A semi-continuum model for fluid imbibition under nanoconfinement: Assessing fluid velocity jumps and meniscus acceleration

Fluid imbibition under nanoconfinement exhibits dynamics that significantly deviate from classical continuum predictions, posing unique challenges in understanding nanoscale transport phenomena. This study presents a semi-continuum model for capillary imbibition of simple fluids in nanochannels, addressing the limitations of traditional frameworks like the Lucas–Washburn model. By incorporating sub-continuum effects—such as precursor films and fluid slippage at the walls—into continuum equations, our model captures molecular-scale phenomena that dominate in confined spaces. Key findings include the prediction of fluid velocity jumps and meniscus acceleration, driven by the interplay between confinement and the precursor film's influence on meniscus curvature and fluid distribution. These anomalies, which contradict classical expectations, are validated against molecular dynamics simulations from the literature. The model offers a robust framework for interpreting nanoscale fluid behavior.