title: Communication: Salt-induced water orientation at a surface of non-ionic surfactant in relation to a mechanism of Hofmeister effect.
abstract: The behavior of water molecules at the surface of nonionic surfactant (monomyristolein) and effects of monovalent ions on the behavior are investigated using the heterodyne-detected vibrational sum frequency generation spectroscopy. It is found that water molecules at the surface are oriented with their hydrogen atoms pointing to the bulk, and that the degree of orientation depends on the anion strongly but weakly on the cation. With measured surface potentials in those saline solutions, it is concluded that the heterogeneous distribution of anions and cations in combination with the nonionic surfactant causes the water orientation. This heterogeneous distribution well explains the contrasting order of anions and cations with respect to the ion size in the Hofmeister series.
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Mafumi
authors.initials: M
authors.lastname: Hishida
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Kaneko
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Masanari
authors.initials: M
authors.lastname: Okuno
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Yamamura
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Ishibashi
authors.affiliation: Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Saito