Molecular dynamics simulation of effects of surfactant on surface wettability in CO_2 environment

In the present of CO2 fluid,molecular dynamics simulations were performed to investigate the effects of perfluoropolyether ammonium carboxylate surfactant(C1 F23O4 COO-NH+4) on the wetting behavior of solid surfaces.The obtained liquid / vapor contact line indicated that the surfactant could partially replace the interfacial CO2 molecules,which resided in the solid / liquid interfacial region on hydrophobic surface.For a weak hydrophilic surface,the addition of surfactant almost made the droplet lose contact with the surface,while on a strong hydrophilic surface,the surfactants enhanced the droplet contact angle and weakened the surface wettability.The height of the center of mass of the droplet,as a function of simulation time,further showed the wetting behavior of the water droplet.The component distributions of surfactant could be seen in the density profiles of water,and surfactant headgroup and tail.It was demonstrated that the surfactant could well improve the wettability of the surface in dense CO2,thus it was in favor of the removal of the hydrophilic substance.