Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene
Open accessAbstract
Thermally 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 W ⋅ m − 1 ⋅ K − 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 nanocrystalline domains; those transmitting across domain boundaries contribute nearly one-third of the thermal conductivity. Our work provides a direct determination of thermal phonon propagation lengths in molecular solids, yielding insights into the microscopic origins of their high thermal conductivity.
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The initial fast decay in the transient grating signal is attributed to thermal relaxation of the Au nanoparticles, while the subsequent slower decay corresponds to thermal conduction in the film.
“The initial fast decay is attributed to the thermal relaxation of the Au nanoparticles, while the subsequent slower decay corresponds to thermal conduction in the film.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
The Transient Grating Spectroscopy section (page unavailable) says the measured polyethylene-film signal follows a single exponential decay, contrary to the claimed fast and slow decays. It identifies ZnO nanoparticles or beta-carotene as light-absorbing additives, not Au nanoparticles. (LLM, conf=0.90)
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredThe mean free paths obtained from transient grating measurements on a DR 7.5 sample in the authors' previous study ranged from 10 to 200 nm.
“The MFPs obtained from TG measurements on a DR 7.5 sample in our previous study ranged from 10 to 200 nm (ref. 58).”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
The Quasiballistic Heat Transport in Polyethylene section reports TG measurements on DR7.5 and finds some phonon mean free paths up to 200 nm. It does not establish 10 nm as the lower end of the measured range, so the stated 10–200 nm range is only partly supported. (LLM, conf=0.86)
Experimental — accuracy not yet measuredRecent studies have provided conflicting explanations for the high thermal conductivity in disentangled UHMWPE, with Xu et al. attributing it to the high thermal conductivity of the amorphous phase and Ronca et al. attributing it to increased extended crystal dimensions.
“Recent studies have provided conflicting explanations for the high thermal conductivity, with Xu et al. 24 attributing it to the high thermal conductivity of the amorphous phase58 but Ronca et al. 23 attributing it to increased extended crystal dimensions.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.
Experimental — accuracy not yet measuredEvidence of ballistic phonons over multiple crystallites has been reported in partially oriented polyethylene samples with low draw ratio about 7.5 using transient grating spectroscopy.
“Evidence of such processes has been reported even in partially oriented PE samples with low DR ~ 7.5 using transient grating spectroscopy (TG)58.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
Compared to polyethylene samples of lower draw ratio about 7.5, the observed grating dependence is significantly more pronounced, indicating the presence of heat-carrying phonons with longer mean free paths in the present samples.
“Compared to PE samples of lower DR ~ 7.5 (ref. 58), the observed trend is significantly more pronounced, indicating the presence of heat-carrying phonons with longer MFPs in the present samples.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
Compared to the mean free paths of a DR 7.5 sample in the authors' prior study, the present mean free paths are clearly larger, as would be expected if the extended crystal dimensions have increased.
“Compared to the MFPs of a DR 7.5 sample in our prior study58, the present MFPs are clearly larger, as would be expected if the extended crystal dimensions have increased.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
Other mechanisms such as molecular conformation disorder do not appear to exhibit the dependence on draw ratio required to explain the results of this study and ref. 58.
“We note that while other mechanisms such as molecular conformation disorder have been proposed to affect the thermal conductivity of crystalline polymers74, these mechanisms do not appear to exhibit the dependence on draw ratio required to explain the results of this study and ref. 58.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
The Microstructure Characterization section discusses structural disorder and phonon scattering at crystalline-domain boundaries, while the Discussion identifies domain-boundary scattering as the dominant mechanism in these samples. Neither passage addresses molecular conformation disorder or whether its effect varies sufficiently with draw ratio. Searches for molecular conformation and conformational defects found no passage that settles the attributed claim; page numbers were unavailable in our copy. (LLM, conf=0.72)
Experimental — accuracy not yet measuredThe signal-to-noise ratio of the present transient grating measurements is generally less than 20, about 30% of that reported for draw ratio 7.5 samples.
