The low-temperature thermal conductivity of polyethylene

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Abstract
Measurements are presented of the temperature variation between 2K and 100K of the thermal conductivity, kappa of several samples of extruded polyethylene. At high temperatures ( approximately 100K) there is an anisotropy in kappa , with the values measured parallel to the extrusion direction up to 5 times greater than those observed in the perpendicular direction. At low temperatures, on the other hand, there is much less variation in kappa and, at helium temperatures, the anisotropy is completely absent. In the direction of the extrusion the thermal resistance of the crystallites is assumed to be negligible, and the variation of kappa with T can be explained on the basis of a recent model for amorphous solids. At low temperatures, where the dominant phonon wavelengths are much greater, the anisotropy of the crystallites is not important, and measurements can be accounted for by the fluctuations in the sound velocity between the crystalline and amorphous regions.

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