An investigation into direct dye aggregation

Abstract

The aggregation characteristics of the direct dye Cl Yellow 162 have been investigated by measuring the optical transmittance at specific temperatures, in the presence and absence of electrolyte and surfactant, using a Hellma quartz immersion probe attached via fibre optical cables to a single-beam Zeiss Specord S 100 spectrophotometer. The experiments indicate that the dye in solution, without electrolyte, was monomolecular at temperatures of 70 °C and higher. The dye solution with electrolyte remained aggregated at temperatures up to 90 °C, a finding contrary to the still widespread assumption that the dyes are monomolecular at elevated temperatures. In the presence of a surfactant the dye appeared to be forming dye-surfactant micelles that were fairly stable even at higher temperatures.