Nucleation Probability Research Articles

Non-invasive monitoring of the growth of metal-organic frameworks (MOFs) via Raman spectroscopy.

The applicability of Raman spectroscopy for phase discrimination of metal-organic frameworks (MOFs) has been demonstrated with F4_MIL-140A(Ce) and F4_UiO-66(Ce); analogues prepared from the same metal and ligand sources. Each analogue exhibits unique Raman peaks, with significant differences in the low frequency region, which is more sensitive to structural variations. Non-invasive Raman monitoring of F4_MIL-140A(Ce) synthesis indicated evolution of a unique MOF Raman peak with reaction progress; conversion of this Raman signal to extent of crystallisation was in good agreement with reported reaction kinetics determined via a synchrotron diffraction method. Additionally, Raman spectroscopy indicated initial rapid consumption of the nitric acid modulator present in the reaction coinciding with an expected high probability of nucleation. Raman spectroscopy is a promising technique for rapid screening of MOFs and can be used to study the mechanism of their formation in situ with kinetic insight into both the solution and solid phases of the reaction medium.

An extended model for chirality selection in single-walled carbon nanotubes.

The chirality selective production of single-walled carbon nanotubes (SWCNTs) continues to represent one of the most important technological challenges. In this study, an extended model which considers all steps of the SWCNT growth process, including adsorption, decomposition, diffusion, and incorporation, is applied, for the first time, to obtain chirality selection in the SWCNT populations. We show that the dependence of the population distribution on chirality, defined as a product of the nucleation probability and the growth rate, has a volcano-shape. The model is in good agreement with the reported experimental studies and supports the results which show the surplus of near armchair or near zigzag SWCNTs. The present work emphasizes the role of the catalyst in chirality selection via optimization of chemisorption strength between the carbon species and the catalyst surface needed to achieve stable nucleation and fast growth rates. The obtained results can be used in catalyst designs to define the pathways towards the growth of SWCNTs with specific chiralities exhibiting distinguished electronic properties.

Study of the Immersion Freezing Theory Using the Classical Nucleation Framework

The classical nucleation theory for immersion freezing was used for the simulation of ice nuclei particle activation under atmospheric conditions. A modification of the surface diffusion energy was introduced that was based on the concept of a two-dimensional diffusion of the adsorbed molecules on the surface of the substrate. Comparison with available laboratory data for kaolinite dust and bacteria cells were performed and qualitative agreement of ice nucleation onset was found. Simulations were performed for specific airborne microorganisms including P. syringae. Additionally, model simulations were performed for a set of 140 different bacteria. Model simulations showed that bacteria activation occurs in the atmosphere, which may be enhanced at lower temperatures. Increasing pre-existing available surface for ice nucleation resulted in higher nucleation probability in agreement with experimental observations. The current study showed that a critical parameter for the determination of IN is the value of the contact angle between the substrate and the critical cluster. Comparison with available parameterizations for P. syringae and dust particles was also performed, and classical nucleation theory showed similar nucleation rates in the temperature range of laboratory experiments from which the parameterizations were derived. In addition, a correction factor to bulk surface tension was applied for small ice clusters. Higher nucleation rates were calculated from this correction by a few orders of magnitude but their effect on nucleation probability was not significant. The classical nucleation theory is based on physical principles and can be further incorporated in General Circulation Models to determine the IN activation in the atmosphere for a mixture of different pre-existing particles including bacteria cells and dust.

