Manuscript_Ballistic.pdf (866.02 kB)
Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene
journal contribution
posted on 2019-07-11, 15:36 authored by Andrew B. Robbins, Stavros Drakopoulos, Ignacio Martin-Fabiani, Sara Ronca, Austin J. MinnichThermally conductive polymer crystals are of both fundamental and practical interest for their high thermal conductivity that exceeds that of many metals. In particular, polyethylene fibers and oriented films
with uniaxial thermal conductivity exceeding 50 Wm−1K−1 have been reported recently, stimulating interest into the underlying microscopic thermal transport processes. While ab-initio calculations have provided insight into microscopic phonon properties for perfect crystals, such properties of actual samples have remained experimentally inaccessible. Here, we report the direct observation of thermal phonons with mean free paths up to 200 nm in semicrystalline polyethylene films using transient grating spectroscopy. Many of the mean free paths substantially exceed the crystalline
domain sizes measured using small-angle x-ray scattering, indicating that thermal phonons propagate ballistically within and across the nano-crystalline domains, with those transmitting across domain boundaries contributing nearly a third of the thermal conductivity. Our work provides the first direct determination of thermal phonon propagation lengths in molecular solids, providing insights into the microscopic origins of their high thermal conductivity.
Funding
ONR Young Investigator Award under Grant No. N00014-15-1-2688 and EPSRC, grant EP/K034405/1.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Published in
Proceedings of the National Academy of SciencesVolume
116Issue
35Pages
17163-17168Citation
ROBBINS, A.B. ... et al, 2019. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proceedings of the National Academy of Sciences, 116(35), pp. 17163-17168.Publisher
National Academy of SciencesVersion
- AM (Accepted Manuscript)
Publisher statement
This paper was accepted for publication in the journal Proceedings of the National Academy of Sciences and the definitive published version is available at https://doi.org/10.1073/pnas.1905492116Acceptance date
2019-07-10Publication date
2019-08-12Copyright date
2019ISSN
0027-8424eISSN
1091-6490Publisher version
Language
- en