Influence of filler/matrix interactions on resin/hardener stoichiometry, molecular dynamics, and particle dispersion of silicon nitride/epoxy nanocomposites

Abstract

The addition of nanofillers can have a significant influence on the resin stoichiometry of thermosetting polymer systems. Based on differential scanning calorimetry (DSC) results, it is estimated that the inclusion of 2 and 5 wt% of silicon nitride nanofiller displaces the resin/hardener stoichiometry of an epoxy/amine network by 6.5 and 18%, respectively. Dielectric spectroscopy results confirm the above findings, in that the spectra of the nanocomposite samples were found to be equivalent to the spectra of unfilled samples when the above stoichiometric effect was taken into account. Therefore, this study provides clear evidence that the presence of a nanofiller can directly and significantly affect the curing process of an epoxy network. Consequently, this should always be considered when introducing nanofillers into thermosetting matrices. These results indicate the presence of covalent bonding between the nanoparticles and the surrounding polymer and, therefore, provide an opportunity to explore the influence of this bonding on the molecular dynamics of the polymer layer around the particles. However, the obtained DSC and dielectric spectroscopy results suggest that, in the system considered here, either the covalent bonding does not have an appreciable influence on the segmental dynamics of the polymer, as revealed by these techniques, or that the thickness of the affected layer is less than 1 nm and therefore too small to be distinguished from experimental uncertainties.

On the Dielectric Behavior of Amine and Anhydride Cured Epoxy Resins Modified Using Multi-Terminal Epoxy Functional Network Modifier

“…However, comparison of the molecular structure of TTE, which contains an unreactive methyl group, with the behavior of FNMs containing long alkyl chains reported in a previous work [34] suggests that the direct influence of TTE on free volume should be small, implying in turn, that alternative factors are at play. Indeed, Morgan et al [35] reported a local minimum in the macroscopic density at maximum T g , which they associated with geometric constraints imposed on segmental packing by the crosslinks, while Alhabil et al [36] suggested that the T g of epoxy resin systems is greatly influenced by the precise network topology that forms.…”

The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO2

“…One common feature present in all the nanocomposites is the emergence of a new dielectric relaxation that is associated with the SiO 2 (between 10 0 Hz and 10 3 Hz) as it is missing in pure epoxy ( Figure 8 b inset). This relaxation occurs at a lower frequency than the eminent β-relaxation, which is associated with the dipoles on the O-H groups in the epoxy chains (or possibly from any unreacted amine groups in the curing agent) [ 36 , 37 ]. The dipoles associated with this new relaxation are therefore ‘stiffer’ than the β-relaxation and are suspected to be related to interfacial polarization effects at the surfaces of the nanoparticle clusters that are formed.…”

Introducing particle interphase model for describing the electrical behaviour of nanodielectrics

“…The surface chemistry of the silicon nitride is characterized by the existence of amine and hydroxyl groups (oxynitride surface chemistry) [44,45]. Previous work has shown that the amine hydrogens can chemically react with the epoxy groups in the resin [46,47]. On one hand, this has the advantage of making silicon nitride inherently compatible with the matrix polymer, which should result in good particle dispersion and, thus, minimize the effect of particle agglomeration.…”

“…On the other hand, this reaction will affect the effective resin/hardener stoichiometry. The latter effect was taken into account by adjusting the resin/hardener stoichiometry to compensate for the epoxy groups reacted with the amine groups on the silicon nitride nanofiller [47].…”