THE INTERACTION BETWEEN <i>p</i>-AMINOAZOBENZENE AND ANIONIC SURFACTANTS

Abstract

The interaction between p-aminoazobenzene and anionic surfactants in aqueous solution was studied by spectral change of the mixed solution and decrease of equilibrium adsorption on dyeing of cellulose acetate in this system.A p-aminoazobenzene molecule with an anionic surfactant molecule, such as sodium dodecylsulfate or sodium dodecylbenzenesulfonate likely forms 1:1-complex in aqueous soltion and a new adsorption band due to this complex spears at about 510mμ, while intensity of maximum adsorption of p-aminoazobenzene at 377mμ decreases.Up to C. M. C. the new band increases in intensity with the concentration of anionics. The spectral change with a fixed concentration of p-aminoazobenzene and varying concentration of anionics has definite isosbestic point at 337mμ and 456mμ.As the absorption of new band decreases with rising temperature, the formation of such complex is an exothermic reaction. There is little difference between the absorption spectra of the cellulose acetate film dyed in p-aminoazobenene aqueous solution in the presence and absence of anionics. From this results, it can be concluded that the complex itself is not taken up by acetate fiber, hence the formation of the complex in the dye bath leads to diminish the effective concentration of p-aminoazobenzene for dyeing.The concentration of the complex in the infinite dye baths which contain different amount of anionics is determined from the decrease of apparent partition coefficient in acetate dyeing at different temperature. The equilibrium coefficients of the complex formation are thus determined at different temperature.The heat of formation, ΔH° and entropy change, ΔS° of the complex formation between p-aminoazobenzene and sodium dodecylsulfate are caluculated to be -11Kcal/mol, -25cal/mol/deg, respectively. As the equiliblium coefficients of the complex formation are in the order of 102 at room temperature and pH=6.4_??_6.6, only a small amount of complex may exist in the dye bath at pratical dyeing temperature.