Model Emulsions\nStabilized with Nonionic Surfactants:\nStructure and Rheology Across Catastrophic Phase Inversion

Abstract

The catastrophic\nphase inversion process of model emulsions\n(water/Span\n80-Tween 80/heptane) from oil-in-water to water-in-oil emulsion was\ninvestigated. During this process, the phase inversion of the emulsion\nwas monitored through Fourier transform infrared spectroscopy (FT-IR).\nIn emulsions without NaCl, oil-in-water gel emulsions are formed prior\nto phase inversion. As the HLB value increases, the oil volume fraction\nrequired for phase inversion becomes higher. Polydisperse distribution\nof the gel emulsion is observed from microscope optical images. The\nTurbiscan Lab stability analyzer indicates that O/W gel emulsions\nbefore the phase inversion has good stability at 50 °C. Rheological\nmeasurements reveal that emulsions exhibit non-Newtonian behavior.\nThe viscosity of the gel emulsions increases significantly prior to\nphase inversion. As the oil volume fraction increases, the storage\nmodulus and loss modulus of the gel emulsion increase to a maximum,\nat which catastrophic phase inversion occurs. In emulsions with NaCl,\nthere is no oil-in-water gel emulsion formed before phase inversion.\nThe physicochemical properties of the emulsion play a crucial role\nin whether gel emulsions are produced during catastrophic phase inversion.\nThese gel emulsions have the potential to diversify the applications\nin crude oil extraction, drug delivery systems, packaging materials,\nand other fields.