Spontaneous oil-in-water emulsification induced by charge-stabilized dispersions of various inorganic colloids

Abstract

Charge-stabilized dispersions of inorganic colloids are shown to induce spontaneous emulsification of hydrophobic (TPM) molecules to stable oil-in-water emulsions, with monodisperse, mesoscopic oil droplet diameters in the range of 30-150 nm, irrespective of the polydispersity of the starting dispersions. The results for cobalt ferrite particles and commercial silica sols extend our first study (Sacanna, S.; Kegel, W. K.; Philipse, A. Phys. ReV. Lett. 2007, 98, 158301) on spontaneous emulsification induced by charged magnetite colloids and show that this type of self-assembly is quite generic with respect to the composition of the nanoparticles adsorbing at the oil-water interface. Moreover, we provide additional experimental evidence for the thermodynamic stability of these mesoemulsions, including spontaneous oil dispersal imaged by confocal microscopy and monitored in situ by time-resolved dynamic light scattering. We discuss the possibility that thermodynamic stability of the emulsions is provided by the negative tension of the three-phase line between oil, water, and adsorbed colloids.