Multi-curvature liquid meniscus in a nanochannel: evidence of interplay between intermolecular and surface forces.

We examined the formation of a multiply curved meniscus inside rectangular nanochannels, whose width ranges from 50 to 800 nm at a constant height of 200 nm. When the channel width is smaller than approximately 400 nm under partial wetting conditions, a distinct multi-curvature meniscus was observed at the advancing front with an edge disjoined from the wall. In contrast, a typical pre-wetting film was observed at the front regardless of the channel size for complete wetting conditions. Our theoretical analysis demonstrated that the multi-curvature meniscus is generated from the increased contribution of an extra pressure due to intermolecular interactions near the wall. In particular, a plug-like meniscus profile was observed at the advancing liquid front for the 50 nm wide channel owing to an overlap between convex curvatures at the channel walls. Finally, we showed that the filling velocity of liquid can be decreased by decreasing the channel size due to the reduced wettability.