Bio-based hydrophobic monomer, triple-shape memory hydrogel and application thereof

Abstract

This invention discloses a bio-based hydrophobic monomer, a triple shape memory hydrogel, and their applications. The preparation method of the bio-based hydrophobic monomer includes the following steps: In an organic solvent, dehydrorosinyl chloride and N-(2-hydroxyethyl)-2-methyl-2-acrylamide are mixed and reacted to obtain the bio-based hydrophobic monomer. This invention prepares a novel bio-based hydrophobic monomer and applies it to hydrogel preparation, obtaining a hydrogel with high strength and triple shape memory function, which can be used for rapid and visual detection of Fe in water. 3+ Concentration and fabrication of large strain sensors.

Description

Technical Field

[0001] This invention relates to the field of shape memory hydrogel technology, specifically to a bio-based hydrophobic monomer, a triple shape memory hydrogel, and their applications. Background Technology

[0002] Hydrogels are a class of materials with three-dimensional polymer networks, exhibiting high water absorption and good biocompatibility, and possessing broad application potential in fields such as environmental monitoring, biomedicine, and soft robotics. Among them, smart responsive hydrogels can sense changes in the external environment and respond accordingly. For example, hydrogels with shape memory function can change shape under stimuli such as temperature, humidity, pH, solvent, magnetic field, or electric field, demonstrating their promising application prospects in numerous fields.

[0003] Existing hydrogels with shape memory function suffer from three major problems: First, their mechanical properties are generally poor, making them unable to withstand physical impacts and repeated shape memory cycles in practical applications, affecting the long-term stable operation of sensors and preventing their use in fields requiring large deformations. Second, their shape memory behavior with solutions or solvents requires a long response time, hindering rapid detection. Third, current technologies only report high-strength conductive hydrogels with dual shape memory functions, with few reports on conductive hydrogels with triple shape memory functions. Triple shape memory could be applied to soft robots to achieve complex grasping actions, or to intelligent drug delivery scaffolds and information encryption. These three problems are key factors hindering the engineering application of intelligent hydrogels; therefore, developing high-strength hydrogels with triple shape memory functions has significant application value. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a bio-based hydrophobic monomer, a triple shape memory hydrogel, and their applications. A novel bio-based hydrophobic monomer is prepared and applied to hydrogel fabrication, resulting in a hydrogel with high strength and triple shape memory function. This hydrogel can be used for rapid and visual detection of Fe in water. 3+ Concentration and fabrication of large strain sensors.

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a bio-based hydrophobic monomer having the following structure:

[0006] .

[0007] A second aspect of this invention provides a method for preparing the bio-based hydrophobic monomer described in the first aspect, comprising the following steps:

[0008] In an organic solvent, compound 1 (dehydrorosinyl chloride) and compound 2 (N-(2-hydroxyethyl)-2-methyl-2-acrylamide) react to obtain the bio-based hydrophobic monomer (DH); wherein the structural formulas of compound 1 and compound 2 are:

[0009] .

[0010] Furthermore, the molar ratio of the compound of formula 1 to the compound of formula 2 is 1:(0.5-1.5).

[0011] And / or, the reaction is carried out at a temperature of 20-30°C for a time of 4-8 hours.

[0012] A third aspect of this invention provides a method for preparing a hydrogel with triple shape memory function, comprising the following steps:

[0013] S1. Dissolve sodium chloride and emulsifier in deionized water, and add the bio-based hydrophobic monomer described in the first aspect to obtain a homogeneous solution;

[0014] S2. Add acrylamide, acrylic acid, nano gold dispersion, crosslinking agent and initiator, heat to react and obtain primary hydrogel;

[0015] S3. The primary hydrogel is sequentially immersed in ferric chloride solution and deionized water to obtain the hydrogel with triple shape memory function.

[0016] The hydrogel with triple shape memory function obtained in this invention has a "quadruple synergistic network structure":

[0017] The first layer of network is a chemically covalently cross-linked network formed by the polymerization of the bio-based hydrophobic monomer (DH), acrylamide (AM), acrylic acid (AA) and cross-linking agent described in the first aspect.

[0018] The second network is a physical microphase separation network, which originates from the fused aliphatic and benzene rings and hydrophobic groups such as alkyl groups on the DH molecular chain. Their steric hindrance and hydrophobicity lead to the formation of hydrophobic microregions in the polymer chain segments, which serve as physical crosslinking points and run through the entire covalent network.

[0019] The third network originates from the gold nanoparticles. The negative charge of the citrate ions on their surface interacts with the carboxyl groups of acrylic acid and the amide groups of DH through electrostatic attraction and hydrogen bonding. Simultaneously, the negative charge of the citrate ions on the gold nanoparticles causes electrostatic repulsion between the particles. These interactions not only prevent the aggregation of the gold nanoparticles but also ensure that their distribution coincides with the physical cross-linking points, achieving in-situ anchoring at the interface of the hydrophobic microregions and forming a unique "polymer chain-gold nanoparticle-polymer chain" structure. The gold nanoparticles also act as additional physical cross-linking points.

