Long-time dynamics and hydrodynamic correlations in quasi-two-dimensional anisotropic colloidal mixtures Article uri icon

abstract

  • The physical properties of multicomponent anisotropic colloidal dispersions are still far from being fully understood. This is mainly due to the fact that dealing with nonspherical particles and highly directional interactions is, from both experimental and theoretical points of view, a complicated task. In fact, experiments are scarce, and we still lack of model colloidal dispersions that allow us to simultaneously simplify and capture the complexity of such systems. In this contribution, we report on an experimental study of the hydrodynamic correlations and the long-time dynamics in anisotropic colloidal mixtures. The latter are composed of monomers and dimers highly confined between two parallel walls. The diffusive behavior is studied from low to intermediate particle concentrations. As concentration increases, crowding plays a significant role on the translational and rotational diffusion coefficients of monomers and dimers at short and long times. Nevertheless, in the short-time regime, the ratio between the dimer diffusion coefficients, parallel and perpendicular to the main axis of the dimer, becomes independent on the composition and total packing fraction; it depends only on the two translational hydrodynamic friction coefficients of the dimer. At long times, the dimer mean-square displacements, both parallel and perpendicular, reach the same value; i.e., the long-time diffusion coefficients seem not to be sensitive to the particle anisotropy and the crowded environment at which the dimer diffuses. Interestingly, both dynamical scenarios are analogous to the reported case for an isolated ellipsoid of similar dimensions, even though the dimer experiences collisions and hydrodynamic interactions with monomers and other dimers. Our findings also point out that the two-dimensional hydrodynamic correlations, monomer-monomer and monomer-dimer, differ mainly at short distances due to the difference in the shape of both types of species. However, contrary to the case of particles in a three-dimensional unbounded fluid, such hydrodynamic correlations decay faster, exhibiting a dipole-like long-ranged behavior with a r-2 dependence, similar to the results previously reported for a monodisperse quasi-two-dimensional colloidal dispersion. Our measurements are corroborated by means of molecular dynamics computer simulations that explicitly include the information of the host solvent. © 2018 American Physical Society.

publication date

  • 2018-01-01