Microscopic Structure Properties Research Articles

Diffusing wave spectroscopy for investigating emulsions: I. Instrumental aspects

Diffusing Wave Spectroscopy (DWS) is a technique used to characterize microscopic structure and rheological properties of turbid samples. This is achieved by analyzing the time evolution of coherence speckles of light that has been multiply scattered within the sample. One attractive feature of DWS is that it is non-invasive, and robust. For this reason, DWS has been selected as a diagnostic tool for an experiment module uploaded onboard the International Space Station (ISS) and devoted to the study of soft matter dynamics –related phenomena, among which, the basic mechanisms responsible for emulsions and foams aging. Moreover, the sensitivity of DWS to tiny motions and to fast time scales allows to extend measurements beyond the limits of usual rheological techniques, of micro-imaging and related techniques. However, the accuracy obtainable by DWS measurements is often limited.Here we revise different experimental approaches to the characterization of emulsions by DWS. We provide quantification of the accuracy of the correlation functions and we discuss how this affects the determination of the mechanical moduli, providing an objective criterion to establish the time window over which DWS results are reliable. These concepts are applied to discuss a laboratory prototype and to address the design of the DWS diagnostics suitable for the emulsion studies to be performed onboard the ISS.

Compression of porous aluminum: combined ultrasonic and microtomography measurements with lattice-Boltzmann permeability simulations

ABSTRACTCombined ultrasonic and X-ray microtomography measurements in situ at high pressure, in conjunction with lattice-Boltzmann simulations, enabled simultaneous investigation several physical parameters including: elastic wave velocities (vp and vs); apparent Poisson’s ratio; pore structure; porosity; and permeability. Experiments were conducted on a simple analog material, porous mold-quality aluminum, in a Paris-Edinburgh cell from 0.14 to 1.36 GPa. Porosity was observed to have a strong inverse dependence on pressure up to ∼0.9 GPa, while permeability has an anisotropic dependence on pressure. Elastic wave velocity (vp, vs) and apparent Poisson’s ratio all increase with pressure, with vp agreeing well with the Hashin–Shtrikman upper bound at lower pressures and higher porosities. These results demonstrate a new methodology combining experimental and analytical methods to provide cross-property links between microscopic structure and macroscopic elastic properties. Future investigations on more complex Earth materials may have important implications for our understanding of the composition of the deep Earth.

Study on Voxel Finite Element Analysis of Open-Cell Polyurethane Foam

Establishment of a design method for the macroscopic stress-strain relationship of open-cell foam has been investigated because of the foam’s complicated microstructures. In this study, a material design method for the mechanical behavior of open-cell polyurethane foam using voxel finite element analysis is proposed to consider the microscopic structure and matrix properties. A finite-strain hyperelastic model was applied to a matrix of polyurethane foam. The Mooney-Rivlin model was adopted for the potential energy function of the hyperelastic model. To determine the mechanical properties of the matrix, original, solid specimens of polyurethane were prepared. The material parameters of the matrix were identified based on the tensile loading test results of the solid specimens. Microstructures of the open-cell polyurethane foam were determined using a CT-scanning system. Finite element models constrained by the original microstructural configurations were applied to numerical simulations. Periodic finite element models based on the modified microstructural configurations, the relative density of which was the same as that of the original models, were applied to the simulation. Based on the numerical results, verification of the design performance of the simulation code for open-cell polyurethane foam was performed. The simulation results were reasonably consistent with compression loading test results up to the plateau region.

Density functional approach to the description of the structure of dimer nanoparticles at liquid-liquid interfaces.

An extension of the density functional approach from our recent work (Phys. Chem. Chem. Phys., 2019, 21, 3073-3082) is developed. It permits us to study the microscopic structure and thermodynamic properties of chain particles at the interface between two partially miscible liquids. Explicit calculations are carried out for a binary symmetric mixture of hard-sphere Yukawa fluids and dimers built of hard-sphere segments. The model is simple, but it captures the interplay between localization of dimers at the interface and their orientation and assembly into layers. The segment density profiles are combined with the site superposition approximation to interpret angle-dependent local densities of dimers. Emphasis is put on self-organization of dimers. The evolution of the interfacial structure of dimers and of fluid species with the amount of added dimers and of the supporting mixture density is explored. Preferential orientations of dimers in the outer and inner layers of the interface are discovered. Changes of the interface width upon changing the parameters of the system are discussed. Similarities and differences between the properties of the interface hosting diatomic and spherical particles are explained.

