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Thermal Transport in Three-Dimensional Nanoarchitected Materials


Dou, Nicholas Gang (2018) Thermal Transport in Three-Dimensional Nanoarchitected Materials. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/TPC8-VH59.


Materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance are highly desirable for engineering applications. However, this combination of properties has never been demonstrated in a single material because thermal and mechanical properties are coupled in most fully dense and porous solids. A new class of lattice materials with nanoscale features, called nanolattices, can fill this void in the material property space by virtue of their architecture and nanoscale dimensions. Extensive work on nanolattice mechanical properties report their excellent stiffness-to-density ratio and recoverability from large compressive strains. In contrast, the framework for studying their thermal properties has not been established. Our work develops the computational and experimental tools necessary to study heat conduction in nanoarchitected materials and applies those tools to prove the viability of octet-truss nanolattices as multifunctional thermal insulators.

We implement significant improvements to a phonon Monte Carlo method to solve the Boltzmann transport equation (BTE) in highly complex geometries like the octet-truss. No prior works solve the BTE in a domain as intricate as a nanolattice, so we create a geometry representation scheme that can model any arbitrary 3-D body. Our enhanced variance-reduced Monte Carlo code incorporates this scheme, allowing us to predict the thermal conductivity of nanolattices and analyze the phonon transport behavior in them. Results suggest that hollow-beam silicon nanolattices indeed reach ultralow thermal conductivities. Based on Monte Carlo and finite element simulations, we develop a predictive thermal conductivity model that accounts for both diffusive and radiative phonon transport in nanolattices.

We also devise custom modifications to the 3ω method to experimentally measure the thermal conductivity of additively manufactured nanolattices. Since the serial fabrication process of nanolattices makes it costly to cover large areas, we design a specialized 3ω sample that minimizes the required structure size while maintaining good experimental sensitivity. We derive a new thermal model to account for conductive losses through the heater line in our novel sample geometry. 3ω measurements and compression tests of hollow-beam alumina nanolattices show that they combine ultralow thermal conductivity with excellent mechanical stiffness and resilience, which proves that nanolattices occupy a previously unreachable region in material property space. Our work provides motivation to further investigate and improve the thermal properties of architected materials.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Multifunctional materials; thermal conductivity; phonon transport; Boltzmann transport equation; Monte Carlo; 3ω
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Awards:Demetriades-Tsafka-Kokkalis Prize in Nanotechnology or Related Fields, 2018.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Minnich, Austin J.
Group:Resnick Sustainability Institute, Kavli Nanoscience Institute
Thesis Committee:
  • Blanquart, Guillaume (chair)
  • Greer, Julia R.
  • Hunt, Melany L.
  • Minnich, Austin J.
Defense Date:13 April 2018
Funding AgencyGrant Number
Air Force Office of Scientific ResearchFA9550-14-1-0266
Record Number:CaltechTHESIS:06022018-070416991
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 2
Dou, Nicholas Gang0000-0001-8199-5588
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11012
Deposited By: Nicholas Dou
Deposited On:04 Jun 2018 19:36
Last Modified:08 Nov 2023 00:34

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