Mechanism of moving particle aggregates in a viscous fluid subjected to a varying uniform external field

A mechanism is proposed for moving aggregates of spherical particles in a viscous fluid, and their dynamics under an applied uniform external field is numerically simulated. A particle aggregate is treated as a set of particles with a charge or dipole moment influenced by both hydrodynamic interaction forces and internal forces retaining the particles in the aggregate. In the absence of an external field, the particles are in the position of minimum interaction energy and the total charge or dipole moment of the system is zero. After applying an external field, the aggregate deforms and, after switching off the field, the aggregate undergoes a restoring process caused by internal forces tending to return it to equilibrium. The relative motion of the aggregate particles gives rise to a viscous flow around the aggregate, which creates a hydrodynamic force shifting the aggregate barycenter in a certain direction with respect to the applied field. The motion of six model aggregates consisting of charged or dipolar particles is numerically simulated. The proposed mechanism of moving the aggregates can be used to control mass transfer in colloidal suspensions.