Ref HAL: hal-01631380_v1
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In this paper we present geometrical measurements made on aqueous polyacrylamide gels withlab-based micro-tomography, one of the most convenient ways of accessing a quantitative measurement of thefascinating shapes that these materials make when hanging under their own weight.

Ref HAL: hal-01495935_v1
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We study experimentally the impact of ultra soft spherical gel balls of millimetric size d0 on a rigid substrate covered by a thin layer of liquid nitrogen to avoid viscous dissipation. The balls largely deform like a pancake at high impact velocities. We measure the maximally deformed size dmax and the the time needed to reach this maximal size after impact τmax, versus the impact velocity ui for various elastic moduli. We do the same type of experiments with liquid droplets of various surface tensions. The experiments reveal a universal scaling behavior of the maximum deformation dmax/d0 of both solid balls and liquid drops provided that both bulk and surface elasticity are properly taken into account. Moreover, we show that, in absence of viscous dissipation, the dynamics of the system can be understood as a conventional spring-mass system with a stiffness given by a combination of surface tension and bulk elasticity and a mass given by that of the ball (or drop); the deformation of the small ball (drop) during the impact linearly depends on the impact velocity, and the contact time scales as the period of this spring-mass system.

Ref HAL: hal-02070620_v1
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The Continuous Droplet Interface Crossing Encapsulation (cDICE) is an easy and robust method for producing, at high yield, monodisperse lipid vesicles with a controlled content as well as capsules with a designed shell. It consists in forcing a droplet through an interface between two imiscible fluids, using an external force such as centrifugation. At high inertia, the droplet entrain fluid that will constitute the shell of the capsule. At low inertia, the presence of amphiphile and the deformable interface interactions lead to monolayers zipping and formation of an amphiphile bilayer around the droplet. We will discuss the physical mechanisms involved in the production of both cDICE vesicles (low droplets inertia) and capsules (at high inertia), and the potential applications of this method. This method founds indeed many applications in biomimetics as it allows to encapsulate various biological solutions (biopolymers, hemoglobin, colloids, polymeric gels, cells. . . ) in membranes that can be composite and/or assymetric, or polymeric, and in the field of microencapsulation.

Ref HAL: hal-01292652_v1
Ref Arxiv: 1603.06703
DOI: 10.1063/1.4972253
WoS: 000392096800036
Ref. & Cit.: NASA ADS
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10 Citations
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We develop and thoroughly test a stress-controlled, parallel plates shear cell that can be coupled to an optical microscope or a small angle light scattering setup, for simultaneous investigation of the rheological properties and the microscopic structure of soft materials under an imposed shear stress. In order to minimize friction, the cell is based on an air bearing linear stage, the stress is applied through a contactless magnetic actuator, and the strain is measured through optical sensors. We discuss the contributions of inertia and of the small residual friction to the measured signal and demonstrate the performance of our device in both oscillating and step stress experiments on a variety of viscoelastic materials.

Résumé:

We demonstrate the instability of the free surface of a soft elastic layer facing downwards. Experiments are carried out using a system consisting in a gel of constant density and shear modulus , put in a rigid cylindrical dish of depth h. When turned upside down, the free surface of the gel undergoes a normal outgoing acceleration g., whereas a steady pattern spontaneously appears in the opposite case. This phenomenon results from the interplay between the gravitational energy and the elastic energy of deformation of the system

Ref HAL: hal-01435953_v1
DOI: 10.1073/pnas.1608074113
WoS: WOS:000388830700047
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73 Citations
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Blood viscosity decreases with shear stress, a property essential for an efficient perfusion of the vascular tree. Shear thinning is intimately related to the dynamics and mutual interactions of RBCs, the major component of blood. Because of the lack of knowledge about the behavior of RBCs under physiological conditions, the link between RBC dynamics and blood rheology remains unsettled. We performed experiments and simulations in microcirculatory flow conditions of viscosity, shear rates, and volume fractions, and our study reveals rich RBC dynamics that govern shear thinning. In contrast to the current paradigm, which assumes that RBCs align steadily around the flow direction while their membranes and cytoplasm circulate, we show that RBCs successively tumble, roll, deform into rolling stomatocytes, and, finally, adopt highly deformed polylobed shapes for increasing shear stresses, even for semidilute volume fractions of the microcirculation. Our results suggest that any pathological change in plasma composition, RBC cytosol viscosity, or membrane mechanical properties will affect the onset of these morphological transitions and should play a central role in pathological blood rheology and flow behavior.

Ref HAL: hal-01236173_v1
DOI: 10.1007/s10853-015-9253-0
WoS: WOS:000359811300015
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2 Citations
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Subcritical crack growth and crack closure are analysed using the double-cleavage-drilled-compression method, in two calcium phosphate based glasses. The measurements of the crack velocity as a function of temperature, from ambient to 250°C, are reported for two different relative humidity levels. Studied glasses present unusual trends characterized by a non gradual shift of V-KI curves versus temperature. Moreover, when the load is released and crack closes, expulsion of a “liquid-like” phase is observed forming droplets along the crack path. These droplets are only formed at certain temperatures, but both under high and low water humidity. They evolve toward residues when temperature is decreased.