Nanocomposites made up of polymer matrices and carbon nanotubes are a class of advanced materials with great application potential in electronics packaging. Nanocomposites with carbon nanotubes as fillers have been designed with the aim of exploiting the high thermal, electrical and mechanical properties characteristic of carbon nanotubes. Heat dissipation in electronic devices requires interface materials with high thermal conductivity. Here, current developments and challenges in the application of nanotubes as fillers in polymer matrices are explored. The blending together of nanotubes and polymers result in what are known as nanocomposites. Among the most pressing current issues related to nanocomposite fabrication are (i) dispersion of carbon nanotubes in the polymer host, (ii) carbon nanotube-polymer interaction and the nature of the interface, and (iii) alignment of carbon nanotubes in a polymer matrix. These issues are believed to be directly related to the electrical and thermal performance of nanocomposites. The recent progress in the fabrication of nanocomposites with carbon nanotubes as fillers and their potential application in electronics packaging as thermal interface materials is also reported.

Nanocomposites were fabricated by using a commercial two part epoxy as a matrix and multiwalled carbon nanotubes, graphite fibers and boron nitride platelets as filler materials. Multiwalled carbon nanotubes (MWCNTs) that were produced by chemical vapor deposition were found to produce nanocomposites with better thermal diffusivity and thermal conductivity than the MWCNTs that were produced by the combustion method. Compared to the MWCNTs produced by both methods and graphite fibers, boron nitride produced nanocomposites with the highest thermal conductivity. Specific heat capacity was measured by using differential scanning calorimetry and thermal diffusivity was measured by using the laser flash.

THERMAL CONDUCTIVITIES of most pure organic liquids vary with temperature in the manner shown in Figure 1, where the abscissa indicates the fractional distance of the saturated liquid from melting point to critical point. On the scale the normal boiling point is usually around e = %. During the past 40 years the number of measurements of liquid conductivities has greatly increased, but all except a few fall in the region below the boiling point, where the variation with temperature is practically linear. The part of Figure 1 above e = % is based on data for eleven liquids obtained by five observers (1-3, 16, 23). Conductivity in the absence of measured values can a t present be calculated by one or another of varyingly successful methods (11, 20) as long as one does not go beyond the linear region (0 less than approximately 0.7). Because of the scarcity of data on any liquid properties a t higher temperatures, none of the methods of prediction has been tested properly for 8 > 0.7. The purpose of the present work was to measure the conductivities of some representative compounds a t these higher temperatures, to establish more firmly the general behavior in this region and to aid in the development of methods of prediction in the absence of direct data. APPARATUSFor the conductivity measurements a steady-state, thinfilm apparatus was used. The conducting liquids were contained in three concentric annular spaces (Figure 2). The cylindrical shape was chosen for convenient control of heat losses as well as adaptability to a high-pressure system. The principle of the thin film to control convection is well known, having been applied by most previous workers, regardless of the shape of the apparatus. Three films in series were used in this work, to increase the magnitude of the basic temperature drop and its accuracy of measurement while meeting Kraussold's criterion for absence of convection.The apparatus was made entirely of stainless steel to km k hc IS OF THE ORDER OF$ km 0 I Figure 1. Typical variation of thermal conductivity of a liquid with temperature QLAm N E WQlWO RESISTME WIRE REFRACTORY TueE THERMOCOUPLE WELL Figure 3. High-temperature experimental arrangement -+

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