title: Surfactant-free microemulsion composed of oleic acid, n-propanol, and H2O.
abstract: Generally, a microemulsion consists of oil, water, surfactant, and sometimes cosurfactant. Herein, we report a surfactant-free microemulsion (denoted as SFME), consisting of oleic acid (oil phase), water, and n-propanol without the amphiphilic molecular structure of a traditional surfactant. The phase behavior of the ternary system was investigated, showing that there were a single-phase microemulsion region and a multiphase region in the ternary phase diagram. The electrical conductivity measurement was employed to investigate the microregions of the single-phase microemulsion region, and three different microregions, that is, water-in-oleic acid (W/O), a bicontinuous (B.C.) region, and oleic acid-in-water (O/W), were identified, which were further confirmed by freeze-fracture and cryogenic transmission electron microscopy (FF-TEM and Cryo-TEM) observations. The polarity and the salt solubility of water domains in the W/O SFME were investigated by UV-visible spectroscopy using methyl orange and potassium ferricyanide as probes, respectively. Experimental results showed that the water domains in the W/O microemulsion had a lower polarity than bulk water and a normal solubility for salt species, indicating that the SFMEs have much significance in the preparation of various nanomaterials.
authors.affiliation: State Key Laboratory Base of Eco-chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, People's Republic of China.
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.forename: Aolin
authors.initials: A
authors.lastname: Yin
authors.forename: Jikuan
authors.initials: J
authors.lastname: Zhao
authors.forename: Dongxiang
authors.initials: D
authors.lastname: Li
authors.forename: Wanguo
authors.initials: W
authors.lastname: Hou