Stratification of polymer mixtures in drying droplets: hydrodynamics and diffusion

TL;DR

This study uses molecular simulations to explore how hydrodynamic interactions influence the stratification of polymer mixtures during droplet drying, revealing that solvent treatment affects the resulting particle morphology.

Contribution

It demonstrates the critical role of hydrodynamic interactions in determining polymer mixture stratification, using comparative simulation methods to elucidate the underlying mechanisms.

Findings

Including hydrodynamic interactions leads to homogeneous dried particles.

Neglecting hydrodynamic interactions results in stratified core-shell structures.

Diffusion coefficients highlight the importance of solvent backflow and polymer interactions.

Abstract

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.