Plug flow down to the nanoscale can induce partial solidification of confined fluids

In this work, we employ molecular dynamics simulation to study the anomalous fluid behavior of plug nanoflows. We find that the simultaneous use of plugging and nano-confinement suppresses the ability of fluids to flow, leading to molecular clogging. Our simulations demonstrate that molecular clogging enhances the fluid/solid friction in a non-linear manner and leads to various novel flow patterns. Our analysis reveals that the non-monotonic friction behavior is a consequence of the sudden transition of the confined fluid from a liquid state to a partial solid-like state when the pore size decreases. The partial solidification features a piecewise response of the liquid velocity, pressure, and density distributions. The solidification in fact originates from the combined action of clogging and interfacial friction: clogging increases friction, inducing an enhanced internal compression of the confined liquid that causes partial solidification. The driving mode also critically alters the flow patterns: constant-velocity driving yields piecewise flow profiles, while constant-force driving triggers abrupt stick-slip transitions in small pores where solidification occurs. Our findings challenge the traditional view of confined fluids as homogeneous liquids and establish a compression-based mechanism linking interfacial friction, molecular clogging, and flow-induced solidification.