Sedimentation dynamics of deformable particles with small density difference to the surrounding fluid

We present experiments of soft particles sedimenting from rest within a rectangular tank. Dur to their deformability, the particles may be subject to elastohydrodynamic interactions with the side walls of the tank, i.e. they might be subject to an extra lift or drag. The particles possess a small density difference to the surrounding fluid, such that the acceleration phase of the particles (until they reach a steady sedimentation velocity) is strongly extended. Depending on the particle's elastic modulus and the particle's position with respect to the wall, we find a variety of sedimentation patterns, in which the terminal sedimentation speed can be faster or slower than the classic Stokes velocity of a rigid sphere. Our findings provide input to the understanding and modeling of dynamics of particle sedimentation in bounded domains. They may be especially relevant for fields such as sedimentation of bioparticles or polymer particles, as in these cases, the density difference to the surrounding fluid can also be very small.