The interface between filler and matrix has long been
a critical
problem that affects the thermal conductivity of polymer composites.
The effects of the interface on the thermal conductivity of the composite
with low filler loading are well documented, whereas the role of the
interface in highly filled polymer composites is not clear. Here we
report on a systematic study of the effects of interface on the thermal
conductivity of highly filled epoxy composites. Six kinds of surface
treated and as received AlN particles are used as fillers. Three kinds
of treated AlN are functionalized by silanes, i.e., amino, epoxy,
and mercapto group terminated silanes. Others are functionalized by
three kinds of materials, i.e., polyhedral oligomeric silsesquioxane
(POSS), hyperbranched polymer, and graphene oxide (GO). An intensive
study was made to clarify how the variation of the modifier would
affect the microstructure, density, interfacial adhesion, and thus
the final thermal conductivity of the composites. It was found that
the thermal conductivity enhancement of the composites is not only
dependent on the type and physicochemical nature of the modifiers
but also dependent on the filler loading. In addition, some unexpected
results were found in the composites with particle loading higher
than the percolation threshold. For instance, the composites with
AlN treated by the silane uncapable of reacting with the epoxy resin
show the most effective enhancement of the thermal conductivity. Finally,
dielectric spectroscopy was used to evaluate the insulating properties
of the composites. This work sets the way toward the choice of a proper
modifier for enhancing the thermal conductivity of highly filled dielectric
polymer composites.
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