PHASE INVERSION IN NONIONIC SURFACTANT OIL-WATER SYSTEMS .3. THE EFFECT OF THE OIL-PHASE VISCOSITY ON CATASTROPHIC INVERSION AND THE RELATIONSHIP BETWEEN THE DROP SIZES PRESENT BEFORE AND AFTER CATASTROPHIC INVERSION

Catastrophic-phase inversion has been studied in surfactant-oil-water (S-O-W) systems. Polyisobutene was dissolved in cyclohexane in order t o change the viscosity of the oil phase. The effect of oil-phase visco sity and stirrer speed on drop sizes before inversion, at the inversio n point, and after inversion has been examined. It is shown that the f ormation of drops within drops (O/W/O) can give rise to a close packed system at the inversion point. Most attention has been given to the i nversion W/O to O/W. There is evidence that the mechanism of drop form ation changes as the oil viscosity increases; a change in Reynold's nu mber affects the drop type. The effective volume fraction of the dispe rsed phase is increased by the formation of O/W/O drops; this did not occur at low viscosity for the class of surfactant used here. The volu me fraction of water required for inversion decreased as the oil visco sity increased. Before inversion, when the viscosity of the oil is 0.0 25 N s m-2, drop diameter, D(owo), is given by D(owo) = 0.08 exp (5f(w )/2) N-0.8 indicating that drop coalescence controls drop size. As the oil-phase viscosity increases, the relationship D(owo) is-proportiona l-to mu(c)-0.35N-0.75 is observed. After inversion, D(ow) is-proportio nal-to N-0.8 and D(ow) is related to D(owo) but D(owo) decreases with increase of oil viscosity, whereas D(ow) increases with oil viscosity. Analysis predicts a relationship between D(owo) and D(ow), a minimum value for D(owo) and a correlation between D(owo) and the volume fract ion of the dispersed phase at inversion. When the oil-phase viscosity is high, the inversion O/W to W/O does not have the same mechanism as the inversion W/O to O/W.