Electroacoustics and electroosmosis in low temperature ionic liquids

The electroacoustic method made it possible to study electrokinetic phenomena at high ionic strengths. Interestingly, the ζ potential does not cease at ionic strengths as high as 3 M in aqueous systems. Here, we show that also in low temperature ionic liquids the electrokinetic phenomena do exist. Dispersions of anatase in 1-alkyl-3-methylimidazolium (alkyl = butyl, hexyl, octyl or decyl) trifluoromethanesulfonates, hexafluorophosphates, and mixed tetrafluoroborate-chloride ionic liquids were studied. These ionic liquids are molten salts at room temperature, and they can be considered as about 3 M salt solutions in the absence of solvent. The electrokinetic potential of anatase determined by means of the electroacoustic method was negative for all ionic liquids studied, although for a few ionic liquids the standard deviation in a series of 20 consecutive measurements was higher than the absolute value. Absorption of moisture by the ionic liquids has rather insignificant effect on the electrokinetic potential of anatase. Electroosmosis in specimens of porous alumina saturated with ionic liquids was studied, and the electrokinetic charge of alumina was also negative.