Multimodal Size Distribution Research Articles

Study on γ′ precipitation behavior in a nickel-based PM superalloy during interrupted continuous cooling

The multi-stage nucleation phenomenon and the subsequent evolution of γ′ precipitation during cooling process of super-solvus heat treatment for a nickel-based powder metallurgy (PM) superalloy are studied by means of Gleeble thermal simulation, field emission scanning electron microscope (FE-SEM), energy dispersive spectrometer (EDS) and three-dimensional atom probe tomography (3D-APT). The results show that the secondary γ′ phases precipitated preferentially at a relatively high temperature during the cooling process. As the temperature decreased with a slow rate, the secondary γ′ phases grew up and changed shape gradually and parts of the tertiary γ′ phases precipitated, resulting in a multimodal size distribution of γ′ phases. While, when the cooling rate is relatively fast, the γ′ phase exhibits a monomodal size distribution. The results of EDS and 3D-APT show that there is a depleted zone of Al and Ti elements near the interface between secondary γ′ and the γ matrix, while Al and Ti elements is enriched in γ matrix away from the secondary γ′ precipitates. The distribution of alloying elements in the γ′ phases and γ matrix change with the decrease of the temperature, and the phase interface is a favorable place for the dynamic exchange of alloying elements.

Development of oil-in-water emulsions based on rice bran oil and soybean meal as the basis of food products able to be included in ketogenic diets

The aim of this work was to develop rice bran oil-in-water emulsions stabilized with proteins and polysaccharides from soybean meal as the basis of food products able to be included in ketogenic diet. The effect of the formulation (ketogenic ratios and oil mass fractions) and the high-pressure homogenization conditions (number of homogenization cycles) on the properties of the resulting O/W emulsions was evaluated. All freshly prepared emulsions showed multimodal particle size distributions and shear-thinning behaviour. At a fixed ketogenic ratio, all emulsions had the same oil to emulsifiers + stabilizers proportion, but increasing their oil mass fraction resulted in systems composed by smaller particles with greater interfacial area, and apparent viscosity. The same effect was observed by increasing the number of homogenization cycles. Meanwhile, increasing the ketogenic ratio (at a fixed oil mass fraction) diminished its apparent viscosity. Most of the studied emulsions were stable for seven days of quiescent refrigerated storage, although some changes in its particle size distributions were observed. Only, the stored emulsions with the highest ketogenic ratio and the lowest oil mass fraction presented gravitational separation but no phase separation. Emulsions prepared after five homogenization cycles presented greater stability to the coalescence than those prepared in one cycle.

Elevated temperature microstructure evolution of a medium-entropy CrCoNi superalloy containing Al,Ti

A new medium-entropy superalloy was produced based on the compositions of equiatomic CrCoNi and Ni-base superalloy Inconel 740H. Initial alloy design was performed using Thermo-Calc. The aging response and microstructural stability were assessed following heat treatment at temperatures between 600 and 900 °C and durations up to 100 h. Aging from a fully recrystallized state resulted in negligible grain growth and produced γ’ and σ phases. The same phases were present after aging from a cold-rolled state, but partially recrystallized microstructures resulted in multi-modal size distributions and heterogeneous spatial arrangements. Room temperature hardness measurements were used to correlate aging conditions with quantitative precipitate measurements and mechanical properties.

Support-free 3D hierarchical nanoporous Cu@Cu2O for fast tandem ammonia borane dehydrogenation and nitroarenes hydrogenation under mild conditions

A support-free hierarchical nanoporous (NP) Cu@Cu2O composite is easily fabricated by dealloying Cu5Al95 alloy in dilute NaOH solution. This bulk material has a support-free spongy structure composed of three-dimensional interconnected ligaments and open pore channels with multimodal pore size distributions. The NP-Cu@Cu2O catalyst exhibits high activity, good chemoselectivity, and excellent recyclability toward one-pot transfer hydrogenation reactions of diverse nitroarenes to anilines. NP-Cu@Cu2O can effectively activate ammonia borane under mild conditions and complete the transfer hydrogenation reactions with high yields within a short time period of 5 min Cu2O formed at the nanoporous surface is proposed to be the actual active site causing this advanced performance. The main reaction intermediates were successfully separated and characterized, and a plausible condensation mechanism has been proposed for nitro reduction.

