Search Results (101)

In bulk liquid or on solid surfaces, nanobubbles (NBs) are gaseous domains at the nanoscale. They stand out due to their extended (meta)stability and great potential for use in practical settings. However, due to the high energy cost of bubble generation, maintenance issues, membrane bio-fouling, and the small actual population of NBs, significant advancements in nanobubble engineering through traditional mechanical generation approaches have been impeded thus far. With the introduction of the electric field approach to NB creation, which is based on electrostrictive NB generation from an incoming population of “electro-fragmented” meso-to micro bubbles (i.e., with bubble size broken down by the applied electric field), when properly engineered with a convective-flow turbulence profile, there have been noticeable improvements in solid-state operation and energy efficiency, even allowing for solar-powered deployment. Here, these innovative methods were applied to a selection of upstream and downstream activities in the oil–water–fuels nexus: advancing core flood tests, oil–water separation, boosting the performance of produced-water treatment, and improving the thermodynamic cycle efficiency and carbon footprint of internal combustion engines. It was found that the application of electric field NBs results in a superior performance in these disparate operations from a variety of perspectives; for instance, ~20 and 7% drops in surface tension for CO₂- and air-NBs, respectively, a ~45% increase in core-flood yield for CO₂-NBs and 55% for oil–water separation efficiency for air-NBs, a rough doubling of magnesium- and calcium-carbonate formation in produced-water treatment via CO₂-NB addition, and air-NBs boosting diesel combustion efficiency by ~16%. This augurs well for NBs being a potent agent for sustainability in the oil and fuels sector (whether up-, mid-, or downstream), not least in terms of energy efficiency and environmental sustainability. Full article

We investigated the morphological patterns, crystalline structures and their thermal stability in solidified Au–Ge nanoparticles ranging in size from 10 to 500 nm. Liquid Au–Ge alloy nanoparticles with hypoeutectic composition were rapidly cooled from a temperature of 500 °C in a TEM and characterized using advanced TEM techniques. We demonstrated that Au–Ge nanoparticles 10–80 nm in size predominantly solidified into a Janus-like morphology with nearly pure single-crystalline hcp Au and diamond cubic Ge domains. These particles remained stable up to the eutectic temperature, indicating that Ge doping and particle size play key roles in stabilizing the hcp Au phase. In turn, larger nanoparticles exhibited a metastable core–shell morphology with polycrystalline Ge shell and hcp Au-Ge alloy core under solidification. It was shown that the mentioned morphology and crystalline structure evolved into the equilibrium Janus morphology with fcc Au and diamond Ge domains at temperatures above ≈160 °C. Full article

Preparative protein crystallization is regarded as an economically sustainable protein purification alternative to chromatography in biotechnological downstream processing. However, protein crystallization is a not-well-understood process that is usually slow and poorly reproducible. A promising strategy for enhancing protein crystallization is exploiting the metastable liquid–liquid phase separation (LLPS) of protein solutions. Here, we report an enhancement of lysozyme-crystallization yield by using a combination of two additives under LLPS conditions. The first additive, NaCl (0.15 M), is necessary to introduce protein–protein attractive interactions and induce LLPS by lowering temperature. The second additive, 4-(2-hydroxyethyl)-1-piperazineethanesulfonate (HEPES, 0.10 M, pH 7.4), accumulates in the metastable protein-rich liquid phase and thermodynamically stabilizes lysozyme crystals. We found that this combination of additives leads to crystallization yields of higher than 90% under LLPS conditions at a lysozyme concentration of 5% by weight and a fairly low ionic strength (0.2 M) within an operational time of the order of one hour. This crystallization yield is more than three-fold larger than that obtained from samples containing NaCl without HEPES at the same pH and ionic strength. Moreover, we determined crystallization yield as a function of incubation time, and temperature below and above the LLPS boundary. As crystallization temperature intersects with LLPS temperature, a significant increase in crystallization yield is observed. This is consistent with LLPS boosting protein crystallization. Our work suggests a possible strategy for increasing the crystallization success of other proteins, with applications in protein purification. Full article

