Chemical Potential Gradient Research Articles

Nonequilibrium Self-Assembly Time Forecasting by the Stochastic Landscape Method.

Many biological systems rely on the ability to self-assemble target structures from different molecular building blocks using nonequilibrium drives, stemming, for example, from chemical potential gradients. The complex interactions between the different components give rise to a rugged energy landscape with a plethora of local minima on the dynamic pathway to the target assembly. Exploring a toy physical model of multicomponents nonequilibrium self-assembly, we demonstrate that a segmented description of the system dynamics can be used to provide predictions of the first assembly times. We show that for a wide range of values of the nonequilibrium drive, a log-normal distribution emerges for the first assembly time statistics. Based on data segmentation by a Bayesian estimator of abrupt changes (BEAST), we further present a general data-based algorithmic scheme, namely, the stochastic landscape method (SLM), for assembly time predictions. We demonstrate that this scheme can be implemented for the first assembly time forecast during a nonequilibrium self-assembly process, with improved prediction power compared to a naïve guess based on the mean remaining time to the first assembly. Our results can be used to establish a general quantitative framework for nonequilibrium systems and to improve control protocols of nonequilibrium self-assembly processes.

Modeling diffusion in ionic, crystalline solids with internal stress gradients

Intracrystalline diffusion is an invaluable tool for estimating timescales of geological events. Diffusion is typically modeled using gradients in chemical potential caused by variations in composition. However, chemical potential is derived for uniform pressure and temperature conditions and therefore cannot be used to model diffusion when there are gradients in stress. Internal stress variations in minerals will create gradients in strain energy which, in addition to gradients in composition, will drive diffusion. Consequently, it is necessary to have a method that incorporates stress variations into diffusion models.To address this issue, we have derived a flux expression that allows diffusion to be modeled in ionic, crystalline solids under arbitrary stress states. Our approach is consistent with standard petrological methods but instead utilizes gradients in a thermodynamic potential called “relative chemical potential.” Relative chemical potential accounts for the lattice constraint in crystalline solids by quantifying changes in free energy due to the exchanges of constituents on lattice sites under arbitrary stress conditions. Consequently, gradients in relative chemical potential can be used to model diffusion when pressure is not uniform (i.e., under conditions of non-hydrostatic stress).We apply our derivation to the common quaternary garnet solid solution almandine–pyrope–grossular–spessartine. The rates and directions of divalent cation diffusion in response to stress are determined by endmember molar volumes or lattice parameters, elastic moduli, and non-ideal activity interaction parameters. Our results predict that internal stress variations of one hundred MPa or more are required to shift garnet compositions by at least a few hundredths of a mole fraction. Mineral inclusions in garnet present a potential environment to test and apply our stress-driven diffusion approach, as stress variations ranging from hundreds of MPa to GPa-level are observed or predicted around such inclusions. The ability to model stress-induced diffusion may provide new information about the magnitudes of both intracrystalline stresses and the timescales during which they occurred, imparting a better understanding of large-scale tectono-metamorphic processes.

Enhanced spin Seebeck effect via oxygen manipulation

Spin Seebeck effect (SSE) refers to the generation of an electric voltage transverse to a temperature gradient via a magnon current. SSE offers the potential for efficient thermoelectric devices because the transverse geometry of SSE enables to utilize waste heat from a large-area source by greatly simplifying the device structure. However, SSE suffers from a low thermoelectric conversion efficiency that must be improved for widespread application. Here we show that the SSE substantially enhances by oxidizing a ferromagnet in normal metal/ferromagnet/oxide structures. In W/CoFeB/AlOx structures, voltage-induced interfacial oxidation of CoFeB modifies the SSE, resulting in the enhancement of thermoelectric signal by an order of magnitude. We describe a mechanism for the enhancement that results from a reduced exchange interaction of the oxidized region of ferromagnet, which in turn increases a temperature difference between magnons in the ferromagnet and electrons in the normal metal and/or a gradient of magnon chemical potential in the ferromagnet. Our result will invigorate research for thermoelectric conversion by suggesting a promising way of improving the SSE efficiency.

