM 450 from FEI Corporation, USA, at a voltage of 5.00 kV. The samples were sputter-coated with gold before testing.

[0083] 3.3 Characterization of the swelling rate S of the electrospun membrane in water along its length.

[0084] Electrospun fiber membranes with dimensions of 20 mm x 5 mm were cut and placed in water at 20℃ and 40℃ (30 s) respectively to test the change in length after swelling equilibrium. S = (L-L0) / L0, where L is the length of the sample after swelling or shrinking, and L0 is the initial length.

[0085] 3.4 Solubility Test

[0086] Solubility test of PNIPAM before and after curing at 160℃: fiber samples before and after curing were placed in beakers containing water at 20℃, stirred for 30 min and observed for dissolution, and then the temperature was raised to 40℃ and the phenomenon was observed.

[0087] 3.5 Humidity Response Test

[0088] At room temperature, a double-layer electrospun membrane (20 mm x 8 mm x 55 μm) was cut and placed on the experimental table. A finger was brought close to the surface of the membrane but not in contact with it. The membrane was observed to bend to its highest point. Then the finger was removed and the membrane was observed to return to its flat shape.

[0089] 3.6 Example of a humidity-responsive switch

[0090] Two 1.5V dry batteries are used as the power source for the light bulb. The wires are fixed to the electrospun membrane. When a finger approaches the membrane, the membrane bends due to the humidity gradient on the finger surface, causing the wires to make contact and form a circuit to light up the bulb. Then, when the finger is removed, the membrane returns to its original position, the wires disconnect, and the bulb goes out.

[0091] 3.7 Photo and video shooting

[0092] The driving process was filmed using a Sony NEX-5R camera from Japan.

[0093] 4. Fabrication of PAN / PNIPAM double-layer electrospun film actuator

[0094] Prepare a polymer solution with a mass ratio of PNIPAM:Ope POSS:EMI = 100:15:0.3. Dissolve 10% of the PAN in a mixed solution with a volume ratio of DMF:THF = 1:1. Stir for 12 h to obtain a clear and transparent solution. Weigh out PAN and dissolve it in DMF to prepare a 10% solution. Stir for 12 h to obtain a pale yellow and transparent solution. Adjust the electrospinning instrument voltage to 20 kV, the receiving distance to 15 cm, the feed rate to 1.2 mL / h, and the receiver rotation speed to 30 r / min. Electrospin the deposited material onto the tin foil covering the roller surface. First, electrospin the PAN for 20 min, then replace the solution with PNIPAM solution and continue electrospinning a layer of PNIPAM film on the surface of the electrospun PAN film (1 h). Then, place it in an oven at 160℃ for 4 h to cure and obtain a double-layer electrospun fiber membrane actuator.

[0095] 5. Results and Discussion

[0096] 5.1 Design scheme for a rapid-response electrospun membrane actuator for humidity and temperature, see [link / reference]. Figure 1 .

[0097] like Figure 1 As shown in Figure a, the bilayer actuator consists of sequentially electrospun PAN fiber layers and PNIPAM fiber layers. PNIPAM is a temperature-sensitive polymer; when placed in water, it shrinks above its LCST temperature and expands below it. The PAN fiber layers, however, are not temperature-responsive and do not change volume with temperature variations. When the ambient temperature fluctuates around the LCST temperature of PNIPAM, the tightly bonded bilayer electrospun membrane experiences expansion mismatch, generating internal stress that activates the braking behavior of the bilayer membrane. Compared to traditional solution-polymerized hydrogel actuators, the electrospun fiber membrane has a larger specific surface area, making its water exchange process exceptionally rapid, thus accelerating the actuation behavior of the bilayer membrane and achieving a temperature-responsive hydrogel actuator. Figure 1In step b, the amide groups on the PNIPAM molecular chain give it a certain degree of hygroscopicity, allowing for rapid adsorption and desorption of gaseous water molecules in the air. During water molecule adsorption, the PNIPAM layer expands; during desorption, it contracts to return to its initial state. The expansion rate increases with increasing humidity. When a humidity gradient exists in the air, the PNIPAM film forms an expansion rate gradient distribution consistent with the humidity gradient along its thickness direction, causing expansion mismatch and internal stress. Since the PNIPAM film is hydrophobic, its volume does not respond to water vapor, thus inducing the driving behavior of the bilayer film. As a result, the bilayer electrospun film achieves a dual rapid response to humidity gradients and temperature.

