Recent Advances in Nonclassical Crystallization: Fundamentals, Applications, and Challenges

Abstract

Ubiquitous crystals play an important role in our daily lives. Recent studies on the properties and formation of crystals have proven the attachment of particles ranging from ion pairs to well-crystallized nanocrystals for crystallization. Compared with the monomer-by-monomer (i.e., atoms, ions, or molecules) addition described in long-standing classical theories, so-called nonclassical crystallization pathways are more complex due to the influence of nonspecific interactions influenced by the variation in system free energy and reaction kinetics. In view of the fact that detailed insights into nonclassical crystallization pathways have broadened the scope of research across various disciplines such as geological events, biomineralization mechanisms, environmental remediation, and the development of functional materials, this paper reviews the current state of the art in nonclassical nucleation (the prenucleation clusters pathway, aggregation pathway, etc.) and growth pathways (oriented attachment and random attachment) based on several highlights. In addition, the observed specific phenomena on crystallization in the last 10 years as well as recent advancements and achievements on the synthesis of mesocrystals are also elucidated. With implications and perspectives of nonclassical crystallization research proposed in this paper, this review aims to summarize research advancements regarding crystallizing systems. Emphasis will be placed on novel insights into nonclassical crystallization of materials, which are expected to provide completely new perspectives on the underlying crystallization mechanisms.

Organic Crystal Growth: Hierarchical Self-Assembly Involving Nonclassical and Classical Steps

“…Organic crystallization is of primary importance in pharmaceutical science, organic electronics, and biological systems. , It has been recognized that organic crystal nucleation and growth are complex processes, involving diverse intermediates and order evolution paths. − These do not fit into the framework of currently accepted theories, , and show a wide range of initial ordering and order evolution dynamics . We note that insufficient mechanistic understanding precludes the rational design of organic crystallization outcomes, as exemplified by the notorious “polymorph problem” in pharmaceutical science, where crystalline structures often form and interconvert unpredictably …”

Oriented Attachment: A Unique Mechanism for the Colloidal Synthesis of Metal Nanostructures

“…Although our discussion centers on metal nanostructures, it is worth noting that OA is a ubiquitous phenomenon and has also been observed in the synthesis of nanostructures with other compositions, including semiconductors, alkali-metal rare-earth double carbonates, and multicomponent heterostructures comprised of different materials. [142][143][144] Despite the significant progress in the fundamental understanding and experimental control of OA growth, there are still challenges and opportunities when pushing this mechanism forward. As discussed at various places, the description of the interactions between attaching particles by DLVO theory fails to explain the direction-specific attachment, in addition to the neglect of other forces affecting colloidal stability, such as steric and hydration forces.…”

Phase transformation of calcium carbonate in acetonitrile/H2O mixed solvents: effects of water content and dielectric constant

“…It seems to be easier to transform from ACC to vaterite at low Ca 2+ concentration as demonstrated by Deng et al 8,30 So, the phase transformation from ACC to vaterite is controlled by the calcium ion concentration and the steady growth of vaterite is effected by a low dielectric constant, and the growth process in the 90% Ace (v/v) group can be considered as an Ostwald ripening process. 35,36 The phase transition process of the final crystal is summarized as shown in Fig. 6, in which the water content and dielectric constant play a key role in controlling the phase transformation of calcium carbonate.…”