Effect of Divalent Cationic Ions on the Adsorption Behavior of Zwitterionic Surfactant at Silica/Solution Interface

Abstract

The adsorption behavior of zwitterionic surfactant dodecyl sulfobetaine (DBS) on a silica/solution interface with Ca(2+), Mg(2+) existing in aqueous solution is explored by atomistic molecular simulations. The interaction energy contribution of van der Waals and electrostatic potentials in the surfactants/water/silica system are respectively calculated, from which the electrical interaction can be found to play a decisive role in the adsorption tendency of DBS on the silica surface with or without inorganic ions, despite different mechanisms. The distinct decrease of energy has been found to be derived from electrical interaction when DBS adsorb on the silica surface covered by Ca(2+) or Mg(2+). Therefore, it can be predicted that the cationic ions combined on the negatively charged silica surface in a mineral water medium might decrease the adsorption trend of DBS on the silica surface, which has been experimentally proven by TOC measurement. Structural information of the close interface layer and the distribution of water molecules are analyzed after the complete molecular dynamics simulation using a ternary model. Ca(2+) and Mg(2+) combined on the silica surface can reduce the adsorption amount of DBS by preventing the direct interaction between DBS and surface, and bringing about the orientation reversal of DBS molecules to break the order of adsorption interface layer. Furthermore, changes in the status of the water spreading on the silica surface caused by the complexation of cations are also an important reason in the adsorption reduction.

Adsorption behavior of cocamidopropyl betaine under conditions of high temperature and high salinity

“…These reduce the adsorption amount of surfactants. Divalent cations, mainly Ca 2+ and Mg 2+ , can weaken the adsorption of betaine‐type amphoteric surfactant DSB on a silica surface through lowering multilayer adsorption by an electrical mechanism in addition to the complexation mechanism …”

Molecular dynamics simulations of aggregation behavior of sodium dodecyl sulfate on SiO2 and CaCO3 surfaces

“…Then, oxygen atoms were exposed to the surface when the crystal system was cleaved with a thickness of approximately 5.405 Å. After that, the surface was added H atoms to make it hydroxylation . To avoid crystal structure deformation during minimization, the silica layer without hydroxyl groups was treated as rigid body by fixing all cell dimensions.…”

“…It was found that the hydroxylation of the solid surface had a certain effect on the aggregation of surfactant. Hu X et al used MD simulation to investigate the contribution of van der Waals and electrostatic potential energy to the interaction energy about the surfactant‐water‐silica system. The results showed that electrostatic interactions play a decisive role on adsorption process of amphoteric surfactant dodecyl betaine.…”

Adsorption of metallic ions from aqueous solution on surfactant aggregates: a molecular dynamics study

“…An alternative tool to investigate such complex processes are computer simulations. For example, Hu et al [12] and Liu et al [13] studied adsorption and desorption phenomena on solid surfaces. In particular, they investigated adsorption of divalent cations and dodecane desorption from silica surfaces in an aqueous dilution of cetyltrimethylammonium bromide (CTAB).…”