  We study the evaporation-induced stratification of a mixture of short and
long polymer chains in a drying droplet using molecular simulations. We
systematically investigate the effects of hydrodynamic interactions (HI) on
this process by comparing hybrid simulations accounting for HI between polymers
through the multiparticle collision dynamics technique with free-draining
Langevin dynamics simulations neglecting the same. We find that the dried
supraparticle morphologies are homogeneous when HI are included but are
stratified in core--shell structures (with the short polymers forming the
shell) when HI are neglected. The simulation methodology unambiguously
attributes this difference to the treatment of the solvent in the two models.
We rationalize the presence (or absence) of stratification by measuring
phenomenological multicomponent diffusion coefficients for the polymer
mixtures. The diffusion coefficients show the importance of not only solvent
backflow but also HI between polymers in controlling the dried supraparticle
morphology.
