Dispersions of small
particles in a fluid are ubiquitous in both natural
phenomena and industrial processes. In this work I will address a few
problems in which hydrodynamic interactions in suspensions of anisotropic or
deformable particles result in unusual collective dynamics.
I will first focus on the
sedimentation of anisotropic particles, which
for all its apparent simplicity is characterized by highly complex dynamics.
Sedimentation processes of orientable particles such as rigid spheroids, and
deformable particles such as viscous droplets, are subject to a
concentration instability by which a well-mixed suspension becomes
inhomogeneous. Theory and numerical simulations are used to investigate the
concentration fluctuations and the microstructure in these systems. Using a
fast algorithm, large-scale suspensions of spheroids are simulated with
various boundary conditions, and it is shown that stratification in bounded
containers leads to a wavenumber selection for the concentration
fluctuations. The case of viscous droplets is also briefly addressed,
confirming that a similar concentration instability takes place in such
suspensions as well.
To conclude I will
briefly describe two additional problems involving
hydrodynamic interactions of anisotropic particles: the induced-charge
electrophoresis of polarizable rods, and the shear-induced migration of
short-chain flexible polymers in pressure-driven channels flows.