Trystan Domenech

Aggregation and Separation in Ternary Particle/Oil/Water Systems with Fully Wettable Particles

We report that a variety of ternary particle/liquid/liquid mixtures heavily aggregate or separate completely if (1) the particles are fully or almost fully wetted by one fluid, and (2) if the wetting fluid volume fraction is comparable to the particle volume fraction. Aggregation and separation do not happen if the particles are partially wetted by both fluids, in which case Pickering emulsions appear at all compositions. Rheological and geometric criteria for aggregation are proposed and compared with a state diagram of a ternary system composed of oil, water, and hydrophilic glass particles. Analogies are drawn to wet granulation and spherical agglomeration, two particle processing operations in which wetting phenomena are important.

Time-evolution of the structure of organoclay/polypropylene nanocomposites and application of the time/temperature superposition principle

We investigated the rheological properties of nanocomposites composed of polypropylene, organoclay, and maleic anhydride grafted polypropylene in small amplitude oscillatory shear. Samples were prepared in two steps: a masterbatch was first obtained by melt extrusion and then diluted into polypropylene using an internal mixer. Three formulations were investigated. The measurement of the storage and loss moduli evolution with time showed that these materials were not stable: the nanostructure obtained after steady shear continuously changed with time, due to the disorientation of the clay platelets and the build-up of a 3D network. The kinetics of the structure build-up (followed via the melt yield stress) showed a two-step process. This feature was found to be valid whatever the nanocomposite formulation. Such evolution of the structure is generally assumed to violate the time–temperature superposition principle. We demonstrate in this paper that the time–temperature equivalence always exists if the same ...

Microstructure, phase inversion and yielding in immiscible polymer blends with selectively wetting silica particles

We examine liquid–liquid–particle ternary blends composed of two immiscible polymers and spherical silica particles across a wide range of compositions. The particles are fully wetted by one of the liquids. Rheological behavior is investigated through continuous shear flow and small/large amplitude oscillatory shear experiments. We observe various percolating structures of the particles bound by capillary interactions, as well as particles-in-drops or drops-in-suspension microstructures. These morphological changes with composition induce significant alteration in a linear viscoelastic response and yielding of the three-phase system. Similarly to the observations in wet granular materials, both the elastic plateau modulus and the yield stress of our ternary system exhibit a maximum as the wetting phase content increases for a fixed particle concentration. We show that this phenomenon is linked to an evolution of the structure from a meniscus-bridged particle network to a selectively filled bicontinuous st...