Eu-p (AAm-co-APDA) hydrogel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of hydrogel materials, and particularly relates to Eu-p (AAm-co-APDA) hydrogel as well as a preparation method and application thereof. According to the invention, the shape memory hydrogel is synthesized, and the hydrogel has a switchable luminescence behavior at the same time. The pH-responsive lanthanide complex can be used as a temporary cross-linking agent to fix the temporary shape of the hydrogel and accompany switchable luminescence properties, so that the hydrogel exhibits both shape memory and luminescence behaviors under alkaline conditions. However, after acid treatment, luminescence is quenched, and the shape is recovered. Besides, the hydrogel can twist and store twist energy, and then the twist energy is released in an acid solution, so that the hydrogel has potential application value in the field of soft intelligent driver materials.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel materials technology, and specifically relates to an Eu-p(AAm-co-APDA) hydrogel, its preparation method, and its application. Background Technology

[0002] Hydrogels have attracted much attention due to their excellent biocompatibility, transparency, and mechanical properties. Among them, stimulus-responsive hydrogels can respond to changes in external environments such as temperature, magnetic fields, pH, and light, and change their size, color, or shape in response to external stimuli. Stimulus-responsive hydrogels have been proposed for various applications, including as functional materials for hydrogel actuators, molecular devices, sensors, information encryption, and drug delivery. Introducing supramolecular interactions (hydrogen bonds, host-guest interactions, metal coordination, and electrostatic interactions) into hydrogels endows them with unique functions, such as self-healing, shape memory, and phase transitions.

[0003] As is well known, the interaction between metal ions and organic ligands is a typical type of stimulus-response dynamic bond. Dynamic metal complexes formed based on this interaction can reversibly bind and dissociate in response to external stimuli, thus achieving stimulus-response behavior. However, most hydrogels have a single stimulus-response function, and integrating multiple response functions into a single hydrogel network remains challenging. Common strategies often only achieve simple functional superposition or static integration, failing to simulate the complex behaviors of multi-signal coupling, dynamic adaptation, and intelligent feedback in biological systems.

[0004] Lanthanide ions can coordinate with organic ligands to form lanthanide complexes, which possess unique metal-controlled photoluminescence properties (through a resonance energy transfer (RET) process, i.e., the antenna effect, absorbing sufficient energy and efficiently transferring it to lanthanide ions), including high luminescence quantum yield, a sharp emission band, a large Stokes shift, and good photochemical stability. Furthermore, the dynamic nature of the lanthanide metal coordination bonds enables them to respond to various stimuli, such as pH, force, temperature, and humidity. This dynamic metal-ligand coordination design approach provides a reliable pathway for stimulus-responsive luminescent materials. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an Eu-p(AAm-co-APDA) hydrogel, its preparation method, and its applications. This invention utilizes the dynamic and reversible coordination characteristics of lanthanide complexes to develop a stimulus-responsive luminescent hydrogel material. This material can exhibit luminescence changes, tunable mechanical properties, and shape memory under acid / alkali stimulation. First, in the presence of the crosslinking agent MBA, p(AAm-co-APDA) hydrogel was synthesized in situ by copolymerizing allyl-modified 2,6-pyridinedicarboxylic acid (APDA) with acrylamide (AAm) monomer. Subsequently, using this gel as a carrier, it was immersed in Eu... 3+ The solution is then treated with alkali to make Eu 3+ It coordinates with APDA in the network, ultimately forming an Eu-p(AAm-co-APDA) hydrogel. Due to Eu... 3+ Lanthanides can coordinate with APDA to form Eu coordination complexes, which not only serve as luminescent centers but also as additional crosslinking bonds to enhance the gel matrix. The dynamic nature of lanthanide coordination allows for the reversible formation and dissociation of these complexes under acid-base stimuli. The resulting hydrogel exhibits reversible luminescence switching and rigid-to-soft transition properties. Furthermore, the dynamic coordination between lanthanide ions and ligands can form reversible temporary crosslinking points within the hydrogel network. This crosslinked network can lock into a temporary shape under external stimuli and dissociate and recover its shape after the stimulus is removed, thus achieving shape memory functionality in the material.

