Effect of silica particles concentration on the physical aging of PMMA/silica nanocomposites

We have monitored the physical aging of poly(methyl methacrylate) (PMMA)/silica nanocomposites, namely the slow evolution occurring to the structure of glasses below the glass transition temperature (T-g), following the time evolution of the enthalpy as measured by differential scanning calorimetry (DSC). We have systematically varied the concentration of silica to provide insight about the influence of the ratio area of silica/volume of PMMA (A(sil)/V-PMMA) on the physical aging process. Our results clearly indicate that physical aging speeds up with increasing silica concentration. Furthermore, the amount of recovered enthalpy decreases with increasing silica concentration, indicating that part of the enthalpy is recovered during the delay time before the first data are collected.