Glass transition behavior of alumina/polymethylmethacrylate nanocomposites

Abstract Alumina/polymethylmethacrylate (PMMA) nanocomposites were synthesized using 39-nm nanoparticles and in situ free-radical polymerization. At filler concentrations greater than 0.5 wt.%, the glass transition temperature, Tg, was observed to decrease precipitously by 25 °C compared to the neat polymer. At smaller weight fractions, there were no changes in the composite Tg. The abrupt changes seem to indicate a threshold at which a significant volume fraction of polymer has higher mobility that brings about the decrease in Tg. Consistent with this behavior, the Tg depression was suppressed by coating the nanoparticles to make them compatible with the matrix.