Theoretical evaluation of microscopic structural and macroscopic thermo-physical properties of molten AF-ThF4 systems (A+ = Li+, Na+ and K+)

The ion specific effects on the microscopic structural and macroscopic thermo-physical properties of molten AF-ThF4 systems (A+ = Li+, Na+ and K+) have been studied using molecular dynamics simulations and quantum chemical calculations. The [ThF8]4− and [ThF7]3− clusters dominate in LiF-ThF4 and KF-ThF4 systems respectively, and they turn out to be comparable in amount in NaF-ThF4. The Th4+-F− clusters become more stable and more isolated along with the size of the alkali species. The alkali ions tend to surround Th4+-F− clusters, and the association between A+ and Th4+-F− cluster becomes stronger when passing from LiF-ThF4 to NaF-ThF4, and then to KF-ThF4. The cage-out time and energy needed for the escape of F− from the first solvation shell of Th4+ show large growth with the size of the alkali species. The electronic structure of the [ThA8F8]4+ complexes indicates that the association between Th4+ and AF is mainly driven by the charge transfer contribution, and the charge transfer between Th centers and AF molecules increase with the size of alkali species. The calculated densities and shear viscosities follow the order of NaF-ThF4 > LiF-ThF4 > KF-ThF4. The computed thermal expansions and massic enthalpies of the three systems increase along with the size of the alkali species. The temperature has little effect on the relative strength of the microscopic Th4+ solvation shells and macroscopic thermos-physical properties for the AF-ThF4 systems.

Effects of pectin and xanthan gum on induced-flocculation phenomenon in an acidic model emulsion system

Mayonnaise is one of the most well-known dressings in the world and has properly found its impossibility to apply thermal processing, the high level of cholesterol and some consumers’ allergy to egg. In this study, the production of egg- free mayonnaise in model system has been investigated with the emphasis on flocculation enhancement in the system. Flocculation of emulsion droplets can have beneficial or harmful effect on food quality depending on product nature. In this study, influence of flocculation inducing on the stability, microscopic structure, zeta potential, droplet size and rheological properties of egg-free mayonnaise system were evaluated. Xanthan (XG), pectin (PE) and modified starch (MS) biopolymers mixed at different concentrations were used as flocculation inducer in emulsion system. XG-MS and PE-MS mixed polymers created depletion flocculation and reduced the speed of the oil droplets movement in the product and thus increased emulsion stability. In addition, an increase of all gum concentration caused an increment in the stability, consistency coefficient and heat stability values. Depending on the desirable level of xanthan gum and pectin gum for creating depletion flocculation, production of egg-free mayonnaise with properties closely matching those of commercial ones with egg is possible.

Uniform and decoupled shape effects on the maximally dense random packings of hard superellipsoids

The superellipsoid model is a rich geometric model and is convenient to study the particle shape effects on random packings. The particle shape significantly influences the macroscopic and microscopic structure properties of random packings. In this work, we find uniform and decoupled shape effects on the maximally dense random packings (MDRPs) of hard superellipsoids. Slightly changing the surface shape or elongating (compressing) the particles may influence the random packing density significantly. The influences of surface shape parameter p and aspect ratio w on the random packing densities are decoupled. For the aspect ratio effects, all the packing density curves show “M” type with various p. Meanwhile, the aspect ratio effects are applicable to all the symmetric particles with three equal main cross sections when w = 1.0. For the surface shape effects, the packing density curve is also in “M” type with various w. The maximum of the random packing density is obtained at p ≈ 0.7, 2.0 and w ≈ 0.7, 1.5. Moreover, we obtain the MDRPs of hard superellipsoids via the inverse Monte Carlo packing method with a wide range of the surface shape parameter. The normalized local cubatic order parameter and a new normalized local bond-orientational order parameter are used to evaluate the order degrees of orientations and bond-orientations in random packings, respectively. The local analyses of the MDRPs of superellipsoids are carried out via the Voronoi tessellation. Two linear relationships between the mean and standard deviation of the reduced Voronoi cell volumes are obtained. Our findings should lead to a better understanding of random packings and are helpful in guiding the granular material design.

