Interaction of Nonionic
Surfactants and Hydrophilic
Ionic Liquids in Aqueous Solutions: Can Short Ionic Liquids Be More
Than a Solvent?
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Abstract
The interaction between an ethoxylated nonionic surfactant
(C<sub>12–14</sub>EO<sub>8</sub>) and three conventional hydrophilic
imidazolium-based ionic liquids (bmim-octyl SO<sub>4</sub>, bmim-methyl
SO<sub>4</sub>, and bmim-BF<sub>4</sub>) in aqueous solution has been
investigated. In most of the reported studies where a surfactant is
dissolved in an ionic liquid aqueous solution, conventional ionic
liquids are merely considered to be solvents. Consequently, the resulting
critical micelle concentration (cmc) is considered to be that of the
surfactant. However, given that the three ionic liquids selected showed
the typical shape of a surface-active compound when the surface tension
was plotted against concentration, the role of these compounds as
secondary surfactants and consequently the possibility of mixed-micelle
formation have been investigated. Different series of experiments
where a surfactant and an ionic liquid were combined in a wide range
of mole ratios have been performed and treated as typical binary surfactant
systems in aqueous solution. It has been found for the three surfactant/ionic
liquid systems that depending on the surfactant mole fraction, α<sub>1</sub>, attractive or repulsive interactions in mixed-micelle formation
are produced. Therefore, when we select the appropriate α<sub>1</sub> these systems can be adjusted to a given application, depending
on whether monomers or micelles are mainly required