Multi-scale multi-mechanism design of tough hydrogels: building dissipation into stretchy networks

Zhao, Xuanhe

doi:10.1039/c3sm52272e

Cited by 1,037 publications

(918 citation statements)

References 201 publications

(316 reference statements)

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“…23,24,25 Following the design principles of tough hydrogels and applying them to NFC-based materials could offer viable routes for preparing strong and tough films that would retain attractive mechanical properties also in the wet state. 26 One such attractive pathway concerning NFC-based materials is physical crosslinking. 27 , 28 Individual physical crosslinks are typically weaker than covalent ones, making them more likely to break upon stress, potentially serving as sacrificial bonds for dissipating energy during deformation.…”

Section: Introductionmentioning

confidence: 99%

Water-Resistant, Transparent Hybrid Nanopaper by Physical Cross-Linking with Chitosan

et al. 2015

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ABSTRACT. One of the major, but often overlooked, challenges towards high end applications of nanocelluloses is to maintain their mechanical stability under hydrated conditions. As such, permanent covalent crosslinking or surface hydrophobization are viable solutions provided that neither processability nor interfibrillar bonding is compromised. Here we show an alternative based on physical crosslinking of nanofibrillated cellulose (NFC, also denoted as microfibrillated cellulose, MFC, and cellulose nanofibers, CNF) with chitosan for the preparation of transparent films. Transparency (~ 80 % throughout the visible spectrum) is achieved by suppressing aggregation and carefully controlling the mixing conditions: Chitosan dissolves in aqueous medium at low pH and under these conditions the NFC/chitosan mixtures form easily processable hydrogels.A simple change in the environmental conditions (i.e. an increase of pH) reduces hydration of chitosan promoting multivalent physical interactions between NFC and chitosan over those with water, resulting effectively in crosslinking. Films of NFC/chitosan 80/20 w/w show excellent mechanical properties in the wet state, with a tensile modulus of 4 and 14 GPa at low (0.5 %) and large (16 %) strains, respectively and an ultimate strength of 100 MPa (with corresponding maximum strain of 28 %). Remarkably, a strength of 200 MPa (with maximum strain of 8%) is measured at 50 % air relative humidity. We expect that the proposed, simple concept opens new pathways toward NFC-based material utilization in wet or humid conditions, a challenge that has remained unresolved.

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Section: Introductionmentioning

confidence: 99%

Water-Resistant, Transparent Hybrid Nanopaper by Physical Cross-Linking with Chitosan

et al. 2015

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“…3,6,7 In each of these applications, control over gel structure and mechanics is critical to obtaining the desired gel behaviour. 8 Many such materials incorporate transient networks, where the use of physical associations as opposed to permanent chemical bonds allows the gels to respond to environmental stimuli such as temperature, 9 pH, 10 ionic strength, 11 and light. 12 These types of physically associated networks also demonstrate mechanical properties not seen in their chemically crosslinked counterparts, including shear thinning at high strain rates, self-healing properties, and stress relaxation at long times.…”

Section: Introductionmentioning

confidence: 99%

Celebrating Soft Matter's 10th Anniversary: Chain configuration and rate-dependent mechanical properties in transient networks

et al. 2015

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Numerical solution of a coupled set of Smoluchowski convection-diffusion equations of associating polymers modelled as finitely extensible dumbbells enables computation of time-dependent end-to-end distributions for bridged, dangling, and looped chains in three dimensions as a function of associating end-group kinetics. Non-monotonic flow curves which can lead to flow instabilities during shear flow result at low equilibrium constant and high association rate from two complementary phenomena: a decrease in the fraction of elastically active chains with increasing shear rate and non-monotonic extension in the population of elastically active chains. Chain tumbling leads to reformation of bridges, resulting in an increased fraction of bridged chains at high Deborah number and significant reduction in the average bridge chain extension. In the start-up of steady shear, force-activated chain dissociation and chain tumbling cause both stress overshoot and stress ringing behaviour prior to reaching steady state stress values. During stress relaxation following steady shear, chain kinetics and extension mediate both the number of relaxations and the length of time required for system relaxation. While at low association rate relaxation is limited by the relaxation of dangling chains and the rate of dangling chain formation, at high association rate coupling of dangling and bridged chains leads to simultaneous relaxation of all chains due to a dynamic equilibrium between dangling and bridged states.

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“…Stretchable, transparent, ionic conductors (e.g., hydrogels and ionogels) enable devices of unusual functions, such as transparent loudspeakers [12], artificial skins [13], artificial axons [14,15], and electroluminescence of giant stretchability [16][17][18]. The interest in the mechanics of stretchable materials has surged [19][20][21][22][23][24][25][26][27][28][29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

Flaw sensitivity of highly stretchable materials

Chen

Wang

Suo

2017

Extreme Mechanics Letters

196

135

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Elastomers and gels can often deform multiple times their original length. The stretchability is insensitive to small cuts in the samples, but reduces markedly when the cuts are large. We show that this transition occurs when the depth of cut exceeds a material-specific length, defined by the ratio of the fracture energy measured in the large-cut limit and the work to rupture measured in the small-cut limit. This conclusion generalizes a result in the fracture mechanics of hard materials. For an acrylic elastomer and a polyurethane, we measure the stretch to rupture as a function of the depth of cut, and show that the experimental data agree well with the prediction of the nonlinear elastic fracture mechanics. In a space of material properties we compare many materials (elastomers, gels, ceramics, glassy polymers, biomaterials, and metals), and find that the material-specific length varies from nanometers to centimeters.

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Multi-scale multi-mechanism design of tough hydrogels: building dissipation into stretchy networks

Cited by 1,037 publications

References 201 publications

Water-Resistant, Transparent Hybrid Nanopaper by Physical Cross-Linking with Chitosan

Water-Resistant, Transparent Hybrid Nanopaper by Physical Cross-Linking with Chitosan

Celebrating Soft Matter's 10th Anniversary: Chain configuration and rate-dependent mechanical properties in transient networks

Flaw sensitivity of highly stretchable materials

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