Understanding the process of healing of thermoreversible covalent adaptable networks

Sheridan, Richard J.; Bowman, Christopher N.

doi:10.1039/c2py20960h

Cited by 36 publications

(24 citation statements)

References 35 publications

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“…aviation, automobile, structures or coatings) [1]. The possibility of forming network structures with tuneable properties and the presence of reversible network relaxation processes make them suitable materials for more demanding applications such as self-healing materials, optical devices or lithographic printing [2,3]. Nowadays, the increasing demand of smart materials with complex shape designs (i.e.…”

Section: Introductionmentioning

confidence: 99%

Phenomenological characterization of sequential dual-curing of off-stoichiometric “thiol-epoxy” systems: Towards applicability

et al. 2017

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An extensive characterization of a sequential dual-curing system based on off-stoichiometric "thiol-epoxy" mixtures was carried out using thiol compounds of different functionality. The intermediate and final materials obtained after each curing stages at different thiol-epoxy ratios were studied by means of thermomechanical and rheological experiments. The storage and loss modulus and the loss factor tan δ were monitored during the curing process to analyse gelation and network structure build-up. The critical ratio for gelation was determined making use of the ideal Flory-Stockmayer theory and compared with experimental results. Intermediate materials obtained in the vicinity of the theoretical critical ratio did not have the mechanical consistency expected for partially crosslinked materials, did not retain their shape and even experienced undesired flow upon heating to activate the second curing reaction. The rheological results showed that the critical ratio is higher than the predicted value and that a softening during the second curing stage affects the shape-retention at this ratio. From the thermomechanical results, a wide range of intermediate and final materials with different properties and applicability can be obtained by properly choosing the thiol-epoxy ratio: from liquid-like to highly deformable intermediate materials and from moderately crosslinked (deformable) to highly crosslinked (brittle) final materials.

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Section: Introductionmentioning

confidence: 99%

Phenomenological characterization of sequential dual-curing of off-stoichiometric “thiol-epoxy” systems: Towards applicability

et al. 2017

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“…The interfacial DCC was employed at the composite interfaces, not only covalently bonds the resins to the filler as is often done with other filler modifications to promote adhesion between the filler and resin, but here this approach also creates composite interfaces capable of stress relaxation and dynamic bond exchange. While DCC approaches such as AFT, [14,15] Diels–Alder, [21,36] transesterification, [18] and others have been used extensively to promote healing and other desirable aspects in conventional materials, [11,32,37] the localization of a dynamic covalent bond to the interface has been little if ever explored, particularly relative to controls in which no such bond exchange is possible. The evolution of material properties including toughness, tensile strength, polymerization shrinkage stress, and the recovery of the dissipative energy in covalently cross-linked, relatively glassy, photo-polymerized thiol-ene composites was explored for both adaptive interface (AI) and passive interface (PI)-based composites.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin–Silica Nanoparticles Interface

Sowan

Cox

Shah

et al. 2018

Adv Materials Inter

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The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin–filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m−3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin–filler interface.

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“…Self-healing is one of the most fascinating features of biological systems, such as skin, bones, and muscle tissues, and this phenomena has inspired the scientific community for decades to design synthetic auto-repairable materials. 5 Several covalent (e.g., Diels-Alder linkages, hydrazone bonds, alkoxyamines, and disulfide linkages) 6,7 and non-covalent interactions (e.g., hydrogen bonding, p-p stacking, ionic interactions, and metal-ligand coordination) 8,9 have been employed to prepare self-healing polymers. 4 The process of healing cracks in natural systems often involves an energy dissipation mechanism, due to the presence of sacrificial bonds that can break and reform dynamically before or while the failure occurs.…”

Section: Introductionmentioning

confidence: 99%

Self-healing hydrogels containing reversible oxime crosslinks

2015

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Self-healing oxime-functional hydrogels have been developed that undergo a reversible gel-to-sol transition via oxime exchange under acidic conditions. Keto-functional copolymers were prepared by conventional radical polymerization of N,N-dimethylacrylamide (DMA) and diacetone acrylamide (DAA). The resulting water soluble copolymers (P(DMA-stat-DAA)) were chemically crosslinked with difunctional alkoxyamines to obtain hydrogels via oxime formation. Gel-to-sol transitions were induced by the addition of excess monofunctional alkoxyamines to promote competitive oxime exchange under acidic conditions at 25 °C. The hydrogel could autonomously heal after it was damaged due to the dynamic nature of the oxime crosslinks. In addition to their chemo-responsive behavior, the P(DMA-stat-DAA) copolymers exhibit cloud points which vary with the DAA content in the copolymers. This thermo-responsive behavior of the P(DMA-stat-DAA) was utilized to form physical hydrogels above their cloud point. Therefore, these materials can either form dynamic-covalent or physically-crosslinked gels, both of which demonstrate reversible gelation behavior.

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Understanding the process of healing of thermoreversible covalent adaptable networks

Cited by 36 publications

References 35 publications

Phenomenological characterization of sequential dual-curing of off-stoichiometric “thiol-epoxy” systems: Towards applicability

Phenomenological characterization of sequential dual-curing of off-stoichiometric “thiol-epoxy” systems: Towards applicability

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin–Silica Nanoparticles Interface

Self-healing hydrogels containing reversible oxime crosslinks

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