[0098] 5.2 Microscopic morphology characterization (SEM)

[0099] like Figure 2 As shown, the diameters of electrospun PAN and PNIPAM fibers are 205-300 nm and 560-870 nm, respectively, and their surfaces are smooth and flat. Compared with PNIPAM gels formed by traditional solution polymerization, this provides the material with a large specific surface area, which can effectively promote the mutual exchange process with the environmental solution during braking. Figure 2 The term "ad" refers to an electrospun PAN fiber membrane. Results showed no significant changes in its macroscopic and microscopic dimensions and appearance before and after curing at 160℃. Figure 2 (ad), and no changes in molecular structure were observed in the FT-IR spectra before and after PAN heating (ad). Figure 6 This indicates that the PAN fibers were not affected during the heating process. Figure 2 In this context, ef refers to an electrospun PNIPAM fiber membrane, whose macroscopic size and state show no significant changes before and after the curing reaction. Figure 2 (e, g), and its microfibers after the curing reaction ( Figure 2 In the f and h sections, partial fusion occurs between the surface parts of the electrospun fibers, and the diameter of these fibers increases slightly, which enhances their stability in water. The remaining fibers show no significant changes.

[0100] like Figure 3 As shown in a and b, the size and appearance of the double-layer electrospun film before and after curing did not change significantly. The SEM images of its cross-section after curing are shown in the figures. Figure 3 As can be seen in c and d), at the interface where the double-layer fibers contact, some PAN fibers are embedded in the PNIPAM layer. At the same time, the electrospun PAN fibers and PNIPAM fibers form a tight entanglement with each other, and the double-layer contact is good, which provides a good foundation for the subsequent braking process.

[0101] 5.3 Infrared Spectroscopy (FT-IR)

[0102] like Figure 4 As shown, the crosslinking reaction during the curing process of PNIPAM nanofibers exhibits low reactivity of HN in N-isopropylacrylamide, even in its reaction with epoxy groups. However, under the catalysis of the strong base 2-ethyl-4-methylimidazole (EMI), the reactivity of HN with epoxy groups is enhanced, leading to improved crosslinking efficiency. Using commercially available PNIPAM and Ope POSS as raw materials, under EMI catalyst and heating conditions, the epoxy groups on Ope POSS undergo an epoxy ring-opening reaction with the active hydrogen on the secondary amine of the PNIPAM molecular chain. One Ope POSS contains eight epoxy groups, and the PNIPAM molecular chain contains multifunctional secondary amine groups, thus forming a crosslinked system after the reaction. This avoids the complex chemical modification process of PNIPAM or its monomers before electrospinning, which is necessary for further crosslinking after spinning in traditional PNIPAM electrospun films.

[0103] Figure 5 The results showed that, prior to the curing reaction, epoxy groups appeared at 911 cm⁻¹ in the mixture of pure Ope POSS and Non-cured Ope POSS / PNIPAM. -1 The characteristic peak at this point was observed, but after reacting at 160 °C for 4 h, the peak of the epoxy group disappeared in the cured Ope POSS / PNIPAM mixture (as shown in the magnified inset in the upper left corner), confirming the ring-opening reaction of the epoxy groups in Ope POSS and thus determining the formation of the cross-linked structure. Next, the macroscopic characteristics of the cross-linked structure were characterized. (In the figure, Non-cured and Cured represent the curves of the Ope POSS / PNIPAM mixture before and after curing.)

[0104] Figure 6 The results show that the chemical structure of PAN material remains stable and does not undergo significant changes during the PNIPAM heating and curing process.

