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Article

Polymer Entanglement-Induced Hydrogel Adhesion

by
Kai Hu
1,
Qingyun Li
2 and
Xiaofan Ji
2,*
1
College of Chemistry and Chemical Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
2
Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Material Chemistry and Service Failure, Hubei Engineering Research Center for Biomaterials and Medical Protective Materials, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
*
Author to whom correspondence should be addressed.
Gels 2024, 10(12), 822; https://doi.org/10.3390/gels10120822
Submission received: 30 October 2024 / Revised: 5 December 2024 / Accepted: 11 December 2024 / Published: 13 December 2024
(This article belongs to the Special Issue Structured Gels: Mechanics, Responsivity and Applications (2nd Edition))
Browse Figures
Versions Notes

Abstract

:
Hydrogels are widely used in the field of adhesive materials. However, hydrogel adhesion has previously required the covalent graft of supramolecular groups on polymeric chains. In contrast to that, here, a hydrogel adhesion induced by covalent polymer entanglement between two hydrogel networks was reported. Hydrogels G1 and G2 contain the monomers M1, with diazonium groups, and M2, with sulfonate groups, respectively. When the two hydrogels come into contact, the monomers diffuse into each other’s networks and assemble into supramolecular polymers (SPs) based on electrostatic interactions, threading the two hydrogel networks. Subsequently, SPs convert into covalent polymers (CPs) under UV light stimulation due to the reaction between the diazonium groups and sulfonate groups, leading to the entanglement of the two hydrogel networks and the production of an adhesive effect. This finding provides a novel strategy for hydrogel adhesion.

Graphical Abstract

1. Introduction

The adhesion phenomenon widely occurs in nature; it is the outcome of interatomic and intermolecular interactions holding different surfaces together [1,2]. Among these adhesion phenomena, soft–soft adhesion commonly exists in our bodies, occurring between soft tissues and other kinds of tissues or organs. In addition, the binding of cells of various kinds is also referred to as soft–soft adhesion [3,4]. In regard to mimicking the adhesion behavior of soft tissues, hydrogel, as a specific kind of soft material, has gained people’s attention [5]. Benefitting from a hydrophilic polymer backbone, hydrogel holds a lot of water and performs macroscopic solid-like rheological behavior [6,7]. Hydrogels possess a rich array of properties, including a self-healing ability, a conductive ability, moldability, adjustable mechanical properties, a shape-memory ability, and a high water content, which have led to their extensive research in various fields, such as biomedicine, electronic sensors, conductive devices, soft robotics, and more [8]. In addition, hydrogels possessing tunable chemical structures, mechanic properties and biocompatibility are also regarded as exceptional adhesion materials [9,10]. Benefitting from these advantages, the adhesion of hydrogels finds important applications in different fields, such as medicine and biological materials [11,12].
Normally, hydrogel adhesion is achieved by noncovalent interactions [13,14,15,16]. Therein, noncovalent interactions embody hydrogen-bonding interactions, metal coordination, electrostatic interactions, and host–guest interactions [17,18]. Noncovalent interactions are reversible and adaptive, showing sensitivity to environments, which allows for facilitating the construction of hydrogel adhesion [19,20,21,22]. The Harada group has made many pioneering contributions in terms of utilizing the supramolecular recognition interactions between cyclodextrin macrocycles and different guest molecules, such as β-cyclodextrin/ferrocene, β-cyclodextrin/pyrene, β-cyclodextrin/dansyl, and β-cyclodextrin /benzyl to achieve hydrogel adhesion and regulate its adhesiveness [23]. Furthermore, Shi, Chen and coworkers reported a kind of hydrogel adhesion based on the host–guest interactions between β-cyclodextrin and azobenzene [24]. Huang, Sessler, and their colleagues constructed fluorescent hydrogel assemblies utilizing the host–guest interactions between tetracationic imidazolium macrocycle and sulfonates, which can be used as information storage materials [25]. Stemming from metal-coordination interactions, another hydrogel adhesion example was reported by He, Zhang, and coworkers, who reported that self-adhesive poly (acrylic acid)–Al3+ hydrogel served as a wearable strain hydrogel sensor [26]. Also, hydrogel adhesion was enabled by electrostatic interactions for which Sun, Wang, and coworkers fabricated strong electrolyte polyampholyte hydrogels via introducing a weak anionic monomer [27]. By means of different kinds of noncovalent interactions, the desired hydrogel adhesion is surely feasible [28,29,30]. However, current approaches for realizing hydrogel adhesion require the covalent graft of supramolecular groups on polymeric chains, entailing a complex synthesis process.
In contrast to previous methods, we put forward an approach that involves forming covalent polymers inside hydrogels to entangle different hydrogel networks, further achieving hydrogel adhesion. Monomer M1-containing diazonium groups and M2-bearing sulfonate groups were synthesized (Scheme 1a). Based on the electrostatic interaction between the diazonium groups and sulfonate groups, self-assembled behaviors between M1 and M2 occurred in water to form supramolecular polymers (SPs). Due to the reaction ability of supramolecular recognition groups to react under UV light stimulation to form covalent compounds [31], SPs could be transformed into covalent polymers (CPs) upon UV irradiation. Then, two kinds of hydrogels G1 and G2, can be fabricated from acrylamide (AAm), N,N′-methylenebis (acrylamide) (MBA) and ammonium peroxidisulfate (APS) by means of radical polymerization [32]. Furthermore, M1 and M2 were incorporated into these hydrogels through physical blending (Scheme 1b). G1 and G2 were placed together for contacting each other, and, after 13 days passed, two hydrogels were fully contacted with the adequate diffusion of M1 and M2. Therefore, as a result of M1 and M2 undergoing supramolecular polymerization, SPs were formed inside hydrogel G3 networks, threading through different hydrogel networks. SPs could be transformed into CPs upon UV light irradiation. Therefore, the CPs in G4 caused different hydrogel networks to be entangled, leading to the adhesion of two hydrogels. This method was used as a good candidate to achieve hydrogel adhesion, leading to the development of polymer science, hydrogel materials, and stimulation-responsive materials.

