Dielectric relaxations in polyoxymethylene and in related nanocomposites: Identification and molecular dynamics

- Full identification of the dielectric relaxation mechanisms in POM is recorded for the first time.
- POM, POM/alumina and POM/LS nanocomposites are studied by means of BDS.
- Five dielectric relaxation mechanisms are detected (IP, α-, β-, γ- and δ-modes).
- β-and δ-modes emerge due to the incorporation of nanoinclusions.
- The connection of β-mode to the glass to rubber transition is established.

Broadband dielectric spectroscopy (BDS) is employed for the study of the dielectric response of Polyoxymethylene/boehmite alumina (POM/alumina) and Polyoxymethylene/Layered Silicates (POM/LS) semi-crystalline nanocomposites, together with the response of pure POM. The compilation of the dielectric responses of all systems reveals the existence of five dielectric relaxation mechanisms assigned, in terms of decreasing temperature at constant frequency, as IP (interfacial polarization), α-, β-, γ- and δ-relaxations. IP, α- and γ-relaxations are detected in all studied systems and they are well documented in the literature. δ-relaxation, been the fastest mechanism, is present only in the POM/LS system and is associated with defect dipoles in the crystalline phase of POM. Finally, β-relaxation is present only in the POM/alumina nanocomposite and its dynamics obey Vogel-Fulcher-Tamann temperature dependence. This work presents a complete mapping of the dielectric relaxation mechanisms of POM and signifies the connection of β-mode with the glass to rubber transition of POM, confirming its cooperative character.

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