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Abstract
Different types of graphene-related materials (GRM) are industrially available and have been exploited for thermal conductivity enhancement in polymers. These include materials with very different features, in terms of thickness, lateral size and composition, especially concerning the oxygen to carbon ratio and the possible presence of surface functionalization. Due to the variability of GRM properties, the differences in polymer nanocomposites preparation methods and the microstructures obtained, a large scatter of thermal conductivity performance is found in literature. However, detailed correlations between GRM-based nanocomposites features, including nanoplatelets thickness and size, defectiveness, composition and dispersion, with their thermal conductivity remain mostly undefined. In the present paper, the thermal conductivity of GRM-based polymer nanocomposites, prepared by melt polymerization of cyclic polybutylene terephtalate oligomers and exploiting 13 different GRM grades, was investigated. The selected GRM, covering a wide range of specific surface area, size and defectiveness, secure a sound basis for the understanding of the effect of GRM properties on the thermal conductivity of their relevant polymer nanocomposites. Indeed, the obtained thermal conductivity appeares to depend on the interplay between the above GRM feature. In particular, the combination of low GRM defectiveness and high filler percolation density was found to maximize the thermal conductivity of nanocomposites.
Highlights
The management of heat transport has progressively become a challenging problem owing to the miniaturization of products, especially in electronics [1]
Different methods have been used to evaluate the defectiveness of graphene-related materials (GRM), including, thermogravimetric analysis [104], X-ray diffraction [15,105], X-ray photoelectron spectroscopy [104,106] and, most importantly, Raman spectroscopy [107,108], the latter being the only technique able to provide a wealth of information related to GRM quality in a few minutes
The shape of the G’ peak might help evaluating the number of layers in multilayer graphene, but applicability is limited to a few layers [109] and this method cannot be exploited in assessing thickness of graphite nanoplatelets (GNP)
Summary
The management of heat transport has progressively become a challenging problem owing to the miniaturization of products, especially in electronics [1]. Chemical functionalization on graphene and related materials have been proposed and exploited for the enhancement of thermal transfer at interfaces between GRM as well as between GRM and the polymer matrix in nanocomposites. Computational studies by molecular dynamics [46,47,48] suggested an increase in thermal conductance when short chains covalently linked to the GRM are strongly interacting with the polymer matrix Both covalent and non-covalent functionalization were exploited to promote dispersion of GRM as well as possibly enhancing the thermal conductance at interfaces, demonstrating significantly enhanced thermal conductivity for nanocomposites prepared with functionalized GRM, compared with their pristine counterparts [49,50,51,52]. Nanomaterials 2020, 10, 2167 identifying a correlation between nanocomposites thermal conductivity, the GRM structural features and their organization into a percolating network
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