2. Results and Discussion

Monomers M1 and M2 were synthesized according to Scheme 2. Moreover, the chemical structures of monomers have been confirmed by 1H NMR spectroscopy and 13C NMR spectroscopy (Figures S1–S3). M1 (83.4 mg, 10 mM) and M2 (98.8 mg, 10 mM) were dissolved in deionized water to prepare the stock solution. Furthermore, the standard solutions of M1 and M2 were prepared by diluting the stock solution via adding the deionized water. The conventional preparation method for hydrogels (Table S1) was as follows: AAm, MBA, and APS, were dissolved in deionized water and allowed to form the hydrogel. M1 and M2 were introduced into hydrogels through physical blending, resulting in hydrogels G1 and G2, respectively. These hydrogels were then brought into contact for subsequent testing. Potential changes in the monomer’s structures during the UV light stimulation process were recorded using 1H NMR spectra, FT-IR spectra, UV-vis spectra, and gel permeation chromatography (GPC) spectra. The experimental details of the preparation and tensile testing of hydrogels are written in the Materials and Methods section.

2.1. The 1H NMR Tests and Viscosity Tests of the Mixture Solution of M1 and M2

In order to study the self-assembly behavior of M1 and M2 in water, the mixtures of M1 and M2 at different concentrations (0.500 mM–10.0 mM) in D2O were tested by 1H NMR spectra. As shown in Figure 1a–c, after mixing equimolar M1 and M2, the signal peak Ha of M1 shifted from 8.46 ppm and 8.44 ppm to 8.43 ppm and 8.40 ppm, respectively, and the Hb signal peak Hb shifted from 7.68 ppm and 7.65 ppm to 7.63 ppm and 7.60 ppm, respectively. Meanwhile, in regard to M2, H1 signal peaks shifted from 7.77 ppm and 7.75 ppm to 7.74 ppm and 7.72 ppm, respectively; H2 shifted from 7.52 ppm to 7.54 ppm; the signal peaks H3 shifted from 7.14 ppm and 7.12 ppm to 7.13 ppm and 7.11 ppm, respectively; and the methylene signal peak (H4) shifted from 5.21 ppm to 5.22 ppm. With the concentration of the mixture increasing from 0.500 mM to 10.0 mM (Figure 1c–h), Ha signal peaks at 8.43 ppm and 8.40 ppm shifted to 8.34 ppm and 8.32 ppm, respectively, exhibiting a phenomenon of shifting towards the upfield. Meanwhile, the signal of Hb shifted upfield, slightly changing from 7.63 ppm and 7.60 ppm to 7.51 ppm and 7.49 ppm, respectively. Similarly, from the spectra, upfield shifts of H1 signals ranging from 7.73 ppm and 7.71 ppm to 7.65 ppm and 7.62 ppm, respectively, were detected. In addition, the proton peaks (H2, H3) of the benzene group shifted to 7.28 ppm, 6.94 ppm, and 6.92 ppm, respectively, and the methylene protons (H4) in monomer M2 underwent significant shifts towards the upfield, shifting from 5.22 ppm to 4.93 ppm. In addition, the above-mentioned peak shapes of signals became broader at 10.0 mM. The proton peaks changes could be attributed to the electrostatic interactions between diazonium groups and sulfonate groups [33]. Regarding the changes in broader peak shapes at high concentrations, it was revealed that only polymeric assemblies were formed [33].
For further studying the self-assembly behavior of M1 and M2 in an aqueous solution, a viscosity test was conducted. As the concentration of M1 increased from 0.500 mM to 1.00 mM, the specific viscosity of the mixture solution gradually rose with the slope of 0.32 (Figure 2). With the concentration of M1 exceeding over 2.00 mM, the specific viscosity of the mixture solution increased significantly with a slope of 1.03. The concentration of monomer corresponding to the intersection point of the two fitted lines (at 0.13 mM) was defined as the critical polymerization concentration (CPC) [34]. The slope within the low-concentration range reflected the characteristics of cyclic species or oligomers expected in dilute solutions. In contrast, the sharp increase in specific viscosity above the CPC was attributed to the formation of linear SPs [34]. Therefore, these results furtherly confirmed that SPs could be assembled by monomers at high concentrations while relatively smaller oligomers could form at lower monomer concentrations.

2.2. The 1H NMR Tests, FT-IR Tests, TGA Tests, and GPC Tests of the Mixture Solution of M1 and M2 After UV Light

