Phase Nucleation Research Articles

Vapor phase nucleation and sedimentation of dispersed nanodiamonds by MPCVD

Microwave plasma assisted chemical vapor deposition (MPCVD) is a technique for preparing high-quality diamonds. However, the low yield and easy bonding between particles are drawbacks in the preparation of nanodiamond (ND). These issues are mainly caused by the adverse phenomena such as substrate nucleation and the continuous growth of particles. To inhibit these phenomena, diamond vapor phase nucleation (VPN) is realized by adjusting the spatial distribution of the carbon and hydrogen groups in plasma. In this environment, NDs nucleate, grow and fall on the disk. As such, dispersed nanodiamonds are obtained and the yield limit of MPCVD prepared NDs is broken. Further, we analyze and improve the VPN growth mechanism. This study presents a new mode of using MPCVD, which can be used to grow dispersed NDs. The development and improvement of this method is expected to provide higher quality NDs for drug transportation, biological imaging, and quantum light sources.

STRUCTURE AND PROPERTIES OF REFRACTORY BIMONOCRYSTAL MICROCOMPOSITES

The features of high-gradient crystallization of refractory quasi-binary alloys have been studied. The processes of phase nucleation and their joint influence on the evolution of the formation of spatially ordered microstructures are considered. The possibility of regulating the volumetric ratio of phases by crystallization of alloys of noneutectic composition has been revealed. The results of expanding the area of compositional growth and the possibility of creating a regular quasi-eutectic microstructure without primary carbides are explained. The mechanism of post-crystallization heat treatment has been determined, leading to the purification of the matrix from interstitial impurities and embrittling carbides, the creation of perfect bi-monocrystalline materials that are thermally stable up to pre-melting temperatures with a high level of ductility and heat resistance.

Characteristic Plasmon Energies for 2D In2Se3 Phase Identification at Nanoscale.

Two-dimensional (2D) materials with competing polymorphs offer remarkable potential to switch the associated 2D functionalities for novel device applications. Probing their phase transition and competition mechanisms requires nanoscale characterization techniques that can sensitively detect the nucleation of secondary phases down to single-layer thickness. Here we demonstrate nanoscale phase identification on 2D In2Se3 polymorphs, utilizing their distinct plasmon energies that can be distinguished by electron energy-loss spectroscopy (EELS). The characteristic plasmon energies of In2Se3 polymorphs have been validated by first-principles calculations, and also been successfully applied to reveal phase transitions using in situ EELS. Correlating with in situ X-ray diffraction, we further derive a subtle difference in the valence electron density of In2Se3 polymorphs, consistent with their disparate electronic properties. The nanometer resolution and independence of orientation make plasmon-energy mapping a versatile technique for nanoscale phase identification on 2D materials.

Is the Local Ion Density Sufficient to Drive NaCl Nucleation from the Melt and Aqueous Solution?

Even though nucleation is ubiquitous in different science and engineering problems, investigating nucleation is extremely difficult due to the complicated ranges of time and length scales involved. In this work, we simulate NaCl nucleation in both molten and aqueous environments using enhanced sampling of all-atom molecular dynamics with deep-learning-based estimation of reaction coordinates. By incorporating various structural order parameters and learning the reaction coordinate as a function thereof, we achieve significantly improved sampling relative to traditional ad hoc descriptions of what drives nucleation, particularly in an aqueous medium. Our results reveal a one-step nucleation mechanism in both environments, with reaction coordinate analysis highlighting the importance of local ion density in distinguishing solid and liquid states. However, although fluctuations in the local ion density are necessary to drive nucleation, they are not sufficient. Our analysis shows that near the transition states, descriptors such as enthalpy and local structure become crucial. Our protocol proposed here enables robust nucleation analysis and phase sampling and could offer insights into nucleation mechanisms for generic small molecules in different environments.

Selective formation of metastable polymorphs in solid-state synthesis.

