Homogeneous Nucleation Research Articles

Chitosan as a Templating Agent of Calcium Phosphate Crystalline Phases in Biomimetic Mineralization: Theoretical and Experimental Studies.

Highlighting the essential role of chitosan (CS), known for its biocompatibility, biodegradability, and ability to promote cell adhesion and proliferation, this study explores its utility in modulating the biomimetic mineralization of calcium phosphate (CaP). This approach holds promise for developing biomaterials suitable for bone regeneration. However, the interactions between the CS surface and in situ precipitated CaP still require further exploration. In the theoretical section, molecular dynamics (MD) simulations demonstrate that, at an appropriate pH level during the prenucleation stage, calcium ions (Ca2+) and hydrogen phosphate ions (HPO42-) form Posner-like clusters. Additionally, the interaction between these clusters and the CS molecule enhances system stability. Together, these phenomena facilitate the transition to subsequent heterogeneous nucleation on the surface of the organic matrix, which is a more controlled process than homogeneous nucleation in solution. Dynamic simulation results suggest that CS acts as a stabilizing matrix at pH 8.0 during biomimetic mineralization. In the experimental section, the effects of pH and the molecular weight of CS were investigated, with a focus on their impact on the crystal structure of the resulting material. X-ray diffraction and scanning electron microscopy analyses reveal that, under conditions of approximately pH 8.0 and a CS molecular weight of 20 000 g/mol, and controlled ion concentration, ultrasound radiation, and temperature, the dominant CaP phases in the material are carbonate-doped hydroxyapatite (CHA) and octacalcium phosphate (OCP). These findings suggest that CS, when adjusted for molecular weight and pH, facilitates the formation of CaP crystal phases that closely resemble the natural inorganic composition of bone, highlighting its protective and regulatory roles in the growth and maturation of crystals during mineralization. The theoretical predictions and experimental outcomes confirm the crucial role of CS as a templating agent, enabling the development of a biomimetic mineralization pathway. CS's ability to guide this process may prove valuable in the design of materials for bone tissue engineering, particularly in developing effective materials for bone tissue healing and regeneration.

How CO2 gas accelerates water nucleation at low temperature.

We conducted homogeneous nucleation experiments for dilute binary H2O-CO2 mixtures in Ar-N2 carrier gas with different CO2/H2O ratios at temperatures of 57 and 75K and total pressures of ∼40 and 70Pa, respectively. Direct experimental information on the number and type of molecules in the clusters and on the cluster number concentration is obtained by mass spectrometric detection of nucleating clusters that form in the uniform region of Laval expansions. Only homo-molecular water clusters are observed in the mass spectra. However, as the CO2/H2O ratio increases, a significant increase in the nucleation rate is observed. A simple kinetic model suggests that this acceleration of nucleation is due to the formation of short-lived, transient hetero-molecular H2O-CO2 dimers. Comparison with homogeneous binary nucleation of toluene-CO2 and unary nucleation of H2O shows that nucleation becomes more efficient in systems with stronger intermolecular interactions and a larger number of degrees of freedom. Such studies at the molecular level will improve our understanding of homogeneous nucleation mechanisms in atmospheric and industrial processes.

Core mechanism for the stability preparation of lithium slag-based SOD zeolite: Evolution of trans-crystallization nucleation/growth kinetics of crystals

SOD nano-zeolite has been widely applied in the separation of small gas molecules since these advantages comprise a high-density framework and favorable acid/alkali resistance. Moreover, the bottleneck for the lithium sector can be ameliorated by industrializing the manufacture of SOD zeolite (SLS) from the hazardous waste lithium slag (LS). However, the stability in industrial production is restricted owing to the ambiguous nature of the lattice nucleation/transformation mechanism. Herein, it was discovered that the highest relative crystallinity (98.8 %) of SLS with a layered spherical structure could be achieved under the crystallization condition of heating at 95 °C for 8 h. The nucleation and growth mechanisms of SLS crystals demonstrated a three-dimensional crystal growth pattern characterized by sporadic and transient nucleation, which is essentially consistent with that of crystallization kinetics. Specifically, the activation energies of the induction, transformation and crystallization phases were 41.33, 27.99 and 46.99 kJ·mol−1, respectively, implying that the directional induction of the transition phase is crucial for obtaining SLS with high crystallinity. Two nucleation processes can also be observed in the transformation stage, involving homogeneous nucleation and polymorphic transformation. Our study explored the crystallization and assembly mechanism of SLS crystals, providing a well-defined concept for the regulation of stability preparation.

