Investigation of the interfacial phenomena in the presence of nonionic surfactants and a silica nanoparticle at the n-decane-water interface: Insights from molecular dynamics simulation

Abstract

In chemical enhanced oil recovery (EOR), the nanoparticles can be employed as conveyors to transfer the surfactants and impede the reduction of surfactant concentration. Here, a set of molecular dynamic simulations were carried out to examine the ability of hydrophobic silica nanoparticle (NP) to deliver the nonionic surfactant (Triethylene glycol monododecyl ether; C12E3) into the n-decane-water interface. Another set of simulations in which only surfactant molecules are initially located at the interface was performed in order to better characterize the influence of NP on the surfactant adsorption film.The NP exhibited high efficiency in delivering surfactant molecules to the n-decane-water interface. In addition, for the C12E3-NP and n-decane-NP, the Coulombic interactions are weaker than the van der Waals interactions confirming the nonpolar property of the silica nanoparticle. The density profiles indicate that as the concentration of surfactants increases at the interface, NP separates more from the surfactant layer. The interfacial tension (IFT) of n-decane-water systems containing only surfactants decreases as the surface coverage of the surfactants increases. Moreover, it was also proved that the intrinsic width of the interface increases with an increment in the surface coverage of surfactants. The surfactant molecules exhibit a great tendency to contribute as acceptors to the formation of hydrogen bonds with water molecules. With an increment in the surface coverage of surfactant molecules, the 2D radial distribution functions between the centers of mass (COMs) of surfactant tails show oscillations. Appeared oscillations represent the correlation between the surfactant tails. Presence of NP causes the oscillations start at lower surfactant coverage than without NP. The surfactant tails choose a random distribution at the low surface coverage of surfactants. In addition, they tend to be oriented partially perpendicular to the interface with an increase in surfactant surface coverage. Besides, NP causes the surfactant tails to orient more perpendicular to the interface than surfactants alone.