Chemical Potential Difference Research Articles

Monitoring Photoinduced Interparticle Chemical Communication In Situ.

Monitoring interparticle chemical communication plays a critical role in the nanomaterial synthesis as this communication controls the final structure and stability of global nanoparticles (NPs). Yet most ensemble analytical techniques, which could only reveal average macroscopic information, are unable to elucidate NP-to-NP interactions. Herein, we employ stochastic collision electrochemistry to track the morphology transformation of Ag NPs in photochemical process at the single NP level. By further statistical analysis of time-resolved current transients, we quantitatively determine the dynamic chemical potential difference and interparticle communication between populations of large and small Ag NPs. The high sensitivity of stochastic collision electrochemistry enables the in situ investigation of chemical communication-dependent transformation kinetics of NPs in photochemical process, shedding light on designing nanomaterials.

Influence of modification of the cast metal structure by solid phase particles on the nucleation of crystallization centers and their stability

The inoculation method has wide possibilities for improving the mechanical and operational properties of cast metal, which makes it possible to create artificial centers of crystallization due to the direct introduction of dispersed refractory particles into the melt. The efficiency of such particles serving as crystallization centers is due to the presence of an activated transition layer on their surface. In this regard, it is promising to use complex modification, in which activating additives are introduced into the melt together with dispersed refractory particles, which form a transition layer with the desired properties on the particles. At the same time, the features of the interaction of particles with activating additives have not been sufficiently studied. A theoretical assessment of the influence of dispersed particles on the nucleation of crystallization centers and their stability was carried out on the basis of a study of the phenomena of wetting, adsorption, and dissolution using the relationship between the critical size of additional nuclei, their wetting angle, and supercooling of the melt. It is shown that if between the particle and the cladding layer the difference in chemical potentials of the contacting phases will exist throughout the entire process, and on the surface of the complex it will have a low value of surface tension, then such a particle will be stable, which takes place during adsorption of a surface-active component from a melt. Therefore, the efficiency of melt heterogenization and modification of the cast metal structure is determined by the thermodynamic activity of the substance of the transition layer to the material of the solid phase particle. The obtained conclusions make it possible to select the composition of complex modifiers that allow controlling the structure of castings in the process of their crystallization.

The characteristic curvature (Cc) definition and its use in assessing Cc for single ionic surfactants

AbstractThe hydrophilic–lipophilic‐difference (HLD) is a set of empirical equations that correlate the formulation conditions at phase inversion (HLD = 0). Based on partition studies for nonionic surfactants, the HLD can be interpreted as a normalized chemical potential difference between the surfactant dissolved in water and oil. The net‐average curvature (NAC) model extrapolates this interpretation into a curvature form that has been used to fit and predict the phase behavior of surfactant‐oil–water (SOW) systems. The curvature interpretation led to renaming the HLD surfactant parameter, sigma (σ), as the characteristic curvature (Cc). This work tests the validity of the curvature interpretation of the HLD, and the Cc concept, for single ionic surfactants and the use of this concept as a method to assess the Cc without the use of reference surfactants or alcohols. To this end, the net curvature of six anionic and two cationic surfactants was evaluated from solubilization data at the characteristic condition of 25°C, no added cosolvent, in the presence of an oil mixture with equivalent alkane carbon number (EACN) of zero, and as a function of salinity. These studies showed that the original HLD equation for ionic surfactant could not be interpreted as chemical potential or curvature because a salinity prefactor (coefficient) “bi” was missing. The revised equation, HLDbi = bi∙ln(S)‐kbi∙EACN+Ccbi ‐aTbi∙(T‐25°C), could now be interpreted as a curvature expression, and it was demonstrated that Cc could be obtained from curvature using the expression Cc = Ccbi/bi. This single surfactant method produces uncertainties that, for most surfactants, ranged from 0.2 to 1 Cc units, similar to the uncertainty obtained with the conventional method of Cc determination using mixtures of test and reference surfactants.

