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Agenda

08:30–09:30 Session 5: Carbon Nanotubes

Professor Matteo Pasquali (Rice University), Chair

• 08:30–08:50
  Novel Nanocomposites Derived from Dispersed Multi-walled Carbon Nanotubes in Polymers: Micro-mechanisms of Deformation, Conduction Percolation, and Nanotube Crosslinking via Surface-Graft Polymerization
  Arnold C.-M. Yang
  Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan
  
  A new class of nanocomposites that promises high toughness, excellent conductivity, and light weight was pursued by dispersing surface-grafted multiwalled carbon nanotubes in host polymers. The mechanical strength was found to increase dramatically when a small fraction of nanotubes were added in the glassy polymers, which clearly was resulted from alternation of micro-drawing mechanisms of the deformation zones. The nanotubes, too rigid to be drawn into large extension, piled up at zone boundaries, restricted widening of the deformation zones, and forced nucleation of new ones, resulting tremendous strength enhancement. The retardation of chain drawing, however, did not lead to transition of deformation mode from crazing to yielding. It eventually prohibited large-scale plastic deformation, when nanotubes fraction increased, and brittleness prevailed finally. The capability of carbon nanotubes to be drawn into large extension emerged to be a key factor deciding whether full mechanical reinforcement could be realized. Homogeneous nanotubes dispersion promoted electric conductivity of the nanocomposites, which was found to follow percolation models. However, the micro-contact zones between percolated nanotubes were found to play a crucial role in imparting nanotube conductance to the composites. Only the nanotubes grafted with conductive polymer were able to construct nanocomposites with excellent electric conductivity as promised by percolated nanotubes. To exploit the intrinsic strength of carbon nanotubes and to create a covalently bonded nanotubes network for novel electric and optoelectronic properties, various synthesis methods were experimented to crosslink carbon nanotubes with long polymer chains. Gels of carbon nanotubes were ultimately synthesized that show interesting prospects.
• 08:50–09:10
  Portable Neutron Generator with ion source based on Carbon Nanotubes
  Jiarui Liu and Wei-kan Chu
  Texas Center for Superconductivity and Physics department, University of Houston, Houston, Texas, 77204
  
  Portable neutron generators are widely used in different areas such as explosives and weapon grade uranium detection, well logging and in-field activation analysis. Present portable neutron generators, like MP-320 (Thermo Electron), can provide neutron yield of 106 – 108n/s.

  Our new portable neutron generator is based on field ionization ion source with carbon nanotubes at room temperature. The yield of 14 MeV D-T neutrons is at 1010 n/s level, which is higher than present portable neutron generators by 3 orders of magnitudes and comparable with movable neutron generators. In this neutron generator, the field ionization source is used to avoid the high power consumption in conventional plasma ion source. One HV power supply of about 100 kV is used for both ion source and acceleration. The main features of this kind of neutron generators are lightweight, lower power consumption, long lifetime, and easy maintenance. In neutron generators with solid Ti-T target, high beam power density will cause the T desorption and short target lifetime. The defocused ion beam or scanned ion beam can be used for long lifetime of the neutron generator. Our field ionization ion source provides non-focused Deuterium ion beam of mA in an area of cm2 with the correspondent neutron yield of 1010 n/s. Further optimization of the field emitters is in progress.

• 09:10–09:30
  Electronic Conduction in Single-Wall Carbon Nanotubes
  Amir Farajian
  Rice University