Rapid Nucleation Research Articles

The growth kinetics of colloidal ZnO nanoparticles in alcohols

We have studied the synthesis of ZnO nanostructures over a wide range of parameters to determine the kinetics of the nanocrystals growth. The initial rapid nucleation and growth is kinetically controlled, the subsequent ZnO nanocrystals growth is thermodynamically controlled through the diffusion limited Ostwald coarsening. The ZnO coarsening rates increased with number of alcohol’s alkyl group carbons and temperature increase, pointing to importance of the solvent viscosity, dielectric constants, surface energy and the bulk solubility. The results are consistent with the Lifshitz–Slyozov–Wagner model. For all alcohols, in the NaOH induced reaction, a lower activation energy was observed compared to the aqueous reaction. A lower ZnO solubility, obtained by the water synthesis could be responsible for these observations. Our results point to the importance of the reactant selection in controlling the kinetics of the nanostructure formation, their size and the nature of the surface defects responsible for their luminescence.

Growth and characterization of electrodeposited Na 0.45VOPO 4, 1.58H 2O materials

The paper reports on a new and original way to prepare sodium vanadophosphate by using the electrochemical oxidation of vanadyl ions in H 3PO 4 solution to produce a deposit onto the electrode. Such a way insured an intimate mixing of the component elements in the solution allowing finer particles and high purity materials to be produced by rapid homogenous nucleation. The experimental conditions to obtain a pure phase are described in the paper. The main determining parameter is the solution pH which had to be adjusted at 1.9 or 2.0 with NaOH. A mixture of sodium vanadophosphate and V 2O 5, 0.5H 2O was obtained for higher pH = 2.2. A series of experiments including an X-ray diffraction study, thermogravimetric analysis, transmission electron microscopy and infrared spectroscopy investigation helped in determining the exact chemical formula of the obtained phase, i.e. Na 0.45VOPO 4, 1.58H 2O. The phase exhibits an orthorhombic structure with a = 8.85 Å, b = 9.01 Å and c = 13.02 Å.

Ground-fixed and on-board measurements of nanoparticles in the wake of a moving vehicle

An integrated experimental methodology has been applied to measure number and size distributions of particles in the 5-560nm size range in the wake of a diesel car running at different speeds. Measurements were made at both ground-fixed (0.10 and 0.25m above the ground level) and on-board (in 12 different sampling locations behind the moving car) measurement configurations using a fast response differential mobility spectrometer (Cambustion DMS50) with a sampling frequency up to 10Hz. Results from both the experimental campaigns were analysed to understand the dynamics, dispersion and transport of nanoparticle emissions in the wake of a moving vehicle. Temporal changes in results were divided into three main stages (pre-evolution, evolution and post-evolution) after the release of exhaust emissions from the tailpipe. Evolution stage is of most interest where all the changes to particle number and size distribution occurred. Up to four evolution sub-stages were observed, each showing distinct evolution patterns of particle size distributions, depending on the particular experimental run. In agreement with previous studies, dilution was found to be the dominant process throughout all the evolution stages. The first evolution sub-stage was common to all the measurements, and consisted of an initial particle number concentrations and distributions change due to rapid (less than 1s) nucleation followed by a rapid increase of accumulation mode particle number concentrations. After this first sub-stage the presence of vehicle wake with recirculating particles and the possible influence of other transformation processes lead to complex interactions. Results from the two experimental datasets clearly confirm the presence of two separate groups of particles: (i) new particles, which are freshly emitted and come directly from the tailpipe and (ii) relatively aged particles, which are entrained within the recirculation vortices of the vehicle wake and reside there for a longer time. The two groups have different characteristics and interact with each other. This interaction has often been overlooked in past studies about local scale dispersion of nanoparticle from moving vehicles.

