Particle manipulation by symmetry breakingin flows: inertial and non-inertial rectification
Conf’luence Sascha HilgenfeldI
Université d ‘Illinois Urbana-Champaign
Jeudi 17 avril à 10 h 30 • Amphithéâtre Nougaro
Controlled manipulation of particles in small-scale flows is a fundamental task in microfluidics, without which applications such as cell sorting, particle filtering, or droplet encapsulation would be impossible. When particles are not responsive to external forces, one has to exploit hydrodynamic interactions to induce deviations of the particle paths from streamlines. Even for small, spherical particles such interactions are not fully understood today. We highlight two themes of hydrodynamic microparticle manipulation: (1) The introduction of inertia via oscillatory flow of e.g. ultrasonic frequencies is a promising recent approach to increase the speed and throughput of particle deflection in microfluidics. We have derived first-principles effects of particle inertia that allow for controlled displacement of particles by size or density. The theory predicts steady displacements observed in experiments, and the results are in quantitative agreement with direct numerical simulations. (2) Even without inertia, i.e., in viscous Stokes flow, density-matched particles will be deflected from an initial streamline when encountering an obstacle or boundary. Well-defined changes in normal and tangential velocity components result from hydrodynamic interaction between particle and boundary. We show that such displacements need not be transient if the geometry of the boundary and/or the flow field break longitudinal and transverse symmetries. In internal vortical Stokes flow, these effects accumulate and can lead to particle concentration as well as to the driving of particles towards the interface, resulting in predictable capture (sticking) by short-range forces. Together, such effects of particle displacement with and without inertia may lead to new protocols of deterministic displacement or particle capture.
