A detailed study of α-relaxation in epoxy/carbon nanoparticles composites using computational analysis

Abstract

Abstract. Nanocomposites were fabricated based on diglycidyl ether of bisphenol A (DGEBA), cured with triethylenetetramine (TETA) and filled with: a) high conductivity carbon black (CB) and b) amino-functionalized multiwalled carbon nanotubes (MWCNTs). The full dynamic mechanical analysis (DMA) spectra, obtained for the thermomechanical characterization of the partially cured DGEBA/TETA/CB and water saturated DGEBA/TETA/MWCNT composites, reveal a complex behaviour as the !-relaxation appears to consist of more than one individual peaks. By employing some basic calculations along with an optimization procedure, which utilizes the pseudo-Voigt profile function, the experimental data have been successfully analyzed. In fact, additional values of sub-glass transition temperature (T i ) corresponding to subrelaxation mechanisms were introduced besides the dominant process. Thus, the physical sense of multiple networks in the composites is investigated and the glass transition temperature T g is more precisely determined, as the DMA !-relaxation peaks can be reconstructed by the accumulation of individual peaks. Additionally, a novel term, the index of the network homogeneity (IH), is proposed to effectively characterize the degree of statistical perfection of the network.

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

“…) and the increase in the value of λ from DMA (Fig. ) the observed reduction in K IC of the nanocomposites is an unexpected result and is the topic of discussion here. Internal stresses are known to develop in epoxy composites during cooling down from its cure temperature.…”

“…These results show good repeatability as well. Thus it appears that the interpretations of interfacial interactions from DMA and fractographic analysis do not directly correlate to the fracture toughness trends in the present nanocomposites.…”

“…Both the E′ and tan δ curves show smooth transition from glassy to rubbery state (Fig. a and b) with no signs of any sub‐T g peaks indicating a near perfect network . The height of the tan δ peak is observed to reduce from 1.07 for the neat epoxy to 1.00–1.03 for the nanocomposites.…”

“…b) is seen to marginally increase upon GO addition in the Sial DETA cured epoxies but the tan δ curves are almost identical for the neat and the filled epoxies (peak height ∼0.57 in all cases).The reduced tan δ peak height (Fig. a) for the Sial T‐403 cured epoxies is indicative that addition of fillers affect the cross linking in these matrices more than in the Sial DETA cured ones . Lesser and Crawford reported that changing the type of amine based curing agents result in the change in λ (curing agent's molecular structure plays a significant role in this) as well as in T g of the epoxy systems.…”

“…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.…”