Solid-liquid Two-phase System Research Articles

Microscopic insights into the aggregation dynamics behavior and tribological properties of graphene

The stable dispersion mechanism of graphene nanoparticles in solid-liquid two-phase lubrication systems still lacks in-depth insights into the dynamic aggregation process at the microscale. Herein, the effects of size difference and defect degree on the agglomeration dynamics behavior and tribological properties of graphene nanosheets were revealed by aggregation, pull-out, and friction molecular dynamics simulations. The results showed that for suspended graphene smaller than 100 nm, the increase in size and defect degree effectively improved the dispersion stability of nanosheets in base oil. Attributed to the rise in size improved solid-liquid chemical affinity and promoted out-of-plane deformation of nanosheets to enhance the steric hindrance effect. The increase in defect degree induced spontaneous wrinkling of nanosheets, leading to enhanced interlayer sliding resistance and thus inhibiting agglomeration behavior. Meanwhile, the rise in nanosheet size and degree of defects sufficiently bear the normal load, effectively avoiding the direct contact of asperities and thus improving the wear and temperature rise at the friction interface. However, friction-induced defective graphene curled to form a “carbon nanotube-like” structure, which reduced the oil film strength and led to deterioration of lubrication performance. The research results will provide certain microscale insights into the dispersion and friction of graphene in base oil.

Solidification process of ABO3-type perovskites: Kinetic two-phase growth method with optimized potential

The functional properties of ABO3-type perovskite materials have garnered extensive attention, yet their solidification properties have remained challenging to investigate due to high-temperature environments and characterization limitations. In this study, molecular dynamics simulations are employed to comprehensively explore the melting, quenching, and crystal growth processes of SrTiO3 (STO) structural evolution. Through iterative fitting and optimization of ion effective charge, a set of potential functions capable of accurately simulating the high-temperature melting of STO are derived. The melting point obtained for STO (2403 K) using the two-phase coexistence method closely corresponds to the empirical value (2333 K), affirming the precision of the optimized potential. Quenching the molten STO yields an amorphous structure characterized primarily by Ti-O six-fold coordination, which increased by 13.09% when reduced to 300 K at a cooling rate of 0.1 K/ps. Notably, the results for different cooling rates revealed that slower cooling rates and lower temperatures yielded more ordered amorphous structures. To circumvent the formation of amorphous states during crystal growth of perovskite materials, we have developed a kinetic two-phase growth (KTPG) method. This approach regulates the cooling rate within a solid-liquid two-phase system, maintaining constant low supercooling at the interface to mimic STO crystal growth kinetics. Cooling at 0.01 K/ps to 1760 K leads to a notable transformation, with the percentage of Ti-O six-fold coordination reaching 90%. This signifies substantial progress in achieving crystal growth through this method, highlighting its efficacy in facilitating crystal formation from the melt phase.

Atomic-Scale Insights Into Graphene/Fullerene Tribological Mechanisms and Machine Learning Prediction of Properties

Abstract Graphene/fullerene carbon–based nanoparticles exhibit excellent tribological properties in solid–liquid two-phase lubrication systems. However, the tribological mechanism still lacks profound insights into dynamic friction processes at the atomic scale. In this paper, the friction reduction and anti-wear mechanism of graphene/fullerene nanoparticles and the synergistic lubrication effect of the binary additive system were investigated by molecular dynamics simulations and tribological experiments. The friction performance was predicted based on six machine learning algorithms. The results indicated that in fluid lubrication, graphene promoted “liquid–liquid” interlayer sliding, whereas fullerene facilitated “solid–liquid” interface sliding, resulting in a decrease or increase in friction force. Under boundary lubrication, graphene/fullerene nanoparticles were adsorbed and anchored at the metal interface to form a physical protective film, which improved the bearing capacity of the lubricating oil film, transformed the direct contact between asperities into interlayer sliding of graphene and roll–slide polishing, filling, and repairing of fullerene, thus improving the frictional wear of the lubrication system as well as the friction temperature rise and stress concentration of the asperities. Furthermore, six machine learning algorithms showed low error and high precision, and the coefficient of determination was greater than 0.9, indicating that all models had good prediction and generalization capabilities, fully demonstrating the feasibility of combining molecular simulation and machine learning applications in the field of tribology.

