Capillary flows of suspensions – POLYSHAPE

Polyphasic liquids (suspensions, emulsions, wetted foams) are ubiquitous in nature and industry (soils, pulps, pastes…). As for conventional liquids, there is an increasing need to optimize capillary flows of these liquids at smaller and smaller scales, with concern to both the overall polyphasic envelope and the dispersed phase inside it. This requires understanding the complex dynamics that emerges from the coupling between the dispersed phase, or particles, and the liquid interface.

This project identifies an emerging research field at the interface between multiphase flows and dynamics of liquid interfaces. These two fields have been largely studied independently one from each other, i.e., in the absence of either an interface or particles. However, the complex dynamics that emerges from the coupling between the interface and the particles is essentially unknown.

It is an ambitious project that aims at obtaining a fundamental knowledge of this coupling, both at the local scale of a particle and at the global scale of the whole capillary object. By focusing on capillary flows of monodisperse solid suspensions of beads and fibers, it will study both how the particles impact the formation and deformation of capillary objects and how the particles themselves are dispersed/concentrated by the dynamics (pinch-off, recession, spreading) of these objects.

To understand these dynamics, three general experimental configurations will be studied, which represent idealized relevant configurations (paradigms) for a general comprehension of the shaping of capillary objects: jets (1D elongated streams), films (2D thin objects), and drops (3D compact objects). They will be used to determine how the coupling depends on the liquid viscosity and the particles density, size, shape and wettability, and how this coupling affects the fragmentation of jets and the detachment of drops, the thickness of films, the spreading/splashing of impacting drops, and the dispersion/concentration of the particles in the fragments, entrained films and spread drops.

The study will have to identify and understand, for both dilute and dense suspensions, the contributions of the proper rheology of the suspension, of the capillary pre-stressing (due to the capillary pressure at the menisci between the particles), and of finite size effects (defects initiating pinch-off, discretization of the drop sizes). This will be achieved by gradually studying the different flow regimes:
- Static configurations for high concentrations in particles,
- ‘Slow’ flows dominated by viscosity,
- ‘Fast’ or impulsive flows when inertia will become relevant,
and analyzing, each time, the individual and collective motions of the particles, and the shape of the interface.

This project will be developed by a junior scientific coordinator, having acquired unique competences abroad on short-time small-scale dynamics of liquid interfaces, who wishes developing in France an original research activity on interfacial and polyphasic thematic. It will be developed at the IUSTI and will actively involve several research groups from the laboratory, whose expertise on suspensions and complex liquids flows is internationally recognized. The project will benefit from the complementarity of these competences that are essential to its success. It will use the synergies created to tackle over 4 years a vast and original problem of fundamental concern.

It is expected that the progresses on the different facets of capillary flows of monodisperse solid suspensions on the representative configurations of jets, films and drops will yield elementary ‘building block’ that help describe and quantify more complex shaping processes or phenomena, and that facilitate future descriptions of capillary flows of polydisperse or fluid suspensions.