Nucleation Of Organic Crystals Research Articles

Nucleation of Organic Crystals—A Molecular Perspective

The outcome of synthetic procedures for crystalline organic materials strongly depends on the first steps along the molecular self-assembly pathway, a process we know as crystal nucleation. New experimental techniques and computational methodologies have spurred significant interest in understanding the detailed molecular mechanisms by which nuclei form and develop into macroscopic crystals. Although classical nucleation theory (CNT) has served well in describing the kinetics of the processes involved, new proposed nucleation mechanisms are additionally concerned with the evolution of structure and the competing nature of crystallization in polymorphic systems. In this Review, we explore the extent to which CNT and nucleation rate measurements can yield molecular-scale information on this process and summarize current knowledge relating to molecular self-assembly in nucleating systems.

The role of chemical interactions and epitaxy during nucleation of organic crystals on crystalline substrates

A tandem strategy to control polymorphism through epitaxial relationships with crystalline substrates reveals the importance of chemical interactions at the nucleation surface compared with the periodic surface potential associated with epitaxy.

Generic Progressive Heterogeneous Processes in Nucleation

The generic heterogeneous effect of foreign particles on 3D nucleation was examined in terms of the relative size and the interfacial interaction and structural match with the crystallizing phase in terms of a so-called interfacial correlation function f(m,x). At low supersaturation, nucleation is controlled by foreign bodies with a relatively small curvature and/or an optimal interfacial interaction and structural match with the crystallizing phase. This is characterized by a small interfacial correlation function f(m,x )( f(m,x) f 0). At high supersaturation, nucleation on foreign particles having a weak interaction and poor structural match with the nucleating phase (f(m,x) f 1) will govern the kinetics. It follows that if a wide range of supersaturations are applied in a crystallization system, a sequence of progressive heterogeneous nucleation processes, characterized by different interfacial correlation function f(m,x)s, can be identified, where genuine homogeneous nucleation can be regarded as the up-limit of heterogeneous nucleation. To check the above results, experiments on the nucleation of organic crystals and CaCO3 from aqueous solutions were carried out under gravity and microgravity. The results are in excellent agreement with our prediction.