Influence of Hot Band Annealing on Cold-Rolled Microstructure and Recrystallization in AA 6016

The influence of an intermediate heat treatment at the end of hot rolling and before cold rolling on Cube texture formation during the final solution annealing of AA 6016 is investigated. Three hot bands with different initial grain sizes and textures are considered: the first one without annealing before cold rolling, while the other two hot bands are heat treated at 540 °C for 1 hour in air before being cold rolled. One of the heat-treated hot bands was left to cool down in air and the other inside the furnace. Electron-backscatter diffraction (EBSD) maps of the cold-rolled specimens and crystal plasticity simulations show no difference in the amount of Cube remaining in the microstructure at the end of cold rolling for all three specimens. The initial grain size of the hot band has no influence on the Cube texture fraction left in the microstructure at the end of cold rolling for thickness reductions higher than 65 pct. Nevertheless, the grain size of the hot band affects the shape and distribution of the Cube grains left in the microstructure and the kernel average misorientation in the cold-rolled specimens. Moreover, the heat treatment decreases the intensity of the beta fiber components (Brass, Copper, and S) in the hot band and promotes the formation of a cold-rolled microstructure with a low kernel average misorientation. Both these factors lower the probability of preferential Cube nucleation during solution annealing and keep the Cube volume fraction after recrystallization below 10 pct, while it reaches 25 pct without intermediate annealing.

Influences of oil collector on surface air nucleation in fine graphite flotation

This paper investigates the effect of an oil collector, namely diesel oil, on surface air nucleation and the influence of nucleation microbubbles on collector adsorption in froth flotation. In order to prepare the condition for air nucleation in flotation, air-oversaturated water was produced using tap water pressurized by high-pressure air in an autoclave. Micro-flotation, single bubble collision experiments, contact angle measurements, microscopic observations, and agglomerations analysis were combined to investigate the effects of the oil collector on air nucleation and agglomerates formation. Furthermore, the free energy changes in an ideal system were utilized to explain the mechanisms. The experimental results and free energy changes show that diesel oil can improve the air nucleation probability on graphite surfaces by decreasing the barrier for nucleation. Meanwhile, the oil collector can also significantly increase the fraction of agglomerates formed in air-oversaturated water to improve the recovery of fine particles. Besides, the results indicate that the formation of nucleation microbubbles before collector conditioning can occupy significant surface areas of the graphite particles and inhibit the collector adsorption on the mineral surfaces.

New Cocrystallization Method: Non-photochemical Laser-Induced Nucleation of a Cocrystal of Caffeine–Gallic Acid in Water

This paper reports for the first time the crystallization of cocrystals (caffeine–gallic acid) in water using the non-photochemical laser-induced nucleation (NPLIN) technique. The nucleation temporal control of NPLIN and the induction time reduction (70 times shorter than spontaneous nucleation) allow the obtention of cocrystals on demand, with excellent repeatability. Prior to NPLIN experiments, solubility measurements, metastable zone limit determination, and spontaneous nucleation (SN) are carried out. Supersaturated solutions at three different molarities of caffeine (0.0158, 0.0167, and 0.0179 M) are prepared and dissolved at 338 K. Supersaturated solutions are exposed to a 532 nm-wavelength nanosecond pulsed laser at 296 K. Some hours later, crystals can be filtered. The impact of supersaturation on probability of nucleation has been studied, and the result shows a higher supersaturation, which implies a higher probability of nucleation. Crystalline form characterization has employed a combination of Raman scattering, high-performance liquid chromatography, thermogravimetry, differential scanning calorimetry, and powder X-ray diffraction; the sizes of the cocrystals are too small for a single-crystal X-ray diffraction experiment. Two different cocrystal forms are obtained: a new polymorph of hemihydrate CAFGAL.0.5H2O from spontaneous nucleation by precipitation and a new hydrate form CAFGAL.1.5H2O from NPLIN and from spontaneous nucleation of a supersaturated solution without evaporation. These results open a promising way to crystallize cocrystals in the context of the pharmaceutical industry.

