Stability of oil-in-water emulsions stabilised by silica particles

We describe the preparation and properties of oil-in-water emulsions stabilised by colloidal silica particles alone. The charge on the particles and their extent of flocculation, assessed via turbidity measurements, can be modified by pH control and addition of simple electrolytes. The stability of emulsions to both creaming and coalescence is low in the absence of electrolyte, and the effects of adding salt are dependent on the type of salt. In systems containing NaCl, emulsions are less stable once the particles are flocculated. In the presence of either LaCl3 or tetraethylammonium bromide (TEAB), emulsion stability increases dramatically for conditions where the silica particles are weakly flocculated; extensive flocculation of the particles however leads to destabilisation of the emulsions. For TEAB, relatively large emulsions of diameter around 40 µm remain very stable for up to 3 months at salt concentrations corresponding to the onset of coagulation of the colloid. Such emulsions are themselves strongly flocculated.