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In this paper, thermal properties of composites are investigated numerically and experimentally. In the numerical study, finite-elements method is used to modelize heat transfer and to calculate the Effective Thermal Conductivity (ETC) of the composite for three elementary cells, such as simple cubic (SC), body-center cubic (BCC) and face-center cubic (FCC). The effect of the filler concentrations, the ratio of thermal conductivities of filler to matrix material and the Kapitza resistance of the contact inclusion/matrix on the effective conductivity was investigated. A periodical method was used to measure simultaneously thermal conductivity, specific heat and diffusivity of the composite consisting of epoxy resin matrix filled with brass spheres. A comparison between the numerically calculated thermal conductivities, measured and analytical ones for various samples is made and the significance of the findings will be discussed in the paper. [ABSTRACT FROM AUTHOR]

Abstract: The addition of thermally conductive particles is an effective way to increase thermal conductivity of polymers. For highly filled composites and therefore for a high effective thermal conductivity, the heat transfer at the matrix/particle interface becomes a key point to obtain further improvement. However the interfacial thermal resistance R i between particles and matrix is difficult to measure because of the low sensitivity of temperature to R i and because of the small size of the particles. A setup has been developed to measure R i between nickel wires (fiber-like particles) of a few tens micrometer diameter and a polymer matrix. The temperature measurement of the heating wire associated with a thermal model allowed to estimate values of R i between 0.3×10−5 and 1.6×10−5 m2 KW−1 and for various wire diameters and sample temperatures. Some R i measurements have been validated using a thermo-elastic model. [Copyright &y& Elsevier]

The addition of conductive filler in a polymer matrix is an effective way to increase the thermal conductivity of the plastic materials, as required by several industrial applications. All quantitative models for the thermal conductivity of heterogeneous media fail for heavily filled composites. The percolation theory allows good qualitative predictions, thus selecting a range for some qualitative effects on the thermal conductivity, and providing a way to choose a range for some experimental parameters. The design of such composite materials requires a study of its thermal features combined with different mechanical, ecological, safety, technical, and economical restrictions. A specific small guarded hot plate device with an active guard, conductive grease layer, and controlled variable pressure was used for measurement of the transverse thermal conductivity on 15 mm sided samples of composite parts. Extensive thermal and composition measurements on filled thermoplastics show that the conductivity of the filler, its size and shape, and its local amount are, with the degree of previous mixing, the main factors determining the effective conductivity of composites. For injection-molded polybutylene terephtalate plates, the best filler is the short aluminum fiber. With fibers of 0.10 mm diameter, it is possible to obtain conductivities larger by factors of 2, 6, and 10 than those of polymer for aluminum contents of 20, 42, and 43.5 vol%, respectively. [ABSTRACT FROM AUTHOR]

Thermal properties of single walled carbon nanotube (SWNT)/polymethylmetacrylate composite thick films have been investigated at room temperature. The introduction of ∼7% SWNT into the polymer matrix enhances the thermal conductivity of the composite by 55% while the electrical conductivity increases by several orders of magnitude. Despite this difference, we show that the (moderate) enhancement of the thermal conductivity is quantified by the percolation of the SWNT network. A thermal conductivity of the SWNT network of ∼55 W/m K is estimated. [ABSTRACT FROM AUTHOR]