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M/F Understanding the rheology of concentrated non-Brownian suspensions

This offer is available in the following languages:
Français - Anglais

Date Limite Candidature : mercredi 17 août 2022

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General information

Reference : UMR7010-ELILEM-001
Workplace : NICE
Date of publication : Wednesday, July 27, 2022
Scientific Responsible name : Elisabeth Lemaire
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 3 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

The physics of non-Brownian suspensions is a very active research topic because of the fundamental questions that are currently raised and the numerous applications in industry (concrete, food, cosmetics...) and in natural flows (blood, mudflows, volcanic lava...). Research over the last ten years has shown that the rheological properties of these concentrated suspensions are essentially controlled by the direct contact forces between particles. The tangential contact is described by a friction law and it has been shown through experiments [1,2], numerical simulations [3] and theoretical models [3,4] that the variation of the friction coefficient with shear stress can account for both the shear-thickening observed in suspensions such as cornstarch suspensions and the shear-thinning present in almost all common suspensions of polymer particles. Normal contact, on the other hand, is characterized by a possible adhesion force, defined as the minimum force that must be applied to separate two contacting particles. Phenomenological links [5,6] have been established between the rheological properties of concentrated suspensions and the adhesion forces between particles, but there is still an effort to make these links truly quantitative and to develop a general framework of the same type as the one that has been constructed to account for and predict the effects of friction on rheology. Moreover, preliminary studies have shown that when particle stiffness decreases, suspension viscosity increases, contrary to the intuitive idea that increasing particle deformability should help the suspension to flow. This paradox can be explained by considering the variation of the contact area of two particles in a flow as a function of their stiffness. When the latter decreases, the contact area increases and the effects of contact forces, whether frictional or adhesive, increase.
Progress in the understanding of the links between particle adhesion, stiffness and suspension rheology is one of the objectives of a collaborative project we are conducting with chemists from the Institute of Polymeric Materials in Lyon (ANR RHEOCOM project). Thanks to them, we have access to particles whose volume and surface properties are very well controlled. The aim of the PhD is to measure by Atomic Force Microscopy (AFM) the frictional and adhesive interactions between particles, to characterize the rheology (viscosity, difference in normal stresses) and to try to establish quantitative links that would provide an explanation or even a prediction of the rheology, knowing the microscopic interactions between particles.

[1] Chatté G. et al. "Shear thinning in non-Brownian suspensions." Soft matter 14.6 (2018): 879-893.
[2] Arshad M. et al. "An experimental study on the role of inter-particle friction in the shear-thinning behavior of non-Brownian suspensions.” Soft Matter, 2021,17, 6088-6097
[3] Lobry L. et al. "Shear thinning in non-Brownian suspensions explained by variable friction between particles." J. Fluid Mech. 860 (2019): 682-710.
[4] Wyart, M. & Cates M.E. "Discontinuous shear thickening without inertia in dense non-Brownian suspensions." Phys. Rev. Lett. 112.9 (2014): 098302.
[5] Papadopoulou A. et al. "On the shear thinning of non-Brownian suspensions: Friction or adhesion?." J.Non-Newton. Fluid Mech. 281 (2020): 104298.
[6] Richards J. et al. "The role of friction in the yielding of adhesive non-Brownian suspensions." J. Rheol. 64.2 (2020): 405-412.

Work Context

The Institut de Physique de Nice is a laboratory with a broad spectrum of research activities in physics ranging from soft matter physics to cold atom physics, including turbulence and wave propagation in complex media. The scientific environment is therefore very stimulating.
The team that will host the PhD student is also very involved in the rheology community in France. It has developed numerous links with researchers in the academic world as well as with industry.

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