Nucleation Rate Density Research Articles

Regulation of nucleation and crystallization for blade-coating large-area CsPbBr3 perovskite light-emitting diodes

Metal halide perovskite light-emitting diodes (PeLEDs) and large-area perovskite color conversion layers for liquid crystal display exhibit great potential in the field of illumination and display. Blade-coating method stands out as a highly suitable technique for fabricating large-scale films, albeit with challenges such as uneven nucleation coverage and non-uniformity crystallization process. In this work, we developed an in-situ characterization measurement system to monitor the perovskite nucleation, and crystallization process. By incorporating formamidine acetate (FAAc) into perovskite precursor solutions, the nucleation rate and nuclei density of perovskite were increased, leading to more uniform nucleation. In addition, we inserted a layer of [2-(9H-carbazol-9-yl)ethyl] phosphonic acid above the poly(9-vinylcarbazole) hole transport layer. This layer acts as an anchor for the perovskite nano-crystal nuclei formed in the precursor, enhancing the steric hindrance of the solute and subsequently slowing down the crystal growth rate, thereby improving crystal quality. Based on these improvements, large-area perovskite nano-polycrystalline films with significantly improved uniformity and enhanced photoluminescence quantum yield were obtained. A small-area PeLED (2 mm × 2 mm) with a maximum external quantum efficiency of 25.91% was realized, marking the highest record of PeLED prepared by blade-coating method to date. An ultra-large-area PeLED (5 cm × 7 cm) was also prepared, which is the largest PeLED prepared by the solution method reported so far.

A study of tin electrodeposition from ethaline: The electrode material effect

AbstractThis article studies the influence of electrode material on tin (Sn) electrodeposition from deep eutectic solvent. The Sn electrodeposition from ethaline‐based electrolyte onto glassy carbon (GC) and Pt substrates has been studied using cyclic voltammetry and chronoamperometry. The patterns and parameters of Sn nucleation and growth processes have been determined by means of Scharifker and Hills and Scharifker–Mostany models. Results show that Sn nucleation onto GCE follows instantaneous 3D nucleation, while in the case of PtE, it is controlled by adsorption, instantaneous 3D nucleation, and residual water reduction. The growth mechanism is diffusion‐controlled for both electrodes. The parameters of Sn electrodeposition onto GCE and PtE such as diffusion coefficient (D), nucleation rate (A), and active site density of Sn nuclei (No) are evaluated. The results showed that A and No increase linearly as the deposition potential is displaced towards more electronegative values while D is almost unchanged, regardless of the involved working electrode. The morphology and the structure of the electrodeposited Sn are also discussed based on scanning electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy investigations.

Hard Sphere Crystal Nucleation Rates: Reconciliation of Simulation and Experiment.

Over the past two decades, a large number of studies addressed the topic of crystal nucleation in suspensions of hard spheres. The shared result of all these efforts is that, at low supersaturations, experimentally observed nucleation rates and numerically computed ones differ by more than 10 orders of magnitude. We present precise simulation results of crystal nucleation rate densities in the metastable hard sphere liquid. To compare these rate densities to experimentally measured ones, we propose an interpretation of the experimental data as a combination of nucleation and crystal growth processes (rather than purely the nucleation process). This interpretation may resolve the long-standing dispute about the differing rates.

Salt-concentration-dependent nucleation rates in low-metastability colloidal charged sphere melts containing small amounts of doublets

We determined bulk crystal nucleation rates in aqueous suspensions of charged spheres at low metastability. Experiments were performed in dependence on electrolyte concentration and for two different particle number densities. The time-dependent nucleation rate shows a pronounced initial peak, while postsolidification crystal size distributions are skewed towards larger crystallite sizes. At each concentration, the nucleation rate density initially drops exponentially with increasing salt concentration. The full data set, however, shows an unexpected scaling of the nucleation rate densities with metastability times the number density of particles. Parameterization of our results in terms of classical nucleation theory reveals unusually low interfacial free energies of the nucleus surfaces and nucleation barriers well below the thermal energy. We tentatively attribute our observations to the presence of doublets introduced by the employed conditioning technique. We discuss the conditions under which such small seeds may induce nucleation.

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces.

