Spectrophotometric Investigation of the Interactions between Disperse Dyes and Sodium Salt of 2-Naphthalenesulfonic Acid-Formaldehyde Condensates

Abstract

The absorption spectra of disperse dye in aqueous solution were changed by addition of the sodium salt of 2-naphthalenesulfonic acid-formaldehyde condensates (abbreviatted as 2-NSF). If all of the binding sites in polymer to a dye are assumed to be equivalent and independent of each other, and if the number of total binding sites is much larger than the number of occupaied sites, the apparent molar absorptivity (e. pp) is given by eap, =(sf-e. pp)/Pel/nK+Eb where ef and eb are the molar absorptivities of the free and bound dye respectively, P is concentration of the polymer, K is the intrinsic binding constant, and n is the number of the binding sites per one polymer molecule.
The binding constant (nK) were obtained from the linear plots of e, versus (ef-e )/P, and the thermodynamic parameters were calculated. All values of the changes in enthalpy were negative and the contribution of enthalpy was generally greater than that of entropy. The binding character of dye with 2-NSF was discussed,