Interaction between water-soluble polymers and azo dyes containing fluorine atoms. I. Monoazo sulphonated dyes containing a trifluoromethyl group

Abstract

The interaction between sulphonated monoazo dyes containing a trifluoro-methyl group and poly vinylpyrrolidone was investigated by means of visible absorption spectrum measurements. To elucidate the effects of fluorine atoms, the corresponding dyes containing a methyl group were also investigated. Dyes having one trifluoromethyl and one sulphonate group exhibited multiple binding equilibria in phosphate buffer and formed aggregates on the polymer chains. However, in pure water a single equilibrium was observed, as in the case of the other dyes. The first binding constant K 1 was determined at 288, 293, 298 and 303 K, and the thermodynamic parameters ΔH and ΔS were obtained. The results suggest that the interaction is greatly affected by the fluorine atoms and sulphonate groups of the dye molecules, as well as by the phosphate ions in solution.