Multifunctional Composite Separator Based on NiS2/NiSe2 Homologous Heterostructure Polyhedron Promotes Polysulfide Conversion for High Performance Lithium-Sulfur Batteries.

The shuttle effect significantly hinders the industrialization of high-energy-density lithium-sulfur batteries. To address this issue, NiS2/NiSe2 homologous heterostructure polyhedron (HHP) composite separators were developed to immobilize polysulfides and promote their swift conversion. An in-situ visualization symmetrical cell was specifically designed to show the rapid polysulfide adsorption capability of NiS2/NiSe2 HHP, while the electrolyte-separator interfacial contact behavior was simulated to elucidate the mechanism of action of the composite separator in affecting the homogeneous nucleation of lithium metal surfaces. The electrochemical experimental result highlights the substantial enhancement in the reaction kinetics of polysulfides facilitated by NiS2/NiSe2 HHP, owing to its high Li+ diffusion coefficient and Li2S deposition capacity. The NiS2/NiSe2 HHP cells demonstrate high initial specific capacity (1224.1 mAh g-1) at 0.2 C and minimal decay rates (0.073%) at 2 C. The NiS2/NiSe2 HHP separator has high electrochemical catalytic activity with multiple adsorption sites, enabling the rapid polysulfide conversion and contributing to the preparation of high-performance lithium-sulfur batteries.

Synthesis of zinc hydroxyl acetate nanosheet-assembled honeycomb-like and flower-like structures by chemical bath deposition method for the construction of hydrophobic surfaces

Layered zinc hydroxyl acetate (LZHA) nanosheet-assembled honeycomb-like and flower-like structures were synthesized by a chemical bath deposition method using aqueous zinc acetate solution as the bath solution and a porous ZnO coating as the substrate. The morphology of LZHA architectures growing on the surface of the substrate depends on the type of LZHA nucleation. The homogeneous nucleation facilitates the adsorption of crumpled LZHA nanosheets generated in the solution onto the substrate surface, whereas heterogeneous nucleation promotes the formation of flat LZHA nanosheets on the substrate surface. The crumpled and flat LZHA nanosheets serving as the seeds undergo cyclic “growth-division” processes to evolve into LZHA nanosheet-assembled honeycomb-like and flower-like structures, respectively. The hierarchical architecture features of the LZHA honeycombs and flowers can be topologically inherited without any crack and collapse when converted into ZnO by calcination. The LZHA honeycomb-like and Ag nanoparticle modified ZnO flower-like structures were characterized by a scanning electron microscope, field-emission scanning electron microscope, energy dispersive X-ray spectrometer and X-ray diffractometer. The synthesized ZnO honeycomb-like and flower-like structures show excellent hydrophobic properties owning to the appropriate roughness provided by the hierarchical structures. In particular, the surface assembled by ZnO honeycombs derived from their LZHA precursors with deposition time of 4 h shows a higher water contact angle of 162.3°. In addition, the Ag nanoparticle modification on the petals of ZnO flowers results in the formation of multi-scale rough surfaces, and thus increases the water contact angle. The synthesized superhydrophobic surfaces exhibit promising applications in fields such as anti-icing, anti-corrosion and reducing fluidic drag.

Modeling of the perovskite nickelate SmNiO3 nucleation from amorphous thin films: A Volmer's thermodynamical approach

We present a thermodynamical model based on Volmer's nucleation theory adapted to the case of the perovskite nickelate SmNiO3 crystallization (SNO) from an amorphous (aSNO) thin film. This amorphous phase is synthesized via reactive magnetron sputtering and then subsequently annealed in air at temperatures between 725 and 925 K to crystallize it. This model allows to predict the theoretical nucleation rate of the crystallized perovskite phase according to the annealing temperature, the type of the nucleation (homogeneous and heterogeneous mechanisms) and to estimate some physical and thermodynamical data related to this transformation. A theoretical evaluation of the nucleation rate shows that the optimum temperature for crystallization is close to 800 K for which the nucleation rate can reach 1021 m-3.s-1 if considering both homogeneous and heterogeneous nucleation mechanisms. As the annealing temperature moves away from 800 K, the theoretical nucleation rate drops drastically, as observed experimentally by X-ray Diffraction (XRD) when we annealed 200 nm thick aSNO films. The good agreement between the presented model and the experimental crystallization results allows us to numerically evaluate some physical parameters not yet reported to date in the literature for SNO perovskites such as the surface energy between the amorphous and the crystallized SNO phases, the strain energy when the crystallization occurs and the enthalpy associated with crystallization.

