Metallic Nanowire-Polymer Composite as Thermal Interface Material
Authors: Razeeb Kafil M. , Hasan Maksudul , Gautam Devendraprakash , Dalton Eric 
Published: February 2020

Thermal properties of nanocomposites have been an area of intensive research for the past decade due to its potential application in electrical interconnection, heat transfer and electronics cooling. Considerable progress has been made in fabricating nanocomposite materials using different filler materials and polymer. Nanocomposites made from nanowires and nanotubes are the subject of recent interest due to the elongated one dimensional shape of the filler materials which shows unique properties e.g. lower percolation threshold, anisotropy, and other one dimensional properties. Most of the reported works used different forms of carbon allotropes (single wall, multiwall, fiber, etc.) or oxide and metallic nanowires as filler materials and mixing with polymer. Early work on carbon nanotube (CNT) based fillers focused on mechanical mixing of nanotubes with polymer and thereby achieving higher thermal conductivity as compared to polymer. Vertically aligned carbon nanotube and fiber is also investigated as thermal interface material [1]. However, the possibility of inadvertently incorporating contaminating impurities, the existence of voids between CNTs, and the growth conditions of CNT arrays greatly affect the effective thermal conductivity of CNTs, typically resulting in a thermal interface material (TIM) with a large performance uncertainty [2, 3]. Thermal properties of graphene-metal-polymer composite was thoroughly investigated in recent years [4]. Similarly, metallic nanowires both dispersed and vertically aligned were also proposed as filler materials in the metal-polymer nanocomposites [5, 6].
Recently, we have demonstrated that the elongated metallic nanowires and nanowire based composites can act as thermal conduit between two surfaces and thereby able to transfer heat more efficiently as compared to carbon nanotube based composite materials [5]. However, it has been observed that heat transport through these one dimensional filler materials is a complex subject of intensive research, which includes different thermal transport mechanism depending on constituent material (whether it is an electrical conductor, semiconductor or insulator) as well its size, shape and the crystallinity [7]. This heat transfer mechanism was explained with a modified effective medium formulation based on Nan’s model [8]. Furthermore, it has been observed that modulus of the nanocomposite plays a vital role in the transferring heat when pressed between two surfaces and lower modulus composite conforms easily to the roughnesses of the mating surface [5].
In this work we investigate the thermal properties of metal (Cu and Sn) nanowire-polymer composites. The thermal diffusivity of the composites was measured using a Xenon flash thermal constant analyzer. A thermal impedance system is employed according to the modified ASTM D5470 standard to measure the thermal impedance of the composites. A thermal impedance of 9±1 °Cmm2W-1is achieved at a pressure of 100 kPa, which is 50% lower thermal impedance compared to the commercial TIM.
Acknowledgements
This work is financially supported by Enterprise Ireland under commercialization fund technology development program.Grant No. CFTD/2008/322.
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