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Sodium dodecyl sulfate (SDS) was employed as a sacrificial template to assist in the preparation of catalysts, which not only modulates the catalyst morphology but also inhibits the Ostwald ripening process, resulting in more active components for the activity improvement. [Display omitted] • Alloy catalyst of sodium dodecyl sulfate (SDS) sacrificial template-assisted preparation is first reported. • Morphology of NiCo-alloy can be modulated with SDS concentration. • Synergistic interaction of Ni-Co decreases the NiOOH generation potential. Designing efficient non-precious metal-based catalysts for urea oxidation reaction (UOR) is essential for achieving energy-saving hydrogen production and the treatment of wastewater containing ammonia. In this study, sodium dodecyl sulfate (SDS) is employed as a sacrificial template to synthesize NiCo alloy nanowires (NiCo(SDS)/CC), and the instinct formation mechanism is investigated. It is found that SDS can inhibit the Ostwald ripening during hydrothermal and calcination processes, which could release abundant active cobalt, thereby modulating the electronic structure to promote the catalytic reaction. Moreover, SDS as a sacrificial template can induce the deposition of metal atoms and increase the specific surface area of the catalyst, providing abundant active sites to accelerate the reaction kinetics. As expected, the NiCo(SDS)/CC exhibits good activity for both UOR and hydrogen evolution reactions (HER) and it requires only 1.31 V and −86 mV to obtain a current density of ±10 mA cm−2, respectively. This work provides a new strategy for reducing the agglomeration of transition metals to design high-performance composite catalysts for urea oxidation. [ABSTRACT FROM AUTHOR]

[Display omitted] • N-doped carbon-coated Si nanocomposites with yolk shell structure (YS-Si@NC-60) derived from covalent organic frameworks (COFs) were prepared by template-free method. • Through an interesting Ostwald ripening, the core–shell Si@COP TBBA is transformed into the yolk-shell Si@COF TBBA. • The well-ordered pore structure of the COFs derived N-doped carbon shell can shorten the transport path of Li+. • The YS-Si@NC-60 with yolk shell structure can not only ease the volume expansion of silicon, but also has high ICE and cycle stability. Silicon (Si) has ultra-high theoretical capacity (4200 mAh g−1) and accordingly is widely studied as anode materials for lithium-ion batteries (LIBs). However, its huge volume expansion during charging/discharging is a fatal challenge. The preparation of Si-based composite materials with yolk shell structure is the key to solving the Si volume expansion. Here, N-doped carbon-coated Si nanoparticles (SiNPs) nanocomposites (YS-Si@NC-60) with yolk shell structure derived from covalent organic frameworks (COFs) was prepared. N-doped carbon shells derived from COFs not only maintain the well-ordered nanosized pores of COFs, which facilitates the transport of Li+ to contact with internal SiNPs, but also provide more extra active sites for Li+ storage. Most importantly, the internal void can effectively alleviate the damage effect of SiNPs volume expansion. The obtained YS-Si@NC-60 as a LIBs anode show high cyclic stability and Li+ storage performances. At 0.1 A g−1, the capacity is 1446 mAh g−1 after 110 cycles, and initial coulomb efficiency is as high as 82.2 %. The excellent performance can be attributed to the unique yolk shell structure. This simple and template-free strategy provides a new idea for preparing Si-C nanocomposites with yolk shell structure. [ABSTRACT FROM AUTHOR]

Ostwald ripening of gas bubbles is a spontaneous mass transfer process that can impact the storage volume of trapped gas in the subsurface. In homogeneous porous media with identical pores, bubbles evolve toward an equilibrium state of equal pressure and volume. How the presence of two liquids impacts ripening of a bubble population is less known. We hypothesize that the equilibrium bubble sizes depend on the surrounding liquid configuration and oil/water capillary pressure. We investigate ripening of nitrogen bubbles in homogeneous porous media containing decane and water using a level set method that alternately simulates capillary-controlled displacement and mass transfer between bubbles to eradicate chemical-potential differences. We explore impacts of initial fluid distribution and oil/water capillary pressure on the bubble evolution. Ripening in three-phase scenarios in porous media stabilizes gas bubbles to sizes that depend on their surrounding liquids. Bubbles in oil decrease in size while bubbles in water increase in size with increasing oil/water capillary pressure. Bubbles in oil reach local equilibrium before the three-phase system stabilizes globally. A potential implication for field-scale gas storage is that the trapped gas fractions in oil and water vary with depth in the oil/water transition zone. • Level set approach to gas bubble ripening on three-phase fluid configurations in porous media. • Equilibrium bubble sizes in oil and water depend on oil/water capillary pressure and gas/liquid interfacial tensions. • Ripening of gas bubbles in three-phase fluid systems displays a different behaviour in porous media than in bulk liquids. • Oil/water capillary pressure impacts the equilibration time for three-phase ripening scenarios in porous media. [ABSTRACT FROM AUTHOR]

The evolution of the Ostwald Ripening presents Ni 2 P@C OWS electrocatalyst of 3D nanoflowers/nanospheres structure with multi-dimensional interfaces. The nanosphere interface of protruding outwards, which is conducive to full contact with the electrolyte while the nanoflower lamellar connection promotes rapid electron transfer and exposes more active sites, and the interspace structure contributes to gas diffusion. [Display omitted] The regulation of the multi-dimensional interface plays an important role in optimizing the electron transport and gas mass transfer during catalysis, which is conducive to promoting the electrocatalytic process. Herein, a self-supporting electrode has been developed with the multistage interface within 3D Ni 2 P@C nanospheres/nanoflowers arrays derived from metal-organic frameworks (MOFs) as template skeletons and precursors. The constructed nanosphere interface protrudes outward to optimize the contact with the electrolyte while the nanoflower lamellar connection promotes rapid electron transfer and exposes more active sites, and accelerates the gas diffusion with the abundant interspace channels. According to theoretical calculation, the synergistic effect between Ni 2 P and C is conducive to the optimal adsorption and desorption of H*, thus contributing to the improvement of catalytic kinetics. With the optimized growth times assembled onto nickel foam substrates, the Ni 2 P@C-12 h requires overpotentials of only 69 mV and 205 mV to drive the current density of 10 mA cm−2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. And it reveals an ultralow cell voltage of 1.55 V at 10 mA cm−2 to achieve overall water splitting (OWS). In addition, the stability of the Ni 2 P@C/NF electrocatalyst emerges as prominent long-term stability, which is attributed to the carbonaceous nanosphere anchors on the substrate to minimize the possibility of oxidation of the catalyst surface. This strategy of in situ growth of MOF-derived phosphates provides a general idea for interfacial engineering modification of OWS electrode materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Enzyme-assisted self-assembly confined within host materials leads to Liesegang-like spatial structuration when precursor peptides are diffusing through an enzyme-functionalized hydrogel. It is shown here that playing on peptide and enzyme concentrations results in a transition from continuous self-assembled peptide areas to individual microglobules. Their morphology, location, size and buildup mechanism are described. Additionally, it is also found that the enzymes adsorb onto the peptide self-assemblies leading to co-localization of peptide self-assembled microglobules and enzymes. Finally, we find that large microglobules grow at the expense of smaller ones present in their vicinity in a kind of Ostwald ripening process, illustrating the dynamic nature of the peptide self-assembly process within host hydrogels. [ABSTRACT FROM AUTHOR]

