Gaining Thermodynamic Insight From Distinct Glass Formation Kinetics of Structurally Similar Organic Compounds.

Thermodynamic and kinetic aspects of crystallization of 12 structurally similar organic compounds were investigated from the supercooled liquid state by calorimetric and rheologic measurements. Based on their crystallization behaviors, these compounds were divided into 3 categories: stable glass formers, poor glass formers, and good glass formers with poor stability on reheating. Correlation was sought between thermodynamic quantities and glass formation based on nucleation and crystal growth theories. Larger values of enthalpy of fusion and melting point were found to correlate with poor glass-forming ability. Conversely, lower entropy of fusion was found to correlate with glass formation. Examination of kinetic aspects of glass formation revealed 2 important facets of good glass formers, that is, rapid increase in viscosity on supercooling and high melting point viscosity compared with non-glass formers. A broader relationship was sought between entropy of fusion and glass formation by including several glass formers from literature. Our analysis indicated that good glass formers tend to have an entropy of fusion closer to 0.3 J cm-3 K-1 . The structural similarity of the compounds in this study provides insights regarding the nature of intermolecular interactions responsible for the observed effect on entropy of fusion, viscosity, and crystallization kinetics.