Highly Dispersed Ag2S Nanoparticles: In Situ Synthesis, Size Control, and Modification to Mechanical and Tribological Properties towards Nanocomposite Coatings

A facile in situ synthesis approach and a size control strategy were established to obtain Ag2S nanoparticles in polyimide (PI) composite coatings. Such Ag2S nanoparticles in the composite coatings were characterized, and the effects of the as-obtained Ag2S nanoparticles of different sizes on the mechanical and tribological properties of the nanocomposite coatings were investigated. Results indicate that the in situ synthesized Ag2S nanoparticles exhibited good dispersibility and bimodal and multimodal size distribution in the nanocomposite coatings. The size of the Ag2S nanoparticles can be effectively controlled by adjusting the substituent alkyl chain length of single-source precursor, and these Ag2S nanoparticles exhibited superior improvement to mechanical and tribological properties of the nanocomposite coatings. More importantly, the Ag2S nanoparticles with the proper grain size and bimodal size distribution provided the optimal mechanical and tribological properties for the nanocomposite coatings, and the excellent tribological properties were attributed to their outstanding mechanical properties and strong ability to form a homogenous and stable protective tribofilm.

A novel microfluidic-based approach to formulate size-tuneable large unilamellar cationic liposomes: Formulation, cellular uptake and biodistribution investigations

Extensive research has been undertaken to investigate the effect of liposome size in vitro and in vivo. However, it is often difficult to generate liposomes in different size ranges that offer similar low polydispersity and lamellarity. Conventional methods used in the preparation of liposomes, such as lipid film hydration or reverse phase evaporation, generally give rise to liposomal suspensions displaying broad, multimodal size distribution combined with uncontrolled degree of lamellarity. In contrast, microfluidics allows highly homogeneous liposome dispersions to be produced and adjustment of microfluidic operating parameters (flow rate ratio (FRR) and total flow rate (TFR)) can offer size-tuning of liposomes (up to 300 nm, depending on the formulation). Herein, we demonstrate a novel method which allows the production of highly monodisperse, cationic liposomes over a wide particle size range (up to 750 nm in size). This is achieved through controlling the concentration of the aqueous buffer during production. Using this method, liposomes composed of 1,2-dioleoyl-sn-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or dimethyldioctadecylammonium (DDA) – DOPE:DOTAP and DOPE:DDA liposomes – of up to 750 nm were prepared and investigated. These investigations demonstrate that the in vitro cellular uptake of small (40 nm) and large (>500 nm) liposomes in bone marrow-derived macrophages (BMDM) is similar terms of percentage of liposome+ cells and mean fluorescence intensity (MFI). However, significant differences are observed in BMDM uptake when represented in terms of number of liposomes, liposome surface area or liposome internal volume. In vivo biodistribution studies in mice show that by creating small (<50 nm) liposomes we can modify the clearance rates of these liposomes from the injection site and increase accumulation to the draining lymphatics.

RSM-CCD design of malachite green adsorption onto activated carbon with multimodal pore size distribution prepared from Amygdalus scoparia: Kinetic and isotherm studies

In the present work, the activated carbon (AC) adsorbent with multimodal pore size distribution prepared from Amygdalus scoparia as low-cost and locally available source was applied for efficient adsorption of malachite green (MG) from aqueous media. The surface properties of the adsorbent were identified by various techniques such as FT-IR, BET and SEM analyses. The dependency of MG adsorption efficiency on the variables such as pH, initial dye concentration, adsorbent dosage and contact time was studied by central composite design (CCD) coupled with response surface methodology (RSM). A good agreement between experimental and predicted data was achieved that proved the efficiency of this model for prediction of real optimum point. Among the well-known previously isotherm models, the experimental equilibrium data were efficiently fitted by the Freundlich model, while maximum adsorption capacity of MG at 0.01 g of the adsorbent was 144.30 mg g−1. The kinetic data were efficiently interpreted by the combination of pseudo-second-order and intra-particle diffusion models. The advantage of the green adsorbent was that a small amount of the adsorbent (0.027 g) is applicable for high adsorption percentage of MG (>99.5%) within a reasonable time (75 min).