A novel method for determining the wax precipitation temperature in wax-based warm mix asphalt

ABSTRACT To accurately determine the wax precipitation temperature (WPT) of wax-based warm mix asphalt binder, a novel algorithm for WPT calculation was proposed, and the process of wax precipitation in asphalt, as well as the effects of aging, cooling rate, and shear rate on wax precipitation characteristics, were investigated through dynamic shear rheometer (DSR) tests and polarised light microscopy (PLM) experiments. The research findings reveal the following: The refined WPT algorithm exhibits heightened precision compared to the traditional viscosity method, showcasing superior reproducibility and mitigating human-induced errors. During the cooling process, wax molecules become oversaturated, leading to the precipitation of wax crystals and the transformation of asphalt into a solid–liquid two-phase system. The aging of asphalt causes changes in its composition, shifting the phase equilibrium towards favouring wax precipitation. The WPT of asphalt is also influenced by the cooling rate and shear rate, and a larger cooling rate and shear rate will reduce the WPT. Wax crystals are less numerous and more regular in shape at low cooling rates.

Chiral Ionic Liquids: Structural Diversity, Properties and Applications in Selected Separation Techniques.

Ionic liquids (ILs) are chemical compounds composed of ions with melting points below 100 °C exhibiting a design feature. ILs are commonly used as the so-called green solvents, reagents or highly efficient catalysts in varied chemical processes. The huge application potential of ionic liquids (IL) justifies the growing interest in these compounds. In the last decade, increasing attention has been devoted to the development of new methods in the synthesis of stable chiral ionic liquids (CILs) and their application in various separation techniques. The beginnings of the successful use of CILs to separate enantiomers date back to the 1990 s. Most chiral ILs are based on chiral cations or chiral anions. There is also a limited number of CILs possessing both a chiral cation and a chiral anion. Due to the high molecular diversity of both ions, of which at least one has a chiral center, we have the possibility to design a large variety of optically active structures, thus expanding the range of CIL applications. Research utilizing chiral ionic liquids only recently has become more popular. However, it is the area that still has great potential for future development. This review aimed to describe the diversity of structures, properties and examples of applications of chiral ionic liquids as new chiral solid materials and chiral components of the anisotropic environment, providing chiral recognition of enantiomeric analytes, which is useful in liquid chromatography, countercurrent chromatography and other various CIL-based extraction techniques including aqueous biphasic (ABS) extraction systems, solid–liquid two-phase systems, liquid–liquid extraction systems with hydrophilic CILs, liquid–liquid extraction systems with hydrophobic CILs, solid-phase extraction and induced-precipitation techniques developed in the recent years. The growing demand for pure enantiomers in the pharmaceutical and food industries sparks further development in the field of extraction and separation systems modified with CILs highlighting them as affordable and environmentally friendly both chiral selectors and solvents.

A new method to calculate sedimentation velocity of particle group with three-plane ECT based on the best correlation function

ABSTRACT A novel method to calculate the flow velocity of solid in a solid–liquid two-phase system is induced in this paper by electrical capacitance tomography (ECT). Taking the slime settlement as an example, the concentration change of three planes in the settling tank is measured using ECT. Moreover, the settling velocity of continuous frames in different sensor planes employing the best correlation function is calculated. The results show that slime has a higher and more uniform settlement velocity in the center area of the settlement tank. A 0.02–0.04 cm/s deviation is found between the calculated velocity of clarifying interfacial layer when slime passing through the ECT sensor and the experimental data. Remarkably, the time point is in good agreement with the experimental result which is between 7 and 13 s, indicating that the method can be used to estimate the settling velocity of solid in a two-phase flow.

Direct numerical simulations of solid-liquid suspension in a transitional stirred tank