Metastable polymorphs often result from the interplay between thermodynamics and kinetics. Despite advances in predictive synthesis for solution-based techniques, there remains a lack of methods to design solid-state reactions targeting metastable materials. Here, we introduce a theoretical framework to predict and control polymorph selectivity in solid-state reactions. This framework presents reaction energy as a rarely used handle for polymorph selection, which influences the role of surface energy in promoting the nucleation of metastable phases. Through in situ characterization and density functional theory calculations on two distinct synthesis pathways targeting LiTiOPO4, we demonstrate how precursor selection and its effect on reaction energy can effectively be used to control which polymorph is obtained from solid-state synthesis. A general approach is outlined to quantify the conditions under which metastable polymorphs are experimentally accessible. With comparison to historical data, this approach suggests that using appropriate precursors could enable targeted materials synthesis across diverse chemistries through selective polymorph nucleation.

A deeper insight into the evaluation of water-in-oil amicroemulsion templated samarium sulfide nanospheres: exploring its role in pickering emulsion formulation for photocatalytic dye degradation and synthesis of PANI@Sm2S3 nanocomposites.

This study examines the effectiveness of W/O microemulsion-mediated Sm2S3 nanospheres in pickering emulsion-based crystal violet (CV) dye degradation and PANI@Sm2S3 nanocomposite synthesis. The evaluation of nanospheres inside the core of reverse micelles was performed through DLS, TEM and FESEM analyses. The formation of nanospheres involve two phases: a nucleation phase (5-30 min) and growth phase (30-120 min). Through in situ hydrophobization of negatively charged (with a zeta value of -4.47 mV at neutral pH) Sm2S3 nanoparticles (0.1 wt%) with a suitable amount of a cationic CTAB surfactant, a stable O/W pickering emulsion was developed. 0.1 wt% Sm2S3in situ hydrophobized with 2.7 mM CTAB offered a stable pickering emulsion with a diameter of 23 μm after 1 day of storage. This pickering emulsion improves the local concentration of CV by efficiently encapsulating dye molecules inside the core of emulsion droplets. Therefore, dye molecules get numerous opportunities to interact with the Sm2S3 photocatalyst and efficiently degrade. The pickering emulsion stabilised by 0.1 wt% of Sm2S3 nanoparticles in situ hydrophobized with 2.7 mM of CTAB results in almost 100% degradation. Moreover, using only solid Sm2S3 (having wt% of 0.025 or 0.075) as a pickering stabiliser, new PANI@Sm2S3 spherical nanocomposites were synthesised via pickering emulsion polymerization. The formation of PANI@Sm2S3 composites was identified via UV-vis, IR, and 1H-NMR investigations. The analysis of FESEM images showed that the amount of nanoparticles used in the dispersion (for 0.025 wt%, 35 nm and 0.075 wt%, 29 nm) strongly influences the size and shape of the composites.

Strategies to alleviate distortive phase transformations in Li-ion intercalation reactions: an example with vanadium pentoxide.

Chemical and electrochemical Li-ion insertion in transition metal oxides, either via a phase transformation reaction (ions insert into specific crystallographic sites of the host lattice) or a solid solution insertion (ions distribute uniformly throughout the host lattice), enables high energy density electrochemical energy storage. Many phase transformation cathode materials, that undergo two-phase reactions, exhibit high theoretical capacities arising from multi-electron redox reactions. However, challenges in distortive phase transformations and uncontrolled phase nucleation, propagation, segregation, and co-existence continue to limit the energy density, (dis)charging rate performances, and cycling stability of available phase transformation cathode materials. Vanadium pentoxide (V2O5), a classical layered intercalation host material with high theoretical capacity, undergoes irreversible structural changes and capacity fading when intercalating more than one lithium ion per V2O5 unit in its thermodynamically stable phase. Here, we review recent synthetic strategies to alter the V-O connectivity, thereby alleviating distortive phase transformations and promoting solid solution-based Li-ion insertion in V2O5. We also summarize several widely accessible and classical molecular-based analytical tools that can provide local structural dynamics and phase transformation mechanism information on the lithiation of V2O5, including single-crystal X-ray diffraction, infrared and Raman spectroscopy, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopy.