[0020] The fourth network is a dynamic ionic cross-linking network, composed of Fe 3+ It is formed by coordination bonds with carboxyl groups in the hydrogel (from citrate groups on the surface of acrylic acid or gold nanoparticles).

[0021] The quadruple network structure of this invention is not only denser, providing a high-strength "fixed phase," but also possesses an energy dissipation mechanism, allowing the network to store more strain energy and exhibiting a "combination of rigidity and flexibility." The former endows the hydrogel with a high shape fixation rate, while the latter endows the hydrogel with a greater recovery driving force, manifested as a faster recovery speed and a higher recovery rate, laying the foundation for the prepared hydrogel to possess high strength and triple shape memory function.

[0022] The hydrogel of this invention, possessing triple shape memory function, exhibits outstanding tensile properties, including high tensile strength (8.1 MPa), high elongation at break (2650%), and high toughness (156.81 MJ / m). 3 This indicates that it can achieve a large-scale, reliable deformation response in applications, and can withstand physical shocks and repeated shape memory cycles in the application environment, ensuring long-term stable operation of the application and laying the foundation for designing visual indicators or mechanically driven sensors based on large deformation.

[0023] This invention relates to a hydrogel with triple shape memory function that can temporarily fix its shape in an iron ion solution within minutes. The concentration of the iron ion solution to be tested can be directly determined based on the amount of change in the hydrogel's temporary shape, enabling rapid and visual detection of iron ion concentration in water. Furthermore, the hydrogel can permanently recover its shape after immersion in a disodium ethylenediaminetetraacetate solution for several minutes to half an hour. This rapid detection is mainly due to the low-barrier exchange mechanism of the hydrogel's "dynamic ion coordination network" and the high-permeability channels provided by its "physical microphase separation network."

[0024] First, the detection mechanism is Fe 3+ The combination and dissociation of Fe 3+ With carboxyl group (-COO) - ), amide group (-CONH) - The coordination bonds between the nano-gold surface ligands and the nano-gold ligands are essentially a dynamic non-covalent bond or supramolecular interaction. They can undergo low-barrier exchange, and the plasma effect (LSPR) of the nano-gold surface in the hydrogel of this invention can accelerate electron transfer, so that the change of coordination environment is completed quickly, thus manifesting as rapid changes in color and shape on a macroscopic scale.

[0025] Secondly, the hydrophobic microdomains construct "molecular channels," providing the physical structure for rapid mass transport. As mentioned earlier, the methyl groups of DH on the molecular chain induce the formation of nanoscale hydrophobic microdomains, which, on the one hand, in Fe... 3+During the diffusion process of sodium oxalate or disodium tetraacetate, a large number of water molecules are repelled, reducing the resistance of the solvation layer to ion diffusion. On the other hand, the hydrophobic environment also affects the positively charged Fe... 3+ It has a certain enrichment effect, making Fe 3+ It can quickly gather around the ligand.

[0026] Third, the high-concentration gold nanoparticles prepared by this invention provide a large reaction interface, allowing Fe... 3+ Disodium oxalate can rapidly coordinate and dissociate with ligands on the surface of gold nanoparticles. Furthermore, due to the plasma effect on the surface of the gold nanoparticles, minute changes in surface concentration are exponentially amplified into significant color changes, allowing for "visual detection" that can be discerned by the naked eye within minutes. In addition to the visual detection judgment provided by shape memory, color judgment is also offered as a basis.

[0027] Furthermore, the preparation method of the gold nanoparticle dispersion is as follows: chloroauric acid, sodium citrate, and deionized water are mixed and reacted at 100-120°C. Preferably, the concentration of the gold nanoparticle dispersion is 5-20 mg / mL.

[0028] Furthermore, the molar ratio of the bio-based hydrophobic monomer, acrylamide, and acrylic acid is (0.5-2):100:(5-25). Preferably, the mass ratio of gold nanoparticles to acrylamide is (5-50):2000.

[0029] Furthermore, the amount of the crosslinking agent added is 0.01-0.5% of the total molar amount of the bio-based hydrophobic monomer, acrylamide, and acrylic acid; the amount of the initiator added is 0.1-1% of the total molar amount of the bio-based hydrophobic monomer, acrylamide, and acrylic acid.

[0030] Furthermore, in S3, the concentration of the ferric chloride solution is 0.01-0.1 mol / L, the immersion time in the ferric chloride solution is 6-24 h, and the immersion time in deionized water is more than 24 h.

[0031] Furthermore, in S2, the heating reaction is carried out at a temperature of 60-70°C for 8-15 hours.

[0032] The fourth aspect of this invention provides a method for preparing a hydrogel with triple shape memory function as described in the third aspect.