Novel Thermokinetic Model for Gas Hydrates: Experimental Validation at Diverse Geological Conditions

Most of the natural gas hydrates are found in deep marine sediments and permafrost regions, where the presence of salts and porous media are quite evident. With this, we develop a computationally efficient mathematical model that can expound the clathrate hydrate dynamics in a reservoir-mimicking environment. Along with proposing the chemical potential difference as the driving force to take care of the thermodynamic aspect, a nonstoichiometric reaction with nth-order kinetics is for the first time introduced in the line of adsorption kinetics. To make this thermokinetic model more rigorous, the diffusion part is further formulated with the kinetic factor, along with incorporating various practical aspects, including reaction surface renewal and hydrate formation in nanometer-sized pores of irregular and distributed particles. Finally, to examine the validity of this rigorous model, experimental case studies of methane (CH4) and carbon dioxide (CO2) hydrate formation in various porous media with pure and saline water are used. In addition, we compare the developed model with the existing formulations of gas hydrate dynamics, and it is perceived that the proposed model outperforms the existing models with reference to the experimental data of methane and carbon dioxide hydrate formation at diverse geological conditions.

Research Development in the Traditional Methods and Water Flow Erosion for Natural Gas Hydrate Production: A Review

Natural gas hydrates are considered a possible sustainable energy source. Various methods have been proposed and developed in the past few decades to exploit hydrate. The purpose of this paper is to review the research advances, application potential, and limitations of hydrate production methods, including four traditional methods (depressurization, thermal stimulation, inhibitor injection, and CO2 replacement), and novel water flow erosion. For the four traditional methods, there still exist many bottlenecks to achieve commercial hydrate production owing to a series of problems such as vast sand production, ice generation, hydrate reformation, lower energy efficiency, and huge water production. For the water flow erosion method, it can be a novel strategy to promote hydrate decomposition by introducing the chemical potential difference and accelerating mass transfer. Significantly, if the traditional methods assist with water flow erosion, the problems such as insufficient decomposition driving force and ice generation are prevented. However, there is always a gap between the experimental results and the practical application of the water flow erosion method. Therefore, future work should be undertaken to investigate the selection criteria of suitable water flow rates for different reservoirs and the ecological security of the hydrate reservoir during the water flow erosion process.

Grain boundary segregation-induced strengthening-weakening transition and its ideal maximum strength in nanopolycrystalline FeNiCrCoCu high-entropy alloys

The combined Monte Carlo and Molecular Dynamics simulations were employed to explore the influence of elemental segregation at grain boundaries (GBs) on the mechanical properties of FeNiCrCoCu high entropy alloys under uniaxial load. The chemical potential difference with respect to Ni atoms was first obtained, and used to reach the equilibrium elemental distributions in sample models with different Cu contents, grain sizes and twin thicknesses. By comparing the random and segregated configurations, the role of GB segregation was analyzed in detail. It is found that the GB segregation trend is Ni<Fe<Co<Cr<Cu. The Cu atoms have no preference to segregate at coherent twin boundaries, and their dominant segregation at GBs prevents the detwinning that usually occurs in softening stage, further increasing twin strength. The segregation with low concentration at GBs can improve the strength by suppressing dislocation emission from GBs and further enhance the GB-mediated plastic deformation; while excessive segregation at GBs results in harmful weakening effect with GB cracking. The transition from strengthening to weakening is closely related to the GB segregated Cu concentration. To estimate the critical segregation amount in case of maximum strength, a theoretical model was established, where three regions (strengthening, transition and weakening) are distinguished. It is revealed that the strengthening region occupies a small area, and the addition of Cu contents should be rigorously tailored. This work deepens the understanding of the strengthening mechanisms arising from GB segregation and provides insights into the design of ultrahigh-strength materials.

