The role of phonon focussing and structure scattering in oriented semicrystalline polymers

Pietralla, M.; Weeger, R. M.; Mergenthaler, D. B.

doi:10.1007/bf01313666

Cited by 10 publications

(16 citation statements)

References 32 publications

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“…The contours are similar to those in Ref. [20] corresponding to the quasitransverse acoustic branch. On the other hand, Fig.…”

Section: Resultssupporting

confidence: 83%

“…We observe this effect throughout the Brillouin zone, irrespective of the plane for which the isoenergy contours are plotted. This phenomenon resembles the degree of focusing calculated for quasilongitudinal acoustic branches [20,21], but in PT the optical branches are also focused.…”

Section: Resultssupporting

confidence: 79%

“…Second, we examine previous treatments of phonon focusing in anisotropic solids. Many previous works employed the Debye approximation because of the assumption of that acoustic phonons dominate the thermal transport [20,21]. Our work demonstrates that phonon focusing has a dramatic effect on both acoustic and optical phonons for nearly all phonons regardless of wave vector because dispersive optical modes persist throughout the thermal phonon frequencies.…”

Section: Discussionmentioning

confidence: 69%

“…We now discuss our results in the context of prior work on polymer crystals. First, many works use an average lifetimes or average mean free paths to analyze thermal transport in polymer crystals due to computational or experimental limitations [17,20]. Using our ab initio calculations, we are able to assess the accuracy of these approximations.…”

Section: Discussionmentioning

confidence: 99%

“…Since the group velocity is the gradient of frequency with respect to wave vector, an ellipsoidal surface will have group velocity vectors preferentially oriented along the short axis of the ellipse. However, many previous works studying phonon focusing as it pertains to thermal conductivity make simplifying assumptions, such as the use of a Debye model for only low-wave-vector, low-frequency acoustic modes [20,21]. Because of these assumptions, it is difficult to determine the intrinsic upper bounds of thermal conductivity in polymer crystals or assess the role phonon focusing plays in setting this upper bound.…”

Section: Introductionmentioning

confidence: 99%

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Thermal transport and phonon focusing in complex molecular crystals: Ab initio study of polythiophene

2019

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Thermally conductive molecular crystals are of fundamental interest because they are unlike typical complex crystals, which conduct heat poorly owing to their large phonon scattering phase space. While molecular crystals with high thermal conductivity in the range of tens of Wm −1 K −1 have been known experimentally for decades, their intrinsic upper limits for thermal conductivity are unclear. Ab initio methods that have been successfully applied to simple crystals have proved difficult to adapt to molecular crystals due to quantum nuclear motion and their complex primitive cells. Here, we report the thermal transport properties of crystalline polythiophene with 28 atoms per primitive cell using an ab initio approach that rigorously includes finite-temperature anharmonicity and quantum nuclear effects. The calculated room temperature thermal conductivity is 198 Wm −1 K −1 along the chain axis, a high value that arises from exceptional phonon focusing along the chain for both acoustic and optical branches for nearly all wave vectors and despite short lifetimes in the picosecond range. Our finding, along with other recent ab initio studies of polyethylene, suggests that the intrinsic upper bounds for the chain axis thermal conductivity of polymer crystals may exceed 100 Wm −1 K −1 .

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“…The contours are similar to those in Ref. [20] corresponding to the quasitransverse acoustic branch. On the other hand, Fig.…”

Section: Resultssupporting

confidence: 83%

Section: Resultssupporting

confidence: 79%

Section: Discussionmentioning

confidence: 69%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%