Undergo Ostwald Ripening Research Articles

Evaluation of properties and structural transitions of Poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) / β-Galactosidase complex coacervates: effects of pH and aging

The coacervates of the Poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) / β-Galactosidase complex are characterized using several techniques (Turbidimetry, dynamic and static light scattering (DLS / SLS), optical microscopy, image dynamic light scattering (IDLS), and ultra-small angles light scattering (USALS)). Turbidity and SLS were used to accurately determine the critical pHs of complex formation (pHc, pHϕ1, pHopt, and pHϕ2), DLS was used to probe the microscopic structure of coacervate droplets rich in proteins and polyelectrolytes in liquid-liquid phase separation, and IDLS and USALS have been introduced to better understand, during aging, the topology of the network formed of materials based on fractals in the dense phase. Observations of the architecture, the spatial inhomogeneity, and the size distributions of liquid complex coacervate droplets and fractal solid precipitates, were performed by optical microscopy. The pair-distance distribution function, P(r), presented in this review, is a new methodology of calculus for determining with precision the radius of gyration Rg of droplets coacervates. These techniques show that aging improves the stability of swollen condensates, the growth of the coacervate droplets is due to the attractive electrostatic interactions within the complex and does not undergo Ostwald ripening, except for the case of pHopt and having fractal dimensions Df generated by diffusion-limited cluster aggregation (DLCA).

Active coacervate droplets are protocells that grow and resist Ostwald ripening

Active coacervate droplets are liquid condensates coupled to a chemical reaction that turns over their components, keeping the droplets out of equilibrium. This turnover can be used to drive active processes such as growth, and provide an insight into the chemical requirements underlying (proto)cellular behaviour. Moreover, controlled growth is a key requirement to achieve population fitness and survival. Here we present a minimal, nucleotide-based coacervate model for active droplets, and report three key findings that make these droplets into evolvable protocells. First, we show that coacervate droplets form and grow by the fuel-driven synthesis of new coacervate material. Second, we find that these droplets do not undergo Ostwald ripening, which we attribute to the attractive electrostatic interactions and translational entropy within complex coacervates, active or passive. Finally, we show that the droplet growth rate reflects experimental conditions such as substrate, enzyme and protein concentration, and that a different droplet composition (addition of RNA) leads to altered growth rates and droplet fitness. These findings together make active coacervate droplets a powerful platform to mimic cellular growth at a single-droplet level, and to study fitness at a population level.

Strategies for reducing Ostwald ripening phenomenon in nanoemulsions based on thyme essential oil.

White thyme essential oil, which can be incorporated in clean-label and food emulsion-based products, is a natural antimicrobial agent. However, emulsions containing essential oils commonly undergo Ostwald ripening as the main destabilization process. The main objective of this work was to evaluate various strategies for the inhibition of Ostwald ripening so as to develop stable nanoemulsions containing white thyme essential oil as food preservative and Kolliphor EL as surfactant. In a first approach, the influence of the surfactant/dispersed phase ratio and the number of cycles through a microfluidizer on droplet size distribution was evaluated. Unfortunately, these emulsions underwent Ostwald ripening, which was demonstrated by the application of the Lifshitz-Slyozov-Wagner theory. In order to reduce this destabilization mechanism, two different techniques based on the modification of the formulation (addition of rosin gum or Aerosil COK84) were analysed using laser diffraction and multiple light scattering techniques. The addition of rosin gum inhibited the Ostwald ripening mechanism, but only partially. Conversely, the incorporation of Aerosil COK84 to the continuous phase led to a gel-like rheological behaviour which seemed to practically avoid Ostwald ripening. Aerosil particles cover the droplets and form a three-dimensional network suggesting a Pickering stabilization, which was confirmed using transmission electronic microscopy. The results confirmed the role of Aerosil COK84, not only as a thickener or gelling agent, but also as an Ostwald ripening inhibitor. © 2019 Society of Chemical Industry.

Individual and Collective Behavior of Emulsion Droplets Undergoing Ostwald Ripening.

Ostwald ripening (OR) is the dominating phase separation mechanism in nanoemulsions consisting of the mass exchange between separated droplets by dissolution and absorption of molecules. Here, we propose a model based on a stochastic equation for the mass exchange coupled to a Brownian dynamics algorithm. Our model accounts for the simultaneous gain and loss of mass within a medium, where the presence of sources and sinks leads to a complex distribution of dissolved oil molecules. Also, a criterion for possible nucleation zones based on the definition of a saturation area around the droplets is found. The predictions of the collective behavior are constructed on the individual contributions of each droplet with its own environment. Individual droplets undergoing molecular exchange exhibited anomalous diffusion, whereas when performing the collective analysis, such a behavior was disguised. We used reported experiments under diverse conditions to validate and test the scope of our model, including the modification to the interfacial tension via Gibbs elasticity, finding close agreements. Our results imply that saturation is not conditional for the occurrence of OR. The ability of this model to extend the limitations imposed by traditional treatments to a broader number of physicochemical conditions makes it a useful complementary tool for predicting and understanding experimental results of emulsions experiencing OR.