A level set approach to Ostwald ripening of trapped gas bubbles in porous media

Ostwald ripening of gas bubbles is a thermodynamic process for mass transfer, which is important for both foam enhanced oil recovery and geological CO2 storage. We present a methodology for simulating Ostwald ripening of gas ganglia surrounded by liquid in arbitrary pore geometries. The method couples a conservative level set model for capillary-controlled displacement and a ghost-bubble technique that calculates mass transfer based on difference in chemical potentials. The methodology is implemented in a software framework for parallel computations. As a validation of the model, we show that simulations of bubble ripening in a pore throat connecting two pore bodies are consistent with previously reported trends in similar geometries. Then we investigate the impact of gas type, compressibility factor, and local capillary pressure on gas-bubble ripening in various water-wet pore geometries. The results confirm that gas solubility and compressibility factor are proportional to the rate of mass transfer. Our simulations suggest that Ostwald ripening has largest impact in heterogeneous or fractured porous structures where differences in gas-bubble potentials are high. However, if the liquid separating the gas bubbles is also a disconnected phase, which can happen in intermediate-wet porous media, the resulting local capillary pressure can limit the coarsening and stabilise smaller bubbles. Finally, we simulated Ostwald ripening on a 3-D pore-space image of sandstone containing a residual gas/water configuration after imbibition. Characterization of gas-bubble morphology during the coarsening shows that large ganglia get more ramified at the expense of small spherical ganglia that cease to exist.

Effects of chemical potential differences on methane hydrate formation kinetics

To underpin the increasing interest in practical applications of gas hydrates, for gas storage and separation for instance, the formation and growth of hydrates at liquid-gas interfaces are of fundamental importance. Although the thermodynamics of hydrate formation has been widely studied and is well understood, the kinetics of these processes is not well characterised. In this work, a high-pressure, low-temperature stirred reactor was used to conduct hydrate formation kinetic studies in a temperature range from 276.5 to 283.5 K and a pressure range from 5 to 10.5 MPa, with a special focus on 1) the impact of agitation conditions on the available water-gas interfacial surface area for mass transfer and growth rate during hydrate formation, and 2) the effect of the chemical potential driving force on the formation rate. Five hydrate growth regimes were identified, with varying degrees of gas mass transfer control across the gas-water interface depending on the extent to which hydrate layers built up at this interface, gas needed to move through solid hydrate layers, and the extent to which the gas was entrained within the water phase. The formation rate in the initial linear growth regime, before the onset of solid hydrate gas mass transfer effects, was found to depend in an essentially exponential manner on the chemical potential difference from the equilibrium state. Semi-empirical models related to Arrhenius-type kinetic models were used to correlate the data, the best of which reproduced the formation rates from the chemical potential differences to within ± 5 %. The approach has general applicability to help determine the balance between kinetic and thermodynamic factors in identifying the optimum pressure-temperature conditions for processes for gas storage, gas separation and other hydrate applications.

Dissipation in a finite-temperature atomic Josephson junction

We numerically demonstrate and characterize the emergence of distinct dynamical regimes of a finite-temperature bosonic superfluid in an elongated Josephson junction generated by a thin Gaussian barrier over the entire temperature range where a well-formed condensate can be clearly identified. Although the dissipation arising from the coupling of the superfluid to the dynamical thermal cloud increases with increasing temperature as expected, the importance of this mechanism is found to depend on two physical parameters associated (i) with the initial chemical potential difference, compared to some characteristic value, and (ii) the ratio of the thermal energy to the barrier amplitude. The former determines whether the superfluid Josephson dynamics are dominated by gradually damped plasmalike oscillations (for relatively small initial population imbalances), or whether dissipation at early times is instead dominated by vortex- and sound-induced dissipation (for larger initial imbalances). The latter defines the effect of the thermal cloud on the condensate dynamics, with a reversal of roles, i.e., the condensate being driven by the oscillating thermal cloud, being observed when the thermal particles acquire enough energy to overcome the barrier. Our findings are within current experimental reach in ultracold superfluid junctions.

