Phase behavior in the biologically important oleic acid/sodium oleate/water system

Stefania Mele, Olle Söderman, Helena Ljusberg-Wahrén, Krister Thuresson, Maura Monduzzi, Tommy Nylander

Research output: Contribution to journalArticlepeer-review

22 Citations (SciVal)


The phase behavior in the oleic acid/sodium oleate/normal saline (0.15 M NaCl aqueous solution) system has been determined. For this purpose visual inspection of samples between crossed polarizers, and Small Angle X-ray diffraction was used to identify the various phases and their unit cell dimensions. A rich phase behavior was observed for the ternary system, featuring reverse micellar, micellar cubic, hexagonal, and cubic phases, and large regions with lamellar phases. As expected the ratio the ‘oleic acid/sodium oleate’ determines the pH and as a consequence the phase behavior. The results could be modeled by an extended Henderson–Hasselbalch (HH) equation, which takes into account the electrostatic potential at the aqueous lipid interface. The knowledge obtained is important for understanding the lipolysis of triglycerides, as the phase behavior of the end-product of the reaction regulates how well the insoluble product can be dispersed and consequently the kinetics of the process.

Original languageEnglish
Pages (from-to)30-36
Number of pages7
JournalChemistry and Physics of Lipids
Publication statusPublished - 2018 Mar 1

Subject classification (UKÄ)

  • Physical Chemistry


  • Degree of dissociation
  • Fatty acid pKa
  • Lipolytic enzymes
  • Liquid crystalline phases
  • Oleic acid
  • Small angle X-ray diffraction
  • Sodium oleate


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