The
details of the curing process of epoxy resins are notoriously
difficult to ascertain, hampering polymer matrix composite manufacturing.
Here, the curing of a series of six epoxy resins containing dilute
spherical nanoparticles was investigated via X-ray
photon correlation spectroscopy (XPCS). The resin formulation was
varied to achieve a range of crosslink densities and topologies. Prior
to gelation, the viscosities obtained from XPCS agreed with bulk rheology.
A clear dynamic transition was detected in all samples, where the q-scaling changes from approximately q
2.2 to q
1, indicating a transition
from sub-diffusive to ballistic-like nanoparticle motion. For the
samples with a high crosslink density, this change was abrupt and
coincided with gelation, and there was no evidence of crosslink heterogeneity.
Chain entanglement played a role in the transition for samples with
lower crosslink density. This work reveals the potential of XPCS to
deliver new quantitative insights into the curing process of thermosetting
resins.