Molecular dynamics of epoxy nanocomposites filled with core–shell and hollow nanosilica architectures

Abstract

Here we contrast the molecular dynamics of epoxy nanocomposites filled with three different types of silica-based nanoparticles with different architectures, namely solid core, core–shell and hollow and with varying degree of crystallinity. The samples are characterised by Fourier transform infrared spectroscopy, differential scanning calorimetry, broadband dielectric spectroscopy and dynamic mechanical analysis (DMA). Widely known relaxations such as α, β, γ, normal mode and interfacial polarisation are observed and discussed. An additional relaxation named omega (ω) is also observed, whose dielectric strength is inversely correlated to the crystallinity of the nanoparticles. We suggest that this may be attributed to the polarizing interaction of the hydroxyl groups of silanols with the hydroxy ether groups of the polymer chain. The ω is absent in DMA confirming it as a polarisation phenomenon. At lower concentration of silanols, the ω largely overlaps with β, effectively becoming an integral part of it. Finally, two interfacial polarisation relaxations are observed in the case of core–shell structures, originating from the core–shell and shell–polymer interface but, due to the similar real permittivity values of the core, shell and the polymer, their dielectric strength is weak.