Solid-liquid stirred tanks are very common in industrial process, for example pharmaceutical engineering, water treatment and crystallization. In these operating units, solid-liquid two-phase flows affect the rates of momentum, mass and heat transfer as well as the chemical reactions significantly. The flow regime in most investigations of solid-liquid suspension is either laminar or turbulent, however the transitional regime is also very important especially when scaling up from bench scale to pilot scale. Therefore, it is important to investigate the hydrodynamic characteristics of solid-liquid suspension in a transitional stirred tank. In this work, the lattice Boltzmann method was used to solve the liquid flow field. The uniform, cubic grids were applied with grid spacing Δ and time step Δ t representing the lattice units in space and time respectively. The stirred tank is a cubic tank with a flat bottom, whose height and side length of the bottom are both equal to 264 Δ. The impeller is a 45° pitched-blade turbine with diameter D =189.6 Δ; width of the impeller blade W =38.4 Δ and it operates under the down-pumping configuration. The impeller-based Reynolds number is 1334, which indicates that the flows belong to transitional regime. The particles are all equally sized solid spheres with diameter d p=9.6 Δ. As for the boundary conditions in this work, the half-way bounce-back rule was used to form the no-slip boundary conditions at all tank walls including top, bottom and side walls. The immersed boundary method was applied to impose the no-slip boundary conditions at the particles surface and the impellers surface. When it comes to the collisions, a hard-sphere collision algorithm based on the two-parameters model (restitution coefficient and friction coefficient) was adopted to carry out the collisions among the particles as well as the collisions between the particles and the tank walls. The collisions between the particles and the impeller were performed by using a soft-sphere collision model. In addition, the lubrication force was applied to deal with the close-range hydrodynamic interaction between the solid surfaces. This paper mainly did the simulations for different solids volume fractions Φ =0%, 1%, 5% and 8% at impeller angle θ =30° and at the same time resolved the impeller angles to 0°, 30° and 60° for solids volume fraction Φ =5%. In terms of simulated results, at first we compare the instantaneous liquid flow field between the single-phase system and the solid-liquid two-phase system, which shows that the exist of particles clearly hindered the liquid flow field especially in the impeller-discharge region. This paper also compares the averaged hydrodynamic characteristics between the single-phase system and the solid-liquid two-phase system. The results show that the averaged liquid velocity did not change obviously with the rise of solids volume fraction from 0% to 1%, however, when the solids volume fraction rose up to 5% or even higher to 8%, the averaged liquid velocity decreased obviously in the impeller-discharge region as well as the region near the bottom of the stirred tank at impeller angles θ =30°. Finally, the turbulent kinetic energy (TKE) of the liquid is compared qualitatively and quantitatively and it shows that the TKE values decreased significantly with the rise of solids volume fraction at impeller angle θ =30°. The peak TKE values decreased more than 50% with the rise of impeller angle θ from 0° to 30° for solids volume fraction Φ =5%, however the peak TKE values did not change obviously with the impeller angle θ rising from 30° to 60°.

Particle image velocimetry experiments and direct numerical simulations of solids suspension in transitional stirred tank flow

Solids suspension in a stirred tank with a down-pumping pitched-blade turbine impeller has been investigated by using particle image velocimetry (PIV) experiments as well as direct numerical simulations (DNS) with a lattice-Boltzmann (LB) method. The flow regime of this solid–liquid two-phase system is transitional with the impeller-based Reynolds numbers Re = 1334. The refractive index matching (RIM) method is applied in the experiments. The overall solids volume fractions are up to 8% in the experiments as well as in the simulations. The liquid flow fields around the particles are highly resolved in both experimental and simulated cases which makes it possible to investigate solid-liquid interactions in detail. The average distributions of the solids over the tank volume as predicted by the simulations are in good agreement with the experimental results. It is shown that the presence of particles reduces the average velocities as well as the turbulent fluctuation levels of the liquid in both the experiments and simulations although the reduction in the simulations is weaker as compared to in the experiments.

High resolution of racemic phenylalanine with dication imidazolium-based chiral ionic liquids in a solid-liquid two-phase system

A novel solid-liquid two-phase system was developed for the chiral separation of racemic phenylalanine with new dication imidazolium-based chiral ionic liquids. Preliminary experiments showed distinct enantioselectivity in amino acid extraction with the novel solid-liquid two-phase system, more L-enantiomer of amino acid cooperatively interacted with ionic liquids and copper ions to be the solid phase. Various factors, including the alkyl chain length of cations of ionic liquids, the amount of copper acetate, the ratio of n(ILs)/n(Cu2+), the amount of water and racemic phenylalanine, the resolution time together with the resolution temperature, were systematically investigated for their influence on resolution efficiency. The results showed that, under a certain condition, the enantiomeric excess value and the yield of phenylalanine in liquid phase (mainly containing D-enantiomer) were 67.8% and 96.5%, the enantiomeric excess value and the yield of phenylalanine in solid phase (mainly containing L-enantiomer) were 99.2% and 85.2%. Finally, 2D NMR technology, infrared spectroscopy and molecular simulation method were used to study the interaction mechanism. The results indicated that L-enantiomer of phenylalanine interacts more strongly with chiral ILs and Cu2+. The novel system has characteristics of free-organic solvent, simple operation, fast separation process and very high resolution efficiency for racemic phenylalanine. This work could provide a new and alternative resolution approach for other chiral separations.

