title: Phase transition of a binary room-temperature ionic liquid composed of bis(pentafluoroethanesulfonyl)amide salts of tetraheptylammonium and N-tetradecylisoquinolinium and its surface properties at the ionic liquid|water interface.
abstract: A binary room-temperature ionic liquid (RTIL) composed of bis(pentafluoroethanesulfonyl)amide (C(2)C(2)N(-)) salts of tetraheptylammonium (THpA(+)) and N-tetradecylisoquinolinium (C(14)Iq(+)) undergoes a phase transition upon increasing the mole fraction of C(14)Iq(+) (x) in the bulk RTIL. The initial decrease with x of the interfacial tension (gamma) at the interface between water (W) and the binary RTIL reaches a break point at x approximately 0.2 irrespective of the values of the phase-boundary potential. The surface tension at RTIL|air interface and the conductivity of the binary RTIL support that the break point at x = 0.2 at the RTIL|W interface is attributable to the change of the bulk property. However, unlike the micelle formation of a surfactant solution, a further increase in x gives rise to a further change in gamma. Whereas the phase transition at x = 0.2 does not depend on the applied potential (E) across the RTIL|W interface, the mode of the change in gamma at x > 0.2 strongly depends on E and the apparent deficit of C(14)Iq(+) at the interface is more pronounced when E is closer to the point of zero charge.
authors.affiliation: Department of Energy, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Ishimatsu
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kitazumi
authors.forename: Naoya
authors.initials: N
authors.lastname: Nishi
authors.forename: Takashi
authors.initials: T
authors.lastname: Kakiuchi