  A comprehensive study has been undertaken on the dimensional swelling of
graphene-reinforced elastomers in liquids. Anisotropic swelling was observed
for samples reinforced with graphene nanoplatelets (GNPs), induced by the
in-plane orientation of the GNPs. Upon the addition of the GNPs, the diameter
swelling ratio of the nanocomposites was significantly reduced, whereas the
thickness swelling ratio increased and was even greater than that of the
unfilled elastomers. The swelling phenomenon has been analyzed in terms of a
modification of the Flory-Rhener theory. The newly-derived equations proposed
herein, can accurately predict the dependence of dimensional swelling (diameter
and thickness) on volume swelling, independent of the type of elastomer and
solvent. The anisotropic swelling of the samples was also studied in
combination with the evaluation of the tensile properties of the filled
elastomers. A novel theory that enables the assessment of volume swelling for
GNP-reinforced elastomers, based on the filler geometry and volume fraction has
been developed. It was found that the swelling of rubber nanocomposites induces
a biaxial constraint from the graphene flakes.