Based on the formation of SPs, we further explore the formation of CPs. According to the reported literature, diazonium groups and sulfonate groups could react under UV light to form covalent compounds. If such reactions can proceed, the newly formed compounds will not contain water-soluble groups and will precipitate out from water. Therefore, the observation of precipitation in the reaction solution can serve as evidence for the occurrence of such reactions. As shown in Figure 3, the color of initial mixed solutions gradually changed from a pale yellow to an orange color after the increase in the monomer concentration. After exposure to UV light, the solution containing 0.500 mM monomers underwent a significant color change from pale yellow to burgundy, and, as the exposure time increased to 180 min, the solution color ultimately turned gray. As the concentration of the solution further increased, the color of the solution after the same exposure time darkened further and a black precipitate gradually formed on the walls of the container. As mentioned above, the change in color and the formation of the precipitate in the mixed solution indicated that M1 could react with M2 under UV light to produce water-insoluble compounds [31,35]. This was potentially a reaction between diazonium groups and sulfonate groups.
To further investigate the reasons for the aforementioned solution changes, a mixture solution containing 10.0 mM monomers was subjected to UV light while simultaneously recording 1H NMR spectra (Figure 4a). After UV light stimulation, the proton peaks of monomer M1 (Ha–Hb) in the solution shifted from 8.34 ppm, 8.32, ppm, 7.51 ppm, and 7.49 ppm to 8.40 ppm, 8.38 ppm, 7.57 ppm, and 7.55 ppm, and the signals of its proton peaks disappeared after 30 min. Meanwhile, the signal peaks of monomer M2 also underwent an initial shift towards the downfield, moving from 7.65 ppm, 7.27 ppm, 6.93 ppm, and 4.97 ppm to 7.75 ppm, 7.73 ppm, 7.52 ppm, 7.13 ppm, and 5.20 ppm, then shifting to 7.78 ppm, 7.54 ppm, 7.16 ppm, and 5.24 ppm, respectively. Within 30 min of UV light irradiation, significant shifts were observed in the proton peak signals of the benzene group in M1 and M2, which could be inferred to indicate structural changes in the diazonium groups and sulfonate groups, suggesting that a chemical reaction occurred between these two groups [33]. Based on these data, further speculation could be made that SPs transformed into CPs under UV light irradiation [35]. In addition, after 30 min of UV irradiation, the disappearance of the signal peak of M1 could be attributed to a partial reaction between M1 and M2 as well as the decomposition of diazonium groups in some M1 under light, leading to its precipitation from the water. According to the previous literature [36,37], the diazonium salt group may react with phenol derivatives or D2O to form ether under prolonged UV light exposure (Scheme S1). Therefore, the signal peak at 6.70 ppm could be attributed to the hydrogen protons on the benzene ring of the compound 4,4′-azanediyldiphenol. Therefore, the unreacted monomer M2 and 4,4′-azanediyldiphenol remained in the solution after 180 min of UV light irradiation.
In addition to monitoring the structural changes in compounds in solution, the precipitates formed after photoreaction also require further investigation. FT-IR technology was employed to record the spectra of monomers and the precipitates. As shown in Figure 5a, the signal peak at 2235 cm−1 was attributed to the diazonium groups in M1. Notably, the diazonium signal peak was absent in the precipitates, further confirming the reactions between the diazonium groups and the sulfonate groups [38] as well as the formation of covalent polymers. As shown in Figure 5b, the M1 solution exhibited two distinct signal peaks at 317 nm and 375 nm, recorded in the UV-vis spectra, attributed to the diazonium groups of M1 [31]. Additionally, M2 did not exhibit any peaks within this wavelength range. After the mixed solution was exposed to UV light for 0.5 h, these signal peaks corresponding to the diazonium groups disappeared and a significant decrease in absorbance intensity was observed. This evidence indicated the decomposition of the diazonium salt structure and the possible formation of new compounds. Subsequently, gel permeation chromatography (GPC) testing was conducted on the covalent polymers to investigate their molecular weights. As illustrated in Figure 5c, a broad peak appeared within the retention time of 18–20 min, with an integrated number-average molecular weight of 6401. Further calculation yields a degree of polymerization of 10.4. These mentioned data demonstrated that the CPs were formed through the reaction between SPs, specifically via the reaction between the diazonium groups and sulfonate groups.

