Dielectric relaxation of nonaqueous ionic liquid microemulsions: polarization, microstructure, and phase transition

Abstract

Two nonaqueous ionic liquid (IL) microemulsions (toluene/TX-100/[bmim][PF₆] and [bmim][BF₄]/TX-100/benzene) were studied by dielectric spectroscopy covering a wide frequency range (40 Hz to 110 MHz). A unique relaxation was observed in the radio frequency (RF) range. By methodically analyzing the dependence of relaxation parameters on the ILs content, the microstructures of the microemulsions were identified. Additionally, based on the interfacial polarization theory and Einstein equation, the mechanism of the relaxation caused by the fluctuation of IL anions along the TX-100 PEO chain was confirmed, what's more, according to the dependence of the dc conductivity of the microemulsions on IL concentration, it was concluded that the hydrophilicity of the IL in the nonaqueous IL microemulsions may play a crucial role in the electrical conduction mechanism: our analysis results suggest that a dynamic percolation process occurs in the toluene/TX-100/[bmim][PF₆] system in which IL is hydrophobic, while a static percolation happens in benzene/TX-100/[bmim][BF₄] where IL is hydrophilic. The otherness of relaxation time provides evidence that there is a possible coupling effect between IL and TX-100. Moreover, there are hints that all of the disparities, such as relaxation time, percolation type, ion migration rate and the size of different micro zones, may just stem from the different hydrophobicity of the two kinds of IL.