A diffusing wave spectroscopy study of the kinetics of Ostwald ripening in protein-stabilised oil/water emulsions

Diffusing wave spectroscopy (DWS) has been used to study the kinetics of ageing processes in n-decane/water emulsions, stabilised by the milk protein _S1-casein. A particular advantage of this particle size measuring technique is its direct applicability to the concentrated emulsion, avoiding the necessity for dilution to single scattering levels demanded by traditional dynamic light scattering methods. The observed droplet growth rates were found to conform to the kinetic law of Ostwald ripening. Monotonic increases in coarsening rates have been observed with increasing oil volume fraction and these results are compared with theoretical predictions. The effect of excess protein has also been measured but no evidence for depletion flocculation due to free _S1-casein was detectable.     

Particulate growth in phase-separated polymer blends

Particle coarsening was investigated in polymer blends containing a minor phase volume of 23% produced by compositional quenching. The scaling exponents for three binary blends (polystyrene/polybutadiene, polystyrene/polyisoprene, and polystyrene/S-B random copolymer) were in reasonable agreement with the expected value of 0.33. The scaling exponent for a ternary blend containing an amphiphile (polystyrene/polybutadiene/S-B block copolymer) was substantially lower at 0.14. The particle size distributions for all the blends were broader than the self-similar distribution expected for Ostwald ripening and became increasingly broad with time. These distributions fit a two parameter coalescence model in which the probability of coalescence is proportional to the particle diameter. However, Ostwald ripening appears to make some contribution, particularly at early times. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2191–2196, 1998     

Synthesis of Highly Dispersed Fe3O4 Submicrometer Spheres in a One‐Pot Anion‐induced Solvothermal System

A facile, anion‐induced, one‐pot solvothermal method was successfully developed to prepare two kinds of highly dispersed magnetic Fe₃O₄ submicrometer spheres at 200°C in 12 h. The diameters of the as‐prepared Fe₃O₄ submicrometer spheres are ~500 and ~200 nm, respectively. With the guidance of OAc ⁻ ions, the size and morphology of the Fe₃O₄ spheres could be well controlled. The saturation magnetization of the Fe₃O₄ spheres was measured to be 84 and 74 emu/g, respectively. The assembly of tiny precursor nuclei into the Fe₃O₄ spheres relies on Ostwald ripening. The synthesized Fe₃O₄ submicrometer spheres show good magnetic response, good water solubility, and uniform size.     

Charge transfer between sensing and targeted metal nanoparticles in indirect nanoplasmonic sensors

In indirect nanoplasmonic sensors, the plasmonic metal nanoparticles are adjacent to the material of interest, and the material-related changes of their optical properties are used to probe that material. If the latter itself represents another metal in the form of nanoparticles, its deposition is accompanied by charge transfer to or from the plasmonic nanoparticles in order to equalize the Fermi levels. We estimate the value of the transferred charge and show on the two examples, nanoparticle sintering and hydride formation, that the charge transfer has negligible influence on the probed processes, because the effect of charge transfer is less important than that of nanoparticle surface energy. This further corroborates the non-invasive nature of nanoplasmonic sensors.     

In Situ Optical Imaging of the Growth of Conjugated Polymer Aggregates

Understanding the mechanisms that contribute to conjugated polymer aggregate formation and growth may yield enhanced control of aggregate morphology and functional properties on the mesoscopic scale. In situ optical imaging of the growth of MEH‐PPV aggregates in real time in controlled swollen films shows that growth occurs through multiple mechanisms and is more complex than previously described. Direct evidence is provided for both Ostwald ripening and aggregate coalescence as operative modes of aggregate growth in solvent swollen films. These growth mechanisms have a distinct and strong impact on the evolution of morphological order of growing aggregates: while Ostwald ripening allows preservation of highly ordered morphology, aggregate coalescence occurs with no preferential orientation, leading to attenuation in degree of ordering.     

