Solid-like film formed by nano-silica self-assembly at oil–water interface

Abstract

Nanoparticles have been widely investigated in enhancing oil recovery for unique interfacial properties. Bare nano-silica (NS) cannot be easily adsorbed at the interface due to a large number of hydroxyls on its surface. In this study, NS was decorated by dodecyl trimethyl ammonium bromide (DTAB), forming NS–surfactant via electrostatic force. In order to investigate the interfacial behavior of NS–surfactant at the oil-water interface, experiments and molecular dynamics simulations were conducted. Results indicated that NS–surfactant can self-assemble at the oil-water interface and solid-like films were observed, which contributed to 10.4% oil recovery of NS–surfactant flooding relative to water flooding. DTAB concentration, pH and NaCl were used to regulate the interfacial behavior of NS–surfactant. Interfacial tension decreased and surface coverage increased with DTAB concentration increase due to more NS–surfactant arranged at oil-water interface. NS–surfactant could arrange at the oil-water interface more closely through increase zeta potential, which could be achieved by adjusting pH and adding NaCl. Lower interfacial tension and higher surface coverage was observed under weakly acidic conditions. The addition of NaCl could greatly reduce the interfacial tension and increase the surface coverage.