Conductivity and bonding structures of aqueous solutions of imidazolium and choline ionic liquids

Ionic liquids (ILs) have gained recognition as a potential alternative to traditional solvents due to their environmentally friendly properties. The ease of handling and higher conductivities of aqueous solutions of ILs has also stimulated research of these green solvents. While 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) is a commonly researched IL, it is more expensive than traditionally used solvents. Whilst [C4mim]Cl is less toxic than many traditional solvents, it is still hazardous to both human and marine life. Betaine hydrochloride (BetHCl) presents a cheaper, low toxicity alternative primarily due to the similar aggregation and bonding exhibited by the pure ILs, and their aqueous solutions. This study investigates the conductivity of aqueous solutions of [C4mim]Cl and BetHCl. We examined these properties across varying water content and temperature, and with added metal salts (CuCl2 and ZnCl2), to develop insights into aggregation, bonding, and IL-metal interactions. Fourier Transform Infrared (FTIR) spectroscopy was used to further explore aggregation and bonding. The conductivity data displayed good agreement with Walden’s rule and the Vogel-Fulcher-Tammann (VFT) equation. Results indicate non-linear relationships between water content and conductivity for both ILs, whereas, near-linear relationships were found between temperature and conductivity. Different interactions were observed between the two metal chlorides and the ILs. Gradual changes in conductivity with varying water content, rather than a step change, suggest the formation of hydrogen bonding networks in aqueous solutions of both [C4mim]Cl and BetHCl. The similar trends exhibited by the ILs imply the potential of BetHCl as a viable, cost-effective alternative to traditional solvents.