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 compressibil

• Surface activity of [C10mim][Br] in aqueous solutions was studied.
• Aggregation behaviour of [C10mim][Br] in aqueous solutions was studied.
• Temperature effect on the micellization and surface activity of [C10mim][Br] was studied.
• Surface activity of [C10mim][Br] increases by decreasing temperature.
• Micellization is favourable for both enthalpy and entropy changes at higher temperatures.

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 298 K 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,cmcVϕ,cmc and Kϕ,cmcKϕ,cmc), apparent molar properties in the micelle phase (Vϕmic and Kϕmic) and the change of apparent molar properties upon micellization (ΔVϕ,mΔVϕ,m and ΔKϕ,mΔKϕ,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 (γcmcγcmc), adsorption efficiency (pC20), effectiveness of surface tension reduction (ΠcmcΠcmc), maximum surface excess concentration (ΓmaxΓmax) 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.

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