Low-temperature thermal conduction in particle-dispersed polyethylene

Abstract

The thermal diffusivity, and specific heat, of polyethylene (76% crystallinity) containing dispersed particles (1%–15% volume fraction) of SiO2 (diameter d=7,16,40 nm; 1,5,10 μm), Fe (d=27 nm), Cu (d=53 nm), and Ag (d=140 nm) have been measured using the laser flash method, and the thermal relaxation method, in the temperature range of 4.2–300 K, and the thermal conductivity was derived from the two quantities. The thermal conductivity was decreased by the addition of particles, and the decrease was more remarkable at lower temperatures for smaller particles. The boundary thermal resistance between the particles and the medium was derived from the change of conductivity due to the nm-diameter dispersed particles. The boundary resistance was independent of the size and the volume fraction of the particles, and was shown to be inversely proportional to the phonon specific heat of particle-dispersed medium in over a wide range of temperatures. The phonon Debye temperature and the strength of the boundary thermal resistance were determined by analyzing the data, and obtained results were quite reasonable.