Hydrodynamic Correlations slow down Crystallization of Soft Colloids

TL;DR

This study demonstrates that hydrodynamic interactions significantly slow down colloidal crystallization by reducing particle diffusion near the crystal surface, challenging the assumption that colloids are ideal models for metal melts.

Contribution

It reveals the impact of hydrodynamic interactions on crystallization kinetics in colloids, showing they cause a slowdown not accounted for in simpler models.

Findings

Hydrodynamic interactions reduce crystal growth velocity.

Hydrodynamic screening occurs near the crystal surface.

Crystallization in suspensions differs from pure melts.

Abstract

Crystallization is often assumed to be a quasi-static process that is unaffected by details of particle transport other than the bulk diffusion coefficient. Therefore colloidal suspensions are frequently argued to be an ideal toy model for experimentally more difficult systems such as metal melts. In this letter, we want to challenge this assumption. To this aim, we have considered molecular dynamics simulations of the crystallization in a suspension of Yukawa-type colloids. In order to investigate the role of hydrodynamic interactions (HIs) mediated by the solvent, we modeled the solvent both implicitly and explicitly, using Langevin dynamics and the fluctuating Lattice Boltzmann method, respectively. Our simulations show a dramatic reduction of the crystal growth velocity due to HIs even at moderate hydrodynamic coupling. A detailed analysis shows that this slowdown is due to the wall-like properties of the crystal surface, which reduces the colloidal diffusion towards the crystal surface by hydrodynamic screening. Crystallization in suspensions therefore differs strongly from pure melts, making them less useful as a toy model than previously thought.