The self-foaming method offers a promising approach for producing AlCuFe metallic foams without the need for external foaming agents. Although it is well established that both alloy composition and heat treatment play a fundamental role in pore formation, the specific influence of annealing time on the resulting microstructure and physical properties remains insufficiently explored. In the present study, the effects of annealing time on the microstructure, phase evolution, and magnetic properties of self-foaming Al₅₈Cu₂₇Fe₁₅ alloys are investigated. Metallic foams were synthesized using the self-foaming method, heat-treating the samples at 850 °C for 6, 9, 15, and 24 h. X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) reveal that prolonged annealing increases porosity, reaching 64% and 61% after 15 and 24 h, respectively. The porosity formation mechanism was attributed to a peritectic reaction involving the liquid metastable τ phase and the solid λ and β phases. Magnetic measurements indicated complex behavior consistent with the Curie–Weiss law, influenced by phase composition and interactions between Coulomb forces, Hund’s rule exchange, and Fe 3d–Al s, p orbital hybridization. Full article

Liquid metals and metallic alloys often exist as metastable phases or can be undercooled below their equilibrium melting point. The Traditional CALPHAD (CALculation of PHAse Diagrams) approach struggles to accurately model these metastable conditions, which are important in rapid quenching techniques like additive manufacturing, and to understand glass formation or oxidation phenomena occurring in the liquid phase during nuclear and high-temperature aerospace applications. On the contrary, the third-generation CALPHAD models have the potential to accurately describe metastable phase diagrams to provide better predictions of molten phase behavior under non-equilibrium conditions. The latter approach is utilized in this study to achieve a more accurate description of the thermodynamic properties of elemental Nb and Zr, with a particular focus on their liquid phases. By incorporating available first-principles data, the representation of the liquid state is improved for both elements, capturing the peculiar behavior of the heat capacity in a wide temperature range. These improvements enable a more reliable prediction of phase stability and liquidus boundaries in the Nb-Zr system. A partial re-assessment of the Nb-Zr binary phase diagram is also conducted with refined predictions of liquidus boundaries that align well with experimental data. Full article

Amorphous solid dispersions are good candidates for improving solubility in water and the oral bioavailability of poorly water-soluble active pharmaceutical ingredients (APIs). Amorphous solids become supercooled liquids when the temperature reaches the glass transition temperature (T_g). For APIs with low melting points, T_g can be below room temperature, which makes it difficult to prepare long-term stable amorphous solids. Studies on the physicochemical properties of supercooled liquids shed light on the design of ASDs for APIs with low melting points. Racemic ibuprofen (IBU) supercooled liquid has been detected using differential scanning calorimetry and powder X-ray diffraction during the melt-quenching of IBU at a low temperature (0 °C). In this work, gram-scaled IBU supercooled liquid was prepared using the melt-quenching method, maintaining a liquid state for minutes at room temperature and for hours at 10 °C, as confirmed by visual observation. The Raman spectra, IR spectra, and UV-vis spectra results indicate that the structure of the IBU supercooled liquid is similar to that of an IBU solution instead of IBU Form I. The rate of recrystallization into Form I can be adjusted by controlling the temperature and additives, as confirmed by visual observation. Moreover, long-term stable IBU dispersions, with improved aqueous solubility, were inspired by the IBU supercooled liquid. The IBU supercooled liquid model can guide the preparation of ASDs for low melting point drugs. Full article

In this paper, the solidification microstructure characteristics of metastable immiscible Cu20Fe alloys under natural cooling conditions and subsequent cold rolling were analysed. The findings demonstrate that the Cu20Fe alloy underwent a liquid–solid transformation under natural cooling conditions. The equiaxed Cu matrix and the Fe dendrites exhibited elongation into ribbon-like structures parallel to the cold rolling direction. Following cold rolling, the mean grain size of the Cu20Fe alloy was considerably refined, and the mechanical properties were improved. After cold rolling, the Cu matrix formed both {112}<111> copper and {110}<112> brass textures. Furthermore, the strengthening mechanisms of the cold-rolled Cu20Fe alloy are primarily dependent on the strengthening of grain boundaries and work hardening. This provides an economically friendly method for the preparation of Cu-Fe alloys with high Fe compositions. Full article

