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Cited by 63Thermal properties of materialsPolymer crystallization and propertiesMaterial Dynamics and Properties

Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals

Open access
Kim, Taeyong, Drakopoulos, Stavros X., Ronca, Sara, Minnich, Austin J.·2022·Nature Communications
DOI 10.1038/s41467-022-29904-2PMC PMC9068786
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Abstract

The thermal transport properties of oriented polymers are of fundamental and practical interest. High thermal conductivities ( ≳ 50 Wm −1 K −1 ) have recently been reported in disentangled ultra-high molecular weight polyethylene (UHMWPE) films, considerably exceeding prior reported values for oriented films. However, conflicting explanations have been proposed for the microscopic origin of the high thermal conductivity. Here, we report a characterization of the thermal conductivity and mean free path accumulation function of disentangled UHMWPE films (draw ratio ~200) using cryogenic steady-state thermal conductivity measurements and transient grating spectroscopy. We observe a marked dependence of the thermal conductivity on grating period over temperatures from 30–300 K. Considering this observation, cryogenic bulk thermal conductivity measurements, and analysis using an anisotropic Debye model, we conclude that longitudinal atomic vibrations with mean free paths around 400 nanometers are the primary heat carriers, and that the high thermal conductivity for draw ratio ≳ 150 arises from the enlargement of extended crystals with drawing. The mean free paths appear to remain limited by the extended crystal dimensions, suggesting that the upper limit of thermal conductivity of disentangled UHMWPE films has not yet been realized.

AI snapshot

Written from the paper’s full text.

TL;DR

Using cryogenic steady-state and transient grating spectroscopy on disentangled UHMWPE films (DR = 196), the paper finds that heat is carried mainly by longitudinal acoustic phonons with mean free paths around 400 nm that are ballistic within enlarged extended crystals. The high thermal conductivity for draw ratio ≳150 is attributed to crystal enlargement, and the upper limit of thermal conductivity in these films has not yet been realized.

Key findings

  • In-plane thermal conductivity at 300 K is ~40 W m⁻¹ K⁻¹ parallel to the draw direction and ~0.4 W m⁻¹ K⁻¹ perpendicular; κ∥ is approximately constant from 300 K to ~220 K, below which it decreases.
  • Transient grating measurements show a marked grating-period dependence up to ~10 μm; at L = 1.5 μm the decay is slower than diffusive prediction, with decay rates slower by up to a factor of 5 at the smallest grating period, indicating ballistic phonons.
  • An anisotropic Debye analysis indicates nearly all heat is carried by the longitudinal acoustic branch, with temperature-independent mean free paths around 400 nm (Λ₀ = 340 nm) up to several THz, constant to ~5.5 THz and then decreasing as ~ω⁻⁴.
  • The high thermal conductivity for DR ≳150 is attributed to enlargement of extended crystals; phonon mean free paths appear limited by extended crystal dimensions, suggesting higher thermal conductivity may be possible with larger crystals.

Methods

  • Disentangled UHMWPE films with DR = 196 were prepared from polymer with Mw = 5.6 × 10⁶ g mol⁻¹ and 1 wt% Au nanoparticles, using compression molding, twin-roll calendering (×7), and tensile stretching (×28).
  • Thermal conductivity was measured using transient grating spectroscopy from 30–300 K with varied grating periods and a PPMS for cryogenic bulk measurements down to ~3 K; heat capacities were taken from ref. 61.
  • Data were interpreted with an anisotropic Debye model for longitudinal acoustic phonons, using vc ~17 km s⁻¹, vab ~3 km s⁻¹, ωc ~10 THz, and a Matthiessen-rule mean free path profile with Λ₀ = 340 nm and a ~ω⁻⁴ decrease above ~5.5 THz.

Limitations

  • Stated: the model qualitatively reproduces the grating-period dependence but quantitative discrepancies exist, and agreement is worse below ~10 K, possibly due to other phonon branches or non-propagating vibrations not included in the model.
  • Stated: heat capacity measurements were unsuccessful, so literature heat capacities were used; TG signal-to-noise was generally <20, about 30% of that for prior DR = 7.5 samples, due to strong light scattering.
  • Evident: conclusions rely on one DR = 196 sample and on model assumptions such as LA-branch dominance, structural scattering, and negligible Au nanoparticle effect; the paper also notes that crystalline and amorphous phase properties cannot be independently measured by bulk thermal conductivity.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/s41467-022-29904-2

Cites

84 of 84 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

31 of 84 cited sources checked · 11 supported · 1 flagged · accuracy not yet measured

  • Premisecitation

    For disentangled UHMWPE of draw ratio ≳150, the thermal conductivity is observed to increase on average by a factor of about 20% despite a lack of detectable change in crystallinity or chain orientation.

    “For disentangled UHMWPE of DR ≳ 150, the increase in thermal conductivity is difficult to interpret using the above models because the thermal conductivity is observed to increase on average by factor of ∼20% despite a lack of detectable change in crystallinity or chain orientation11–13,23,24.”
    Quote in the paperSubstantial claim2 of 5 sources checked
    • cites [11] Choy, C. L., Chen, F. C. & Luk, W. H. Thermal conductivity of oriented crystalline polymers. J. Polym. Sci.: Polym. Phys. Ed. 18, 1187–1207 (1980). source
    • cites [12] Choy, C. L., Luk, W. H. & Chen, F. C. Thermal conductivity of highly oriented polyethylene. Polymer 19, 155–162 (1978). source
    • cites [13] Choy, C. L., Wong, Y. W., Yang, G. W. & Kanamoto, T. Elastic modulus and thermal conductivity of ultradrawn polyethylene. J. Polym. Sci. Part B: Polym. Phys. 37, 3359–3367 (1999). source
    • cites [23] Ronca, S., Igarashi, T., Forte, G. & Rastogi, S. Metallic-like thermal conductivity in a lightweight insulator: solid-state processed ultra high molecular weight polyethylene tapes and films. Polymer 123, 203–210 (2017). source

