Glass Transition in Ultrathin Polymer Films: Calorimetric Study

The ultrasensitive differential scanning calorimetry is used to observe the glass transition in thin (1–400 nm) spin-cast films of polystyrene, poly (2-vinyl pyridine) and poly (methyl methacrylate) on a platinum surface. A pronounced glass transition is observed even at a thickness as small as 1–3 nm. Using the high heating ($20–200\mathrm{K}/\mathrm{m}\mathrm{s}$) and cooling ($1–2\mathrm{K}/\mathrm{m}\mathrm{s}$ in glass transition region) rates which are typical for this technique, we do not observe appreciable dependence of the glass transition temperature over the thickness range from hundreds of nanometers down to 3 nm thick films. The evolution of calorimetric data with film thickness is discussed in terms of broadening of transition dynamics and loss of transition contrast.