[Display omitted] Ternary mixtures, containing one hydrotrope and two immiscible fluids, both being soluble in the hydrotrope at any proportion, exhibit unexpected solubilization power and unusual mesoscopic properties, which are a subject of long-standing controversies for decades. This work investigates the entire monophasic region of ternary trans -anethol/ethanol/water system, where multiscale nanostructurings with correlation lengths exceeding dimensions of individual molecules are identified by dynamic light scattering. The physical properties of the ternary mixture are characterized, with revealing the compositional dependence of refractive index and dynamic viscosity. In surfactant-free microemulsion (SFME) regime, the single phase consists of two distinct nanoscopic domains in equilibrium, one trans -anethol-rich aggregate at the molecular scale (∼ 1 nm) and one mesoscopic droplet at the mesoscale (∼ 100 nm). However, only a tiny fraction of the hydrophobic component trans -anethol (< ∼ 0.025 %) are initially incorporated in mesoscale structures, and the vast majority are molecularly dissolved or in the form of aggregates. The concentration of mesoscopic droplets increases sharply when shifting toward the miscibility gap, but their size exhibits a weak compositional dependence. The nanoscopic domains exhibit long-term physical stability, and the Ostwald ripening is still the primary mechanism governing such mesoscopic droplet aging, but with a rather low ripening rate. [ABSTRACT FROM AUTHOR]

The evolution of α-Fe 2 O 3 nanostructures from pie-like α-Fe 2 O 3 spheres (P-Fe 2 O 3), to hollow bowl-like α-Fe 2 O 3 spheres (B-Fe 2 O 3) and then to α-Fe 2 O 3 nanorings (R-Fe 2 O 3) have been successfully achieved through a facile hydrothermal approach and the designed hollow bowl-like α-Fe 2 O 3 (B-Fe 2 O 3) spheres exhibit great advantages as a LIB anode material. [Display omitted] The design and synthesis of hollow-nanostructured transition metal oxide-based anodes is of great importance for long-term operation of lithium ion batteries (LIBs). Herein, a special hollow bowl-like α-Fe 2 O 3 nanostructure is controllably synthesized through a facile hydrothermal technique and exhibits great electrochemical lithium storage performance when used as LIBs anode. Under a facile hydrothermal condition, α-Fe 2 O 3 nanostructures evolve from solid pie-like structure to hollow bowl-like structure and finally α-Fe 2 O 3 nanorings through the regulation of HPO 4 - derived from ionized Na 3 PO 4 ·12H 2 O and Ostwald ripening process. The designed hollow bowl-like α-Fe 2 O 3 nanostructure not only has the merits of hollow structure, which can accelerate the diffusion of lithium ions and electrons, but also shows great mechanical strength to disperse stress when compared to solid pie-like and ring-like α-Fe 2 O 3 nanostructures, which would avoid collapse during charge/discharge process. As a result, the as-synthesized hollow bowl-like α-Fe 2 O 3 nanostructure displays an initial reversible capacity of 1616 mAh g−1 at a current density of 1 A g−1, an excellent cycling performance with a reversible capacity of 1018 mAh g−1 after 500 cycles and an outstanding rate capability (68.1% capacity retention at current densities from 100 to 2000 mA g−1). This work provides not only a novel hollow bowl-like α-Fe 2 O 3 nanostructure with high specific surface area and stable structure as potential electrode materials for energy storage, but also a facile self-templated strategy free of any surfactants and templates for hollow nanostructures. [ABSTRACT FROM AUTHOR]

The hierarchical carbon-encapsulated yolk-shell nickelic composites were fabricated by a general MOF-derived route via Ostwald ripening and anion exchange strategy. Benefitting from the unique yolk-shell carbon framework, synergistic effect and satisfied phys-chemical characters, the nickel phosphide displays superior sodium storage properties compared with sulfide and selenide counterparts. [Display omitted] Transition-metal compounds have attracted enormous attention as potential energy storage materials for their high theoretical capacity and energy density. However, the most present transition-metal compounds still suffer from severe capacity decay and limited rate capability due to the lack of robust architectures. Herein, a general metal–organic framework-derived route is reported to fabricate hierarchical carbon-encapsulated yolk-shell nickelic spheres as anode materials for sodium-ion batteries. The nickelic metal–organic framework (Ni-MOF) precursors can be in situ converted into hierarchical carbon-encapsulated Ni 2 P (Ni 2 P/C), NiS 2 (NiS 2 /C) and NiSe 2 (NiSe 2 /C) by phosphorization, sulfuration, and selenation reaction, respectively, and maintain their yolk-shell sphere-like morphology. The as-synthesized Ni 2 P/C sample can deliver much lower polarization and discharge platform, smaller voltage gap, and faster kinetics in comparison with that of the other two counterparts, and thus achieve higher initial specific capacity (3222.1/1979.3 mAh g−1) and reversible capacity of 765.4 mAh g−1 after 110 cycles. This work should provide new insights into the phase and structure engineering of carbon-encapsulated transition-metal compound electrodes via MOFs template for advanced battery systems. [ABSTRACT FROM AUTHOR]

Carbon nitride hollow spheres (CNHS) with adjustable sizes were successfully constructed via a template-free strategy for superior photocatalytic hydrogen generation. [Display omitted] Carbon nitride hollow spheres (CNHS) with adjustable sizes were successfully fabricated via a template-free supramolecular pre-assembly strategy, in which melamine-cyanuric acid (MCA) hollow spheres were constructed through hydrogen bonds. A feasible formation mechanism was proposed, which coupled an inside-out Ostwald ripening with the supramolecular pre-assembly process. Interestingly, the sizes of MCA could be manipulated by changing the pre-assembly temperature. Consequently, the sizes of CNHS were adjustable. The optimal CNHS exhibited excellent photocatalytic hydrogen evolution rate (98.6 μmol/h) in the visible-light region, which was approximately 11 times higher than that of bulk carbon nitride calcined by melamine. The significantly improved performance was due to the contributions including: the unique architectures with remarkable light absorption ability, high electrical conductivity, relatively narrowed band gap, fast charge separation. This work provides a facile template-free supramolecular pre-assembly strategy to fabricate carbon nitride hollow spheres with adjustable sizes for the first time. [ABSTRACT FROM AUTHOR]

Ordered arrays of Ag nanoparticles-assembled cavities are fabricated by templated electrodeposition and post-growth. Oriented attachment and Ostwald ripening are proposed to drive the post-growth process. Such Ag cavity array shows high surface-enhanced Raman scattering sensitivity to pesticides (thiram and paraquat). [Display omitted] • Three-dimensional Ag nanostructure arrays have been fabricated by a simple method. • Ag nanoparticles-assembled micro-cavity arrays were achieved using templated electrodeposition and post-growth. • The three-dimensional substrate with dense hotspots showed high SERS sensitivity. • The fabricated SERS substrate showed high spectral uniformity and reproducibility. • Sensitive SERS detection of pesticide residues on fruits was realized. Three-dimensional (3D) plasmonic nano-arrays can provide high surface-enhanced Raman scattering (SERS) sensitivity, good spectral uniformity and excellent reproducibility. However, it is still a challenge to develop a simple and efficient method for fabrication of 3D plasmonic nano-arrays with high SERS performance. Here we report a facile approach to construct ordered arrays of silver (Ag) nanoparticles-assembled spherical micro-cavities using polystyrene (PS) sphere template-assisted electrodeposition and post-growth. The electrodeposited small Ag nanoparticles grow into bigger stable nanoparticles during the post-growth process, which could significantly improve the SERS sensitivity. The Ag nanoparticles-assembled 3D micro-cavity array provides much more hotspots in the excitation laser beam-covered volume than the two-dimensional counterpart. The relative standard deviation (RSD) of 612 cm−1 peak of rhodamine 6G (R6G) was calculated to be 8%, and the RSD of the characteristic peak taken from substrates of different batches was less than 10%. The detectable lower concentration as low as 1 fM was achieved for an aqueous solution of R6G. Such SERS substrate also showed high sensitivity to thiram (fungicide) and paraquat (herbicide) in water with limits of detection of 0.067 nM and 2.5 nM respectively. Furthermore, it also demonstrated that SERS detection of pesticide residues on fruits can be realized, showing a potential application in rapid monitoring food safety. [ABSTRACT FROM AUTHOR]

