Adsorption Behavior of Short Alkyl Chain Imidazolium Ionic Liquids at N-Butyl Acetate + Water Interface: Experiments and Modeling

The adsorption behavior of three amphiphilic ionic liquids (ILs), 1-alkyl-3-methylimidazolium chloride {[Cnmim][Cl], n=6-8}at the interface of n-butyl acetate + water system was studied with IL concentration range of 1.00×10-4-1.00×10-1 mol•dm-3 and temperature range of 293.2-318.2 K. The ILs behave as strong surfactants in this chemical system and significantly reduce the interfacial tension with the order of their alkyl chain length and is consistent with their hydrophobicity nature. An almost linear decrease of interfacial tension with temperature was also relevant. The experimental data were satisfactorily reproduced with Szyszkowski equation, implying an ideal ILs adsorption. In this regard, the Langmuir maximum interface excess and equilibrium adsorption constant were obtained at different temperatures for each IL. Accordingly, effectiveness of adsorption and adsorption tendency increase with the alkyl chain length. At the saturated interface, increasing temperature leads to declining Langmuir maximum interface excess due to disrupting surrounding water molecules around ILs hydrophobic portions. However, adsorption tendency of ILs increases slightly with temperature.