      Table 2 reports further thermal-conductivity increases at high draw ratios, including 44.3 to 51.5 W/m K for PE_6_7 between TDR 160 and 220, but it does not report an average increase of about 20% for DR ≳150. The Results and discussion say crystal orientation is almost complete by TDR 80, yet the XRD ratio still decreases slightly with further stretching; the crystallinity discussion does not establish no detectable change at DR ≳150. The paper instead suggests increased crystal size as a possible contributor to the later conductivity increase (Results and discussion; page not supplied). (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [24] Xu, Y. et al. Nanostructured polymer films with metal-like thermal conductivity. Nat. Commun. 10, 1–8 (2019). source

      The Results section, “Strong field ionization of the neon dimer” (page unavailable), describes laser ionization of Ne₂, not polyethylene. Searches for UHMWPE, draw ratio, thermal conductivity, crystallinity, and chain orientation found no passage addressing the claimed observation. (LLM, conf=0.78)

      Experimental — accuracy not yet measured
  • Premisecitation

    High thermal conductivities of about 50 W m−1 K−1 or more have recently been reported in disentangled ultra-high molecular weight polyethylene (UHMWPE) films, considerably exceeding prior reported values for oriented films.

    “High thermal conductivities ( ≳ 50 Wm−1K−1) have recently been reported in disentangled ultra-high molecular weight polyethylene (UHMWPE) films, considerably exceeding prior reported values for oriented films.”
    Quote in the paperSubstantial claim2 of 2 sources checked
    • cites [23] Ronca, S., Igarashi, T., Forte, G. & Rastogi, S. Metallic-like thermal conductivity in a lightweight insulator: solid-state processed ultra high molecular weight polyethylene tapes and films. Polymer 123, 203–210 (2017). source
    • cites [24] Xu, Y. et al. Nanostructured polymer films with metal-like thermal conductivity. Nat. Commun. 10, 1–8 (2019). source

      The Methods (Experimental) and Results (Double-slit interference in linearly polarized light) passages concern neon-dimer ionization and photoelectron interference. Searches for disentangled UHMWPE films and thermal conductivities of about 50 W m−1 K−1 found no passage addressing the claimed conductivity or comparison with oriented films. (LLM, conf=0.78)

      Experimental — accuracy not yet measured
  • Premisecitation

    Evidence 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.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source
  • Interpretationown data

    The authors' results support the hypothesis of ref. 23 that high thermal conductivity is attributed to the enlargement of extended crystal dimensions.

    “Our results therefore support the hypothesis of ref. 23 in which the high thermal conductivity compared to the prediction including only crystallinity and anisotropy factors for DR ≳ 180 (Fig. 7 in ref. 23) was attributed to the enlargement of extended crystal dimensions.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [23] Ronca, S., Igarashi, T., Forte, G. & Rastogi, S. Metallic-like thermal conductivity in a lightweight insulator: solid-state processed ultra high molecular weight polyethylene tapes and films. Polymer 123, 203–210 (2017). source

      The Results and discussion section attributes the further rise in thermal conductivity at high draw ratios to a possible increase in crystal size along the draw direction. It also reports a deviation from a fitted model at higher draw ratios, where crystal extension may occur. Our copy does not identify a prediction based only on crystallinity and anisotropy or locate that comparison at DR ≳ 180 in Fig. 7. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
  • Interpretationown data

    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.”
    Quote in the paperSubstantial claim2 of 2 sources checked
    • cites [74] Zhang, T., Wu, X. & Luo, T. Polymer nanofibers with outstanding thermal conductivity and thermal stability: fundamental linkage between molecular characteristics and macroscopic thermal properties. J. Phys. Chem. C 118, 21148–21159 (2014). source
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

      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 measured
  • May combine two claims. 37
  • Classified as probably not a substantial claim. 24
  • The quote only partly states this claim. 3

  • May combine two claims.

    Interpretationcitation

    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.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

      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 measured

  • Classified as probably not a substantial claim.

    Premisecitation

    The introduction of disentangled UHMWPE films with higher crystallinities and less entangled amorphous regions compared to prior samples has led to reports of high thermal conductivities exceeding 60 W m−1 K−1.

    “In macroscopic samples, the introduction of disentangled ultra-high molecular weight polyethylene (UHMWPE) films21,22 with higher crystallinities and less entangled amorphous regions compared to prior samples has led to reports of high thermal conductivities exceeding 60 Wm−1 K−1 (refs. 23,24).”
    Quote in the paperSubstantial claim2 of 2 sources checked
    • cites [23] Ronca, S., Igarashi, T., Forte, G. & Rastogi, S. Metallic-like thermal conductivity in a lightweight insulator: solid-state processed ultra high molecular weight polyethylene tapes and films. Polymer 123, 203–210 (2017). source

      The Results and discussion report 65 W/m K for a macroscopic, uniaxially drawn UHMWPE tape, supporting the reported conductivity above 60 W/m K. But the Conclusions report only 18.4 W/m K for biaxially stretched films. The paper describes reduced entanglements and increased crystallinity during drawing, but does not establish that its films have higher crystallinity than prior samples. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [24] Xu, Y. et al. Nanostructured polymer films with metal-like thermal conductivity. Nat. Commun. 10, 1–8 (2019). source

      The Introduction and Results discuss photoelectron interference in neon dimers, not polyethylene films. Searches for UHMWPE, crystallinity, entanglement, and thermal conductivity above 60 W m−1 K−1 found no passage addressing the claim in our copy. (LLM, conf=0.78)

      Experimental — accuracy not yet measured

  • Classified as probably not a substantial claim.

