  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.
