Probing stability of the charge-reversed nanoparticles in electrolyte and surfactant solutions

Abstract

Anionic silica nanoparticles show an interesting re-entrant phase behavior, where the system transforms from stable one-phase to two-phase (aggregated state) and returns back to one-phase as varying concentration of multivalent counterions. The re-entrant phase arises due to charge inversion of nanoparticles via excessive condensation of multivalent counterions. The nanoparticles in the re-entrant regime are found to have contrasting stability in the presence of monovalent salt and non-ionic surfactant, when compared to original phase. The charge-reversed nanoparticles show very high stability against NaCl, whereas very low stability against surfactant-induced depletion attraction. These observations are explained based on modifications in inter-particle interactions.