Diffusio-osmosis of oil–CO2 mixture in inorganic nanopores

Abstract

Diffusio-osmosis is the interfacial transport induced by solute density gradient and plays an essential role in many micro/nanofluidic systems. Here, we report the molecular dynamics simulations of the diffusio-osmosis of oil–CO2 mixture in silica and calcite nanopores. We show that, under the high solute (CO2) density considered, although the enrichment of CO2 near calcite walls is substantially higher than that near silica walls, the diffusio-osmosis in calcite pores is only marginally stronger. This phenomenon is attributed to the significantly different molecular structures and hydrodynamic properties of interfacial fluids in the two pores caused by the CO2 adsorption on their walls, which is in turn traced to the different physical chemistry of the silica and calcite walls. Using continuum simulations parameterized by the diffusio-osmosis characteristics obtained in our molecular modeling, we show that, for the oil transport through slit pores driven by pressurized CO2, the diffusio-osmosis becomes important compared to the Poiseuille flow when the pore width decreases below a few tens of nanometers and its significance compared to the Poiseuille flow increases quadratically as the pore width decreases.