Phase Behavior and Filling Dynamics of Water inside Isolated Carbon Nanotubes

Isolated single-walled carbon nanotubes with diameters between 0.8 and 2.5 nm offer unprecedented opportunities to study phase behavior and dynamics of water and other fluids under nanoscale confinement. Within this size regime of so-called single digit nanopores, fluid phase boundaries are shifted dramatically, slip flow generates huge enhancements over flow predictions, and physical properties like the dielectric constant may vary widely and non-monotonically with confining diameter. Here, we introduce a new experimental platform for lithographic segmentation of carbon nanotubes, generating multiple copies – some empty, some filled, and others partly filled – of the same type of carbon nanotube. We develop Raman spectroscopy techniques that allow unambiguous assignment of carbon nanotubes in real time as either filled or empty at various points along their length. Analysis of carbon nanotube filling under a variety of conditions allows us to address several key questions about the physical chemistry of fluids under nanoscale confinement, including water phase behavior, the formation of nanoscale droplets, comparisons between filling with water and non-aqueous fluids, and the dynamics of capillary condensation inside a single carbon nanotube.