Mapping the influence of impurity interaction energy on nucleation in a lattice-gas model of solute precipitation.

We study nucleation in the two dimensional Ising lattice-gas model of solute precipitation in the presence of randomly placed static and dynamic impurities. Impurity-solute and impurity-solvent interaction energies are varied whilst keeping other interaction energies fixed. In the case of static impurities, we observe a monotonic decrease in the nucleation rate when the difference between impurity-solute and impurity-solvent interaction energies is increased. The nucleation rate saturates to a minimum value with increasing interaction energy difference when the impurity density is low. However the nucleation rate does not saturate for high impurity densities. Similar behaviour is observed with dynamic impurities both at low and high densities. We explore a broad range of both symmetric and anti-symmetric interactions with impurities and map the regime for which the impurities act as a surfactant, decreasing the surface energy of the nucleating phase. We also characterise different nucleation regimes observed at different values of interaction energy. These include additional regimes where impurities play the role of inert-spectators, bulk-stabilizers or cluster together to create heterogeneous nucleation sites for solute clusters to form.

Inhibition of cytotoxic self-assembly of HEWL through promoting fibrillation by new synthesized α-hydroxycarbamoylphosphinic acids.

The main objective of the present study is to investigate the potency of new synthesized hydroxycarbamoyl phosphinic acid derivatives in modulating cytotoxic fibrillogenesis of hen egg white lysozyme (HEWL), as a common model in protein aggregation studies. Hydroxycarbamoyl phosphinic acid derivatives were prepared by the reaction of α-hydroxyalkylphosphinic acids with isocyanates (or isothiocyanates) in the presence of trimethylsilyl chloride (TMSCl). The designed process involves the condensation reaction leading to formation of new C sp2-P bond formation. The synthesis and purity of novel designed compounds were confirmed by NMR, LC-MS, and HPLC techniques. A range of experiments, including thioflavin T (ThT) and 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence assays, Congo red binding measurement, atomic force microscopy imaging, MTT-based cell viability and hemolysis assays were employed to investigate anti-amyloidogenic effects of tested compounds. The obtained results demonstrate that these compounds are able to significantly modulate the self-assembly process of HEWL via shortening of nucleation phase leading to the acceleration of fibrillation and appearance of very large and thick fibrils with decreased surface hydrophobicity and cytotoxicity. Based on ANS binding data, we suggest that increased exposure of hydrophobic patches of oligomeric species is the possible mechanism by which tested compounds promote self-assembly process of HEWL. Fluorescence anisotropy and molecular docking studies indicate the interaction of both synthesized compounds with HEWL, and more specifically with residues that are situated in the highly aggregation-prone β-domain region of protein. This study unveils the potential of hydroxyalkylphosphinic acids as modulators of amyloid fibrillation highlighting these compounds as a promising approach for targeting protein aggregates associated with neurodegenerative diseases.

Raman Gain in Transparent Nanostructured Glass-Ceramic

Stimulated Raman scattering in transparent glass-ceramics (TGCs) based on bulk nucleating phase Ba2NaNb5O15 were investigated with the aim to explore the influence of micro- and nanoscale structural transformations on Raman gain. TGCs are composed of nanocrystals that are 10–15 nm in size, uniformly distributed in the residual glass matrix. A significant Raman gain improvement for both BaNaNS glass and TGCs with respect to SiO2 glass is demonstrated, which can be clearly related to the nanostructuring process.

Protein Compartments Modulate Fibrillar Self-Assembly.

