Thermal history-dependent nanoscale ordering in supercooled propylene carbonate revealed by DSC and FTIR spectroscopy.

Nanoscale molecular ordering in supercooled propylene carbonate (PC) and its dependence on thermal history are investigated using differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy. DSC measurements over an extended temperature range reveal an exothermic feature at Tc ≈ 183 K (≈ 1.17 Tg), well above the glass transition temperature (Tg ≈ 157 K). This feature is attributed to the formation of nanoscale molecular aggregates or locally ordered molecular clusters. This temperature coincides with crossover temperatures reported from dielectric, scattering, viscosity, and solvation dynamics studies, indicating a possible link between dynamic anomalies and underlying structural evolution. FTIR spectroscopy provides independent support by revealing temperature-dependent changes in intermolecular interactions and the emergence of distinct local environments. Importantly, both calorimetric and spectroscopic signatures exhibit a pronounced dependence on thermal history. Taken together, the DSC and FTIR results support a scenario in which the dynamic crossover in PC is accompanied not only by kinetic slowing down but also by the development of spatially heterogeneous structures.