“The signal-to-noise ratio (SNR) of the present measurements is generally <20, which is about 30% of that reported in ref. 58 for DR = 7.5 samples.”
From Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals (2022) · cites this paper as [58]
The TG and Data Analysis section (page unavailable) shows a transient-grating signal for a DR7.5 sample, but gives no signal-to-noise ratio. Searches for “SNR,” “signal-to-noise ratio,” and “noise” found no value from which to verify the cited comparison. The <20 SNR describes the citing authors’ present measurements, not measurements attributed to this source. (LLM, conf=0.74)
Experimental — accuracy not yet measured
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Cites
Thermal Conductivity Spectroscopy Technique to Measure Phonon Mean Free Paths
Minnich, A. J., Johnson, J. A., Schmidt, A. J., Esfarjani, K., Dresselhaus, M. S., Nelson, K. A., & Chen, G. (2011) · Physical Review Letters · doi:10.1103/physrevlett.107.095901 · Cited by 556 · see citing works
Self-citationSiemens, M. E., Li, Q., Yang, R., Nelson, K. A., Anderson, E. H., Murnane, M. M., & Kapteyn, H. C. (2010) · Nature Materials · doi:10.1038/nmat2568 · Cited by 443 · see citing works
Johnson, J. A., Maznev, A. A., Cuffe, J., Eliason, J. K., Minnich, A. J., Kehoe, T., Torres, C. M. S., Chen, G., & Nelson, K. A. (2013) · Physical Review Letters · doi:10.1103/physrevlett.110.025901 · Cited by 421 · see citing works
Self-citationDetermining Phonon Mean Free Paths from Observations of Quasiballistic Thermal Transport
Minnich, A. J. (2012) · Physical Review Letters · doi:10.1103/physrevlett.109.205901 · Cited by 196 · see citing works
Self-citation
Flagged first, then by citations
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Cited by
Sorted by citations
Kim, T., Drakopoulos, S. X., Ronca, S., & Minnich, A. J. (2022) · Nature Communications · doi:10.1038/s41467-022-29904-2 · Cited by 63 · see citing works
“[57], we fit the signal with a multi-exponential function; the time constant of the slower decay yields the thermal diffusivity of the sample.”
BackgroundMethodInfluentialSelf-citation
- Authors
- Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S., & Minnich, A. J.
- Affiliations
- California Institute of Technology (US)
- Loughborough University (GB)
- Department of Materials, Loughborough University, Loughborough LE11 3TU, United Kingdom
- Venue
- Proceedings of the National Academy of Sciences
- Publisher
- National Academy of Sciences
- Published
- 2019-08-12
- Volume
- 116
- Issue
- 35
- Pages
- 17163-17168
- ISSN
- 0027-8424 (ISSN-L)
- 1091-6490
- PMC
- PMC6717268
- OpenAlex
- W2961995104
- Cited by
- 38
- References
- 4
- Citations by year
- 2026: 4 · 2025: 3 · 2024: 7 · 2023: 2 · 2022: 8 · 2021: 8 · 2020: 6
- FWCI
- 1.99
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Proceedings of the National Academy of Sciences (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- CaltechAUTHORS (California Institute of Technology) (submittedVersion)
- Loughborough University Institutional Repository (Loughborough University) (submittedVersion, cc-by-nc-nd)
- Figshare (submittedVersion, cc-by-nc-nd)
- Funders
- DOD | United States Navy | Office of Naval Research (N00014-15-1-2688)
- RCUK | Engineering and Physical Sciences Research Council (EP/K034405/1)
- Topics
- Physical Sciences › Materials Science › Materials Chemistry › Thermal properties of materials
- Physical Sciences › Materials Science › Polymers and Plastics › Polymer crystallization and properties
- Physical Sciences › Materials Science › Materials Chemistry › Material Dynamics and Properties
- Keywords
- thermal phonons, ballistic phonon transport, polyethylene, nanocrystalline domains, thermal conductivity, mean free path, transient grating spectroscopy, semicrystalline polymers, polymer crystals, domain boundaries
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