[0006] This invention is achieved through the following technical solution: A method for preparing an Eu-p(AAm-co-APDA) hydrogel includes the following steps: S1. Allyl-modified 2,6-pyridinedicarboxylic acid APDA was added to distilled water, NaOH was added dropwise, followed by acrylamide AAM and N,N'-methylenebisacrylamide MBA, and then photoinitiator DEAP was added. After purging with nitrogen to remove oxygen, the mixture was injected into a mold and subjected to free radical copolymerization under a mercury lamp to obtain p(AAm-co-APDA) gel. S2. The p(AAm-co-APDA) hydrogel is sequentially immersed in EuCl3 solution and NaOH solution, so that EuCl3 solution is dissolved in NaOH solution. 3+ It coordinates with APDA to form Eu-p(AAm-co-APDA) rigid hydrogel.

[0007] Furthermore, the molar ratio of APDA to AAM is 1:(31.4-125.5). By adjusting the APDA / AAm molar ratio, the fracture stress of the hydrogel is increased from 0.023MPa to 0.25MPa.

[0008] Furthermore, the quality ratio of MBA to APDA is 50:1.

[0009] The present invention also provides a hydrogel prepared by the above preparation method, wherein the hydrogel has a transparency of 86%.

[0010] Furthermore, the hydrogel exhibits reversible light-emitting switching characteristics. After treatment with HCl, the light emission intensity is quenched by 85%, and the light emission lifetime decreases from 0.95ms to 0.16ms; after treatment with NaOH, the light emission performance is restored.

[0011] Furthermore, Eu in Eu-p(AAm-co-APDA) rigid hydrogel 3+ / Tb 3+ When the ratio changes from 10:0 to 0:10, the emitted color transitions from red through yellow to green.

[0012] Furthermore, the hydrogel exhibits reversible rigid-to-soft transition properties: after treatment in HCl solution, the metal coordination bonds dissociate, and the hydrogel changes from rigid to soft; after treatment with NaOH solution, it regains its rigidity, and the reversible rigid-to-soft transition properties are accompanied by synchronous changes in luminescence properties.

[0013] Furthermore, the hydrogel possesses shape memory function, through Eu 3+ It coordinates with APDA and is temporarily shaped after being treated with NaOH solution. It recovers its original shape by immersion in HCl solution, and the shape recovery time is completed within 360 seconds. The shape memory process is accompanied by synchronous changes in luminescent properties.

[0014] The present invention also provides the application of the hydrogel material in pH-responsive light-emitting sensors, reversible light-emitting switching elements, shape memory materials, and soft intelligent actuator materials.

[0015] The beneficial technical effects of this invention are as follows: This invention successfully develops a novel shape memory hydrogel that simultaneously exhibits switchable luminescence behavior. A pH-responsive lanthanide complex can be used as a temporary crosslinking agent to fix the temporary shape of the hydrogel, accompanied by switchable luminescence properties. Therefore, this hydrogel exhibits both shape memory and luminescence behavior under alkaline conditions. However, upon acid treatment, the luminescence is quenched, and the shape is restored. Furthermore, this hydrogel can be twisted and store twisting energy, which is then released in an acidic solution, giving it potential application value in the field of soft intelligent actuator materials. Attached Figure Description

[0016] Figure 1 Schematic diagram of the preparation process of Eu-p(AAm-co-APDA) hydrogel.

[0017] Figure 2 FTIR spectra of APDA, AAm monomers and Eu-p (AAm-co-PDA) hydrogels.

[0018] Figure 3 Excitation and fluorescence emission spectra of Eu-P (AAm-co-APDA) hydrogel.

[0019] Figure 4 Fluorescence emission spectra of Eu-P (AAm-co-APDA) hydrogel under different concentrations of HCl.

[0020] Figure 5 The intensity variation curves of Eu-P (AAm-co-APDA) hydrogel at 615 nm under different concentrations of HCl.

[0021] Figure 6 Fluorescence emission spectrum of Eu-P (AAm-co-APDA) hydrogel under acid-base cycling stimulation.

