Epoxy-Based Hydrogels Investigated by High-Frequency Dielectric Relaxation Spectroscopy

Using high-frequency dielectric relaxation spectroscopy, nanophase-separated structures of epoxy-based hydrogels were investigated as a function of water content at 25 °C. The dielectric spectra resulting from the hydrogels were reasonably decomposed into two Debye-type and two Cole–Cole-type relaxation modes. The fastest Debye-type mode, found at 8.3 ps, was attributed to the rotational relaxation process of free water molecules in the bulk state. The other Debye-type mode, at ca. 20–34 ps, originates from the exchange process of water molecules that are hydrogen-bonded to the hydrophilic epoxy network portions for free bulk ones. The first Cole–Cole-type mode observed, at ca. 20–370 ps, was assigned to the complicated dynamics for electric dipole moments of the hydrophilic groups in the epoxy networks (mainly monomeric oxyethylene units). The slowest major Cole–Cole-type mode, at 5–29 ns, was attributed to the Maxwell–Wagner–Sillars polarization process and confirmed the presence of the nanophase-separa...