Precipitation of Oppositely Charged Nanoparticles by Dilution and/or Temperature Increase

Abstract

Mixtures of oppositely charged nanoparticles (NPs) exhibit anomalous solubility behavior and precipitate either upon dilution or upon temperature increase. Precipitation is reversible and can be explained by a thermodynamic model that accounts for changes in the electrostatic interactions due to the adsorption/desorption of counterions from the surface of the NPs. Specifically, decreasing the salt concentration via dilution or increasing the temperature causes dissociation of counterions from the NP surfaces, increasing the magnitude of electrostatic interactions between NPs and resulting in their precipitation. Model predictions of NP solubility are in quantitative agreement with the experimental observations. Such predictions are of practical importance for the preparation of "patchy" electrostatic coatings and ionic-like NP supracrystals.