The geometric shape, symmetry, and topology of colloidal particles often allow for controlling colloidal phase behavior and physical properties of these soft matter systems. In liquid crystalline dispersions, colloidal particles with low symmetry and nontrivial topology of surface confinement are of particular interest, including surfaces shaped as handlebodies, spirals, knots, multi-component links, and so on. These types of colloidal surfaces induce topologically nontrivial three-dimensional director field configurations and topological defects. Director switching by electric fields, laser tweezing of defects, and local photo-thermal melting of the liquid crystal host medium promote transformations among many stable and metastable particle-induced director configurations that can be revealed by means of direct label-free three-dimensional nonlinear optical imaging. The interplay between topologies of colloidal surfaces, director fields, and defects is found to show a number of unexpected features, such as knotting and linking of line defects, often uniquely arising from the nonpolar nature of the nematic director field. This review article highlights fascinating examples of new physical behavior arising from the interplay of nematic molecular order and both chiral symmetry and topology of colloidal inclusions within the nematic host. Furthermore, the article concludes with a brief discussion of how these findings may lay the groundwork for new types of topology-dictated self-assembly in soft condensed matter leading to novel mesostructured composite materials, as well as for experimental insights into the pure-math aspects of low-dimensional topology. Full article

Nanobubbles (NBs) are gaseous domains at the nanoscale that can exist in bulk liquid or on solid surfaces. They are noteworthy for their high potential for real-world applications and their long (meta)stability. “Platform-wide” applications abound in medicine, wastewater treatment, hetero-coagulation, boundary-slip control in microfluidics, and nanoscopic cleaning. Here, we compare and contrast the industrial NB-generation performance of various types of commercial NB generators in both water-flow and submerged-in-water settings—in essence, comparing electric-field NB-generation approaches versus mechanical ones—finding that the former embodiments are superior from a variety of perspectives. It was found that the electric-field approach for NB generation surpasses traditional mechanical approaches for clean-water NB generation, especially when considering the energy running cost. In particular, more passive electric-field approaches are very operationally attractive for NB generation, where water and gas flow can be handled at little to no cost to the end operator, and/or submersible NB generators can be deployed, allowing for the use of photovoltaic approaches (with backup batteries for night-time and “low-sun” scenarios and air-/CO₂-pumping paraphernalia). Full article

Nucleation is a fundamental and general process at the initial stage of first-order phase transition. Although various models based on the classical nucleation theory (CNT) have been proposed to explain the energetics and kinetics of nucleation, detailed understanding at nanoscale is still required. Here, in view of the homogeneous bubble nucleation, we focus on cavity formation, in which evaluation of the size dependence of free energy change is the key issue. We propose the application of a formula in stochastic thermodynamics, the Jarzynski equality, for data analysis of molecular dynamics (MD) simulation to evaluate the free energy of cavity formation. As a test case, we performed a series of MD simulations with a Lennard-Jones (LJ) fluid system. By applying an external spherical force field to equilibrated LJ liquid, we evaluated the free energy change during cavity growth as the Jarzynski’s ensemble average of required works. A fairly smooth free energy curve was obtained as a function of bubble radius in metastable liquid of mildly negative pressure conditions. Full article

Phase equilibria studies were performed in the Li₂O-SiO₂ system for heat-treated samples using Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The temperature of the eutectic reaction (Liq. ⇌ Li₄SiO₄ + Li₂SiO₃) was experimentally determined at 1289 K using Differential Thermal Analysis (DTA). No evidences of the Li₆Si₂O₇ formation was found by the experimental investigation and therefore, it was not considered. Heat capacity of the Li₈SiO₆ phase was measured using Differential Scanning Calorimetry (DSC). Solid phases of the Li₂O-SiO₂ system were described as stoichiometric compounds and liquid phases by two-sublattice partially ionic liquid model. Four stoichiometric intermediate compounds were considered to be stable (Li₈SiO₆, Li₄SiO₄, Li₂SiO₃ and Li₂Si₂O₅). The polymorphic transformation in Li₂Si₂O₅ phase was accounted and the metastable liquid miscibility gap on SiO₂-rich side was reproduced. The calculated phase diagram satisfactorily agrees with the experimental phase equilibria as well as calculated thermodynamic properties reproduces experimental values within uncertainty limits. Full article

