Formation, Stability, and Rheology of Particle Stabilized Emulsions: Influence of Multivalent Cations

Recently, it has been shown that hydrophilic colloidal silica particles (Ludox) can be rendered sufficiently hydrophobic to stabilize oil in water (O/W) emulsions simply by changing the pH of the suspending medium to ∼2, and such emulsions have been shown to display novel rheology (shear thickening) compared to conventional emulsions (Wolf et al. J. Rheol., 2007, 51, 465 ). However, while lowering pH can render nanosized silica (∼10 nm) sufficiently hydrophobic so as to stabilize O/W emulsions, this method does not appear to generalize to larger silica particles (∼200 nm). In this present study, we explore a different approach, which employs hydrophilic, (i.e., not surface modified) colloidal silica particles to stabilize O/W emulsions in the presence of a range of cations. It appears that certain cations at high pH (in particular La3+) will render various inorganic oxide surfaces more hydrophobic. As such this makes the combination of silica particles with appropriate concentrations of Lanthanum cations an attractive model system for the study of the formulation, stability, and rheological behavior of Pickering emulsions. We present initial investigations exploring the formulation of such emulsions and of how their rheology and stability compare with more conventional emulsions.