  In this work, we demonstrate that use of dimethylformamide (DMF) as a solvent
leads to better dispersion of graphene nanoplatelets in epoxy matrix compared
to acetone solvent, in turn leading to higher thermal conductivity
epoxy-graphene nanocomposites. While role of solvents in enabling superior
mechanical properties has been addressed before, outlined study is the first to
address the effect of solvents on thermal conductivity enhancement and provides
novel pathways for achieving high thermal conductivity polymer composite
materials. Uniform dispersion of graphene nanoparticles into epoxy can improve
thermal contact with polymer leading to superior interface thermal conductance
between polymer matrix and graphene. Organic solvents are typically employed to
achieve efficient dispersion of graphene into the epoxy matrix. In this study,
we compare the effect of two organic solvents, dimethylformamide (DMF) and
acetone, in terms of their efficiency in dispersing graphene into the epoxy
matrix and their effect on enhancing thermal conductivity of the composite. We
find that polymer-graphene composites made with DMF solvent show 44% higher
thermal conductivity compared to those made using acetone at 7 weight% filler
composition. Laser scanning confocal microscopy (LSCM) imaging reveals that
graphene-epoxy composites, prepared using DMF as solvent, exhibit more uniform
dispersion of graphene-nanoplatelets compared to the case of acetone with
acetone-based samples exhibiting up to 211% larger graphene agglomerations.
Comparison with effective medium theory reveals an almost 35% lower interface
thermal resistance between graphene and epoxy for DMF relative to acetone
prepared composite. These results provide fundamentally new avenues to achieve
higher thermal conductivity graphene-epoxy composites, of key importance for a
wide range of thermal management technologies.