This work achieves an effective regulation of the ORR activity and stability for PtNi alloy nanowires by the synergistic effect of WO x on Pt. [Display omitted] • The ORR activity of WO x -PtNi NWs shows a volcano trend with W content. • Synergistic effect of WO x on Pt can accelerate the ORR kinetics. • WO x with unsaturated coordination can stabilize the surface atoms of PtNi alloy NWs. PtNi alloy nanoparticles display promising catalytic activity for oxygen reduction reaction (ORR), while the Ostwald ripening of particles and the dissolution/migration of surface atoms greatly affect its stability thus restricting the application. Herein, the WO x -surface modified PtNi alloy nanowires (WO x -PtNi NWs) exhibiting enhanced ORR catalytic property is reported, which has high aspect ratio with the diameter of only 2 ∼ 3 nm. It is found that the WO x -PtNi NWs shows a volcano relationship between the ORR activity and the content of WO x. The WO x-(0.25) -PtNi NWs has the best performance among all the synthesized catalysts. Its mass activity (0.85 A mg−1 Pt) is reduced by only 23.89% after 30k cycles durability test, which is much more stable than that of PtNi NWs (0.33 A mg−1 Pt , 45.94%) and Pt/C (0.14 A mg−1 Pt , 57.79%). Hence this work achieves an effective regulation of the ORR activity for PtNi alloy NWs by the synergistic effect of WO x on Pt. [ABSTRACT FROM AUTHOR]

[Display omitted] Monodisperse nanodroplet generation in quenched hydrothermal solution (MAGIQ) is a newly developed bottom-up process for preparing nanoemulsions. In this process, homogeneous solutions of oil in supercritical water are quenched by adding cold water containing a surfactant to induce rapid phase-separation, during which oil molecules self-assemble to form nano-sized oil droplets. The droplet size in MAGIQ is known to be influenced by the interplay of the phase‐separation dynamics, coalescence kinetics of the droplets, and adsorption kinetics of the surfactant on the droplet surface; however, the primary stages of the droplet formation are still elusive. Octane‑in‑water nanoemulsions containing 0.5, 1, and 3 vol% octane were prepared by the MAGIQ method. Their ripening was studied by dynamic light scattering, and the phase diagram was established. The nanoemulsions containing 0.5 and 1 vol% octane transformed to thermodynamically stable microemulsions containing swollen micelles, whereas the nanoemulsion containing 3 vol% octane underwent Ostwald ripening. The initial formation of the nano-sized droplets in the former was ascribed to a unique mechanism of droplet formation in MAGIQ—the droplets are first formed by the phase separation of homogeneous binary solutions of oil in supercritical water and then stabilized upon surfactant adsorption. [ABSTRACT FROM AUTHOR]

The synergism of dual-functional effect of Sn, optimized electronic structure by the ligand effect, and unique atomic arrangement endow the dendritic intermetallic PtSnBi nanoalloys high electrocatalysis toward MOR and EOR with enhanced CO tolerance. [Display omitted] Developing effective and robust novel electrocatalysts for direct alcohol fuel cells has been gaining much attention. However, the widely used Pt catalyst suffers from limitations including the sluggish kinetics, severe CO poisoning, and catalyst lost caused by aggregation and Ostwald ripening during alcohol oxidation reaction. Herein, dendritic intermetallic PtSnBi nanoalloys were synthesized via a facile hydrothermal approach with high electrocatalytic performance and enhanced CO resistance for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) owing to the synergism of the chosen three elements and unique three-dimensional morphology. Specifically, the PtSnBi nanoalloys display 4.6 and 6.7 times higher of mass activity (7.02 A mg−1 Pt) and specific activity (16.65 mA cm−2) toward MOR than those of commercial Pt/C, respectively. The mass activity of PtSnBi nanoalloys still retains 75.7% of the initial value after 800 cycles of stability test, superior to Pt/C (38.0%). The dual-functional effect of Sn, optimized electronic structure by the ligand effect, and unique atomic arrangement are responsible for the enhanced MOR activity and stability of PtSnBi nanoalloys. Furthermore, the PtSnBi nanoalloys with highlighted anti-CO poisoning capacity also improve the electrocatalytic performance toward EOR, indicating their great promise as broad energy electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A formalism is devised which accounts for both seed growth and formation of secondary particles in an initially over-saturated aqueous solution. • Seed growth and nucleation/growth of secondary particles are strongly coupled and prevail in separate regions of the kinetic parameter values. • An alternative interpretation of recent experimental results on amorphous silica nanoparticle synthesis is proposed. Seed-mediated methods are widely used in industrial or academic laboratories for the synthesis of nanoparticles of controlled shape and size. In the natural medium, precipitation of secondary minerals also often take place on seeds. In this context, we have devised a formalism which accounts for the competition between seed growth and nucleation and growth of secondary particles in an initially over-saturated aqueous solution. Based on the classical nucleation theory, it involves a size-dependent growth law which accounts for Ostwald ripening effects, unlike most water–rock interaction codes. We find that, in such closed system, seed growth and nucleation/growth of secondary particles are strongly coupled. In the multi-dimensional parameter space, regions where one or the other process prevails are well-separated by a rather abrupt transition. In general, the value of the initial seed total surface area is insufficient to fully orientate the synthesis. Relying on this approach, we propose an alternative interpretation of recent experimental results on amorphous silica nanoparticle synthesis. Besides fundamental understanding of the kinetics of precipitation, the interest of the present approach is to serve as a guideline to experimentalists or industrialists working in seed-mediated syntheses and warn on the undesired formation of secondary particles when monodispersed distributions of nano- or micro-particles are searched. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hollow spheres of non-stoichiometric perovskite KNi 1- x Co x F 3- δ K (x = 0.2; δ = 0.33) were synthesized via Ostwald ripening during solvothermal treatment. • The as-synthesized perovskite yielded a specific capacity/capacitance of 714.8 C g−1 (1435 F g−1) at 1 A g−1 based on anion-intercalation mechanism. • The as-prepared asymmetric supercapacitor delivered an energy density of 40 Wh kg−1 with an excellent cyclic stability of 98% for 10,000 cycles. The continual increase in energy demand and inconsistent supply have attracted attention towards sustainable energy storage/conversion devices, such as electrochemical capacitors with high energy densities and power densities. Perovskite oxides have received significant attention as anion-intercalation electrode materials for electrochemical capacitors. In this study, hollow nanospheres of non-stoichiometric cubic perovskite fluorides, KNi 1− x Co x F 3− δ (x = 0.2; δ = 0.33) (KNCF-0.2) have been synthesized using a localized Ostwald ripening. The electrochemical performance of the non-stoichiometric perovskite has been studied in an aqueous 3 M KOH electrolyte to categorically investigate the fluorine-vacancy-mediated charge storage capabilities. High capacities up to 198.55 mA h g−1 or 714.8 C g−1 (equivalent to 1435 F g−1) have been obtained through oxygen anion-intercalation mechanism (peroxide pathway, O - ). The results have been validated using ICP (inductively coupled plasma mass spectrometry) analysis and cyclic voltammetry. An asymmetric supercapacitor device has been fabricated by coupling KNCF-0.2 with activated carbon to deliver a high energy density of 40 W h kg−1 as well as excellent cycling stability of 98% for 10,000 cycles. The special attributes of hollow-spherical, non-stoichiometric perovskite (KNCF-0.2) have exhibited immense promise for their usability as anion-intercalation type electrodes in supercapacitors. [ABSTRACT FROM AUTHOR]

