Thermal conductivity of polymers

We have observed that the thernal conductivity of zincsulphide is increased by adding large particles of highly conducting diamond, but lowered by the addition of sub-micron size particles of diamond. This effect is explained in terms of the interfacial thermal resistance which becomes increasingly dominant as the particles becomes smaller (because that increases their surface to volume ratio). A phenomonological model in which the interface resistance is expressed as an effective Kapitza radius, ak, is presented. The conductivity of the composite is analyzed for different values of α, which is defined to be equal to the Kapitza radius divided by the particle radius. If α = 1, that is, the actual particle radius is equal to ak then the effective thermal conductivity of the particles is equal to that of the matrix. If α > 1, that is the particles are very small, then the contribution of the particles to the thermal conductivity of the composite is dominated by interfaces; if α < 1 then the bulk property of the particles is important. Our measurements yield ak ≈ 1.5 μm for the ZnS-diamond interface.

The effect of particle size on the thermal conductivity of ZnS/diamond composites

Thermal, mechanical and electrical properties of copper powder filled low-density and linear low-density polyethylene composites

The introductory and more elementary ideas and results of micromechanics of heterogeneous media are collected in the survey. The central problem under discussion is “homogenization.” It replaces such media by homogeneous ones, which behave macroscopically in the same way and possess certain gross effective properties. These properties are related in a complicated manner to the prescribed internal structure of the medium and their evaluation, in general, represents a profound challenge in any specific situation. A brief historical survey is given, underlying the reappearance of essentially the same “homogenization” quest in numerous guises and contexts over the last two centuries. Within the framework of the volume-averaging approach the basic notions are introduced and some of the central, now classical, results are then derived and discussed such as perturbation expansions, Hashin-Shtrikman’s bounds, variational estimates and Levin’s cross-property relation. A general “one-particle” scheme for approximate evaluation of the effective properties (in the static case) is detailed in its various implementations like selfconsistency, iterated limits and effective field. Illustrations concern conductivity, elasticity, and absorption phenomena in heterogeneous particulate media, as well as a simple self-consistent model for polycrystals’ homogenization.

/pdf/elementary-micromechanics-of-heterogeneous-media-1b5r6x54yb.pdf

Elementary Micromechanics of Heterogeneous Media

http://www.123seminarsonly.com/Seminar-Reports/2013-04/52623239-Tribology.pdf

Solid particle erosion wear characteristics of fiber and particulate filled polymer composites: A review

The thermal conductivity of composites made from epoxy-resin Epikote 828 with metal-powder fillers has been measured from 1.7 to 300K. The metals were Cu, Ag, Au, Al, Sn, Pb, stainless steel and bronze, and in almost all cases the particles were spherical or rounded. At 20K and above the thermal conductivity is independent of the particle size and is in good agreement with the relation of Meredith and Tobias (1960) (extension of Rayleigh's theory). Below 20K the thermal conductivity of the composite is lower than predicted by the theory especially for specimens containing smaller particles, and it can even be less than that of the unfilled resin. This is due to an acoustic mismatch of the phonons at the resin-particle interfaces. An effective particle conductivity which takes account of this mismatch can be computed, which when incorporated into the theory leads to reasonable agreement with experiment.

https://iopscience.iop.org/article/10.1088/0022-3727/9/4/017/pdf

F F T Araujo

Papers

The thermal conductivity of epoxy-resin/metal-powder composite materials from 1.7 to 300K