Temperature Effect on Phase Formation of Nanocrystalline Bismuth Titanate Synthesized via Hot Injection Method

Nanocrystalline bismuth titanate materials were synthesized via hot injection method for the first time. Bismuth nitrate and titanium butoxide were used as precursors of Bi and Ti, respectively. The synthesis method was modified to use aqueous solution as the solvent instead of non coordinating solvent which enable production of nanosized compounds at lower reaction temperature. During the synthesis process, titanium precursor was injected into mixture of bismuth nitrate and oleic acid at 130°C, leading to a rapid burst nucleation and followed by nuclei growth at room temperature. The synthesized compound was heated at various temperatures. XRD results showed formation of cubic phase bismuth titanate compound with space group of Fm3m at room temperature after the reaction. Presence of cubic phase bismuth titanate compound with space group of I23 was observed as secondary phase at 300°C. Meanwhile, a single phase cubic form, space group I23 was obtained for material synthesized at 600°C. FESEM images indicated nano particles of bismuth titanate materials were produced at lower temperatures. However, sintering effect was observed in material heated at 600°C, resulting micro-sized particles.

Novel Features of Aerosol Coagulation in Nonisothermal Environments

Local supersaturations and the rapid homogeneous nucleation of often subcooled nanometric particles occur when vapors from a high-temperature source diffuse into adjacent regions of much lower temperature. While earlier experimental and theoretical studies were focused on the macroscopic mass transfer rate consequences of such localized condensation (Turkdogan and Mills (1964), Epstein and Rosner (1970)), we identify and describe here, from a broader perspective, several expected novel features of aerosol coagulation dynamics in nonisothermal environments, including the expected particle size “spectra”. In the simplest (limiting) case, differential thermal particle drift down the local temperature gradient dominates the Brownian diffusion-controlled collision rate, and, for a population of thermally conductive mist droplets coagulating by this mechanism, we have calculated and displayed (e.g., Rosner, D. E.; Arias-Zugasti, M. Thermophoretically-dominated aerosol coagulation. Phys. Rev. Lett.2011, 106, 015502.) the expected coagulation-aged “self-preserving” droplet size distribution. However, in most applications the more familiar Brownian diffusion contribution to the coagulation rate must also be included, and we summarize here our recent analysis of this combined case, which enables another test of the frequently made assumption of “additive rate constants” and leads to quasi-self-preserving droplet size distributions. Because fully miscible mist droplets may also be distributed with respect to composition (and, hence, thermal conductivity) we take this opportunity to outline how these, and more general phoretic mechanisms (including thermocapillary flow), can be incorporated into the present formulation.

Photochemical loading of metal nanoparticles on reduced graphene oxide sheets using phosphotungstate

Well-dispersed reduced graphene oxide (r-GO) sheets loaded with metal nanoparticles were produced in dimethylformamide (DMF). The r-GO suspension was prepared through the photocatalytic reduction of graphene oxide (GO) using a phosphotungstate as a homogeneous photocatalyst under UV irradiation. Immediately after UV lamp was turned off, the injection of precursors of Ag, Au, and Pd caused the rapid nucleation because photoreduced phosphotungstates as well as electrons stored in r-GO directly reduced metal ions. Furthermore, the r-GO sheets not only provided the nucleation sites but also prohibited the metal nanoparticles from agglomeration. As a result, relatively uniform-sized metal nanoparticles were formed on the r-GO sheets. With phosphotungstates and UV light irradiation, both GO and metal ions can be reduced to form the hybrids of Ag, Au, and Pd/r-GO as a suspension in DMF or an isolated paper sheet without using any toxic reagents.

Architecture and Assembly of a Divergent Member of the ParM Family of Bacterial Actin-like Proteins

Eubacteria and archaea contain a variety of actin-like proteins (ALPs) that form filaments with surprisingly diverse architectures, assembly dynamics, and cellular functions. Although there is much data supporting differences between ALP families, there is little data regarding conservation of structure and function within these families. We asked whether the filament architecture and biochemical properties of the best-understood prokaryotic actin, ParM from plasmid R1, are conserved in a divergent member of the ParM family from plasmid pB171. Previous work demonstrated that R1 ParM assembles into filaments that are structurally distinct from actin and the other characterized ALPs. They also display three biophysical properties thought to be essential for DNA segregation: 1) rapid spontaneous nucleation, 2) symmetrical elongation, and 3) dynamic instability. We used microscopic and biophysical techniques to compare and contrast the architecture and assembly of these related proteins. Despite being only 41% identical, R1 and pB171 ParMs polymerize into nearly identical filaments with similar assembly dynamics. Conservation of the core assembly properties argues for their importance in ParM-mediated DNA segregation and suggests that divergent DNA-segregating ALPs with different assembly properties operate via different mechanisms.

