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Dielectric relaxation phenomena of UV-cured epoxy systems treated with layer-by-layer nanosilica assemblies

This work focuses on dielectric relaxation phenomena of hybrid organic-inorganic epoxy systems obtained through the application of a Layer-by-Layer (LbL) silica assembly on a UV-cured epoxy system, based on the copolymerization of a cycloaliphatic diepoxy monomer (namely 3,4-epoxycyclohexylmethyl-3',4'-epoxy-cyclohexane carboxylate-CE) with a flexibilizing comonomer (1,6-hexanediol diglycidyl ether-HDGE). More specifically, UV-cured HDGE/CE films (containing 30 wt.% CE) were LbL treated by 10 and 20 silica bilayers (positively charged/negatively charged) on both sides. The dielectric properties of the LbL treated films were investigated and compared to those of the untreated counterparts, using broadband dielectric spectroscopy over a wide range of frequencies (10-1 Hz-1 MHz) and over a temperature span ranging from 173 to 373 K. The frequency dependence of the dielectric losses for the analysed films allowed to highlight three relaxation peaks, associated with molecular motions of the polymer chains (γ, β and α), which turned out to evolve as a function of temperature. Furthermore, the thermal properties obtained using thermogravimetric analysis and differential scanning calorimetry have been assessed. The results were correlated with the structural morphology of the copolymer film with the nanosilica bilayers.