Enthalpic Relaxation of Silica-Polyvinyl Acetate Nanocomposites

Although the effects of filler nanoparticles size and surface treatment on the glass transition temperature of the matrix phase have received well-deserved attention, nanofiller effects on other physical parameters associated with the glass transition have received less interest. To better understand how the incorporation or nanofillers affects the enthalpic relaxations associated with the glass transition, differential scanning calorimeter measurements were carried out on silica-polyvinyl acetate nanocomposites with respect to filter content, annealing temperature, and annealing period. As expected, longer annealing periods below the glass transition temperature resulted in an increase of the subsequent enthalpic relaxations. However, the presence of filler substantially reduces the enthalpic relaxation relative to that of the neat polymer at longer annealing periods only. The underlying enthalpic relaxations and the effects suppressed by the fillers are specific to the annealing temperature. These results suggest a significant alteration in the physical state of the matrix because of the presence of the filler particles. However, this does not imply the existence of a glassy layer or layers with a glass transition gradient near the filler surface. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2733-2740, 2008