On the macroscopic modeling of the rheology and Ostwald ripening of dilute stabilized emulsions

Stabilized-emulsions often undergo Ostwald ripening owing to the higher solubility of the smaller droplets. Their rheological properties are a direct result of the interplay between their microstructure and flow, which in turn affect their processing as well as their applications. In a recent study [Mwasame et al., “On the macroscopic modelling of dilute emulsions under flow,” J. Fluid Mech. 831, 433–473 (2017)], the use of a unit determinant conformation tensor to represent morphological changes has been advanced within the context of a thermodynamically consistent theory for a dilute monodisperse emulsion. The resulting model was validated against previously developed asymptotic theory that was also used to obtain all model parameters. In the present work, the first key innovation is to show how this theory can be extended to allow for multiple conformation tensors, subject to a single joint constraint originating from the mass conservation of the dispersed phase, in order to allow for the representation of dilute polydisperse emulsions undergoing Ostwald ripening. The second enabling innovation of this work is to show how to introduce correct dissipative terms into the dissipation bracket to account for mass transfer processes. The approach is illustrated for the particular case of a bidisperse emulsion. The model illustrates how multiple transport phenomena and thermodynamic effects can be seamlessly combined within a thermodynamically consistent approach. This work allows for not only the coexistence of a bimodal population of droplets but also the evaluation of their deformability and effective rheology in the presence of Ostwald ripening as the largest size droplets increase in mass at the expense of the smaller ones.

Nanocluster irradiation evolution in Fe-9%Cr ODS and ferritic-martensitic alloys

The objective of this study is to evaluate the influence of dose rate and cascade morphology on nanocluster evolution in a model Fe-9%Cr oxide dispersion strengthened steel and the commercial ferritic/martensitic (F/M) alloys HCM12A and HT9. We present a large, systematic data set spanning the three alloys, three irradiating particle types, four orders of magnitude in dose rate, and doses ranging 1–100 displacements per atom over 400–500 °C. Nanoclusters are characterized using atom probe tomography. ODS oxide nanoclusters experience partial dissolution after irradiation due to inverse Ostwald ripening, while F/M nanoclusters undergo Ostwald ripening. Damage cascade morphology is indicative of nanocluster number density evolution. Finally, the effects of dose rate on nanocluster morphology provide evidence for a temperature dilation theory, which purports that a negative temperature shift is necessary for higher dose rate irradiations to emulate nanocluster evolution in lower dose rate irradiations.

The Definition of “Critical Radius” for a Collection of Nanoparticles Undergoing Ostwald Ripening

An improved, exact analysis of surface Ostwald ripening of a collection of nanoparticles is presented in an effort to redefine the critical radius involved in the kinetic models of ripening. In a collection of supported particles of different sizes, the critical radius is the size of the particle that is in equilibrium with the surrounding adatom concentration. Such a particle neither grows nor shrinks due to Ostwald ripening, whereas larger particles grow and smaller particles shrink. We show that previous definitions of critical radius are applicable only for limiting regimes where the Kelvin equation has been linearized. We propose a more universally applicable definition of critical radius that satisfies the constraints of mass balance.

Impact of Oil Type on Nanoemulsion Formation and Ostwald Ripening Stability

The formation of stable transparent nanoemulsions poses two challenges: the ability to initially create an emulsion where the entire droplet size distribution is below 80 nm, and the subsequent stabilization of this emulsion against Ostwald ripening. The physical properties of the oil phase and the nature of the surfactant layer were found to have a considerable impact on nanoemulsion formation and stabilization. Nanoemulsions made with high viscosity oils, such as long chain triglycerides (LCT), were considerably larger ( D = 120 nm) than nanoemulsions prepared with low viscosity oils such as hexadecane ( D = 80 nm). The optimization of surfactant architecture, and differential viscosity eta D/eta C, has led to the formation of remarkably small nanoemulsions. With average sizes below 40 nm they are some of the smallest homogenized emulsions ever reported. What is more remarkable is that LCT nanoemulsions do not undergo Ostwald ripening and are physically stable for over 3 months. Ostwald ripening is prevented by the large molar volume of long chain triglyceride oils, which makes them insoluble in water thus providing a kinetic barrier to Ostwald ripening. Examination of the Ostwald ripening of mixed oil nanoemulsions found that the entropy gain associated with oil demixing provided a thermodynamic barrier to Ostwald ripening. Not only are the nanoemulsions created in this work some of the smallest reported, but they are also thermodynamically stable to Ostwald ripening when at least 50% of the oil phase is an insoluble triglyceride.

