Formation of a Stable Bridge between Two Disjoint Nanotubes withSingle-File Chains of Water

Abstract

It was recently demonstrated that stable waterbridges can form between two relatively large disjoint nano-channels, such as carbon nanotubes (CNTs), under an appliedpressure drop. Such bridges are relevant to fabrication ofnanostructured materials, drug delivery, water desalination devices,hydrogen fuel cells, dip-pen nanolithography, and several otherapplications. If the nanotubes are small enough, however, then onehas only single-file hydrogen-bonded chains of water molecules.The distribution of water in such nanotubes manifests unusualphysical properties that are attributed to the low number of hydrogen bonds (HBs) formed in the channel since, on average, eachwater molecule in a single-file chain forms only 1.7 HBs, almost half of the value for bulk water. Using extensive molecular dynamicssimulations, we demonstrate that stable bridges can form even between two small disjoint CNTs that contain single-file chains ofwater. The structure, stability, and properties of such bridges and their dependence on the applied pressure drop and the length ofthe gap between the two CNTs are studied in detail, as is the distribution of the HBs. We demonstrate, in particular, that theefficiency offlow through the bridge is at maximum at a specific pressure difference.