Determination of the Phase Inversion Temperature of Orange Oil/Water Emulsions by Rheology and Microcalorimetry

Abstract

In low-energy emulsification processes, phase inversion occurs when the phases of a dispersion exchange, because of changes in the medium's properties. This paper reports experiments to determine the phase inversion temperature (PIT) of orange oil/water emulsions stabilized by nonionic surfactants. Two techniques were employed: rheology, which is already commonly used to obtain the PIT, and microcalorimetry, which has been proposed as a new technique. Continuous monitoring of the emulsions' viscosity permitted identifying different phenomena that occur while the temperature varies. For all the dispersions prepared, the rheological curves obtained showed two peaks, one attributed to the phase separation process and the other to the phase inversion phenomenon. The microcalorimetry technique showed two endothermic transitions as the dispersion's temperature increased. The initial temperatures were comparable to those obtained by rheology. The influence of the surfactant concentration and the hydrophilic-lipophilic balance (HLB) of the mixture of surfactants and the reduction in volume of the phases at the phase inversion temperature were also evaluated. In general, both methods used to evaluate the phase inversion of the orange oil/water systems (rheology and microcalorimetry) presented concordant results, both for the phase separation process and the phase inversion temperature.

Keywords:

• Cloud point
• emulsions
• nonionic surfactants
• phase inversion temperature

We thank Oxiteno do Brasil for donating the polyoxide samples, and the Research Center of PETROBRAS (CENPES), the Coordinating Office for Improvement of University Researchers (CAPES), the National Council for Scientific and Technological Research (CNPq), the Office to Finance Studies and Projects (FINEP) and the National Petroleum Agency (ANP) for financial support.

Notes

^a Confirmed by hydrogen nuclear magnetic resonance (¹H NMR).

Source: Data supplied by Oxiteno do Brasil.

^a Cloud point values of aqueous surfactant solutions, without oil phase.

Note. Oil phase concentration = 20 wt% and surfactant concentration = 10 wt%.