Effects of the complex interaction between nanoparticles and surfactants on the rheological properties of suspensions

The mixture of nanoparticles and surfactants widely exist in many industrial applications for which rheological behavior is one of important properties. Herein, the effect of interaction between titania nanoparticles and SDS molecules on the rheology of nanoparticle-surfactant suspensions has been investigated over a wide pH value and temperature range. It turned out that pH value has remarkable effect on the rheological properties of nanoparticle-surfactant suspensions. When the pH value is equal to or slightly below the isoelectric point (IEP), the suspensions showed the shear thinning behavior at relatively higher temperature, as it does when the pH is high enough. However, suspensions behave as the Newtonian fluid when the pH is low enough or slightly above the IEP. The observed phenomenon has been attributed to the electrostatic forces and the assembly structure between the nanoparticles and surfactants. Our results indicated that the nanoparticle-surfactant suspensions could be controlled to be either Newtonian or non-Newtonian fluid by precisely adjusting the pH values under corresponding temperature. It is also expected to be valuable for mechanistic understanding of the rheology of such nanoparticle-surfactant complex systems.