Self-assembled monolayers presenting imidazolium ions at the tail ends (SAMIMs) having different counteranions have been prepared on Au, and the measurement of water contact angles of the surfaces proved to be an extremely valuable simple technique for quantifying the effects of counteranions on hydrophilicity and hydrophobicity of SAMIMs, which will be extrapolated to the water miscibility of the related ionic liquids.

Water wettability of Si/SiO2 surfaces was controlled by the formation of SAMs terminating in 1-alkyl-3-(3-silylpropyl)imidazolium ions and the anion exchange on the surfaces ("direct anion exchange"). The exchange was confirmed by X-ray photoelectron spectroscopy, and the water wettability was measured as a water contact angle by contact angle goniometry. We found that anions played a great role in determining water wettability of Si/SiO 2 surfaces. For example, water contact angles of Si/SiO2 surfaces presenting 1-methyl-3-(3-silylpropyl)imidazolium ions changed from 28 to 42°when the counteranion Clwas exchanged with PF6 -. In addition to the anions, the N-alkyl groups of imidazolium cations were also found to be important in determining water wettability: we did not observe any significant changes in the contact angles of Si/SiO 2 surfaces presenting 1-butyl-3-(3-silylpropyl)imidazolium ions by the anion exchange. We also demonstrated that the reaction rate of the direct anion exchange was affected by a choice of solvents: the anion exchange from Clto PF6was the fastest in an aqueous solution.