    Premisecitation

    The nascent structure of polyethylene consists of spherulites composed of unoriented stacked lamella in which folded chains are bridged by intra- and inter-lamella tie molecules.

    “The nascent structure consists of spherulites27 which are in turn composed of unoriented stacked lamella in which folded chains are bridged by intra- and inter-lamella tie molecules28.”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [27] Bunn, C. W. & Alcock, T. C. The texture of polythene. Trans. Faraday Soc. 41, 317–325 (1945). source
    • cites [28] Keller, A. Polymer crystals. Rep. Prog. Phys. 31, 623–704 (1968). source

      Section 11.1 (Morphology; page unavailable) describes polyethylene’s crystalline units as lamellar, and section 11.6 (Fractionation; page unavailable) discusses chains that fold within a layer or traverse between lamellae. The paper also reports interlamellar links, but these passages do not establish intralamellar tie molecules or characterize the stacked lamellae as unoriented. The separate citation attached to “spherulites” is not being judged here. (LLM, conf=0.85)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Thermal conductivity values around 20-30 W m−1 K−1 and ≳60 W m−1 K−1 have been reported in polyethylene microfibers and nanofibers, respectively.

    “Recently, thermal conductivity values around 20−30 Wm−1 K−1 and ≳60 Wm−1 K−1 have been reported in PE microfibers14,18 and nanofibers19,20, respectively.”
    Quote in the paperNot a substantial claim1 of 4 sources checked
    • cites [14] Liu, J., Xu, Z., Cheng, Z., Xu, S. & Wang, X. Thermal conductivity of ultrahigh molecular weight polyethylene crystal: defect effect uncovered by 0 k limit phonon diffusion. ACS Appl. Mater. Interfaces 7, 27279–27288 (2015). source
    • cites [18] Wang, X., Ho, V., Segalman, R. A. & Cahill, D. G. Thermal conductivity of high-modulus polymer fibers. Macromolecules 46, 4937–4943 (2013). source
    • cites [19] Shen, S., Henry, A., Tong, J., Zheng, R. & Chen, G. Polyethylene nanofibres with very high thermal conductivities. Nat. Nanotechnol. 5, 251–255 (2010). source
    • cites [20] Shrestha, R. et al. Crystalline polymer nanofibers with ultra-high strength and thermal conductivity. Nat. Commun. 9, 1–9 (2018). source

  • May combine two claims.

    Interpretationown data

    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.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

  • May combine two claims.

    Interpretationown data

    The thermal diffusivity depends on temperature, ruling out a constant relaxation time for all phonon polarizations as suggested in ref. 20.

    “First, the thermal diffusivity is observed to depend on temperature, ruling out a constant relaxation time for all phonon polarizations as suggested in ref. 20.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [20] Shrestha, R. et al. Crystalline polymer nanofibers with ultra-high strength and thermal conductivity. Nat. Commun. 9, 1–9 (2018). source

      In Results > Thermal transport in crystalline PENF (page unavailable), the paper reports temperature-dependent thermal conductivity and assumes the same phonon mean free path at low temperatures. It does not report temperature-dependent thermal diffusivity or suggest a constant relaxation time for all phonon polarizations; mean free path and relaxation time are different quantities. (LLM, conf=0.82)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Study design and conductcitation

    The value of κ∥ is in reasonable agreement with that obtained on a sample without Au nanoparticles using the laser flash method, indicating that 1 wt% Au nanoparticles does not measurably affect the thermal transport properties of the present sample.

    “The value along the draw direction is in reasonable agreement with that obtained on a sample without Au nanoparticles using the laser flash method in ref. 23, indicating that the 1 wt% of AuNPs does not measurably affect the thermal transport properties of the present sample.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [23] Ronca, S., Igarashi, T., Forte, G. & Rastogi, S. Metallic-like thermal conductivity in a lightweight insulator: solid-state processed ultra high molecular weight polyethylene tapes and films. Polymer 123, 203–210 (2017). source

  • May combine two claims.

    Premisecitation

    Extensive structural characterization indicates that the crystallinity of samples with draw ratio around 200 is nearly 90%, and that enlarged crystals with a dimension of about 400-500 nm are separated by fragmented inter-crystalline bridges.

    “First, extensive structural characterization of highly drawn samples indicates that the crystallinity of samples with draw ratio around 200 is nearly 90%47,59, and that the enlarged crystals with a dimension of ∼400−500 nm are separated by fragmented inter-crystalline bridges44,46,47.”
    Quote in the paperSubstantial claim1 of 4 sources checked
    • cites [47] Litvinov, V. M. et al. Morphology, chain dynamics, and domain sizes in highly drawn gel-spun ultrahigh molecular weight polyethylene fibers at the final stages of drawing by SAXS, WAXS, and 1H solid-state NMR. Macromolecules 44, 9254–9266 (2011). source
    • cites [59] Drakopoulos, S. X., Tarallo, O., Guan, L., Martin-Fabiani, I., & Ronca, S. Nanocomposites of Au/disentangled UHMWPE: a combined optical and structural study. Molecules 25, 3225 (2020). source

      Split into 2 atoms — 0 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 1 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
    • cites [44] Brady, J. M. & Thomas, E. L. Conversion of single crystal mats to ultrahigh modulus polyethylene: the formation of a continuous crystalline phase. Polymer 30, 1615–1622 (1989). source
    • cites [46] Hu, W.-G. & Schmidt-Rohr, K. Characterization of ultradrawn polyethylene fibers by NMR: crystallinity, domain sizes and a highly mobile second amorphous phase. Polymer 41, 2979–2987 (2000). source

  • May combine two claims.