[0033] The fifth aspect of this invention provides the application of the hydrogel with triple shape memory function described in the fourth aspect in strain sensors and the detection of iron ion concentration in water.

[0034] The beneficial effects of this invention are:

[0035] This invention prepares a novel bio-based hydrophobic monomer and applies it to the preparation of hydrogels, obtaining hydrogels with high strength and triple shape memory function. The hydrogels have a "quadruple synergistic network structure", which is not only more compact and provides a high-strength "fixed phase", but also has an energy dissipation mechanism, which allows more strain energy to be stored inside the network, exhibiting the characteristics of "rigidity and flexibility".

[0036] The hydrogel with triple shape memory function of this invention has outstanding tensile properties. It can achieve a large range of reliable deformation response in applications and can withstand physical impacts and repeated shape memory cycles in the application environment, ensuring long-term stable operation. This lays the foundation for designing visual indicators or mechanically driven sensors based on large deformation.

[0037] The hydrogel of this invention, which has a triple shape memory function, can fix a temporary shape in an iron ion solution in just a few minutes. The concentration of the iron ion solution to be tested can be directly determined based on the amount of change in the temporary shape of the hydrogel, so as to achieve rapid and visual detection of the concentration of iron ions in water. It can also restore its permanent shape after soaking in a disodium ethylenediaminetetraacetate solution for a few minutes to half an hour. Attached Figure Description

[0038] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of the synthesis of DH in Example 1;

[0040] Figure 2 This is the 1H NMR spectrum of DH in Example 1;

[0041] Figure 3 This is the carbon NMR spectrum of DH in Example 1;

[0042] Figure 4 This is the high-resolution mass spectrum of DH in Example 1;

[0043] Figure 5 This is a photograph of the wine-red gold nanoparticle dispersion prepared in step (2) of Example 1;

[0044] Figure 6 This is the UV-Vis absorption spectrum of the gold nanoparticle dispersion in Example 1;

[0045] Figure 7 These are scanning electron microscope images of the gold nanoparticle dispersion in Example 1;

[0046] Figure 8These are the tensile stress-strain curves of the hydrogels obtained in the examples and comparative examples;

[0047] Figure 9 The bar chart shows the toughness of the hydrogels obtained in the examples and comparative examples;

[0048] Figure 10 This is a digital photograph of FAP20 based on the shape memory behavior of iron ion solutions;

[0049] Figure 11 This is a digital photograph of the shape memory behavior of FAP20 based on ethanol and N,N'-dimethylformamide;

[0050] Figure 12 This is a digital photograph of FAP20 based on the triple shape memory behavior of iron ion solution and ethanol;

[0051] Figure 13 This is a digital photograph of the triple shape memory behavior of the hydrogel FAPAN obtained in Comparative Example 1;

[0052] Figure 14 This is a digital image of the triple shape memory behavior of the hydrogel FP24 obtained in Comparative Example 2;

[0053] Figure 15 This is a digital image of the shape memory behavior of the hydrogel PAD obtained in Comparative Example 3;

[0054] Figure 16 The conductivity tests are performed on the hydrogels obtained in the examples and comparative examples;

[0055] Figure 17 The shape fixation and recovery behavior of FAP20 when detecting 0.01 mol / L iron ions;

[0056] Figure 18 The shape fixation rate and shape recovery rate were calculated for the detection of 0.01 mol / L iron ions.

[0057] Figure 19 The shape fixation and recovery behavior of FAP20 when detecting 0.1 mol / L iron ions;

[0058] Figure 20 The graph shows the relationship between the resistance change rate (ΔR / R0) and strain of FAP24 hydrogel applied to a strain sensor.

[0059] Figure 21 The graph shows the relationship between the rate of change of resistance (ΔR / R0) of hydrogel FAP24 applied to strain sensors under 10% and 50% strain and strain.

[0060] Figure 22The graph shows the relationship between the rate of change of resistance (ΔR / R0) of hydrogel FAP24 applied to strain sensors under cyclic tensile strain of 100% and 200% and strain.

[0061] Figure 23 The graph shows the rate of change of electrical resistance (ΔR / R0) of hydrogel FAP24 when joint strain is detected in the finger area;

[0062] Figure 24 The graph shows the rate of change of resistance (ΔR / R0) of hydrogel FAP24 at the wrist when joint strain is detected. Detailed Implementation

[0063] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0064] Example 1

[0065] This embodiment relates to a method for preparing a hydrogel with triple shape memory function, comprising the following steps:

[0066] (1) Preparation of bio-based hydrophobic monomers

[0067] 5.217 g of compound 1 (dehydrorosinyl chloride) was dissolved in 15.00 mL of dichloromethane to obtain solution A. 2.150 g of compound 2 (N-(2-hydroxyethyl)-2-methyl-2-acrylamide) and 2.526 g of triethylamine were dissolved in 10.00 mL of dichloromethane to obtain solution B. Under N2 protection at 3 °C, solution A was slowly added dropwise to solution B over 20 min; the reaction was then continued at 25 °C for 6 h. After the reaction was complete, the mixture was washed with 5% sodium bicarbonate solution, separated, and the organic phase was collected and dried over anhydrous sodium sulfate to obtain dehydrorosinyl methylacrylamide, denoted as DH.