[0105] 5.4 Solubility Test of Cured PNIPAM Electrospun Film

[0106] like Figure 7 As shown in a and b, because the uncured PNIPAM electrospun fibers have a linear molecular structure, they swell and dissolve rapidly when placed in water at 20°C, forming a clear and transparent solution. At 40°C, above its LCST, a phase transition can be observed, and the solution's transparency rapidly decreases, turning a pale white color. Figure 7In diagrams c and d, it can be observed that the cured PNIPAM membrane swells in water at 20°C to form a transparent gel film, but does not dissolve. When the temperature rises to 40°C, above its LCST, the PNIPAM molecules undergo a phase transition, and the molecular chain contraction causes a macroscopic reduction in the volume of the fiber membrane. This further confirms that an epoxy ring-opening reaction occurs between PNIPAM molecules and Ope POSS molecules to form a three-dimensional cross-linked insoluble network. Thus, the cured PNIPAM electrospun membrane can remain stable in water and successfully complete the temperature-responsive phase transition behavior, laying the foundation for the realization of rapid response-driven technology.

[0107] 5.5 Humidity Response-Driven Behavior of Electrospun Films

[0108] The PNIPAM molecular chain contains numerous hydrophilic amide groups, which can interact with gaseous water molecules, giving the PNIPAM electrospun membrane a rapid adsorption and desorption capacity for water vapor. When the electrospun membrane adsorbs water vapor, it expands; upon desorption, it contracts. The amount of adsorbed water vapor increases with increasing humidity; therefore, the higher the humidity, the more water vapor is adsorbed, and the greater the expansion rate. Thus, if a humidity gradient exists in the air, the PNIPAM membrane placed within it will form an expansion rate distribution structure in the thickness direction consistent with the humidity gradient, creating an expansion mismatch that triggers bending actuation behavior. Figure 8 As shown, a natural humidity gradient field exists on the surface of our fingers, with higher humidity closer to the finger. When our fingers approach the electrospun membrane, the membrane undergoes bending actuation within 6 seconds. Removing the finger causes the membrane to return to its initial flat state within 12 seconds due to the disappearance of the humidity gradient. This actuation behavior is completely reversible, triggered by the establishment of the humidity gradient and recovering when the gradient disappears.

[0109] 5.6 Example of a humidity-responsive switch for electrospun film

[0110] The experimental results above show that the electrospun membrane can be driven under a humidity gradient. Therefore, we designed a humidity-responsive switch to demonstrate its potential energy conversion function. Figure 9 As shown, initially the wire is fixed to the membrane surface, and the circuit is in an open state. When a finger approaches the membrane surface, driven by the humidity gradient, the electrospun membrane bends after 4 seconds, causing the disconnected wire to come together and form a circuit, thus lighting the light. When the finger is removed for 2 seconds, the wire separates as the electrospun membrane recovers, forming an open circuit, and the light goes out.

[0111] 5.7 Test of swelling rate of electrospun membrane in water

[0112] like Figure 10As shown in ac, the PAN electrospun film has no temperature response, and its size does not change significantly with temperature changes, remaining the same as the initial sample. Its expansion rate is -0.17% (20 ℃) ​​and 0% (40 ℃). Figure 10 The data shows that, due to the thermosensitivity of PNIPAM, its electrospun film swells upon absorbing water at 20°C (less than LCST = 31°C) and shrinks when the temperature rises to 40°C (greater than LCST), with swelling rates of 9.17% (20°C) and -48.33% (40°C) (see relevant swelling rate data). Figure 11 ).

[0113] 5.8 Temperature-Responsive Behavior of Electrospun Films

[0114] like Figure 12 As shown, when the double-layer actuator is placed in water at 20°C, it expands due to the temperature being lower than the LCST temperature of PNIPAM (31°C). The PAN fiber layer, however, does not respond to temperature changes. This expansion mismatch in the tightly bonded double-layer electrospun membrane generates internal stress, activating rapid bending behavior of the double-layer membrane towards the PAN layer (t=5 s). When placed in water at 40°C, it contracts due to the temperature being higher than the LCST temperature of PNIPAM. The PAN fiber layer does not change volume with temperature changes. This new expansion mismatch in the tightly bonded double-layer electrospun membrane generates internal stress, inducing rapid bending of the double-layer membrane in the opposite direction (t=3 s).

