Thermal conductivity enhancement of graphene nanoplatelet/epoxy composites - Covalent functionalization with nitrene chemistry for reducing the interfacial thermal resistance

Polymer composites with high thermal conductivity are in strong demand for
efficient thermal management in many modern applications such as electronics,
batteries, aerospace structural materials, LED lightings, etc.
Nanocarbon fillers have recently attracted a lot of interest due to their extremely
high intrinsic thermal conductivity. Nevertheless, the effective thermal conductivity
achieved with nanocarbon-polymer composites is below the expectations. In
particular, at low fillers loading due to the large interfacial thermal resistance at the
nanocarbon-polymer interface.
Covalent functionalization of nanocarbons has been suggested to reduce the
interfacial thermal resistance in nanocarbon-polymer composites. However, large
scale covalent functionalization of nanocarbons is usually achieved with harsh
oxidizing conditions, causing a dramatic decrease of the intrinsic thermal
conductivity of the nanocarbon fillers.
In this thesis, we developed and optimized a non-disruptive covalent
functionalization for graphene nanoplatelets (GNP), based on nitrene chemistry. We
achieved unprecedented functionalization yields. The fillers functionalized by nitrene
chemistry produced a significant thermal conductivity enhancement (TCE)
compared to pristine and oxidized fillers. However, increasing the chain length or
introducing heteroatoms in the functional chain afforded reduced performances.
In parallel, we developed an innovative combination of SEM and µCT analyses
to afford an unprecedented description of nanocarbon-polymer composites. This
allowed us to elucidate the contradictory results, reported in the literature, on the
influence of the aggregation level and the geometrical parameters of the fillers on the
TCE. In this thesis we propose a novel and detailed description of the parameters
responsible of TCE in GNP-epoxy composites. Moreover, we demonstrate that
covalent functionalization of GNP by nitrene chemistry reduces the interfacial
thermal resistance in epoxy composites and improves the thermal conductivity.