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Hydrodynamic interactions between solutes in multiparticle collision dynamics

Multiparticle collision dynamics (MPCD) enables to simulate fluid dynamics including both hydrodynamics and thermal fluctuations. Its main use concerns complex fluids, where the solvent interacts with concentrated solutes, may they be colloidal particles, polymers or electrolytes. A key difficulty concerns the way one couples the fluid to the solute particles, without losing the key advantages of the MPCD method in term of computational efficiency. In this paper, we investigate the dynamical properties of solutes that are coupled to the fluid within the collision step, {\em i.e.} when local momentum exchange between fluid particles occurs. We quantify how the volume where momentum exchange is performed (the size of the collision cells) constrains the hydrodynamic size of the solute. Moreover, we show that this volume should be taken smaller than the structural size of the solutes. Within these constraints, we find that the hydrodynamic properties of a 1-1 electrolyte solution are similar to the behaviour predicted by the Fuoss-Onsager theory of electrolyte dynamics, and we quantify the limitations of the theory for 2-1 and 2-2 electrolytes. However, it is also clear that mapping the diffusion time scale to that of a real system cannot be done quantitatively with this methodology.