Dynamics of liquid—liquid phase inversion using non-ionic surfactants

Abstract

A study has been made of phase inversions which can occur in agitated liquid—liquid dispersions of hydrocarbons (“oil”) and water when non-ionic surfactants are present. Various modes of phase behaviour have been established and the role of the surfactant phase is clarified. Transitional inversion was induced at room temperature by changing the surfactant composition; this altered the hydrophile—lipophile balance (HLB) of the surfactant. This inversion occurred over a very narrow range of HLB when three phases existed. Transitions could also be induced by changing the water—oil ratio (WOR). In these cases, transitions were not reversible; the value of WOR for transition when oil was added to water was not the same as the value observed when water was added to oil. These transitions could not always be described as true inversions and the formation of complex drops (double emulsions) was possible. The location of boundaries for phase inversion, which resulted from changing the WOR, depended on the intensity of agitation and on the ratio of liquid addition to the dispersion. With any particular system of oil, water and surfactant, phase behaviour and inversion boundaries can be represented on a single map. The form of the map was influenced by the type of non-ionic surfactant that was used.