In Situ ESEM Study of Liquid Interactions With Carbon Nanopipes

Abstract

The wetting and fluidic properties of various types of carbon nanotubes (CNT) are currently being studied for various applications, including their use as nanopipes for the controlled transport of fluids to well-defined locations, such as a cell. While numerous studies on the modeling of the behavior of liquids in nanotubes and nanopores have already been reported, very few experimental observations have been published. In this research, the field emission Environmental Scanning Electron Microscope (ESEM) has proved to be a powerful tool in the in situ analysis of the wetting of CNT with diverse liquids at high magnification. Additionally, the ability of the ESEM to condense and evaporate liquids within the chamber has enabled the dynamic study of CNT/liquid interactions. As a result, hydrophilic and hydrophobic behavior of diverse types of commercial carbon nanofibers (CNF) and CNT has been observed. The fluidic behavior of CNF depends largely on surface chemistry and structure. The presence of defects and end groups may cause partial wetting, while graphitized CNF are extremely hydrophobic. Nevertheless, water still becomes drawn into hydrophobic CNF due to surface tension and capillary forces. CNT fabricated by chemical vapor deposition (CVD) with straight, thin walls appear transparent under the electron beam of the ESEM. When studying the interaction of these CNT with water, it was possible to see liquid menisci inside the CNT. From the measured contact angles, it is clear that these CNT are hydrophilic. Furthermore, the wetting behavior observed is very similar to that of closed hydrothermal CNT under high pressures in TEM. Finally, rupture of these thin-walled CNT was observed inside the ESEM chamber as a result of rapid changes in pressure at constant temperatures.