Preparation of water-in-diesel oil nano-emulsion using nonionic surfactants with enhanced stability and flow properties

Formation of water-in-diesel oil (w/o) nano-emulsion has been achieved by a low-energy emulsification method by stabilizing a new combination of nonionic sorbitan esters surfactants, that is PEG20-sorbitan monostearate and sorbitan monooleate in mixed proportions. Different combinations of the surfactants (T6?+?S8) have been tested and the best possible combination of mixed surfactants is found at a surfactants ratio of 35:65 (wt/wt) for T6:S8 at hydrophile–lipophile balance (HLB)?=?8.01, which resulted in smaller droplet size of 44.87?nm. A phase diagram study is performed to identify the zones of formation of transparent, translucent, and opaque emulsions (44?nm?ripening, with inference describing a decrease in particle size with the Ostwald ripening rate. In case of nano-emulsion of droplet size 64.28?nm, the Oswald ripening rate is found as 0.0874?×?10^?27?m³?·?s^?1. Comparison of Ostwald ripening rate with other sets of surfactants obtained by different authors showed the lowest rate among them, indicative of enhanced stability. A rheological study of the tested set of nano-emulsions depicts the Newtonian behavior (1.0371?≤?n?≤?1.0826) over a wider range of shear rates (10–1000?s^?1) at different temperatures (25–40°C).     

Modification of interface anisotropy and its effect on microstructural evolution during ostwald ripening

We performed an experiment to study the role of anisotropy in interfacial energy during the coarsening of a complex oxide CaCu₃Ti₄O₁₂ (CCTO) material system. When we altered the interface anisotropy, we observed that evolution and sizes of spherical grains completely altered to facetted cubes. When interface became anisotropic, crystal growth appears to occur by the surface attachment/detachment, the motion of ledges, and the nucleation of new layers. Our observations showed that new layers grew by screw dislocation mechanism. This suggests that nucleation limited coarsening is occurring by the development of a transient bimodal grain size distribution consisting of large growing grains with step. In presence of PbO we always observed the development of shaped nucleus which grew larger. Sometimes very complex shaped crystals grew as a metastable shape. These shapes became uniform as the growth progressed and size of grains became larger. This process produces smaller grains that act as a source of material for the growing less defective larger grains.     

Features of formation of CdSe nanoparticles in aqueous sodium polyphosphate solutions

A study was carried out on the features of formation of stable aqueous colloidal solutions containing CdSe nanoparticles stabilized by sodium polyphosphate resulting from a reaction between cadmium chloride and sodium selenosulfate. The major parameters determining the size of the CdSe nanoparticles are the reaction medium temperature and the ratio of the starting reagent concentrations. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 102–106, March–April, 2006.     

Nonuniversality in Low-Volume-Fraction Ostwald Ripening

We study Ostwald ripening in the regime of small volume fraction and consider spatially periodic systems whose size is smaller than the screening length. Within the snapshot perspective we obtain an explicit characterization of the leading-order deviation to the classical mean-field theory by Lifshitz, Slyozov and Wagner (LSW). Using this representation, we show that the corrections are not universal, in the sense that the mean value has a strong dependence on geometry, and arbitrarily large fluctuations can happen with finite probability. AMS Subject classification: 35B27, 74N20, 82C26.     

Dependence of emulsion stability on particle size: Relative importance of drop concentration and destabilization rate on the half lifetimes of O/W nanoemulsions

This study reports the behavior of ionic dodecane-in-water nanoemulsions in distinct salt concentrations. Systems of smaller particle size (74–285 nm) were synthesized by a sudden dilution of an equilibrated mixture. Larger size systems (384–670 nm) were obtained from a set of formerly smaller nanoemulsions that evolved unperturbed for 2 weeks. Characteristic destabilization times for flocculation, coalescence, and Ostwald ripening were evaluated. In general, it was observed that stability increases with drop size. However, this size dependence is largely the consequence of the lower particle concentration of the coarser emulsions.