Thermal behaviour below and inside the glass transition region of a submicron P3HT layer studied by fast scanning chip calorimetry

Fast scanning chip calorimetry was utilized to investigate the thermal behaviour of a submicron layer of P3HT, an important polymer for organic electronics, when isothermally treated below and inside the glass transition region. A similar study was performed on the conventional polyester PBT, for comparison. It was observed that a heating and cooling rate of 30 000 K s(-1) was sufficient to avoid all non-isothermal effects for P3HT, while the faster reordering kinetics of PBT still allowed reordering upon heating at these scanning rates. For both materials, treatments clearly below the glass transition region yield enthalpic relaxation of the glass phase. When treatments are performed inside the glass transition region, however, a combined process of both enthalpic relaxation and the melting of small (nano-sized), imperfect crystals is observed. Due to the influence of the glass phase on the crystallization process, it seems that large, more stable crystals can not be formed. Significant isothermal perfectioning can be observed for the imperfect crystals in P3HT, while very fast non-isothermal reordering upon heating is seen for PBT. An approach based on a 2-step nucleation mechanism of crystallization may be used to interpret the observations of polymer crystallization around and in the glass transition region. (C) 2015 Elsevier Ltd. All rights reserved.