The effect of surfactant adsorption on surface wettability and flow resistance in slit nanopore: A molecular dynamics study

Abstract

Hypothesis: Due to large surface/volume ratio, fluid flow resistance in nanopores is affected dramatically by surfactants adsorption, which dictates wettability and friction. Surfactants with different aggregated morphology and molecular alignment at solid/water interface are expected to affect friction and mobility of surfactant adsorption layer, both of which should be possible to contribute to surfactant drag reduction mechanism in nanopores.Simulations: Molecular dynamics (MD) simulations were adopted to study the morphology of the adsorption layer of different types of surfactants on negatively charged hydrophilic silica surface and their effect on flow resistance in slit nanopores.Findings: Flow resistance differs as surfactant adsorption morphologies vary. Adsorption layer composed of hemimicelles with “head on” orientation in low adsorption amount exhibits low flow resistance. As adsorption amount increases, adsorption layer evolves into the double layer in which less polar surfactant composition is found to be beneficial for improving hydrophobicity of pore wall and interfacial water diffusion. More ordered and tight intermolecular packing and high mobility of the adsorption layer are found to be propitious to reduce the flow friction.