Selective permeation up a chemical potential gradient to enable an unusual solvent purification modality

The need for energy-efficient recovery of organic solutes from aqueous streams is becoming more urgent as chemical manufacturing transitions toward nonconventional and bio-based feedstocks and processes. In addition to this, many aqueous waste streams contain recalcitrant organic contaminants, such as pharmaceuticals, industrial solvents, and personal care products, that must be removed prior to reuse. We observe that rigid carbon membrane materials can remove and concentrate organic contaminants via an unusual liquid-phase membrane permeation modality. Surprisingly, detailed thermodynamic calculations on the chemical potential of the organic contaminant reveal that the organic species has a higher chemical potential on the permeate side of the membrane than on the feed side of the membrane. This unusual observation challenges conventional membrane transport theory that posits that all permeating species move from high chemical potential states to lower chemical potential states. Based on experimental measurements, we hypothesize that the organic is concentrated in the membrane relative to water via favorable binding interactions between the organic and the carbon membrane. The concentrated organic is then swept through the membrane via the bulk flow of water in a modality known as "sorp-vection." We highlight via simplified nonequilibrium thermodynamic models that this "uphill" chemical potential permeation of the organic does not result in second-law violations and can be deduced via measurements of the organic and water sorption and diffusion rates into the carbon membrane. Moreover, this work identifies the need to consider such nonidealities when incorporating unique, rigid materials for the separations of aqueous waste streams.

Progression of the dealloying front in bilayer Cu–Al and Cu–Zn nanoporous foams

The role of interfaces and the controlling synthesis parameters of graded dealloyed nanoporous metallic materials are investigated, focusing on the dealloying front progression in complex precursor materials with multiple alloy compositions. Specifically, the effects of relative density and chemical potential on the dealloying front in sputtered bilayer copper alloy films are explored with two case studies: Cu–Al/Cu–Al and Cu–Al/Cu–Zn. Cross-sectional scanning electron (SEM) micrographs and energy-dispersive X-ray spectroscopy mapping trace the dealloying front across three time intervals, while top-surface and cross-sectional SEM probes the final dealloyed foam morphology. Final ligament sizes were found to be independent of the synthesis parameters (21–28 nm), due to a combination of fast reaction times and phosphate-inhibited surface diffusion of Cu atoms. The chemical potential gradient yielded faster reaction times, whereas slower reaction times and a higher at.% of Cu in the top layer of precursor material produced a more uniform morphology.Graphical abstract

Efficiency at Maximum Power in a Parallel Connected Two Quantum Dots Heat Engine

In this paper, we proposed a model in which a single level of two quantum dots is connected in parallel and embedded between two leads with different temperatures and chemical potentials. The temperature and chemical potential gradient help the electron flow cyclically and act as a heat engine. We explore the thermodynamic properties of the model such as heat flux and power as a function of dot energy. We also carried out analytical and numerical solutions for efficiency at maximum power of the thermoelectric engine. The resulting efficiency of our engine agrees with the Curzon–Ahlborn expression up to quadratic terms in Carnot efficiency.

Phase field modeling and computation of vesicle growth or shrinkage.

We present a phase field model for vesicle growth or shrinkage induced by an osmotic pressure due to a chemical potential gradient. The model consists of an Allen-Cahn equation describing the evolution of the phase field parameter that describes the shape of the vesicle and a Cahn-Hilliard-type equation describing the evolution of the ionic fluid. We establish conditions for vesicle growth or shrinkage via a common tangent construction using free energy curves. During the membrane deformation, the model ensures total mass conservation of the ionic fluid, and we weakly enforce a surface area constraint of the vesicle. We develop a stable numerical scheme and an efficient nonlinear multigrid solver to evolve the phase and concentration fields, and we use this to evolve the fields to near equilibrium for 2D vesicles. Convergence tests confirm an [Formula: see text] accuracy for our scheme and near-optimal convergence for our multigrid solver. Numerical results reveal that the diffuse interface model captures the main features of cell shape dynamics: for a growing vesicle, there exist circle-like equilibrium shapes if the concentration difference across the membrane and the initial osmotic pressure are large enough; while for a shrinking vesicle, there exists a rich collection of finger-like equilibrium morphologies.

