Oil-water interactions under nonequilibrium conditions with nanoparticles and surfactants*

The combined effects of surfactants and nanoparticles at the oil-water interface under shear flow are investigated with dissipative particle dynamics computations. Anisotropic Janus particles (JPs)^1,2 with amidine polystyrene latex and gold surfaces were simulated³  at a dodecane-water interface and with octaethylene glycol monododecyl ether (C12E8). The water flow was driven by a body force on water. It was found that when the driving force for the flow was higher than a critical value the droplets of oil could pinch off one of the channel walls and transition to a stratified flow, or they could extend along the channel wall in the form of slag. Compared to bare oil, nanoparticles provided a more stable interface; but pinch-off occurred at the same three-phase contact angle, regardless of particle numbers or properties. The presence of  surfactants caused the oil to become unstable at lower pressure drops. Computational methodologies will be discussed and their validation, as well as the mechanisms of stabilizing the oil-water interface.

1. N. Glaser et al., Langmuir 22, 5227 (2006).

2. A. Walther et al., Soft Matter 4, 663 (2008).

3. T.V. Vu et al., J. Colloid & Interface Sci. 609 158 (2022)