MOLECULAR-DYNAMICS SIMULATION OF ISOPROPYL NAPHTHALENE SULFONATE AT THE WATER HEPTANE INTERFACE/

Stable water-in-crude oil (w/o) emulsions occur at many stages during the production and processing of crude oil. The breaking of these emul sions is an essential step, frequently carried out by the addition of chemical demulsifiers. The stability of any surfactant-stabilized emul sion is strongly dependent on the nature of the interfacial film, whic h provides a resistance to either flocculation or coalescence, towards the final equilibrium state of phase separation. Thus, effective demu lsifiers must be capable of displacing preformed, rigid, incompressibl e interfacial films, and/or significantly reducing the rate of build-u p of the surfactant layer. This work presents the results of molecular dynamics simulations of a flat section for a w/o interface covered by a nonionic surfactant, either pure or contaminated by an anionic demu lsifier. The simulation of aqueous and oleic solutions of surfactant a nd demulsifier were also performed by using 3D amorphous cells with 3D periodicity, while the interface was modeled by a 3D layered cell est ablishing 2D periodic boundary conditions. This made it possible to de monstrate changes in the amphiphile bimolecular interactions and diffu sion properties at the w/o interface once the demulsifier is adsorbed, which could be related to the loss of stability of the surfactant fil m.