Browsing by Author "Banerjee, Soumik"
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- Molecular Simulation Of Nanoscale Transport PhenomenaBanerjee, Soumik (Virginia Tech, 2008-06-16)Interest in nanoscale heat and mass transport has been augmented through current trends in nanotechnology research. The theme of this dissertation is to characterize electric charge, mass and thermal transport at the nanoscale using a fundamental molecular simulation method, namely molecular dynamics. This dissertation reports simulations of (1) ion intake by carbon nanotubes, (2) hydrogen storage in carbon nanotubes, (3) carbon nanotube growth and (4) nanoscale heat transfer. Ion transport is investigated in the context of desalination of a polar solution using charged carbon nanotubes. Simulations demonstrate that when either a spatially or temporally alternating charge distribution is applied, ion intake into the nanotubes is minimal. Thus, the charge distribution can either be maintained constant (for ion encapsulation) or varied (for water intake) in order to achieve different effects. Next, as an application of mass transport, the hydrogen storage characteristics of carbon nanotubes under modified conditions is reported. The findings presented in this dissertation suggest a significant increment in storage in the presence of alkali metals. The dependence of storage on the external thermodynamic conditions is analyzed and the optimal range of operating conditions is identified. Another application of mass transport is the growth mode of carbon nanostructures (viz. tip growth and base growth). A correct prediction of the dominant growth mode depends on the energy gain due to the addition of C-atoms from the carbon-metal catalyst solution to the graphene sheets forming the carbon nanostructures. This energy gain is evaluated through molecular dynamics simulations. The results suggest tip growth for Ni and base growth for Fe catalysts. Finally, unsteady nanoscale thermal transport at solid-fluid interfaces is simulated using non-equilibrium molecular dynamics simulations. It is found that the simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity. Temperature discontinuities are observed between the solid-like interfaces and their neighboring fluid molecules. With an increase in the temperature of the solid wall the interfacial thermal resistance decreases.
- Molecular simulation of the carbon nanotube growth mode during catalytic synthesisBanerjee, Soumik; Naha, Sayangdev; Puri, Ishwar K. (AIP Publishing, 2008-06-01)Catalyzed growth of carbon nanostructures occurs mainly through two modes, i.e., base growth when the metal nanoparticle remains at the bottom of the nanotube, or when it is lifted by the growing carbon nanostructure due to tip growth. A correct prediction of the dominant growth mode depends on the energy gain due to the addition of C atoms from the carbon-metal catalyst solution to the graphene sheets forming the carbon nanostructures. We determine this energy gain through atomistic scale molecular dynamics simulations. Our results suggest tip growth for Ni and base growth for Fe catalysts. (c) 2008 American Institute of Physics.
- Unsteady nanoscale thermal transport across a solid-fluid interfaceBalasubramanian, Ganesh; Banerjee, Soumik; Puri, Ishwar K. (American Institute of Physics, 2008-09-15)We simulate unsteady nanoscale thermal transport at a solid-fluid interface by placing cooler liquid-vapor Ar mixtures adjacent to warmer Fe walls. The equilibration of the system towards a uniform overall temperature is investigated using nonequilibrium molecular dynamics simulations from which the heat flux is also determined explicitly. The Ar-Fe intermolecular interactions induce the migration of fluid atoms into quasicrystalline interfacial layers adjacent to the walls, creating vacancies at the migration sites. This induces temperature discontinuities between the solid-like interfaces and their neighboring fluid molecules. The interfacial temperature difference and thus the heat flux decrease as the system equilibrates over time. The averaged interfacial thermal resistance R(k,av) decreases as the imposed wall temperature T(w) is increased, as R(k,av) alpha T(w)(-4.8). The simulated temperature evolution deviates from an analytical continuum solution due to the overall system heterogeneity. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2978245]