A Comparative Study on the Interface Behaviour of Short-chain and Long-chain Ionic Liquids

Ionic liquids (ILs) are phenomenal group of green chemicals with the potential to improve development in organic chemistry and chemical technology. ILs are salts exclusively composed of ions with low melting points and unique physico-chemical properties such as low vapor pressure, non-flammability and ion conductivity and because of less environmental pollution have been regarded as „„green solvents‟‟. Asymmetry of the ions is responsible for the low melting points of ionic liquids. Surfactant behavior of ILs has recently attracted much attention, since they demonstrate excellent surface/interface activity and micelle formation. Here, interface behaviour of amphiphilic short-chain and long-chain, with twice chain length, imidazolium ionic liquids, 1-alkyl-3-methylimidazolium chloride ([Cnmim][Cl] with n = 6 and 12) on the interfacial tension of n-butyl acetate + water system, as recommended system for investigations, was studied.The used ILs act as excellent surfactants and significantly reduce the interfacial tension of this system. Also the influence is more effective for the IL with longer hydrocarbon chain, n=12, because of its higher hydrophobicity nature. An almost linear interfacial tension decrease by temperature was relevant in all cases. The Szyszkowski adsorption equation was revealed as a satisfactory model to fit the experimental data; therefore, IL molecules behaved ideal with no interaction at the interface. In this regard, the Langmuir maximum interface excess and equilibrium adsorption constant were obtained at different temperatures. Accordingly, both of them increase with methylene bridge (–CH2–) in the ILs tail because of longer alkyl chain which causes further adsorption efficiency.

Keywords:

Ionic liquids , Imidazolium , Interfacial tension , Szyszkowski equation