[0068] (2) Preparation of nano-gold dispersion

[0069] 1 mL of chloroauric acid aqueous solution (concentration 1 mmol / L) and 99 mL of deionized water were added to a 250 mL three-necked flask and stirred and refluxed at 110 °C for 40 min. 10 mL of 1% sodium citrate aqueous solution was quickly added, and stirring was continued at 110 °C for 20 min to obtain a wine-red liquid. Heating was stopped, and the mixture was cooled and stirred to room temperature. 100 mL of the gold nanoparticle dispersion was centrifuged at 11000 r / min for 30 min. The supernatant was collected, and the remaining portion was diluted to 10 mL and ultrasonically dispersed to obtain a high-concentration (16 mg / mL) wine-red gold nanoparticle dispersion, which was stored at 4 °C for later use.

[0070] (3) Preparation of hydrogels

[0071] At 25°C, 0.292 g of sodium chloride was added to 9.00 mL of deionized water and stirred until dissolved. Then, 1.200 g of emulsifier cetyltrimethylammonium bromide was added and stirred until homogeneous to obtain a homogeneous solution C. 0.115 g of DH synthesized in step (1) was added to solution C and stirred for 6 h to form a homogeneous solution D. Then, 2.000 g of acrylamide, 0.304 g of acrylic acid, 1.00 mL of the nano-gold dispersion synthesized in step (2) and 5.0 mg of crosslinking agent N,N'-methylenebisacrylamide were added to homogeneous solution D in sequence and stirred until homogeneous. Then, 0.0369 g of initiator ammonium persulfate was added and stirred for another 10 min to obtain hydrogel precursor solution E.

[0072] The hydrogel precursor solution E was poured into a mold and polymerized at 65°C for 12 hours to obtain a hydrogel, denoted as hydrogel G. Hydrogel G was immersed in a 0.05 mol / L ferric chloride aqueous solution for 20 hours; then immersed in deionized water for 24 hours to obtain a high-strength hydrogel (FAP20) with triple shape memory function.

[0073] Example 2

[0074] The difference between this embodiment and Example 1 is that the hydrogel G prepared in Example 1 was immersed in a 0.05 mol / L ferric chloride aqueous solution for 24 hours; and then immersed in deionized water for 24 hours to obtain a high-strength hydrogel (FAP24) with triple shape memory function.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that step (1) DH preparation step is omitted, and DH in step (3) is replaced with acrylonitrile. Other steps and parameters remain unchanged, and the resulting hydrogel is denoted as FAPAN.

[0077] Comparative Example 2

[0078] The difference between Comparative Example 2 and Example 2 is that step (2) is omitted, and a nano-gold dispersion is added in step (3) to obtain a hydrogel denoted as FP24.

[0079] Comparative Example 3

[0080] (1) Preparation of hydrogel precursor solution

[0081] 2.000g of polyvinyl alcohol (PVA) and 9.00mL of deionized water were poured into a three-necked flask and mixed. The mixture was heated to 85°C and stirred until dissolved. Then it was cooled to room temperature. 0.304g of acrylic acid, 1.00mL of the nano-gold dispersion prepared in step (2) of Example 1, and 5.0mg of N,N'-methylenebisacrylamide were added. After stirring, 0.0369g of ammonium persulfate was added and the mixture was stirred for 10min to obtain hydrogel precursor solution L.

[0082] (2) Preparation of hydrogels

[0083] The hydrogel precursor solution L was poured into a mold and polymerized at 65°C for 12 hours. Then it was frozen at -20°C for 12 hours and thawed at 25°C for 6 hours. This freeze-thaw cycle was repeated 3 times to obtain the hydrogel (PAD).

[0084] Figure 1 This is a flowchart of the synthesis of DH in Example 1.

[0085] Figure 2 This is the 1H NMR spectrum of DH in Example 1 ( 1 (H-NMR), the characteristic peak at δ=7.98ppm corresponds to the hydrogen atom of the amide group, the characteristic peak at δ=7.18-6.75ppm corresponds to the hydrogen atom on the benzene ring in the tricyclic phenanthrene structure, and the characteristic peak at δ=5.67-5.23ppm corresponds to the hydrogen atom on the unsaturated double bond.

