A model polycyclic aromatic hydrocarbon (PAH) compound, anthracene, was incorporated into a thermosetting epoxy matrix as a reinforcing moiety via physical dispersion and/or chemical modification. In order to understand the “additive effect” of glass transition temperature (Tg) observed with the variation of free anthracene (AN) and bonded 2-aminoanthracene (2-AM) loading, the relaxation dynamics were investigated by broadband dielectric spectroscopy. Within the measurement range of 0.01 Hz–1 MHz and −60 to 130 °C, three relaxation processes, namely normal mode (n-mode) relaxation, α relaxation, and β relaxation, were observed for all epoxy composites with bonded and/or unbound anthracene. After eliminating the strong effect of ionic conduction by using the logarithmic derivative approximation ε''∝[Formula presented]lnω, derived from the Kramers-Kronig relations, the n-mode relaxation occurring at low frequencies above Tg for the rigid epoxy system is revealed. The Arrhenius diagram showing the temperature dependence of each relaxation process for the PAH-epoxy composites was obtained after parametric fitting using the Havriliak-Negami (HN) function in the frequency domain. The segmental α relaxation was more strongly impacted than the long-range n-mode relaxation by the different reinforcing approaches. The correlation of Tg -scaled fragility to molecular structures reveals the different mechanisms for the retardation effects on cooperative segmental and chain relaxation time. The localized β relaxation below Tg was not seemingly affected by the incorporation of bound and/or unbound anthracenes as indicated by the characteristic relaxation time and the activation energy.
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This manuscript has been authored by Honeywell Federal Manufacturing & Technologies under Contract No. DE-NA-0002839 with the U.S. Department of Energy . The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.
© 2017 Elsevier Ltd
- Dielectric relaxation
- Glass transition
- PAH-Epoxy composites