Browsing by Author "Green, Micah J."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Competing mechanisms and scaling laws for carbon nanotube scission by ultrasonication
    (National Academy of Sciences, 2012) Pagani, Guido; Green, Micah J.; Poulin, Philippe; Pasquali, Matteo; Richard E. Smalley Institute for Nanoscale Science and Technology
    Dispersion of carbon nanotubes (CNTs) into liquids typically requires ultrasonication to exfoliate individuals CNTs from bundles. Experiments show that CNT length drops with sonication time (or energy) as a power law t?m. Yet the breakage mechanism is not well understood, and the experimentally reported power law exponent m ranges from approximately 0.2 to 0.5. Here we simulate the motion of CNTs around cavitating bubbles by coupling Brownian dynamics with the Rayleigh-Plesset equation. We observe that, during bubble growth, CNTs align tangentially to the bubble surface. Surprisingly, we find two dynamical regimes during the collapse: shorter CNTs align radially, longer ones buckle.We compute the phase diagram for CNT collapse dynamics as a function of CNT length, stiffness, and initial distance from the bubble nuclei and determine the transition from aligning to buckling. We conclude that, depending on their length, CNTs can break due to either buckling or stretching. These two mechanisms yield different power laws for the length decay (0.25 and 0.5, respectively), reconciling the apparent discrepancy in the experimental data.
  • Thumbnail Image
    Item
    Dissolution of graphite, graphite and graphene nanoribbons in superacid solutions and manipulation thereof
    (2017-01-03) Tour, James M.; Pasquali, Matteo; Behabtu, Natnael; Lomeda, Jay R.; Kosynkin, Dmitry V.; Duque, Amanda; Green, Micah J.; Parra-vasquez, A. Nicholas; Young, Colin; Rice University; United States Patent and Trademark Office
    Methods for dissolving carbon materials such as, for example, graphite, graphite oxide, oxidized graphene nanoribbons and reduced graphene nanoribbons in a solvent containing at least one superacid are described herein. Both isotropic and liquid crystalline solutions can be produced, depending on the concentration of the carbon material The superacid solutions can be formed into articles such as, for example, fibers and films, mixed with other materials such as, for example, polymers, or used for functionalization of the carbon material. The superacid results in exfoliation of the carbon material to produce individual particles of the carbon material. In some embodiments, graphite or graphite oxide is dissolved in a solvent containing at least one superacid to form graphene or graphene oxide, which can be subsequently isolated. In some embodiments, liquid crystalline solutions of oxidized graphene nanoribbons in water are also described.