Efficient and Stable Inverted Perovskite Solar Cells Enabled by a Fullerene‐Based Hole Transport Molecule

AbstractDesigning an efficient modification molecule to mitigate non‐radiative recombination at the NiOx/perovskite interface and improve perovskite quality represents a challenging yet crucial endeavor for achieving high‐performance inverted perovskite solar cells (PSCs). Herein, we synthesized a novel fullerene‐based hole transport molecule, designated as FHTM, by integrating C60 with 12 carbazole‐based moieties, and applied it as a modification molecule at the NiOx/perovskite interface. The in situ self‐doping effect, triggered by electron transfer between carbazole‐based moiety and C60 within the FHTM molecule, along with the extended π conjugated moiety of carbazole groups, significantly enhances FHTM's hole mobility. Coupled with optimized energy level alignment and enhanced interface interactions, the FHTM significantly enhances hole extraction and transport in corresponding devices. Additionally, the introduced FHTM efficiently promotes homogeneous nucleation of perovskite, resulting in high‐quality perovskite films. These combined improvements led to the FHTM‐based PSCs yielding a champion efficiency of 25.58 % (Certified: 25.04 %), notably surpassing that of the control device (20.91 %). Furthermore, the unencapsulated device maintained 93 % of its initial efficiency after 1000 hours of maximum power point tracking under continuous one‐sun illumination. This study highlights the potential of functionalized fullerenes as hole transport materials, opening up new avenues for their application in the field of PSCs.

Strategy for Regulation from Heterogeneous Nucleation to Homogeneous Nucleation: Application of Ultrasound

Strategy for Regulation from Heterogeneous Nucleation to Homogeneous Nucleation: Application of Ultrasound

Thermally Stable High-Entropy Layered Double Hydroxides for Advanced Catalysis.

Layered double hydroxides (LDHs), especially high-entropy LDHs (HE-LDHs), have gained increasing attention. However, HE-LDHs often possess poor thermal stability, restricting their applications in thermo-catalysis. Herein, a novel complexing nucleation method is proposed for engineering HE-LDHs with enhanced thermal stability. This approach precisely controls the nucleation of metal ions with different solubility products, achieving homogeneous nucleation and effectively mitigating phase segregation and transformation at elevated temperatures. The prepared HE-LDH sample demonstrated exceptional thermal stability at temperatures up to 300°C, outperforming all previously reported LDHs. Importantly, these HE-LDHs preserve both Lewis and Brønsted acidic sites, enabling the 100% removal of aromatic sulfides and alkaline nitrogen compounds from fuel oils in thermo-catalytic oxidation reactions. Experimental and characterization findings reveal that the metal-hydroxide bonds in the prepared HE-LDHs are strengthened by associated hydroxyl groups, inducing negative thermal expansion and augmenting the presence of acidic sites, thereby ensuring structural stability and enhancing catalytic activity. This study not only proposes a strategy for engineering HE-LDHs with remarkable thermal stability but also highlights potential applications of LDHs in thermo-catalysis.

Scalable Synthesis of Organic Core/Shell Architectures toward Dual-Wavelength Optical Waveguides.

Organic core/shell heterostructures have undergone rapid progress in materials chemistry owing to the integration of a wide array of unique properties. Nonetheless, the intricate challenge of regulating homogeneous nucleation and phase separation processes in excessively analogous cocrystal structures presents a formidable barrier to expanding the synthesis strategy for organic core/shell heterostructures. Herein, we successfully achieved a phase separation growth process facilitated by the organic alloy interface layer through a dynamic visualization to capture the intricate morphological evolution. By finely regulating the nucleation process, homogeneous self-assembly induced by high chemical and structural compatibility is circumvented, enabling the formation of organic core/shell heterostructures. Notably, this core/shell architecture boasts dual-wavelength emission at 496 and 696 nm, accompanied by an optical loss coefficient of 0.092 dB per micrometer. This methodology shows potential for extending to the scalable design of other conformational cocrystal heterostructure systems, thereby offering valuable insights into the realm of organic photonics.

On the theory of the nucleation of gas bubbles at grain boundaries and incoherent inclusions

On the base of the critical analysis of two-dimensional models of the nucleation of gas filled bubbles at grain boundaries of helium-implanted specimens under the action of tensile stresses, a new model is developed within the framework of the Reiss theory of homogeneous nucleation in binary systems. This approach considers that gas bubbles are formed as a result of agglomeration in a binary system of vacancies and gas atoms at grain boundaries, avoiding significant simplifications of previous models based on the classical nucleation theory for single-component (unary) systems. The new model is extended to consider the nucleation of Xe bubbles at grain boundaries in UO2 under irradiation conditions and can be used for numerical analysis of experimental observations after the foreseen implementation in a fuel performance code. A similar approach can be applied to the nucleation and growth of gas bubbles on incoherent inclusions, such as those observed in irradiated ODS steels.