Assessing the Variability of Heavy Metal Concentrations in Liquid-Solid Two-Phase and Related Environmental Risks in the Weihe River of Shaanxi Province, China

Accurate estimation of the variability of heavy metals in river water and the hyporheic zone is crucial for pollution control and environmental management. The biotoxicities and potential ecological risks of heavy metals (Cu, Zn, Pb, Cd) in a solid-liquid two-phase system were estimated using the Geo-accumulation Index, Potential Ecological Risk Assessment and Quality Standard Index methods in the Weihe River of Shaanxi Province, China. Water and sediment samples were collected from five study sites during spring, summer and winter, 2013. The dominant species in the streambed sediments were chironomids and flutter earthworm, whose bioturbation mainly ranged from 0 to 20 cm. The concentrations of heavy metals in surface water and pore water varied obviously in spring and summer. The degrees of concentration of Cu and Cd in spring and summer were higher than the U.S. water quality Criteria Maximum Concentrations. Furthermore, the biotoxicities of Pb and Zn demonstrated season-spatial variations. The concentrations of Cu, Zn, Pb and Cd in spring and winter were significantly higher than those in summer, and the pollution levels also varied obviously in different layers of the sediments. Moreover, the pollution level of Cd was the most serious, as estimated by all three assessment methods.

Phase field modeling of the evolution of partical interface shape distribution during coarsening

Three-dimensional simulations of particles coarsening in a solid-liquid two-phase system are investigated using the multiphase-field model. The evolution of the interface shape distribution during coarsening is analyzed. And the influences of the volume fraction on the interface shape distribution and coarsening rate are studied under different coalescence conditions. The simulation results show that the influence of volume fraction on the change of coarsening rate is delayed when there exists coalescence between solid particles under high volume fraction. Moreover, with the evolution of coarsening, proportion of the hyperboloid with high curvature decreases and the proportion of ellipsoid with low curvature increases. No matter whether the coalescence between particles occurs, the interface shape distribution has self-similarity after a period of time of evolution. But it will take a longer time for the system to reach the steady state with the increasing of volume fraction.

Biodegradation of Endocrine Disruptors in Solid-Liquid Two-Phase Partitioning Systems by Enrichment Cultures

Naturally occurring and synthetic estrogens and other molecules from industrial sources strongly contribute to the endocrine disruption of urban wastewater. Because of the presence of these molecules in low but effective concentrations in wastewaters, these endocrine disruptors (EDs) are only partially removed after most wastewater treatments, reflecting the presence of these molecules in rivers in urban areas. The development of a two-phase partitioning bioreactor (TPPB) might be an effective strategy for the removal of EDs from wastewater plant effluents. Here, we describe the establishment of three ED-degrading microbial enrichment cultures adapted to a solid-liquid two-phase partitioning system using Hytrel as the immiscible water phase and loaded with estrone, estradiol, estriol, ethynylestradiol, nonylphenol, and bisphenol A. All molecules except ethynylestradiol were degraded in the enrichment cultures. The bacterial composition of the three enrichment cultures was determined using 16S rRNA gene sequencing and showed sequences affiliated with bacteria associated with the degradation of these compounds, such as Sphingomonadales. One Rhodococcus isolate capable of degrading estrone, estradiol, and estriol was isolated from one enrichment culture. These results highlight the great potential for the development of TPPB for the degradation of highly diluted EDs in water effluents.