[0022] Figure 7 The change in luminescence intensity at 615 nm of Eu-P (AAm-co-APDA) hydrogel under acid-base cycling stimulation.

[0023] Figure 8 Different Eu 3+ / Tb 3+ Fluorescence emission spectrum of the molar ratio hydrogel, corresponding CIE1931 chromaticity diagram, and digital photograph under 254nm ultraviolet light.

[0024] Figure 9 Tensile stress-strain curves of Eu-p(AAm-co-APDA) hydrogels with different proportions of APDA and AAM.

[0025] Figure 10 Stress-strain curves of Eu-P(AAm-co-APDA) hydrogel under 200% strain during loading and unloading.

[0026] Figure 11 Eu-P(AAm-co-APDA) hydrogel under different strains under continuous loading-unloading tensile stress-strain curves.

[0027] Figure 12 Stress-strain curves of Eu-P(AAm-co-APDA) hydrogel after hydrochloric acid treatment at 200% strain.

[0028] Figure 13 Eu-P(AAm-co-APDA) hydrogel subjected to hydrochloric acid treatment, continuous loading-unloading tensile stress-strain curves under different strains.

[0029] Figure 14 The tensile stress-strain curve of Eu-P(AAm-co-APDA) hydrogel under acid-base cycling stimulation.

[0030] Figure 15 A bar chart of the maximum stress of Eu-P(AAm-co-APDA) hydrogel under acid-base cycling stimulation.

[0031] Figure 16 Digital photographs showing the transformation of Eu-P (AAm-co-APDA) hydrogel from stiff to soft under acid and alkali stimulation.

[0032] Figure 17 A schematic diagram of the shape memory behavior of a strip-shaped hydrogel and its bending angle-time curve in hydrochloric acid aqueous solution, and a digital photograph of the synergistic changes in shape and fluorescence of a flower-shaped hydrogel under 254nm ultraviolet light irradiation.

[0033] Figure 18 A schematic diagram of hydrogel deformation-driven rotation and its rotation angle-time curve, and a digital photograph of the hydrogel being pre-twisted by external force and then releasing internal stress under hydrochloric acid triggering to drive the object to rotate. Detailed Implementation

[0034] Example 1

[0035] Preparation of Eu-p(AAm-co-APDA) hydrogel S1. Add APDA (20 mg, 0.09 mmol) to 960 μL of distilled water, and add NaOH (7.2 mg, 0.18 mmol) dropwise to the mixture. Then, add acrylamide (AAm) (200 mg, 2.81 mmol) and N,N'-methylenebisacrylamide MBA (40 μL, 10 mg / mL) to the pregel solution. Next, add the photoinitiator 2,2-diethoxyacetophenone (DEAP) (1 μL). Purge the mixture with nitrogen for 10 minutes to remove dissolved oxygen. Finally, pour the anaerobic pregel solution into a square container (20 × 10 mm) and place it under a mercury lamp for free radical copolymerization for 1 hour to obtain p(AAm-co-APDA) gel.

[0036] S2. Immerse the p(AAm-co-APDA) hydrogel in 50mM EuCl3·6H2O solution for 20 minutes, then immerse it in NaOH solution for 10 minutes to allow the EuCl3·6H2O to dissolve. 3+ Coordinated with APDA, Eu-p(AAm-co-APDA) rigid hydrogel was obtained.

[0037] like Figure 1 As shown, in the presence of MBA as a covalent crosslinking agent, allyl-modified 2,6-pyridinedicarboxylic acid (APDA) and acrylamide AAM undergo in-situ copolymerization in water to generate p(AAm-co-APDA) hydrogel. Subsequently, p(AAm-co-APDA) is immersed in EuCl3 solution to allow EuCl3 to form a hydrogel.3+ The Eu-p(AAm-co-APDA) hydrogel is then infiltrated into the hydrogel network and immersed in NaOH solution to form Eu coordination complexes, ultimately yielding Eu-p(AAm-co-APDA) hydrogel.

