Homogeneous Crystal Nucleation in Poly (butylene succinate--butylene adipate): Challenging the Nuclei-Transfer Step in Tammann's Method.

The kinetics of homogeneous crystal nucleation and the stability of nuclei were analyzed for a random butylene succinate/butylene adipate copolymer (PBSA), employing Tammann's two-stage crystal nuclei development method, with a systematic variation of the condition of nuclei transfer from the nucleation to the growth stage. Nuclei formation is fastest at around 0 °C, which is about 50 K higher than the glass transition temperature and begins after only a few seconds. Due to the high nuclei number, spherulitic growth of lamellae is suppressed.

Nucleation, crystal growth, nuclei stability, and polymorph selection in supercooled tolbutamide melt.

Nucleation is an essential step of overall crystallization, yet crystal nuclei are elusive to direct observation due to their small size and transient nature. A method for assessing the nuclei size distribution and growth rate based on selective melting/dissolving was developed recently, making use of the rapid heating/cooling rate available in fast scanning calorimetry. The method was first employed to study the nuclei in the polymer poly-L-lactic acid.

Reorganization of Poly(Butylene Succinate) Containing Crystals of Low Stability.

Poly(butylene succinate) (PBS) forms small and imperfect crystals of low melting temperature at high supercooling of the melt. Slow heating allows reorganization of the obtained semicrystalline structure with the changes of the crystallinity and of the size and perfection of crystals analyzed by differential scanning calorimetry (DSC) and temperature-resolved X-ray scattering techniques. Crystals generated at 20 °C begin to melt and reorganize at a few K higher temperature with their initial imperfection and thickness unchanged upon heating to 70-80 °C.

Stability of Rapidly Crystallizing Sulfonamides Glasses by Fast Scanning Calorimetry: Crystallization Kinetics and Glass-Forming Ability.

Production and evaluation of the kinetic stability of the amorphous forms of active pharmaceutical ingredients are among the current challenges of modern pharmaceutical science. In the present work, amorphous forms of several sulfonamides were produced for the first time using Fast Scanning calorimetry. The parameters, characterizing the glass-forming ability of the compounds, i.

Effects of Structural Relaxation of Glass-Forming Melts on the Overall Crystallization Kinetics in Cooling and Heating.

In the theoretical treatment of crystallization, it is commonly assumed that the relaxation processes of a liquid proceed quickly as compared to crystal nucleation and growth processes. Actually, it is supposed that a liquid is always located in the metastable state corresponding to the current values of pressure and temperature. However, near and below the glass transition temperature, Tg, this condition is commonly not fulfilled.