The boehmite hollow microspheres with excellent adsorption performance for CR were successfully prepared by N,N- dimethylformamide (DMF) assisted facile hydrothermal method using Al 2 (SO 4) 3 ·18H 2 O as the aluminum source. Their crystallinities and hollow degrees increase with accelerating hydrolysis rates of the amides as precipitants. Especially, dimethylamine as the hydrolysis product of DMF can act as structure directing agent to make the pore size distribution of the microspheres center at 3–4 nm which are beneficial to their adsorption for CR. Furthermore, the boehmite microspheres not only show fast adsorption kinetic with an adsorption amount of 484.1 mg/g at 60 min, but also show the high maximum adsorption capacity of 847.5 mg/g fitted by Langmuir isotherm model. • DMF assisted hydrothermal preparation of boehmite hollow/solid microspheres. • Dimethylamine can promote the formation of boehmite microspheres. • Dimethylamine is beneficial to forming pore sizes distribution centering at 3–4 nm. • The pore sizes distribution centering at 3–4 nm is beneficial to their adsorption. • boehmite hollow microspheres show excellent adsorption performance for Congo red. A series of boehmite microspheres with highly effective adsorption performance for Congo red (CR) were successfully prepared via amides assisted hydrothermal method at 180 °C. Effects of dosages and hydrolysates of N,N- dimethylformamide (DMF), amides species including DMF, N -methylformamide (MF) and formamide (FA), and reaction times on their physicochemical properties were studied in detail. It was found that increase on their crystallinity and shell thickness results from the different hydrolysis rates of the amides; amorphous alumina hydrate, boehmite core-shell structure and hollow microspheres were obtained at hydrothermal times of 60, 140 and 360 min, respectively due to the Ostwald ripening. Especially, dimethylamine (DMA) as a hydrolysate of DMF, can effectively regulate the morphologies of the boehmites together with the sulfate ions, and make their pore sizes distribution (PSD) centering at 3–4 nm. Importantly, the boehmite microspheres with specific surface area of 221.3 m2/g shows the maximum adsorption capacity of 847.5 mg/g for CR calculated from Langmuir isotherm model, and its adsorption amount reached a high value of 484.1 mg/g at 60 min due to the mentioned PSD. This template-free hydrothermal method using DMF as precipitant provides an alternative approach for preparing high-performance hydrated alumina for environmental applications. [ABSTRACT FROM AUTHOR]

Emulsions are metastable and can be destabilized by coalescence and Ostwald ripening, which lead to phase separation. Immobilizing emulsion droplets in a solid material shall improve their stability during storage. Miniemulsions and dispersions of nanocapsules are electrospun to immobilize colloids in polymer nanofibers. The nanofibers are dissolved after various period of time to re-disperse nanodroplets and nanocapsules. The size of nanodroplets and nanocapsules are close to the size of the original colloids before electrospinning, meaning that the emulsion droplets are efficiently stored overtime in nanofibers. Entrapping droplets in nanofibers by electrospinning allows a reduction of weight and volume of the emulsion of up to 82%. This method is therefore beneficial for improving shelf-life of emulsions, decreasing storage volume, and decreasing energy consumption for transportation of emulsions. [ABSTRACT FROM AUTHOR]

The role of interfacial coatings in gas transport dynamics in foam coarsening is often difficult to quantify. The complexity of foam coarsening measurements or gas transport measurements between bubbles requires assumptions about the liquid thin film thickness profile in order to explore the effects of interfacial coatings on gas transport. It should be possible to independently quantify the effects from changes in film thickness and interfacial permeability by using both atomic force microscopy and optical microscopy to obtain time snapshots of this dynamic process. Further, it is expected that the surfactant and polymer interfacial coatings will affect the mass transfer differently. We measure the mass transfer between the same nitrogen microbubbles pairs in an aqueous solution using two methods simultaneously. First, we quantify the bubble volume changes with time via microscopy and second, we use Atomic Force Microscopy to measure the film thickness and mass transfer resistances using a model for the gas transport. Modelling of the interface deformation, surface forces and mass transfer across the thin film agrees with independent measurements of changes in bubble size. We demonstrate that an anionic surfactant does not provide a barrier to mass transfer, but does enhance mass transfer above the critical micelle concentration. In contrast, a polymer monolayer at the interface does restrict mass transfer. [ABSTRACT FROM AUTHOR]

Currently, the synthesis of nanostructured inorganic materials with tunable morphology is still a great challenge. In this study, almond skin extract was employed for the biogenic synthesis of selenium nanoparticles with tunable morphologies such as rods and brooms. The effects of various synthesis parameters on morphologies were investigated using UV–Visible spectroscopy and scanning electron microscopy (SEM) which indicated that selenium brooms (SeBrs) were best synthesized using almond skin extract and optimized conditions of SeO 2 , ascorbic acid, pH, incubation temperature and time. Based on these results, the mechanism of SeBrs synthesis is proposed as having involved four stages such as nucleation, self-assembly, Ostwald ripening, and decomposition. Further, the test of antibacterial activity together with minimum inhibitory concentrations and minimum bactericidal concentrations indicated the selective, specific and good activity against B. subtilis. In addition, in situ coating of SeBrs on cotton fabric and its investigation by SEM demonstrated successful coating. Evident from plate-based assay and study of growth kinetics, coated fabric exhibited excellent anti -B. subtilis activity which demonstrated that biogenic SeBrs can be employed to coat cotton fabrics that can be used in operation theatres to reduce the episodes of Bacillus related Bacteraemia. [ABSTRACT FROM AUTHOR]

The objective of this study was to provide insights into the mechanisms involved in the mass transport of antimicrobial compounds from essential oil nanoemulsions to bacterial cell membranes. Origanum oil-in-water nanoemulsions were produced using spontaneous emulsification by titrating a mixture of essential oil, ripening inhibitor, and surfactant (Tween 80) into 5 mM sodium citrate buffer (pH 3.5). Stable nanoemulsions containing relatively small droplets (d < 60 nm) were produced using this low-energy method. The nature of the ripening inhibitor used in the oil phase of the nanoemulsions affected the antimicrobial activity of the nanoemulsions: corn (LCT) > medium-chain triglycerides (MCT). Differences in antimicrobial activity were attributed to the differences in the rate of transfer of hydrophobic antimicrobial constituents from the nanoemulsion to the MCT emulsion, which was used to mimic the hydrophobic region of the bacterial cell membranes. Each antimicrobial nanoemulsion was separated from the MCT emulsion by a dialysis tubing. Dialysis tubing with two different pore sizes was used, one excluding nanoemulsion droplet and micelle delivery, allowing the delivery of antimicrobial compounds only through the aqueous phase and the other by both the aqueous phase and micelles. For origanum oil nanoemulsions, the delivery of all antimicrobial agents occurred more efficiently when micelles were present. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Greater sustainability in mass manufacturing is essential to alleviating anthropogenic climate change. High surface-area, micro- and nano-patterned films have become a fundamental tool in materials science, however these technologies are subject to a dwindling petrochemical supply, increasing costs and disposability concerns. This paper describes the production of patterned biopolymer films utilizing controlled phase separation of biopolymeric thin films into nanopatterns using easily transferable variables and methods. Similar morphologies to those commonly observed with synthetic block-copolymers (BCPs) were achieved across a large range of feature sizes, from 160 nm to >5 μm: Bicontinuous, porous, droplet-matrix, particulated and dimpled. Protein and polysaccharide type, protein to polysaccharide ratio, casting method and ambient humidity were primary conditions found to influence the pore morphology of the films. High protein concentrations (4:1 and 2:1 blends) generally resulted in porous structures whereas high polysaccharide concentrations (1:2 and 1:4 blends) resulted in spherical structures. High humidity conditions (60% + relative humidity) resulted in the growth of large protuberances up to 10 µm in diameter while lower humidity (10–30%) resulted in discrete features smaller than 200 nm. [ABSTRACT FROM AUTHOR]