Anomalous magnetohydrodynamics with temperature-dependent electric conductivity and application to the global polarization

We have derived the solutions of the relativistic anomalous magnetohydrodynamics with longitudinal Bjorken boost invariance and transverse electromagnetic fields in the presence of temperature or energy density dependent electric conductivity. We consider the equations of states in a high temperature limit or in a high chiral chemical potential limit. We obtain both perturbative analytic solutions up to the order of \hbar and numerical solutions in our configurations of initial electromagnetic fields and Bjorken flow velocity. Our results show that the temperature or energy density dependent electric conductivity plays an important role to the decaying of the energy density and electromagnetic fields. We also implement our results to the splitting of global polarization for \Lambda and \bar{\Lambda} hyperons induced by the magnetic fields. Our results for the splitting of global polarization disagree with the experimental data in low energy collisions, which implies that the contribution from gradient of chemical potential may dominate in the low energy collisions.

Peculiar roles of nickel diffusion in intermetallic compound formation at the dissimilar metal interface of magnesium to steel spot welds

There is an increased need to join magnesium alloys to high-strength steels to create multi-material lightweight body structures for fuel-efficient vehicles. Direct joining of these two metals is difficult, primarily because pure Mg and pure Fe are immiscible. Although a variety of interlayer materials have been used to facilitate the dissimilar joining in the literature, it is not well understood how the interlayer material affects the joint properties. In this study, a newly developed process, ultrasonic interlayered resistance spot welding (Ulti-RSW), was used to join an Mg alloy to a dual phase high-strength steel with two different interlayer materials: austenitic stainless steel and pure nickel. The IMCs formed with the two interlayers were drastically different, and computational thermodynamics and diffusion simulations revealed that such different IMCs resulted from the peculiar difference in nickel dissolution governed by local chemical potential gradients and diffusion kinetics. The joint with austenitic stainless steel interlayer had an under one micron thick Al-Fe IMC layer and a joint efficiency superior than that with the nickel interlayer as well as other joining processes in the literature.

Microstructure evolution, growth kinetics and formation mechanisms of silicon-rich NbSi2 coatings on Nb substrate

A Si-rich NbSi2 coating was prepared on Nb substrate by hot dip silicon plating process, which mainly consists of Nb5Si3 interfacial layer, NbSi2 intermediate layer and silicon-rich NbSi2 outer layer. The Si-rich NbSi2 coating has flat surface and dense structure, and the surface roughness is only 0.218–0.548 μm. Raising the deposition temperature can also significantly increase the growth rate of the Si-rich NbSi2 coating. The hot-dip silicon plating process has an extremely low reaction activation energy (249.99 kJ mol−1), which indicates that there are a large number of activated molecules during hot dip silicon plating. The silicon atoms in the molten bath deposited on the Nb surface and maintained a high chemical potential gradient continuously. Therefore, the solid diffusion reaction of Nb–Si was continuous, and the Nb5Si3 phase was generated and consumed continuously, and transformed into NbSi2 phase, which led to a higher growth rate of coating (1.7 × 10−13 to 4.3 × 10−13 m2 s).

