Short-time dynamics of monomers and dimers in quasi-two-dimensional colloidal mixtures

TL;DR

This study investigates the short-time dynamics of monomers and dimers in quasi-two-dimensional colloidal mixtures, demonstrating that hydrodynamic interactions influence their diffusion in a predictable, factorable manner, supported by experiments and simulations.

Contribution

It provides new insights into how hydrodynamic interactions affect diffusion coefficients in confined colloidal mixtures, combining experimental measurements with molecular dynamics simulations.

Findings

Diffusion coefficient ratios are independent of concentration.

Hydrodynamic effects are identical for monomers and dimers.

Experimental results agree with hydrodynamic theory and simulations.

Abstract

We report on the short-time dynamics in colloidal mixtures made up of monomers and dimers highly confined between two glass-plates. At low concentrations, the experimental measurements of colloidal motion agree well with the solution of the Navier-Stokes equation at low Reynolds numbers, which takes into account the increase of the drag force on each particle due to wall-particle hydrodynamic forces. We find that the ratio of the short-time diffusion coefficients of the monomer and that of the center of mass of the dimer remains independent of both the total packing fraction and the dimer molar fraction up to concentrations near to the crystallization transition. The same physical scenario is observed for the ratio between the parallel and perpendicular components of the short-time diffusion coefficients of the dimer. This dynamical behavior is corroborated by means of Molecular Dynamics computer simulations that explicitly include the particle-particle hydrodynamic forces induced by the solvent. Thus, our results point out toward that the effects of the particle-particle hydrodynamic interactions on the diffusion coefficients are identical and, thus, factorable in both species.