Lubricant-infused surfaces (LISs) can promote stable dropwise condensation and improve heat transfer rates due to a low nucleation free-energy barrier and high droplet mobility. Recent studies showed that oil menisci surrounding condensate microdroplets form distinct oil-rich and oil-poor regions. These topographical differences in the oil surface cause water microdroplets to rigorously self-propel long distances, continuously redistributing the oil film and potentially refreshing the surface for re-nucleation. However, the dynamic interplay between oil film redistribution, microdroplet self-propulsion, and droplet nucleation and growth is not yet understood. Using high-speed microscopy, we reveal that during water condensation on LISs, the smallest visible droplets (diameter: ∼1 μm, qualitatively representing nucleation) predominantly emerge in oil-poor regions due to a lower nucleation free-energy barrier. Considering the significant heat transfer performance of microdroplets (<10 μm) and transient characteristic of microdroplet movement, we compare the apparent nucleation rate density and water collection rate for LISs with oils of different viscosities and a solid hydrophobic surface at a wide range of subcooling temperatures. Generally, the lowest lubricant viscosity leads to the highest nucleation rate density. We characterize the length and frequency of microdroplet movement and attribute the nucleation enhancement primarily to higher droplet mobility and surface refreshing frequency. Interestingly and unexpectedly, hydrophobic surfaces outperform high-viscosity LISs at high subcooling temperatures but are generally inferior to any of the tested LISs at low temperature differences. To explain the observed nonlinearity between LISs and the solid hydrophobic surface, we introduce two dominant regimes that influence the condensation efficiency: mobility-limited and coalescence-limited. We compare these regimes based on droplet growth rates and water collection rates on the different surfaces. Our findings advance the understanding of dynamic water-lubricant interactions and provide new design rationales for choosing surfaces for enhanced dropwise condensation and water collection efficiencies.

Crystallization kinetics, crystalline structures and properties of PB/PP blends regulated by poly(butene-block-propylene) copolymers

Blending isotactic polybutene-1 (PB) with isotactic polypropylene (PP) is a facial strategy to improve the mechanical properties and promote polymorphous transformation of PB. As the immiscible polymer pairs with strong crystallizability, the interactions between PP and PB in the melt state influence the subsequent processes like phase separation and crystallization, and then determine the crystalline structures and properties of the blends. Herein, two kinds of poly(butene-block-propylene) (PB-b-PP) copolymers with different sequence structures fractionated from PB/PP in-reactor alloy using temperature rising elution fractionation were utilized to compatibilize the PB/PP (80/20) blend. The phase morphologies, crystallization kinetics of PP and PB phases, and crystalline structures in PB/PP/PB-b-PP blends were characterized by phase contrast optical microscopy (PCOM), differential scanning calorimeter (DSC), and small-angle X-ray scattering (SAXS). The PB-b-PP copolymer with longer PP blocks (A) showed more satisfied compatibilization for PB/PP blends and PB/PP/PB-b-PP-2.5 blend with 2.5 wt% copolymer as compatibilizer exhibited the most stable phase morphology with the smallest PP domains in melt state at 200 °C. During isothermal crystallization processes of the PB/PP/PB-b-PP blends at 135 °C for PP crystallization and then 90 °C for PB crystallization, the crystallization rate including nucleation rate and nucleation density, and crystallinity of PP and PB (form II) increased, and achieved the largest when the copolymer concentration was 2.5 wt% in PB/PP/PB-b-PP blend. The copolymer A significantly accelerated crystallization rate of PP compared with that of copolymer B. The PB/PP/A-2.5 blend with the largest lamellae thickness and highest crystallinity of PB form I, combined with the smallest spherulites, exhibited the highest modulus, tensile strength and toughness. The compatibilizing mechanism and roles of PB-b-PP copolymers for PB/PP blends were discussed to understand the physical and mechanical behaviors of the blends.

Nanocrystalline equiatomic CoCrFeNi alloy thin films: Are they single phase fcc?

The bulk quaternary equiatomic CoCrFeNi alloy is studied extensively in literature. Under experimental conditions, it shows a single-phase fcc structure and its physical and mechanical properties are similar to those of the quinary equiatomic CoCrFeMnNi alloy. Many studies in literature have focused on the mechanical properties of bulk nanocrystalline high entropy alloys or compositionally complex alloys, and their microstructure evolution upon annealing. The thin film processing route offers an excellent alternative to form nanocrystalline alloys. Due to the high nucleation rate and high density of defects in thin films synthesized by sputtering, the kinetics of microstructure evolution is often accelerated compared to those taking place in the bulk. Here, thin films are used to study the phase evolution in nanocrystalline CoCrFeNi deposited on Si/SiO2 and c-sapphire substrates by magnetron co-sputtering from elemental sources. The phases and microstructure of the films are discussed in comparison to the bulk alloy. The main conclusion is that second phases can form even at room temperature provided there are sufficient nucleation sites.

