Softness, Elasticity, and Toughness of Polymer Networks with Slide-Ring Cross-Links

Mayumi, Koichi; Liu, Chang; Yasuda, Yusuke; Ito, Kohzo

doi:10.3390/gels7030091

Cited by 34 publications

(27 citation statements)

References 44 publications

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“…The incorporation of sliding cross-links into polymer networks has been demonstrated as an interesting strategy to achieve high stretchability and mechanical elasticity, in addition to promoting self-healing. − For example, the introduction of polyrotaxanes (PRs) constitutes a representative method in the development of slidable polymer networks . PRs are necklace-like supramolecules in which cyclodextrins (CDs) are threaded onto linear polymer chains that are capped with bulky end groups.…”

Section: Introductionmentioning

confidence: 99%

Slidable Cross-Linking Effect on Liquid Crystal Elastomers: Enhancement of Toughness, Shape-Memory, and Self-Healing Properties

Choi

Kim

Park

et al. 2022

ACS Appl. Mater. Interfaces

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The network structures of liquid crystal elastomers (LCEs) are crucial to impart rubbery behavior to LCEs and enable reversible actuation. Most LCEs developed to date are covalently linked, implying that the cross-links are fixed at a particular position. Herein, we report a new class of LCEs integrating polyrotaxanes (PRs) as slidable cross-links (PR-LCEs). Interestingly, the incorporation of a low loading (0.3–2.0 wt %) of the PR cross-linkers to the LCE causes a significant impact on various properties of the resulting PR-LCEs due to the pulley effect. The optimum PR loading is determined to be 0.5 wt %, at which point the toughness and damping behavior are maximized. The robust mechanical properties of the PR-LCE offers a superior actuation performance to that of the pristine LCE along with an excellent quadruple shape-memory effect. Furthermore, the incorporation of PR is useful to enhance the efficiency of shape-memory-assisted self-healing when heating above the nematic–isotropic transition.

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Section: Introductionmentioning

confidence: 99%

Slidable Cross-Linking Effect on Liquid Crystal Elastomers: Enhancement of Toughness, Shape-Memory, and Self-Healing Properties

Choi

Kim

Park

et al. 2022

ACS Appl. Mater. Interfaces

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“…In SR gel models, the axis chains are covered by cyclic molecules. Each cyclic molecule comprises eight beads, whose inner diameter was sufficiently large to slide freely on an axis chain. , Mayumi et al reported that the crack propagation resistance was dependent on the slidable range for cross-links, which is dominated by the number of axis chain monomers, instead of the cross-link density. , Thus, we set the same number of cross-links for SR gels with various coverages to ensure that the number of axis chain monomers per cross-links is the same to clarify the effect of coverage on the mechanical properties at the same slidable range for cross-links. We prepared various SR gels with different coverages by changing the number of cyclic molecules per axis chain, M .…”

Section: Methodsmentioning

confidence: 99%

Molecular-Level Elucidation of a Fracture Process in Slide-Ring Gels via Coarse-Grained Molecular Dynamics Simulations

et al. 2022

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Slide-ring (SR) gels with slidable cross-linked cyclic molecules exhibit considerably higher fracture toughness than conventional fixed cross-link (FC) gels. However, the mechanical properties of SR gels are still unsatisfactory, and thus, these gels cannot be practically applied. Therefore, molecular scale insights into the fracture mechanism of SR gels are required to improve their mechanical properties. This study conducted tensile strain simulations of FC and SR gels using a coarse-grained molecular dynamics (CGMD) method to elucidate the fracture mechanism of SR gels. The CGMD simulations showed that the SR gels exhibited higher fracture toughness than the FC gels. In the FC gels, the axis chains easily broke under a low strain because fixed cross-links constrain the polymer chain, resulting in stress concentration on the axis chains. On the contrary, in the SR gels, the axis chains did not break until a high strain was applied because the cross-linked cyclic molecules slide not to accumulate stress concentration. The analysis of the fracture mechanism of the SR gels revealed that the chain-ends are the origin of the fracture in the SR gels. The cross-linked and un-cross-linked cyclic molecules slide on the axis chains and are stacked around the chain-ends. The stacked cross-linked cyclic molecules induced stress concentrations around the chain-ends. Next, we investigated the effect of coverage on the SR gels. We found that low-coverage SR gels exhibited higher fracture toughness and ultimate strength than highcoverage SR gels because the stacked un-cross-linked cyclic molecules prevent cross-linked cyclic molecules from sliding, leading to a low fracture toughness caused by the stress concentration at the chain-ends. The axis chains of the low-coverage SR gels with a high fracture toughness deformed to the strain direction until a high strain. Thus, the low-coverage SR gels showed a high orientation toward the strain direction. A high orientation contributes to the uniform distribution of mechanical stress on the chains, leading to a high ultimate strength. Although the SR gels generally exhibit a low ultimate strength, SR gels with a low coverage ratio of 5% showed a higher ultimate strength than FC gels. Finally, we propose that, compared with the high-coverage SR gels, the low-coverage SR gels exhibit both higher fracture toughness and ultimate strength, based on the atomistic insight pertaining to the mechanism by which the low-coverage SR gels possess free space for cross-linked cyclic molecules to move to the chain-ends until a high strain is applied.

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“…The conformational change between ring and chain has a decisive effect on the mechanical properties of glide ring gel. Reducing the covering area of the ring and increasing the length of the shaft chain can improve the toughness [ 45 , 46 ]. Because of the existence of the ring-chain, the selection of monomer is also limited, and the influence of conformation change on mechanical properties leads to more complex mechanical behavior.…”

Section: Mechanical Reinforcement Methodsmentioning

confidence: 99%

Recent Advances in Mechanical Reinforcement of Zwitterionic Hydrogels

Lin

Wei

Liu

et al. 2022

Gels

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As a nonspecific protein adsorption material, a strong hydration layer provides zwitterionic hydrogels with excellent application potential while weakening the interaction between zwitterionic units, leading to poor mechanical properties. The unique anti-polyelectrolyte effect in ionic solution further restricts the application value due to the worsening mechanical strength. To overcome the limitations of zwitterionic hydrogels that can only be used in scenarios that do not require mechanical properties, several methods for strengthening mechanical properties based on enhancing intermolecular interaction forces and polymer network structure design have been extensively studied. Here, we review the works on preparing tough zwitterionic hydrogel. Based on the spatial and molecular structure design, tough zwitterionic hydrogels have been considered as an important candidate for advanced biomedical and soft ionotronic devices.

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Softness, Elasticity, and Toughness of Polymer Networks with Slide-Ring Cross-Links

Cited by 34 publications

References 44 publications

Slidable Cross-Linking Effect on Liquid Crystal Elastomers: Enhancement of Toughness, Shape-Memory, and Self-Healing Properties

Slidable Cross-Linking Effect on Liquid Crystal Elastomers: Enhancement of Toughness, Shape-Memory, and Self-Healing Properties

Molecular-Level Elucidation of a Fracture Process in Slide-Ring Gels via Coarse-Grained Molecular Dynamics Simulations

Recent Advances in Mechanical Reinforcement of Zwitterionic Hydrogels

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