From an immiscible water-oil system to the ultralow interfacial tension of a microemulsion

In industrial applications such as enhanced oil recovery (EOR), pharmaceutics, or cosmetics, it is often necessary to mobilize and transport hydrophobic substances in aqueous media. The ideal way to do this is to form a microemulsion, i.e. a thermodynamically stable dispersion. When trying to synthesize such mixtures, the interfacial tension (IFT) between water and the hydrophobic phase can range from 50 mN/m for the raw substances to values as low as 10^‑5 mN/m for the fractions of a successfully created microemulsion. In search of just the right composition, it is helpful to use a measuring instrument that covers this very broad IFT spectrum.

In this Application Report, we first demonstrate how an impressively wide range of IFT can be measured by means of the Spinning Drop Tensiometer – SDT, starting with a simple system consisting of a water phase, an oil phase (cyclohexane) and a hydrotrope (tert-butyl alcohol). The measured values from 50 mN/m down to 0.1 mN/m are in good agreement with published data of a Force Tensiometer – K20 and even show a better reproducibility. By extending the analyses to a phase system of ultralow IFT, we could show that the instrument is capable of giving reliable results over a range of six decades, i.e. down to 2.7·10^‑5 mN/m.