posted on 2023-12-01, 11:20authored byHaley
K. Beech, Shu Wang, Devosmita Sen, Dechen Rota, Tatiana B. Kouznetsova, Akash Arora, Michael Rubinstein, Stephen L. Craig, Bradley D. Olsen
The fracture of polymer networks is tied to the molecular
behavior
of strands within the network, yet the specific molecular-level processes
that determine the mechanical limits of a network remain elusive.
Here, the question of reactivity-guided fracture is explored in otherwise
indistinguishable end-linked networks by tuning the relative composition
of strands with two different mechanochemical reactivities. Increasing
the substitution of less mechanochemically reactive (“strong”)
strands into a network comprising more reactive (“weak”)
strands has a negligible impact on the fracture energy until the strong
strand content reaches approximately 45%, at which point the fracture
energy sharply increases with strong strand content. This aligns with
the measured strong strand percolation threshold of 48 ± 3%,
revealing that depercolation, or the loss of a percolated network
structure, is a necessary criterion for crack propagation in a polymer
network. Coarse-grained fracture simulations agree closely with the
tearing energy trend observed experimentally, confirming that weak
strand scissions dominate the failure until the strong strands approach
percolation. The simulations further show that twice as many strands
break in a mixture than in a pure network.