Abstract
Dyeing behavior of C. I. Reactive Blue 19 (RB19) on cellulose and its aggregation properties in aqueous solutions were investigated. The results suggested that the dyeing behavior of RB19 on cotton in aqueous alkaline solutions was closely related to the dye aggregation which was influenced by the addition of salt and by the dyeing temperature. Small angle X-ray scattering (SAXS) study showed that, at a temperature of 20°C without addition of salt, the aggregation began to occur at a concentration as low as 3×10-5mol/L and fairly stable hexamer of RB19 was formed in the concentration range between 3.97×10-3and 9.52×10-2mol/L. At 70°C, the number of RB19 constituting the aggregate decreased to 3.2, while it increased up to 19 at 20°C by the addition of NaCl at a concentration of 0.3mol/L. The amount of dye fixed on cotton as well as the dye partition index (proposed in the previous paper) as a function of salt concentration and dyeing temperature were found in good consistence with the results found by SAXS. The dimension and the shape of the hexamer determined by SAXS were explainable by a model simulated by molecular mechanics and molecular dynamics. In the latter, the structure of environmental water was taken into consideration.
