Comparison of Rheological Methods to Obtain a Sufficient Sensitivity with Shear Interfacial Rheology in the Presence of Nanoparticles at Liquid/Liquid Interfaces

Interfacial shear rheology can give a lot of information on the organization of the nanoparticles at the liquid/liquid and at the liquid/air interfaces. The measurements are challenging and not easy to conduct in a safe way to obtain reliable data. In the present study, the operating windows and the useful methods to obtain a reliable and sensitive response of the rheometer at the liquid/liquid interface in the presence of anchored nanoparticles are addressed. Hydrophobized silica adsorbed at the dodecane/water interface are mainly used while, in particular situations, non-ionic surfactant, and mixtures of nanoparticles and surfactant are also employed. The silica content is varied between 0.01 wt.% and 10 wt.% relative to the oil phase. Three mechanical solicitations modes and strengths of the interface including interfacial flow, creep, and oscillatory stress sweep at low amplitude are addressed in order to find the more sensitive and accurate one to probe the structural characteristics. The sensitivity and limits of the interfacial methods are significantly impacted by the strength and the mode of the mechanical solicitation applied to the dodecane/water interface. The oscillatory stress sweep at low amplitude appears as the most sensitive method since it allows to discriminate between the rheological behavior of the different silica contents and systems. It is recommended to use rheological methods for which the cumulated strain at the interface is moderate and does not destroy the structure of the silica film at the dodecane/water interface by the mechanical stress.