A notable feature of complex cellular environments is protein-rich compartments that are formed via liquid-liquid phase separation. Recent studies have shown that these biomolecular condensates can play both promoting and inhibitory roles in fibrillar protein self-assembly, a process that is linked to Alzheimer's, Parkinson's, Huntington's, and various prion diseases. Yet, the exact regulatory role of these condensates in protein aggregation remains unknown. By employing microfluidics to create artificial protein compartments, the self-assembly behavior of the fibrillar protein lysozyme within them can be characterized. It is observed that the volumetric parameters of protein-rich compartments can change the kinetics of protein self-assembly. Depending on the change in compartment parameters, the lysozyme fibrillation process either accelerated or decelerated. Furthermore, the results confirm that the volumetric parameters govern not only the nucleation and growth phases of the fibrillar aggregates but also affect the crosstalk between the protein-rich and protein-poor phases. The appearance of phase-separated compartments in the vicinity of natively folded protein complexes triggers their abrupt percolation into the compartments' core and further accelerates protein aggregation. Overall, the results of the study shed more light on the complex behavior and functions of protein-rich phases and, importantly, on their interaction with the surrounding environment.

Phase-Pure α-FAPbI3 Perovskite Solar Cells via Activating Lead-Iodine Frameworks.

Narrow bandgap cubic formamidine perovskite (α-FAPbI3) is widely studied for its potential to achieve record‑breaking efficiency. However, its high preparation difficulty caused by lattice instability is criticized. A popular strategy for stabilizing the α-FAPbI3 lattice is to replace intrinsic FA+ or I- with smaller ions of MA+, Cs+, Rb+, and Br-, whereas this generally leads to broadened optical bandgap and phase separation. Studies show that ions substitution-free phase-pure α-FAPbI3 can achieve intrinsic phase stability. However, the challenging preparation of high-quality films has hindered its further development. Here, a facile synthesis of high-quality MA+, Cs+, Rb+, and Br--free phase-pure α-FAPbI3 perovskite film by a new solution modification strategy is reported. This enables the activation of lead-iodine (Pb─I) frameworks by forming the coated Pb⋯O network, thus simultaneously promoting spontaneous homogeneous nucleation and rapid phase transition from δ to α phase. As a result, the efficient and stable phase-pure α-FAPbI3 PSC is obtained through a one-step method without antisolvent treatment, with a record efficiency of 23.15% and excellent long-term operating stability for 500 h under continuous light stress.

NAGPKin: Nucleation-and-growth parameters from the kinetics of protein phase separation.

The assembly of biomolecular condensate in eukaryotic cells and the accumulation of amyloid deposits in neurons are processes involving the nucleation and growth (NAG) of new protein phases. To therapeutically target protein phase separation, drug candidates are tested in in vitro assays that monitor the increase in the mass or size of the new phase. Limited mechanistic insight is, however, provided if empirical or untestable kinetic models are fitted to these progress curves. Here we present the web server NAGPKin that quantifies NAG rates using mass-based or size-based progress curves as the input data. A report is generated containing the fitted NAG parameters and elucidating the phase separation mechanisms at play. The NAG parameters can be used to predict particle size distributions of, for example, protein droplets formed by liquid-liquid phase separation (LLPS) or amyloid fibrils formed by protein aggregation. Because minimal intervention is required from the user, NAGPKin is a good platform for standardized reporting of LLPS and protein self-assembly data. NAGPKin is useful for drug discovery as well as for fundamental studies on protein phase separation. NAGPKin is freely available (no login required) at https://nagpkin.i3s.up.pt.

Microstructure and Crystallographic Texture Evolution of β-Solidifying γ-TiAl Alloy During Single- and Multi-track Exposure via Laser Powder Bed Fusion

