Micheline ABBAS

I am interested in the dynamics of dispersed systems commonly called suspensions (liquid containing particles, drops, vesicles, self-assembled objects). These materials are frequently encountered in industrial and environmental applications as well as living systems: waste water, mud, paint, paste, concrete, nutritional or biological fluids, etc. My research is concerned by confined systems, where walls affect the dynamics. When submitted to flow, the behavior of suspensions is considerably dependent on the loading (concentration of the dispersed phase), on micro-scale interactions and on confinement.

More particularly, I am motivated by understanding the macroscopic transport properties (phase transition, turbulence) and local dynamic quantities (effective viscosity, normal stresses, osmotic pressure) in flowing suspensions compared to pure fluids. The behavior of the dispersed phase (diffusion, aggregation or segregation) is also of interest. These macroscopic features are often intimately related to physical interactions at the particle scale, associated with single or many-body hydrodynamic forces, interfacial interactions and/or external forces. External forces include for example gravity or magnetic fields used to manipulate particles. Hydrodynamic forces are associated with local modification of the pressure and viscous stresses due to the presence of the dispersed phase. As for interfacial interactions, their nature depends on particle size : solid contact (friction, rebound) is of importance at finite inertia whereas colloidal interactions (electrostatic, van der Waals, hydrophobic/hydrophylic) are crucial for submicronic particles.

Methods

We develop/adapt numerical models and combine them with experiments when possible. For suspensions where scale separation is three orders of magnitude or larger, we use the continuum description for the entire material (based for instance on the Suspension Balance Model). However, when the macroscale is one or two orders of magnitude larger than the particle scale, we use numerical methods that fully solve the fluid motion based on continuum fluid mechanics and the discrete particle motion (Force Coupling Method, Immersed Boundary Method). This allows to capture many-body hydrodynamic interactions. Central pairwise forces and torques account for body forces or interfacial interactions. More recently, we are considering a mesoscopic approach (based on the Dissipative Particle Dynamics) in order to study the dynamics of colloidal particles near soft interfaces.

Applications

Multiphase transport, fluidization, particle manipulation / cell detection, filtration, drug delivery. More information can be found at the webpage: Dynamique des milieux dispersés

Research advisor

• PhD students: Vincent Loisel (2013), Guiquan Wang (2017), Qing Li (2019), Adriana Bentes Correia (ongoing), Salahudin Sheikh (ongoing)
• Post-docs (Anupam Gupta, Maike Baltussen, Hamid Tavassoli, Ali Ozel)

Teaching activities

Chemical Engineering students (BS and Master level): Transport phenomena. Physics and modelling of granular media. Physical analysis of industrial processes. Reaction engineering. CFD.

Collaborators

• Olivier Masbernat, Patrice Bacchin, Kevin Roger (LGC, Toulouse),
• Eric Climent, Jacques Magnaudet, Matthieu Mercier, Laurent Laccaze (IMFT, Toulouse),
• Barbara Lonetti (IMRCP)
• Christine Lafforgue, Pascale Magaud (INSA, Toulouse),
• Pavel Kuzhir, Georges Bossis (Institut de Physique de Nice),
• Jeff Morris (CCNY, USA), Martin Maxey (Brown University, USA),   Zhen Li (Clemson University), Martin Van der Hoef (Twente University, the Netherlands),