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Accueil du site > Évènements > Séminaires > Séminaires IUSTI > Archives IUSTI > 2015

Lundi 1 Juin 2015 / IUSTI

publié le , mis à jour le

Séminaire exceptionnel IUSTI

Microscopic mechanism for the shear-thickening of non-Brownian suspensions

Orateur :Nicolas Fernandez
ETH - Swiss Federal Institute of Technology, Department of Materials, Laboratory for Surface Science and Technology

Résumé : Shear-thickening can lead to large-scale processing problems of dense pastes in a host of practical applications [1]. Despite extensive efforts to describe its microscopic origin [1-4], current explanations fail to address the mechanism behind the shear-thickening of dense granular pastes. In such systems networks of contacting particles can develop and transmit positive normal stresses [5]. Moreover, viscosity can suddenly diverge under flow (discontinuous shear-thickening [6-7]) with dramatic effects. Previous experiments have demonstrated that the features of the viscosity increase (slope, critical stress) can be controlled by tuning particle surface properties such as roughness[8] and/or by adsorbing polymers[9]. These findings suggest that inter-particle contacts play a crucial role in the macroscopic flow at high volume fractions and that a precise description of these contacts is essential to interpret the rheological behavior. We propose a simple model, supported by contact-dynamics simulations as well as rheology and friction measurements, which links the transition from continuous to discontinuous shear-thickening in dense granular pastes to distinct lubrication regimes in the particle contacts. In particular we identify a local characteristic number (Sommerfeld number) that determines the transition from Newtonian to shear-thickening flows, and then show that the suspension’s volume fraction and the boundary lubrication friction coefficient control the nature of the shear-thickening transition, both in simulations and experiments. The generality and consistency of our data and of the proposed model sets a global framework in which the tribological (friction) and rheological properties of dense non-colloidal systems are intimately connected. This concept is expected to have an impact on a host of practical applications and relates fundamental issues such as flow localization [10] and minimum local shear rate of granular pastes [6].

References :

[1] H. Barnes, J. Rheol, 329 (1989).
[2] R. A. Bagnold, P. Roy. Soc. A, 225, 49 (1954).
[3] N. J. Wagner and J. Brady, Phys. Today, 27 (2009).
[4] X. Cheng, J. H. McCoy, J. N. Israelachvili, and I. Cohen, Science 333, 1276 (2011).
[5] M. Cates, J. Wittmer, J. Bouchaud, and P. Claudin, Phys. Rev. Lett. 81, 1841 (1998).
[6] A. Fall, F. Bertrand, G. Ovarlez, and D. Bonn, J. Rheol. 56(3) (2012).
[7] E. Brown \& al., Nat. Mater. 9, 220 (2010).
[8] D. Lootens, H. Van Damme, Y. Hémar, and P. Hebraud, Phys. Rev. Lett. 95 (2005).
[9] F. Toussaint, C. Roy, and P. H. Jézéquel, Rheol. Acta 48, 883 (2009).
[10] N. Huang, G. Ovarlez, F. Bertrand, and S. Rodts, Phys. Rev. Lett. 94 (2005).

Date et lieu : le Lundi 1er Juin à 11h en salle 250 - IUSTI