After three wonderful years at the Levich Institute in CCNY, I am moving today to a new post-doc position in the University of Cambridge. I will be working under supervision of Mike Cates in DAMTP. Lots of exciting times to come!
In the last couple of years, several groups (including ours) have shown good evidence that the shear-thickening observed in dense non-Brownian suspensions is likely a transition from a “frictionless” flow, where particle interactions are lubricated, to a “frictional” flow, where the dominant interactions are frictional contacts, when the shear stress increases. In these works, the competition at the root of the non-Newtonian behavior is between the applied stress and some sort of short-range elastic repulsion (which can be the force used to stabilize the suspension, or the stiffness involved in the deformation of surface asperities). One open question is to understand if this scenario extends to the case of Brownian suspensions, i.e., if the Brownian forces can play the role of a short-range repulsive interaction. It is an important issue as most shear-thickening fluids are in the colloidal range, with sub-micrometer particles.read more
I am usually writing LaTeX documents using emacs and the “standard” AUCTeX package. This setup provides a very good environment with more possibilities and shortcuts that my brain and fingers can remember. I am quite happy with this setup, but I recently used LaTeX and git more often than not. Although some git support packages exist for emacs, I never really spent time trying to use git with emacs. Last year I learned about Atom, a new editor which is supposed to be natively git aware (it is build by GitHub).read more
How similar is shear thickening to a first order transition? Ryohei Seto, Jeff Morris and Morton Denn and I show that in a stress-controlled simulation, we can observe non-monotonic flow curves analogous to non-monotonic equations of state giving rise to usual liquid-gas like transitions. Interestingly, the uniformly sheared system is stable in the decreasing part of the flow curve, i.e. we do not observe the equivalent of a phase separation.
Ryohei Seto, Jeff Morris and Morton Denn and I extend our work on shear thickening of dense suspensions. In a new article, we explore the relation between jamming and shear thickening. We show that shear thickening is an indirect consequence of the shift of the jamming transition to lower volume fractions as friction between solid particles increases.
Solving force balance equations in a granular packing can be seen as a constraint satisfaction problem defined on the network of contacts. What if we consider this network as a random graph? Well, the problem becomes a nice playground for applying the cavity method. This is what we did with Lin Bo, Chaoming Song and Hernán Makse, and we got the mean-field results for the force distribution as well as the minimum contact number for random packings of spheres, as a function of the friction coefficient.