    Interpretationown data

    The measured bulk thermal conductivity is in reasonable agreement with transient grating data for grating period 9.8 μm, indicating that phonon mean free paths are shorter than about 1.5 μm.

    “Second, within the uncertainty of the measurements, the measured bulk thermal conductivity is in reasonable agreement with the TG data for L = 9.8 μm, indicating that the phonon mean free paths are shorter than ∼9.8/2π∼1.5 μm (ref. 64).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [64] Minnich, A. J. Determining phonon mean free paths from observations of quasiballistic thermal transport. Phys. Rev. Lett. 109, 205901 (2012). source

      The discussion of thermal conductivity spectroscopy explains that phonons with mean free paths longer than the thermal length scale have suppressed heat flux, supporting the general inference behind the claim. The application to transient-grating measurements concerns a 390 nm silicon membrane, however; our copy does not report agreement between a measured bulk conductivity and data at a 9.8 μm grating period, or draw the stated 1.5 μm conclusion from that comparison. The indexed passages provide no page numbers. (LLM, conf=0.78)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingcitation

    The thermal conductivity exhibits a marked dependence on grating period up to about 10 μm, a value comparable to that observed in other covalent crystals with higher thermal conductivity such as silicon.

    “The thermal conductivity exhibits a marked dependence on grating period up to ∼10 μm, a value comparable to that observed in other covalent crystals with higher thermal conductivity such as silicon60,65.”
    Quote in the paperSubstantial claim2 of 2 sources checked
    • cites [60] Johnson, J. A. et al. Direct measurement of room-temperature nondiffusive thermal transport over micron distances in a silicon membrane. Phys. Rev. Lett. 110, 025901 (2013). source
    • cites [65] Ravichandran, N. K., Zhang, H. & Minnich, A. J. Spectrally resolved specular reflections of thermal phonons from atomically rough surfaces. Phys. Rev. X 8, 041004 (2018). source

      The Experiment section (page unavailable) identifies the measured samples as silicon membranes, and the Results section reports grating-period-dependent thermal conductivity. The Results describe a transition at approximately 20 μm at 80 K, however, rather than establishing the claimed ∼10 μm scale; the copy therefore supports the silicon comparison but not its specific value. (LLM, conf=0.82)

      Experimental — accuracy not yet measured
    • The authors state this as an assumption: One-dimensional heat transfer can be assumed in the interpretation of the transient grating signal.

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Recent 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.”
    Quote in the paperSubstantial claim3 of 3 sources checked
    • cites [24] Xu, Y. et al. Nanostructured polymer films with metal-like thermal conductivity. Nat. Commun. 10, 1–8 (2019). source

      Split into 2 atoms — 0 confirmed, 0 partially supported, 0 disputed, 0 misattributed, 2 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

      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 measured
    • cites [23] Ronca, S., Igarashi, T., Forte, G. & Rastogi, S. Metallic-like thermal conductivity in a lightweight insulator: solid-state processed ultra high molecular weight polyethylene tapes and films. Polymer 123, 203–210 (2017). source

      Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Experimental characterization of similar samples indicates that the nanoparticles are oriented in linear chains in the amorphous regions.

    “Experimental characterization of similar samples using polarized light microscopy, among other methods, indicates that the nanoparticles are oriented in linear chains in the amorphous regions59.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [59] Drakopoulos, S. X., Tarallo, O., Guan, L., Martin-Fabiani, I., & Ronca, S. Nanocomposites of Au/disentangled UHMWPE: a combined optical and structural study. Molecules 25, 3225 (2020). source

  • May combine two claims.

    Findingcitation

    A rough estimate from UV-VIS spectra yields an optical absorption depth of 30-40 μm, on the order of the sample thickness.

    “A rough estimate of the absorption depth from UV–VIS spectra yields a value of 30–40 μm59, indicating that the optical absorption depth is on the order of the sample thickness.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [59] Drakopoulos, S. X., Tarallo, O., Guan, L., Martin-Fabiani, I., & Ronca, S. Nanocomposites of Au/disentangled UHMWPE: a combined optical and structural study. Molecules 25, 3225 (2020). source

      Section 2.1 (page not provided) reports VIS absorption spectra and a sample thickness of approximately 50 μm; Section 3.3.3 describes the spectrophotometer. Searches for an absorption or penetration depth of 30–40 μm found no such estimate in our copy. The cited numerical value therefore cannot be verified from this source. (LLM, conf=0.74)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The 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).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

      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 measured

  • May combine two claims.

    Interpretationreasoning

    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.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductreasoning

    The 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.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [58] Robbins, A. B., Drakopoulos, S. X., Martin-Fabiani, I., Ronca, S. & Minnich, A. J. Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene. Proc. Natl Acad. Sci. USA 116, 17163–17168 (2019). source

      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

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingcitation

    The average molecular weight of the synthesized disentangled UHMWPE is 5.6 × 10^6 g/mol, as measured by rheological measurements.

    “The average molecular weight (Mw) was characterized to be Mw = 5.6 × 106 gmol−1 (ref. 59), as measured using rheological measurements.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [59] Drakopoulos, S. X., Tarallo, O., Guan, L., Martin-Fabiani, I., & Ronca, S. Nanocomposites of Au/disentangled UHMWPE: a combined optical and structural study. Molecules 25, 3225 (2020). source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    Heat capacities from ref. 61 were used for the analysis.

