Significance of epoxy network properties for the toughening effect of flaky and fullerene‐like WS₂ nanoparticles

Abstract

This work deals with the toughening effect of flaky WS 2 and fullerene-like WS 2 (IF-WS 2 ) nanoparticles on epoxy with varying network properties. Reducing the amount of curing agent resulted in decreased crosslink density as measured by dynamic-mechanic analysis and double-quantum nuclear magnetic resonance spectroscopy. Although that lead to moderate changes in the epoxy's tensile properties, its fracture toughness dropped drastically, probably due to an increased defect fraction. IF-WS 2 could be dispersed significantly more effectively within epoxy resin than flaky WS 2 , possibly due to its spherical shape, but caused less toughening. IF-WS 2 tended to debond from the epoxy, while flaky WS 2 introduced more secondary cracks. Both increased the fracture toughness of the (brittle) substoichiometric, but not that of the (tough) stoichiometric epoxy, possibly due to their interaction with molecular defects. Irrespective of which mechanism resulted in the toughening effect, its effectiveness depended strongly on the epoxy matrix.

Atomic‐Force Microscopy Investigations on Fracture Surfaces of Inorganic, Fullerene‐Like WS2(IF‐WS2)–epoxy Nanocomposites

“…According to the manufacturer, the primary particles have diameters of 50 nm to 150 nm and they consist of 10 to 100 WS 2 layers, with an interlayer spacing of 0.62 nm. Transmission electron microscopy (TEM) images of the IF‐WS 2 used in this work indicate NP diameters ranging between about 70 nm and 150 nm consistent with the manufacturer's data …”

“…The IF‐WS 2 NP powder (trade name Nanolub R ) was obtained from the same supplier ( NanoMaterials Ltd ., Israel) as that used in research published by others earlier . According to the manufacturer, the primary particles have diameters of 50 nm to 150 nm and they consist of 10 to 100 WS 2 layers, with an interlayer spacing of 0.62 nm.…”

“…When used as an additive to polymers, it was shown to not only considerably improve their tribological properties, but also their fracture toughness . However, this toughening effect seems to depend strongly on the particular epoxy system investigated, that is to say, on the particular combination of epoxy resin and curing agent and the respective amounts thereof. The way NPs affect the fracture behavior of polymers can be investigated best from microscopic images of the fracture surfaces, primarily gathered with scanning electron microscopy (SEM) and with even more quantitative information on the surface roughness by atomic‐force microscopy (AFM) .…”

Interfacial interaction and the fracture toughness (KIC) trends in epoxy nanocomposites filled with functionalized graphene‐based fillers

“…These results show good repeatability as well. Thus it appears that the interpretations of interfacial interactions from DMA [29,31] and fractographic analysis [8, As has been already discussed, the crosslink density is strongly influenced by the curing agent [33] which in turn also influences the fracture toughness (K IC ) of an epoxy system [19,35]. Hence, the choice of a highly crosslinked and more brittle neat epoxy system (Sial DETA cured, 11.1 phr) has been made to study the significance of K IC of the neat matrix on the toughness of the nanocomposites.…”

“…It is expected that the surface functionalities present on both the fillers will promote filler‐matrix interfacial interaction . There is also considerable argument in literature on the influence of the neat epoxy matrix on their toughenability , with claims that not all epoxy matrices can be toughened . Processing nanocomposites cured with an aliphatic amine based curing agent would help understand the viability of this premise in view of filler‐matrix interfacial interaction.…”