The change in acid strength of acidic dye molecule and organic ligand on the micelle surface.

Abstract

The interaction between acidic dye molecule and positive charges on the micelle surface has been investigated. The protolytic dissociation of acidic dye molecule containing a hydroxyl group on one end of the conjugated system and nitro or carbonyl group on the other end is promoted on the micelle surface. The interaction between dipole of acidic dye molecule and positive charges on the micelle surface causes a transfer of an electron from the electrondonating group to the electron-attracting group. The effect of quaternary ammonium salt on the acid strength increases with the increase of the dissociation constant of hydroxyl group on the dye molecule. The increase of ionic strength and the decrease of dielectric constant weaken the interaction. With the quaternary ammonium salt, the lower the critical micelle concentration, the stronger is the interaction between dye molecule and micelle. Dye molecules or ligands involving -SO3H group are liable to be absorbed on the micelle surface. It is found that the complexes of higher order are readily formed on the micelle surface, and the analytical sensitivity increases if the absorption of the complex is due to π→π* transition of organic ligands.