Dielectric permittivity of room temperature ionic liquids: a relation to the polar and nonpolar domain structures.

We measured microwave transmission and reflection spectra for typical room temperature ionic liquids, [C(4)min][TFSA], [C(4)min][PF(6)], [C(6)min][PF(6)], and [C(8)min][PF(6)], at frequencies between 40 MHz and 40 GHz in the temperature range up to 100 degrees C. The transmission spectra were analyzed using complex dielectric functions, and the static permittivity epsilon(S) was determined as a function of temperature. Applying the effective medium approximation to epsilon(S), we have estimated that the static permittivity of the polar domain is around 20, and that of the nonpolar domain around 2.5.