The Porosity of Samples of the Disperse Dye, C.I. Disperse Blue 79

Abstract Nitrogen adsorption isotherms have been determined on commercial samples of the disperse dye, C.I. Disperse Blue 79. The samples contain approximately equal amounts of dye and dispersing agent. Low B.E.T. surface areas (0.5 – 0.9 m 2 g −1 ) and c-values (5 – 19) were obtained. Nearly all the isotherms exhibit hysteresis, although there are considerable variations in the character of the hysteresis loops from sample to sample. Frenkel-Halsey-Hill (F.H.H.) plots of the nitrogen isotherms have also been constructed. For some dye samples, these plots become linear at relative pressures of 0.6 – 0.7; for the other samples, the plots have no clear linear region at all. Analysis of the F.H.H. plots and of the hysteresis loops indicates the presence of mesopores, probably within aggregates of the dye samples. The mesoporous structures of some of the samples appear much more rigid than those of the others. This range of behaviour correlates well with variations found in the stabilities of dispersions of the dye samples in water.