Adsorption of n -Dodecyl-beta-d -maltoside on Solids

Adsorption of a typical sugar-based surfactant, n -dodecyl-beta-d -maltoside (DM), on hydrophilic solids, silica, alumina, titania, and hematite, and a hydrophobic solid, graphite, was studied. Effects of salts and pH on the adsorption on alumina as well as the electrokinetic potential of the particles after surfactant adsorption were studied to determine the adsorption mechanisms. Hydrophobicity and settling rate were measured to explore the surfactant conformation on the particle surfaces. For hydrophilic solids, DM was found to adsorb strongly on alumina, titania, and hematite but weakly on silica. While hydrogen bonding is postulated to be the major driving force for the adsorption on hydrophilic solids, for hydrophobic solid, the adsorption is mainly due to the hydrophobic interactions. The different behaviors of surfactant on hydrophilic and hydrophobic solids were attributed to the different interactions between surfactant and solids. Also, the surfactant is estimated to form a bilayer on alumina while on graphite it forms a monolayer. The surface hydrophobicity and stability of the solids are discussed in terms of the adsorbed monolayer/bilayer formation on the particles.