Spatial and thermal signatures of alpha and beta relaxations in glassy and glacial aliphatic ionic liquids

摘要

The competition between Coulomb and van der Waals interactions brings forth unique dynamic features and broad applications to ionic liquids. Herein, we present a combined calorimetric, X-ray diffraction, incoherent elastic, and quasi-elastic neutron scattering study, over a wide temperature range (180-340 K), of the relaxational dynamics of the liquid, supercooled liquid, crystalline, glassy, and glacial states of two model ionic liquids: tributylmethylammonium (a good glass-former) and butyltrimethylammonium (a good crystal-former) cations and the bis(trifluoromethanesulfonyl) imide anion. In both systems, we observed two distinct relaxation processes. The Q-dependence of the respective relaxation time shows that the alpha-process is diffusive, while the beta-process is modulated by the structure of the liquids.