Quantum nucleation of topological solitons

The chiral soliton lattice is an array of topological solitons realized as ground states of QCD at finite density under strong magnetic fields or rapid rotation, and chiral magnets with an easy-plane anisotropy. In such cases, topological solitons have negative energy due to topological terms originating from the chiral magnetic or vortical effect and the Dzyaloshinskii-Moriya interaction, respectively. We study quantum nucleation of topological solitons in the vacuum through quantum tunneling in 2 + 1 and 3 + 1 dimensions, by using a complex ϕ4 (or the axion) model with a topological term proportional to an external field, which is a simplification of low-energy theories of the above systems. In 2 + 1 dimensions, a pair of a vortex and an anti-vortex is connected by a linear soliton, while in 3 + 1 dimensions, a vortex is string-like, a soliton is wall-like, and a disk of a soliton wall is bounded by a string loop. Since the tension of solitons can be effectively negative due to the topological term, such a composite configuration of a finite size is created by quantum tunneling and subsequently grows rapidly. We estimate the nucleation probability analytically in the thin-defect approximation and fully calculate it numerically using the relaxation (gradient flow) method. The nucleation probability is maximized when the direction of the soliton is perpendicular to the external field. We find a good agreement between the thin-defect approximation and direct numerical simulation in 2 + 1 dimensions if we read the vortex tension from the numerics, while we find a difference between them at short distances interpreted as a remnant energy in 3 + 1 dimensions.

The tunneling wavefunction in Kantowski-Sachs quantum cosmology

We use a path-integral approach to study the tunneling wave function in quantum cosmology with spatial topology S 1 × S 2 and positive cosmological constant (the Kantowski-Sachs model). If the initial scale factors of both S 1 and S 2 are set equal to zero, the wave function describes (semiclassically) a universe originating at a singularity. This may be interpreted as indicating that an S 1 × S 2 universe cannot nucleate out of nothing in a non-singular way. Here we explore an alternative suggestion by Halliwell and Louko that creation from nothing corresponds in this model to setting the initial volume to zero. We find that the only acceptable version of this proposal is to fix the radius of S 1 to zero, supplementing this with the condition of smooth closure (absence of a conical singularity). The resulting wave function predicts an inflating universe of high anisotropy, which however becomes locally isotropic at late times. Unlike the de Sitter model, the total nucleation probability is not exponentially suppressed, unless a Gauss-Bonnet term is added to the action.

Carbon Dioxide Triggers Carbon Nanotube Nucleation: Isotope Labeling Study on the Growth Process of Individual Nanotubes

Growing long and high-density arrays of semiconducting single-walled carbon nanotubes is the key to building high-performance electronics. From the growth process perspective, the density and length of carbon nanotubes are determined by their nucleation probability from individual catalysts, subsequent growth rates, and growth lifetime. Here, we study the effects of additive oxygen-containing species on the growth process at the individual nanotube level during alcohol chemical vapor deposition. When tracing the growth process by isotope labeling techniques, the growth rates are slowed down upon the addition of CO2 due to carbon removal from catalysts. This simultaneously leads to a noticeable extension of the growth lifetime, which has the overall effect of lengthening the nanotube arrays. According to the relationship between the timing of CO2 supply and the growth initiation time of each nanotube, we surprisingly find that the oxidants also trigger the growth initiation, leading to the improvement of nanotube density. As all these effects of the additive oxidants can be explained by the tuning of the supersaturation level of carbon on catalysts, our results suggest the importance of choosing the appropriate balance of carbon sources and oxidants for the simultaneous control of density and length of carbon nanotube arrays.

Influence of MIBC on the surface-air nucleation and bubble-particle loading in graphite froth flotation

This paper investigates one aspect of surface air nucleation in froth flotation, namely the impact of frother-type surfactants like Methyl isobutyl carbinol (MIBC). During this study, tap water was pressurized in an autoclave to produce air-oversaturated water for air nucleation precondition in flotation. Various experiments were carried out with graphite particles to investigate the influences of gas nucleation and MIBC on flotation: micro-flotation, single bubble collision experiments in hydrodynamic conditions and pick-up experiments in static conditions. In addition, microscopic observations were combined with agglomeration analysis to clarify the effects of the frother MIBC on the air nucleation and agglomerate formation. The experimental results show the combination of MIBC and air nucleation can significantly increase the graphite recovery compared to using air-oversaturated water or normal tap water with MIBC alone, respectively. The analysis indicates that MIBC can improve the air nucleation probability on graphite surfaces by enhancing the stability of the air nuclei to form more microbubbles on the surface. Meanwhile, the surface microbubbles can collide with other particles forming coarser aggregates, improving their collision probability and with this increasing the recovery of fine particles. Furthermore, the results show that MIBC can reduce the detachment of particles from the surface of nucleation bubbles, leading to an increase in particle load of the bubble-particle aggregates in hydrodynamic conditions, improving the graphite recovery significantly.

