Adsorption behavior of long alkyl chain imidazolium ionic liquids at the n-butyl acetate + water interface

Abstract

The adsorption behavior of amphiphilic long alkyl chain imidazolium ionic liquids (ILs), 1-alkyl-3-methylimidazolium chloride {[Cnmim][Cl], n=12, 14, 16} at the interface of n-butyl acetate+water system was studied. Within IL bulk concentration range of 1.00·10−5–1.00·10−2mol/dm3 and temperature of 293.2–318.2K, the used ILs act as excellent surfactants and reduce the interfacial tension significantly. The corresponding interfacial activity appeared logically in the order of [C16mim][Cl]>[C14mim][Cl]>[C12mim][Cl]. An almost linear decrease in interfacial tension was also relevant by temperature. For modeling, the Szyszkowski adsorption equation was used to reproduce the experimental data. The consistent fittings confirm the ideal adsorption of the used IL molecules at the interface. Results also show that adsorption effectiveness increases with the alkyl chain length; however, it declines with temperature. On the other hand, adsorption tendency increases with alkyl chain length as well as with temperature. Negative standard free energy values indicate simultaneous adsorption for all cases.