Redistribution of hydrocarbon and water within graphene mesopores under an external electric field: Evidences from molecular dynamics simulations

Abstract

The behavior of confined fluids under external electric fields is central to the development of field-responsive technologies in catalysis and separations. Here, we use Molecular Dynamics simulations to explore the structural response of water–hydrocarbon mixtures (methane, $n$-butane, and $n$-pentane) confined within graphene slit pores, subjected to electric field strengths ranging from 1.5 to 7.5 V${\mathrm{nm}}^{-1}$. In the absence of an electric field, the system exhibits clear phase separation along the confinement axis, with hydrocarbons preferentially adsorbed near the graphene walls and water localized at the center. As the electric field increases, this organization becomes disrupted, with a lateral redistribution of water molecules and reduced interfacial definition. The spatial rearrangement is confirmed through density profiles along multiple axes, while analysis of the order parameter indicates negligible dipolar alignment of water molecules. Dielectric permittivity calculations reveal anisotropic polarization responses, supporting a mechanism dominated by positional, rather than orientational, field effects. The observed redistribution is significant above 3.0 V${\mathrm{nm}}^{-1}$ and intensifies with stronger fields. These results provide molecular-level insights into the design of nanoconfined systems where electric fields are used to modulate fluid organization. Implications are far-reaching: in electric swing adsorption (ESA), field-induced redistribution offers new levers for controlling selectivity and regeneration; in electrostatic catalysis, particularly Fischer–Tropsch synthesis (FTS), dynamic positioning of polar intermediates such as CO and H₂O near catalytic surfaces could fine-tune reaction pathways and improve selectivity. Overall, this work provides a foundational framework for designing electric-field-responsive nanoconfined systems relevant to gas separations and catalytic processes.