Ref HAL: hal-01488613_v1
Exporter : BibTex | endNote
Résumé:

Characterization and microscopic precursors of failure in a polymer network

Ref HAL: hal-01441941_v1
Exporter : BibTex | endNote
Résumé:

none

Ref HAL: hal-01425041_v1
DOI: 10.1103/PhysRevX.6.041057
WoS: 000390287900001
Exporter : BibTex | endNote
12 Citations
Résumé:

Interfacial tension between immiscible phases is a well-known phenomenon, which manifests itself in everyday life, from the shape of droplets and foam bubbles to the capillary rise of sap in plants or the locomotion of insects on a water surface. More than a century ago, Korteweg generalized this notion by arguing that stresses at the interface between two miscible fluids act transiently as an effective, nonequilibrium interfacial tension, before homogenization is eventually reached. In spite of its relevance in fields as diverse as geosciences, polymer physics, multiphase flows, and fluid removal, experiments and theoretical works on the interfacial tension of miscible systems are still scarce, and mostly restricted to molecular fluids. This leaves crucial questions unanswered, concerning the very existence of the effective interfacial tension, its stabilizing or destabilizing character, and its dependence on the fluid's composition and concentration gradients. We present an extensive set of measurements on miscible complex fluids that demonstrate the existence and the stabilizing character of the effective interfacial tension, unveil new regimes beyond Korteweg's predictions, and quantify its dependence on the nature of the fluids and the composition gradient at the interface. We introduce a simple yet general model that rationalizes nonequilibrium interfacial stresses to arbitrary mixtures, beyond Korteweg's small gradient regime, and show that the model captures remarkably well both our new measurements and literature data on molecular and polymer fluids. Finally, we briefly discuss the relevance of our model to a variety of interface-driven problems, from phase separation to fracture, which are not adequately captured by current approaches based on the assumption of small gradients.

Ref HAL: hal-01414119_v1
DOI: 10.1016/j.jfoodeng.2016.06.009
WoS: WOS:000382349300005
Exporter : BibTex | endNote
7 Citations
Résumé:

Wheat flours are essential ingredients of daily food products like bread, cookies or pastries. Their quality depends on the milling process and mechanical strength of wheat grains. Although it is well known that the strength and rupture of grains are strongly controlled by the endosperm microstructure, the respective roles of the starch and polymer volume fractions and their adhesion are not yet fully understood. This typical biological microstructure can be modeled as a cemented granular material, where the two size populations of starch granules (large:A-type, small:B-type) are the particles, and the protein matrix, which partially fills the space between granules, plays the role of a cement. This structural model of wheat endosperm is used, together with mechanical characteristics of starch and proteins obtained by means of Atomic Force Microscopy (AFM) measurements, to simulate the mechanical behavior and breakage of wheat endosperm in milling process. We find that the porosity outweighs the effect of other parameters for the elastic modulus, which declines as a nearly linear function of porosity. We also show that the tensile strength is an increasing function of the amount and connectivity of starch granules with increasing concentration of stresses along chains of granules. This effect is more significant at low porosity where stress distribution is mainly controlled by the contact network between starch granules. This effect explains why the protein content is not fully correlated to vitreousness, and samples of similar protein content can be different in vitreosity. Finally, we find that the starch-granule adhesion strongly affects the tensile strength whereas the effect of starch volume fraction appears mainly at high interface adhesion, which is the case of hard type wheat grains.

Ref HAL: hal-01407654_v1
DOI: 10.1088/0957-0233/27/12/125902
WoS: WOS:000387150000001
Exporter : BibTex | endNote
7 Citations
Résumé:

To investigate the interplay between microscopic dynamics and macroscopic rheology insoft matter, we couple a stress-controlled-rheometer equipped with a Couette cell to a lightscattering setup in the imaging geometry, which allows us to measure both the deformationfield and the microscopic dynamics. To validate our setup, we test two model systems. For anelastic solid sample, we recover the expected deformation field within 1 μm. For a pure viscousfluid seeded with tracer particles, we measure the velocity profile and the dynamics of thetracers, both during shear and at rest. The velocity profile is acquired over a gap of 5 mm witha temporal and spatial resolution of 1 s and 100 μm, respectively. At rest, the tracer dynamicshave the expected diffusive behavior. Under shear, the microscopic dynamics corrected for theaverage drift due to solid rotation scale with the local shear rate, demonstrating that our setupcaptures correctly the relative motion of the tracers due to the affine deformation.

Ref HAL: hal-01370655_v1
Exporter : BibTex | endNote
Résumé:

We study the destabilization mechanism of thin liquid sheets expanding in air and show that dilute oilin-water emulsion-based sheets disintegrate through the nucleation and growth of holes that perforatethe sheet [1]. The velocity and thickness fields of the sheet outside the holes are not perturbed by holesand hole opening follows a Taylor-Culick law. We find that a pre-hole, which widens and thins out thesheet with time, systematically precedes the hole nucleation. The growth dynamics of the pre-holefollows the law theoretically predicted for a liquid spreading on another liquid of higher surfacetension due to Marangoni stresses. Classical Marangoni spreading experiments quantitativelycorroborate our findings.

Ref HAL: hal-01366306_v1
Ref Arxiv: 1607.02271
DOI: 10.1021/acsmacrolett.6b00516
WoS: 000385913800002
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
6 Citations
Résumé:

We investigate the nucleation and propagation of cracks in self-assembled viscoelastic fluids, which are made of surfactant micellesreversibly linked by telechelic polymers. The morphology of the micelles can be continuously tuned, from spherical to rodlike towormlike, thus producing transient double networks when the micelles are sufficiently long and entangled and transient singlenetworks otherwise. For a single network, we show that cracks nucleate when the sample deformation rate involved is comparable tothe relaxation time scale of the network. For a double network, by contrast, significant rearrangements of the micelles occuras a crack nucleates and propagates. We show that birefringence develops at the crack tip over a finite length, ξ, whichcorresponds to the length scale over which micelle alignment occurs. We find that ξ is larger for slower cracks, suggesting anincrease of ductility.