A Boson–Fermion theory that goes beyond the BCS approximations for superconductors

A detailed analysis is given of the effects of common and recurring approximations used in conventional superconductivity theories on the condensation energy values, whose magnitudes are notoriously smaller than those of other energies as the superconducting energy gap and the chemical potential. These approximations come from using the density of states N(ɛ) and the chemical potential μ(T) either constant or temperature-dependent, respectively. We use these approximations, a total of three, to calculate the critical temperature Tc, the superconductor energy gap Δ(T), the chemical potential μ(T) and the thermodynamic potential Ω(T) which are needed to obtain the condensation energy, and compare them with the exact case, i.e., where no approximations are used. To do this, we use a ternary Boson–Fermion theory of superconductivity composed of unbound electrons (or holes) as fermions plus two-electron and two-hole Cooper pairs, both as bosons. Although all these approximations lead to reasonable values of Tc and Δ(T), the resulting thermodynamic and chemical potentials are quite different, so that the condensation energy value could be incorrect. However, when N(ɛ) and μ(T) variables are used, together with a correct physical interpretation of the condensation energy as the sum of the thermodynamic and chemical potential differences, it leads to a better agreement with reported experimental data, compared to the one obtained when taking them as constants, particularly so for low temperatures.

Degradation of a Li1.5Al0.5Ge1.5(PO4)3-Based Solid-State Li-Metal Battery: Corrosion of Li1.5Al0.5Ge1.5(PO4)3 against the Li-Metal Anode

Solid-state Li-metal batteries were widely studied to reach an energy density of 500 mAh kg–1 before 2030. However, the interfacial parasitic reaction between the Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid-state electrolyte and Li metal generates a mixed conducting interphase (MCI), which grows continuously and leads to the fast degradation of the battery. In previous work, the role of electron transport in the corrosion of LAGP is highlighted. Herein, it has been found that Li-ion transport also plays an important role in the corrosion of LAGP. In the degradation of LAGP, the Li-ion injection through Li1 sites on the (012) plane leads to the fast corrosion of the plane, as detected by grazing incidence X-ray diffraction. The extra Li ion brings electrons to occupy the nearby Ge4+. Simultaneously, the additional interstitial Li ion distorts the local structure and breaks the PO4 tetrahedron. As a result, the corner-shared GeO6 octahedron and PO4 tetrahedron are destructed. The decomposition of LAGP generates a Li-rich MCI, which shows increased electronic conductivity compared with pristine LAGP. The high chemical potential of the Li atom at the MCI results in the continuous corrosion of LAGP. Furthermore, it has been found that ambipolar diffusion at the interface plays an important role in the growth of MCI. The MCI grows faster when ions and electrons are diffused in the same direction motivated by the chemical potential differences of the Li atom. If the cell is cycled at a small current of 0.05 mA cm–2 to separate the diffusion of electrons and ions, the MCI grows at a slower rate. Therefore, the corrosion of LAGP can be ascribed to the chemical diffusion of the Li atom. The ion and electron transport play equally important roles in the electrochemical corrosion of LAGP.

In Situ TEM Observation of Stagnant Liquid Layer Activation in Nanochannel.

The kinetics of mass transfer in a stagnant fluid layer next to an interface govern numerous dynamic reactions in diffusional micro/nanopores, such as catalysis, fuel cells, and chemical separation. However, the effect of the interplay between stagnant liquid and flowing fluid on the micro/nanoscopic mass transfer dynamics remains poorly understood. Here, by using liquid cell transmission electron microscopy (TEM), we directly tracked microfluid unit migration at the nanoscale. By tracking the trajectories, an unexpected mass transfer phenomenon in which fluid units in the stagnant liquid layer migrated two orders faster during gas-liquid interface updating was identified. Molecular dynamics (MD) simulations indicated that the chemical potential difference between nanoscale liquid layers led to convective flow, which greatly enhanced mass transfer on the surface. Our study opens up a pathway toward research on mass transfer in the surface liquid layers at high spatial and temporal resolutions.

Evaluation of membrane quality and entrance pressure of oil-based mud at elevated temperatures

AbstractThis study fully explored the impact of temperature on the membrane quality of oil-based mud (OBM) using static gravimetric measurements, membrane efficiency and entrance pressure tests. More than 30 shale samples were used to assess the membrane behavior of several OBMs under elevated temperatures. Results suggested that OBM acted as a semi-permeable membrane at low temperatures (25–55˚C) since ion flow out of OBM and into shale was restricted despite the existence of a large ionic concentration gradient, while water flowed freely out of shale and into OBM because of the existence of a chemical potential difference. For temperatures higher than 55˚C, relatively higher ion flux into shale and slightly lower water flow out of shale was observed. Excessive heat may have possibly destabilized or even destroyed the emulsifier's structure that serves as a mechanism through which OBM performs as a semi-permeable membrane. The instability of OBM's emulsifier was further confirmed through entrance pressure testing where an appreciable reduction in entrance pressure of OBM was measured at high temperatures.

