Two-dimensional plastic flow of foams and emulsions in a channel: experiments and lattice Boltzmann simulations

Abstract

International audienceIn order to understand the flow profiles of complex fluids, a crucial issue concerns the emergence of spatial correlations among plastic rearrangements exhibiting cooperativity flow behaviour at the macroscopic level. In this paper, the rate of plastic events in a Poiseuille flow is experimen-tally measured on a confined foam in a Hele-Shaw geometry. The correlation with independently measured velocity profiles is quantified by looking at the relationship between the localisation length of the velocity profiles and the localisation length of the spatial distribution of plastic events. To complement the cooperativity mechanisms studied in foam with those of other soft-glassy systems, we compare the experiments with simulations of dense emulsions based on the lattice Boltzmann method, which are performed both with, and without, wall friction. Finally, unprecedented results on the distribution of the orientation of plastic events show that there is a non-trivial correlation with the underlying local shear strain. These features, not previously re-ported for a confined foam, lend further support to the idea that cooperativity mechanisms, orig-inally invoked for concentrated emulsions (Goyon et al. 2008), have parallels in the behaviour of other soft-glassy materials

Fluidization and wall slip of soft glassy materials by controlled surface roughness

“…The numerical model is in continuity with a number of works by some of the authors [28,35,39] (see Sec. II of ESI).…”

“…To this aim we applied a novel procedure to detect rearrangements in geometries with arbitrary complex boundaries [41]. This made it possible to study the phenomena related to droplets plasticity with unprecedented statistics [28,35]. Shortly, we compared two consecutive configurations by using the corresponding Delaunay triangulations built starting from the centers of mass of the droplets.…”

“…the inverse viscosity for the system. An important result of KEP relates the fluidity field with the rate Γ of plastic rearrangementsThe relation between the rate of plastic rearrangements and the flow profiles is highly non-trivial [34], and with the exception of a few studies [24,28,35], has not been researched in detail. Experimental studies report that surface roughness can change the material structural properties, trigger and promote rearrangements, and describe this scenario by ad-hoc parameters, e.g.…”

“…This solidto-liquid transition and the corresponding flowing properties have been widely studied [8], but still pose a series of challenging questions, relevant both for applications [9][10][11] and for a better understanding of the statistical mechanics of SGM [12][13][14][15][16][17][18][19][20]. Recent studies [21][22][23][24][25][26][27][28][29] showed that their flow bahavior is characterized by "nonlocality" [21,22], meaning that the relation between the local stress σ and the local shear rateγ cannot be explained with a unique master curve. This non-local behaviour depends on both confinement and surface roughness [22,25,26], and it is ascribed to the presence of plastic rearrangements [21,22], i.e.…”

Lamella Division in a Foam Flowing through a Two-Dimensional Porous Medium: A Model Fragmentation Process

“…For each site and each fragmentation, we measure the size of the mother bubble and the sizes of the two daughter bubbles, using a procedure described in the Supplementary Materials, which includes Refs. [25][26][27]. We thus recorded a list of 563 mother bubble areas, N frag (a), with a minimum a min and a maximum a max .…”