Polar/apolar domains' dynamics in alkylimidazolium ionic liquids unveiled by the dual receiver NMR 1H and 19F relaxation experiment

The dual receiver 1H/19F inversion-recovery NMR method is applied to measure simultaneously the spin-lattice relaxation times, T1, of both cation and anion forming ionic liquid (ILs) materials. Two representative classes of ILs comprising 1-alkyl-3-methylimidazolium [CnMIm]+ (n = 2, 12) as cation and bis(trifluoromethylsulfonyl)imide [TFSI]- or tetrafluoroborate [BF4]- as anions have been considered. The experimental data, acquired on a wide range of temperature (278-333 K), have been analysed according to the Bloembergen, Purcell, and Pound model and provide the rotational dynamic parameters, such as the activation energy and the correlation time ?c of the rotational segmental motion. The overall dynamic behaviour is dictated by the length of the alkyl chain and the capability of the anion to disrupt or stabilize the apolar domain structure.