Quentin FERREIRA

Lubricated elastohydrodynamics

When an object is moving in a viscous fluid, it follows the classical laws of hydrodynamics. If those hold very well in the bulk, they need to be adjusted when the object arrives in the vicinity of an interface. This is called lubrication, and one can typically observe this phenomenon when throwing a Frisbee : the closer it is to the ground, the more it decelerates until finally, it touches down.

In the case of rigid object and interface, the behaviour of the system is very well known, however most biological and modern systems are composed of soft objects interacting with deformable interfaces, yielding an interesting array of questions. Why do our red blood cells flows further away from our vein’s walls than white cells ? Why do people with a degraded cartilage (which is a deformable solid) suffer arthrosis while still having synovial liquid to lubricate their articulations ? What causes the initial loss of adherence when a car undergoes aquaplaning ?  Can we imagine new systems to target and fight cancerous cells (notably known to be softer than healthy cells) ?

Elastohydrodynamics (EHD) is the field of study of the coupling between elasticity and hydrodynamic fields. Since the middle of the last century, it has provided answers to a lot of mechanical problems involving deformation and fluid flow, such as the motility of small parasites, the dissipation of industrial bearings, etc… But recently, EHD lubrication theoretical studies has found that this framework allows the emergence of spectacular new non-inertial forces, among which one could find a low-Reynold lift force for example. Another force predicted by those studies seems to describe a dynamical adhesion process, which could have implication in biological adhesion.

My current work consists in using a colloidal probe atomic force microscope (AFM) in order to investigate this novel force.  I use this model system to unveil its properties depending on the composition of the system (deformability of the rigid body, viscosity of the media, velocity of the bead, etc…).

To be continued…

References :

– Introduction to the analytical description of EHD lubrication emergents forces : T. Salez & L. Mahadevan (2015)
– Review on the experimental studies of EHD lift force : L. Bureau, G. Coupier and T. Salez (2023)
– Total analytical description of a sphere moving close to a deformable interface : V. Bertin et al. (2021)

Thermal AFM near soft boundaries

Dawning project with Nicolas Fares in order to probe the influence of elastic boundaries on Brownian motion using colloidal probe thermal AFM.
To be continued…

Shuttlesworth’s effect in glassy polymers

Future project about the ongoing controversy on the existence (or not) of a Shuttlesworth’s effect in glassy polymers. The Shuttlesworth’s effect is well known in crystals : if we stretch a crystal (which are composed of well-organized lattice of molecules), the atoms are further away from each other, we thus modify the surface properties of the crystal. However, it is currently not clear if this effect also exists on glassy polymers, which are way more complex materials. Our aim will be to use AFM in order to probe the surface properties of the polymers and observe their behaviour when we stretch them.
To be STARTED…

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