Characterization of Sn-xIn Solders and Thermomigration-Induced Interfacial IMC Growth of Cu/Sn-xIn/Cu Micro Solder Joints

The melting behavior and microstructure of bulk Sn-xIn (x = 6, 12 and 24, wt.%) solders and the thermomigration, elemental distribution and intermetallic compound (IMC) growth in Cu/Sn-xIn/Cu micro solder joints during soldering and aging under temperature gradient (TG) were investigated. The results indicate that In addition effectively decreased the melting temperature of the bulk solders. Only the InSn4 phase was detected when In addition was increased to 24 wt.%. During soldering under TG, the growth rate of the interfacial IMC layer at the cold end interfaces gradually decreased as the In content increased. The mechanism of microstructure evolution and elemental distribution in the micro solder joints was revealed based on the TG-induced atomic thermomigration (TM). The chemical potential gradient of atoms was enhanced by TM, and the rapid diffusion of atoms in the liquids resulted in a uniform distribution of In element in both solders and the IMC phase during soldering. While during aging under TG, there was a smaller chemical potential gradient due to the slow atomic diffusion rate. At this time, TG dominated the atomic migration, which resulted in a nonuniform distribution of the In element in the whole joints. This study provides further insight into the application of In-containing solders in electronic packaging.

Impact of composition and aeration on the migration of TAGs in sandwich type confectionery products

A sandwich type confectionery product is made with a soft filling and a chocolate coating. The fats used for these two parts are generally different to provide specific organoleptic sensations. Thus, their compositions, in terms of the triacylglycerols (TAGs) profile, are different. Depending on the ambient temperature conditions, the chemical potential gradient at the interface for TAGs, and the microstructures in the bulk of two parts, the migration of TAGs is influenced. We have studied the impact of different filling recipes on the migration of specific TAGs from the filling to the coating and vice versa with a newly developed tool, referred to as lipstick method. Also, the influence of the micro-aeration of the filling on the transfer process is evaluated. Furthermore, Fick’s law of diffusion-based model is developed. The migration of TAGs as predicted by the model is compared to the experimental measurements, and limitations of the model are discussed. This approach can be used to tune the recipes of coating and filling to enhance the shelf-life stability of such products while delivering on specific liking attributes of taste.

The criterion of development of processes of the self-organization of subsystems of the second level in tribosystems of diesel engine

The paper shows the possibilities of processes in the tribosystems of diesel engines, ensuring the development of self-organization processes in them. The criterion for the possibility of development of processes of the self-organization of subsystems of the second level shows that in a real irreversible process there is a decrease in the flow of mechanical energy. The paper considers three cases of the possibility of developing the processes of self-organization of subsystems of the second level on the example of the tribosystem “crankshaft-insert” for the operating conditions of a diesel engine 10D100. It was determined that in order to reduce the wear rate of the tribosystems of diesel engine it is necessary to provide the flow of the energy-mass transfer process on their contacting surfaces of friction by the gradients of chemical potentials and dislocation density of the interacting materials. The obtained expression is the criterion of possibility of development of processes of the self-organization of subsystems of the second level which indicates that the system would lose the stability, if the density of mobile dislocations or the wear rate of the tribosystems of diesel engine increases.

Experimental simulations of hydrogen migration through potential storage rocks

In the framework of future decarbonization of the energy industry, the safe and effective storage of hydrogen is an important approach to add to a climate-friendly energy system. Until the development of sufficiently large electrical storage systems, the storage of hydrogen in the order of GWh to TWh is envisaged in salt caverns or porous geological formations with a gas-tight covering of salt or claystone. In order to calculate gas losses from these H2 storage facilities, the H2 diffusivity of the storage and cap rocks must be known. To determine the hydrogen diffusion rates in these rocks, an experimental set-up was designed, constructed and tested. The set-up comprises two gas chambers, separated by the rock sample under investigation with an exposed area of approximately 7 cm2. The driving force for gas migration through the rock sample from the hydrogen-containing feed gas chamber to the hydrogen-free permeate chamber is the chemical potential (concentration) gradient. With respect to hydrogen migration behaviour, hydrogen breakthrough times and hydrogen diffusion coefficients were determined for dry and wet Bentheimer sandstone, Werra rock salt and Opalinus clay samples. Breakthrough times varied between less than 1 h and 843 h. Based on concentration changes at the permeate side, hydrogen diffusion coefficients were derived ranging from 10−9 to 10−8 m2/s. The differences between the materials and the effect that wetted or water-saturated samples have higher hydrogen retention due to closed pores and microcracks were clearly shown. The experimental set-up proves to be a suitable approach to determine site-specific rock characteristics such as hydrogen diffusion coefficients and breakthrough times for natural geomaterials.

