The ability of the Environmental Scanning Electron Microscope (ESEM) to condense and evaporate liquids has enabled the in situ dynamic study of condensation, evaporation and transport of water inside carbon nanotubes. It has been possible to see liquid menisci inside straight, CVD-fabricated carbon nanotubes (CNTs) having disordered walls. From the measured contact angles, it is clear that these CNTs are hydrophilic. Complex meniscus shapes and slow liquid dynamics due to water confinement and strong interaction with tube walls have been observed.

The above ESEM images show the dynamic behavior of a water plug close to the open end of a nanotube. The meniscus shape changes when, at a constant stage temperature, the vapor pressure of water in the chamber is changed (a) 5.5 Torr, (b) 5.8 Torr, (c) 6.0 Torr, (d) 5.8 Torr and (e) 5.7 Torr, where the meniscus returns to the shape seen in (a). The asymmetrical shape of the meniscus, especially the complex shape of the meniscus on the right side in (a, e), is a result of the difference in the vapor pressure caused by the open left end and closed right end of the tube. (f) TEM image showing a similar plug shape in a closed CNT under pressure.

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