The microstructural evolution and crystallographic texture formation of β-solidifying Ti-44Al-6Nb-1.2Cr alloy were identified under single- and multi-track exposures via laser powder bed fusion (L-PBF) for various process parameters. Under single-track exposure, the microstructure of the melt pool was divided into the band-like α2 phase in the melt pool boundary and β phase in the melt pool center. Numerical and thermodynamic simulations revealed that the underlying mechanism of phase separation was related to the variation in the cooling rate in the melt pool, whereas microsegregation induced a shift in the solidification path. Meanwhile, the crystallographic texture of the α2 phase region was identical to that of the substrate owing to the epitaxial growth of the β phase and subsequent α phase nucleation. In contrast, the β phase exhibited a ± 45° inclined <100> alignment in the melt pool, which was tilted to align along the build direction toward the center of the melt pool corresponding to the simulated thermal gradient direction. Furthermore, the narrow hatch space condition maintained the crystallographic texture to the subsequent scan, forming a continuous band-like α2 phase with a strong selection. However, the crystallographic texture in a wide hatch space condition manifested a random distribution and constituted a fine mixture of the β and α2 phases. For the first time, these results will offer an understanding of an anisotropic microstructure control via the L-PBF process and ensure the tailoring of the mechanical properties in the β-solidifying γ-TiAl-based alloys by approaching hatch spacing control.Graphic

Regulating microstructures of aerogels by controlling phase separation mechanism for improving specific surface area and energy harvesting

Aerogels with 3D porous structures have been attracting increasing attention among functional materials due to their advantages of being lightweight and high specific surface area. Precise control of the porous structure of aerogel is essential to improve its performance. In this work, polylactic acid (PLA) aerogels with distinctly different microstructures were fabricated by precisely controlling the phase separation behavior of the ternary solution system. Rheological and theoretical analyses have revealed that the interactions between polymer molecules, solvents and non-solvents play a crucial role in determining the nucleation and growth of poor olymer and rich polymer phases. By adjusting the non-solvent type and the solution composition, aerogels with spider network structure, bead-like connected microsphere structure, and cluster petal structure were obtained. Ideal spinodal phase separation conditions were obtained to produce aerogels with a homogeneous fiber network structure. The optimum PLA aerogel achieved an extremely porosity of 96 % and a high specific surface area of 114 m2/g, which rendered it with excellent triboelectric generation performance. Thus, this work provides fundamental insights into the precise regulation of the phase separation behavior and the structure of the aerogel, which can help boost the performance and expand the applications of PLA aerogels.

Atomic-level characterization of η-twins with non-homogeneous nucleation on the E(Al18Mg3Cr2) phase in 7075 alloy: TEM observations and DFT calculations

In this work, an uncommon type of η-twin with non-homogeneous nucleation on the surface of the E-phase is characterized, and two defects and growth processes of the twin are analyzed. According to the transmission electron microscopy image analysis, heterogeneous nucleation of the η phase at the dominant site of the E phase can lead to the formation of such η-twin only when a rather strict site-direction relationship is satisfied as well as when it is at the interface adjacent to the E phase. The formation of twin defects is related to the E phase but ultimately determined by the nature of the η phase, and the crystallographic relationship between the defect structure and the E phase is self-consistent. Combined with the analytical results from STEM, first-principles calculations show that the solute segregation at the defects reduces the total energy of the system, which favors the transition of the η phase of the heterogeneous nucleation and the formation of twins, and that solute Al is more favorable than Mg. In addition, the elemental distribution and effects in the precipitation-free zone were analyzed by EDS mapping.

Coherent and semicoherent α/β interfaces in titanium: structure, thermodynamics, migration

The α/β interface is central to the microstructure and mechanical properties of titanium alloys. We investigate the structure, thermodynamics and migration of the coherent and semicoherent Ti α/β interfaces as a function of temperature and misfit strain via molecular dynamics (MD) simulations, thermodynamic integration and an accurate, DFT-trained Deep Potential. The structure of an equilibrium semicoherent interface consists of an array of steps, an array of misfit dislocations, and coherent terraces. Analysis determines the dislocation and step (disconnection) array structure and habit plane. The MD simulations show the detailed interface morphology dictated by intersecting disconnection arrays. The steps are shown to facilitate α/β interface migration, while the misfit dislocations lead to interface drag; the drag mechanism is different depending on the direction of interface migration. These results are used to predict the nature of α phase nucleation on cooling through the α-β phase transition.