Enhancing oxide scale growth and adhesion via electrochemically regulating ion diffusion

Pre-oxidation is a common surface treatment approach to enhance the corrosion resistance of metals, which suffers from slow ion diffusion kinetics, bad oxide scale adhesion, and weak compactness. Herein, we propose an electrochemical oxidation approach in molten carbonate to improve the oxide scale growth and adhesion via electrochemically regulating ion diffusion in the formed oxide scale. An anodic polarization applied at the metal substrate enlarges the chemical potential gradient of oxygen and offers a favorable electric field across the metal/oxide interface to the oxide scale/molten salt interface, thereby speeding up the oxide scale growth rate in terms of increasing the diffusion rate of metal cations and oxygen ions through the oxide scale. At the same time, the oxide scale adhesion is remarkedly improved because the metal vacancies at the oxide/alloy interface are filled by the newly formed oxide. After being treated by electrochemical oxidation, the corrosion rate of the Ni-16Fe-4Mo alloys in molten Li2CO3-Na2CO3-K2CO3 decreased ten-fold. Overall, electrochemical oxidation enables the rapid formation of an adherent and corrosion-resistant oxide scale on the metal substrate, offering a general and effective way to fabricate corrosion-resistant films to survive in various aggressively corrosive media.

Thermodynamic characteristics of gas-liquid phase change investigated by lattice Boltzmann method

The chemical potential is an important thermodynamic parameter during irreversible phase changes. Mass is always transferred from the phase with the higher chemical potential to the lower. The chemical potential can help describe non-equilibrium behavior to reveal phase change mechanism. This paper proposes a method to calculate the chemical potential in the phase change process using the pseudopotential lattice Boltzmann model. It is a new way to understand the phase change mechanism based on the non-equilibrium thermodynamic principle. The results show that the chemical potential varies during the phase change process. In the droplet evaporation process, the chemical potential inside the droplet is higher than that of vapor, and an apparent chemical potential gradient is found at the gas–liquid interface. When the gas superheat increases from 0.09Ts to 0.13Ts, the maximum chemical potential gradient near the phase interface increases by 39%. In the bubble growth process, apparent chemical potential gradients appear at the gas–liquid interface and the nucleation site. The chemical potential gradient at the gas–liquid interface decreases with time. The chemical potential gradient at the nucleation site for the superheat of 0.18Ts is 2.55 times greater than that for the superheat of 0.16Ts. Meanwhile, it is found that the region where the phase change occurs coincides with the region where the chemical potential gradient is large.

The reverse flow and amplification of heat in quantum-dot systems

For classical systems, heat is impossible to be transferred from a cool bath to a hot bath without the existence of any external agency. Here, we show that such a phenomenon can occur in quantum systems through a simple device that a quantum dot is embedded between the two reservoirs described by different statistical distribution functions. The reverse flow and amplification of heat in the device can be realized by regulating the energy levels of the quantum dot and the chemical potentials of reservoirs. It is of particular interest to discover that because of the existence of the quantum tunneling effect in the device, this new quantum phenomenon can be observed even when the chemical potential gradient and the temperature gradient are in the same direction. Moreover, the reverse heat flow and amplification coefficient of the quantum device are calculated. The novelty of this device is that the reverse flow of heat does not need externally driving force and this seemingly paradoxical phenomenon does not violate the laws of thermodynamics. It is further expounded that the quantum device has some practical applications. For example, the device can work as a micro/nano cooler. The performance characteristics of the cooler are revealed for different distribution functions. The coefficients of performance of the cooler operated at different conditions are calculated and the optimum selection criteria of key parameters are supplied.

