Computational studies on the behavior of Sodium Dodecyl Sulfate (SDS) at TiO2(rutile)/water interfaces

SDS surfactant is adsorbed by either its hydrophilic or hydrophobic part on the different cell orientations [Display omitted] ► Properties of SDS surfactant at rutile/water interfaces are investigated. ► Rutile cell orientations (100), (001) and (110) are studied. ► Different SDS structures are formed at the different cell orientations. ► Behavior of surfactant molecules on the (100) surface is similar to that in graphite. Molecular dynamics simulations to study the behavior of an anionic surfactant close to TiO2 surfaces were carried out where each surface was modeled using three different crystallographic orientations of TiO2 (rutile), (001), (100) and (110). Even though all three surfaces were made with the same atoms the orientation was a key to determine adsorption since surfactant molecules aggregated in different ways. For instance, simulations on the surface (100) showed that the surfactant molecules formed a hemicylinder structure whereas the molecules on the surface (110) were attached to the solid by forming a hemisphere-like structure. Structure of the aggregated molecules and surfactant adsorption on the surfaces were studied in terms of tails and headgroups density profiles as well as surface coverage. From density profiles and angular distributions of the hydrocarbon chains it was possible to determine the influence of the solid surface. For instance, on surfaces (100) and (001) the surfactant molecules formed molecular layers parallel to the surface. Finally, it was found that in the solids (100) and (110) where there are oxygen atoms exposed on the surface the surfactant molecules were attached to the surfaces along the sites between the lines of these oxygen atoms.