Model suspensions of functionalized particles : an experimental study on the impact of microscopic properties on macroscopic rheological properties

Overview & Synopsis

Suspensions consist of mixtures of particles dispersed in a liquid. They are ubiquitous in natural phenomena (sediment transport in rivers and oceans, landslides, avalanches, pyroclastic flows) and in industrial processes (food and cosmetic industry, civil engineering, petroleum industry, paper and composite industries). While the rheology of low particle volume fraction suspensions has been understood since Einstein's calculations, where hydrodynamic interactions between particles predominate, the behavior in concentrated regimes is far from being fully elucidated. Indeed, at these volume fractions, particle contacts become predominant, leading to a viscosity divergence up to a blocking transition known as "jamming", where flow comes to a halt. In this concentration regime, the major challenge is to link grain-scale mechanics to macroscopic rheological properties. Recently, theoretical and numerical studies have emphasized the role of friction between particles and, more broadly, interactions between these particles (electrostatic, steric, for example). Nevertheless, it is experimentally challenging to explore suspensions across the entire range, from particles with purely lubricated interactions (without frictional contact) to particles with solid contact and friction. This project aims at addressing this by functionalizing chemically the surfaces of particles. This functionalization provides control on interparticle interactions as well as on interactions between particles and the suspending fluid, potentially allowing the examination of the transition between suspensions of frictionless particles and suspensions with frictional grains. The objective of this thesis is, therefore, to develop particles with controlled functionality and their rheological studies. We are studying two types of particles, namely (i) chemically responsive permeable particles and (ii) inorganic particles onto which we graft solution-responsive polymer chains. We observe strong correlations between the physicochemical surface properties and the macroscopic friction properties of these particles in concentrated suspension.