Micelle formation by N-alkyl-N-methylpiperidinium bromide ionic liquids in aqueous solution

The micelle formation by the surface active ionic liquids (ILs) N-alkyl-N-methylpiperidinium bromide CnPDB (n = 12, 14, 16) in aqueous solution has been investigated through the characterizations of surface tension, electrical conductivity and steady-state fluorescence measurements. From the curves of surface tension vs CnPDB concentration at 25 °C, the critical micelle concentration (cmc), the effectiveness of the surface tension reduction (Πcmc), the maximum surface excess concentration (Гmax) and the minimum area (Amin) occupied per surfactant molecule at the air/water interface are calculated. Through the electrical conductivity measurements, the cmc values at different temperatures and a series of thermodynamic parameters (ΔGm°, ΔHm° and ΔSm°) for the formation of micelles are evaluated in the temperature range of 25–45 °C. The steady-state fluorescence measurement is also employed to investigate the micelle formation of CnPDB.

Graphical abstractThe micelle formation by the surface active ionic liquids (ILs) N-alkyl-N-methylpiperidinium bromide CnPDB (n = 12, 14, 16) in aqueous solution is investigated through the characterizations of surface tension, electrical conductivity, and steady-state fluorescence measurements.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Micelles are formed by N-alkyl-N-methylpiperidinium (CnPDB) bromides in aqueous solution. ► CnPDB surface activity is compared with other surfactants of N-heterocycle headgroups. ► Micelle formation is entropy- or enthalpy-driven at low or high temperatures.