2.3. The Tensile Tests of Hydrogels G01’, G02’, and G4

With the aim to study hydrogel adhesion induced by polymer entanglement, G1 and G2 were contacted and subsequently treated with UV light for testing the adhesion behaviors. Hydrogels G1 and G2 were allowed to contact each other for 13 days before being subjected to UV irradiation for 30 min for tensile testing. Meanwhile, the control groups G01’ and G02’ were obtained by contacting the blank hydrogel G0 with G1 and G2, respectively, for 13 days, followed by UV light treatment. As shown in Figure 6a and Movie S1, at a speed of 5 mm min−1, after undergoing a tensile displacement, the hydrogels G01’, G02’, and G4 all exhibited dissociation behavior (Figures S4 and S5). In the stress–strain curves (Figure 6b), the ultimate tensile stress and strain of G4 were 38.7 kPa and 99.12%, respectively, which were significantly higher than those of the control groups (the ultimate tensile stress and strain of G01’ were both 32.0 kPa and 62.86%, respectively; the ultimate tensile stress and strain of G02’ were also both 28.9 kPa and 67.28%, respectively). This suggested that, during prolonged contact between the hydrogels, the two monomers diffused into the other hydrogel network and formed SPs through electrostatic interactions, entangling the two hydrogel networks at the interface [39,40]. Subsequently, under UV light treatment, the SPs converted into CPs, causing the entanglement of the two hydrogel networks to become even tighter [41,42] and resulting in stronger hydrogel adhesion. Compared to the state where monomers were uniformly distributed in solution, monomers tended to accumulate at the gel interface due to their diffusion behaviors [43]. This monomer aggregation phenomena favored the formation of longer supramolecular polymers at the interface [44], leading to the formation of longer covalent polymers and a good adhesion effect.

