Molecular dynamics simulation of electroosmotic flow in sinusoidally rough nanochannels on interfacial and flow characteristics

Research on electroosmotic flow (EOF) under different surface characteristics enables precise control and prediction of its behavior. In this study, molecular dynamics simulations are used to investigate EOF features and interfacial structure in sinusoidally rough nanochannels, examining how roughness amplitude and wavelength affect ion distributions and velocity profiles. The results show that water molecules near the wall form layered structures, and geometric confinement makes the first density peak of water molecules in the expansion region (ER) 27% higher than that in the contraction region (CR). Variations in the electric field distribution at different locations lead to asymmetric ion distributions at the opposing surfaces. In the contraction region, enhanced ordering of interfacial water suppresses counterion adsorption, leaving the first Cl− density peak 57% of the second. Owing to changes in cross-sectional area, the contraction region exhibits an average EOF velocity about 55% higher than the expansion region, and near-wall reverse flow is observed. As the roughness amplitude decreases and the wavelength increases, Cl− shifts from the Stern layer toward the diffuse layer, which raises the Cl− drift velocity and thereby increases the volumetric flow rate. For a channel with short wavelengths, the interplay of geometric confinement and the local electric field depresses the first Cl− peak near the wall at the widest cross section, with the second about 3.4 times higher. With increasing channel flatness, the Na+–Cl− spatial correlation is weakened, leading to a more uniform Na+ distribution across the channel. These findings improve the understanding and control of EOF in practical nanochannels.