From nanowires to nanoislands: Morphological evolutions of erbium silicide nanostructures formed on the vicinal Si(001) surface

The growth behavior and morphology evolution of erbium silicide nanostructures are studied on the vicinal Si(001) surface with a 4° miscut angle towards the [110] direction as the functions of annealing temperature, annealing time, and Er coverage. Three kinds of nanostructures can be observed on the surface: nanowires, rectangular nanoislands and square nanoislands. The experimental results reveal that nanowires in AlB2-type structure and the nanoislands in ThSi2-type structure can be formed at 600–650 and 700–750°C, respectively. At the final growth stage, the nanowires of erbium silicide undergo Ostwald ripening. At high coverage of two monolayers, many AlB2-type nanoislands will appear in a rectangular shape on the sample surface. According to the AlB2-type crystalline structure of ErSi2 and the scanning tunneling microscopy results obtained on the flat and vicinal substrate surfaces, a model is suggested to describe the ErSi2∕Si(001) interfacial structure. This model explains the spatial orientation relationship between erbium silicide nanowire and Si dimer row, and is consistent with Er-induced (2×3) reconstruction at the initial stage of Er growth on the Si(001) surface.

The development of spatial correlations during Ostwald ripening: a test of theory

The coarsening of solid-Sn particles in a Pb–Sn liquid was studied under microgravity conditions. Spatial correlation functions were measured on plane sections in a low-volume fraction system undergoing Ostwald ripening. The correlation functions changed with time in a way that indicated that the microstructure initially consisted of clusters of particles and evolved into one which was more dispersed. The model by Akaiwa and Voorhees (AV) was used to study the effect of spatial correlations on the ripening process. We found that the initially highly correlated structure had no observable effect on the evolution of particle size distributions, but did have an effect on the coarsening rate of the system. Specifically, we determined that a structure consisting of clusters of particles coarsened faster than a system with a random, spatial arrangement of non-overlapping particles. We also found that the approach of the microstructure towards the steady-state regime could be monitored more sensitively using spatial correlations rather than using particle size distributions. The spacial correlations and the particle size distributions measured from the experiment agreed well with those calculated from the AV simulations using the initial experimental correlations and size distribution.

X-ray diffraction and micro-Raman spectroscopy analysis of new nickel hydroxide obtained by electrodialysis

Industrial nickel hydroxide samples produced by electrodialysis have been characterized both by X-ray diffraction (XRD) and by micro-Raman spectroscopy. A comparison with some commercial products of β-type Ni(OH) 2 is made. Aged in KOH solution, these nickel hydroxides are transformed to the β-Ni(OH) 2 phase and undergo Ostwald ripening, leading to crystallite sizes ranging between 260 and 380 Å with a reduction in defects. The anisotropic broadening of the XRD peaks in the β-Ni(OH) 2 pattern is interpreted in terms of crystalline lattice micro-strains and crystallite size. For the first time, Rietveld refinement has been performed on industrial Ni(OH) 2. The results indicate that the micro-strain effects increase the peak width according to the sequence of families ( hk0)→(00 l)→( h0 l). This study shows that the presence of proton vacancies leads to a lower degree of distortion in the crystalline lattice than does the presence of stacking faults or the adsorption of inorganic species at the border of the crystallites. A very high concentration of point defects inducing strong distortions in the crystal lattice is correlated with the presence of high energy Ni–O bond vibrations in the Raman spectra, with a frequency shift towards unusually high values.

Energetics of Self-Interstitial Clusters in Si

The transient supersaturation in a system undergoing Ostwald ripening is related to the cluster formation energy ${E}_{\mathrm{fc}}$ as a function of cluster size $n$. We use this relation to study the energetics of self-interstitial clusters in Si. Measurements of transient enhanced diffusion of B in Si-implanted Si are used to determine $S(t)$, and inverse modeling is used to derive ${E}_{\mathrm{fc}}(n)$. For clusters with $n>15$, ${E}_{\mathrm{fc}}\ensuremath{\approx}0.8\mathrm{eV}$, close to the fault energy of ${113}$ defects. For clusters with $n<10$, ${E}_{\mathrm{fc}}$ is typically 0.5 eV higher, but stabler clusters exist at $n\ensuremath{\approx}4$ ( ${E}_{\mathrm{fc}}\ensuremath{\approx}1.0\mathrm{eV}$) and $n\ensuremath{\approx}8$ ( ${E}_{\mathrm{fc}}\ensuremath{\approx}0.6\mathrm{eV}$).

