Inducing stratification of colloidal mixtures with a mixed binary solvent

BH Liu and GS Grest and SF Cheng, SOFT MATTER, 19, 9195-9205 (2023).

DOI: 10.1039/d3sm01192e

Molecular dynamics simulations are used to demonstrate that a binary solvent can be used to stratify colloidal mixtures when the suspension is rapidly dried. The solvent consists of two components, one more volatile than the other. When evaporated at high rates, the more volatile component becomes depleted near the evaporation front and develops a negative concentration gradient from the bulk of the mixture to the liquid-vapor interface while the less volatile solvent is enriched in the same region and exhibit a positive concentration gradient. Such gradients can be used to drive a binary mixture of colloidal particles to stratify if one is preferentially attracted to the more volatile solvent and the other to the less volatile solvent. During solvent evaporation, the fraction of colloidal particles preferentially attracted to the less volatile solvent is enhanced at the evaporation front, whereas the colloidal particles having stronger attractions with the more volatile solvent are driven away from the interfacial region. As a result, the colloidal particles show a stratified distribution after drying, even if the two colloids have the same size. Colloidal mixtures suspended in a binary solvent can be driven into stratification by the concentration gradients of the solvent components that have developed during rapid evaporation.

Return to Publications page