Synthesis of metal oxide nanomaterials by plasma treatment – A SEM investigation of Nb2O5 nanowires

Plasma techniques for rapid synthesis of large quantities of metal oxide nanoparticles are presented. Suitable metal foils are exposed to cold oxygen plasma with a large density of neutral oxygen atoms of the order of 1021 m−3 and the ion density of the order of 1016 m−3. Depending on the flux of neutral atoms onto the sample surface as well as other plasma parameters, such as the positive ion kinetic energy and the sample temperature, different types of nanoparticles are synthesized, such as nanowires, nanocones and nanobelts. Nanowires are synthesized at extremely large flux of neutral oxygen atoms on the sample surface, often exceeding 1 × 1024 m−2 s−1. Other features are synthesized at moderate flux of atoms of the order of 1023 m−2 s−1. The phenomenon is explained by rapid nucleation of metal oxide on the sample surface followed by a one -dimensional growth of the nanowires due to balanced supply of neutral atoms and ions to the surface. Controlling the plasma parameters, a fair control on the nanostructure size as well as shape is achieved. The technique allows for synthesis of nanowires at the rate of almost 1 g/h, and therefore assures huge quantities of this material. The synthesis of niobium oxide nanowires is studied to some details by scanning electron microscopy.

Molybdenum Atomic Layer Deposition Using MoF6 and Si2H6 as the Reactants

Mo ALD has been demonstrated by fluorosilane elimination chemistry using MoF6 and Si2H6 as the reactants. The nucleation and growth characteristics of Mo ALD were investigated using a variety of in situ and ex situ techniques in both high vacuum and viscous flow reactors. Quartz crystal microbalance (QCM) and X-ray reflectivity (XRR) investigations showed that Mo ALD has significant growth rate of 500−600 ng/cm2 per cycle or 6−7 Å per cycle for temperatures between 90 and 150 °C. The large growth rates could result from extra Mo deposition by MoF6 → Mo + 3F2 that may be facilitated by the very exothermic reaction of MoF6 with silicon-containing surface species. The QCM studies revealed that the Mo ALD surface chemistry is self-limiting. The QCM and Auger electron spectroscopy (AES) studies indicated that Mo ALD nucleates very rapidly on Al2O3 ALD surfaces and reaches the linear growth regime after only 4−5 ALD cycles. Oscillatory behavior for the total mass gain and individual mass gains was observed versus ALD cycle number during the nucleation region. The AES studies revealed that Mo films grown in a high vacuum reactor do not contain silicon impurities. In contrast to the AES results, Rutherford backscattering spectroscopy (RBS) analysis showed that Mo ALD films grown in a viscous flow reactor contain ∼16 at % Si impurities. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of silicon and showed that varying temperature, precursor dose and purge parameters did not lower the Si impurities significantly. Glancing incidence X-ray diffraction (GIXRD) studies indicated that Mo ALD films were nanocrystalline. The Si impurities may exist at grain boundaries or amorphous Mo silicides as a result of Si2H6 decomposition during the highly exothermic fluorosilane elimination reaction. Fourier transform infrared (FTIR) analysis revealed that MoFx surface species are reduced to metallic Mo during the Si2H6 exposure. Because of its rapid nucleation rate, Mo ALD films could serve as ultrathin continuous conducting films or as adhesion layers for other metal ALD systems on oxide surfaces.

