Concentrated emulsions of perflubron in aqueous media.

Flocculation of o/w emulsions consisting of a perfluorochemical (PFC) emulsified by either phospholipids or decaglyceroldioleate (10-2-O) was assessed both by direct observation and through photon correlation spectroscopy (PCS) and viscoelasticity measurements in unsteady oscillatory flow. Flocculation gives rise to emulsion instability but can be prevented (a) by the addition of a negatively charged surfactant to either phosphatidylcholine (PC) or 10-2-O, respectively the zwitterionic phospholipid and the nonionic surfactant used as primary emulsifiers, or (b) by using a saccharide solution as the continuous phase. The study indicates that both electrostatic (Coulombic) repulsive forces and hydration (steric) forces play a role in preventing flocculation. Various minor components of the egg yolk phospholipids (EYP) used in commercial emulsion preparation probably stabilize the emulsion by increasing both electrostatic and hydration repulsion.