The Nanostructure of Alkyl-Sulfonate Ionic Liquids: Two 1-Alkyl-3-methylimidazolium Alkyl-Sulfonate Homologous Series

Abstract

The functionalization of polymers with sulfonate groups has many important uses, ranging from biomedical applications to detergency properties used in oil-recovery processes. In this work, several ionic liquids (ILs) combining 1-alkyl-3-methylimidazolium cations [CnC1im]+ (4 ≤ n ≤ 8) with alkyl-sulfonate anions [CmSO3]− (4 ≤ m ≤ 8) have been studied using molecular dynamics simulations, totalizing nine ionic liquids belonging to two homologous series. The radial distribution functions, structure factors, aggregation analyses, and spatial distribution functions reveal that the increase in aliphatic chain length induces no significant change in the structure of the polar network of the ILs. However, for imidazolium cations and sulfonate anions with shorter alkyl chains, the nonpolar organization is conditioned by the forces acting on the polar domains, namely, electrostatic interactions and hydrogen bonding.

Unraveling the Morphology of [CnC1Im]Cl Ionic Liquids Combining Cluster and Aggregation Analyses

“…Notably, for n ≥ 4 the polar and nonpolar networks seem to coexist without destructively perturbing each other. This is a sign of stark microheterogeneity in the IL, which has also been observed in prior studies. ,,,,− At this point, it remains unclear what the exact composition of the nonpolar domains in the n = 2–8 systems is.…”

“…This is a sign of stark microheterogeneity in the IL, which has also been observed in prior studies. 10 , 20 , 22 , 24 , 57 − 62 At this point, it remains unclear what the exact composition of the nonpolar domains in the n = 2–8 systems is.…”

“…In the present work, we focus on the common n -alkyl-methyl-imidazolium chloride ILs (with n ∈ {2, 4, 6, 8, 10, 12}) and aim at unraveling the morphology of this specific IL family. We acknowledge previous works that investigate the structure and/or related properties of different imidazolium-based ILs or IL families. − To commence this investigation, classical nonpolarizable molecular dynamics (MD) simulations of the ILs were performed. Subsequently, cluster and aggregation analyses from TRAVIS − and AGGREGATES were carried out.…”