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1. Pre-nucleation Clusters and Complex Nucleation in Soft Matter and the Potential Roles of Space Experiments

   Katamreddy, S.; Cho, Y. C.; Lee, S.; Lee, G. W.; Lee, J. (July 2022, IJMSA)

   N/A (Ed.)

   For more than a century, Classical Nucleation Theory (CNT) has been used to explain the process of crystallization in supersaturated solutions. According to CNT, nucleation is a single-step process that occurs via monomer-by-monomer addition. However, recent findings from experiments and numerical simulations have shown that nucleation is a multi-step process that occurs via more complex pathways that involve intermediate species such as ion complexes, dense liquid precursors, or even nanocrystals. Such non-classical pathways observed in protein solutions, colloidal suspensions and electrolytes are reviewed in this paper. The formation of stable Pre-nucleation Clusters (PNCs) in the crystallization of biominerals is also discussed. In spite of the mounting evidence for non-classical nucleation behaviors, the knowledge about the structural evolution of the intermediate phases and their role in polymorph selection is still limited. It has also been observed that gravitational force interferes with the crystallization behavior of materials thereby posing limitation to ground-based experiments. Microgravity conditions, coupled with containerless processing techniques provide a suitable alternative to overcome these limitations. 

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2. RSeeds: Rigid Seeding Method for Studying Heterogeneous Crystal Nucleation

   https://doi.org/10.1021/acs.jpcb.3c00910  

   Yuan, Tianmu; DeFever, Ryan S; Zhou, Jiarun; Cortes-Morales, Ernesto Carlos; Sarupria, Sapna (May 2023, The Journal of Physical Chemistry B)

   Heterogeneous nucleation is the dominant form of liquid-to-solid transition in na- ture. Although molecular simulations are most uniquely suited to study nucleation, the waiting time to observe even a single nucleation event can easily exceed current computational capabilities. Therefore, there exists an imminent need for methods that enable computationally fast and feasible studies of heterogeneous nucleation. Seeding is a technique that has proven successful at dramatically expanding the range of computationally accessible nucleation rates in simulation studies of ho- mogeneous crystal nucleation. In this paper, we introduce a new seeding method for heterogeneous nucleation called Rigid Seeding (RSeeds). Crystalline seeds are treated as pseudo-rigid bodies and simulated on a surface with metastable liquid above its melting temperature. This allows the seeds to adapt to the surface and identify favorable seed–surface configurations, which is necessary for reliable predictions of crystal polymorphs that form and the corresponding heterogeneous nucle- ation rates. We demonstrate and validate RSeeds for heterogeneous ice nucleation on a flexible self-assembled monolayer surface, a mineral surface based on kaolinite, and two model surfaces. RSeeds predicts the correct ice polymorph, exposed crystal plane, and rotation on the surface. RSeeds is semiquantitative and can be used to estimate the critical nucleus size and nucleation rate when combined with classical nucleation theory. We demonstrate that RSeeds can be used to evaluate nucleation rates spanning many orders of magnitude. 

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3. Membrane nucleation rates from holography

   https://doi.org/10.1007/JHEP12(2022)141  

   Arcos, Maite; Fischler, Willy; Pedraza, Juan F.; Svesko, Andrew (December 2022, Journal of High Energy Physics)

   A bstract Membrane nucleation, a higher dimensional analog of the Schwinger effect, is a useful toy model for vacuum decay. While a non-perturbative effect, the computation of nucleation rates has only been accomplished at weak coupling in the field theory. Here we compute the nucleation rates of spherical membranes using AdS/CFT duality, thus naturally including the effects of strong coupling. More precisely, we consider the nucleation of spherical membranes coupled to an antisymmetric tensor field, a process which renders the vacuum unstable above a critical value of the field strength. We analyze membrane creation in flat and de Sitter space using various foliations of AdS. This is accomplished via instanton methods, where the rate of nucleation is dominated by the semi-classical on-shell Euclidean action. Our findings generalize the holographic Schwinger effect and provide a step toward holographic false vacuum decay mediated by Coleman-De Luccia instantons. 

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4. In Situ Liquid‐Cell TEM Observation of Multiphase Classical and Nonclassical Nucleation of Calcium Oxalate

   https://doi.org/10.1002/adfm.202007736  

   Banner, David J.; Firlar, Emre; Rehak, Pavel; Phakatkar, Abhijit H.; Foroozan, Tara; Osborn, Jodi K.; Sorokina, Lioudmila V.; Narayanan, Surya; Tahseen, Talia; Baggia, Yusuf; et al (February 2021, Advanced Functional Materials)

   Abstract Calcium oxalate (CaOx) is the major phase in kidney stones and the primary calcium storage medium in plants. CaOx can form crystals with different lattice types, water contents, and crystal structures. However, the conditions and mechanisms leading to nucleation of particular CaOx crystals are unclear. Here, liquid‐cell transmission electron microscopy and atomistic molecular dynamics simulations are used to study in situ CaOx nucleation at different conditions. The observations reveal that rhombohedral CaOx monohydrate (COM) can nucleate via a classical pathway, while square COM can nucleate via a non‐classical multiphase pathway. Citrate, a kidney stone inhibitor, increases the solubility of calcium by forming calcium‐citrate complexes and blocks oxalate ions from approaching calcium. The presence of multiple hydrated ionic species draws additional water molecules into nucleating CaOx dihydrate crystals. These findings reveal that by controlling the nucleation pathways one can determine the macroscale crystal structure, hydration state, and morphology of CaOx. 

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5. Comparison of nanocrystalline cellulose dispersion versus surface nucleation in poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) crystallization

   https://doi.org/10.1002/pls2.10011  

   Haham, Hai; Shen, Mo‐Yuan; Billington, Sarah L.; Frank, Curtis W. (September 2020, SPE Polymers)

   Abstract Nanocrystalline cellulose (NCC), which is a known crystal nucleating agent, is utilized to improve poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) thermal properties. Since NCC aggregation in PHBV negatively affects composite properties and processability, NCC crystal nucleation effectiveness was examined at low concentrations (<1%) under isothermal and nonisothermal conditions. NCC was dispersed in PHBV solutions using a solvent exchange method and then cast into films. We found that NCC was an effective nucleating agent in amounts as low as 0.25%, resulting in an increase in PHBV crystallization rate by more than 50%. However, increasing to 1% NCC resulted in aggregation in PHBV, with the NCC becoming less effective compared to lower NCC concentrations. In an attempt to improve NCC dispersion, we added cellulose acetate (CA) or stearic acid (SA) to the casting solution, anticipating that CA or SA would preferentially adsorb on the NCC. With such pretreatment, dispersion was indeed improved but NCC became less effective as a PHBV nucleating agent. This work shows the advantage of using low NCC concentrations (<0.5%) for promoting PHBV crystallization, but the lack of improved nucleation upon addition of CA and SA supports the importance of NCC surface accessibility. 

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