Abstract

Electrophoretic mobility measurements by laser-Doppler electrophoresis are reported for selected alkali and alkaline-earth fluorides in different organic solvents. These measurements coupled with FTIR/transmission spectroscopy (FTIR/TS) studies allow for the sign of the surface charge to be predicted for fluoride salts in organic solvents. On the basis of this analysis, the electrokinetic behavior in both hydrogen and non-hydrogen bonding liquids can now be explained. Analysis of these results show that the surface charge of fluorides in methanol (hydrogen bonding liquid) is positive as it is in water. Importantly, the surface charge of fluoride salts in other organic solvents (non-hydrogen bonding liquids) can be either positive or negative depending on the nature of the organic solvent. For example fluoride salts are negatively charged in acetone due to the strong solvation of the cation relative to the fluoride ion. The opposite is true for water and other protic solvents where the fluoride ion is more extensively solvated.