Effect of temperature on the aggregation behaviour and thermodynamic properties of surface active ionic liquid 1-decyl-3-methylimidazolium bromide in aqueous solutions: Surface tension, vapour pressure osmometery, conductivity, volumetric and compressibility study

Abstract

The self-aggregation behaviour and thermodynamic properties of surface active ionic liquid (SAIL) 1-decyl-3-methylimidazolium bromide ([C10mim][Br]) in aqueous solution have been investigated by means of surface tension, vapour pressure osmometery, electrical conductivity, volumetric and compressibility measurements at different temperatures. The critical micelle concentrations (cmc) obtained from the different thermodynamic properties investigated show that the curves of cmc against temperature show a shallow minimum at about 298K and an increasing trend at the higher temperature range. From the electrical conductivity measurements, the values of the degree of ionization of the counter ion on the micelles (α), thermodynamic properties of micellization (ΔGm∘, ΔHm∘, ΔSm∘) and infinite dilution molar conductivity (Λm∘) for the SAIL investigated at different temperatures were obtained. The temperature dependency of infinite dilution partial molar properties (Vm∘ and Km∘), apparent molar properties at the critical micelle concentration (Vϕ,cmc and Kϕ,cmc), apparent molar properties in the micelle phase (Vϕmic and Kϕmic) and the change of apparent molar properties upon micellization (ΔVϕ,m and ΔKϕ,m) were derived from the experimental volumetric and compressibility values. The surface tension measurements provided a series of parameters, including surface tension at the cmc (γcmc), adsorption efficiency (pC20), effectiveness of surface tension reduction (Πcmc), maximum surface excess concentration (Γmax) and minimum surface area per molecule (Amin) at interface of air/solution for the investigated SAIL at different temperatures. Finally, the osmotic properties of the binary mixture of [C10mim][Br] and water including the water activity, osmotic coefficient and vapour pressure were studied by using the vapour pressure osmometry.