Heat conduction in highly oriented polyethylene

Ballistic thermal phonons traversing nanocrystalline domains in oriented polyethylene

“…To place these results in context, we compare them with prior estimations and calculations for polymer crystals. Our measured MFPs are far longer than prior estimates based on anisotropic kinetic theory (6,21), which predicted MFPs of only tens of nanometers. We additionally compare our results with a recent ab initio calculation for a perfect PE crystal, which reported a κ of 164 W•m −1 •K −1 (28) at room temperature.…”

“…polymers | polyethylene | thermal conductivity | mean free path | ballistic transport T hermal conduction in oriented polymers is of intense interest as their thermal conductivities rival those of many covalent solids (1)(2)(3)(4). While unoriented polymers typically exhibit isotropic and low thermal conductivity, κ, on the order of 0.2 W•m −1 •K −1 (5), oriented polymers may have uniaxial thermal conductivity orders of magnitude larger due to conduction via stiff covalent bonds along the polymer backbone and phonon focusing effects (6). Early studies of the κ of polymers reported enhancements in oriented amorphous polymers (7) and oriented semicrystalline polymers like polyethylene (8)(9)(10) and polypropylene (2).…”

“…Early studies of the κ of polymers reported enhancements in oriented amorphous polymers (7) and oriented semicrystalline polymers like polyethylene (8)(9)(10) and polypropylene (2). Since then, numerous works have examined the many factors contributing to increased κ in a variety of oriented polymers, including amorphous polymers (11,12), polyethylene (1,3,6,(13)(14)(15)(16)(17)(18)(19), polyacetylene (20), and polymer fibers like Kevlar (21).…”

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

“…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 [63], as estimated using LA specific heat of ∼ 2.8 × 10 −4 Jcm −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 [16]. At higher frequencies ∼ 6 THz, IXS has been used to obtain a MFP of ∼ 50 nm for DR 5.5 [42], which is in reasonable agreement with the values inferred from transport studies.…”

“…The enhancement was attributed to various mechanisms including increased chain alignment along the drawing direction [7,14], phonon focusing in the elastically anisotropic crystalline phase [15,16], and increased crystallinity [12,17]. Recently, thermal conductivity values around 20 − 30 Wm −1 K −1 and 60 Wm −1 K −1 have been reported in PE microfibers [14,18] and nanofibers [19,20], respectively.…”