High-performance recyclable cross-linked polyurethane with orthogonal dynamic bonds: The molecular design, microstructures, and macroscopic properties

Polyurethane materials (PUs) have been widely used in industry and daily life due to the versatile chemistry. However, despite the rapid advance in synthetic chemistry, it still remains a significant challenge for the facile fabrication of PUs with a single cross-linked network embedded with excellent mechanical properties and recyclability. Herein, in this study, we proposed a simple strategy to fabricate a high-performance recyclable cross-linked PU and revealed the relationship between microscopic structure and macroscopic properties. The UPy (2-ureido-4-[1H]-pyrimidione) motifs were incorporated into the backbone chains of PUs, where the quadruple hydrogen bonding interactions between UPy dimers can significantly enhance the mechanical strength and toughness. Furthermore, a single small molecular Diels-Alder adduct was utilized as the chemical crosslinker, rendering the final cross-linked PUs healable and recyclable. The thermal reversibility of the Diels-Alder reaction was well verified by DSC and solid-state NMR spectroscopy. Notably, it was found that the incorporation of UPy motifs could enhance the strain-induced crystallization (SIC), leading to a large stress at break. The structural and dynamic changes induced by SIC were quantitatively addressed by proton multiple-quantum NMR spectroscopy and SAXS experiments, where SIC further imposed restrictions on the mobility of surrounding polymer chains in the soft domain and led to the change of microphase separated nanostructures. Overall, a simple strategy is proposed here for the facile fabrication of high performance recyclable PUs, and the detailed investigation here on the structure-property relationship may further provide insights into developing high performance polymeric materials.

Effects of ion concentration and solvent composition on the properties of water-methanol solutions of NaCl. NPT molecular dynamics computer simulation results

Isothermal-isobaric molecular dynamics simulations are used to examine the microscopic structure and other properties of a model solution consisting of NaCl salt dissolved in water-methanol mixture. The SPC/E water model and the united atom model for methanol are combined with the force field for ions by Dang [J. Amer. Chem. Soc., 1995, 117, 6954] to describe the entire system. Our principal focus is to study the effects of two variables, namely, the solvent composition and ion concentrations on the solution's density, on the structural properties, self-diffusion coefficients of the species and the dielectric constant. Moreover, we performed a detailed analysis of the first coordination numbers of the species. Trends of the behaviour of the average number of hydrogen bonds between solvent molecules are evaluated.

A molecular simulation approach to the computation of mutual solubility of water and organic liquids: Application to fatty acids

The phase equilibria knowledge of fatty acid and water mixtures play a crucial role in the design and operation of processes such as bio-diesel synthesis, sea water desalination and novel solvent design. Experimental data on the mutual solubility of fatty acid and water are scattered and limited. Atomistic molecular simulation approach can be a viable substitute for these predictions. In this work, a molecular simulation method is proposed that does not require molecular transfer between dense phases as in the Gibbs ensemble method and is based on determining phase equilibria by computing and equating the fugacity of water in the two phases. Assuming that the fugacity of water-rich phase is identical to that of pure water, an expression for the solubility of fatty acid in water is derived. In the current formalism, fugacity is determined by computing the residual chemical potential of water and fatty acids via thermodynamic integration. Mutual solubility between water and three different fatty acids are calculated over a range of temperatures and shown to yield good agreement with experimental data. Microscopic structural properties elucidating the role of the hydrogen bonding interactions between water and fatty acid and the aggregation of water molecules which gives rise to the observed macroscopic properties are also studied.

Real-Time Observation of Order-Disorder Transformation of Organic Cations Induced Phase Transition and Anomalous Photoluminescence in Hybrid Perovskites.

A fundamental understanding of the interplay between the microscopic structure and macroscopic optoelectronic properties of organic-inorganic hybrid perovskite materials is essential to design new materials and improve device performance. However, how exactly the organic cations affect the structural phase transition and optoelectronic properties of the materials is not well understood. Here, real-time, in situ temperature-dependent neutron/X-ray diffraction and photoluminescence (PL) measurements reveal a transformation of the organic cation CH3 NH3+ from order to disorder with increasing temperature in CH3 NH3 PbBr3 perovskites. The molecular-level order-to-disorder transformation of CH3 NH3+ not only leads to an anomalous increase in PL intensity, but also results in a multidomain to single-domain structural transition. This discovery establishes the important role that organic cation ordering has in dictating structural order and anomalous optoelectronic phenomenon in hybrid perovskites.

