Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 99961

99961 - Molecular Dynamics Analysis of Mode-Resolved Phonon Scattering by Embedded Nanoparticles 

Embedded nanoparticle composites have demonstrated a great potential as low-cost but high figure-of-merit thermoelectric materials. In 2006, Kim and Majumdar introduced an analytical model for the phonon-nanoparticle scattering rate, developed from perturbation theory and ideas of light wave scattering by spherical particulates. The model has been used by several subsequent numerical works that implement the scattering rate definition into the Boltzmann Transport Equation to evaluate the thermal conductivity of an embedded nanoparticle composite, prompting suggestions for nanoparticle sizes, density contrasts, and volume fractions that may achieve low thermal conductivity. While simple, researchers have identified deficiencies in the model such as poor patching of the Rayleigh and Geometric regimes to describe the Mie regime and define the full scattering rate, lack of elastic contrast dependence, and no details regarding wavevector and mode-specific interactions. Additional effects such as phonon localization and multiple and dependent scattering due to multiple nanoparticles are also not considered. Several other analytical approaches, leveraging ideas from acoustic wave theory and effective medium approximations, have been made to improve on Kim and Majumdar’s model. Still, these new solutions are incomplete in capturing the full complex physics of nanoparticle-phonon interactions and are often limited in applicability due to simplifying assumptions made to keep the mathematics tractable. To better describe nanoparticle-phonon scattering, we diverge from analytical study and turn towards molecular dynamics (MD) methods for empirical analysis. We use the phonon wave-packet (PWP) method to study wavevector and mode-specific phonon transport through the nanoparticle. This calculation yields information about the phonon scattering geometry, energy transmission coefficients, and mode-conversion. We study the wave-vector and mode dependence of these variables for different nanoparticle sizes as well as different density and elastic contrasts. We also use non-equilibrium molecular dynamics (NEMD) simulations to provide data for heat current spectral phonon transmission calculations and interfacial thermal conductance. This information provides a more concrete study of the mode-resolved effect of nanoparticles on thermal transport. By coupling the spectral data from our NEMD simulations and wavevector/mode specific analyses from our PWP simulations, we elucidate details of nanoparticle-phonon interactions neglected by analytical treatments and supersede the numerical works in studying how the phonon physics leads to changes in thermal behavior. Our findings provide a more comprehensive understanding of nanoparticle-phonon interactions and we thus conclude our work by applying our MD results to provide an outlook on designs to reduce thermal conductivity in embedded nanoparticle composites for potential improved thermoelectric performance.

Presenting Author: Theodore Maranets University of Nevada, Reno

Presenting Author Biography: Theodore is a graduate student in the Mechanical Engineering department at the University of Nevada, Reno. He joined the department's PhD program in August 2021 and is supported by the nuclear power graduate fellowship from US Nuclear Regulatory Commission.

Authors:

Theodore Maranets University of Nevada, Reno
Yan Wang University of Nevada, Reno