We review recent work on Ising-like models with “compressible cells” of fluctuating volume that, as such, are naturally treated in $NpT$ and $\mu pT$ ensembles. Besides volumetric phenomena, local entropic effects crucially underlie the models. We focus on “compressible cell gases” (CCG), namely, lattice gases with fluctuating cell volumes, and “compressible cell liquids” (CCL) with singly occupied cells and fluctuating cell volumes. CCGs contemplate singular diameters and “Yang–Yang features” predicted by the “complete scaling” formulation of asymmetric fluid criticality, with a specific version incorporating “ice-like” hydrogen bonding further describing the “singularity-free scenario” for the low-temperature unusual thermodynamics of supercooled water. In turn, suitable CCL variants constitute adequate prototypes of water-like liquid–liquid criticality and the freezing transition of a system of hard spheres. On incorporating vacant cells to such two-state CCL variants, one obtains three-state, BEG-like models providing a satisfactory description of water’s “second-critical-point scenario” and the whole phase behavior of a simple substance like argon. Future challenges comprise water’s crystal–fluid phase behavior and metastable states. Full article

A new equation of state for argon was developed with the view of extending the range of validity of the equation of state previously proposed by Tegeler et al. and obtaining a better physical description of the experimental thermodynamic data for the whole fluid region (single-phase, metastable, and saturation states). As proposed by Tegeler et al., this equation is also based on a functional form of the residual part of the reduced Helmholtz free energy. However, in this work, the fundamental equation for Helmholtz free energy was derived from the measured quantities C_V(ρ, T) and P(ρ, T). The empirical description of the isochoric heat capacity C_V(ρ, T) was based on an original empirical description explicitly containing the metastable states. The thermodynamic properties (internal energy, entropy, and free energy) were then obtained by combining the integration of C_V(ρ, T). The arbitrary functions introduced by the integration process were deduced from a comparison between calculated and experimental pressure P(ρ, T) data. The new formulation is valid for the whole fluid region from the melting line to 2300 K and for pressures up to 50 GPa. It also predicts the existence of a maximum of the isochoric heat capacity C_V along isochors, as experimentally observed in several other fluids. For many applications, an approximate form of the equation of state for the liquid phase may be sufficient. A Tait–Tammann equation is therefore proposed between the triple-point temperature and 148 K. Full article

It is a valid path to realize the zero discharge of coal chemical wastewater by using the fractional crystallization method to recycle the miscellaneous salt in high-salinity wastewater. In this study, the thermodynamics and nucleation kinetics of sodium chloride (NaCl) and sodium sulfate (Na₂SO₄) crystallization in coal chemical wastewater were systematically studied. Through analyses of solubility, metastable zone width, and induction period, it was found that the impurity dimethoxymethane would increase the solid–liquid interface energy and critical crystal size during the nucleation of Na₂SO₄. Ternary phase diagrams of the pseudo-ternary Na₂SO₄-NaCl-H₂O systems in simulated wastewater were plotted in the temperature range of 303.15 to 333.15 K, indicating that a co-ionization effect existed between NaCl and Na₂SO₄, and NaCl had a strong salting out effect on Na₂SO₄. Finally, the nucleation rate and growth rate of Na₂SO₄ crystals under simulated wastewater conditions were determined by the intermittent dynamic method, and the crystallization kinetic models of Na₂SO₄ were established. The crystallization nucleation of Na₂SO₄ crystals was found to be secondary nucleation controlled by surface reactions. The basic theoretical research of crystallization in this study is expected to fundamentally promote the application of fractional crystallization to realize the resource utilization of high-salinity wastewater in the coal chemical industry. Full article

We consider the influence of different nanoparticles or micrometre-scale colloidal objects, which we commonly refer to as particles, on liquid crystalline (LC) orientational order in essentially spatially homogeneous particle–LC mixtures. We first illustrate the effects of coupling a single particle with the surrounding nematic molecular field. A particle could either act as a “dilution”, i.e., weakly distorting local effective orientational field, or as a source of strong distortions. In the strong anchoring limit, particles could effectively act as topological point defects, whose topological charge q depends on particle topology. The most common particles exhibit spherical topology and consequently act as q = 1 monopoles. Depending on the particle’s geometry, these effective monopoles could locally induce either point-like or line-like defects in the surrounding LC host so that the total topological charge of the system equals zero. The resulting system’s configuration is topologically equivalent to a crystal-like array of monopole defects with alternating topological charges. Such configurations could be trapped in metastable or stable configurations, where the history of the sample determines a configuration selection. Full article