    “Therefore, heat capacities from ref. 61 were used.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [61] Chang, S. Heat capacities of polyethylene from 2 to 360 K. II. Two high density linear polyethylene samples and thermodynamic properties of crystalline linear polyethylene. J. Res. NBS A Phys. Chem. 3, (1974). source
    • Rests on an assumption: The heat capacity of the disentangled UHMWPE samples is adequately represented by the heat capacities from ref. 61.

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    The in-plane thermal conductivity of the disentangled UHMWPE film with draw ratio 196 is about 40 W m−1 K−1 parallel to the draw direction and about 0.4 W m−1 K−1 perpendicular to it.

    “The thermal conductivity is ~40 Wm−1 K−1 at 0° (κ∥, parallel to grating), and decreases to 0.4 Wm−1 K−1 at 90° (κ⊥, perpendicular to grating).”
    Quote in the paperSubstantial claim

  • The quote only partly states this claim.

    Findingown data

    The thermal diffusivity along the chain direction from transient grating spectroscopy with grating period 9.8 μm increases linearly with decreasing temperature between 30 and 300 K.

    “The diffusivity exhibits a linearly increasing trend with decreasing temperature, a qualitatively similar trend as that reported in microscale crystalline fibers14.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [14] Liu, J., Xu, Z., Cheng, Z., Xu, S. & Wang, X. Thermal conductivity of ultrahigh molecular weight polyethylene crystal: defect effect uncovered by 0 k limit phonon diffusion. ACS Appl. Mater. Interfaces 7, 27279–27288 (2015). source

  • May combine two claims.

    Findingown data

    The measured transient grating signal for grating period 1.5 μm decays slower than expected based on the bulk thermal conductivity value, indicating the presence of ballistic phonons on the length scale of the grating period.

    “The decay is clearly slower than expected based on the bulk thermal conductivity value, indicating the presence of ballistic phonons on the length scale of the grating period.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: One-dimensional heat transfer can be assumed in the interpretation of the transient grating signal.

  • May combine two claims.

    Findingown data

    The measured decay rate is close to that predicted by the bulk thermal conductivity at q2 ≤ 0.3 μm−2, above which the decay rate is slower by up to a factor of 5 at the smallest grating period.

    “The measured decay rate is close to that predicted by the bulk thermal conductivity at q2 ≤ 0.3 μm−2, above which the decay rate is slower by up to a factor of 5 at the smallest grating period.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Within measurement uncertainty, the thermal conductivity along the chain axis remains constant from room temperature to about 220 K, below which it decreases.

    “Within the uncertainty of the measurement, the thermal conductivity remains constant from room temperature to ∼220 K, below which the thermal conductivity decreases.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Above 10 K, the trend of thermal conductivity versus temperature is qualitatively similar to those reported previously for polyethylene films of various draw ratios, although the thermal conductivity of the present sample is consistently higher.

    “Above 10 K, the trend is qualitatively similar to those reported previously for PE films of various DR as shown in Fig. 3, although the thermal conductivity of the present sample is consistently higher.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    Similar power laws to the best-fit mean free path profile also yield similar qualitative agreement with the data.

    “although similar power laws also yield similar qualitative agreement (see Supplementary Material Section 3 for results using other candidate profiles).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The best fit to the measured TG and PPMS thermal conductivity data is obtained with a constant mean free path Λ0 = 340 nm up to about 5.5 THz, beyond which the mean free path decreases as approximately ω−4.

    “After extensive comparison, we found that the best fit is obtained using a constant Λ0 = 340 nm up to ∼5.5 THz, beyond which the MFP decreases as ∼ω−4, although similar power laws also yield similar qualitative agreement (see Supplementary Material Section 3 for results using other candidate profiles).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The mean free paths in both samples exhibit a clear maximum in the low THz frequencies and are independent of temperature.

    “The MFPs in both samples exhibit a clear maximum in the low THz frequencies and are independent of temperature, suggesting that phonon scattering is predominantly due to reflections at crystalline domain boundaries.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    Scanning electron microscope images show highly oriented fibers extending over tens of microns.

    “In both images, highly oriented fibers extending over tens of microns are visible.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The grating period dependence of the thermal conductivity is qualitatively reproduced by the calculation, although quantitative discrepancies exist.

    “The grating period dependence of the thermal conductivity is also qualitatively reproduced by the calculation in Fig. 4C, and Fig. S2 in Supplementary Material Section 2, although quantitative disrepancies exist.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning

    The calculated cryogenic thermal conductivity shows a similar qualitative trend above about 10 K but worse agreement below this temperature.

    “Although a similar qualitative trend is observed above ∼10 K, the agreement is worse below this temperature.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The calculated thermal conductivity in transient grating with L = 9.8 μm is close to the bulk value, consistent with the good agreement between the transient grating and PPMS measurements.

    “The calculated thermal conductivity in TG with L = 9.8 μm is close to the bulk value, consistent with the good agreement between the TG and PPMS measurements.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisereasoning

    The physical origin of the high thermal conductivity of disentangled UHMWPE remains unclear.

    “As a result, the physical origin of the high thermal conductivity of disentangled UHMWPE remains unclear.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    From SAXS, the crystalline domains of nascent polyethylene have long periods of about 10-30 nm, with the corresponding size of the crystalline domain inside the unit being around 90% of the long period.

