Y. Chen and G. Xu,Improvement of Ca2+-tolerance by the introduction of EO groups for the anionic surfactants: Molecular dynamics simulation,Colloids Surf. A,2013,424(0), 26-32.

The influence of Ca2+ on the aggregation of sodium dodecyl sulfate (SDS), sodium dodecyl oxyethylene sulfate (SDES), sodium dodecyl benzene sulfate (SDBS) and sodium dodecyl benzene oxyethylene sulfate (SDBES) at air-water interface were compared to investigate the role of oxyethylene unit by means of the molecular dynamics simulation. In the SDES and SDBES systems, the interaction between -O-SO3- groups and Na+ions decreases, the diffusion coefficient of Na+ increases, while the interaction between surfactants and Ca2+ ions increases, and the diffusion coefficient of Ca2+ ions decreases. Unlike SDS and SDBS systems, the EO groups introduced may bind Ca2+ ions and the interaction between Ca2+ ions -O-SO3- groups is weakened, consequently, the precipitation of anionic surfactant by Ca2+ ion is restrained, i.e., the Ca2+-tolerance of anionic surfactants via the introduction of EO groups may be improved. The present results could help in choosing of anionic surfactants used in aqueous solution with inorganic salts.