Glass transition temperature of thin polycarbonate films measured by flash differential scanning calorimetry

Flash differential scanning calorimetry was used to study the glass transition temperature T_gof polycarbonate ultrathin films. The investigation was made as a function of film thickness from 22 to 350 nm and over a range of cooling rates from 0.1 to 1000 K/s. Polycarbonate spin cast films were floated on a layer of grease on the calorimetric chip. The results show a greatly reduced glass temperature for the thinnest films relative to the macroscopic value. We also observed that the magnitude of the glass temperature reduction decreases as the cooling rate increases with the highest cooling rates showing little thickness dependence of the T_g. Dynamic fragility and activation energy at T_gwere found to decrease with decreasing film thickness. The results are discussed in the context of literature reports for supported and freely standing polycarbonate films.