High-Frequency Mechanical Energy Harvester with Direct Current Output from Chemical Potential Difference

High-Frequency Mechanical Energy Harvester with Direct Current Output from Chemical Potential Difference

A mechanism of ion exchange by interface-coupled dissolution-precipitation in the presence of an aqueous fluid

The equilibration of minerals in the presence of an aqueous fluid phase, with which it is out of equilibrium, has been described in terms of a number of potential mechanisms, specifically mainly either by solid state exchange of elements within the solid phase and the aqueous solution, or by interface-coupled dissolution-precipitation where equilibration is approached by the incremental dissolution of the parent solid and the coupled precipitation of a new solid. The conditions determining the equilibration mechanism can be defined by the specific chemical potential differences at the mineral interface, the kinetics of potential reactions, the solubility of the solid phase in the specific fluid and physical properties such as the mineral: fluid ratio as well as the surface area: fluid ratio, temperature and pressure. This review focusses on the mechanism of ion exchange in a range of solids by interface-coupled dissolution-precipitation in the presence of an aqueous solution.

High-temperature ferromagnetic metallic phase in LaMnO3/Sr3Al2O6 heterostructure

• Oxygen migration occurs at the interface due to the stronger oxygen affinity of Al. • Continuously tunable strain can be generated by adjusting the thickness of SAO. • In-plane tensile strain would stabilizes d x 2 -y 2 occupancy and increases T c . To achieve a flexible single-crystal multifunctional membrane, the freestanding process of a rigid epitaxial transition metal oxide thin film via a buffered water-dissolution sacrificial layer has attracted reasonable attentions. Owing to the difference in chemical potential, specific element affinity, and lattice constant between the target membrane and the sacrificial layer, the freestanding process may cause an indelible change of physics property once the target thin film is sensitive to the above factors. Here, the heterostructures composed of the generally adopted sacrificial layer Sr 3 Al 2 O 6 (SAO) and LaMnO 3 (LMO) have been systematically investigated. The electrical and magnetic properties of LMO show extreme sensitivity to the thickness of SAO ( t SAO ). Then we have also found that LMO/SAO heterostructures can exhibit the coexistence of two ferromagnetic phases, the significantly enhanced Curie temperature ∼ 342 K, and the large magnetoresistance -23.3% at 300 K, which is similar to the optimal-doped manganite such as La 2/3 Sr 1/3 MnO 3 . X-ray diffraction results show that continuously tunable strain from out-of-plane tension to relaxation and then to compression can be generated by adjusting t SAO . This strain can stabilize the migrated oxygen from LMO to SAO, which is induced by the large oxygen affinity difference between B-site Mn and Al. It is believed that these unexpected electrical/magnetic phenomena are originated from the combined effects of interfacial element diffusion and strain. Our study provides a strategy for designing new magnetic phases, and a reference for the fundamental understanding of strongly correlated transition metal oxide systems in the freestanding process.

Transport of spin and mass at normal-superfluid interfaces in the unitary Fermi gas

Transport in strongly interacting Fermi gases provides a window into the non-equilibrium behavior of strongly correlated fermions. In particular, the interface between a strongly polarized normal gas and a weakly polarized superfluid at finite temperature presents a model for understanding transport at normal-superfluid and normal-superconductor interfaces. An excess of polarization in the normal phase or a deficit of polarization in the superfluid brings the system out of equilibrium, leading to transport currents across the interface. We implement a phenomenological mean-field model of the unitary Fermi gas, and investigate the transport of spin and mass under non-equilibrium conditions. We consider independently prepared normal and superfluid regions brought into contact, and calculate the instantaneous spin and mass currents across the normal-superfluid (NS) interface. For an unpolarized superfluid, we find that spin current is suppressed below a threshold value in the driving chemical potential differences, while the threshold nearly vanishes for a critically polarized superfluid. The mass current can exhibit a threshold in cases where Andreev reflection vanishes, while in general Andreev reflection prevents the occurrence of a threshold in the mass current. Our results provide guidance to future experiments aiming to characterize spin and mass transport across NS interfaces.

