Do lateral wall effects really matter? Revisiting slip length estimation in graphene nanofluidic channels

Carbon-based nanofluidic channels have been shown to exhibit enhanced water and ion transport compared with conventional hydrophilic channels owing to the presence of hydrodynamic slip at the channel walls. Recently, Chen et al. [“Slip length measurement in rectangular graphene nanochannels with a 3D flow analysis,” Carbon 189, 162 (2022)] argued that the one-dimensional (1D) flow model fails to accurately describe flow in graphene nanochannels, even for aspect ratios exceeding 100, because of lateral wall effects. To clarify this issue, we develop a rigorous two-dimensional (2D) analytical formulation with physically appropriate boundary conditions and reexamine slip length estimation in graphene and graphene–glass nanochannels using representative experimental data reported in the literature. The results demonstrate that the proposed 2D model yields slip length estimates that are nearly identical to those obtained using the 1D model, even for graphene nanochannels with aspect ratios below 10. We therefore conclude that the 1D model remains applicable to most slip-dominated graphene nanochannels. Our results further reveal that accurately determining the contact angle under nanoconfinement is critical for reliable slip-length estimation in graphene and graphene–glass nanochannels. The estimated graphene slip length ranges from 36 to 71 nm when contact angles representative of nanoconfinement are considered. Furthermore, graphene–glass nanochannels exhibit saturation in flow enhancement at large graphene slip lengths, limiting the ability to distinguish large slip lengths from flow measurements. These findings provide important insights into the accurate characterization of slip-dominated transport and the design of graphene-based nanofluidic systems.