Through Diffusion Measurements of Molecules to a Numerical Model for Protein Crystallization in Viscous Polyethylene Glycol Solution

Protein crystallography has become a popular method for biochemists, but obtaining high-quality protein crystals for precise structural analysis and larger ones for neutron analysis requires further technical progress. Many studies have noted the importance of solvent viscosity for the probability of crystal nucleation and for mass transportation; therefore, in this paper, we have reported on experimental results and simulation studies regarding the use of viscous polyethylene glycol (PEG) solvents for protein crystals. We investigated the diffusion rates of proteins, peptides, and small molecules in viscous PEG solvents using fluorescence correlation spectroscopy. In high-molecular-weight PEG solutions (molecular weights: 10,000 and 20,000), solute diffusion showed deviations, with a faster diffusion than that estimated by the Stokes–Einstein equation. We showed that the extent of the deviation depends on the difference between the molecular sizes of the solute and PEG solvent, and succeeded in creating equations to predict diffusion coefficients in viscous PEG solutions. Using these equations, we have developed a new numerical model of 1D diffusion processes of proteins and precipitants in a counter-diffusion chamber during crystallization processes. Examples of the application of anomalous diffusion in counter-diffusion crystallization are shown by the growth of lysozyme crystals.

Microfluidic Platform with Serpentine Geometry Providing Chaotic Mixing in Induction Time Experiments.

We present a droplet microfluidic platform mixing the contents of the droplet chaotically in microfluidic induction time measurements, a promising method for quantifying nucleation kinetics with minute amounts of solute. The nucleation kinetics of aqueous potassium chloride droplets dispersed in mineral oil without surfactants is quantified in the presence and absence of chaotic mixing. We demonstrate the ability of the proposed platform to dictate droplet size, to provide a homogeneous temperature distribution, and to chaotically mix the droplet contents. Chaotic mixing in induction time measurements is facilitated by the motion of droplets through serpentine micromixer bends, while the extent of mixing is controlled by how much droplets move. Different nucleation kinetics are observed in experiments where the droplets are static, mixed, and in motion. We hypothesize that the droplet motion induces formation of a thin-liquid Bretherton film surrounding the droplets. The thin film shields droplets from solid boundaries that are more efficient heteronucleant surfaces compared to liquid–liquid interfaces. We observed that repeated microfluidic induction time measurements, particularly with moving droplets, produce significantly distinct cumulative nucleation probability curves, indicating that the measured nucleation kinetics depend strongly on the details of the experimental procedure, which we discuss in detail. Finally, we compare the microfluidic experiments to well-mixed, milliliter volume, turbidity-based measurements in the context of classic nucleation theory.

Uncertainty Quantification for Microstructure-Sensitive Fatigue Nucleation and Application to Titanium Alloy, Ti6242

Microstructure of polycrystalline materials has profound effects on fatigue crack initiation, and the inherent randomness in the material microstructure results in significant variability in fatigue life. This study investigates the effect of microstructural features on fatigue nucleation life of a polycrystalline material using an uncertainty quantification framework. Statistical volume elements (SVE) are constructed, where features are described as probability distributions and sampled using the Monte Carlo method. The concept of SVE serves as the tool for capturing the variability of microstructural features and consequent uncertainty in fatigue behavior. The response of each SVE under fatigue loading is predicted by the sparse dislocation density informed eigenstrain based reduced order homogenization model with high computational efficiency, and is further linked to the fatigue nucleation life through a fatigue indicator parameter (FIP). The aggregated FIP and its evolution are captured using a probabilistic description, and evolve as a function of time. The probability of fatigue nucleation is measured as the probability that the predicted FIP exceeds the local critical value which represents the ability of material to resist the fatigue load. The proposed framework is implemented and validated using the fatigue response of titanium alloy, Ti-6Al-2Sn-4Zr-2Mo (Ti-6242).