Revealing the nucleation kinetics of primary Si particles in hypereutectic Al\u2013Si alloys under the influence of P inoculation

A quantitative study on the kinetics of nucleation of primary Si particles (PSPs), especially under the effect of P inoculation, during isothermal melt solidification of hypereutectic Al–Si(–Cu) alloys has been realized for the first time by using a unique micro-focus in situ X-radiography method, which is impossible by synchrotron X-radiography or tomography methods. The nucleation undercooling and nucleation rate of PSPs have been measured. Besides, TP-1 type solidification test has been carried out. It is found that nucleation undercooling of PSPs is reduced, while nucleation rate and number density of PSPs is increased significantly by P inoculation. Moreover, the influence of cooling rate on the nucleation kinetics of PSPs in the P inoculated alloy was investigated in situ. It is observed that higher cooling rate has the influence of increasing the peak nucleation rate and extending the nucleation temperature ranges of PSPs, in terms of earlier nucleation at lower undercooling and nucleation stopping at higher undercooling, which results in higher number density of PSPs. The decrease in minimum nucleation undercooling with increasing cooling rate in the P inoculated alloy is unexpected, which has been attributed to the extremely slow growth rate of faceted Si crystal on AlP substrates under low undercooling.

Secondary Nucleation Kinetics of AIBN Crystallisation in Methanol: Online Imaging-Based Measurement and Modelling

The secondary nucleation process of 2,2-azobisisobutyronitrile (AIBN) seeded crystallisation in methanol in a stirred tank reactor was studied at varying initial supersaturation levels, temperatures, crystal seed numbers, and stirrer speeds. The average secondary nucleation rate, induction time, and agglomeration ratio were measured using on-line microscopic imaging. The initial supersaturation level, temperature, and stirrer speed were found to be positively correlated with the secondary nucleation rate. A small change in the crystal seed number, i.e., 1-20, did not substantially affect the secondary nucleation rate throughout the secondary nucleation process. An increase in the initial supersaturation level and crystal seed number decreased the induction time, and an increase in the strength of agitation promoted the initiation of secondary nucleation at a stirring rate greater than 250 revolutions per minute (rpm). Temperature exerted a complex effect on the induction time. Regarding the agglomeration ratio, the initial supersaturation level positively correlated with the agglomeration ratio, while the stirrer speed negatively correlated with this parameter. Finally, based on the measured data, the average secondary nucleation rate, induction time, and final crystal suspension density were correlated. This study provides guidance for the control of supersaturation, induction time, stirring, and other factors in the crystal seed addition process in AIBN crystallisation.

Production and computational fluid dynamics-based modeling of PMMA nanoparticles impregnated with ivermectin by a supercritical antisolvent process

The aim of this study was to encapsulate ivermectin in poly(methyl methacrylate) (PMMA) using a supercritical antisolvent (SAS) process. The Box–Behnken method was employed for obtaining a lower average particle diameter (dexp) of ivermectin-impregnated PMMA nanoparticles. The encapsulation efficiency was 73.08 ± 3.22%, and the nanoparticles were characterized morphologically, thermally, and conformationally using the following techniques: scanning electron microscopy, differential thermogravimetric analysis, and attenuated total-reflectance Fourier-transform infrared spectroscopy. The in vitro release kinetics showed that the drug had a controlled release of approximately 100 h, and that the Higuchi, Peppas–Sahlin, and Korsmeyer–Peppas models were able to correctly describe the drug diffusion processes. The precipitation kinetic parameters were determined from dexp using the population balance equation. This equation showed that the nucleation rate and nucleation population density were dominant for R6 (9 MPa, 313.15 K, 3 mL/min), and that the growth rate had little variation across all experiments.

Coupling of sedimentation and liquid structure: Influence on hard sphere nucleation.