[0038] like Figure 2 As shown, the Fourier transform infrared (FTIR) spectrum reveals that at 1593 cm⁻¹... -1 and 1611cm -1 The peaks at the [value] are attributed to the double-bonded functional groups of APDA and AAm, respectively. After hydrogel formation, these double bonds almost completely disappeared, indicating that APDA had successfully copolymerized with AAm. Furthermore, FTIR spectroscopy confirmed the APDA-Eu [polymerization / polymerization]. 3+ The presence of coordination complexes. The 1723 cm⁻¹ corresponding to the C=O stretching vibration in APDA. -1 The disappearance of the peak at that point indicates that APDA and Eu 3+ The ions underwent coordination.

[0039] The photoluminescence properties of Eu-p(AAm-co-APDA) hydrogel were investigated. Figure 3 By monitoring at 615nm 5 D0→ 7 F2 transition, obtaining Eu-containing 3+ Excitation spectrum of the hydrogel. A broadband spectrum in the 250-350 nm range was observed, attributed to the absorption of the APDA ligand, indicating APDA to Eu conversion. 3+ Energy transfer. Contains Eu. 3+ The emission spectrum of the supramolecular hydrogel shows five sharp peaks at 582, 594, 615, 650, and 694 nm, which can be attributed to... 5 D0→ 7 F J (J=0-4) transition. Specifically, at 615nm... 5 D0→ 7 The F2 transition band is the main source of red emission.

[0040] Due to the luminescence of hydrogels on H + The luminescence intensity was highly sensitive to changes in concentration, therefore the relationship between luminescence intensity and HCl concentration was investigated. A series of hydrogels of the same size were immersed in aqueous HCl solutions of different concentrations (0.01 to 0.2 M) for 10 minutes. The luminescence intensity of the hydrogels gradually decreased until the concentration reached 0.2 M. Figure 4 As shown, the luminescence intensity of the hydrogel was quenched after treatment with 0.2M HCl solution, with a quenching efficiency of approximately 85%. This is because the protonation of the carboxylic acid and pyridine nitrogen leads to the ligands APDA and Eu... 3+The dissociation of the luminescence disrupts the "antenna effect" and causes luminescence quenching. More importantly, the luminescence response of the hydrogel is reversible. The fluorescence of the hydrogel can be restored upon the addition of 0.2M NaOH. The luminescence changes of Eu-p(AAm-co-APDA) were further investigated over three cycles by adding HCl and NaOH. Although the luminescence intensity decreased, its luminescence switching characteristics were reversible under the influence of alkali and acid. Figure 6 ,7).

[0041] Furthermore, thanks to Eu in the metal solution 3+ and Tb 3+ With the flexibility of ion ratios, we successfully prepared color-tunable luminescent hydrogels. Figure 8 When Eu 3+ With Tb 3+ When the ratio of ions changes from 10:0 to 0:10, Eu 3+ The characteristic emission intensity of the hydrogel gradually decreases, while that of the Tb hydrogel gradually increases. Correspondingly, the CIE chromaticity map coordinates also transition from the red region to the yellow region, and finally to the green region, which corresponds to its optical image.

[0042] Example 2

[0043] The difference between Example 2 and Example 1 is that the molar ratio of APDA to AAM is 1:125.5, while all other conditions are exactly the same.

[0044] Example 3

[0045] The difference between Example 3 and Example 1 is that the molar ratio of APDA to AAM is 1:62.8, while all other conditions are exactly the same.

[0046] Example 4

[0047] The difference between Example 4 and Example 1 is that the molar ratio of APDA to AAM is 1:41.8, while all other conditions are exactly the same.

[0048] Examples 1-4 investigate the influence of the ratio of APDA to AAM in Eu-P(AAm-co-APDA) hydrogels on the mechanical properties of the hydrogels. Monomer C AAm The total concentration was fixed at 2.81M, and the chemical crosslinking agent C MBA The concentration is fixed at 0.1 mol% (relative to the monomer). For example... Figure 9 As shown, variations in the APDA / AAm ratio affect the mechanical properties of Eu-P(AAm-co-APDA) hydrogels. After stretching, the original p(AAm-co-APDA) hydrogel exhibits continuous elongation, capable of withstanding fracture stresses up to 0.023 MPa, with an elongation exceeding four times its original length. However, at 50 mM Eu...3+ After soaking in the solution and treating with NaOH solution, the hydrogel hardened significantly, the APDA / AAm ratio increased from 1:125.5 to 1:31.4, and the fracture stress increased to a maximum of 0.25 MPa. This was due to the increased crosslinking density through the formation of coordination bonds.