[0115] 6. Summary

[0116] By combining electrospinning technology with temperature-inert PAN and temperature-sensitive PNIPAM, the spun fiber diameters of 205-300 nm and 560-870 nm, respectively, significantly improve the specific surface area and porosity of the hydrogel, thereby achieving rapid temperature-responsive actuation (3 s) and recovery (5 s) behavior, whereas actuation of traditional bulk hydrogel materials often takes tens of minutes. Simultaneously, the amide groups on the PNIPAM chains endow the bilayer membrane with humidity-responsive properties, allowing it to be used as a humidity-responsive switch. This electrospun fiber membrane endows the gel with rapid response and multiple responsiveness, expanding the gel's application range.

[0117] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, some modifications or improvements can be made to it based on the present invention, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A temperature and humidity responsive driver characterized by comprising: The actuator is a double-layer electrospun film actuator, which consists of a sequentially electrospun polyacrylonitrile fiber layer and a poly(N-isopropylacrylamide) fiber layer; The polyacrylonitrile fiber layer is prepared by stirring and electrospinning using polyacrylonitrile as raw material and N,N-dimethylformamide as solvent; the poly(N-isopropylacrylamide) fiber layer is prepared by stirring, electrospinning and curing using poly(N-isopropylacrylamide), 2-ethyl-4-methylimidazolium and octaglycidyl polyhedral oligomeric silsesquioxane as raw materials and N,N-dimethylformamide and tetrahydrofuran as solvent. The diameter of the polyacrylonitrile fiber layer is 205-300 nm; the diameter of the poly(N-isopropylacrylamide) fiber layer is 560-870 nm. The method for preparing the temperature and humidity responsive actuator includes the following steps: (1) Weigh out poly(N-isopropylacrylamide), octaglycidyl polyhedral oligomeric silsesquioxane, and 2-ethyl-4-methylimidazole, and prepare the polymer according to a certain mass ratio. Dissolve it in a mixed solution of N,N-dimethylformamide and tetrahydrofuran at a mass fraction of 10%. After stirring for 12 h, a clear and transparent solution is obtained, which is mixed solution A. (2) Weigh out polyacrylonitrile and dissolve it in N,N-dimethylformamide to prepare a 10% solution by mass. Stir for 12 h to fully dissolve it into a light yellow transparent solution, and obtain mixed solution B. (3) Adjust the settings of the electrospinning instrument and electrospin the deposits onto the tin foil covering the surface of the roller; (4) First, electrospin the mixed solution B for 20 min, then replace the mixed solution B with the mixed solution A for 60 min, that is, continue to electrospin a layer of poly(N-isopropylacrylamide) film on the surface of the electrospun polyacrylonitrile film, and then put it in the oven to cure, and obtain a double-layer electrospun fiber film driver composed of sequentially electrospun polyacrylonitrile fiber layer and poly(N-isopropylacrylamide) fiber layer. The mass ratio mentioned in step (1) is: poly(N-isopropylacrylamide): octaglycidyl polyhedral oligomeric silsesquioxane: 2-ethyl-4-methylimidazolium = 100:15:0.3; The volume ratio of dimethylformamide to tetrahydrofuran in step (1) is: dimethylformamide: tetrahydrofuran = 1:1; The parameters set in step (3) are: voltage 20 kV, receiving distance 15 cm, feeding rate 1.2 mL / h, and receiver rotation speed 30 r / min; The curing conditions described in step (4) are: curing temperature 160℃ and curing time 4 h.

2. The temperature and humidity responsive actuator according to claim 1, characterized in that, The N,N-dimethylformamide mentioned in step (2) can also be replaced with N,N-dimethylacetamide.

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