Mild stratification in drying films of colloidal mixtures

Abstract

Analysis on the size stratifications in bidisperse colloidal film drying using the implicit and explicit solvent simulations.

Dynamic density functional theory for drying colloidal suspensions: Comparison of hard-sphere free-energy functionals

“…We have also made a consistent freedraining approximation of the particle dynamics in both the DDFT calculations and BD simulations, but there is evidence that solvent-mediated hydrodynamic interactions between particles play an important role in setting the structure of drying suspensions. 24,28,34,35 Faithfully modeling these dynamic effects in DDFT 79,80 ulti-mately still requires an accurate underlying free-energy functional, so this work constitutes an important step in building improved DDFT models for drying suspensions.…”

“…47 The former approximation is reasonable for many experiments; however, the latter simplification is believed to cause significant discrepancies between simulations and experiments of drying films, particularly for mixtures of particles with different sizes. 15,23,24,28,34,35 Nonetheless, the BD model is well suited for assessing thermodynamic approximations of the DDFT models: the DDFT models will be constructed to have exactly the same particle dynamics as BD so that any deviations between the two must be due to approximations in DDFT.…”

“…It has been shown that neglect of solvent-mediated hydrodynamic interactions may lead to overprediction of stratification and incorrect dependence on d B compared to predictions made using a fluidmechanics analysis accounting for the solvent. 24,28,34,35 Faithfully capturing the role of the solvent in stratification is an important topic but it is not the focus of this work, and the BD simulations remain suitable for testing the DDFT free-energy functionals.…”

“…To determine the particle flux, DDFT requires two inputs: a free-energy functional encoding the particle interactions and a model for the particle dynamics. Comparison with experiments and particle-based simulations suggests that both inputs may affect the accuracy of DDFT models, 8,23,24,28,34,35 and it is accordingly critical to identify appropriate choices.…”

Inducing stratification of colloidal mixtures with a mixed binary solvent

“…22 Fortini et al later discovered the unexpected small-on-top stratification in the case of extremely fast drying rates. 23 This discovery has triggered a series of experimental, [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] theoretical, [40][41][42][43][44][45] and computational [46][47][48][49][50][51][52][53][54][55][56][57][58] studies to reveal the underlying physical mechanism. It is now generally believed that the small-on-top stratification can be explained on the basis of diffusiophoresis, where colloidal particles are driven by the concentration gradient of other solutes (e.g., another type of particles) in the suspension.…”