The Absolute Heat Capacity of Polymer Grafted Nanoparticles Using Fast Scanning Calorimetry*

The absolute heat capacity of a matrix-free polystyrene grafted silica nanocomposite system is investigated using ultrafast Flash differential scanning calorimetry (Flash DSC) and compared to results for a neat polystyrene sample of similar molecular weight. The heat capacity of the polymer in the nanocomposite is 8% lower than that of the neat polystyrene. In addition, the step change in heat capacity at the glass transition T-g is 15% lower, indicating a 2 nm-thick immobile layer of polymer around the nanoparticles. There is neither an increase in the nanocomposite heat capacity towards that of the neat material nor any additional increment C-p steps, indicating that the glassy layer around the nanoparticles remains immobile up to 300 degrees C. In addition to the analysis of the absolute heat capacity, the dynamic temperature gradient in the Flash DSC sample increases linearly with increasing rate of measurement, whereas the noise in the heat capacity data increases linearly with the reciprocal of the scanning rate; the optimum rate for measurements lies between 300 and 1000 K/s for the samples studied here and will depend on the sample thickness.