Surfactant adsorption on solid surfaces in relation to wettability

Abstract

The main propose of the first part of this research was to investigate the relation of surfactant adsorption and wettability on various hydrophobic surfaces. Surface tension was measured as a function of surfactant concentration for three cationic and three anionic surfactants. In addition, advancing contact angles and surfactant adsorptions on eight polymers were measured. Thus, a mathematical analysis was developed by using Zisman’s equation to calculate the interfacial tensions at solid/vapor (γsv) and solid/pure water (γoSL), which are rarely directly measured. γsv was found to be 33.3 mN/m and to not depend on polymer structure. From the surfactant adsorption isotherms on polymer surfaces carried out by the solution depletion method with varying the solution pH, the surfactant adsorption increased with the surfactant tail length for both cationic and anionic surfactants below these CMCs. Whereas sodium octanoate (C8) adsorption was highest at plateau region due to less polarity of carboxylate group. The pH level only slightly affected the adsorption level. Finally, the fundamental mechanism of flotation deinking was studied by using a hydrophobic carbon black and a hydrophilic office paper. Sodium dodecyl sulphate (SDS) and C8 were chosen for adsorption in this study. The adsorption of C8 onto carbon black is higher than that of SDS, resulting to the wide use of C8 surfactant in flotation deinking operations. Moreover, the calcium is used as the effective activator since it can improve surfactant adsorption on carbon black, while not enhancing surfactant adsorption on paper fiber that will be easily removed with carbon black in flotation process.