[0049] To further understand the mechanical properties of the hydrogel, loading / unloading tensile tests with different stretch ratios and continuous tensile tests stretched to twice the original length were conducted. The area of ​​the region formed by the loading-unloading curve was defined as the energy dissipation during the tensile process, and this value can be used as an indicator of internal fracture of the hydrogel. As shown in the figure, the hydrogel is composed of Eu... 3+ Eu-p(AAm-co-APDA) hydrogels formed by coordination of APDA on polymer chains exhibited hysteresis in the same loading / unloading test. Figure 10 Furthermore, it can be seen that as the stretching ratio increases, energy dissipation also gradually increases. Figure 11 This indicates that Eu 3+ Ions coordinate with APDA on the polymer chain, and these non-covalent bonds effectively disperse the stress on the hydrogel network under tension.

[0050] Due to the dynamic characteristics of metal coordination bonds, the rigid hydrogel obtained in Example 1, after being immersed in a 0.2M HCl solution for 10 minutes, undergoes mechanical transformation into a soft hydrogel due to the dissociation of the metal coordination bonds. For example... Figure 12 As shown, no significant hysteresis was observed in the HCl-treated Eu-p(AAm-co-APDA) hydrogel during the same tensile loading / unloading test. Furthermore, it can be seen that the hysteresis loop remains small with increasing stretch ratio. Figure 13 In other words, when the hydrogel is stretched, there is no effective energy dissipation between the polymer chains in the hydrogel network. It is noteworthy that the stiff-soft transition is reversible in the stiff-soft transition cycling test. Figure 14-16 ).

[0051] In summary, based on the unique properties of lanthanide complexes, the hydrogel obtained in this invention can simultaneously achieve changes in luminescence and shape through a dynamic dissociation-coordination process under acid-base stimulation. First, the shape memory behavior of the hydrogel is investigated: such as... Figure 17 As shown, the original hydrogel sample, which was in the shape of a straight strip, was bent into an "O" shape and first immersed in Eu. 3+ The solution was used to allow ions to permeate into the gel network for 20 minutes, followed by treatment with NaOH solution for 10 minutes, and then passed through Eu... 3+The Eu complex forms a temporary crosslinking point with the APDA on the polymer chain, fixing the temporary shape. Upon transfer of the hydrogel to an HCl solution, the Eu complex dissociates, restoring the original straight strip shape within 360 seconds. Based on this property, a hydrogel with both shape memory and luminescence switching functions was constructed. Figure 17 As shown, the hydrogel is programmed into a preset three-dimensional flower shape, and then processed by Eu... 3+ The solution and NaOH solution were processed stepwise. During this process, Eu... 3+ It rapidly penetrates into the gel network, coordinating with the coordinating groups (APDA) on the polymer chains to form a stable dynamic coordination crosslinking network. This successfully locks the three-dimensional flower morphology into a temporary shape and simultaneously triggers the Eu... 3+ The characteristic emission resulted in bright red fluorescence. Subsequently, the hydrogel, which had been fixed into a three-dimensional flower shape and emitted bright red light, was transferred to an HCl solution. The acidic environment promoted Eu... 3+ The complex undergoes controlled dissociation, and the dynamic cross-linking points disappear accordingly. Under this stimulus, the hydrogel, relying on the restoring force of its elastic network, rapidly and accurately recovers to its original two-dimensional flat flower shape. Furthermore, along with the dissociation of the complex, its characteristic red light is simultaneously quenched. This experiment directly demonstrates that the material possesses both excellent shape retention and shape recovery capabilities, while clearly showcasing the dual response and synergistic change process of "deformation-luminescence," highlighting its potential application value in fields such as intelligent bionics and flexible devices.

