Molecular Dynamics Study of the Effect of Calcium Ions on the Monolayer of SDC and SDSn Surfactants at the Vapor/Liquid Interface

Citations Over TimeTop 16% of 2011 papers

Abstract

The effect of Ca(2+) ions on the hydration shell of sodium dodecyl carboxylate (SDC) and sodium dodecyl sulfonate (SDSn) monolayer at vapor/liquid interfaces was studied using molecular dynamics simulations. For each surfactant, two different surface concentrations were used to perform the simulations, and the aggregation morphologies and structural details have been reported. The results showed that the aggregation structures relate to both the surface coverage and the calcium ions. The divalent ions can screen the interaction between the polar head and Na(+) ions. Thus, Ca(2+) ions locate near the vapor/liquid interface to bind to the headgroup, making the aggregations much more compact via the salt bridge. The potential of mean force (PMF) between Ca(2+) and the headgroups shows that the interaction is decided by a stabilizing solvent-separated minimum in the PMF. To bind to the headgroup, Ca(2+) should overcome the energy barrier. Among contributions to the PMF, the major repulsive interaction was due to the rearrangement of the hydration shell after the calcium ions entered into the hydration shell of the headgroup. The PMFs between the headgroup and Ca(2+) in the SDSn systems showed higher energy barriers than those in the SDC systems. This result indicated that SDSn binds the divalent ions with more difficulty compared with SDC, so the ions have a strong effect on the hydration shell of SDC. That is why sulfonate surfactants have better efficiency in salt solutions with Ca(2+) ions for enhanced oil recovery.

Related Papers

• → Potentials of mean force of simple ions in ambient aqueous solution. II. Solvation structure from the three-dimensional reference interaction site model approach, and comparison with simulations(2000)132 cited
• → Micro hydration structure of aqueous Li+ by DFT and CPMD(2020)19 cited
• → Confinement effects on the solvation structure of solvated alkaline metal cations in a single-digit 1T-MoS2 nanochannel: A first-principles study(2021)12 cited
• → The solvent influence on the electrochemical transfer of divalent ions(2000)17 cited
• → Interaction of K+with a Phospholipid Bilayer: A Molecular Dynamics Study(1997)24 cited