Effect of urea on the aqueous solubility of dispersed dyes

Effects of sulfonated surfactants on parallel diffusion of mono azo dye with high aggregation constant into cellulose membranes

“…Such an increase was observed once when 1 mol/dm 3 urea was added to this system,11 in which the addition of urea reduced the aggregation of the dye and increased the pore diffusivity. Urea is known to break the water structure 12–15. It has been reported that hydrating water molecules around the dye play an important role in the aggregation process of the dye 16.…”

Physical Chemistry of Dyeing: State of Dye in Dyebath and in Substrate

“…114,115 On the other hand, from spectrophotometric and diffusion measurements, Craven and Datyner 116 ' 117 have given evidence of interaction between acid anthraquinone wool dyes and nonionic surfactants, and have observed that the extent of interaction increases with the hydrophobicity of the dye molecule, particularly when nonpolar aliphatic side chains are present, but decreases due to the presence of solubilizing sulfonate groups in the dye molecule. 126 With aromatic sulfonic acids, solubilization is effected through hydrophobic as well as van der Waals interactions. This deduction has been further substantiated from the measurements of cloud points and c.m.c.…”

Effect of Urea on Solubility

“…Katayama et al (9) showed the effect of urea on the aqueous solubility of a series of azo-dyes. They noted that urea had a more pronounced effect on the solubility of those compounds having the larger "hydrophobic surface.…”

“…Thermodynamic Considerations-When considering the process where a compound is transferred from water to urea solution, the following equation may be written (5,9): compd. in water (mole fraction NO) -+ compd.…”

“…I n this case the free energy of partitioning ( A F ) may be determined from the following expression (9):…”