Measurement of the Particle Size of a High-Lightfastness Direct Dye in Cellulose by p-Nitrophenol Adsorption

The p-nitrophenol adsorption method has been used to determine the specific surface, and hence the particle size and aggregation number, of a high-lightfastness direct dye (C.I. Direct Green 26) in regenerated cellulose film. The particle size found at high concentrations is of the same order as that found for other dyes of this type, in cellulose film, by Weissbein and Coven, using electron microscopy. The aggregation number rises rapidly with rise in dye concentration in the film to a maximum of the order of 106 at shade depths above about two percent pure dye on film weight.