Proton Transport in Imidazoles: Unraveling the Role of Supramolecular Structure

Abstract

The impact of supramolecular hydrogen bonded networks on dynamics and charge transport in 2-ethyl-4-methylimidazole (2E4MIm), a model proton-conducting system, is investigated by broadband dielectric spectroscopy, depolarized dynamic light scattering, viscometry, and calorimetry. It is observed that the slow, Debye-like relaxation reflecting the supramolecular structure in neat 2E4MIm is eliminated upon the addition of minute amounts of levulinic acid. This is attributed to the dissociation of imidazole molecules and the breaking down of hydrogen-bonded chains, which leads to a 10-fold enhancement of ionic conductivity.

Associating Imidazoles: Elucidating the Correlation between the Static Dielectric Permittivity and Proton Conductivity

“…In addition, although we conjectured that addition of levulinic acid to 2-ethyl-4-methylimidazole leads to disruption of the supramolecular hydrogen-bonded chains, this hypothesis could not be confirmed since much higher concentrations (≥2.5 mol %) of the acid were used in the previous study. [30] In addition to the new insights obtained from the present study regarding the interplay between the static dielectric permittivity and proton transport, the use of suitable diluents makes it possible to verify the previous hypothesis regarding the shortening of the supramolecular chains upon addition of levulinic acid.…”

“…It is worth noting that a similar effect is observed when one compares the magnitude of the static dielectric permittivity for neat 2E4MIm of different purities of 95% and 99%, reported in the previous studies. [29,30] In both cases, slightly shifted minima in the plot of the versus temperature are observed, but the characteristic timescales remain unaltered. It should be noted that in previous studies of 2-ethyl-4methylimidazole, no analysis and discussion of the temperature dependence of was provided.…”

“…relaxation is attributed to reorientation of supramolecular hydrogen-bonded chains. [29,30] However, in the case of 2E4MIm the ratio between and remains approximately constant over the entire temperature range in which transitions from above to below 1, suggesting that the average lengths of the supramolecular structures remain relatively unaltered in the entire range.…”

Slow rheological mode in glycerol and glycerol–water mixtures

“…The hydrogen-bonded structures can also give rise to an additional peak in the static structure factor at low Q-vectors [25,27], although the reverse is not true, a prepeak in the structure is not systematically associated with a slower than structural relaxation feature in the dynamics [28,29]. The family of liquids displaying a dielectric Debye process [30] includes, besides monoalcohols, secondary amides [31], protic ionic liquids [32], and several pharmaceuticals [33,34].…”

Broadband dielectric spectroscopy of Nafion‐117, sulfonated polysulfone (sPSF) and sulfonated polyether ketone (sPEK) membranes

“…Broadband dielectric spectroscopy (BDS) is extensively used to investigate a wide range of inorganic, organic, and polymeric materials . These investigations include molecular dynamics and conductivity in polymers of intrinsic microporosity, proton transport in multi‐scale hybrid membranes and supramolecular hydrogen bonded‐network . Moreover, BDS is used to investigate composite membranes, the effect of casting solvent and concentration on polymer blends, and to track kinetics of step growth polymerization process .…”