ma6b01964_si_001.pdf (3.64 MB)
Synergistic Toughening of Epoxy Modified by Graphene and Block Copolymer Micelles
journal contribution
posted on 2016-12-09, 17:51 authored by Tuoqi Li, Siyao He, Andreas Stein, Lorraine F. Francis, Frank S. BatesBinary composites formed by individually
mixing exfoliated graphene
oxide modified with amine-terminated poly(butadiene–acrylonitrile)
(GA) and a spherical micelle forming poly(ethylene oxide)-b-poly(ethylene-alt-propylene) (OP) diblock
copolymer with a thermoset epoxy, and the associated GA/OP/epoxy ternary
composites, were prepared and studied as a function of the molecular
weight Mc between cross-links. The rigid
GA filler dispersed well in the cured epoxies as established by transmission
electron microscopy (TEM). The toughening efficacy of GA alone was
found to depend strongly on the modifier concentration and the matrix
cross-link density with an optimal 1.7-fold increase in the critical
strain energy release rate (GIc) over
the neat epoxy obtained with a 0.04 wt % loading in the most lightly
cross-linked (Mc = 6100 g/mol) material.
Addition of 5 wt % OP to this epoxy resin enhanced GIc by a factor of 12. Combining the hard GA and soft OP
modifiers at the same loading levels (0.04 and 5 wt %, respectively)
resulted in 18 times the GIc of the unmodified
material, a 31% improvement over the effect anticipated by simple
addition of the fracture properties of the binary composites. Decreasing Mc to 700 g/mol eliminated this synergistic effect
while reducing the overall improvement in GIc to just 3 times that of the neat epoxy. Topological features on
the fracture surfaces, imaged using a scanning electron microscope
(SEM), suggest that the synergistic toughening of the GA/OP/epoxy
ternary composite involves concurrent mechanisms operating on different
length scales, including micelle cavitation and graphene debonding,
resulting in simultaneous shear yielding, crack pinning, and crack
deflection.