    “from SAXS the crystalline domains have long periods ∼10−30 nm31–33 with the corresponding size of the crystalline domain inside the unit being around 90% of the long period34.”
    Quote in the paperNot a substantial claim0 of 4 sources checked
    • cites [31] Fischer, E. W. & Schmidt, G. F. Long periods in drawn polyethylene. Angew. Chem. Int. Ed. Engl. 1, 488–499 (1962). source
    • cites [32] KOBAYASHI, K. & KUROKAWA, M. Small-angle diffraction of polyethylene. Nature 196, 538–539 (1962). source
    • cites [33] Yeh, G. S. Y. & Geil, P. H. Selected-area small-angle electron diffraction. J. Mater. Sci. 2, 457–469 (1967). source
    • cites [34] Geil, P. H., Anderson, F. R., Wunderlich, B. & Arakawa, T. Morphology of polyethylene crystallized from the melt under pressure. J. Polym. Sci. Part A: Gen. Pap. 2, 3707–3720 (1964). source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The reported thermal conductivity of oriented polyethylene ranged from about 14 W m−1 K−1 for draw ratio 25 up to about 40 W m−1 K−1 for solution-processed polyethylene with a draw ratio of 350.

    “In particular, the reported thermal conductivity of oriented polyethylene ranged from ∼14 Wm−1 K−1 (ref. 12) for draw ratio DR = 25 up to ∼40 Wm−1 K−1 for solution processed PE with a DR of 350 (ref. 13).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [12] Choy, C. L., Luk, W. H. & Chen, F. C. Thermal conductivity of highly oriented polyethylene. Polymer 19, 155–162 (1978). source
    • cites [13] Choy, C. L., Wong, Y. W., Yang, G. W. & Kanamoto, T. Elastic modulus and thermal conductivity of ultradrawn polyethylene. J. Polym. Sci. Part B: Polym. Phys. 37, 3359–3367 (1999). source

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    On drawing, stacked lamella transition to micro-fibrils and eventually to chain-extended crystals.

    “On drawing, Peterlin proposed a sequence of processes occur in which stacked lamella transition to micro-fibrils and eventually to chain-extended crystals35.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [35] Peterlin, A. Molecular model of drawing polyethylene and polypropylene. J. Mater. Sci. 6, 490–508 (1971). source

  • May combine two claims.

    Interpretationown data

    The trend and values of thermal conductivity from PPMS and transient grating spectroscopy with grating period 9.8 μm are in reasonable agreement, suggesting that phonon mean free paths are less than about 1.5 μm.

    “The trend and corresponding values from PPMS and TG with L = 9.8 μm are in reasonable agreement, suggesting that phonon mean free paths are less than ~L/2π~1.5 μm.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    The perpendicular thermal conductivity of about 0.4 W m−1 K−1 is close to that of unoriented polyethylene, which is attributed to heat conduction by interchain van der Waals interactions.

    “The value of κ⊥ ~ 0.4 Wm−1 K−1 is close to that of unoriented PE, which is attributed to the heat conduction by interchain van der Waals interactions62.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [62] Choy, C. Thermal conductivity of polymers. Polymer 18, 984–1004 (1977). source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Several recent studies have reported high thermal conductivity up to 20-30 W m−1 K−1 in diverse polymers besides polyethylene, including polybenzobisoxazole, polyethylene oxide, and amorphous polythiophene.

    “Several recent studies have also reported high thermal conductivity up to 20–30 Wm−1 K−1 in a diverse set of polymers besides PE, including polybenzobisoxazole18, polyethylene oxide25, and amorphous polythiophene26.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [18] Wang, X., Ho, V., Segalman, R. A. & Cahill, D. G. Thermal conductivity of high-modulus polymer fibers. Macromolecules 46, 4937–4943 (2013). source
    • cites [25] Lu, C. et al. Thermal conductivity of electrospinning chain-aligned polyethylene oxide (PEO). Polymer 115, 52–59 (2017). source
    • cites [26] Singh, V. et al. High thermal conductivity of chain-oriented amorphous polythiophene. Nat. Nanotechnol. 9, 384–390 (2014). source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The initial crystalline fraction of nascent polyethylene is on the order of 60-70%, as measured using nuclear magnetic resonance or heat capacity measurements.

    “The initial crystalline fraction is on the order of ∼60−70%, as measured using nuclear magnetic resonance (NMR)29 or heat capacity measurements30”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [29] Wilson III, C. W. & Pake, G. E. Nuclear magnetic resonance determination of degree of crystallinity in two polymers. J. Polym. Sci. 10, 503–505 (1953). source
    • cites [30] Peterlin, A. & Meinel, G. Heat content of amorphous regions of drawn linear polyethylne. J. Polym. Sci. Part B: Polym. Lett. 3, 783–787 (1965). source

  • May combine two claims.

    Premisecitation

    For 10 ≲ draw ratio ≲ 50, micro-fibrils aggregate with concurrent tautening of tie-molecules and marginal changes in crystallinity.

    “Subsequently, for 10 ≲ DR ≲ 50 the micro-fibrils aggregate with concurrent tautening of the tie-molecules and marginal changes in the crystallinity.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [35] Peterlin, A. Molecular model of drawing polyethylene and polypropylene. J. Mater. Sci. 6, 490–508 (1971). source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The enhancement of thermal conductivity in oriented polyethylene was attributed to mechanisms including increased chain alignment along the drawing direction, phonon focusing in the elastically anisotropic crystalline phase, and increased crystallinity.