[0052] In addition, hydrogels can be used as a driving force to propel objects into motion. Figure 18 This demonstrates how hydrogel materials can utilize shape memory to store energy after twisting into long strips of hydrogel and release that energy under acidic conditions. For example... Figure 18 As shown, this shape memory material holds promise for use as a smart actuator to facilitate the rotation of objects. First, an elongated strip of the original hydrogel is twisted by external force, then it is immersed in Eu... 3+ In the solution, an alkaline solution is used to store torsional energy. Then, a 5g dovetail clip is suspended below the hydrogel, and finally immersed in an HCl solution. The twisted hydrogel rapidly returns to its original straight shape, and the dovetail clip rotates rapidly, from 0 degrees to 280 degrees within 200 seconds. This is due to the energy released by the dissociation of the metal coordination complex. This efficient conversion of microscopic intermolecular interaction changes into macroscopic mechanical motion through the reversible formation and dissociation of dynamic coordination bonds shows great application potential in intelligent hydrogel actuators.

Claims

1. A method for preparing Eu-p(AAm-co-APDA) hydrogel, characterized in that, Includes the following steps: S1. Allyl-modified 2,6-pyridinedicarboxylic acid APDA was added to distilled water, NaOH was added dropwise, followed by acrylamide AAM and N,N'-methylenebisacrylamide MBA, and then photoinitiator DEAP was added. After purging with nitrogen to remove oxygen, the mixture was injected into a mold and subjected to free radical copolymerization under a mercury lamp to obtain p(AAm-co-APDA) gel. S2. The p(AAm-co-APDA) hydrogel is sequentially immersed in EuCl3 solution and NaOH solution, so that EuCl3 solution is dissolved in NaOH solution. 3+ It coordinates with APDA to form Eu-p(AAm-co-APDA) rigid hydrogel.

2. The method for preparing Eu-p(AAm-co-APDA) hydrogel according to claim 1, characterized in that, Includes the following steps: The molar ratio of APDA to AAM is 1:(31.4-125.5). By adjusting the APDA / AAm molar ratio, the fracture stress of the hydrogel is increased from 0.023MPa to 0.25MPa.

3. The method for preparing Eu-p(AAm-co-APDA) hydrogel according to claim 1, characterized in that, The quality ratio of MBA to APDA is 50:

1.

4. An Eu-p(AAm-co-APDA) hydrogel prepared by any one of claims 1-3, characterized in that: The hydrogel has a transparency of 86%.

5. The Eu-p(AAm-co-APDA) hydrogel according to claim 4, characterized in that: The hydrogel has reversible light-emitting switching characteristics. After treatment with HCl, the light emission intensity is quenched by 85%, and the light emission lifetime decreases from 0.95ms to 0.16ms. After treatment with NaOH, the light emission performance is restored.

6. The Eu-p(AAm-co-APDA) hydrogel according to claim 4, characterized in that: Eu in Eu-p(AAm-co-APDA) rigid hydrogel 3+ / Tb 3+ When the ratio changes from 10:0 to 0:10, the emitted color transitions from red through yellow to green.

7. The Eu-p(AAm-co-APDA) hydrogel according to claim 4, characterized in that: The hydrogel has reversible rigid-to-soft transition properties: after treatment in HCl solution, the metal coordination bonds dissociate, and the hydrogel changes from rigid to soft. After treatment with NaOH solution, the rigidity is restored, and the reversible rigid-to-soft transition property changes synchronously with the luminescence properties.

8. The Eu-p(AAm-co-APDA) hydrogel according to claim 4, characterized in that: The hydrogel has shape memory function, which is achieved through Eu 3+ It is coordinated with APDA and temporarily shaped after being treated with NaOH solution. It is then immersed in HCl solution to restore its original shape. The shape restoration time is completed within 360 seconds. The shape memory process is accompanied by synchronous changes in luminescent properties.

9. An application of the hydrogel as described in claims 4-8, characterized in that: Applications of the hydrogel material in pH-responsive light-emitting sensors, reversible light-emitting switching elements, and shape memory materials.

10. An application of the hydrogel as described in claims 4-8, characterized in that: Application of the hydrogel material in soft smart actuator materials.

Images