Relating Metabolism Suppression and Nucleation Probability During Supercooled Biopreservation.

Aqueous supercooling provides a method by which to preserve biological matter at subfreezing temperatures without the deleterious effects of ice formation. The extended longevity of the preserved biologic is a direct result of a reduction in the rate of metabolism with decreasing temperature. However, because the nucleation of ice from a supercooled solution is a stochastic process, supercooled preservation carries the risk of random ice nucleation. Theoretical supercooled biopreservation research to date has largely treated these biological and thermophysical phenomena separately. Here, we apply a statistical model of stochastic ice nucleation to demonstrate how the possible reduction in metabolic rate is inherently related to supercooling stability (i.e., the likelihood of ice nucleation). We develop a quantitative approach by which to weigh supercooling stability versus potential metabolic reduction, and further show how the stability-metabolism relationship varies with system size for two assumed modes of nucleation. Ultimately, this study presents a generalizable framework for the informed design of supercooled biopreservation protocols that considers both phase transformation kinetics and biochemical or biophysical kinetics.

The Intrinsic Thermodynamic Difficulty and a Step-Guided Mechanism for the Epitaxial Growth of Uniform Multilayer MoS2 with Controllable Thickness.

Multilayer MoS2 shows superior performance over the monolayer MoS2 for electronic devices while the growth of multilayer MoS2 with controllable and uniform thickness is still very challenging. It is revealed by calculations that monolayer MoS2 domains are thermodynamically much more favorable than multilayer ones on epitaxial substrates due to the competition between surface interactions and edge formation, leading accordingly to a layer-by-layer growth pattern and non-continuously distributed multilayer domains with uncontrollable thickness uniformity. The thermodynamics model also suggests that multilayer MoS2 domains with aligned edges can significantly reduce their free energy and represent a local minimum with very prominent energy advantage on a potential energy surface. However, the nucleation probability of multilayer MoS2 domains with aligned edges is, if not impossible, extremely rare on flat substrates. Herein, a step-guided mechanism for the growth of uniform multilayer MoS2 on an epitaxial substrate is theoretically proposed. The steps with proper height on sapphire surface are able to guide the simultaneous nucleation of multilayer MoS2 with aligned edges and uniform thickness, and promote the continuous growth of multilayer MoS2 films. The proposed mechanism can be reasonably extended to grow multilayer 2D materials with uniform thickness on epitaxial substrates.

Wafer-scale epitaxial modulation of quantum dot density

Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-densities for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/µm2 and periods ranging from several millimeters down to at least a few hundred microns. This method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer.

A direct test of Auger cascade induced nucleation from heavy element contamination in C3F8 bubble chambers

Understanding and quantifying the gamma-induced bubble nucleation background in clean nuclear recoil detection bubble chambers is of utmost importance to bubble chamber based dark matter searches. We present data confirming the hypothesis that large Auger cascades from high-Z elements such as iodine and xenon dramatically increase the response of C3F8 bubble chambers to gamma rays. These tests, performed with a small calibration bubble chamber filled with C3F8+\U0001d4aa(10) ppm xenon, show that the probability of bubble nucleation scales with the rate of xenon inner-shell vacancies, reaching values >10% per K-Shell vacancy for Seitz thresholds of interest to future dark matter searches in bubble chambers. We also place an upper limit on bubble nucleation probability for argon Auger events, relevant to large future bubble chambers which may contain some residual atmospheric argon after the active fluid fill.

