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Unformatted text preview: Effect of interface scattering on phonon thermal conductivity percolation in random nanowire composites Weixue Tian and Ronggui Yang a ! Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, Colorado 80309-0427 s Received 11 May 2007; accepted 1 June 2007; published online 26 June 2007 d The effect of phonon-interface scattering on the percolation of the phonon thermal conductivity in random nanowire composites is investigated by solving the phonon Boltzmann transport equation using the Monte Carlo simulation. The forming of a geometric percolating network does not lead to dramatic increase of the thermal conductivity in nanowire composites because of the dominance of the phonon-interface scattering. The thermal conductivity of nanocomposites is much less sensitive to the thermal conductivity contrast ratios of the constituent materials than that of bulk composites, especially when the volumetric concentration of the high thermal conductivity constituent is below the percolation threshold. © 2007 American Institute of Physics . f DOI: 10.1063/1.2751610 g Due to their unique and tunable properties, nanocompos- ites may be used in a number of applications such as high efficiency thermoelectric devices, 1 – 3 thermal management system, 4 and dye sensitized solar cells. 5 Many nanocompos- ite synthesis techniques such as hot pressing tend to create composites in which nanoparticles or nanowires are ran- domly distributed. Most previous studies on random com- posites made of materials with highly different thermal con- ductivity were focused on bulk composite materials, 6 – 10 where the thermal transport is a diffusion process and is gov- erned by the Fourier heat conduction theory. Rather limited work can be found in literature to study the thermal conduc- tivity of random nanocomposites where the ballistic phonon transport is governed by the Boltzmann transport equation. Similarly, recent modeling efforts 11 – 14 on thermal transport in carbon nanotube-polymer composites have limited applica- bility because the thermal transport in these nanocomposites was either modeled by Fourier’s law, 12 , 14 which might not be valid in nanocomposites, or a simplified random walk model. 13 Furthermore, these models cannot be used to pre- dict the thermal conductivity of a wider range of nanocom- posites because carbon nanotubes typically have very high aspect ratio and occupy very low volumetric fractions in the composites s in dilute limit d . Previous studies solving the phonon Boltzmann equation based on the periodic unit cell approach found that the thermal conductivity of the nano- composites is significantly smaller than that of their bulk counterparts due to phonon-interface scattering 15 – 19 Results of these simulations also showed that the thermal conductiv- ity of nanocomposites cannot be simply modeled by solving the Fourier heat diffusion equation with added thermal boundary resistance between the matrix and particles. How-boundary resistance between the matrix and particles....
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