On the physicochemical and surface properties of 1-alkyl 3-methylimidazolium bis(nonafluorobutylsulfonyl)imide ionic liquids

Abstract

In this study, a series of 1-alkyl-3-methylimidazolium ionic liquids with bis(nonafluorobutylsulfonyl)imide anion ([NNf2]-anion) was synthesized. Their physicochemical properties and surface behaviours were analysed and compared to the widely used 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imides ([NTf2]-anion) ionic liquids. For the [NNf2]-ionic liquids, a dominating influence of the anion on physical properties such as thermal transitions, viscosity and polarity than the [NTf2]-IL was observed. With the high-precision drop shape analysis (HPDSA) approach static and dynamic wetting behaviours on both hydrophilic and hydrophobic substrates were characterised and compared to water and imidazolium ionic liquids with perfluoroalkyl-bearing cations. The [NNf2]-ionic liquids exhibited only minor differences of their static wetting properties, but showed noticeable differences of their dynamic wetting properties. It is shown that the wetting properties strongly depend on the degree and position of the fluorous side chain (for both in the cation and anion), but only slightly depend on the elongation of the alkyl side chain.