Photocurable Poly(ethylene glycol) Diacrylate Resins with Variable Silica Nanoparticle Loading

Photocurable nanocomposites have tremendous potential in tissue engineering, advanced manufacturing, and structural, multifunctional materials. This project investigates the effect of silica (SiO2) nanoparticle loading content on the thermal, mechanical, physical, and morphological characteristics of the nanocomposite. An increased concentration of SiO2 nanoparticles causes a decrease in the gel fraction of the nanocomposite, which, at low nanoparticle loading, degrades the thermal and mechanical properties. However, further addition (>3.8 wt %) causes an increase in the glass-transition temperature, Young’s modulus, and ultimate compressive strength. The addition of the nanoparticles had no significant effect on the hydrophilicity according to water uptake experiments. Small-angle X-ray scattering experiments, in conjunction with scanning electron microscopy and transmission electron microscopy, indicated a multimodal particle size distribution and the presence of large-scale aggregates.

Characterization of colloidal nanoparticles in mixtures with polydisperse and multimodal size distributions using a particle tracking analysis and electrospray-scanning mobility particle sizer

Characterization of polydisperse liquid-borne particles was investigated using a particle tracking analysis (PTA) and electrospray-scanning mobility particle sizer (ES-SMPS). The results showed PTA measurements based on light scattering accurately predicted mode sizes of monodisperse colloidal particles, but the geometric standard deviation of 40 nm polystyrene latex (PSL) particles was underestimated because of a screening effect that makes the smaller particles less visible. ES-SMPS could precisely predict the size distributions with sizes and standard deviations of monodisperse particles when compared to scanning electron microscopy data. From the results for the mixture of 40 nm Au and PSL and mixtures of 40 nm Au and 100, 150 and 240 nm PSL, it was shown that ES-SMPS is a very promising method to characterize colloidal particles with a wide or multimodal size distributions. Therefore, the results of this study provide detailed insights into various applications that require accurate characterizations of polydisperse colloidal particles.

Origin and prevention of broad particle size distributions in carbon-supported palladium catalysts prepared by liquid-phase reduction

Carbon-supported palladium (Pd/C) catalysts often display broad or multimodal Pd particle size distributions detrimental for their performance. Therefore, the formation of large particles during preparation should be better understood and avoided. We prepared catalysts with up to 10 wt% Pd supported on oxygen-functionalized carbon nanotubes and activated carbon via liquid-phase reduction. It was inferred that small Pd particles (∼1 nm) were formed from Pd ions adsorbed on the carbon. At higher loadings, up to 65% of the Pd ended up in larger particles (>10 nm) probably formed from Pd ions in solution, lowering the Pd-normalized activity in the hydrogenation of cinnamaldehyde 4-fold compared to samples with small particles only. Three key factors were identified for preparing Pd/C catalysts with exclusively ∼1 nm Pd particles: a support with a high density of acid sites and high specific surface area, and a metal loading at molar ratio Pd/acid sites <0.5.

Study of Microporosity of Polymer Glasses Using Techniques of Positron Annihilation and Low-Temperature Sorption of Carbon Dioxide

The nature of micropore size distribution in a number of amorphous polymer glasses (membrane materials and sorbents) has been discussed on the basis of data on positron annihilation lifetime spectroscopy (PALS) and low-temperature CO2 gas sorption (LTGS). The LTGS (CO2) technique in combination with mathematical processing by the density functional theory gives a multimodal size distribution of micropores in the range of effective diameters of 0.5–1.5 nm for PIM-1 type polymers of intrinsic microporosity. The positron annihilation data (time distribution of annihilation emission events) are also satisfactorily processed under the assumption of multimodality. The results have been discussed in terms of the “local rigidity” of the materials under consideration.