[0086] Figure 3 This is the carbon NMR spectrum of DH in Example 1 ( 13 (C-NMR), the characteristic peak at δ=179.11ppm corresponds to the carbon atom in the ester group, the characteristic peak at δ=168.37ppm corresponds to the carbon atom in the amide group, the characteristic peak at δ=145.84ppm corresponds to the carbon atom shared by the benzene ring and the six-membered carbon ring, the characteristic peak at δ=124.15ppm corresponds to the carbon atom adjacent to the carbon atom shared by the benzene ring and the six-membered carbon ring, the characteristic peak at δ=119.95ppm corresponds to the carbon atom para to the carbon atom shared by the benzene ring and the six-membered carbon ring, the characteristic peak at δ=134.60ppm corresponds to the carbon atom in the double bond that is substituted with methyl, and the characteristic peak at δ=126.92ppm corresponds to the other carbon atom in the double bond.

[0087] Figure 4 This is the high-resolution mass spectrum of DH in Example 1, and the [M+H] obtained by testing+ The value is 412.2859, which is consistent with the theoretical value.

[0088] Figure 5 This is a photograph of the wine-red gold nanoparticle dispersion prepared in step (2) of Example 1.

[0089] Figure 6 The UV-Vis absorption spectrum of the gold nanoparticle dispersion in Example 1 shows only one absorption peak with a peak wavelength of approximately 520 nm, indicating that the gold nanoparticles exhibit plasmon resonance, thus demonstrating the successful synthesis of the gold nanoparticles.

[0090] Figure 7 The image shown is a scanning electron microscope image of the gold nanoparticle dispersion in Example 1. It can be seen that the gold nanoparticles are spherical and have a particle size of about 25 nm.

[0091] Figure 8 These are the tensile stress-strain curves of the hydrogels obtained in the examples and comparative examples. Figure 9 The bar chart shows the toughness of the hydrogels obtained in the examples and comparative examples. It can be seen that the high-strength hydrogel FAP20 with triple shape memory function prepared in Example 1 possesses high tensile strength (8.1 MPa), high elongation at break (2650%), and high toughness (156.81 MJ / m). 3 The high-strength hydrogel (FAP24) prepared in Example 2 exhibits an elongation at break of up to 3150%, demonstrating outstanding mechanical properties and potentially expanding the application range of hydrogels. Existing conductive hydrogels with shape memory function and tensile strength greater than 5 MPa all exhibit dual shape memory function, and their elongation at break is less than 500%, limiting their application in scenarios such as large-strain visual indication or sensing. However, the hydrogel obtained in Comparative Example 1 has a tensile strength, elongation at break, and toughness of 3.06 MPa, 461%, and 7.41 MJ / m, respectively. 3 The tensile strength, elongation at break, and toughness of Comparative Example 2 were only 38%, 17%, and 4.7% of those of the hydrogel FAP20 prepared in Example 1, indicating that the structure of Comparative Example 1 did not possess the "rigid-flexible" characteristics. This is because Comparative Example 1 used acrylonitrile, which has lower hydrophobicity than DH used in Example 1. DH is mainly composed of non-polar alicyclic, benzene ring, and alkyl hydrophobic groups, while acrylonitrile contains strongly polar cyano groups, exhibiting prominent hydrophilicity. Therefore, Comparative Example 1 struggled to form good hydrophobic microdomains in the polymer chain segments, thus failing to effectively construct a physical microphase separation network and assist in the construction of the gold nanoparticle network. Ultimately, this resulted in the tensile properties of hydrogel FAPAN being significantly inferior to those of hydrogel FAP20 prepared in Example 1. In Comparative Example 2, the tensile strength, elongation at break, and toughness were 3.38 MPa, 2088%, and 58.64 MJ / m, respectively. 3The values ​​were all lower than those of FAP24 prepared in Example 2, indicating that the presence of gold nanoparticles is an important factor in obtaining high mechanical properties of hydrogels.

[0092] Figure 10 This is a digital photograph of the shape memory behavior of FAP20 based on iron ion solution. The shape change and recovery steps are as follows: (1) A rod-shaped sample of the high-strength hydrogel FAP20 with triple shape memory function in Example 1 was immersed in dilute hydrochloric acid with a pH of about 1 to 2 for 30 min to eliminate some of the coordination between iron ions and carboxyl groups. The pretreated hydrogel was denoted as P0. At this time, the sample was light yellow. (2) The pretreated hydrogel P0 was taken out, fixed with external force, and then soaked in 0.05 mol / L ferric chloride solution for 4 min to obtain a high-strength hydrogel sample with triple shape memory function with a temporary shape (approximately U-shaped) (denoted as P1). At this time, the sample turned reddish-brown. (3) The high-strength hydrogel P1 with triple shape memory function with a temporary shape was immersed in dilute hydrochloric acid with a pH of about 1 to 2 for 30 min to obtain a rod-shaped hydrogel again. At this time, the sample was light yellow. The hydrogel FAP20 exhibits shape memory behavior based on iron ions, and the sample is accompanied by obvious color changes.

