Enthalpic relaxation of silica–polyvinyl acetate nanocomposites

Abstract

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 of 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 filler 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.

Immobilized Polymer Fraction in Hyperbranched Polymer/Silica Nanocomposite Suspensions

“…The decrease in ΔH r occurred even though the suspensions had not been annealed below their T g , in contrast with previous results on silica/poly(vinyl acetate) nanocomposites. 62 In this latter case the nanoparticles affected the annealing peak only at long time scales, which the authors interpreted as a confirmation of the lack of an immobilized glassy layer at the surface of the particles, which otherwise should have given rise to measurable effects already at small annealing times. Nevertheless, the fact that ΔH r decreased with filler content for different annealing times and temperatures confirmed that the particles affected the molecular motion of the polymer matrix.…”

Free volume holes diffusion to describe physical aging in poly(mehtyl methacrylate)/silica nanocomposites

“…In this case, the vast majority of experimental works reports a reduction 17,[43][44][45][46][47][48][49] or even a suppression 45,50,51 of physical aging. In this case, the vast majority of experimental works reports a reduction 17,[43][44][45][46][47][48][49] or even a suppression 45,50,51 of physical aging.…”

Structural Arrest and Thermodynamic Scaling in Filler-Reinforced Polymers

“…One consequence is an increase in the pressure-dependence of the dynamic crossover temperature, demarcating the onset of strong intermolecular cooperation of the dynamics. These results may be connected to the observation that filler slows the rate of structural relaxation in the glassy state; 62,63 such physical aging is governed by the loss of volume. Current efforts are directed to assessing whether the enhanced volume sensitivity of the segmental dynamics is a general phenomenon in filled polymers.…”