Determination of potentially homogeneous-nucleation-based crystallization ino-terphenyl and an interpretation of the nucleation-enhancement mechanism

Abstract

A homogeneous-nucleation-based crystallization was found in 0-terphenyl in the glass-transition ternperature region with an adiabatic calorimeter, and the crystallization process was investigated by direct microscopic observation. The crystallization showed its maximum rate at 248 and ceased at 250 K, while the ordinary crystal-growth process was observed to proceed only above 255 K. The two crystals formed at 248 and 297 K showed the same x-ray-diffraction patterns, indicating that they were in the same crystalline phase. The nucleation-based crystallization was observed in the temperature range of 225 to 250 K as advance of the crystal front into the liquid phase under the microscope, and the crystalline phase exhibited the appearance of the aggregation of fine crystallites which was consistent with the presence of residual entropy and the premelting property. From these results, the crystallization process was interpreted to proceed through the coalescence of crystal embryos into the crystalline phase on the liquid-crystal interface. It was concluded that the decrease in the effective interfacial energy of the embryo due to the coalescence produced an enhancement of the crystal nucleation, and that the enhancement mechanism must have played an essential role for the macroscopically observable crystallization below 250 K.

Stability of Amorphous Pharmaceutical Solids: Crystal Growth Mechanisms and Effect of Polymer Additives

“…We review below key observations concerning these growth modes and their current explanations. Figure 1 shows that while the crystal growth rate u tracks the diffusion coefficient D above T g , u becomes orders of magnitude faster with a temperature drop of a few K (filled circles) (21,22). This growth mode, termed GC (glass-to-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid.…”

Glasses crystallize rapidly at free surfaces by growing crystals upward

“…These studies might not observe surfaceenhanced crystal growth if the phenomenon is more pronounced in glasses. Finally, a fast bulk mode of crystal growth (GC mode) has been observed to emerge in some organic liquids near the glass transition temperature, causing an abrupt increase of crystal growth rate (3,4). For such systems, surface-enhanced crystal growth could be less noticeable.…”

“…One such growth mode [the glass-to-crystal (GC) mode] exists in the bulk and can cause an increase of crystal growth rate by a factor of 10 4 with a temperature drop by a few kelvin (3,4). Another new growth mode occurs at the free surface and can lead to much faster crystal growth than in the bulk (5)(6)(7)(8).…”

“…Recent studies have discovered that different modes of crystal growth can emerge as a liquid is cooled to form a glass (3)(4)(5)(6)(7)(8), causing crystal growth fronts to advance at velocities much faster than predicted by standard theories. One such growth mode [the glass-to-crystal (GC) mode] exists in the bulk and can cause an increase of crystal growth rate by a factor of 10 4 with a temperature drop by a few kelvin (3,4).…”

Faceting and Branching in 2D Crystal Growth

“…Besides, in some organic glasses discontinuous enhancement of crystal growth is observed [12][13][14], which is associated with diffusionless crystallization [15]. Although various theories have been developed to explain the existence of diffusion-controlled and diffusionless rapid modes [14][15][16], none of them predicts a facetednonfaceted morphological transition often associated with different crystallization modes, when interpreting experiments [3]. Growth mode (i) and mode (ii) have also been observed in simple mean-field models [17], although these theories address anisotropic crystal growth in a phenomenological way.…”