title: Dilute or Concentrated Electrolyte Solutions? Insight from Ionic Liquid/Water Electrolytes.
abstract: When room-temperature ionic liquids (IL) are used as an electrolyte, their transport behaviors are still under heavy debate due to their complicated ion-associations. In this article, we conducted molecular dynamics simulations to study the molecular scale ion associations from the very dilute 1-butyl-3-methylimidazolium iodide/water solution to the pure IL. It revealed that ions are localized in a multicoordinated ion cage structure with nanoseconds in concentrated IL solutions. Dynamics analyses indicate that the transport of this solution can be depicted by the Debye-Hückel model only in dilute IL/water electrolyte. The velocity and rotational correlation functions showed that the lifetime of translational and rotational motions are at the level of picoseconds and nanoseconds, respectively, because of the ion cage effect. The lifetime of ion association demonstrated that the recombination of association ions was prevalent in IL solutions. It means that the dipolar or stable contact ion-pairs model may not be suitable for depicting the IL transport.
authors.affiliation: Department of Chemistry and Chemical Engineering, Hefei Normal University , Hefei 230061, P. R. China.
authors.forename: Maolin
authors.initials: M
authors.lastname: Sha
authors.affiliation: Department of Chemistry and Chemical Engineering, Hefei Normal University , Hefei 230061, P. R. China.
authors.forename: Huaze
authors.initials: H
authors.lastname: Dong
authors.affiliation: Department of Chemistry and Chemical Engineering, Hefei Normal University , Hefei 230061, P. R. China.
authors.forename: Fabao
authors.initials: F
authors.lastname: Luo
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201800, P.B. Box 800-204, P. R. China.
authors.forename: Zhongfeng
authors.initials: Z
authors.lastname: Tang
authors.affiliation: Institute of Atomic and Molecular Physics, Anhui Normal University , Wuhu 241000, P. R. China.
authors.forename: Guanglai
authors.initials: G
authors.lastname: Zhu
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201800, P.B. Box 800-204, P. R. China.
authors.forename: Guozhong
authors.initials: G
authors.lastname: Wu
keywords: Ionic liquid; correlation function; electrolyte; ion association; ion cage; molecular dynamics simulation