Designing Solid Materials from Their Solute State: A Shift in Paradigms toward a Holistic Approach in Functional Materials Chemistry

Abstract

“Non-classical” notions consider formation pathways of crystalline materials where larger species than monomeric chemical constituents, i.e., ions or single molecules, play crucial roles, which are not covered by the classical theories dating back to the 1870s and 1920s. Providing an outline of “non-classical” nucleation, we demonstrate that prenucleation clusters (PNCs) can lie on alternative pathways to phase separation, where the very event of demixing is primarily based on not the sizes of the species forming, as in the classical view, but their dynamics. Rationalizing, on the other hand, that precursors that can be analytically detected in pre-nucleation stages and that play a role in phase separation must be considered PNCs and cannot be explained by classical notions, we outline a variety of systems where PNCs are important. Indeed, in recent years, with the advent of “non-classical” theories, a primary focus of research concentrated on the fundamental understanding of oligomeric/polymeric and particulate species involved in nucleation and crystallization processes, respectively. At the same time, the near-to unfathomable potential of “non-classical” routes for the synthesis of inorganic functional materials slowly unfolds. An overview of recent developments in the fundamental and mechanistic understanding of “non-classical” nucleation and crystallization in this Perspective then allows us to map out the potential of cluster/particle-driven mineralization pathways to intrinsically tailor the properties of inorganic functional (hybrid) materials via structuration from the nano- to the mesoscale. This is of utter importance for the functionality and performance of materials, as it may even confer emergent properties such as self-healing. Biomineralsoften formed via particle accretion mechanismsdemonstrate this impressively and thus can serve as a further source of inspiration how to exploit nonclassical crystallization routes for syntheses of structured and functional materials. These new avenues to synthetic approaches may finally provide a holistic material concept, in which fundamental chemistry and materials science synergistically alloy.

Polyamorphism Mirrors Polymorphism in the Liquid–Liquid Transition of a Molecular Liquid

“…1(b)) even though the liquid-1 viscosity is continuous and there is no sign of having reached the homogeneous nucleation temperature. 35,36 This discontinuous behaviour is fully consistent with a LLT occurring below 226 K. However, the time-resolved infrared spectroscopy experiments ( Fig. 1(a), Fig.…”

Liquid Metastable Precursors of Ibuprofen as Aqueous Nucleation Intermediates

“…for CaCO 3 involves the formation of prenucleation clusters in solution, decrease in their dynamics and densification as the key step for phase separation, formation of a liquid phase, solidification, and finally crystallization . While both two‐step nucleation and the prenucleation cluster pathway consider liquid intermediates, the former mechanism relies on the formation of critical nuclei within the liquid intermediate for crystallization, while the latter is based on the aggregation and dehydration of larger entities that cannot be accounted for in such classical notions of nucleation …”

“…[18] While both two-step nucleation and the prenucleation cluster pathway consider liquid intermediates,the former mechanism relies on the formation of critical nuclei within the liquid intermediate for crystallization, while the latter is based on the aggregation and dehydration of larger entities that cannot be accounted for in such classical notions of nucleation. [19,20] However,f or small organic molecules the experimental evidence for metastable liquid phases within at wo-step nucleation or aprenucleation cluster pathway is rather poor. Supersaturated glycine solutions underwent laser-induced nucleation at rates much faster than those of control solutions.…”

Stable Prenucleation Calcium Carbonate Clusters Define Liquid–Liquid Phase Separation

“…[27] The corresponding notions of Cahn and Hilliard [28] were employed for the derivation of a phase diagram of the aqueous calcium carbonate system by Zou et al, [29] which exhibited an upper critical solution temperature, in contrast to previous models. [27,30] Despite the explanatory power of the so-called "prenucleation cluster (PNC) pathway", [31,32] sometimes referred to as "nonclassical nucleation", however, a corresponding quantitative theory for phase separation in the aqueous calcium carbonate system is still lacking.…”