Study of the Electromagnetic Properties of Nano (MxZn1−x)Fe2O4 (M=Cu, Ni) as a Function of the Sintering Temperature

In this study, the chemical co-precipitation method was used to prepare a nanoscale ferrite powder with Cu-Zn and Ni-Zn compositions. Ferrite, in different Cu-Zn stoichiometric ratios, showed optimal composition of saturated magnetization for Cu0.7Zn0.3Fe2O4; under an air environment and calcined at 900 °C, the saturated magnetization was 60.19 M(emu/g). The average particle diameter was 10 nm for the non-calcined sample, while when the sintering temperature was 900 °C, the particle diameter was about 150 nm. In addition, in different Ni-Zn stoichiometric ratios, the optimal composition of the saturated magnetization was Ni0.5Zn0.5Fe2O4; under an air environment and calcination at 900 °C, the saturated magnetization was 91.40 M(emu/g). The average particle diameter for the non-calcined sample was about 10 nm, but when the sintering temperature was 1200 °C, the particle diameter was 201.06 nm. The prepared ferrite nano-powder was characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), and vibrating sample magnetometer(VSM) to reveal its microscopic structure and related electromagnetic properties. Ferrite powders of either Cu-Zn or Ni-Zn composition can be used as catalysts for chemical reactions or iron core materials.

Understanding the Relationship Between Structure and Thermophysical Properties of CaO-SiO2-MgO-Al2O3 Molten Slags

In the present work, the relationship between the microscopic structure and macroscopic thermophysical properties in a basic CaO-SiO2-MgO-Al2O3 quaternary system was identified using Fourier transformation infrared, Raman and 27Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The Raman spectra quantitatively proved that with increasing Al2O3 content, the concentrations of the symmetric units of Q0(Si) and Q2(Si) decreased, while those of the asymmetric units of Q1(Si) and Q3(Si) increased; consequently, the degree of polymerization of the networks increased, which resulted in an increase in slag viscosity. The 27Al MAS-NMR spectra demonstrated that three structural units of Al atoms, namely, AlO4, AlO5, and AlO6, mainly existed in the networks. With increasing Al2O3 content, the concentration of AlO4 slightly decreased, while those of AlO5 and AlO6 increased; overall, Al2O3 acted as a network former in the present system. The increasing Al2O3 content led to additional AlO6 and Si-NBO-Ca-NBO-Al frameworks, which replaced Si-NBO-Ca-NBO-Si in the networks (NBO: non-bridging oxygen) and induced a change in the primarily precipitated crystalline phase from Ca2MgSi2O7 and Ca2Al2SiO7 to MgAlO4.

Exploring Electronic Structure and Order in Polymers via Single-Particle Microresonator Spectroscopy.

PSS, a transparent electrically conductive polymer, finds widespread use in electronic devices. While empirical efforts have increased conductivity, a detailed understanding of the coupled electronic and morphological landscapes in PEDOT:PSS has lagged due to substantial structural heterogeneity on multiple length-scales. We use an optical microresonator-based absorption spectrometer to perform single-particle measurements, providing a bottom-up examination of electronic structure and morphology ranging from single PEDOT:PSS polymers to nascent films. Using single-particle spectroscopy with complementary theoretical calculations and ultrafast spectroscopy, we demonstrate that PEDOT:PSS displays bulk-like optical response even in single polymers. We find highly ordered PEDOT assemblies with long-range ordering mediated by the insulating PSS matrix and reveal a preferential surface orientation of PEDOT nanocrystallites absent in bulk films with implications for interfacial electronic communication. Our single-particle perspective provides a unique window into the microscopic structure and electronic properties of PEDOT:PSS.

Quality of giant freshwater prawn (Macrobrachium rosenbergii) during the storage at −18°C as affected by different methods of freezing

ABSTRACTThis study investigated the effects of liquid nitrogen quick-freezing, −35°C air-blast freezing, and −18°C refrigerator direct-freezing on quality retention of frozen giant freshwater prawns using various indicators: microscopic structure, physicochemical, texture, and color properties. The results showed that the shelf lives of prawns treated with liquid nitrogen quick-freezing, −35°C air-blast freezing, and −18°C refrigerator direct-freezing were about 20, 12, and 8 weeks, respectively, in terms of total volatile basic nitrogen content and K-value. Meanwhile, liquid nitrogen quick-freezing could effectively improve texture property of frozen giant freshwater prawn. These findings confirm that liquid nitrogen quick-freezing is a promising method to extend the shelf life of frozen prawns.

On the composition dependence of the microscopic structure, thermodynamic, dynamic and dielectric properties of water-dimethyl formamide model mixtures. Molecular dynamics simulation results

Isothermal-isobaric molecular dynamics simulations have been performed to examine an ample set of properties of the model water-N,N-dimethylformamide (DMF) mixture as a function of composition. The SPC-E and TIP4P-Ew water models together with two united atom models for DMF [Chalaris M., Samios J., J. Chem. Phys., 2000, 112, 8581; Cordeiro J., Int. J. Quantum Chem., 1997, 65, 709] were used. Our principal analyses concern the behaviour of structural properties in terms of radial distribution functions, and the number of hydrogen bonds between molecules of different species as well as thermodynamic properties. Namely, we explore the density, excess mixing molar volume and enthalpy, the heat capacity and excess mixing heat capacity. Finally, the self-diffusion coefficients of species and the dielectric constant of the system are discussed. In addition, surface tension of water-DMF mixtures has been calculated and analyzed.

