Fracture of a biopolymer gel as a viscoplastic disentanglement process

Fracture processes are ubiquitous in soft materials, even in complex fluids, subjected to stresses. To investigate these processes in a simple geometry, we use a model self-assembled transient gel and study the instability patterns obtained in a radial Hele-Shaw cell when a low viscosity oil pushes the more viscous transient gel. Thanks to an analysis of the morphology of the patterns, we find a discontinuous transition between the standard Saffman-Taylor fingering instability and a fracturing instability as the oil injection rate increases. Our data suggest that the flow properties of the gel ahead of the finger tip controls the transition towards fracturing. By analyzing the displacement field of the gel in the vicinity of the fingers and cracks, we show that in the fingering regime, the oil gently pushes the gel, whereas in the fracturing regime, the crack tears apart the gel, resulting in a strong drop of the gel velocity ahead of the crack tip as compared to the tip velocity. We find a unique behavior for the whole displacement field of a gel around a crack, which is drastically different from that around a finger, and reveals the solid-like behavior of the gel at short time. Our experiments and analysis provide quantitative yet simple tools to unambiguously discriminate a finger from a crack in a visco-elastic material.

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“…2c). This is similar to what has been measured for gelatin 19 . The extrapolation of J towards 0 velocity yields J 0 = (45 ± 12)mJ/m 2 .…”

Section: Resultssupporting

confidence: 91%

The fingering to fracturing transition in a transient gel

et al. 2013

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“…The measured toughness of cis-polyisoprene was almost 2-3 times larger than the predicted values. Since the calculated values were based on several assumptions, this level of agreement is considered excellent by previous researchers 14,23 . The figure also contains two data sets from single network hydrogels.…”

Section: Discussionsupporting

confidence: 78%

Effect of First Network Topology on the Toughness of Double Network Hydrogels

et al. 2013

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The fracture toughness of a double network (DN) hydrogel is shown here to be directly proportional to the toughness of the first-formed network. A series of DN gels was prepared in which the cross-link density of the first (tighter) network was controlled by varying the monomer and cross-linker concentrations. The toughness, tensile strength and elastic modulus of the DN gels increased significantly with an increase in the cross-link density of the first network and with identically prepared second networks. Moreover, the toughness of the double network was found to be linearly related to the toughness of the first network with an amplification factor of 150 times. Existing models of DN fracture based on network strand scission are utilized to quantify the relationship between the first network toughness and the DN toughness. ABSTRACTThe fracture toughness of a double network (DN) hydrogel is shown here to be directly proportional to the toughness of the first-formed network. A series of DN gels was prepared in which the crosslink density of the first (tighter) network was controlled by varying the monomer and crosslinker concentrations. The toughness, tensile strength and elastic modulus of the DN gels increased significantly with an increase in the crosslink density of the first network and with 2 identically-prepared second networks. Moreover, the toughness of the double network was found to be linearly related to the toughness of the first network with an amplification factor of ~150 times. Existing models of DN fracture based on network strand scission are utilised to quantify the relationship between the first network toughness and the DN toughness.

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“…After an initial transient, the crack reaches a steady regime at a velocity V which increases with the "energy release rate" G imposed by the opening ∆. We found that, in this slow, subsonic regime (V < 30 mm/s):with G 0 ≃ 2.5 J.m −2 , Γ ≃ 10 6 , and were able to assign this strong V -dependence to the fact that, in such a reversible gel, fracture occurs via scissionless chain pull-out, the high dissipation being due to viscous drag [10,11]. The results reported here were obtained on gels with a 5 wt.% content of gelatin in the solvent (pure water except when otherwise specified).…”

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confidence: 78%

Magic Angles and Cross-Hatching Instability in Hydrogel Fracture

et al. 2008

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The full 2D analysis of roughness profiles of fracture surfaces resulting from quasi-static crack propagation in gelatin gels reveals an original behavior characterized by (i) strong anisotropy with maximum roughness at V -independent symmetry-preserving angles, (ii) a sub-critical instability leading, below a critical velocity, to a cross-hatched regime due to straight macrosteps drifting at the same magic angles and nucleated on crack-pinning network inhomogeneities.Step height values are determined by the width of the strain-hardened zone, governed by the elastic crack blunting characteristic of soft solids with breaking stresses much larger that low strain moduli.PACS numbers: 62.20. Mk, 83.80.Kn Over the past two decades, considerable effort has been devoted to characterizing and understanding the statistical properties of the roughness of fracture surfaces in linear elastic disordered materials. Investigation of a wide variety of systems, ranging from brittle silica glass to ductile metallic alloys, has revealed the ubiquity of wide roughness spectra exhibiting self-affine characteristics on sizeable wavelength ranges. On the basis of analysis of height-height correlation functions in a single direction, E. Bouchaud et al.[1] first conjectured a fully universal behavior summed up into a single Hurst exponent. The discrepancies between the predictions of various subsequent theoretical models have pointed toward the importance of also investigating possible anisotropies of the scaling properties [2]. Work along this line indeed reveals different scaling exponents along the crack propagation direction and the (orthogonal) crack front one. From this, Ponson et al. [3] conclude that the self-affinity of the roughness is described by a Family-Vicsek scaling, hence by a set of two exponents. Within their new analysis, full universality is no longer the case since they evidence the existence of at least two classes of materials.However, on the basis of their theoretical work, Bouchbinder et al. [4] have recently raised several new issues. In particular, they point to the necessity of a full 2D analysis of the correlations and find, when reexamining some experimental data, that a host of up to now unidentified exponents appear. They insist on the need to focus on the effects of departures from linear elasticity in the fracture process.In this spirit we report here on the nature of surface morphologies resulting from the fracture of gelatin, a highly compliant thermally reversible hydrogel, in the strongly subsonic regime. We show that these surfaces present very striking anisotropic features. Namely, the rms roughness R(θ), measured along a direction at angle θ from the propagation one Ox, exhibits two symmetrypreserving maxima for θ = ±θ m . For gels with a fixed gelatin concentration, this "magic angle" θ m is constant over more than one decade of both crack velocity V and solvent viscosity η. Moreover, below a critical, η-dependent, velocity V c a new regime develops, characterized by a cross-hatched (CH) mo...

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Fracture of a biopolymer gel as a viscoplastic disentanglement process

Cited by 98 publications

References 36 publications

The fingering to fracturing transition in a transient gel

The fingering to fracturing transition in a transient gel

Effect of First Network Topology on the Toughness of Double Network Hydrogels

Magic Angles and Cross-Hatching Instability in Hydrogel Fracture

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