Mechanisms of Resonant Infrared Matrix-Assisted Pulsed Laser Evaporation

For the last decade, a variant of pulsed laser ablation, Resonant-Infrared Matrix-Assisted Pulsed Laser Evaporation (RIR-MAPLE), has been studied as a deposition technique for organic and polymeric materials. RIR-MAPLE minimizes photochemical damage from direct interaction with the intense laser beam by encapsulating the polymer in a high infrared-absorption solvent matrix. This review critically examines the thermally-induced ablation mechanisms resulting from irradiation of cryogenic solvent matrices by a tunable free electron laser (FEL). A semi-empirical model is used to calculate temperatures as a function of time in the focal volume and determine heating rates for different resonant modes in two model solvents, based on the thermodynamics and kinetics of the phase transitions induced in the solvent matrices. Three principal ablation mechanisms are discussed, namely normal vaporization at the surface, normal boiling, and phase explosion. Normal vaporization is a highly inefficient polymer deposition mechanism as it relies on collective collisions with evaporating solvent molecules. Diffusion length calculations for heterogeneously nucleated vapor bubbles show that normal boiling is kinetically limited. During high-power pulsed-FEL irradiation, phase explosion is shown to be the most significant contribution to polymer deposition in RIR-MAPLE. Phase explosion occurs when the target is rapidly heated (108 to 1010 K/s) and the solvent matrix approaches its critical temperature. Spontaneous density stratification (spinodal decay) within the condensed metastable phase leads to rapid homogeneous nucleation of vapor bubbles. As these vapor bubbles interconnect, large pressures build up within the condensed phase, leading to target explosions and recoil-induced ejections of polymer to a near substrate. Phase explosion is a temperature (fluence) threshold-limited process, while surface evaporation can occur even at very low fluences.

The Japanese Mutant Aβ (ΔE22-Aβ1−39) Forms Fibrils Instantaneously, with Low-Thioflavin T Fluorescence: Seeding of Wild-Type Aβ1−40 into Atypical Fibrils by ΔE22-Aβ1−39

The ΔE693 (Japanese) mutation of the β-amyloid precursor protein leads to production of ΔE22-Aβ peptides such as ΔE22-Aβ(1-39). Despite reports that these peptides do not form fibrils, here we show that, on the contrary, the peptide forms fibrils essentially instantaneously. The fibrils are typical amyloid fibrils in all respects except that they cause only low levels of thioflavin T (ThT) fluorescence, which, however, develops with no lag phase. The fibrils bind ThT, but with a lower affinity and a smaller number of binding sites than wild-type (WT) Aβ(1-40). Fluorescence depolarization confirms extremely rapid aggregation of ΔE22-Aβ(1-39). Size exclusion chromatography (SEC) indicates very low concentrations of soluble monomer and oligomer, but only in the presence of some organic solvent, e.g., 2% (v/v) DMSO. The critical concentration is approximately 1 order of magnitude lower for ΔE22-Aβ(1-39) than for WT Aβ(1-40). Several lines of evidence point to an altered structure for ΔE22-Aβ(1-39) compared to that of WT Aβ(1-40) fibrils. In addition to differences in ThT binding and fluorescence, PITHIRDS-CT solid-state nuclear magnetic resonance (NMR) measurements of ΔE22-Aβ(1-39) are not compatible with the parallel in-register β-sheet generally observed for WT Aβ(1-40) fibrils. X-ray fibril diffraction showed different D spacings: 4.7 and 10.4 Å for WT Aβ(1-40) and 4.7 and 9.6 Å for ΔE22-Aβ(1-39). Equimolar mixtures of ΔE22-Aβ(1-39) and WT Aβ(1-40) also produced fibrils extremely rapidly, and by the criteria of ThT fluorescence and electron microscopic appearance, they were the same as fibrils made from pure ΔE22-Aβ(1-39). X-ray diffraction of fibrils formed from 1:1 molar mixtures of ΔE22-Aβ(1-39) and WT Aβ(1-40) showed the same D spacings as fibrils of the pure mutant peptide, not the wild-type peptide. These findings are consistent with extremely rapid nucleation by ΔE22-Aβ(1-39), followed by fibril extension by WT Aβ(1-40), and "conversion" of the wild-type peptide to a structure similar to that of the mutant peptide, in a manner reminiscent of the prion conversion phenomenon.

