title: Surfactant-free microemulsions of 1-butyl-3-methylimidazolium hexafluorophosphate, propylamine nitrate, and water.
abstract: Generally, surfactants (or amphiphiles) are believed to be necessary components of microemulsions. However, it has been demonstrated that, in the absence of traditional surfactants, microemulsions can also form from a ternary system of two immiscible fluids (i.e., oil and water phases) and an amphi-solvent, but the current understanding of such surfactant-free microemulsions (SFMEs) is very limited. Herein, we report an SFME consisting of the hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), the protic IL propylamine nitrate (PAN), and water, in which bmimPF6and PAN are used as the oil phase and the amphi-solvent, respectively. The microstructures and structural transitions of the SFME were investigated using cyclic voltammetry, fluorescence spectroscopy, and ultraviolet-visible spectroscopy. The SFME exhibited water-in-bmimPF6(W/IL), bicontinuous (BC), and bmimPF6-in-water (IL/W) microstructures, depending on the composition of the ternary system, similar to the case of traditional surfactant-based microemulsions (SBMEs). The three kinds of microstructures were confirmed by cryogenic transmission electron microscopy (cryo-TEM) observations. To the best of our knowledge, this is the first report on SFMEs composed of two ILs as components, especially where one is used as the amphi-solvent.
authors.affiliation: State Key Laboratory Base of Eco-chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China.
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.affiliation: State Key Laboratory Base of Eco-chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China.
authors.forename: Huanhuan
authors.initials: H
authors.lastname: Deng
authors.affiliation: State Key Laboratory Base of Eco-chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China.
authors.forename: Yunlei
authors.initials: Y
authors.lastname: Fu
authors.affiliation: State Key Laboratory Base of Eco-chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China.
authors.forename: Yuquan
authors.initials: Y
authors.lastname: Chen
authors.affiliation: State Key Laboratory Base of Eco-chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Colloid and Interface Chemistry (Ministry of Education), Shandong University, Jinan 250100, P. R. China. wghou@sdu.edu.cn.
authors.forename: Wanguo
authors.identifier: http://orcid.org/0000-0001-7883-509X
authors.initials: W
authors.lastname: Hou