Adsorption characteristics of ionic and nonionic surfactants on hydrophobic pigment in aqueous medium



The current study is based on the investigation of the adsorption properties of ionic and nonionic surfactants on an organic hydrophobic pigment powder, namely, β-copper phthalocyanine, in aqueous medium. The nonionic surfactants, selected systematically to represent varying degrees of ethoxylation, are nonylphenol ethoxylates, whereas the ionic surfactant is sodium oleate, a carboxylate-type anionic reagent. The adsorption of surfactants was assessed qualitatively by surface analysis of powders, before and after the adsorption of the surfactants. The experimental results were explained by the structural and other properties of the surfactants and the surface properties of the pigment. The specific adsorption of surfactants on pigments was verified by zeta potential measurements, as they altered the zeta potential values to a great extent. Nonionic surfactants decreased the absolute value of the zeta potential of the powder; whereas anionic surfactant sodium oleate shifted the zeta potential to more negative values. On the one hand, Fourier Transform–infrared and X-ray diffraction examinations of the pigments did not show any noticeable evidence for surfactant untreated or treated copper phthalocyanine. On the other hand, thermal analysis (both thermogravimetric and differential thermal analysis) showed clear evidence of the surfactants on both pigments, as substantial changes in thermogravimetric curves were assessed.