Interaction and microstructure in the binary mixture systems of ionic liquid and acetone by dielectric spectroscopy

We present a dielectric relaxation spectroscopy study on two binary mixture systems composed of ionic liquids (ILs) and acetone, i.e., 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/acetone system and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])/acetone system, respectively. Two significant relaxations were observed around 1-10 GHz and 20 GHz, respectively. The low-frequency relaxation, whose mechanism was from the orientation polarization of ionic liquid (IL), was mainly studied in this paper. The acetone concentration dependencies of the dielectric increment Δε and relaxation time τ for low-frequency relaxation presented an abrupt change at the acetone mass fraction of 60% for [bmim][PF6]/acetone and 70% for [bmim][BF4]/acetone. The inflection points reflected the change in the micro-structure of the IL/acetone binary mixture. Moreover, based on the dielectric parameters, the ion association, ion solvation and ion conductivity were also investigated. The result shows that the acetone molecules mainly interact with the cation of ILs.