Sorption-diffusion in heterogeneous systems. Part 3.—Experimental models of dye sorption

Experimental studies are made of the sorption dynamics of dye molecules on rigid potous substrates (silica-alumina spheres) of known pore structure. The apparent diffusivity of the dye molecules is shown to vary by several orders of magnitude for different substrate/dye sorption affinities . However, the true diffusivity, derivable by methods described previously,1, 2 has the magnitude characteristic of free diffusion in the solvent for non-aqueous solvents. For cationic dyes in water, the true diffusivities, low at room temperature, also approach the classical diffusivity, as the temperature is raised in order to destroy a mobility inhibiting mechanism . At lower temperature, dye aggregation leads to dye entities sufficiently large compared to the pore dimensions.