3. Conclusions

In summary, we reported a design for achieving hydrogel adhesion by means of forming covalent polymers inside hydrogels to entangle different hydrogel networks. At higher concentrations, M1 could assemble with M2 to form SPs based on electrostatic interactions. The formation of SPs was verified via conducting 1H NMR spectra and viscosity studies. Upon UV light stimulation, SPs transformed into CPs, which was confirmed through characterization by FT-IR spectroscopy and GPC. M1 and M2 were introduced into hydrogels, respectively, and these two hydrogels were placed into contact with each other. Upon the time passing, adequate diffusion of M1 and M2 proceeded, thereby forming SPs based on electrostatic interactions. The SPs were threaded throughout hydrogel networks. Subsequently, under UV light exposure, the SPs transformed into CPs, causing further entanglement between these two hydrogel networks. Then, tensile tests confirmed the hydrogel adhesion. This approach allowed for offering a new strategy for hydrogel adhesion, avoiding the complex covalent graft of supramolecular groups on polymeric chains. In addition, this new adhesion mechanism broadened the application scope of covalent polymers and promoted the development of supramolecular chemistry, polymer materials, photoresponsive materials, adhesion materials, and hydrogel materials.

4. Materials and Methods

All reagent materials mentioned in this article were purchased from commercial suppliers and were used directly without any additional treatment. 4,4′-iminobisbenzenamine, D2O, DMSO-d6, 4-hydroxybenzenesulfonate sodium and LiBr were purchased from Energy Chemical company (Wuhan, China). H2SO4, NaNO2, acetone and dichloromethane were obtained from SINOPHARM (Shanghai, China). 1,4-bis(chloromethyl)benzene, potassium carbonate, acrylamide and ammonium peroxydisulfate were purchased from Aladdin (Shanghai, China). N,N′-methylenebis(acrylamide) was obtained from Macklin (Shanghai, China). DMF (HPLC grade) was obtained from Thermo Fisher Scientific Inc. (Shanghai, China). The monomers M1 and M2 were synthesized according to procedures found in the literature [29,35]. 1H NMR spectra and 13C NMR spectra studies were performed using a Bruker Advance 400 MHz spectrometer (Billerica, MA, USA). Fourier transform infrared (FT-IR) spectra were recorded on a Bruker Equinox 55 (Billerica, MA, USA). Gel permeation chromatography (GPC) analyses were performed on a Waters 1515 instrument (Milford, MA, USA) equipped with a Waters 4.6 × 30 mm guard column and three Waters WAT054466, WAT044226, and WAT044223 columns (Polymer Laboratories: linear range of molecular weight = 500 − 4 × 106), as well as a differential refractive index detector, using DMF (HPLC grade, containing 50 mmol/L LiBr) as the eluent at 35 °C with a flow rate of 1 mL min−1. An electronic universal testing machine (CMT4104, Shenzhen San Testing Machine Co., Shenzhen, China) was used to investigate the mechanical properties of hydrogels.

4.1. Synthesis and Characterization of M1 and M2

In a 100 mL flask, 4,4′-iminobisbenzenamine (0.021 mol, 4.19 g) was mixed with crushed ice (30 g) and 30% H2SO4 (40 mL) (Scheme S1) [29,35]. Subsequently, a solution containing NaNO2 (0.050 mol, 3.45 g) in 10 mL water was added dropwise to the mixture. The mixed solution was then allowed to react in an ice-water bath for 2 h before being filtered to collect the filtrate. Concentrated H2SO4 was added to the filtrate to precipitate the diazonium salt, yielding monomer M1. 1H NMR (400 MHz, D2O) δ 8.45 (d, J = 9.2 Hz, 4H), 7.67 (d, J = 9.4 Hz, 4H).
In dry acetone (15 mL), 1,4-bis(chloromethyl)benzene (1.4 mmol, 243 mg) was mixed with 4-hydroxybenzenesulfonate sodium (3.5 mmol, 686 mg) and dried potassium carbonate (3.5 mmol, 483 mg), and the mixture was heated under N2 with reflux for 48 h [45]. After the reaction was completed, the mixture was allowed to cool and then evaporated to dryness under reduced pressure. The residue was extracted with dichloromethane. The aqueous layer was washed twice with dichloromethane and the organic layers were combined. The crude product was recrystallized from a mixture of dichloromethane and hexane, yielding monomer M2. 1H NMR (400 MHz, DMSO-d6) δ 7.51 (d, J = 8.5 Hz, 4H), 7.45 (s, 4H), 6.93 (d, J = 8.6 Hz, 4H), 5.11 (s, 4H). 13C NMR (100 MHz, D2O) δ 160.18, 136.33, 135.18, 128.38, 127.38, 115.10, 70.02.

