Self-aggregation of ionic liquid 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [C4mmim][BF4] in aqueous media: A conductometric, volumetric and spectroscopic study

• Self-aggregation behaviour of [C4mmim][BF4] has been studied using various techniques.
• Thermodynamic parameters showing aggregation is an entropy-driven process.
• Volumetric analysis indicates aggregation is influenced by solute–solvent interactions.
• 1H NMR revealed formation of loosely bound aggregates in the system.

Aggregation behaviour of ionic liquid (IL), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, [C4mmim][BF4] in aqueous media has been studied by electrical conductivity, density and speed of sound measurements across temperature range (288.15–308.15) K. The critical aggregation concentration (cac), the standard Gibb’s free energy of aggregation, ΔG°agg, adiabatic compressibility, βS and changes in the adiabatic compressibility upon aggregation, ΔβS,agg for the IL in aqueous solution have been derived from the experimental data. Further to get the deeper insights into the aggregation process spectroscopic study using 1H NMR measurements have been carried out. The aggregation behaviour observed from conductance and volumetric approaches has been found to be in good agreement with each other. NMR study revealed the formation of loosely bound ion associates as aggregates in the system upon aggregation.