[0093] Figure 11 This is a digital photograph of the shape memory behavior of FAP20 based on ethanol and N,N'-dimethylformamide. The shape change and recovery steps are as follows: (1) Fix a rod-shaped FAP20 sample with external force, and then immerse it in ethanol for 10 min or N,N'-dimethylformamide for 20 min to obtain a high-strength hydrogel with a temporary shape (U-shaped) and triple shape memory function (denoted as P2); (2) Immerse the above-mentioned high-strength hydrogel P2 with a temporary shape (U-shaped) and triple shape memory function in deionized water for 30 min to obtain a rod-shaped hydrogel again.

[0094] Figure 12This is a digital photograph of the triple shape memory behavior of FAP20 based on iron ion solution and ethanol. The shape change and recovery steps are as follows: (1) Immerse a rod-shaped hydrogel FAP20 sample in dilute hydrochloric acid with a pH of about 1~2 for 30 min to eliminate some of the coordination between iron ions and carboxyl groups. The resulting pretreated hydrogel (denoted as P0) is light yellow at this time; (2) Fix P0 with external force to form an arc structure with a single bend (temporary shape I), and then immerse it in 0.05 mol / L ferric chloride solution for 4 min to obtain a high-strength hydrogel with triple shape memory function (P3) with temporary shape I. The sample is reddish brown; (3) The sample with triple shape memory function has a single bend arc structure. High-strength hydrogel P3 was fixed by external force into a temporary shape with two opposite bends, resembling the letter "S". It was then immersed in ethanol for 10 minutes to obtain a high-strength hydrogel with triple shape memory function (P4) having a temporary shape II with double bends. The sample was still reddish-brown. (4) The high-strength hydrogel P4 with triple shape memory function was immersed in deionized water for 30 minutes to obtain a high-strength hydrogel with triple shape memory function (P5) having a single bend arc structure. The sample was reddish-brown. (5) P5 was immersed in dilute hydrochloric acid with a pH of about 1 to 2 for 30 minutes to obtain a hydrogel with an approximately rod-shaped shape. At this time, the sample was light yellow. The above shows that the high-strength hydrogel FAP20 with triple shape memory function can achieve triple shape change based on ethanol and iron ion solution.

[0095] The triple shape memory behavior of the hydrogel FAPAN obtained in Comparative Example 1 was tested. Digital photos of the testing process are available in [link to test]. Figure 13 The triple shape memory process of the hydrogel FAP20 prepared in Example 1 ( Figure 12 Compared to other materials, FAPAN exhibits poorer shape memory fixation and recovery performance under the same soaking time. It requires a longer iron ion soaking time to fix the temporary shape and a longer deionized water soaking time to recover the shape. This is because FAPAN hydrogel lacks "molecular channels" composed of well-developed hydrophobic microregions that enable rapid material transport. Therefore, shape fixation and recovery are slower, and the hydrophobic association formed by cyano groups is weak, resulting in insufficient and weak shape recovery, further diminishing the shape recovery effect.

[0096] Figure 14This is a digital image of the triple shape memory behavior of hydrogel FP24 obtained in Comparative Example 2. The triple shape change and recovery steps of hydrogel FP24 based on solvent (ethanol) and iron ion solution are as follows: (1) A rod-shaped hydrogel FP24 sample was immersed in dilute hydrochloric acid with a pH of about 1~2 for 30 min to eliminate part of the coordination between iron ions and carboxyl groups, and the pretreated hydrogel (denoted as FP0) was obtained; (2) FP0 was fixed by external force into an arc-shaped structure with a single bend (temporary shape I), and then immersed in 0.05 mol / L ferric chloride solution for 4 min to obtain hydrogel with temporary shape I (FP1). The shape fixation effect of this temporary shape is worse than that of FAP20 prepared in Example 1 under the same iron ion immersion time. This may be because hydrogel FP24 was not (3) The hydrogel FP1 with a single curved arc structure was fixed by external force into a temporary shape with two opposite bends, resembling the letter "S". Then it was immersed in ethanol for 10 min to obtain a hydrogel (FP2) with a temporary shape II with double bends. (4) The hydrogel FP2 with double bends was immersed in deionized water for 30 min and could only recover part of the shape memory to obtain a hydrogel (FP3). This may be due to the irregular hydrophobic association crosslinking of the hydrogel. (5) The hydrogel FP3 was immersed in dilute hydrochloric acid with a pH of about 1 to 2 for 30 min. Although it could basically recover the rod shape, it still had the bending characteristics fixed by the solvent. This shows that the hydrogel has triple shape memory function, but requires a long response time. This is because the hydrogel FP24 does not have a special "polymer chain-nano gold particle-polymer chain" structure formed by nano gold particles. The driving force is weak when the shape is fixed and restored, so a long fixation time and recovery time are required.