Nonequilibrium statistical thermodynamics of multicomponent interfaces

Nonequilibrium interfacial thermodynamics has important implications for crucial biological, physical, and industrial-scale transport processes. Here, we discuss a theory of local equilibrium for multiphase multicomponent interfaces that builds upon the "sharp" interface concept first introduced by Gibbs, allowing for a description of nonequilibrium interfacial processes such as those arising in evaporation, condensation, adsorption, etc. By requiring that the thermodynamics be insensitive to the precise location of the dividing surface, one can identify conditions for local equilibrium and develop methods for measuring the values of intensive variables at the interface. We then use extensive, high-precision nonequilibrium molecular dynamics (NEMD) simulations to verify the theory and establish the validity of the local equilibrium hypothesis. In particular, we demonstrate that equilibrium equations of state are also valid out of equilibrium, and can be used to determine interfacial temperature and chemical potential(s) that are consistent with nonequilibrium generalizations of the Clapeyron and Gibbs adsorption equations. We also show, for example, that, far from equilibrium, temperature or chemical potential differences need not be uniform across an interface and may instead exhibit pronounced discontinuities. However, even in these circumstances, we demonstrate that the local equilibrium hypothesis and its implications remain valid. These results provide a thermodynamic foundation and computational tools for studying or revisiting a wide variety of interfacial transport phenomena.

Critical role of chemical potential to assure effective encapsulation

HypothesisIn emulsification-polymerisation avoiding monomer escape from emulsion droplets is the key to successful encapsulation. So far, it is believed that (1) a hydrophobe needs to be included and (2) free-micelles of surfactant need to be depleted. However, these criteria do not always work. The paper explores the critical role of the chemical potential difference between the inside and outside of the emulsion droplet for successful encapsulation. ExperimentsCrossflow membrane emulsification was used to produce uniform droplets of 1–2 µm of solutions of 3-iodoprop-2-yn-1-yl butylcarbamate (a biocide), castor oil (hydrophobe) in methyl 2-methylprop-2-enoate (monomer) into aqueous solutions with a large amount of free-micelles of surfactant. The encapsulation was followed by polymerisation. The size distribution of microcapsule from different formula were examined. FindingsThe biocide encapsulation depends on castor oil content: >12% (full); 6–12% (either full or partial); <6% (minor). Results show a critical molar fraction ratio of the monomer in the droplet to water in the aqueous phase that provides a definitive criterion to assure size retention and full encapsulation. This critical value corresponds to an energy barrier of 116 J/mol to prevent the monomer escaping. This finding is proposed to be used as an advanced rule to guide precision formulation for desired microencapsulation.

Core-shell-like BiOBr@BiOBr homojunction for enhanced photocatalysis

Constructing junctions into the photocatalyst with built-in chemical potential differences is important to separate photogenerated electrons and the holes. We first discovered that BiOBr samples prepared from hydrothermal method and hydrolysis way separately show different band structures and crystal sizes. Based on this, we build core-shell homojunction between the two different BiOBr materials through in-situ precipitation assembly. In the BiOBr@BiOBr core-shell-like homojunction, the hydrolysis synthesized BiOBr nanosheets are uniformly grown on the surface of the hydrothermally synthesized BiOBr plates. For the removal Bisphenol A (BPA) in water and nitric oxide (NO) in air, under simulated sunlight irradiation, the homojunction exhibits improved photocatalytic activity over two types of pure BiOBr. The enhanced photocatalytic ability is attributed to increased UV/vis light harvest, and more critically the formation of junction between two types of BiOBrs which allows for efficient charge separation. Our work demonstrates that the design on this new isotype junction could provide a new perspective to promote the photocatalytic activity of BiOBr based materials.