New Insight into the Molecular Dynamics of Epoxy/Aluminum Hydroxide Nanocomposites by Terahertz Time-Domain Spectroscopy

Nanodielectrics have shown many superior properties than conventional dielectrics. Nanocomposites based on epoxy resin and nanoaluminum hydroxide were fabricated to obtain material systems. In this paper, we investigated molecular dynamics of the nanocomposites by the combination of broadband dielectric relaxation spectroscopy, terahertz time-domain spectroscopy (THz-TDS), and thermally stimulated depolarization current (TSDC). We decompose the molecular dynamics into four relaxation processes according to their typical frequency at room temperature. Relaxation process in THz range is regarded as γ-process, which is well represented by Debye equation. At low-frequency range 10^-1-10⁶ Hz, α-process and Johari-Goldstein β-process play dominant role. Additionally, a fast β-process is expected to appear at intermediate frequencies. TSDCs results confirm the existence and change of all relaxation process. Each relaxation process changes differently with increasing filler content. Our results suggest that it is molecular dynamics at different time and space scales rather than free volume result in the change of dielectric property. This paper indicates that THz-TDS is extremely beneficial to understand the underlying mechanism of interface region in nanocomposites. We anticipate that THz-TDS is a prospective tool in future development and analysis of nanocomposites.