Post-Doc - Post-doctorat : Viscoelastic migration in confined flows

Description :
At the low Reynolds numbers involved in flows at small scales (micro and nano-fluidics), the trajectory of very dilute solid particles is deterministic and follows the liquid streamlines, in Newtonian fluids. In contrast, it has been shown (Leshansky, PRL 2007) that in viscoelastic liquids – typically polymer solutions -, a transverse net force is exerted on a rigid particle, due to a gradient of normal stress anisotropy. This force leads to a transverse migration of the particles, usually towards the center of the channel. When the particles are confined (i.e. for particle diameter greater than a tenth of the channel size), this force is rather high as this elastic migration could be observed even when the elasticity of the liquid is very low and too small to be measurable using traditional rheometry. Vicscoelastic migration is very promising for sorting applications, since the net force acting on the particle scales as 𝑎 to the power 3, where 𝑎 is the particle size. In particular, we are working in collaboration (in the framework of ANR MicroLAS) with the group of Aurélien Bancaud in Toulouse and with Picometrics Technology who have shown that in combination with an electric field, elastic migration is very efficient for DNA separation (patent WO/2014/020271 (CNRS)).
However, basic knowledge is required in order to be able to optimize and level up this separation strategy. In this project, we aim at better understanding and describing in details the phenomena involved, using a rationalized and fundamental approach and combining experiments and numerics. The tasks devoted to the recruited post-doc will be mainly experimental. The elastic migration force will measure both indirectly by acquiring individual particle trajectories in a Poiseuille flow, and directly using optical tweezers. We will consider in a first step rigid particles of a few micrometers in microfluidic channels of a few tens of micrometers. We will test several viscoelastic liquids that will be independently characterized, in order to accurately relate the migration force with the rheological properties and to perform direct comparisons with numerical predictions. Then, we will characterize the role of a relative velocity in the flow direction, controlled by an electric field. Investigations towards unsteady regimes ore oscillatory ones are also in the scope of the project. Possible outlooks also deal with deformable particles and DNA.
Qualifications :
The applicants must hold a Ph.D. in soft condensed matter, chemical engineering, or fluid mechanics. Experimental skills in microscopy, rheology or microfluidics are expected.
Applications :
CV, motivations and references should be sent to hugues.bodiguel@univ-grenoble-alpes.fr.

Reference :

Date de démarrage : 01 juin 2017

Durée : 2 years

Contacter :
Laboratoire Rheologie et Procédés, Grenoble (France)
Hugues Bodiguel

email : hugues.bodiguel@univ-grenoble-alpes.fr