Solubility of Disperse Dye in Water Containing Dispersing Agent and Concentration of Complex Formed between Them

Abstract

The basic idea of the previously reported spectrophotometric determination of the solubility of dye, defined as concentration of monomer in equilibrium with a large amount of fine- crystalline dye dispersed in water, has been extended to estimate solubility, S₁, of dye in the presence of dispersing agent of concentration bellow its CMC and concentration, S_c, of complex formed between them by means of the following simultaneous equations,
Here K is an equilibrium constant of complex formation, C_s is concentration of dispersing agent at equilibrium, and A₀ is extrapolated absorbance of linear plot of over -all absorbance against-dy-econcentration at its higher concentration region. ε₁, ε_c and ε_s are molar extinction coefficients of dye monomer, complex and dispersing agent, respectively. ε is mean molar extinction coefficient (apparent) of fine-crystalline dye. The disperse dyes used in these experiments are C. I. Disperse Orange 3 (DO 3) and 1, 4-diaminoanthraquinone (DAA), and the dispersing agent is sodium 2-naphthalenesulfonate-formaldehyde condensate (NaNSF). Experimental results revealed that with increasing concentration of NaNSF S_c increases but S₁ levels off to a almost constant value after initial slight drop. Both S₁ and S_c increase with increasing temperature. In particular, the fact that S₁ increases exponentially with increasing temperature suggests that dissolution of disperse dye is dominated also by its fusion process in the present case. The total concentration of the molecular aggregates of dye and complex decreases gradually to zero in case of DO 3 but increases in case of DAA with increasing concentration of NaNSF.