Dynamics of Drops as Confined Systems Containing Nanoparticles-Reformation of Nanoparticles and Evaporation of Water

Abstract

Brine is used to displace crude oil in a reservoir and its performance improves when brine contains nanoparticles. It is the presence of nanoparticles in confinements, such as at dynamic contact lines and in thin films, which is of importance. The investigators here have determined a fast way to obtain confined systems by evaporating a small drop of water containing nanoparticles. Water droplets containing nanoparticles of alumina or silica were evaporated on surfaces of polyethylene terephthalate sheets, which are partially wet by water, and glass which is fully wet. After the liquid in the drops evaporated, the residues were examined under a microscope and sintering and melting effects, crystals growth and dendritic formations for alumina and monoliths for silica were seen. The coffee stains are seen in most cases; however measurements show that the contact lines are not always pinned. Turbidity measurements showed that no significant reformation could have taken place in the bulk liquid. A simple model for evaporation, based on geometric measurements, showed that much of the film seen on the solid arose out of evaporation of water that forced the particles down. Sintering rates into the interior could be quantified and shown to be unstable.