Spatiotemporal analysis of aerosol dynamics in bismuth nucleation using multivariate Monte Carlo simulation

Aerosol evolution is a sensitive process which strongly depends on the spatiotemporal environment, especially for the nucleation serving as the source term. Challenges and interests are rising when insights are needed to evaluate the dynamic events within the process. In our recent study, a multivariate population balance Monte Carlo (PBMC) simulation coupled with computational fluid dynamics (CFD) was verified with experimental results measured in the homogenous nucleation from bismuth vapor. Therefore, a further analyze relating the main mechanisms is established, which covers the nucleation, condensation, coagulation and wall deposition. The nucleation is found the most significant and great discrepancies in aerosol parameters are contributed by different theories. Competition of vapor consumption between the nucleation and condensation determines the concentration of primary particles and following aggregate growth. The coagulation dominates the evolution after the nucleation, while the radial migration leading to wall deposition helps in averaging the spatiotemporal aerosol concentration.

Numerical investigation of non-equilibrium condensation of carbon dioxide from a gas mixture of carbon dioxide and argon in a supersonic nozzle under cryogenic conditions

This study involved a numerical investigation of the homogeneous nucleation of CO2 from a CO2–Ar gas mixture in a supersonic nozzle with a throat size of 2.11 mm, a total pressure of 61.15 kPa, and a total temperature of 293.15 K. The flow conditions covered the cryogenic temperature range (∼75 K). Therefore, the surface tension of the clusters was calculated using the Tolman–Tanaka correction, and nucleation growth was evaluated considering both free molecular and continuum regimes. Numerical simulations were conducted for a wide range of CO2 mole fractions (3%–39%). In particular, the effect of the CO2 mole fraction on the condensation-shock position—approximately the Wilson point—was investigated. For 3%, 12%, 24%, and 39%, the condensation shock occurred at 0.048, 0.043, 0.046, and 0.054 m from the throat, respectively. When the mole fraction was low (≤10%), the condensation-shock position moved downstream as the mole fraction decreased. This trend was attributed to a lower nucleation rate. In contrast, when the mole fraction was high (≥10%), the condensation-shock position moved downstream as the mole fraction increased. This was because the CO2 equilibrium pressure rose more rapidly than the CO2 vapor pressure as the mole fraction increases.

Modeling homogeneous ice nucleation from drop-freezing experiments: impact of droplet volume dispersion and cooling rates

Modeling homogeneous ice nucleation from drop-freezing experiments: impact of droplet volume dispersion and cooling rates

Li2ZnCu3 modified Cu current collector to regulate Li deposition

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high‐loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy‐modified Cu foil is reported as a stable current collector to fulfill the stable high‐loading Li deposition. Benefiting from the in‐situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm‐2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2% at 3 mA cm‐2/6 mAh cm‐2 over 200 cycles. Moreover, the Li‐Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5% after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm‐2), the cell exhibits a high energy density of 407.4 Wh kg‐1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high‐capacity, dendrite‐free, and dense Li deposition for high‐performance Li metal batteries.

Li2ZnCu3 Modified Cu Current Collector to Regulate Li Deposition.

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high-loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy-modified Cu foil is reported as a stable current collector to fulfill the stable high-loading Li deposition. Benefiting from the in situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm-2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2 % at 3 mA cm-2/6 mAh cm-2 over 200 cycles. Moreover, the Li-Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5 % after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm-2), the cell exhibits a high energy density of 407.4 Wh kg-1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high-capacity, dendrite-free, and dense Li deposition for high-performance Li metal batteries.

Direct quenching and tempering to achieve high strength and toughness of GPa-Grade nano-precipitated steel: The effect of precipitation behavior and variant selectivity

In order to satisfy the application requirements for strength and toughness of hydropower steels for large pumped storage power plants. In this study, based on the synergy of deformation and phase transition, the trade-off between strength and toughness was broken, and the GPa-grade nano-precipitated steel was prepared by direct quenching and tempering. The effects of Nb–V–Ti composite nano-precipitation behavior and martensite variant selectivity on the strengthening and toughening mechanisms were highlighted. The results show that directly quenched steel has the optimal comprehensive mechanical properties after tempering at 550 °C. Combining the contributions of various strengthening mechanisms, the increase in the yield strength relative to off-line quenching and tempering is mainly attributed to additional dislocation strengthening (∼33 MPa) and precipitation strengthening (∼174 MPa). Direct quenching enhances the homogeneous nucleation of finer mono- and binary precipitates and their stable growth during tempering, while the ternary precipitates do not suffer from elemental inhomogeneities due to lack of re-dissolution. Furthermore, the high-frequency variants of the dominant close-packed plane group tend to form high-angle grain boundaries with different orientations and planar alignments, derived from the refinement of Bain groups induced by the self-plasticity modulation of martensite transition due to the accumulation of deformed geometrically necessary dislocations and finite dislocation slip.

