Thermal Transport on Graphene-Based Thin Films Prepared by Chemical Exfoliations from Carbon Nanotubes and Graphite Powders

Jian-De Xie,Si-Yong Gu,Houan Zhang

doi:10.3390/coatings7090138

Abstract

Thermal conductivities (k) of different graphene nanosheet (GN)-based heat sinks are investigated within the temperature range of 323–423 K. One- and two-step modified Hummers’ methods are adopted to chemically exfoliate GNs from two kinds of carbon precursors: carbon nanotubes (CNTs) and graphite powders. The two-step method offers an improved exfoliation level of GN products, especially for the CNT precursor. Experimental results show that the GN-based heat sink—exfoliated from graphite powders after the two-step approach—delivers an enhanced k value to 2507 W/m K at 323 K, as compared to the others. The k value is found to be a decreasing function of the porosity of the heat sink, revealing the importance of solid/void fraction (i.e., volumetric heat capacity). The improved thermal efficiency mainly originates from the long phonon mean free path and the low void fraction of GN-based heat sinks, thus inducing highly efficient thermal transport in the GN framework.

Highlights

One- and two-dimensional carbon nanostructures—especially carbon nanotubes (CNTs) and graphene nanosheets (GNs)—have attracted a great deal of scientific and technological attention, owing to their extraordinary electrical and thermal properties, exhibiting their applicable feasibility [1,2]
High-resolution transmission electron microscopy (HR-TEM) micrographs for GN samples prepared by the one- and two-step Hummers’ method from CNTs and graphite powders are illustrated in Figure 1c–f, showing different morphologies
Regarding the two-step approach, the GN–CNT2 sample looks like a broken graphene layer, in which the tubular-type structure was unzipped through the two-step exfoliation route

Summary

Introduction

One- and two-dimensional carbon nanostructures—especially carbon nanotubes (CNTs) and graphene nanosheets (GNs)—have attracted a great deal of scientific and technological attention, owing to their extraordinary electrical and thermal properties, exhibiting their applicable feasibility [1,2]. Both CNTs and GNs have been demonstrated to display high theoretical thermal conductivities (k), heralding beneficial applications in heat exchangers and thermal management systems. To resolve the above problems, one strategy is to adopt nanostructural carbon materials (e.g., GNs) as heat sinks, capable of conducting heat efficiently and preventing structural damage to electronic components [5]

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Conclusion