title: Surface nanocrystallization of an ionic liquid.
abstract: Surface crystallization at the vapor-liquid interface of the ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) is observed in synchrotron x-ray diffraction studies. Sharp Bragg reflections emerge in grazing-angle x-ray diffraction patterns 37 °C above the bulk melting temperature, indicating the presence of a long-range ordered phase at the surface in coexistence with the bulk parent liquid. The unique structure of the vapor-liquid interface where butyl chains attached to the cations are expelled to the vapor side facilitates interionic electrostatic interactions that lead to the crystallization. Our results demonstrate the complexity of ionic-liquid structure with their tendency to spontaneously phase separate into nanodomains with finite correlation lengths in coexistence with the liquid phase. By virtue of interfacial boundary conditions, these nanodomains grow laterally to form quasi-two-dimensional crystals.
authors.affiliation: Department of Physics, Sogang University, Seoul 121-742, Korea.
authors.forename: Yoonnam
authors.initials: Y
authors.lastname: Jeon
authors.forename: David
authors.initials: D
authors.lastname: Vaknin
authors.forename: Wei
authors.initials: W
authors.lastname: Bu
authors.forename: Jaeho
authors.initials: J
authors.lastname: Sung
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ouchi
authors.forename: Woongmo
authors.initials: W
authors.lastname: Sung
authors.forename: Doseok
authors.initials: D
authors.lastname: Kim