A facile template-free Ostwald ripening method is developed for the preparation of the reduced graphene oxide supported splode-like NiCo 2 O 4 hollow microsphere (SNHM/rGO). The graphene oxide used in the reaction mixture is found to play a crucial role in the formation of the SNHM/rGO. It promotes the formation of the NiCo-glycerol microspheres suitable for the Ostwald ripening to form the reduced graphene oxide supported hollow NiCo-glycerol microspheres, which is important for the subsequent calcination to form the SNHM/rGO. The obtained SNHM/rGO shows a great promise as the anode for lithium-ion batteries and can deliver a stable reversible capacity of 1048.1 mA h g −1 at the current density of 100 mA g −1 . The performance of the SNHM/rGO is much higher than that of most NiCo 2 O 4 -based materials reported previously, strongly suggesting that the SNHM/rGO could be used as the anode for practical applications. This is well supported by the higher performance of the LiCoO 2 //SNHM−rGO full cell. The excellent electrochemical performance can be attributed to the specific structure of the SNHM/rGO, which comprises the splode-like hollow NiCo 2 O 4 microspheres with the reduced graphene oxide integrated. [ABSTRACT FROM AUTHOR]

Foaming of particulate suspensions, followed by foam drying, is developed as an efficient method for production of highly porous materials with various applications. A key factor for success is the appropriate choice of surfactants which both modify the particle surface and stabilize the foam. Here we compare the efficiency of this method for silica suspensions containing two surfactants which lead to very different types of foam stabilization. Cationic TTAB leads to particle-stabilized foams (Pickering stabilization) whereas zwitterionic CAPB – to surfactant-stabilized foams. Thus we determined the general (common) features shared between the various surfactant systems: (1) The foaminess is controlled exclusively by the suspension viscosity under shearing conditions which mimic precisely the foaming process; (2) The foam stability to drainage and coarsening is controlled exclusively by the suspension yield stress; (3) The surfactant adsorption on the particle surface should occur in the time scale of seconds to minutes, thus ensuring appropriate rheological properties of the foaming suspension. Similar kinetic effects could be of high interest to other colloid systems and processes, e.g. for kinetic control of the internal structure and properties of aerogels produced from sheared suspensions, and for control of the transient rheological properties and non-Newtonian flow of particulate gels. [ABSTRACT FROM AUTHOR]

The technique of stray field diffusion NMR is adapted to study the diffusion properties of water in monodisperse wet foams. We show for the first time, that the technique is capable of observing q -space diffusion diffraction peaks in monodisperse aqueous foams with initial bubble sizes in the range of 50–85 μm. The position of the peak maximum can be correlated simply to the bubble size in the foam leading to a technique that can investigate the stability of the foam over time. The diffusion technique, together with supplementary spin-spin relaxation analysis of the diffusion data is used to follow the stability and coarsening behaviour of monodisperse foams with a water fraction range between 0.24 and 0.33. The monodisperse foams remain stable for a period of hours in terms of the initial bubble size. The duration of this stable period correlates to the initial size of the bubbles. Eventually the bubbles begin to coarsen and this is observed in changes in the position of the diffusion diffraction maxima. [ABSTRACT FROM AUTHOR]

Zinc–aluminum layered double hydroxides with nitrate intercalated (Zn(n)Al–NO 3 , n = Zn/Al) is an intermediate material for the intercalation of different functional molecules used in a wide range of industrial applications. The synthesis of Zn(2)Al–NO 3 was investigated considering the time and temperature of hydrothermal treatment. By examining the crystallite size in two different directions, hydrodynamic particle size, morphology, crystal structure and chemical species in solution, it was possible to understand the crystallization and dissolution processes involved in the mechanisms of crystallite and particle growth. In addition, hydrogeochemical modeling rendered insights on the speciation of different metal cations in solution. Therefore, this tool can be a promising solution to model and optimize the synthesis of layered double hydroxide-based materials for industrial applications. [ABSTRACT FROM AUTHOR]

Hypothesis Understanding the coarsening behavior of foams is of great interest for their deliberate design. In order to systematically quantify the influence of surfactants and other chemical parameters, identifying robust descriptive features of observed foam aging dynamics is essential. Existing coarsening theories for both wet and dry foams provide concise models with respective descriptive parameters. Experiment Multiple micro computed tomography scans of moderately wet polydisperse β -Lactoglobulin foam are recorded over a period of 15 min. The growth behavior of a large fraction of about 5 × 10 4 pores that constitute the imaged volume is individually observed and statistically analyzed as a function of pore radius as well as number of neighboring pores. Findings The three-dimensional analog of von Neumann’s law for dry foams by Glazier is confirmed as a suiting empirical model, whereby a critical number of 13 ± 7 neighbors and a diffusion coefficient of ( 1.8 ± 0.8 ) × 10 - 11 m 2 / s are found for an exemplary sample. The pores growth can as well be related to their radius by means of Lemlich’s coarsening model for wet foams though, whereby a critical radius marking the transition between shrinkage and growths is found to be R c = ( 300 ± 85 ) μ m . Although different, both models fit similarly well given the broad variance of the observed growth rates. [ABSTRACT FROM AUTHOR]

Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50 days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1 day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz–Slyozov–Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. [ABSTRACT FROM AUTHOR]

One powerful method to make nanoparticles is template-based approach. Because such templates confine the size and shape of nanoparticles, diverse nanoparticles can be prepared through such method. For example, hollow gold (Au) nanoparticles are easily fabricated using silver (Ag) nanoparticles as templates. Ag nanoparticles in a solution containing Au 3+ are readily oxidized to Ag + and dissolved into the solution, while Au 3+ are reduced and deposited near Ag nanoparticles. Because the reactivity of Au 3+ is lower than that of Ag + , this exchange reaction readily occurs, resulting in hollow Au nanoparticles. In this paper, we use morphology-controlled silver oxide (Ag 2 O) mesoparticles as a sacrificial template to make well-defined Ag mesoparticles. The hexapod-shaped Ag 2 O mesoparticles are synthesized by retarding its reaction rate using bis ( p -sulfonatophenyl) phenylphosphine dehydrate dipotassium as a ligand, and reduced into Ag hexapods by sodium borohydride. Complete conversion of Ag 2 O into Ag is confirmed by a series of characterization procedure, and the shape and size of Ag 2 O hexapods are retained during the reduction process. Reduced Ag hexapods have hollow inner structure, and interestingly show single crystalline phase, which is contrary to the previous report. A new mechanism is introduced to explain formation of hollow structure and its single crystalline phase. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hierarchical flower-like Al2(O3PC6H5)3·H2O microspheres were synthesized. [•] The growth mechanism relies on Ostwald ripening and oriented attachment. [•] The hierarchical nanoporous AlPO4 micro-flowers were obtained by sintering. [•] Peptide enrichment properties were demonstrated and proved to be promising. [•] A general synthesis procedure is developed for metal phosphonate spheres. [ABSTRACT FROM AUTHOR]

