Neutron scattering studies on short- and long-range layer structures and related dynamics in imidazolium-based ionic liquids

Abstract

Alkyl-methyl-imidazolium ionic liquids CnmimX (n: alkyl-carbon number, X: anion) have short-range layer structures consisting of ionic and neutral (alkylchain) domains. To investigate the temperature dependences of the interlayer, interionic group, and inter-alkylchain correlations, we have measured the neutron diffraction (ND) of C16mimPF, C9.5mimPF, and C8mimPF in the temperature region from 4 K to 470 K. The quasielastic neutron scattering (QENS) of C16mimPF was also measured to study the dynamics of each correlation. C16mimPF shows a first-order transition between the liquid (L) and liquid crystalline (LC) phases at T = 394 K. C8mimPF exhibits a glass transition at T = 200 K. C9.5mimPF, which is a 1:3 mixture between C8mimPF and C10mimPF, has both transitions at T = 225 K and T = 203 K. In the ND experiments, all samples exhibit three peaks corresponding to the correlations mentioned above. The widths of the interlayer peak at ca. 0.2 Å changed drastically at the L-LC transitions, while the interionic peaks at ca. 1 Å exhibited a small jump at T. The peak position and area of the three peaks did not change much at the transition. The structural changes were minimal at T. The QENS experiments demonstrated that the relaxation time of the interlayer motion increased tenfold at T, while those of other motions were monotonous in the whole temperature region. The structural and dynamical changes mentioned above are characteristic of the L-LC transition in imidazolium-based ionic liquids.

Enhanced Microscopic Dynamics of a Liver Lipid Membrane in the Presence of an Ionic Liquid

“…Our measurements suggest that the incorporation of the IL in the membrane modulates both of these dynamical processes. We note that the dynamics of ILs have also been investigated using the QENS technique (Triolo et al, 2006;Mamontov et al, 2009;Aoun et al, 2010;Burankova et al, 2018;Nemoto et al, 2018), however in this work we focus on the dynamics of the lipids and how they are affected by the presence of IL, and not on the dynamics of the IL themselves, since the concentration is small (see experimental details).…”

Direct observation of interlayer molecular translational motion in a smectic phase and determination of the layer order parameter

“…So far, we showed that QEGS has enough spatial and energy resolution to resolve interlayer molecular translational motions occurring in the 100-ns timescale in the Sm phase [21]. A recent neutron spin echo study for an ionic liquid system with Sm-A order suggested a similar timescale for the interlayer motion [22]. In this study, we measure interlayer molecular translational motions in the Sm-A phase of 8CB with varying temperature (T) toward the Sm-A-N transition.…”

Substituted Azolium Disposition: Examining the Effects of Alkyl Placement on Thermal Properties

“…For instance, it has already been demonstrated that ILCs may be used as non-volatile electrolytes in dye-sensitized solar cells [10][11][12], as organized reaction media [13], and as active components in electrochromic devices that do not require additional electrolytes [14][15][16]. On a more fundamental level, a comprehensive knowledge of the structural parameters that determine the thermal properties of ILCs and the long-range supramolecular organization in their mesophases contributes to a better understanding of the short-range nanosegregation phenomena that occur in room-temperature ionic liquids (ILs) [17][18][19][20][21][22][23][24][25][26][27]. Such structure-property relationships may also improve molecular designs of new ILCs and ILs, and facilitate tailoring for specific applications.…”