    “The enhancement was attributed to various mechanisms including increased chain alignment along the drawing direction7,14, phonon focusing in the elastically anisotropic crystalline phase15,16, and increased crystallinity12,17.”
    Quote in the paperNot a substantial claim0 of 6 sources checked
    • cites [7] Hansen, D. & Bernier, G. A. Thermal conductivity of polyethylene: the effects of crystal size, density and orientation on the thermal conductivity. Polym. Eng. Sci. 12, 204–208 (1972). source
    • cites [14] Liu, J., Xu, Z., Cheng, Z., Xu, S. & Wang, X. Thermal conductivity of ultrahigh molecular weight polyethylene crystal: defect effect uncovered by 0 k limit phonon diffusion. ACS Appl. Mater. Interfaces 7, 27279–27288 (2015). source
    • cites [15] Pietralla, M., Weeger, R. M. & Mergenthaler, D. B. The role of phonon focussing and structure scattering in oriented semicrystalline polymers. Z. Phys. B Condens. Matter 77, 219–228 (1989). source
    • cites [16] Mergenthaler, D. B. & Pietralla, M. Heat conduction in highly oriented polyethylene. Z. Phys. B Condens. Matter 94, 461–468 (1994). source
    • cites [12] Choy, C. L., Luk, W. H. & Chen, F. C. Thermal conductivity of highly oriented polyethylene. Polymer 19, 155–162 (1978). source
    • cites [17] Gibson, A. G., Greig, D., Sahota, M., Ward, I. M. & Choy, C. L. Thermal conductivity of ultrahigh-modulus polyethylene. J. Polym. Sci.: Polym. Lett. Ed. 15, 183–192 (1977). source

  • May combine two claims. The quote only partly states this claim.

    Interpretationown data

    The lack of clear temperature dependence in the grating dependence indicates the dominance of structural scattering, consistent with the trend of the bulk thermal conductivity versus temperature.

    “This finding indicates the dominance of the structural scattering, consistent with the trend of the bulk thermal conductivity versus temperature in Fig. 2B.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: One-dimensional heat transfer can be assumed in the interpretation of the transient grating signal.

  • May combine two claims.

    Premisecitation

    The diameter of the extended crystal is about 10-20 nm and its longitudinal dimension is around 100-250 nm or greater.

    “These various techniques indicated that the diameter of the extended crystal is ∼10−20 nm and of longitudinal dimension around 100–250 nm or greater47.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [47] Litvinov, V. M. et al. Morphology, chain dynamics, and domain sizes in highly drawn gel-spun ultrahigh molecular weight polyethylene fibers at the final stages of drawing by SAXS, WAXS, and 1H solid-state NMR. Macromolecules 44, 9254–9266 (2011). source

  • May combine two claims.

    Interpretationcitation

    For other phonon branches to contribute, their lifetimes would need to be orders of magnitude larger than those of the longitudinal acoustic branch to compensate their low group velocity; such long lifetimes are inconsistent with ab-initio studies.

    “For other branches to contribute, their lifetimes would need to be orders of magnitude larger than those of the LA branch to compensate their low group velocity; such long lifetimes are inconsistent with the findings of ab-initio studies68.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [68] Shulumba, N., Hellman, O. & Minnich, A. J. Lattice thermal conductivity of polyethylene molecular crystals from first-principles including nuclear quantum effects. Phys. Rev. Lett. 119, 185901 (2017). source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning

    Λ0 should be interpreted as an average dimension of the crystallites for phonon scattering, which may not coincide precisely with their actual physical dimension depending on the phonon transmission coefficient across the boundary.

    “We note that Λ0 should be interpreted as an average dimension of the crystallites for phonon scattering, which may not coincide precisely with their actual physical dimension depending on the phonon transmission coefficient across the boundary.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationown data

    The decrease in signal-to-noise ratio is because the highly oriented samples scatter visible light intensely owing to increased inhomogeneity over length scales comparable to the optical wavelength.

    “This decrease is because the highly oriented samples scatter visible light intensely owing to the increased inhomogeneity over length scales comparable to the optical wavelength, as evidenced by AFM images perpendicular to the fiber alignment direction”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationown data

    The discrepancy between calculated and measured cryogenic thermal conductivity below about 10 K could be attributed to heat conduction by other types of atomic vibrations which may make the primary contribution below about 10 K.

    “This discrepancy could be attributed to heat conduction by other types of atomic vibrations which may make the primary contribution to thermal conductivity below ∼10 K.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisenone given

    At low frequencies below a few THz, the approximation that the longitudinal density of states is nearly one-dimensional is poor, necessitating the use of the anisotropic Debye model.

    “Note that although the longitudinal density of states is nearly one-dimensional at a sufficiently high frequency, at low frequencies below a few THz this approximation is poor, necessitating the use of the anisotropic Debye model.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The group velocities of phonons all point along the chain axis.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    The model-predicted dependence of thermal conductivity versus grating period on temperature is difficult to discern considering the experimental uncertainty.

    “In particular, the dependence of the thermal conductivity versus grating period on temperature predicted by the model is difficult to discern considering the experimental uncertainty and will be the topic of future study.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    The decrease in mean free path at frequencies exceeding about 5.5 THz is consistent with the increase in broadening reported in inelastic X-ray scattering, although the increase occurred at higher frequencies in their data.

    “The decrease in MFP at frequencies exceeding ∼5.5 THz is also consistent with the increase in broadening reported in IXS42, although this increase occurred at higher frequencies in their data.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [42] Mermet, A., David, L., Lorenzen, M. & Krisch, M. Inelastic x-ray scattering from stretch-oriented polyethylene. J. Chem. Phys. 119, 1879–1884 (2003). source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationreasoning

    The PPMS thermal conductivity represents an average over a larger spatial dimension than transient grating spectroscopy, which may account for the slightly lower values obtained from PPMS at around 100 K.

