(425d) Nanofluidic Phase Behavior, Droplets, and Condensation of Water inside Isolated Single-Walled Carbon Nanotubes

Isolated single-walled carbon nanotubes with diameters between 0.8 and 2.5 nm offer unprecedented opportunities to study water phase behavior and dynamics 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 phase separation may be vastly different than in larger nanofluidic or microfluidic conduits or in the bulk. Here, we demonstrate that Raman spectroscopy allows unambiguous assignment of carbon nanotubes as either filled or empty. 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. Analysis of carbon nanotube filling under a variety of conditions allows us to address several key questions about the physical chemistry of water under nanoscale confinement, including phase boundaries, the formation and size distribution of nanoscale droplets, and the dynamics of capillary condensation inside a carbon nanotube as tracked spectroscopically in real time.