4.2. Preparation of Hydrogels G0, G1 and G2

Acrylamide (9.64 mmol, 0.684 g), N,N′-methylenebis(acrylamide) (5.96 × 10−3 mmol, 0.924 mg) and ammonium peroxydisulfate (19.7 × 10−3 mmol, 4.50 mg) were dissolved in 2.00 mL of deionized water to obtain a precursor solution. The precursor solution was poured into a glass mold with an array of cubic cavities (10 × 10 × 0.2 cm, length × width × height). The mold was then left at R.T. for 10 h to obtain the blank hydrogel G0. Following this preparation method of hydrogel G0, M1 (10 mM) and M2 (10 mM) were separately added to obtain hydrogels G1 and G2, respectively.

4.3. Preparation of Hydrogels G01’, G02’ and G4

The hydrogels G0, G1, and G2 were each cut into rectangular strips (2 × 0.5 cm, length x width). Subsequently, strip G0 was placed in contact with strips G1 and G2, respectively, with a contact area of 0.5 × 0.5 cm. The samples were then stored in sealed bags in the dark for 13 days. After this period, the strips were taken out and exposed under a mercury lamp for 0.5 h. Following the UV light exposure, tensile tests were performed on the strips (G01’ and G02’). The preparation of the strip G4 followed the same preparation procedure.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/gels10120822/s1. Figure S1: 1H NMR spectrum (400 MHz, D2O, 298 K) of M1; Figure S2: 1H NMR spectrum (400 MHz, DMSO-d6, 298 K) of M2; Figure S3: 13C NMR spectrum (100 MHz, D2O, 298 K) of M2; Figure S4: Stress-strain curves of G3 and G4; Figure S5: The tensile curves of hydrogels (a) G01, (b) G02, and (c) G4 as well as (d) summarized final fractured strain and final fractured stress of themselves. Movie S1: Tensile tests of G01’, G02’ and G4. Table S1: Preparation of hydrogels; Scheme S1: Synthesis route of 4,4′-azanediyldiphenol-d.

Author Contributions

Conceptualization, X.J.; methodology, K.H. and Q.L.; formal analysis, K.H. and Q.L.; investigation, K.H. and Q.L.; resources, K.H. and Q.L.; data curation, K.H. and Q.L.; writing—original draft preparation, K.H.; writing—review and editing, Q.L. and X.J.; supervision, X.J.; funding acquisition, X.J. All authors have read and agreed to the published version of the manuscript.

Funding

X. Ji appreciates the support from the Interdisciplinary Research Program of HUST (2023JCYJ013). X. Ji also appreciates the support from the Huazhong University of Science and Technology, where he is being supported by the Fundamental Research Funds for the Central Universities (Grant 2020kfyXJJS013). X. Ji also thanks the Open Research Fund (No. 2024JYBKF04) of the Key Laboratory of Material Chemistry for Energy Conversion and Storage (HUST), Ministry of Education.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article and Supplementary Materials. The original contributions presented in the study are included in the article and Supplementary Materials, further inquiries can be directed to the corresponding author.

Acknowledgments

X.J. thanks Hui Xiong from the Center for Experimental Chemistry (School of Chemistry and Chemical Engineering, HUST) for his support in the tensile tests; Shitao Fu from the Center for Experimental Chemistry (School of Chemistry and Chemical Engineering, HUST) for his support in the NMR tests.

Conflicts of Interest

The authors declare no conflicts of interest.