Full-scale pore structure and its controlling factors of the Wufeng-Longmaxi shale, southern Sichuan Basin, China: Implications for pore evolution of highly overmature marine shale

Shale gas primarily exists in nanopores in shale as different occurrence phases. Studies on pore structure characterization and its controlling factors are the key to understand shale gas occurrence and gas accumulation mechanism. Mercury intrusion capillary pressure (MICP), low-pressure N2 and CO2 adsorption were applied to quantify pore structure of all sizes for Wufeng-Longmaxi shale from southern Sichuan Basin, China. These shales are currently highly overmature, and their total organic carbon (TOC) contents range from 0.04% to 5.19%. Quartz content is positively correlated with TOC content in the clay-poor shales, whereas it exhibits no correlation with TOC in the clay-rich shales. Different relationships are likely due to difference in quartz origins, since the clay-poor shales contain more biogenic quartz than the clay-rich shales. Furthermore, multimodal pore size distributions were observed. Total pore volume, ranging from 1.41 to 3.03 cm3/100 g, is mainly provided by pores less than 10 nm in diameter, whereas most of the specific surface area, ranging from 19.55 to 36.64 m2/g, is provided by pores less than 2 nm in diameter. Organic matter contributes mostly to micro- and mesopore development. Clay minerals, mainly illite, also make a contribution to pore structure, especially in the organic-lean shales. The porosity development of micro- and mesopores is also controlled by thermal evolution of organic matter. Micro- and mesopores were developed at the immature to early mature stages due to pore rearrangement, expulsion of liquid hydrocarbon, and dissolution of unstable minerals. The following decrease during the late mature stage was mainly caused by oil and bitumen infill. Both micro- and mesopores were reopened at the postmature stage, which was driven by the secondary cracking of residual oil and bitumen. The final significant decline of micro- and mesopore volumes at the overmature stage was caused by persistent compaction and OM carbonization.

Avaliação da saturação efetiva ar-LNAPL em solos lateriticos com distribuição multimodal de tamanho de poros

Este trabalho visa avaliar a adequabilidade do modelo desenvolvido pela API (2007) na obtenção indireta de curvas de saturação efetiva para sistemas ar-LNAPL em solos de características lateríticas e com distribuição multimodal de tamanho de poros, tal como os encontrados em diferentes territórios do Brasil. Para esse objetivo, amostras de um solo típico do estado de São Paulo foram submetidas a testes para determinação das saturações efetivas de sistemas ar-água e ar-LNAPL a partir do hanging column test, bem como do papel filtro. Os resultados mostraram curvas de retenção típicas de solo com distribuição de tamanho de poros multimodal, sejam para sistemas ar-água ou ar-LNAPL. Adicionalmente, a obtenção de curvas de saturação efetiva ar-LNAPL a partir de sistemas ar-água por meio de equações foram coerentes, desde que sejam utilizados modelos de pressão capilar trimodais. Finalmente, tal como apontado por Alfaro Soto e Chang (2015), deve-se ressaltar que a modificação de modelos de previsão de volumes específicos de contaminantes para remediação em solos tropicais é necessária, devido às suas características de retenção diferenciadas.

