Nanotubes have the potential to be a revolutionary material for many different applications. Though often touted as versatile and tunable materials, the difficulty of their reliable large-scale production for any specified property is a hurdle in their wide-scale implementation. Interactions at nanotube interfaces dictate overall performance of their growth, radiation resistance, and nanofluidics properties. In this dissertation, I present in-situ experiments using an environmental transmission electron microscope (ETEM). Numerous aspects of interfacial mechanisms of nanotubes are examined at the atomic scale and models considered for the observed behavior.

First, I study the interface between nanotubes and catalyst particles during single-walled carbon nanotube (SWCNT) growth. The structure and phase transformation of cobalt catalysts are elucidated for inactive, active, and deactivated nanoparticles by ETEM imaging. Through in-depth studies of multiple distinct cobalt nanoparticles, I establish the dominant nanoparticle phase for SWCNT growth. I also identify the preferred lattice planes and a threshold for work of adhesion for the anchoring and liftoff of SWCNTs.

Second, the nanotubes are tested for their radiation resistance properties. I study the resistance of nanotube degradation in an ionizing environment with oxygen pressure, where the damage initiates at the interface with the gas phase. Observations show boron nitride nanotubes (BNNTs) have a higher resistance to damage than carbon nanotubes (CNTs). By computing knock-on threshold energies for the atoms impacted by incoming electrons, a model can be formulated for the oxygen-assisted radiation damage pathway. I provide further validation to the model with heating experiments that demonstrate a surprising increase in damage resistance.

Lastly, interfaces between nanotubes and water are studied. The goal is to capture the ordering dynamics of water at the BNNT interface using in-situ characterization at cryogenic temperatures. Water is hyper-quenched to liquid nitrogen temperatures for the formation of low density amorphous (LDA) ice. High resolution images are then acquired, preserving the original water structure. Crystallization of LDA ice is induced by both environmental heating and electron beam irradiation. I present a comparison of the structural evolutions of LDA ice with and without the presence of BNNT, which indicates the presence of nascent ordering at the interface.