The discrepancy in nucleation rate densities between simulated and experimental hard spheres remains staggering and unexplained. Suggestively, more strongly sedimenting colloidal suspensions of hard spheres nucleate much faster than weakly sedimenting systems. In this work, we consider first the effect of sedimentation on the structure of colloidal hard spheres by tuning the density mismatch between solvent and colloidal particles. In particular, we investigate the effect on the degree of the fivefold symmetry present. Second, we study the size of density fluctuations in these experimental systems in comparison to simulations. The density fluctuations are measured by assigning each particle a local density, which is related to the number of particles within a distance of 3.25 particle diameters. The standard deviation of these local densities gives an indication of the fluctuations present in the system. Fivefold symmetry is suppressed by a factor of two when sedimentation is induced in our system. Density fluctuations are increased by a factor of two in experiments compared to simulations. The change in fivefold symmetry makes a difference to the expected nucleation rates, but we demonstrate that it is ultimately too small to resolve the discrepancy between experiment and simulation, while the fluctuations are shown to be an artefact of 3d particle tracking.

Influence of Edge Energy on Modeling the Growth Kinetics of Quantum Dots

Recent experimental results suggest that the growth of elongated quantum dots with a rectangular base and quantum wires is possible under certain conditions in a germanium–silicon system. However, the role of formation of additional edges during the creation of such structures is still poorly researched. This paper evaluates the influence of the energy contribution from formation of additional edges in the change in free energy during quantum dot nucleation. A refinement has been carried out on the existing kinetic model of quantum dot formation and growth in the Stranski–Krastanow mode. In view of this contribution, the islands’ nucleation rate and surface density and the distribution function of quantum dots by size have been calculated. It is shown that taking the additional energy from the creation of edges into account is essential for obtaining more realistic estimates for the parameters of quantum dots arrays during numerical modeling of their growth.

Nucleation and crystal growth in a suspension of charged colloidal silica spheres with bi-modal size distribution studied by time-resolved ultra-small-angle X-ray scattering.

A suspension of charged colloidal silica spheres exhibiting a bi-modal size distribution of particles, thereby mimicking a binary mixture, was studied using time-resolved ultra-small-angle synchrotron X-ray scattering (USAXS). The sample, consisting of particles of diameters d(A) = (104.7 ± 9.0) nm and d(B) = (88.1 ± 7.8) nm (d(A)/d(B) ≈ 1.2), and with an estimated composition A(0.6(1))B(0.4(1)), was studied with respect to its phase behaviour in dependance of particle number density and interaction, of which the latter was modulated by varying amounts of added base (NaOH). Moreover, its short-range order in the fluid state and its eventual solidification into a long-range ordered colloidal crystal were observed in situ, allowing the measurement of the associated kinetics of nucleation and crystal growth. Key parameters of the nucleation kinetics such as crystallinity, crystallite number density, and nucleation rate density were extracted from the time-resolved scattering curves. By this means an estimate on the interfacial energy for the interface between the icosahedral short-range ordered fluid and a body-centered cubic colloidal crystal was obtained, comparable to previously determined values for single-component colloidal systems.

Experimental determination of the nucleation rates of undercooled micron-sized liquid droplets based on fast chip calorimetry

Accurate thermal analyzes and calorimetry measurements depend on careful calibration measurements. For conventional differential scanning calorimeters (DSC) the calibration procedure is well known. The melting point of different pure metals is measured and compared with literature data to adjust the temperature reading of the calorimeter. Likewise, the measured melting enthalpies of standard reference substances serve for enthalpy calibration. Yet for fast chip calorimetry, new procedures need to be established. For the medium-area and large-area calorimeter chips, this procedure needs to be modified, because the calibration behavior depends on the position of the sample on the measurement area. Additionally, a way to calibrate the calorimeter for measurements performed during cooling will also be shown. For this second aspect, the athermal and diffusionless martensitic phase transformation of Ni49.9–Ti50.1 at% was used. The well-calibrated sensor chips are ideally suited to perform nucleation rate density analyzes based on a statistical approach. Here, the nucleation rate densities of micron-sized pure Sn droplets that had been coated with a non-catalytic coating have been determined by experimental analysis of the statistical variance of the undercooling response.