Simulating multimodal floc size distributions of suspended cohesive sediments with lognormal subordinates: Comparison with mixing jar and settling column experiments

The Floc Size Distributions (FSDs) of suspended fine-grained sediment flocs play a prime role to estimate their own fate and the transport of contaminates attached to the flocs. However, developing an efficient flocculation model that is capable of simulating continuous and multimodal FSDs is still a challenge. Recently, the population balance equation solved by the Quadrature-Based Method of Moments (QBMM) with lognormal kernel density functions has been developed to investigate the aggregation and breakage processes. It coincides with some recent observations which describe a measured FSD in coastal waters with a set of constituted lognormal distributions. The newly developed lognormal QBMM was tested with several ideal flocculation kinetic kernels, none of which, however, was used for interpreting cohesive sediment dynamics. Therefore, it raised our interest to evaluate the model performance for fine-grained sediments in shear turbulence dominated environments. In this study, additional validations against two kaolinite laboratory experiments were tested in the framework of the extended QBMM. It is hypothesized that these subordinate lognormal distributions share the same value of standard deviation. Different from the previous methods, the common standard deviation is determined empirically to reduce the number of tracers and better represent the FSDs. With sediment flocculation kinetics, the predicted FSDs reasonably reproduce the FSDs observed in both the mixing chamber and the settling column experiments. Despite the lacking of explicit descriptions of microbial effects at the current stage, this model has the potential to be implemented into large-scale particle transport models and deserves a more in-depth study in the future.

The Impacts of Matrix Compositions on Nanopore Structure and Fractal Characteristics of Lacustrine Shales from the Changling Fault Depression, Songliao Basin, China

The Lower Cretaceous Shahezi shales are the targets for lacustrine shale gas exploration in Changling Fault Depression (CFD), Southern Songliao Basin. In this study, the Shahezi shales were investigated to further understand the impacts of rock compositions, including organic matters and minerals on pore structure and fractal characteristics. An integrated experiment procedure, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), low pressure nitrogen physisorption (LPNP), and mercury intrusion capillary pressure (MICP), was conducted. Seven lithofacies can be identified according to on a mineralogy-based classification scheme for shales. Inorganic mineral hosted pores are the most abundant pore type, while relatively few organic matter (OM) pores are observed in FE-SEM images of the Shahezi shales. Multimodal pore size distribution characteristics were shown in pore width ranges of 0.5–0.9 nm, 3–6 nm, and 10–40 nm. The primary controlling factors for pore structure in Shahezi shales are clay minerals rather than OM. Organic-medium mixed shale (OMMS) has the highest total pore volumes (0.0353 mL/g), followed by organic-rich mixed shale (ORMS) (0.02369 mL/g), while the organic-poor shale (OPS) has the lowest pore volumes of 0.0122 mL/g. Fractal dimensions D1 and D2 (at relative pressures of 0–0.5 and 0.5–1 of LPNP isotherms) were obtained using the Frenkel–Halsey–Hill (FHH) method, with D1 ranging from 2.0336 to 2.5957, and D2 between 2.5779 and 2.8821. Fractal dimensions are associated with specific lithofacies, because each lithofacies has a distinctive composition. Organic-medium argillaceous shale (OMAS), rich in clay, have comparatively high fractal dimension D1. In addition, organic-medium argillaceous shale (ORAS), rich in TOC, have comparatively high fractal dimension D2. OPS shale contains more siliceous and less TOC, with the lowest D1 and D2. Factor analysis indicates that clay contents is the most significant factor controlling the fractal dimensions of the lacustrine Shahezi shale.

Innovative released-active drug for the treatment of neurological diseases: Results of preclinical studies

A numerical inversion method known from the analysis of light scattering by colloidal dispersions is now applied to magnetization curves of ferrofluids. The distribution of magnetic particle sizes or dipole moments is determined without assuming that the distribution is unimodal or of a particular shape. The inversion method enforces positive number densities via a non-negative least squares procedure. It is tested successfully on experimental and simulated data for ferrofluid samples with known multimodal size distributions. The created computer program MINORIM is made available on the web.

