Aggregation behaviour of an azo dye containing a trifluoromethyl group on poly(vinylpyrrolidone)

Abstract

The aggregation behaviour of an azo dye containing a trifluoromethyl group (p-FTS) in aqueous solutions has been investigated by means of visible absorption measurements. The thermodynamic parameters for aggregation were calculated from the dependence of the aggregation constants on temperature. The thermodynamic parameters for the corresponding dye containing a methyl group (p-TS) were different from those of p-FTS, suggesting that the fluorine atoms of the dye molecule affect its aggregation behaviour. To elucidate the effects of poly(vinylpyrrolidone), the binding constants of the dyes with the polymer were determined. Furthermore, considering the binding constants, the aggregation constants on the polymer chains were estimated. The thermodynamic parameters determined for the aggregation on the polymer chains were different from those for the aggregation in water, indicating that the aggregation mechanism on the polymer chains is different from that in water. From this result, some models of the dye aggregates are proposed.