Color Change of Disperse Dyes on Nylon 6 Films with Dye Concentration

Abstract

Spectral changes of disperse dyes on nylon 6 film are investigated with decreasing dye concentration ( Cf). The visible absorption maxima (λmax) of most azo disperse dyes shift to longer wavelengths with decreasing C f. The shift is significant for dyes with dipole structures caused by the intramolecular charge transfer. The spectral change is analyzed in detail for CI Disperse Orange 3 and 5, practical disperse dyes, in terms of McRae's equation and a factor analysis. The λmax values for these dyes on film in the range of low Cf are much longer wavelengths than those estimated by McRae's equation and shift to shorter wavelengths with increasing temperature. The results of the factor analysis indicate that the visible absorption spectra of dyed films with decreasing Cf can be described as the sum of two distinct spectra, designated as species I and II. Species I has λmax at longer wavelengths than species II. The ratio of [species I]/[species II] increases with decreasing C f, causing a red shift of λmax with decreasing Cf. This result is consistent with the sorption behavior of these dyes by nylon 6 film from water, where the dyes are sorbed by the polymer as two distinct species: L—species—dye taken up by the polymer through the Langmuir sorption mechanism, and P—species—dye taken up by Nemst-type partitioning. For both dyes, the relations between C f and the concentrations of species I and II are very similar to the relations between Cf and the concentrations of the L- and P-species. We estimate that species I and II in this study correspond to L- and P-species in sorption studies, respectively.