Influence of alkyl chain length on thermophysical, structural properties and molecular dynamics of new pyridinium-ester based room temperature ionic liquids

Abstract

In present work, a series of new pyridinium-ester-based room-temperature ionic liquids (RTILs) have been synthesized. Thermal stability and the changes of viscosity properties of these RTILs have been studied on the basis of the ester functionality on pyridinium cation moiety and with alkyl chain length size. Drastic change in viscosity is explained on basis of hydrogen bonding interaction and microheterogeneity. The origin of microscopic properties and the heterogeneity of these ILs are examined in terms of the interactions between cations and anions. Viscosity results of these RTILs are fitted and analysed by using Arrhenius model and Vogel-Tammann-Fulcher (VTF) model. Furthermore, Natural Bond Orbital (NBO) analysis is conducted to enhance the understanding of intermolecular interactions through second-order perturbation energy calculations. Complementary computational methods, including Atoms in Molecules (AIM) analysis, Non-Covalent Interaction (NCI) analysis, Electron Localization Function (ELF), as well as Localized Orbital Locator (LOL), offer valuable insights into the characteristics and nature of non-covalent interactions in these RTILs. Based on our experimental results, these RTILs exhibit excellent viscosity properties and may have the potential to be used as lubricants for suitable designs and future applications. © 2025 The Authors.