Molecular Dynamics Simulation of Thermal Conductivity of Diamondoid Crystals
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1022-II05-06
Molecular Dynamics Simulation of Thermal Conductivity of Diamondoid Crystals Ming Hu1, Sergei Shenogin1, Pawel Keblinski1, and Arun Majumdar2 1 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY, 12180 2 Departments of Mechanical Engineering and Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, 94720
ABSTRACT Hydrocarbon molecules with diamond structure, called diamondoids have gain considerable interest as promising nanoscale building blocks. Very large mismatch between strong, covalent intramolecular bonding and weak intermolecular bonding suggests interesting phonon related properties for diamondoid crystal. We use molecular dynamics (MD) simulations to examine thermal transport of diamondoid crystals. In particular, thermal conductivity of small molecule adamantane and larger molecule pentamantane crystal is studied by equilibrium and non-equilibrium MD. The thermal conductivity of both materials is low, but comparable with that characterizing C60 crystal.
INTRODUCTION The development and advances in thermal management applications mostly focus on the design of two extreme classes of materials: (i) highly conductive and (ii) thermally insulating. For thermal insulation purposes at low and moderate temperatures isotropic polymers are attractive due to their low cost and processing ease. At higher temperatures more thermally stable materials are required, such as oxides. In this context, molecular solid of diamond molecules (diamondoids) provide an opportunity of a new class of thermally insulating materials based on hydrocarbons, yet distinctly different from polymeric materials. Since they were first discovered and isolated from petroleum in 1933, diamondoids have shown promise in a variety of fields and have been used as templates and building blocks for nanotechnology. Recent advances in separation processes at Chevron Texaco [1] allow to obtain a range of diamond structure molecules from crude oil and generate significant interest in these materials. Furthermore, as shown in figure 1 (left panel), diamondoids form molecular crystals thus creating novel solid materials composed of highly rigid and stable hydrocarbon molecules bonded by soft van der Waals forces. Such solids might provide an alternative to solid polymers due to their higher thermal stability, unique optical and electron emission properties or thermomechanical properties [1,2]. For example, rigid and very strong covalent intramolecular bonding in conjunction with soft intermolecular bonding can likely lead to decoupling of intra and intermolecular motion and thereby producing low thermal conductivity. In addition, van der Waals forces are typically highly anharmonic which
will lead not only to reduced thermal conductivity but also strong dampening of mechanical waves (see right panel in figure 1). With this motivation we use classical molecular dynamics (MD) simulations to examine thermal transport in small molecule adamantane and larger molecule pentam
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