Temperature Dependence of the High-Pressure Denatured State of Lambda Repressor

When dropped from 2500 atm to 1 atm in a fast pressure jump experiment, the YG mutant of the five-helix bundle lambda repressor refolds close to the “speed limit”, about 40 times faster than observed in a temperature jump experiment. We carried out molecular dynamics simulations to address the question of why refolding from the pressure denatured state is so much faster than refolding upon temperature jump.The temperature dependence of the high-pressure denatured state of the YG mutant was investigated for this purpose. The high pressure used in the simulation favors denaturation, but also slows down protein dynamics.High temperature was employed to speed up the dynamics. The high-pressure denatured state was identified as a compact structure with the helices I and IV being the most stable elements. Rapid nucleation of helices I and IV may be a major factor in enhancing the refolding rate once the pressure is dropped to 1 atm.

Synthesis of monodispersed nanocrystalline materials in supercritical ethanol: a generalized approach

We report a generalized approach for synthesis of a variety of nearly monodisperse inorganic nanostructured materials with different sizes and shapes using supercritical ethanol (SCE). In the present synthetic strategy the inorganic precursor and stabilizer (long chain amines) were co-solubilised in ethanol. Decomposition of the precursor occurred under supercritical conditions and facilitated rapid homogeneous nucleation, growth, and crystallization of the desired nanoparticles in near monodisperse state. The size and shape of the synthesized nanoparticles were tuned by varying the synthetic parameters. The particles exhibited size- and shape-dependent properties, and could be readily dispersed in hexane and toluene. Controlled evaporation of solvent from the dispersions yielded fairly ordered 2D structures.

Preparation of TiO2 Continuous Fibers with Oxygen Vacancies and Photocatalytic Activity

TiO2 continuous fibers were prepared by a modified sol-gel method combined with centrifugal spinning and different heat treatment processes. The prepared fibers were characterized by TG-DSC, XRD, SEM, N2 adsorption-desorption and XPS. The photocatalytic degradation of X-3B aqueous solution was used as a probe reaction to evaluate their photocatalytic activities. The results indicated that heat treatment in steam was conductive to the rapid nucleation of anatase nanocrystal and could effectively suppress the anatase-rutile transformation. Compared with samples calcined in air, products heat treated in steam were long fibers with oxygen vacancies and abundant mesoporous structures, which enhanced their photocatalytic activities. The fibers with a high specific surface area of 87.6 m2·g−1 and the largest pore volume of 0.24 cm3·g−1 were obtained when heat treated at 400°C in steam. The sample exhibited the best photocatalytic activity and the removal rate of X-3B was 99.5% after 90 min under visible light irradiation.

Design Principles for Broad-Spectrum Protein-Crystal Nucleants with Nanoscale Pits

Growing high-quality crystals is a bottleneck in the determination of protein structures by x-ray diffraction. Experiments find that materials with a disordered pitted surface seed the growth of protein crystals. Here we report computer simulations of rapid crystal nucleation in nanoscale pits. Nucleation is rapid, as the crystal forms in pits that have filled with liquid via capillary condensation. Surprisingly, we find that pits whose surfaces are rough are better than pits with crystalline surfaces; the roughness prevents the growing crystal from trying to conform to the pit surface and becoming strained.

Colloidal Synthesis of Air-Stable Crystalline Germanium Nanoparticles with Tunable Sizes and Shapes

Nanoparticles of elemental germanium have interesting optical and electronic properties and relatively low toxicity, making them attractive materials for biological and optoelectronic applications. The most common routes to colloidal Ge nanoparticles include metathesis reactions involving Zintl salts, hydride reduction of Ge halides, and thermal decomposition of organogermane precursors. Here we describe an alternative “heat-up” method for the synthesis of size- and shape-tunable Ge nanoparticles that are both crystalline and air stable. The readily available reagents GeI4, oleylamine, oleic acid, and hexamethyldisilazane are combined in one pot and heated to 260 °C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystalline Ge form. By varying the concentration of GeI4, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cube-shaped particles, and switching the solvent to octadecene yields one-dimensional nanostructures. The Ge nanoparticles, which are fully air stable for more than 6 months, were characterized by XRD, TEM, HRTEM, EDS, XPS, DRIFT, and UV−visible spectroscopy.