Abstract: The shelf stability of nanoemulsions made by ultrasound, phase inversion composition, and the Ouzo effect was studied using a range of hydrocarbons, as the model oils, and surfactants. The cube of the average drop radius of the nanoemulsions displayed a linear increase with time. Both Ostwald ripening and coalescence can exhibit such behaviour. A new approach, based on the time evolution of drop size distribution, is proposed for unravelling the aging mechanism of nanoemulsions. Sequences of fall and rise in the average drop size of nanoemulsions were clearly observed. The decrease in the drop size could unambiguously be attributed to Ostwald ripening, but the increase could be due to either Ostwald ripening or coalescence/flocculation. Coalescence was identified as the dominant growth mechanism at low surfactant concentrations evidenced by drop size distribution broadening with time associated with the rise in the average drop size. Ostwald ripening was the dominant mechanism at higher surfactant concentrations where the drop size distributions broadened with time during the falls and narrowed with time during the rises of the average drop size. The nanoemulsions produced via the Ouzo process, displayed a coalescence-dependent transient stage and an Ostwald ripening dominated asymptotic regime in the absence of surfactant. The nanoemulsion produced via phase inversion was found to be the most stable one, however, still showed vulnerability to Ostwald ripening and flocculation in the long term. [Copyright &y& Elsevier]

Abstract: Persimmon-like NaLa(WO4)2 microarchitectures were prepared via hydrothermal process with using trisodium citrate (Na3Cit) as chelated reagent and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and fluorescent dynamics. The influences of Na3Cit concentration, organic additivities, and reaction time on the morphologies of NaLa(WO4)2 phosphor were studied. The results revealed that Na3Cit species had double functions of strong ligand and structure-directing reagent that could efficiently control the formation of persimmon-like NaLa(WO4)2 microarchitectures. The possible mechanism for the growth of persimmon-like NaLa(WO4)2 microarchitectures was attributed to the Ostwald ripening mechanism. The energy transfer from Tb3+ to Eu3+ in the persimmon-like NaLa(WO4)2 phosphors was observed. The energy transfer efficiencies and emission colors can be tuned by changing the concentration of Eu3+. Finally, it was deduced that the electric dipole–dipole interaction (D–D) is the main mechanism for energy transfer between Tb3+ and Eu3+ in the persimmon-like NaLa(WO4)2 phosphor. [Copyright &y& Elsevier]

Abstract: The influence of interfacial crosslinking, layer thickness and layer density on the kinetics of Ostwald ripening in multilayered emulsions at different temperatures was investigated. Growth rates of droplets were measured by monitoring changes in the droplet size distributions of 0.5% (w/w) n-octane, n-decane, and n-dodecane oil-in-water emulsions using static light scattering. Lifshitz–Slyozov–Wagner theory was used to calculate Ostwald ripening rates. A sequential two step process, based on electrostatic deposition of sugar beet pectin onto fish gelatin or whey protein isolate (WPI) interfacial membranes, was used to manipulate the interfacial properties of the oil droplets. Laccase was added to the fish gelatin–beet pectin emulsions to promote crosslinking of adsorbed pectin molecules via ferulic acid groups, whereas heat was induced to promote crosslinking of WPI and helix coil transitions of fish gelatin. Ripening rates of single-layered, double-layered and crosslinked emulsions increased as the chain length of the n-alkanes decreased. Emulsions containing crosslinked fish gelatin–beet pectin coated droplets had lower droplet growth rates (3.1±0.3×10−26 m3/s) than fish gelatin-stabilized droplets (7.3±0.2×10−26 m3/s), which was attributed to the formation of a protective network. Results suggest that physical or enzymatic biopolymer-crosslinking of interfaces may reduce the molecular transport of alkanes between the droplets in the continuous phase. [Copyright &y& Elsevier]

Abstract: Titanium dioxide sols were synthesized by hydrothermal reactions with addition of poly (ethylene glycol) (Mw=20,000). Using techniques of X-ray diffraction, transmission electron microscopy, dynamic light scattering, and scanning electron microscopy, effect of PEG on the crystallographic properties, particle size, aggregating behavior, and the morphological properties of nanoparticles in the sols were studied. It was found that growth of anatase nanocrystallites was retarded by PEG. Average crystallite size of anatase nanocrystallites first decreased from 20.7nm to 10.5nm as the polymer concentration increased from 1g/L to 3g/L, and then changed little. Meanwhile, small amount of rutile phases like rutile nanowires, twin crystallites, and the “flowers” appeared continuously when the concentration increased from 3g/L to 5g/L. Mono-dispersion was obtained with relatively lower PEG concentration. The observed evolvement was discussed based on the interaction between the polymers and the nanocrystallites with assistance of FTIR. The coverage of polymer chains on surface of nanocrystallites leads to isolated reactors, which benefits the uniform coarsening rate of the nanocrystallites. The synthesized TiO2 sols were utilized in dye sensitized solar cells. Performance parameters of the solar cells were discussed with assistance of dye desorption experiments. The improved dispersion in sols was found to benefit the photovoltaic performance of the cells. [Copyright &y& Elsevier]

Abstract: Birnessite flower-like and α-type tubular MnO2 nanostructures were selectively synthesized through simple decomposition of KMnO4 under hydrochloric acid condition by controlling reaction temperature using a microwave-assisted hydrothermal method. The as-prepared samples were characterized in detail by various techniques including X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform-infrared spectroscopy, and Raman scattering spectroscopy. While the growth of flower-like birnessite-MnO2 might follow a widely accepted Ostwald ripening process, we proposed a formation mechanism of the nanotubular α-MnO2 based on our evidence, which was assembly of nanorods through an “oriented attachment” process. [Copyright &y& Elsevier]

Abstract: Hollow magnetic microspheres with micro-mesoporous shells were constructed with layered cobalt-based ferrocenyl coordination polymers (Co-Fc-HCPS) through a one-step Ostwald ripening process. The diameters of microspheres and corresponding cavities were controlled in the range of several microns by tuning the reaction time and reactant concentration, which would attribute the microspheres with high loading, and enhanced mass diffusion and transfer efficiency. The high crystallinity of hollow microspheres allowed determination of the crystal structure of cobalt-based ferrocenyl coordination polymer, which crystallized in Brucite-type layered structure with the formula of Co4(OH)4(FcDC)2, (H2FcDC=1,1′-ferrocenedicarboxylic acid), by combination of powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), element analysis (EA), and Fourier transform infrared spectroscopy (FT-IR). N2 adsorption/desorption investigation revealed the existence of both mesopores around 3.81nm and micropores of ca. 1nm in the shells. The hollow microspheres exhibited spin-canted antiferromagnetism with weak ferromagnetic ordering below ∼52K, which showed a remanent magnetization (Mr) of 1.0 μ B and a large coercive field (Hc) of 5 kOe at 7K. [Copyright &y& Elsevier]

Abstract: In order to examine the applicability of the diffusion-limited Ostwald ripening model to the growth kinetics of nanocrystals, platinum nanocrystals prepared by two different methods have been investigated by a combined use of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). One of the methods of synthesis involved the reduction of chloroplatinic acid by sodium citrate while in the other method reduction was carried out in the presence of polyvinylpyrrolidone (PVP) as a capping agent. The growth of platinum nanocrystals prepared by citrate reduction in the absence of any capping agent follows a Ostwald ripening growth with a D 3 dependence. In the presence of PVP, the growth of platinum nanocrystals does not completely follow the Ostwald ripening model, making it necessary to include a surface reaction term in the growth equation. Thus, the growth of platinum nanocrystals in the presence of PVP has contributions both from diffusion and surface reaction, exhibiting a D 3 + D 2 type behavior. [Copyright &y& Elsevier]

