The role of hydrodynamic interactions in models and simulations of drying

Nonequilibrium molecular modeling is valuable for predicting the microstructure of drying films. For example, simulations were recently key to uncovering the “small-on-top” stratification of binary colloidal mixtures. In the absence of solvent effects, drying can be well-described using implicit models without hydrodynamic interactions; however, these models tend to overestimate the solute migration speeds and stratification observed in experiments. Here, I will highlight two examples from our recent work that clearly demonstrate the important role of hydrodynamic interactions in nonequilibrium models of drying. I will first discuss the evaporation-induced crystallization of a colloidal dispersion, where we found that the crystal nucleation and growth depended sensitively on the hydrodynamic interactions because of the colloid distribution in the drying film. I will then discuss the stratification of a mixture of two differently sized polymers; the mixture stratified without hydrodynamic interactions, as predicted, but did not stratify when they were included. Our work shows that although implicit-solvent models neglecting hydrodynamic interactions are computationally efficient, the corresponding sacrifice in accuracy may not be acceptable for faithfully predicting structure in drying films.