Physicochemical investigations on the aqueous solution of an ionic liquid, 1-butyl-3-methylimidazolium methanesulfonate, [bmim][MS], in a concentrated and dilute regime

The physicochemical properties of the ionic liquid (IL) 1-butyl-3-methylimidazolium methanesulfonate ([bmim][MS]) in combination with water were evaluated through density, viscosity, surface tension, conductance, cyclic voltammetry, absorption and emission spectroscopic measurements. Binary mixtures were studied both in the water-rich and [bmim][MS]-rich regions (0.01 mM–4.96 M). The static and dynamic properties of the binary combinations were evaluated through density and viscosity measurements. The [bmim][MS] decreased the surface tension of the water, from which the surface excess and area per molecule of the ionic liquid were determined at the air–liquid surface. The equivalent conductance of [bmim][MS] at an infinite dilution was determined from the conductance data because the system obeyed the Debye–Hückel–Onsager formalism. Cyclic voltammetry measurements revealed the formation of some metastable organized structures at specific compositions. The absorption and emission spectral behavior of the anionic dye eosin Y were found to be dependent on the concentration of [bmim][MS] in the water-rich region. A significant change in the steady state anisotropy and excited state lifetime of the fluorophore occurred above 1.0 M [bmim][MS] in water, which correlated with the viscosity of the medium. It was concluded that the aggregation of [bmim][MS] into micelle-like aggregates occurred above the specific concentration, which significantly altered the different physiochemical parameters of the [bmim][MS] binary mixture.