Self-propelled colloids provide a convenient synthetic model to study by proxy bacterial mobility. These artificial swimmers can be used to answer fundamental questions linked to the hydrodynamic interactions of microorganisms with external fields or structures.
I currently investigate the importance of symmetry on various aspects relevant to the motility of rod-like microswimmers. These studies aim at resolving the fundamental interactions of so-called pushers or pullers elongated swimmers in the presence of an external flow field (rheotaxis) or boundaries (rectified motion). From there my hope is to provide optimized solutions for non-invasive directed motion for cargo delivery applications. I also seek to link the these phenomenon to a better understanding of the emergence of collective dynamics in living systems.
Beyond colloids I am also looking for new route leading to the self-propulsion of soft/deformable materials e.g. droplet, capsules or vesicles that are nowadays engineered as reservoir containers [Updates pending...].
Electrohydrodynamic interplay with fluid interfaces have been extensively discussed since the seminal work of G.I. Taylor in the 1960's. In this field, I am interested in the exploration of non-linear behavior occurring above critical field strength. Among them Quincke rotation, interfacial deformation and breakup.
In large DC electric fields the interface of a drops can undergo various breakup scenario. As an example, tip streaming arising at a conductive drop interface is a rather a well-known phenomenon used in industrial processes. Dielectric in the contrary are known to breakup through chaotic processes . A fine tuning of both the conductivity ratio and the viscosity ratio between a dielectric drop and its suspending fluid can lead to a smooth interfacial breakup. The "Equatorial-streaming" describes the emission of large amount of droplet isotropically around the equator of an oblately deformed drop.
This process is reminiscent to "splashing" dynamics. It follows a downsizing cascade: from one macro-drop, to a thin edge-sheet, to concentric fluid rings, to thousands of monodisperse micro-droplets.
This intricate yet mesmerizing phenomenon poses fundamental question. Namely the stability of capillary sheet in an electric field and the formation of concentric rings are processes that require deeper understanding. Finally the rapid output of thousand of droplets via equatorial-streaming opens possible route for electro-emulsification in industrial processes. [Read more]
I experimentally revisited the well know Quincke effect in order to bring insight on the behavior of a single ellipsoidal "rotor" (prolate and oblate), as a prelude to collective dynamic studies. Equations of motion for a prolate ellipsoid predict two stable-states in an electric field: alignment of the particle long axis along the field, and a rotation about the prolate long axis perpendicular to the electric field. The experiments validated the theoretical prediction of these two state as well as a bistability region where rotation and alignment are equally probable.
Further investigations to the case of a prolate rotor laying on a planar surface, reveal richer dynamics. In this case lubrication forces from the underlying substrate prevents the rotation of particles about its long axis. Instead, new regimes of oscillations and tumbling of the particle parallel to the surface are observed. [Read more]. Similar work is currently carried for oblate rotors. [Updates pending...].
Microfluidics provides means to create emulsion droplets accurately controlled in size, composition at high-throughput (several Kdroplets/s). On-chip dynamical rheology is a series of applications based on droplet deformability in a flow field and aimed at the characterization different mass transport phenomena that modify the interface properties. This project informed on the precise mechanisms underlying the kinetics of surfactant adsorption in microfluidic environment and thus bring insight in the prediction of emulsion stability [Read more]. This technique also allows to monitor kinetics of interfacial polymerization reactions for various compounds widely used in polyurea capsule formation [Read more].