Phase field modeling of the influence of interfacial wettability and solid volume fraction on the kinetics of coarsening

Coarsening of solid particles in a solid-liquid two-phase system with high solid volume fraction is studied using the multiphase-field model. The influences of interfacial wettability and solid volume fraction on growth exponent, coarsening rate, and particle size distribution (PSD) are analyzed. It is found that the growth exponent is independent of the volume fraction, while the coarsening rate constant and the PSD are closely related to the interfacial wettability and the solid volume fraction. Under the completely wetting condition the coarsening rate constant increases with volume fraction increasing, but this variation is insignificant under the incompletely wetting condition. Moreover, when the wettability is low and volume fraction is high, the coarsening rate may also decrease with volume fraction increasing. The simulation results also show that with the increase of volume fraction, the peak frequency decreases and the PSD becomes broader, but the fall of the peak frequency under the incompletely wetting condition is slower than under the completely wetting condition. The simulation results provide an insight into the discrepancy between different experimental observations.

Enhanced Biotransformation of 2-Phenylethanol with Ethanol Oxidation in a Solid–Liquid Two-Phase System by Active Dry Yeast

2-Phenylethanol (2-PE) can be produced from L: -phenylalanine (L: -Phe) with the oxidation degradation of ethanol by active dry yeast. In this study, the catalysis effect of ethanol on biotransforming L: -Phe into 2-PE by yeast was evaluated and optimized. The results indicated that increasing ethanol concentration was beneficial for enhancing 2-PE concentration but lowered the 2-PE productivity. Initial ethanol concentration above 25 g/l could strongly inhibit the 2-PE production. To obtain 2-PE with desirable concentrations with an economical operation mode, three fed-batch biotransformation operation methods using ethanol or/and glucose were carried out in a solid-liquid two-phase system. When using ethanol alone with the initial concentration of 10 g/l, the total concentration and overall productivity of 2-PE were 7.6 g/l and 0.065 g l(-1) h(-1), respectively. Furthermore, an experiment with controlled glucose solely (higher than 2 g/l) was finished. In this case, phenylacetaldehyde (PA) was detected along with ethanol accumulation, suggesting that reaction of PA → 2-PE in Ehrlich pathway was inhibited. To further enhance 2-PE production by using glucose only, a novel operation strategy to simultaneously control rates of glucose glycolysis and ethanol oxidative degradation with the aid of ISPR techniques was developed. With this strategy, 2-PE concentration and yield based on glucose consumption reached a higher level of 14.8 g/l and 0.12 g-PE/g-glucose, respectively, and these are the highest values reported up to date with the fed-batch biotransformation operation mode.

Asymmetric C–C bond formation via Darzens condensation and Michael addition using monosaccharide-based chiral crown ethers

Liquid–liquid phase asymmetric Darzens condensations were promoted by d-glucose- and d-mannose-based crown ethers. The corresponding aromatic and heteroaromatic α,β-epoxyketones were obtained with moderate to high enantioselectivities (up to 96%) as well as diastereoselectivities (up to 98:2) under mild reaction conditions. The absolute configurations of several of the epoxyketones were determined by single crystal X-ray analysis. The Michael additions of diethyl acetylaminomalonate to trans-β-nitroalkenes were carried out in a solid–liquid two-phase system in the presence of a d-glucose-based crown catalyst with up to 99% ee.

Preparation of heparin-immobilized PVA and its adsorption for low-density lipoprotein from hyperlipemia plasma

In this study, heparin was covalently coupled by glutaraldehyde to Poly(vinyl alcohol) [PVA] in solid-liquid two-phase reaction system by two-step synthesis method to prepare a LDL-selective adsorbent. The parameters (the material ratio, reaction time and dosage of catalyzer) were investigated to evaluate their effect upon the immobilized amount of heparin onto the surface of PVA, IR was used to verify the covalent immobilization result and the heparin-modified PVA was also undergone the evaluation of its adsorption capability for low-density lipoprotein from hyperlipemia plasma, and its hemocompatibility was preliminarily evaluated by platelet adhesion test. Results showed: (1) under optimized reaction conditions the highest immobilization amount of heparin onto PVA surface within the experiments of this study has been obtained; (2) the optimized reaction conditions were: (i) at the refluxing temperature 78 degrees C; (ii) the material ratio of "PVA(g): 50% glutaraldehyde (ml)" was about "1:3"; (iii) the reaction time was about 5 h; and (iv) the amount of catalyzer (concentrated HCL) was about 1% of the 50% glutaraldehyde; (3) within the experiments of this study the highest immobilization amount would be up to 25 microg heparin on the surface of per g PVA granules; (4) the heparin-modified PVA granules showed significant adsorption for LDL under faintly alkaline environment (pH=7.2-9.5) ; (5) The result of platelet adhesion test showed no platelet adhered to its surface. Therefore, immobilization of heparin onto the surface of a support is one approach to prepare a kind of LDL adsorbent for blood purification.

