A new application of ionic liquids: hydrophobic properties of tetraalkylammonium-based poly(ionic liquid)s

Abstract

The potential of using poly(ionic liquid)s as a new family of hydrorepellent materials has been explored. Free-radical polymerization of a series of ionic liquids based on the polymerizable cation [2-(methacryloyloxy)ethyl]trimethylammonium and on the hydrophobic anions bis(trifluoromethylsulfonyl)imide, nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate led to the corresponding poly(ionic liquid)s that were characterized by TGA and DSC analysis, SEM, MALDI-TOF and XPS spectroscopy. Contact angle investigations show that the nature of the surface of the poly(ionic liquid)s based on the nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate anions are featured by remarkable hydrophobic properties with advancing contact angles (θ_adv) lying in the range 113–118°, while to the polymer poly[2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethylsulfonyl)imide is associated poor hydrorepellent activity (θ_adv = 76°). The tensiometric measurements also experience receding contact angles (θ_rec) lying in the range 16–20° and a consequent high hysteresis suggesting that, on the outermost layers of the polymers, very high and very low-energy surface portions are present.