    “We note that the PPMS thermal conductivity represents an average value over a larger spatial dimension than that in TG (∼5 mm sample length in PPMS versus 500 μm beam diameter in TG), which may account for the slightly lower values obtained from PPMS at around 100 K.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Prior mean free path values for oriented polyethylene at around 1 THz are about 80 nm for DR 40 and about 60 nm for DR 6 at 10 K.

    “For frequencies around 1 THz, prior values inferred from literature data using the dominant phonon approximation at cryogenic temperatures are ∼80 nm using κ ~ 0.34 Wm−1 K−1 for DR 40 (ref. 73), as estimated using LA specific heat of ∼2.8 × 10−4 J cm−3 K−1 at 10 K using the model described above. This value is comparable to an estimated value of ∼60 nm for DR 6 at 10 K (ref. 16).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [73] Nysten, B., Gonry, P. & Issi, J.-P. Intra-and interchain thermal conduction in polymers. Synth. Metals 69, 67–68 (1995). Proceedings of the International Conference on Science and Technology of Synthetic Metals. source
    • cites [16] Mergenthaler, D. B. & Pietralla, M. Heat conduction in highly oriented polyethylene. Z. Phys. B Condens. Matter 94, 461–468 (1994). source

  • May combine two claims.

    Interpretationown data

    Heat conduction in disentangled UHMWPE is due to longitudinal atomic vibrations that are ballistic within the extended crystal phase, scattered primarily by reflections at the boundaries between the crystals.

    “We infer that heat conduction in disentangled UHMWPE is due to longitudinal atomic vibrations that are ballistic within the extended crystal phase, scattered primarily by reflections at the boundaries between the crystals.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    All these prior mean free path values are comparable to but distinctly smaller than the present value, expected as the present samples exhibit higher thermal conductivity.

    “All of these values are comparable to but distinctly smaller than the present value, expected as the present samples exhibit higher thermal conductivity.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    Heat capacity measurements were attempted but were not successful owing to experimental difficulties in mounting the sample.

    “Heat capacity measurements were attempted but were not successful owing to experimental difficulties in mounting the sample.”
    Quote in the paperNot a substantial claim
55 of 55

  • The authors state this as an assumption.

    One-dimensional heat transfer can be assumed in the interpretation of the transient grating signal.

    “Considering that the grating periods used in the present work are around an order of magnitude smaller than the cross-plane length scales, one-dimensional heat transfer was assumed in the interpretation of the TG signal.”

  • The authors state this as an assumption.

    The heat-carrying atomic vibrations can be treated as usual phonons in a crystal, with disordered regions serving as perturbations that induce scattering.

    “Therefore, we treat the heat-carrying atomic vibrations as the usual phonons in a crystal, with the disordered regions serving as pertubations that induce scattering.”

  • The authors state this as an assumption.

    Any temperature dependence of the phonon mean free paths can be neglected at first order.

    “indicating that any temperature-dependence of the MFPs can be neglected at first order.”

  • The authors state this as an assumption.

    The group velocities of phonons all point along the chain axis.

    “The marked elastic anisotropy of PE can be accounted for to good approximation by assuming the group velocities all point along the chain axis15.”

  • The paper relies on this without support.

    The 1 wt% Au nanoparticles in the samples do not significantly affect the measured thermal conductivity of the polyethylene films.

    “Although our samples contained Au nanoparticles, we here note that the heat capacities of gold on a mass basis are smaller by a factor of 4–10 compared to that of the PE (at 300 K, 0.13 in ref. 79 vs. 1.75 J g−1 K−1 in ref. 61). The contribution of 1 wt% of the Au to the total heat capacity in our sample will therefore be negligible.”

  • The paper relies on this without support.

    The heat capacity of the disentangled UHMWPE samples is adequately represented by the heat capacities from ref. 61.

    “Therefore, heat capacities from ref. 61 were used.”
6 of 6

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

  • Stated heat-capacity ratio does not match the 300 K values

    Minor

    At 300 K, the stated PE and gold heat capacities have a ratio of 1.75/0.13 ≈ 13.46, outside the claimed factor of 4-10.

    Reported 10 · recomputed 13.461538

1 of 1

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Authors
Kim, T., Drakopoulos, S. X., Ronca, S., & Minnich, A. J.
Affiliations
  • California Institute of Technology (US)
  • Loughborough University (GB)
Corresponding author
Minnich, Austin J.
ORCID
Venue
Nature Communications
Publisher
Springer Science and Business Media LLC
Published
2022-05-04
Volume
13
Issue
1
Pages
2452-2452
ISSN
2041-1723 (ISSN-L)
DOI
10.1038/s41467-022-29904-2
PMC
PMC9068786
OpenAlex
W3215901113
Semantic Scholar
a81ff902c86158b05a7ef06c2631c95f8d168f1e
Cited by
63
References
84
Citations by year
2026: 12 · 2025: 21 · 2024: 18 · 2023: 10 · 2022: 2
FWCI
3.42
Type
journal article
Language
en
Open access
Licence
Locations
  • Nature Communications (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • PubMed Central (submittedVersion, cc-by)
  • CaltechAUTHORS (California Institute of Technology) (submittedVersion, cc-by)
  • RePEc: Research Papers in Economics (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
  • arXiv (Cornell University) (cc-by)
Funders
United States Department of Defense | United States Navy | Office of Naval Research (N-00014-18-1-2101)
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
ultra-high molecular weight polyethylene, thermal conductivity, ballistic phonons, mean free path, draw ratio, transient grating spectroscopy, heat carrier, polymer crystallization

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-20.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-20.

Cited sources are checked by gpt-6-sol.

Statistics and arithmetic are recomputed, not judged.

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