Parallel fully implicit chemical potential-based modeling of unconventional shale gas reservoirs

The design of novel mathematical models and state-of-the-art simulators for unconventional shale gas reservoirs plays an increasingly important role in the current energy mix of the world’s growing energy demand. In this paper, we present a robust and scalable framework, which is based on the chemical potential-based modeling and the fully implicit method (FIM), to model and simulate this highly nonlinear flow transport problem on a large scale. In the proposed approach, a thermodynamically consistent mathematical model of gas flow in shale formations, which employs the gas density and the chemical potential gradient, is developed to satisfy the second law of thermodynamics and meanwhile guarantee the energy dissipation property. And then the family of fully implicit finite element algorithms is utilized to accurately capture the complicated flow physics behind the transport process in shale media on high resolution grids. In particular, our approach further enhances the numerical formulation by proposing the family of Newton–Krylov methods for efficiently computing, and the parallel implementation of the simulator is achieved by using the domain decomposition technique. Numerical experiments are presented to demonstrate the robustness and parallel scalability of the solution strategies for several interesting shale gas flow problems in two or three dimensions. With the proposed parallel method, large-scale reservoir simulation can be obtained on the Shaheen-II supercomputer with up to 40960 processors, which enables to achieve a good strong scalability by saving more than 90 percent of computing time, when the problem size is enlarged to hundreds of millions of degrees of freedom.

Nanopores as versatile single-molecule tools: From DNA turbines to protein sequencing.

Nanopores offer ample opportunities for studying single biomolecules. I will present some recent examples of nanopore research from my lab: (1) DNA origami turbines powered by nanoscale flow. We demonstrated driven rotary motion of a nanoscale DNA origami turbine which harnesses energy from a water/ion flow generated by a static chemical or electrical potential gradient in a solid-state nanopore. Sustained unidirectional rotary motion of up to 20 revolutions/s were observed. These artificial nano-engines operate autonomously in physiological conditions, converting energy into useful mechanical work. (2) Nanopore-based sequential reading of peptides. We demonstrated a nanopore-based single-molecule peptide reader capable of reliably detecting single amino-acid substitutions within individual peptides. A peptide is linked to a DNA molecule and sequentially pulled through a biological nanopore by a DNA helicase in single amino-acid steps. Stepping ion-current signals enable discrimination of single-amino-acid substitutions in single reads. Notably, we demonstrated the capability to ‘rewind’ peptide reads, obtaining indefinitely many independent reads of the same molecule, yielding an undetectably low read errors. Recently, we expanded this concept to discriminating single post-translational modifications within peptides of mixed charge. These proof-of-concept experiments constitute a promising basis for the development of a single-molecule protein sequencer.

Dry glass reference perturbation theory predictions of the pervaporation separation of solvent mixtures using PIM-1 membranes

In this paper a new model to predict the pervaporation separation of solvent mixtures with glassy polymer membranes is proposed. The diffusion theory is that of Maxwell-Stefan diffusion with a concentration gradient driving. The specific form of the diffusion theory allows for the solution of systems of algebraic equations, as opposed to differential equations when chemical potential gradient driving forces are used. The bulk phase behavior is modelled using the perturbed-chain statistical associating fluid theory (PC-SAFT). The guest species solubilities in the membrane at the retentate and permeate boundaries are evaluated with the dry glass reference perturbation theory (DGRPT) closure of the non-equilibrium thermodynamics of glassy polymers (NETGP). The approach is applied to the pervaporation of solvent mixtures with PIM-1 glassy polymer membranes. It is demonstrated that the model can accurately predict the pervaporation of binary solvent mixtures, using only pure vapor solubility data to parameterize DGRPT, and pure component diffusivities measured from pure vapor diffusion in PIM-1 films. This predictability and comparatively simple form of the theory will allow for the implementation in process simulators to allow for the screening of membrane-based processes based on a minimum of data.