Article dans Communications Physics “Surface-wave instability without inertia in shear-thickening suspensions”
Baptiste Darbois Texier, Henri Lhuissier, Yoël Forterre & Bloen Metzger
‘The New Wave’
Oobleck continues to fascinate us. Researchers from Aix-Marseille University in France showed that, as it flows down an inclined slope, Oobleck forms very regular and prominent surface waves. Similar waves can be observed on gutters and windows on rainy days. However, scientists have shown that here, for Oobleck, the origin of wave formation is completely different: they do not arise from the effect of inertia as for water, but from Oobleck’s specific flowing properties.
Under impact, as shown by recent studies, Oobleck suddenly changes from liquid to solid because of the activation of frictional contacts between the starch particles. When flowing down a slope, this proliferation of frictional contacts leads to a very curious behavior: the flow velocity of the suspension decreases when the imposed stress is increased (As if stepping on the gas pedal would suddenly make your car decelerate !). Researchers have shown that this effect couples to the flow free-surface and can spontaneously generate a regular wave pattern.
The proposed mechanism is very generic. These findings could thus provide new grounds to understand other flow instabilities observed in various configurations, particularly in industrial processes facing problematic flow instabilities when conveying Oobleck like materials, such as concrete, chocolate or vinyl materials.
ref : Baptiste Darbois Texier, Henri Lhuissier, Yoël Forterre & Bloen Metzger, « Surface instability without inertia in shear-thickening suspensions », Communications Physics 3:232 (2020) https://doi.org/10.1038/s42005-020-00500-4
see the Highlight in Nature Reviews Physics https://www.nature.com/articles/s42254-020-00277-z, (shareable link at https://rdcu.be/cc9BE) and in the newspaper Le Monde (in french) https://www.lemonde.fr/sciences/article/2021/01/13/la-maizena-fait-des-vagues_6066135_1650684.html.
Contact : Bloen Metzger, Laboratoire IUSTI, CNRS UMR 7343,Aix-Marseille Université
Projet financé par l’ERC PLANTMOVE, l’ANR Science-Friction et le LABEX MEC