Formation, evolution and annihilation of interstitial clusters in ion implanted Si

Formation, thermal evolution and annealing kinetics of self-interstitial clusters in ion implanted Si have been investigated. Deep level transient spectroscopy measurements performed on epitaxial and Czochralski Si samples implanted with Si ions at energies of 145 keV or 1.2 MeV reveal that these clusters are formed for fluences above 10 12/cm 2 and annealing temperatures higher than 550°C. Interstitial clusters introduce seven well defined levels in the Si band gap at E V + 0.33 eV, E V + 0.52 eV, E C − 0.58 eV, E C − 0.50 eV, E C − 0.37 eV, E C − 0.29 eV and E C − 0.14 eV. Analysis of the annealing kinetics at temperatures in the range 550–700°C reveal that the clusters undergo Ostwald ripening and anneal out with a characteristic dissociation energy of ∼2.3 eV for a Si fluence of 1 × 10 12/cm 2. Furthermore, their annealing temperature increases with implantation fluence. These results indicate that small interstitial clusters act as the source of interstitial supersaturation that drive transient enhanced dopant diffusion in the absence of extended defects.

Ostwald ripening in emulsions

The rates of Ostwald ripening in decane O/W emulsions were measured as a function of sodium dodecylsulphate concentration and of droplet volume fraction. It was found that the presence of micelles had only a small but systematic effect upon the rate of ripening, contrary to expectation, where the presence of micelles might be expected to aid the process of ripening through solubilization of oil. This small effect was discussed in terms of Kabal'nov's treatment of the process. It was concluded that the micelles were not in true equilibrium with the material diffusing from the droplets undergoing Ostwald ripening, and that only a small fraction of the micelles could, at any time, solubilize material from the droplets. This would lead to the reduced effect of micellar concentration on the rate of ripening. No systematic variation in rate was found with the volume fraction of the oil phase in the range 0–0.3. Theoretical treatments due to a number of authors suggest that the rate should increase by a factor of 2.5 in this range of volume fractions. The lack of volume fraction dependence was attributed to the presence of micelles which would appear to mask the effect of interactions between neighbouring diffusion fields surrounding the droplets.

Solution to the multi-particle diffusion problem with applications to ostwald ripening—II. Computer simulations

The multi-particle diffusion solution developed in Paper I is used to determine the collective behavior of a system of dispersed second phase particles undergoing Ostwald ripening. Since the multi-particle diffusion solution was employed to determine the diffusion field within the matrix, interparticle diffusional interactions are specifically included in the treatment. Both the transient and long-time behavior of given initial distributions of particle sizes were examined over a wide range of volume fractions of the coarsening phase. It was found in the transient region that the collective behavior of the coarsening ensemble was highly dependent on the initial distribution. When these distributions were scaled by the average particle radius, they all eventually evolved to identical time-independent distributions which were functions of the volume fraction of the coarsening phase. These time-independent distributions are, in general, significantly different from the classic Lifshitz-Slyozov-Wagner distribution, and become progressively broader and more symmetric with increasing volume fraction. The ripening kinetics were also found to be a function of the volume fraction, the kinetics increasing by a factor of five upon changing the volume fraction from zero to 0.5. The statistical nature of Ostwald ripening was investigated by examining the influence of the volume fraction on the distribution of individual particle source/sink strengths. This statistical information is used to show the self-consistency of the numerical approach.

Niederschlagsbildung—III: Kristallwachstum und einfluss der fremdionenkonzentration in der bariumsulfatfällung

The influence of foreign ions on the particle size of barium sulphate precipitates has been investigated by sedimentation experiments, establishing that NaCl, NaNO 3, KBr, KNO 3, and other salts at high concentrations powerfully hinder the growth of the crystals even at high supersaturation. The linear growth rate has been measured as a function of BaSO 4 concentration, foreign ion concentration and [BaCl 2]/[K 2SO 4] ratio. Because the growth is already diffusion controlled at a fivefold supersaturation, the BaSO 4 precipitates will not undergo Ostwald ripening. A suitable apparatus has been devised for the investigations.

The kinetic behavior of precipitate particles under Ostwald ripening conditions

The theory advanced by other investigators, on the asymptotic nature of particle size distributions undergoing Ostwald ripening, is used to evaluate the kinetic behavior of individual particles of which the distributions are constituted. Assuming asymptotic conditions, expressions are derived for the particle radius as a function of time and initial conditions for both diffusion-controlled and interface-controlled ripening. These expressions are then used to calculate the dissolution time for particles as a function of initial conditions.