Multi-functional piezoelectric nanogenerator based on relaxor ferroelectric materials (BSTO) and conductive fillers (MWCNTs) for self-powered memristor and optoelectronic devices

Nowadays self-charging memristors and photodetectors open the path for future research into energy-autonomous electronics which hold the promise of enabling exceptionally efficient applications in memory storage, small portable electronics, neuromorphic computing, and optoelectronics devices. Hence, in the recent era, much research work has been focused on the development of nanogenerators for technological applications. In this regard, the main aim of the present study is to develop a multi-functional piezoelectric nanogenerator based on relaxor ferroelectric materials having three-phase MWCNTs/BSTO/PVDF nanocomposites. BSTO and CNT fillers promote >80 % electroactive phase nucleation in PVDF, making it appropriate for piezoelectric energy harvesting devices. Incorporating conductive fillers (CNTs) and dielectric fillers (BSTO) into the PVDF matrix enhances the piezoelectric nanogenerator's dielectric, ferroelectric, and output performance. PENG based on an optimized BSTO-CNTs-PVDF composite (with 20 % BSTO and 0.20 % CNTs loading) produced an output power of 31.5 µW with a high open-circuit voltage of 42 V and a short-circuit current of 9 µA, it demonstrates enough capability to power up small portable electronic devices. This work can also be used for a realistic technique for generating self-powered memristors and photodetectors for extremely efficient memristive neural networks and optoelectronics devices. Demonstration of power generation of the prepared device by different activities is demonstrated.

Phase stability and nucleation kinetics of salts in confinement

Of fundamental importance to energy storage, electrochemistry and separation processes, ionic liquids in confinement exhibit unexpected thermodynamic behaviors. Such complex behaviors highlight the need for multi-scale descriptions of the thermodynamics and dynamics of nanoconfined ionic liquids. Here, we probe the impacts of confinement on the freezing point and nucleation kinetics of a simple molten salt which shares important features with ionic liquids. Using molecular modeling techniques, the melting temperature of salt in confinement is found to be larger than its bulk counterpart. Relying on conventional thermodynamic models (Clapeyron and Gibbs-Thomson equations), we capture the crystal/liquid coexistence in bulk and confinement with simple parameters derived from molecular simulations. Then, by considering different nucleation mechanisms – bulk, surface, and confined nucleation, the metastability barrier upon salt formation is shown to decrease upon confinement, therefore providing theoretical insight into the larger nucleation rate constants observed in experiments on nanoconfined ionic liquids. We also discuss the effects of wettability on capillary freezing of ionic liquids at various confining surfaces through varying the contact angle. These findings provide a practical means to predict the melting point, wettability, and freezing kinetics of ionic liquids at various surface conditions from simple thermodynamic data.

Insights into the development of Fe modified Ti-Nb alloy: A powder metallurgy perspective

This study explores a cost-effective method for fabricating Ti95-xFexNb5 ternary alloys along with investigating the influence of Fe addition. Spark Plasma Sintering at low sintering temperatures followed by heat treatment was used to obtain fully dense and homogenized compacts. Initially for composition with 0% Fe by weight, a Widmanstätten microstructure was observed along with coarse α plates that nucleated on the grain boundaries. The addition of Fe refined the microstructure reducing the size of α plates. The solute-drag effect of Fe led to a progressive decrease in parent β grain size. In alloy with 10% Fe by weight, Widmanstätten structure transformed into β grains while α phase nucleation was greatly suppressed. Moreover, the incorporation of Fe in β phase lattice led to a strong partitioning effect at microstructural level and lattice distortion effect at atomic level. These factors resulted in a pronounced strengthening of the alloy increasing the hardness and tensile strength. However, these factors also led to the embrittlement of the composition containing 10% Fe by weight. The study highlight the potential of powder metallurgy approach which offers avenues for cost efficient Ti alloy production. However, incorporation of high Fe concentrations should be paralleled with careful microstructural design.