The liquid phase catalytic hydrogenation of furfural to furfuryl alcohol

We report the hydrogenation of furfural (FF) to furfuryl alcohol (FA) with Pd-containing catalysts stabilized by hypercrosslinked polystyrene (HPS). FF is one of the major ingredients of biooil produced by biomass pyrolysis, while FA is a source of value-added chemicals, thus, creating an effective path from biomass to important compounds. Different palladium precursors (PdCl2(CH3CN)2, Pd(CH3COO)2) were used for the catalysts synthesis. The nature of the precursor influences the size of palladium nanoparticles. The TEM and SAXS data showed that when using PdCl2(CH3CN)2, a monomodal distribution of particles size with mean diameter 5.4 ± 1.2 nm was observed, whereas for Pd(CH3COO)2, multimodal particle size distribution with the mean particle sizes up to 13.8 ± 5.4 nm was observed. The comparison of the catalytic activities of Pd-containing catalysts indicated that the more disperse sample of palladium showed higher values of FF conversion and selectivity to FA because of small particles.

Rapid and low-cost laser synthesis of hierarchically porous graphene materials as high-performance electrodes for supercapacitors

Development of 3D hierarchically porous graphene (HPG) with supercapacitor performances at low cost has remained a challenge in electrochemical devices. Recently, laser engraving technology has been proposed as a promising and very useful method to inscribe self-designed electrode array directly onto polymeric substrates by instantaneously converting the starting material into few-layer graphene. Here we show HPG fabrication on commercial bakelite resulting in porous graphene embedded in polymer surface using the high repetition nanosecond fiber laser engraving under nitrogen atmosphere. The results showed that the as-prepared HPG presents a combination of interconnected macro-, meso- and micropores with a multi-modal pore size distribution. The morphologies, microstructures and their properties of HPG films can be governed by the laser processing parameters. Moreover, the HPG-based supercapacitors show outstanding electrochemical performance with specific capacitance superior to other supercapacitors reported previously. The simple, rapid and low-cost approach proposed in this work has great potential in large-scale applications of electronic and energy storage devices.

Evolution of the Ligand Shell Around Small ZnO Nanoparticles During the Exchange of Acetate by Catechol: A Small Angle Scattering Study

AbstractThe core‐shell structure of colloids surrounded by ligands is of great importance for their later application as it can significantly alter the chemical and physical properties of the nanoparticles (NPs). A combination of small angle X‐ray and neutron scattering (SAXS/SANS) in the native solution with additional ex situ measurements (titration‐UV) was applied to study the NP/ligand interface of ZnO NPs after functionalization with catechol derivatives. Based on SAXS data, it was found that within the multimodal particle size distribution the fraction of agglomerates is shifted to smaller sizes and nearly disappeared upon the binding of ethyl 3,4‐dihydroxybenzoate (CAT) molecules. This is ascribed to improved stabilization at the primary particle level by CAT molecules. By combining the neutron scattering contrast with the input of bound CAT molecules from a previously developed titration‐UV method, the heterogeneous composition of the ligand shell became accessible for the first time.

Soft‐templating Synthesis of Mesoporous Metal–Organic Frameworks with Enhanced Toluene Adsorption Capacity

AbstractMetal–organic frameworks (MOFs) commonly have uniform micropores (pore dimension &lt; 2 nm), which may restrict their practical applications involving large molecules. Although quite a little approaches have been developed to prepare mesoporous metal–organic frameworks (meso‐MOFs), challenge remains in the preparation of meso‐MOFs with controllable/tunable porosity. Here we developed a reliable method to rationally design and synthesize meso‐Cu‐BTC materials through utilizing a novel amphiphilic surfactant as the template. X‐ray diffraction, nitrogen adsorption isotherms and pore size distributions were applied to characterize the attained meso‐MOF products, the characterization analyses indicated that the as‐synthesized products possess multimodal pore size distribution with micropores and well‐ordered mesopores. Moreover, the porosity properties of the meso‐Cu‐BTC could be systematically controlled by varying the ratio of H2O/EtOH, the amount and type of the template. Owing to the well‐order mesoporous structure, the meso‐Cu‐BTC exhibited high uptake capacity of 152 cm3⋅g−1, about 20% higher as compared with conventional counterpart (128 cm3⋅g−1) for the capture of toluene. This work provides a new strategy to prepare meso‐MOFs with tunable porosity that would fulfill a wide range of applications involving large molecules.