Influence Of The Aromatic Substituente on the Aggregation Properties of Direct Dyes Derived from 4,4\'-Diaminostilbene-2,2\'-Disulphonic Acid

Dyes ions have a tendency to self-associate in aqueous solutions. Since almost all textile dyes are applied from aqueous systems, it is important to understand the association of dyes in water, and to determine the number of chemical species presented in the system. The main factors influencing aggregation are dye concentration, electrolyte concentration, and temperature. In the present work, the influence of the coupling component structure on the dye aggregation is presented. The molecular aggregation has been studied spectrophotometrically in aqueous solutions as a function of dye concentration (10^-6 ¸ 10^-3 mol/L). As the concentration increases, different changes were observed in the dyes UV-vis spectra indicating that the molecules are beginning to aggregate. The shapes of the obtained spectra were totally different as the coupling component structure was changed in the dye molecule.From the matriceal analysis, the number of chemical species presented in the system (in domain of concentrations studied) was determined. The mathematical calculations confirm the experimental data regarding the aggregation of the investigated dyes.