Backtracking of colloids: a multiparticle collision dynamics simulation study

TL;DR

This study uses multiparticle collision dynamics simulations to investigate how sound influences the motion of colloids, revealing that sonic effects are significant at short times but negligible in the long-term.

Contribution

It demonstrates the impact of sound on colloid dynamics and confirms that sonic effects can be ignored at long times in mesoscale systems.

Findings

Sound causes backtracking in colloid motion due to wave interference.

Sonic effects diminish and vanish at long times.

Simulations validate theoretical predictions of viscoelastic-like behavior.

Abstract

The role of sound in the dynamics of mesoscale systems is typically neglected, since frequently the associated time scales are much smaller than all the other time scales of interest. However, for sufficiently small objects embedded in a solvent with a sufficiently small sound velocity, sound can play a crucial role. In particular, behavior resembling viscoelasticity has been theoretically predicted for non-viscoelastic fluids. This effect is due to the interference of the propagation of sound waves caused by the solute particle's motion and hydrodynamic vortex formation. We demonstrate this effect, known as backtracking, in computer simulations employing the method of multiparticle collision dynamics. We systematically study the influence of sound on the dynamics of the solute particle, and find that it disappears in the long-time limit. Thus, we confirm that sonic effects at the single-particle level can be neglected at sufficiently long times.