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Gels 10 00822 sch001
Scheme 1. (a) Cartoon representation of the formation of supramolecular polymers (SPs) assembled by monomers M1 and M2 as well as the formation of covalent polymers (CPs); (b) schematic illustration of the preparation process of hydrogel G4 and the adhesion behaviors achieved by the entanglement of polymers inside the hydrogel networks. The orange balls represent the benzenediazonium groups, and the purple balls represent the benzenesulfonic acid groups.
Scheme 1. (a) Cartoon representation of the formation of supramolecular polymers (SPs) assembled by monomers M1 and M2 as well as the formation of covalent polymers (CPs); (b) schematic illustration of the preparation process of hydrogel G4 and the adhesion behaviors achieved by the entanglement of polymers inside the hydrogel networks. The orange balls represent the benzenediazonium groups, and the purple balls represent the benzenesulfonic acid groups.
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Scheme 2. Synthesis route of monomers M1 and M2.
Scheme 2. Synthesis route of monomers M1 and M2.
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Figure 1. Partial 1H NMR spectra (400 MHz, D2O, 298 K) of (a) M1 (10.0 mM), (b) M2 (10.0 mM) and the mixtures of M1 and M2 at different concentrations of (c) 0.500 mM, (d) 1.00 mM, (e) 2.00 mM, (f) 5.00 mM, (g) 8.00 mM and (h) 10.0 mM. The orange balls represent the benzenediazonium groups, and the purple balls represent the benzenesulfonic acid groups.
Figure 1. Partial 1H NMR spectra (400 MHz, D2O, 298 K) of (a) M1 (10.0 mM), (b) M2 (10.0 mM) and the mixtures of M1 and M2 at different concentrations of (c) 0.500 mM, (d) 1.00 mM, (e) 2.00 mM, (f) 5.00 mM, (g) 8.00 mM and (h) 10.0 mM. The orange balls represent the benzenediazonium groups, and the purple balls represent the benzenesulfonic acid groups.
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Figure 2. Plot of the specific viscosity of equimolar mixtures of M1 and M2 in H2O versus M1 concentration at 298 K. The pink star represents the specific viscosity corresponding to a certain monomer concentration. The red circle represents the critical polymerization concentration (CPC).
Figure 2. Plot of the specific viscosity of equimolar mixtures of M1 and M2 in H2O versus M1 concentration at 298 K. The pink star represents the specific viscosity corresponding to a certain monomer concentration. The red circle represents the critical polymerization concentration (CPC).
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Figure 3. Photographs of the mixture solutions of M1 and M2 at different times (0–180 min) under UV light.
Figure 3. Photographs of the mixture solutions of M1 and M2 at different times (0–180 min) under UV light.
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Figure 4. (a) Representation of the formation of CPs transformed from SPs under UV light; (b) partial 1H NMR spectra (400 MHz, D2O, 298 K) of SPs assembled by M1 (10.0 mM) and M2 (10.0 mM) under UV light at different times (0–180 min).
Figure 4. (a) Representation of the formation of CPs transformed from SPs under UV light; (b) partial 1H NMR spectra (400 MHz, D2O, 298 K) of SPs assembled by M1 (10.0 mM) and M2 (10.0 mM) under UV light at different times (0–180 min).
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Figure 5. (a) FT-IR spectra of M1, M2 and CP; (b) UV-vis spectra of M1 (10.0 mM), M2 (10.0 mM), and the mixture of M1 and M2 after being exposed to UV light for 0.5 h; (c) GPC curve of CP.
Figure 5. (a) FT-IR spectra of M1, M2 and CP; (b) UV-vis spectra of M1 (10.0 mM), M2 (10.0 mM), and the mixture of M1 and M2 after being exposed to UV light for 0.5 h; (c) GPC curve of CP.
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Figure 6. (a) Photographs of G01’, G02’ and G4 in the tensile process; (b) stress–strain curves of G01’, G02’, and G4.
Figure 6. (a) Photographs of G01’, G02’ and G4 in the tensile process; (b) stress–strain curves of G01’, G02’, and G4.
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Hu, K.; Li, Q.; Ji, X. Polymer Entanglement-Induced Hydrogel Adhesion. Gels 2024, 10, 822. https://doi.org/10.3390/gels10120822

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Hu K, Li Q, Ji X. Polymer Entanglement-Induced Hydrogel Adhesion. Gels. 2024; 10(12):822. https://doi.org/10.3390/gels10120822

Chicago/Turabian Style

Hu, Kai, Qingyun Li, and Xiaofan Ji. 2024. "Polymer Entanglement-Induced Hydrogel Adhesion" Gels 10, no. 12: 822. https://doi.org/10.3390/gels10120822

APA Style

Hu, K., Li, Q., & Ji, X. (2024). Polymer Entanglement-Induced Hydrogel Adhesion. Gels, 10(12), 822. https://doi.org/10.3390/gels10120822

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