[0097] Figure 15 This is a digital image of the shape memory behavior of the hydrogel PAD obtained in Comparative Example 3. A rod-shaped sample of the hydrogel PAD was fixed by external force and then immersed in a 0.05 mol / L ferric chloride solution for 20 min, resulting in a hydrogel sample with a temporary shape (approximately C-shaped) (denoted as PAD1). Immersing the hydrogel PAD1 with its temporary shape (approximately C-shaped) in dilute hydrochloric acid with a pH of approximately 1-2 for 30 min essentially failed to eliminate the temporary shape-fixing effect of iron ions. Therefore, the hydrogel PAD does not possess shape memory function based on iron ions, nor does it possess triple shape memory function based on the interaction of iron ions and solvent. This is because the polyacrylic acid chains in the hydrogel PAD cannot form a good cross-linked network structure with the polyvinyl alcohol chains, i.e., there is no good temporary phase, thus requiring a long time for shape fixation. Furthermore, due to the loose structure of this hydrogel, a strong recovery driving force cannot be formed during shape recovery; therefore, this hydrogel cannot complete shape memory behavior based on iron ions.

[0098] Figure 16 The conductivity tests of the hydrogels obtained in the examples and comparative examples are shown. The conductivity of hydrogel FAP20 in Example 1 is 0.058 mS / cm, and the conductivity of hydrogel FAP24 in Example 2 is 0.131 mS / cm. The conductivity of the hydrogels originates from iron ions and gold nanoparticles. The conductivity of Example 2 is higher than that of Example 1 because the longer immersion time for iron ions increases the number of free iron ions, thereby enhancing conductivity. The conductivity of hydrogel FP24 in Comparative Example 2 is 0.064 mS / cm, lower than that of hydrogel FAP24 prepared in Example 2. This indicates that the presence of gold nanoparticles effectively constructs conductive pathways, thus endowing the hydrogel with good conductivity.

[0099] Application Example 1: Detection of iron ions in water

[0100] The high-strength hydrogel FAP20 with triple shape memory function prepared in Example 1 was applied to the rapid visual detection of iron ions in water. The specific steps are as follows: (1) A rod-shaped hydrogel FAP20 sample was soaked in a 0.3 mol / L EDTA-2Na aqueous solution for 10 min to eliminate some of the coordination between iron ions and carboxyl groups. The sample was light yellow. (2) The hydrogel obtained in step (1) was fixed by external force and then immersed in 0.01 mol / L or 0.1 mol / L ferric chloride solution for a certain period of time. At this time, iron ions and carboxyl groups in the hydrogel formed a coordination effect, thereby obtaining a hydrogel with a temporary fixed shape (approximately V-shaped) in a short time. The sample was reddish brown. After the external force was removed, the temporary fixed shape remained unchanged. The concentration of iron ions in the test solution could be judged based on the change in the temporary fixed shape. Then, the hydrogel with a temporary fixed shape is immersed in a 0.3 mol / L sodium ethylenediaminetetraacetate aqueous solution. The coordination between iron ions and carboxyl groups dissociates, the temporary fixed shape is restored, and the sample becomes a light yellow rod, thus enabling repeated testing of the material.

[0101] Figure 17 This study investigated the shape fixation and recovery behavior of FAP20 in detecting 0.01 mol / L iron ions. Pretreated FAP20 hydrogel rods were immersed in a 0.01 mol / L iron ion solution. Initially, the rods were light yellow and formed a temporary, approximately V-shaped form within 10 minutes. The shape was essentially fixed after approximately 90 minutes, resulting in a reddish-brown rod. When the approximately V-shaped rods were immersed in a 0.3 mol / L EDTA-2Na aqueous solution for shape recovery, they regained their rod shape within 10 minutes, and the color returned to light yellow.

[0102] Figure 18To assess the shape fixation rate and shape recovery rate when detecting 0.01 mol / L iron ions, FAP20 exhibited a rapid shape fixation rate in the first 10 minutes when immersed in the iron ion solution, reaching a maximum shape fixation rate of 85.6% at 90 minutes. When immersed in an aqueous solution of disodium ethylenediaminetetraacetate (EDTA-2Na), FAP20 reached a maximum shape recovery rate of 97% at 10 minutes.

[0103] Figure 19 The FAP20 exhibits excellent shape fixation and recovery behavior when detecting 0.1 mol / L iron ions. It can completely fix its shape in just 5 minutes. After detection, the hydrogel strip can recover its rod shape within 4 minutes when immersed in a 0.3 mol / L EDTA-2Na aqueous solution. The strip also shows a color change from light yellow to reddish brown and then back to light yellow during the detection process.

[0104] The above demonstrates that the hydrogel FAP20 prepared in Example 1 of this invention can detect iron ions in water based on the shape memory behavior of the hydrogel, and can also be used to assist in the judgment based on the color change of the hydrogel sample.

