Filling and chemical modification of carbon nanotubes

In order to utilize carbon nanotubes in nanofluidic device applications as well as nanocomposite reinforcement, more research on filling, surface chemistry and interaction of carbon nanotubes with liquids must be done. Understanding the penetration of fluids into nanochannels is important for the efficient storage of liquids as well as composite manufacturing. Transmission electron microscopy, Infrared spectroscopy, mass spectroscopy have been used in this research as the investigation tools. In this research, an autoclave high temperature-high pressure system was built. Carbon nanotubes were shown to be successfully filled by using this autoclave treatment. The conditions have been determined for the filling of different types of carbon nanotubes and carbon nanofibers of different diameters with water and ethylene glycol. Water has been demonstrated and confirmed to be trapped inside heat-treated carbon nanofibers of 50-200 nm in diameter, chemical vapor deposited nanotubes of 2.5-5 nm in diameter, and possibly double wall carbon nanotubes and single wall carbon nanotubes with diameters of 1.5-2 nm. At the scale of 5 nm or less, water molecules were observed in-situ below the continuum limit, where they were shown to form clusters and chains. The effect of diameter on water filling of chemical vapor deposited nanotubes is observed. These tubes have a much less filling yield (15%) compared to heat-treated carbon nanofibers, which have a 30% filing yield. Optimum conditions of water filling have been determined to be 650°C and 80 MPa for most nanotubes studied in this research. Conversely, when ethylene glycol was mixed and treated with carbon nanotubes by autoclave conditions, it tends to polymerize and possibly form a polyester outside and inside of the nanotubes. Besides studying the filling of carbon nanotubes with water and ethylene glycol, careful investigation of surface structure of different types of carbon nanotubes have been performed. Hydrothermal nanotubes are shown to have hydrophilic surfaces with at least carboxyl and hydroxyl groups existing.