Abstract: The interaction between organic molecules and the surface of nanoparticles (NPs) strongly affects the size, properties and applications of surface-modified metal sulfide semiconductor nanocrystals. From this viewpoint, we compared the influence of cationic surfactants with various chain lengths and anionic surfactants with different head groups, as surface modifiers during synthesis of ZnS NPs in aqueous medium. The surfactant adsorbs on the surface of the particles as micelle-like aggregates. These aggregates can form even at the concentration lower than critical micelle concentration (cmc) due to interaction between the polar groups and the NPs. The nature of interaction depends specifically on the surfactant polar group. The ability of surfactant to form the micelle-like aggregates on the surface of the NPs correlates with their cmc. This leads to the fact that the surfactant with longer tail stabilizes the NPs better since its cmc is lower. The adsorption of the surfactant on the NPs also stabilizes them by the change of their charge which is in accordance with the correlation of zeta potential with the particles stability. The energetics of surface states generating interesting photoluminescence (PL) properties in ZnS NPs has been governed by the nature of surfactant molecules. In general, the size, structure, and stability of the ZnS NPs can be controlled by the choice of suitable surfactant. [Copyright &y& Elsevier]

Abstract: Pulsed-field gradient nuclear magnetic resonance, previously used for measuring droplet size distributions in emulsions, has been used to measure bubble size distributions in a non-overflowing pneumatic gas–liquid foam that has been created by sparging propane into an aqueous solution of 1.5g/l (5.20mM) SDS. The bubble size distributions measured were reproducible and approximated a Weibull distribution. However, the bubble size distributions did not materially change with position at which they were measured within the froth. An analysis of foam coarsening due to Ostwald ripening in a non-overflowing foam indicates that, for the experimental conditions employed, one would not expect this to be a significant effect. It is therefore apparent that the eventual collapse of the foam is due to bubble bursting (or surface coalescence) rather than Ostwald ripening. This surface coalescence occurs because of evaporation from the free surface of the foam. An analytical solution for the liquid fraction profile for a certain class of non-overflowing pneumatic foam is given, and a mean bubble size that is appropriate for drainage calculations is suggested. [ABSTRACT FROM AUTHOR]

Abstract: The rate of Ostwald ripening was measured, using light scattering, in 2wt.% and 10wt.% decane-in-water and dodecane-in-water emulsions. Sodium dodecyl sulfate and several nonionic ethylene oxide dodecyl ethers—surfactants with tails containing 12 carbons, but with various headgroups—were used to form the emulsions. Emulsions were formed with sufficient quantities of the surfactant to saturate the droplet interfaces. The influence of surfactant micelles in the continuous phase was then explored by adding 1–5wt.% surfactant to the water. The increase in the average droplet radius in the absence of micelles was found to agree qualitatively with Lifshitz–Slyozov–Wagner theory for the different surfactant types. The addition of micelles increased the rate of Ostwald ripening, by factors between 2 and 50, depending on the type and concentration of surfactant. However, there was no systematic correspondence between the increased rate and the equilibrium solubilization capacity of the micelles, nor was the rate decreased with increased strength of repulsive interactions between micelle and the droplet interface. It is proposed that the complex influence of surfactant on Ostwald ripening kinetics may depend on the ability of micelles to become supersaturated with oil—i.e., to incorporate solute temporarily above their equilibrium solubilization capacity. [Copyright &y& Elsevier]

Abstract: The influence of both the nature of the surfactant and surfactant concentration on the processes of droplet break-up and coalescence in the formation of decane-in-water nano-emulsions in a high-pressure homogenizer was investigated. Emulsions were produced using a Christison Scientific M110-S microfluidiser with an impinging jet high-shear chamber. For all six surfactants studied (Tween 20, Tween 80, Brij 96v, sucrose monolaurate, sucrose monomyristate and sucrose monopalmate), the droplet size decreased with increasing surfactant concentration reaching a limiting droplet size at a surfactant concentration of 15mM. The limiting droplet size for the different surfactants used were; Tween 20 (∼250±30nm), Tween 80 (∼320±40nm), Brij 96v (∼200±20nm) and the three sucrose monoesters had very similar sizes of ∼250±20nm. A hydrophobic fluorescent dye (1-undecylpyrene) was used to establish the extent of competition between droplet break-up and coalescence in the emulsification process. For all the emulsifiers studied, droplet coalescence in the process reduced as the amount of emulsifier increased, becoming zero at concentrations of about 15mM, i.e. the same concentration as that required to produce the limiting minimum droplet size. This shows that in the emulsification process droplet size is determined by both break-up and re-coalescence events, and at lower surfactant concentrations (<15mM) that the final droplet size is probably a consequence of multiple break-up events. Emulsion stability over 200h was investigated by measuring changes in the droplet size using dynamic light scattering. The increase in droplet volume was shown to be linear with respect to time, indicating an Ostwald ripening process. The observed ripening rate for the three sucrose monoesters (monopalmitate, monomyristate and monolaurate) was approximately 20nm3 s−1, which is the ripening rate calculated using the Lifshitz–Slesov–Wagner (LSW) theory. This ripening rate is the change in radius that results from movement of the oil through the continuous phase, taking into account the oil solubility in water and the diffusion coefficient of the decane-in-water. The ripening rate for Brij 96v was about three times larger than the calculated rate and there is an indication that the ripening rate increases slightly with increasing surfactant concentration, indicating that some enhancement due to the presence of micelles has occurred. With Tween 80 and 20 the ripening rates were 20 and 40 times, respectively, larger than those calculated using the solubility and diffusion coefficients. The increased rate has been shown to be first order with respect to the surfactant concentration indicating micelle mediated ripening. It is hypothesized that an optimum formulation for the sub-micron emulsion with these types of surfactant, will balance surfactant concentration to minimize droplet size during processing while aiming to minimize or prevent Ostwald ripening. [Copyright &y& Elsevier]

Abstract: A forced Ostwald ripening experiment is performed on a single foam bubble. The bubble size is followed as the system is wetted with a constant liquid flow rate delivered from one of the bubble Plateau borders. Obtained ripening velocities cannot be described with a model based on a constant film thickness assumption. Within these well-controlled experimental conditions, the film thickness is measured and found to depend on the imposed liquid flow rate. It is shown that the bubble growth rate is well predicted as the films thickness evolution is explicitly introduced in the ripening model. Finally, it is suggested that existing results for the coarsening of draining foams could be understood following the approach validated on the bubble scale. [Copyright &y& Elsevier]

Abstract: The rate of domain growth in phase-separated, mixed Langmuir–Blodgett (LB) monolayers of arachidic acid, C19H39COOH (AA) and perfluorotetradecanoic acid, C13F27COOH (PA) was tracked via atomic force microscope measurements. The growth rate of domains comprised of phase-separated AA was consistent with that predicted by the Lifshitz–Slyozov model for diffusion-limited Ostwald ripening. In addition to Ostwald ripening, some evidence for domain coalescence was also observed when LB films were deposited under conditions of low temperature and short incubation times, though this tendency disappeared at higher deposition temperatures. [Copyright &y& Elsevier]