Recycling of electric arc furnace dust into glass-ceramic

Electric arc furnace dust was vitrified by SiO2, NaCO3 and CaO. The glass-ceramic produced from steel making dust was investigated in three aspects; stability of compounds, microscopic structure and mechanical properties. Leaching tests on electric arc furnace dust showed that the amount of Zn and Cd exceeded the environmental regulatory levels and the tests on glass ceramics exhibited that these products were chemically so stable. X-ray diffraction studies on them indicated that dominant phase in most samples was wollastonite. Scanning electron microscopy images of glass-ceramics corroborated that general shapes of crystalline phases were dendritic. By applying heat treatment, hardness of the product was significantly reduced and their mechanical strength was extremely increased. It showed that produced glasses had an average of 800 Vickers microhardness (HV) and after transformation to glass-ceramic by applying heat treatment, it was reduced to 500 HV.

Growing pressure sensors from bacteria

Synthetic Biology Mimicking the way that biological organisms combine organic and inorganic materials with microscopic structural properties, Cao et al. show that pattern-forming bacteria can be engineered to support construction of miniature pressure sensors. Bacteria modified with a genetic regulatory circuit produced patterns of excreted inorganic matrix materials. These materials interacted with metal particles to make patterns that depended on the properties of a membrane on which the bacteria were grown. Gold nanoparticles could thus be layered to make domelike structures that, when opposed to one another, formed pressure sensors. They could even be combined into circuits to allow noise filtering or signal amplification. Nat. Biotechnol. 10.1038/nbt.3978 (2017).

On understanding the chemical origin of band gaps.

Conceptual DFT and quantum chemical topology provide two different approaches based on the electron density to grasp chemical concepts. We present a model merging both approaches, in order to obtain physical properties from chemically meaningful fragments (bonds, lone pairs) in the solid. One way to do so is to use an energetic model that includes chemical quantities explicitly, so that the properties provided by conceptual DFT are directly related to the inherent organization of electrons within the regions provided by topological analysis. An example of such energy model is the bond charge model (BCM) by Parr and collaborators. Bonds within an ELF-BCM coupled approach present very stable chemical features, with a bond length of ca. 1 Å and 2[Formula: see text]. Whereas the 2[Formula: see text] corroborate classical views of chemical bonding, the fact that bonds always expand along 1 Å introduces the concept of geometrical transferability and enables estimating crystalline cell parameters. Moreover, combining these results with conceptual DFT enables deriving a model for the band gap where the chemical hardness of a solid is given by the bond properties, charge, length, and a Madelung factor, where the latter plays the major role. In short, the fundamental gap of zinc-blende solids can be understood as given by a 2[Formula: see text] bond particle asymmetrically located on a 1 Å length box and electrostatically interacting with other bonds and with a core matrix. This description is able to provide semi-quantitative insight into the band gap of zinc-blende semiconductors and insulators on equal footing, as well as a relationship between band gap and compressibility. In other words, merging these different approaches to bonding enables to connect measurable macroscopic behavior with microscopic electronic structure properties and to obtain microscopic insight into the chemical origin of band gaps, whose prediction is still nowadays a difficult task. Graphical Abstract Conceptual DFT couples to quatum chemcial topology to explain the band gap of zinc-blende solids.

Monte Carlo Simulation of Supercritical Carbon Dioxide Adsorption in Carbon Slit Pores

CO2 adsorption on carbon is a CO2 geo-storage mechanism, and a potential technique for CO2 removal from flue gas or pressurized fuel gas streams produced from hydrocarbon reservoirs (which frequently contain CO2, sometimes at very high concentrations). However, the detailed mechanism of precisely how CO2 is adsorbed on the carbon surface is only poorly understood. We thus simulated supercritical CO2 adsorption in carbon slit pores at the molecular level by Grand Canonical Monte Carlo calculations. Adsorption isotherms and microscopic structural properties were examined for different pore widths, pressures, and temperatures. Our results demonstrate that the excess adsorption density isotherm of supercritical CO2 in a carbon slit pore has a maximum value, and it is not a monotonically increasing function of pressure. However, supercritical CO2 cannot be effectively adsorbed at very high temperatures (≥850 K) as the excess adsorption density is extremely small. Mechanistically, multiadsorption layers were ob...