Numerical simulation of particle formation in the rapid expansion of supercritical solution process

In this paper, we numerically study particle formation in the rapid expansion of supercritical solution (RESS) process in a two dimensional, axisymmetric geometry, for a benzoic acid+CO2 system. The fluid is described by the classical Navier–Stokes equation, with the thermodynamic pressure being replaced by a generalized pressure tensor. Homogenous particle nucleation, transport, condensation and coagulation are described by a general dynamic equation, which is solved using the method of moments. The results show that the maximal nucleation rate and number density occurs near the nozzle exit, and particle precipitation inside the nozzle might not be ignored. Particles grow mainly across the shocks. Fluid in the shear layer of the jet shows a relatively low temperature, high nucleation rate, and carries particles with small sizes. On the plate, particles within the jet have smaller average size and higher geometric mean, while particles outside the jet shows a larger average size and a lower geometric mean. Increasing the preexpansion temperature will increase both the average particle size and standard deviation. The preexpansion pressure does not show a monotonic dependency with the average particle size. Increasing the distance between the plate and the nozzle exit might decrease the particle size. For all the cases in this paper, the average particle size on the plate is on the order of tens of nanometers.

Influence of Random Pinning on the Crystallization Process in Suspensions of Hard Spheres

We discuss crystal formation in supersaturated suspensions of monodisperse hard spheres with a concentration of hard spheres randomly pinned in space and time. The pinning procedure introduces an external length scale and an external time scale that restrict the accessible number of configureurations and ultimately the number of pathways leading to crystallization. We observe a significant drop in the nucleation rate density at a characteristic pinning concentration that can be directly related to the structure of the critical nucleus and the dynamics of its formation in the unpinned system.

A visualization system for observing plastic foaming processes under shear stress

Previous studies offered theories to explain shear-induced bubble nucleation and growth phenomena in plastic foaming processes, but empirical verification was limited due to difficulty in observing these processes in situ under an easily adjustable and uniform shear flow. This study presents a novel visualization system that successfully achieved this goal. The system allows easy control of the critical experimental parameters: applied shear strain, shear strain rate, temperature, pressure, pressure drop rate, plastic material and blowing agent. From a foaming visualization study of polystyrene, it was observed that cell nucleation rate and maximum cell density increased with the applied shear strain, which was due to the decreased local system pressure, detachment and growth of microvoids, and elongation of bubbles. This foaming visualization system provides a direct and effective way to investigate the mechanisms of bubble nucleation and growth under dynamic conditions that simulates industrial plastic foaming processes.

Influence of MPS concentration on copper electrocrystallisation from acidic sulphate electrolyte with MPS additive systems

Copper electrocrystallisation on a glassy carbon electrode from acid sulphate electrolytes in the presence of different concentrations of 3-mercapto-1-propanesulphonate sodium salt (MPS) and its combinations with chloride ions (Cl) or/and polyethylene glycol (PEG) have been investigated by utilising chronoamperometry (CA) technique and scanning electronic microscopy (SEM). The CA and SEM results indicate that copper nucleation follows instantaneous nucleation with three-dimensional growth (3DI) from all baths at the deposition potentials studied. With increasing MPS concentration, copper nucleation rate and nuclei number density N increase in the MPS, MPS–Cl and MPS–PEG–Cl baths, but decrease in the MPS–PEG bath.

Crystallization in suspensions of hard spheres: a Monte Carlo and molecular dynamicssimulation study

The crystallization of a metastable melt is one of the most important non-equilibriumphenomena in condensed matter physics, and hard sphere colloidal model systems havebeen used for several decades to investigate this process by experimental observation andcomputer simulation. Nevertheless, there is still an unexplained discrepancy between thesimulation data and experimental nucleation rate densities. In this paper we examine thenucleation process in hard spheres using molecular dynamics and Monte Carlo simulation.We show that the crystallization process is mediated by precursors of low orientationalbond-order and that our simulation data fairly match the experimental data sets.

Copper electrocrystallization from acidic sulfate electrolyte containing MPS additive

Copper electrodeposition and nucleation on a glassy carbon electrode from acid sulfate electrolytes in the presence of 3-mercapto-1-propanesulfonate sodium salt (MPS) and its combinations with chloride ions (Cl) or/and polyethylene glycol (PEG) were investigated by utilizing cyclic voltammetry (CV), chronoamperometry (CA) and scanning electron microscopy (SEM). CV results indicate that MPS and MPS–PEG inhibit whereas MPS–Cl and MPS–PEG–Cl accelerate copper deposition. CA and SEM results suggest that copper nucleation follows an instantaneous nucleation mechanism with three-dimensional growth from all baths at the studied deposition potentials. The copper nucleation rate and nuclei number density are increased greatly in the MPS–Cl and MPS–PEG–Cl baths.