Influence of pressure and temperature on microemulsion stability

Abstract

For three different microemulsion systems the stability of the one-phase region in pressure–temperature (P/T) space has been studied. We also report P/T stability studies of the sodium bis(2-ethylhexyl) sulphosuccinate (AOT)–water–n-alkane microemulsion droplet system using the straight-chain alkanes from the homologous series propane to n-decane as oil. On progressively decreasing the carbon number of the oil the P/T phase boundaries of these systems exhibit a reversal of behaviour. By plotting microemulsion stability on the oil density–temperature surface we have normalised the phase behaviour observed in P/T space for AOT–water–n-alkane systems. Further, the oil density–temperature plots suggest that a minimum oil density of ca. 0.5 × 10³ kg m^–3 is required for AOT-stabilised microemulsion droplets to exist as discrete entities.