Study of physicochemical and dielectric proprieties of dicationic ionic liquids: the effect of the nature of the cation

In this paper a comparative study of three dicationic ionic liquids (DILs) is presented, these latter are characterized by sharing tetrafluoroborate [2BF4(-)] as anion and have three different structure piperidinium based cations [R-1(CH2)(n)PPI2+]; namely: bis-methyl piperidinium propylidene [MPrPPI2+], bis-methyl piperidinium butylidene [MBPPI2 divided by]and bis-ethyl piperidinium butylidene [EBPPI2 divided by], their structures were characterized by using H-1, C-13, F-19-NMR and FT-IR techniques. In the frequency range [from 10(-2) to 10(6) Hz] and over the temperature range from [212 to 248 K], real dielectric (epsilon(1)), imaginary dielectric (epsilon"), conductivity (sigma) and complex electrical modulus (M*)-frequency (omega) relationships of these three ILs were investigated using dielectric spectroscopy and electric modulus formalism. In this context, the dielectric permittivity, conductivity and the activation energy values are observed to be increased respectively; on one hand, with the spacer length from [MPrPPI2+] to [MBPPI2+] and on the other hand, with the alkyl chain length attached to the cationic from [MBPPI2+] to [EBPPI2+] of the dicationic ionic liquids. Also, the results suggest that the effect of alkyl chain length is more important to the spacer length effect on the dielectric permittivity and conductivity proprieties. Finally, the activation energy is determined in order to understand the relaxation processes in our DILs.