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Calorimetric Monitoring of the Sub-Tg Crystal Growth in Molecular Glasses: The Case of Amorphous Nifedipine
Authors: Svoboda Roman
Year: 2025
Type of publication: článek v odborném periodiku
Name of source: Molecules
Publisher name: MDPI
Place: BASEL
Page from-to: 1679
Titles:
Language Name Abstract Keywords
cze Kalorimetrické monitorování krystalového růstu pod skelným přechodem v molekulárních sklech: Studie amorfního nifedipinu Neizotermní DSC a Ramanova spektroskopie byly použity pro studium krystalizačního chování jemného prášku amorfního nifedipinu. Studie byla zaměřena na nedifúzní růstový mód ve skle vyskystující se v oblasti pod teplotou skelného přechodu. Během krystalizace vznikala alfa polymorfní fáze, což bylo prokázáno Ramanovou spektroskopií. Více než 50 % stupně krystalinity bylo dosaženo již při ponechání amorfních prášků po 7 hodin při 20 °C. Naměřená DSC data byla proložena autokatalytickým kinetickým modelem. amorfní nifedipin; růst krystalů; Ramanova mikroskopie; DSC; kinetická predikce
eng Calorimetric Monitoring of the Sub-Tg Crystal Growth in Molecular Glasses: The Case of Amorphous Nifedipine Non-isothermal differential scanning calorimetry (DSC) and Raman microscopy were used to study the crystallization behavior of the 20-50 mu m amorphous nifedipine (NIF) powder. In particular, the study was focused on the diffusionless glass-crystal (GC) growth mode occurring below the glass transition temperature (Tg). The exothermic signal associated with the GC growth was indeed directly and reproducibly recorded at heating rates q+ <= 0.5 degrees C<middle dot>min-1. During the GC growth, the alpha p polymorphic phase was exclusively formed, as confirmed via Raman microscopy. In addition to the freshly prepared NIF samples, the crystallization of the powders annealed for 7 h at 20 degrees C was also monitored-approx. 50-60% crystallinity was achieved. For the annealed NIF powders, the confocal Raman microscopy verified a proportional absence of the crystalline phase on the sample surface (indicating its dominant formation along the internal micro-cracks, which is characteristic of the GC growth). All DSC data were modeled in terms of the solid-state kinetic equation paired with the autocatalytic model; the kinetic complexity was described via reaction mechanism based on the overlap of 3-4 independent processes. The kinetic trends associated with decreasing q+ were identified, confirming the temperature-dependent kinetic behavior, and used to calculate a theoretical kinetic prediction conformable to the experimentally performed 7 h annealing at 20 degrees C. The theoretical model slightly underestimated the true extent of the GC growth, predicting the crystallinity to be 35-40% after 7 h (such accuracy is still extremely good in comparison with the standard kinetic approaches nowadays). Further research in the field of kinetic analysis should thus focus on the methodological ways of increasing the accuracy of considerably extrapolated kinetic predictions. amorphous nifedipine; GC growth; Raman microscopy; DSC; kinetic prediction

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