Numerical simulation of kinetics of the cobalt gradient change in WC–Co during liquid phase sintering

Abstract During liquid phase sintering, WC–Co composite is a solid–liquid two-phase system in which the inter-particle spaces between solid WC grains are filled with liquid Co. When there exists heterogeneity with respect to cobalt content within the composite, liquid Co tends to migrate from regions with higher Co content to other regions with lower Co content, thus causing the redistribution of Co within the WC–Co composite. The kinetics of Co redistribution are of great practical importance for the liquid phase sintering of functionally graded WC–Co composite materials. This paper describes numerical simulations of the kinetic process of Co redistribution, demonstrating how the Co gradient in a WC–Co composite changes with time under various conditions.

Mathematical modeling of liquid phase migration in solid–liquid mixtures: Application to the sintering of functionally graded WC–Co composites

Liquid phase migration (LPM) is an interfacial-energy-driven flow that takes place in a solid–liquid two-phase system. This phenomenon is similar to but different from the well-known capillary-driven flow. Understanding and controlling LPM is crucial for liquid phase sintering of various functionally graded materials, including WC–Co, with composition gradients. To date, there have been few studies that focus on the LPM phenomenon, partially because it is a complex process that involves mass transport with moving boundaries and changing volumes. This paper describes a quantitative study on the kinetics of LPM. The governing equation for LPM that takes into account the changes in volume was derived and a novel “grid-tracking” numerical technique was also developed for solving the governing equation. The methodology and techniques described in this paper can be applied to simulate and predict the kinetics of LPM during liquid phase sintering and the composition gradients as the result of LPM.

Crystallization under external pressure

The influence of external pressure on the dynamics of crystallization is examined by considering a solid–liquid two-phase system in a cylinder closed by a piston. The dynamic equations are derived using three methods, namely, Rational Thermodynamics (Liu’s procedure), the Matrix Model, and the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) formalism. The constitutive relation for the multiphase pressure on the piston is identical for all three methods, whereas some aspects of the result for the phase change dynamics differ. The rational thermodynamics treatment constrains the phase change dynamics of only those structural variables that enter into the dissipation inequality, whereas the other two formalisms make statements about the phase change of all structural variables. Nevertheless, all three methods show, first, that the phase change happens instantaneously at constant volume and, second, where morphological detail can be built into the model without violating thermodynamic principles. It is discussed how an appropriate choice of the morphological variables allows one to incorporate impingement of crystals and depletion zone effects, as well as to distinguish crystal shapes.

Aso94: Aso seismic observation with broadband instruments

We deployed a network of broadband seismometers for one year around the Naka-dake first crater of Aso volcano in Kyushu, Japan, to reveal the mechanism of long period tremors (LPTs) emitted from the volcano. It is observed that LPTs with a dominant period of about 15s are always emitted regardless of the surface activity of the volcano. A typical LPT has a short duration less than a minute and its spectrum shows mode peaks at 15, 7.5, 5, and 3s. The particle motion in the frequency band for the lowest two modes at stations within a few kilometers from the crater is rectilinear, pointing in the direction of the crater. A waveform semblance technique to locate sources of LPTs is devised to utilize the rectilinearity of waveforms. The LPT sources are located at depths of 1–1.5km beneath the bottom of the crater. When the volcano is explosively ejecting steam and mud, on the other hand, a very long period (∽100s) displacement (VLPD) polarized outward from the crater often precedes an eruptive event by a few minutes. A typical VLPD is accompanied by a few long period pulses, first positively polarized and concurrent with the onset of VLPD, then negatively polarized just before the eruption. The source of VLPDs is inferred to coincide approximately with that of LPT. On the basis of these observations, a qualitative model is constructed for the hydrothermal system beneath the Naka-dake first crater. An explanation for the unusually long period nature of the LPT is discussed in terms of a class of slow waves, which exist in solid–liquid two-phase systems. A possibility of realtime monitoring at Aso volcano using the observed long period seismic signals is also discussed.