Abstract: Paraffin oil-in-water nano-emulsions stabilized by Tween 80/Span 80 were prepared using the emulsion inversion point method at different emulsification temperatures. Nano-emulsions with droplet size below 200 nm were formed above a critical surfactant-to-oil ratio of 0.20 at 50 °C. The main destabilization mechanism of the systems was found to be Ostwald ripening. An interesting phenomenon was that the Ostwald ripening rate declined as the surfactant concentration rose. Furthermore, flocculation was also found to contribute to the instability of the nano-emulsions, especially for those with low surfactant concentrations. Study on the electrophoretic properties of emulsion droplets revealed a negative value of the zeta potential, which was strongly dependent on the pH of the systems. [Copyright &y& Elsevier]

Abstract: Controlling stability and aging of emulsions is important from commercial and scientific perspectives. Achieving such control comes through gaining an understanding of the relationship between emulsion constituents and microstructure and how these influence the kinetics and mechanism of destabilisation. We present here an investigation determining the rate of destabilisation as a function of time for a series of water/n-alkane/Triton X-100 oil-in-water emulsions. The time dependence of the emulsions was investigated using static light scattering, PFG-NMR and measurement of gross phase separation. By changing the chain length of the oil from hexane to tetradecane, an almost five orders of magnitude variation in emulsion lifetime could be achieved, while maintaining most of the other chemical and physical characteristics of the emulsions. Further, we show that while Ostwald ripening is the dominant destabilisation mechanism, two distinct regimes are evident. Initially, we observed an enhanced Ostwald ripening regime due to the presence of oil-swollen micelles in the aqueous continuum, that is a depletion flocculation mechanism is followed. The presence of oil-swollen micelles was confirmed using PFG-NMR. The micelles aid the gross oil transport between the discrete oil domains. Upon phase separation the oil-swollen micelles are predominantly removed from the emulsion along with the excess water resulting in a concomitant reduction in the ripening rate, producing the more general Ostwald ripening cubic dependence of droplet radius as a function of time for the lower molecular weight oils. The oils with higher molecular weight (decane and above), however, were observed to switch over to destabilisation via creaming. PFG-NMR was shown to be a powerful technique to fully probe emulsion microstructure as a function of time with droplet size and spacing being directly obtained from the data. [Copyright &y& Elsevier]

Abstract: Water transportation through the oil phase in W/O emulsions and in W1/O/W2 systems (W/O emulsion in contact with water) was examined. Substance diffusion through interfaces led to interface instability and spontaneous emulsification which caused nanodispersion formation. The photomicrographs of Pt/C replicas of emulsions showed the presence in the continuous oil phase a lot of nanodispersion droplets with a diameter in the range 17–25 nm. Diffusion coefficient (D) of water calculated on the base of Lifshiz–Slezov–Wagner (LSW) equation was about 15 times lower than the coefficients of molecular diffusion. Since such emulsions were extremely unstable toward coalescence, the growth of water droplets took place through as Ostwald ripening as coalescence. In three-phase W1/O/W2 systems diffusion of water, Rhodamine C, and ethanol was studied. D calculated on the base of the equation of nonstationary diffusion were approximately 1000 times lower than molecular ones. It was assumed, that nanodispersion droplets were more likely water carriers in investigated W/O emulsions stabilized by sorbitan monooleate. [Copyright &y& Elsevier]

Abstract: The reaction between silver nitrate and poly(N-vinyl-2-pyrrolidone) (PVP) in pyridine at ambient conditions could lead to the formation of spherical nanoparticles or quadrilateral and triangular silver nanoplates, depending on the silver-to-PVP ratio used. It is proposed that the spherical Ag nanoparticles, which were formed early in the reaction, were transformed into nanoplates through an Ostwald ripening process driven by the bridging flocculation of small spherical Ag nanoparticles. This unique and hitherto unreported shape evolution process was carefully followed by a combination of techniques, viz., UV–visible spectroscopy, TEM, and powder X-ray diffraction. [Copyright &y& Elsevier]

Abstract: The aging mechanisms of perfluorocarbon emulsions were investigated using image analysis. Oil-in-water emulsions of two perfluorocarbons, n-perfluorohexane and perfluorodecalin, were prepared with three emulsifiers, Lecithin, Span 20, and Pluronic F-68. The effect of the temperature and the replacement of water by an aqueous phase consisting of a microbial culture medium were also studied. The emulsions were prepared by sonication and their stability was followed through analysis of the evolution of mean droplet size. The results indicate that the stability of perfluorocarbon in water emulsions depends on all the parameters investigated and that two aging mechanisms, coalescence and molecular diffusion, may take place. Analysis of the evolution of the mean droplet size during long time periods indicate that coalescence is more common than previously reported for these systems and seems to be favored by a temperature increase. [Copyright &y& Elsevier]

Abstract: The formation of O/W nano-emulsions by the PIT emulsification method in water/mixed nonionic surfactant/oil systems has been studied. The hydrophilic–lipophilic properties of the surfactant were varied by mixing polyoxyethylene 4-lauryl ether () and polyoxyethylene 6-lauryl ether (). Emulsification was performed in samples with constant oil concentration (20 wt%) by fast cooling from the corresponding HLB temperature to 25 °C. Nano-emulsions with droplet radius 60–70 nm and 25–30 nm were obtained at total surfactant concentrations of 4 and 8 wt%, respectively. Moreover, droplet size remained practically unchanged, independent of the surfactant mixing ratio, XC12E6. At 4 wt% surfactant concentration, the polydispersity and instability of nano-emulsions increased with the increase in XC12E6. However, at 8 wt% surfactant concentration, nano-emulsions with low polydispersity and high stability were obtained in a wide range of surfactant mixing ratios. Phase behavior studies showed that at 4 wt% surfactant concentration, three-liquid phases (W+D+O) coexist at the starting emulsification temperature. Furthermore, the excess oil phase with respect to the microemulsion D-phase increases with the increase in XC12E6, which could explain the increase in instability. At 8 wt% surfactant concentration, a microemulsion D-phase is present when emulsification starts. The low droplet size and polydispersity and higher stability of these nano-emulsions have been attributed, in addition to the increase in the surface or interfacial activity, to the spontaneous emulsification produced in the microemulsion D-phase. [Copyright &y& Elsevier]

A thermodynamic model in order to study a single-component system where droplets or bubbles are inside smooth crevices is presented. Liquid–vapor interface curvature radius can change its sign as the droplet or bubble volume change. The results suggest that there is always dispersed phase inside smooth crevices of microscopic dimensions, even in the expected single-phase region. Thus, the occurrence of an anti-ripening phenomenon is predicted from a microscopic point of view; meanwhile the occurrence of a ripening phenomenon is energetically favorable at a macroscopic scale. The relevance of these results on the heterogeneous nucleation process is analyzed. [Copyright &y& Elsevier]

A thermodynamic model to obtain the radius of bubbles or droplets in a single-component system for a given temperature, total volume, and phase distribution is developed. The general formulation of the model includes bubbles or droplets in the form of spheres, truncated spheres on a flat solid surface or inside conical walls. In these three geometries the liquid–vapor curvature radius is positive but in the case of conical walls it can be also negative. States with different dispersed-phase distributions are compared using the total free energy of the system. When the curvature radius is positive, it has a minimum nonvanishing value and the occurrence of the Ostwald ripening is energetically favorable. On the other hand, when the curvature radius is negative, it is energetically more favorable to find the dispersed phase even in the expected single-phase region, and the occurrence of an anti-ripening phenomenon. The PV isotherms obtained from the model and the applicability of the results to the nucleation process are discussed. [Copyright &y& Elsevier]