[0105] Existing technologies require a long soaking time (90 min) and a recovery time (300 min) when detecting 0.1 mol / L iron ion solutions. However, the hydrogel FAP20 prepared in Example 1 of this invention can fix its temporary shape in only 5 min when detecting 0.1 mol / L iron ion solutions, and can recover in only 4 min. When detecting 0.01 mol / L iron ion solutions, it requires a 90 min soaking time to fix the shape, but only 10 min to recover.

[0106] Application Example 2: Strain Sensor

[0107] The high-strength hydrogel FAP24 with triple shape memory function from Example 2 was applied to a strain sensor. Specifically, the FAP24 hydrogel was cut into rectangular strips, clamped onto the fixture of a universal testing machine, and connected to a digital multimeter. While the universal testing machine stretched the sample, the digital multimeter recorded the change in resistance of the high-strength hydrogel with triple shape memory function.

[0108] A high-strength hydrogel with triple shape memory function was applied to detect the movement of human joints (fingers and wrists). The specific method involves cutting the FAP24 hydrogel into rectangular strips, connecting the strips to a digital multimeter using copper tape and wires, and recording the changes in the resistance of the high-strength hydrogel with triple shape memory function using the digital multimeter while the joint is in motion.

[0109] Figure 20The graph shows the relationship between the resistance change rate (ΔR / R0) and strain of the FAP24 hydrogel applied to a strain sensor. The sensitivity (GF) of this hydrogel is 0.64 and 1.21 at 0-200% strain and 200-500% strain, respectively, indicating that the FAP24 hydrogel has strain sensing capability.

[0110] Figure 21 The graph shows the relationship between the rate of change of resistance (ΔR / R0) of hydrogel FAP24 applied to strain sensors under cyclic tensile strain of 10% and 50% and strain. The resistance of the hydrogel under repeated strain has an approximate rate of change of resistance, indicating that hydrogel FAP24 can ensure a fast and stable response under small strain.

[0111] Figure 22 The graph shows the relationship between the rate of change of resistance (ΔR / R0) of hydrogel FAP24 applied to the strain sensor under cyclic tensile strain of 100% and 200% and the strain. Under repeated strain, the resistance of the hydrogel has an approximate rate of change of resistance, indicating that hydrogel FAP24 can ensure a fast and stable response under large strain.

[0112] Figure 23 The graph shows the rate of change of electrical resistance (ΔR / R0) of hydrogel FAP24 in the finger joint when joint strain is measured. Figure 24 The graph shows the rate of change of resistance (ΔR / R0) of hydrogel FAP24 when detecting joint strain at the wrist. The stable signal recognition at the finger or wrist joint and the cyclic stability indicate that hydrogel FAP24 has good flexural response and stability in use.

[0113] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing a hydrogel with triple shape memory function, characterized in that, Includes the following steps: S1. Dissolve sodium chloride and emulsifier in deionized water, then add a bio-based hydrophobic monomer to obtain a homogeneous solution; the bio-based hydrophobic monomer has the following structure: ； S2. Add acrylamide, acrylic acid, nano gold dispersion, crosslinking agent and initiator, heat to react and obtain primary hydrogel; S3. The primary hydrogel is sequentially immersed in ferric chloride solution and deionized water to obtain the hydrogel with triple shape memory function.

2. The method for preparing a hydrogel with triple shape memory function as described in claim 1, characterized in that, The preparation method of the bio-based hydrophobic monomer includes the following steps: In an organic solvent, the compound of formula 1 and the compound of formula 2 are mixed and reacted to obtain the bio-based hydrophobic monomer; The structural formulas of compounds of formula 1 and formula 2 are as follows: 。 3. The method for preparing a hydrogel with triple shape memory function as described in claim 2, characterized in that, The molar ratio of the compound of Formula 1 to the compound of Formula 2 is 1:(0.5-1.5). And / or, the reaction is carried out at a temperature of 20-30°C for a time of 4-8 hours.

4. The method for preparing a hydrogel with triple shape memory function as described in claim 1, characterized in that, The preparation method of the nano-gold dispersion is as follows: chloroauric acid, sodium citrate and deionized water are mixed and reacted at 100-120℃.

5. The method for preparing a hydrogel with triple shape memory function as described in claim 1, characterized in that, The molar ratio of the bio-based hydrophobic monomer, acrylamide, and acrylic acid is (0.5-2):100:(5-25).

6. The method for preparing a hydrogel with triple shape memory function as described in claim 1, characterized in that, In S3, the concentration of the ferric chloride solution is 0.01-0.1 mol / L, the immersion time in the ferric chloride solution is 6-24 h, and the immersion time in deionized water is more than 24 h.

7. The method for preparing a hydrogel with triple shape memory function as described in claim 1, characterized in that, In S2, the heating reaction is carried out at a temperature of 60-70°C for 8-15 hours.

8. A hydrogel with triple shape memory function prepared by any one of claims 1-7.

9. The application of the hydrogel with triple shape memory function as described in claim 8 in strain sensors and iron ion concentration detection in water.

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