Surface tension of binary mixtures of ionic liquids with the common bistriflamide anion

J. Coutinho1, M. Perez2, M. Freire1 and O. Cabeza2

1Departamento de Química, CICECO, Universidade de Aveiro, Aveiro, Portugal
2Dpto de Física, Facultade de Ciencias, Universidade da Coruña, Coruña, Spain

Keywords: mixtures
property: surface tension
material: ionic liquids

The importance of surface tensions and interfacial properties of diverse mixtures relays on their application in fields like the dried and humidification of cloths, interfacial interactions in membranes of biological cells, dispersion of crude oils, among others. Thus, the determination of the surface tension of a liquid mixture gives us information on the distribution of the molecules between the internal volume of the liquid and the liquid-vapor interface. Here, we present the surface tension of two series of ionic liquids’ mixtures. In the first approach, mixtures of the 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [C4mim][NTf2], with other [NTf2]-based ionic liquids for which the cation is a derivative of the 1-alkyl-3-methyl-imidazolium, were studied. The binary mixtures measured were: [C4mim][NTf2] + [C1mim][NTf2], + [C2mim][NTf2], + [C4C1mim][NTf2], + [C5mim][NTf2], + [C6mim][NTf2], + [C8mim][NTf2], + [C10mim][NTf2]. In the second series, the anion [NTf2]- was kept while changing the family of the cation: 3-methyl-1-propylpyridinium, [C3mpy]+, 1-methyl-1-propylpyrrolidinium, [C3mpyr]+, and 1-methyl-1-propylpiperidinium, [C3mpip]+. The binary mixtures studied were: [C4mim][NTf2] + [C3mpy][NTf2], + [C3mpyr][NTf2] and + [C3mpip][NTf2]. All mixtures have been measured using a Dataphysics contact angle system OCA20 at 298.15 K and atmospheric pressure, over the whole composition range. The uncertainty of the surface tension measured is ± 1•10-2 mN•m-1. From the data obtained the surface tension deviations were extracted, which provide us with information on intermolecular interactions occurring at the surface for a given mixture. The binary mixture results were fitted with a Redlich-Kister type equation. Finally, we calculated the relative Gibbs adsorption isotherm considering the ideality of the bulk liquid phase.

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