posted on 2024-03-01, 08:03authored byB. Ruşen Argun, Antonia Statt
Polymer networks are widely used in applications, and
the formation
of a network and its gel point can be predicted. However, the effects
of spatial and topological heterogeneity on the resulting network
structure and ultimately the mechanical properties, are less understood.
To address this challenge, we generate in silico random networks of
cross-linked polymer chains with controlled spatial and topological
defects. While all fully reacted networks investigated in this study
have the same number of end-functionalized polymer strands and cross-linkers,
we vary the degree of spatial and topological heterogeneities systematically.
We find that spatially heterogeneous cross-linker distributions result
in a reduction in the network’s primary loops with increased
spatial heterogeneity, the opposite trend as observed in homogeneous
networks. By performing molecular dynamics simulations, we investigated
the mechanical properties of the networks. Even though spatially heterogeneous
networks have more elastically active strands and cross-linkers, they
break at lower extensions than the homogeneous networks and sustain
slightly lower maximum stresses. Their shear moduli are higher, i.e.,
stiffer, than theoretically predicted, and higher than their homogeneous
gel counterparts. Our results highlight that topological loop defects
and spatial heterogeneities result in significantly different network
structures and, ultimately, different mechanical properties.