Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer >5 nm thick can be present on the outer CNT surface. The experimentally observed nonlinear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and ab initio studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system.National Science Foundation (U.S.) (NSF Grant No. CMMI-1130437)National Science Foundation (U.S.) (NSF Award Number ECS-0335765)United States. Army Research Office (contract W911NF-07-D-0004

Impact of carbon nanotube length on electron transport in aligned carbon nanotube networks

Here, we quantify the electron transport properties of aligned carbon nanotube (CNT) networks as a function of the CNT length, where the electrical conductivities may be tuned by up to 10× with anisotropies exceeding 40%. Testing at elevated temperatures demonstrates that the aligned CNT networks have a negative temperature coefficient of resistance, and application of the fluctuation induced tunneling model leads to an activation energy of ≈14 meV for electron tunneling at the CNT-CNT junctions. Since the tunneling activation energy is shown to be independent of both CNT length and orientation, the variation in electron transport is attributed to the number of CNT-CNT junctions an electron must tunnel through during its percolated path, which is proportional to the morphology of the aligned CNT network.United States. Army Research Office (contract W911NF-07-D-0004)United States. Army Research Office (contract W911NF-13-D-0001)United States. Air Force Office of Scientific Research (AFRL/RX contract FA8650-11-D-5800, Task Order 0003)National Science Foundation (U.S.) (NSF Award No. ECS-0335765)United States. Dept. of Defense (National Defense Science and Engineering Graduate Fellowship

Structure-property relations of nanostructured carbon systems as a function of processing

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 49-51).Due to their intrinsic properties and nanometer scale, carbon nanotubes (CNTs) are commonly used to enhance the material properties of engineering materials. However, structural defects can significantly alter the intrinsic properties of CNTs, thereby limiting the physical properties of aligned CNT nanocomposite architectures. Previous studies have shown the difficulty in getting quantitative data for CNT quality once embedded within a carbon matrix. Therefore, studies that focused on the CNTs and carbon matrix separately were necessary. A study on the CNTs and carbon matrix response to pyrolyzation temperatures has recently been completed and is used to inform and motivate the research reported here. This research will focus primarily on the effects of different temperature ramping rates (TRR's) during pyrolysis of phenolic resin to form the ceramic matrix. Preliminary X-Ray Diffraction (XRD), Raman spectroscopy and Vickers Hardness results indicate that increasing the temperature ramping rate (in the range of 10°C/min - 40°C/min) increases the prevalence of defects in the nanocomposite system as well as increasing the standard error of both crystallite sizes and hardness, while maintaining the mean of the distribution. Future studies exploring aligned CNT carbon matrix nanocomposites (A-CMNCs) and more extreme temperature ramping rates are proposed.by Mackenzie E. Devoe.S.B

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer >5 nm thick can be present on the outer CNT surface. The experimentally observed nonlinear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and <i>ab initio</i> studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system