Molecular dynamics study of interstitial He clusters in nickel

This study presents a molecular dynamics analysis focusing on the behavior of interstitial helium (He) clusters in nickel (Ni), examining their formation, stability, and migration energetics. We found that the binding energies of interstitial He with a He cluster are positive and increase with the cluster size, indicating a preference for He atoms to cluster together. While the formation energy increases monotonically with cluster size, binding energy shows non-monotonic. trend Importantly, small He clusters were found to be thermally unstable at reactor operational temperatures (approximately 600 K), with the He2 cluster exhibiting instability even at room temperature. With a binding energy of 0.44 eV for a He4 cluster, we hypothesize that for He bubbles to form via homogeneous nucleation (i.e., through trap mutation) at reactor operating temperatures, the He concentration must be high enough to facilitate the formation of He clusters of at least size 4 or larger. At finite temperatures, He clusters of size 7 and larger trap mutate immediately. However, clusters of size 10 and larger will trap mutate even at 0 K. As expected, interstitial He and small He clusters are highly mobile, and found to be mobile even at temperatures as low as 200 K. Furthermore, the mean squared displacement method has been utilized to determine the activation energies and the corresponding prefactors for clusters ranging from He1 to He6

Microscopic in situ observation of electromechanical instability in a dielectric elastomer actuator utilizing transparent carbon nanotube electrodes.

Electromechanical instability (EMI) restricts the performance of dielectric elastomer actuators (DEAs), leading to premature electrical breakdown at a certain voltage. However, macro-level observations using traditional carbon grease electrodes have failed to capture the detailed features of EMI. In this study, we investigated EMI at the microscopic scale by fabricating transparent and conductive single-walled carbon nanotube (SWCNT) electrodes. Our findings reveal that EMI predominantly occurs in highly localized regions with dimensions on the order of tens of micrometers. This snap-through instability is likely induced by pre-existing defects within the elastomer, such as air voids or conductive particles, which reduce the critical voltage required for EMI in the flawed areas. From the perspective of phase transition principles, these defects act as heterogeneous nucleation sites for new phase embryos, thereby lowering the energy barrier for the electromechanical phase transition (i.e., EMI) compared to homogeneous nucleation in an ideally impurity-free elastomer. This study clarifies the longstanding discrepancy between theoretically predicted deformation bursts and the experimentally observed macroscopic continuous expansion of DEAs under low pre-stretch conditions. Additionally, it underscores the critical importance of material purity in mitigating electromechanical instability.

Mechanisms of electromagnetic field control on mineral scaling in brackish water reverse osmosis: Combined homogenous and heterogeneous nucleation

Electromagnetic field (EMF) treatment has emerged as a promising approach for scaling control due to its cost-effectiveness, simplicity, and low energy consumption. However, there is a limited understanding of the mechanisms by which applied EMF impacts mineral scaling in reverse osmosis (RO) systems. This has led to inconclusive and varied results and uncertainties regarding its effectiveness. This study elucidates the impacts of EMF on homogenous and heterogeneous nucleation and membrane performance during RO desalination of different feedwaters. Our results reveal that EMF exhibits greater efficacy in treating near-saturated water (SI∼0), especially when coupled with extended hydraulic flushing (HF). For saturated brackish water desalination, heterogeneous scaling predominantly occurs on membrane surfaces, with the effectiveness of EMF in inhibiting scaling primarily attributed to the hydration effect. In supersaturated solutions, EMF promotes bulk precipitation due to the magnetohydrodynamic effect, quickly blocking membrane pores. Thus, when the saturation reaches a certain high level during RO desalination, magnetohydrodynamic EMF effects can accelerate flux decline caused by homogeneous scaling. This work provides an efficient method for predicting EMF efficiency, emphasizing the importance of saturation conditions and HF cleaning duration in determining membrane performance, suggesting these show promise for improving undersaturated or near-saturated feedwater desalination via RO.