(65o) Investigation of Dynamic Relaxation Properties of Poly(methyl methacrylate)/Silica Nanocomposites

Understanding the relaxation characteristics of polymers and polymer nanocomposites can offer insight into the nature of the chain motion and, in the case of nanocomposites, potential chemical and physical interactions at the particle-polymer interface. Using dynamic mechanical analysis and broadband dielectric spectroscopy, we studied the sub-glass and glass transitions of poly(methyl methacrylate) nanocomposites containing up to 30 wt% native and surface-modified silica nanoparticles. In systems containing the latter, favorable surface interactions between the polymer and the nanoparticles were observed, and at sufficiently high concentrations a second glass transition event was detected, suggesting a restriction of local chain motion in the vicinity of the nanoparticle surface. Dielectric spectroscopy was used to probe the influence of increasing nanoparticle concentration on the sub-glass and glass-rubber transitions, as well as the polarizability of the nanocomposite system, namely the interfacial polarization encountered at high temperatures and low frequencies. Although an expected increase in interfacial polarization was observed with increased nanoparticle loading, the particles did not have a discernable effect on either the sub-glass or glass transitions of the nanocomposite systems.