Synthesis of hybrid nanographite particles using fluidized bed system

Nanographite coated with ferromagnetic substances such as iron or iron oxide is a potential material for microwave absorption because of its favorable structural, magnetic, and electrical characteristics. In this paper, deposition on surfaces of acid functionalized and microwave-exfoliated nanographite particles with the use of fluidized bed system is reported. Acid functionalization improves iron adhesion and exfoliation reduces the flake thickness. The parameters influencing the deposition process are considered. It is demonstrated that Faraday’s laws of electrolysis can be used for these systems if the charge transfer from solid cathode to bed particles is uniform. This requirement is satisfied only above some critical values of suspension density, electrolyte concentration, and stirring rate. The optimized values of current density are required for each specific system, as low current density leads to non-uniform deposition with local nucleation, when high a current density induces too rapid nucleation and promotes iron hydroxo complex formation. Deposition time also should be optimized for any specific system, as the expected amount of deposit cannot be formed longer because of side reactions.

A Mild Phosphine-Free Synthesis of Alkylamine-Capped CdSe Nanocrystals

A new phosphine-free approach has been developed to synthesize high-quality cadmium selenide (CdSe) nanocrystals with cubic zinc-blende structure, by using the highly reactive selenium (Se) precursor at milder temperature than that used in the traditional phosphine route. This Se precursor was obtained from the reduction of Se powder by sodium borohydride in N,N-dimetbylformamide, in the absence of phosphine. Without the addition of other long-chain coordinating substances in this approach, the alkylamines such as dodecylamine (DDA) and octylamine (OA) were used as reaction solvents, and they also acted as surface capping reagents to produce DDA-capped and OA-capped CdSe NCs, respectively. The rapid nucleation and slow growth were observed by ultraviolet-visible absorption spectrum. The resulting OA-capped CdSe NCs grew faster compared with DDA-capped CdSe NCs under the same other conditions. These as-synthesized CdSe nanocrystals showed relatively narrow size distribution and high photoluminescence quantum efficiency (up to 9.4% for OA-capped CdSe NCs). This mild approach is low cost, relatively low danger and high production yield (approximately 80%), indicating that it is very effective for the phosphine-free synthesis of alkylamine-capped CdSe nanocrystals.

Interfacial voids in aluminum created by aqueous dissolution

Nanometer-scale voids in aluminum formed by aqueous room-temperature corrosion were detected and characterized by a combination of electron microscopy techniques, atomic force microscopy, and positron annihilation spectroscopy. Void-containing layers were found within 100 nm of the metal surface, containing voids of 10–20 nm width with a number density of 10 8 – 10 9 c m − 2 . The voids were generated continuously during dissolution. The rapid nucleation and growth of voids suggest elevated concentrations of hydrogen-vacancy defects near the dissolving surface. Using the measured void radius and thickness of the void layer, the hypothesis that voids grow by vacancy condensation led to reasonable calculated values of the diffusion coefficient, and vacancy concentrations in agreement with independent estimates.

Micronization of creatine monohydrate via Rapid Expansion of Supercritical Solution (RESS)

In the pharmaceutical industry, an even greater number of products are in the form of particulate solids. In the case of pharmaceutical substances the particle size is quite important since it can limit the bioavailability of poorly water soluble drugs. Since the mid-1980s, a new method of powder generation has appeared involving crystallization with supercritical fluids. In this study, RESS was used to micronize the creatine monohydrate particles. The RESS process consists in solvating the product in the fluid and rapidly depressurizing this solution through an adequate nozzle, causing an extremely rapid nucleation of the product into a highly dispersed material. In addition, the effect of six different RESS parameters including, extraction temperature (313–333 K), extraction pressure (140–220 bar), nozzle length (2–15 mm), effective nozzle diameter (450–1700 μm), spraying distance (1–7 cm) and pre-expansion temperature (353–393 K) were investigated on the size and morphology of the precipitated particles of creatine monohydrate. The characterization (size and morphology) of the precipitated particles of creatine monohydrate was determined by scanning electron microscopy (SEM). The results show great reduction in the size of the precipitated particles of creatine monohydrate (0.36–9.06 μm) compared with the original particles of creatine monohydrate. Moreover, a slight change into spherical form was observed for the precipitated particles of creatine monohydrate while the original particles were irregular in shape.