Texture Evolution by Strain-Induced Boundary Migration during Hot Deformation of Fe-3.0 wt.% Si Alloy: Experiment and Modeling

Texture and microstructure evolution during high-temperature plane-strain compression in Fe-3.0 wt.% Si alloy has been investigated by micro-texture analysis and modeling. In this study, hot deformation test is performed on the temperature range of 900 °C~1150 °C with a strain rate scope of 0.01 s−1~5 s−1, and the effect of deformation parameters is investigated by means of electron backscattered diffraction. Nucleation and growth assisted by strain-induced boundary migration result in strong {001}<110> and {001}<210> texture components with low Taylor factors, and the grain size of λ fiber increases significantly by consuming the {111}<110> and {111}<112> texture components with high Taylor factors. The critical Taylor factor above which nucleation by strain-induced boundary migration cannot occur, decreases continuously during hot deformation. With the decreasing critical Taylor factor, the increment rate of low-Taylor-factor orientation depends more sensitively on Taylor factor than the decrement rate of high-Taylor-factor orientation. The boundary separating enhanced and weakened orientations moves towards lower Taylor factor with the deformation proceeding, and medium-Taylor-factor texture components may experience a reversed change from enhancement to weakness. A quantitative model is proposed to describe texture development by incorporating the oriented nucleation probability dependent on a variable critical Taylor factor and the selective growth driven by a variable Taylor factor difference between adjacent grains. The present work can provide an efficient method for optimizing hot deformation texture by means of strain-induced boundary migration.

Nucleation probability of Type-A tetra-n-butyl ammonium bromide semi-clathrate hydrate via the memory effect

The memory effect in clathrate hydrates is known to produce recrystallization under milder conditions than those needed for the initial nucleation. Tetra-n-butyl ammonium bromide (TBAB) forms tetragonal (type A) as well as orthorhombic (type B) semi-clathrate hydrate in aqueous solution. Here we investigate the nucleation probability for recrystallization of type A TBAB hydrate via the memory effect. Using optical microscopy, we observed recrystallization in situ under various concentrations of aqueous solution. After their initial nucleation, the hydrate crystals were dissociated by raising the temperature and then cooled to slightly below the equilibrium temperature while measuring the nucleation probability and induction times for recrystallization. We found the nucleation probability to be highest at about 20 wt%, which is about half of the stoichiometric weight fraction of 40 wt%, and found the shortest induction time at about 30 wt%. These results suggest the importance of free water in solution to nucleate TBAB hydrate crystal with the memory effect. We also found that the nucleation occurred near the location of prior dissociation and the nucleation probability decreased when we increased the temperature of dissociation. Both of these findings support the concept that there exists a residual water structure from the dissociated hydrate that promotes nucleation.

Developing parametrically upscaled constitutive and crack nucleation models for the [formula omitted] Ti64 alloy

This paper develops Parametrically Upscaled Constitutive Model (PUCM) and the Parametrically Upscaled Crack Nucleation Model (PUCNM) for a commercially used α/β-phase Ti64 alloy. These thermodynamically consistent macroscopic constitutive models bridge spatial scales through the explicit representation of Representative Aggregated Microstructural Parameters (RAMPs). The PUCNM is an indicator of the probability of crack nucleation in the local underlying microstructure. A symbolic regression-based machine learning method operates on data-sets generated by image-based micromechanical crystal plasticity simulations to derive constitutive coefficients as functions of the RAMPs. The PUCM/PUCNMs development (both calibration and validation) uses data from microstructural characterization as well as mechanical tests, including constant strain-rate, creep, and strain-controlled dwell tests for the Ti64 alloy. Parametric study is conducted with the experimentally-validated PUCM and PUCNM to investigate the effect of RAMPs on dwell fatigue crack nucleation life. Finally, the combined PUCM/PUCNM tool is used for examining the impact of microstructure on fatigue crack nucleation in an engine blade model under simulated operating conditions. The results from these examples clearly exhibit the promise of the PUCM/PUCNM models in predicting fatigue crack nucleation in the microstructure of real structural applications, as well as demonstrating the microstructural influence.