arXiv subjects

Yoav Tsori

Publications and source records attributed to Yoav Tsori.

At least 19 recordsLinked to original sources

arXiv2026

Electrolyte flows under magnetic fields: Manning-like counterion condensation in one dimension

We present a theoretical framework for unidirectional electromagnetohydrodynamic flow of dilute electrolytes under perpendicular magnetic fields. Starting from the Navier--Stokes equation coupled with the Poisson--Nernst--Planck formulation, we show that the problem admits a sequential decoupling: the Stokes equation is solved first to obtain the velocity profile, which defines a hydrodynamic potential entering the Nernst--Planck description of ions. This Lorentz-force-induced potential competes with electrostatic attraction and significantly alters ionic distributions. We analyze this mechanism in two canonical geometries. In planar Couette shear, it produces a Manning--Oosawa-like condensation transition in one dimension, a phenomenon absent in classical electrostatics. We derive an eigenvalue equation predicting a sharp threshold between counterion enrichment and depletion at the charged wall. In cylindrical Taylor--Couette flow, the same effect shifts the classical Manning criterion by a magnetic parameter, enabling tunable control of condensation. These findings extend Manning--Oosawa phenomenology to driven, non-equilibrium systems and provide a basis for magnetic manipulation of screening in electrolytes, with implications for microfluidics, electrochemical systems, and nonlinear boundary-value theory.

physics.flu-dyn↗

arXiv2024

The effect of ion solvation on ion-induced nucleation -- a generalized Thomson model

We present a model for ion-induced nucleation, focusing on the effect of dissociated ions embedded in the fluid surrounding a charged core or colloid. The model includes the ions' direct electrostatic energy and preferential solvation. The integrated ions' free energy has two terms: The first can be short- or long-range, depending on their density. The second is proportional to the nucleus' volume and can shift the state from undersaturation to supersaturation at high ion concentration. The inclusion of the Gibbs transfer energies of ions in the free energy leads to a modified Poisson-Boltzmann equation for the potential around the core. The integrated ions' free energy is added to the fluids' interfacial and bulk terms to establish a generalized Thomson model. In the Debye-Huckel limit, the model is solved analytically, while in the nonlinear regime, it is solved numerically. The state diagram in the plane of saturation and core charge includes regions with a homogeneous phase, electro-prewetting, metastable vapor, metastable nucleus, and spontaneous nucleation states. The lines separating these regions depend sensitively on the preferential solvation. Our model shows nucleation asymmetry to the sign of the nucleus' charge. This sign asymmetry is due to the Gibbs transfer energies of ions.

cond-mat.soft↗

arXiv2024

Electrolubrication in liquid mixtures between two parallel plates

We describe theoretically ``electrolubrication'' in liquid mixtures, the phenomenon where an electric field applied transverse to the confining surfaces leads to concentration gradients that alter the flow profile significantly. When the more polar liquid is the less viscous one, the stress in the liquid falls on two electric-field-induced thin lubrication layers. The thickness of the lubrication layer depends on the Debye length and the mixture correlation length. For the simple case of two parallel and infinite plates, we calculate explicitly the liquid velocity profile and integrated flux. The maximum liquid velocity and flux can be increased by a factor $α$, of order $10$--$100$ or even more. For a binary mixture of water and a cosolvent, with viscosities $η_w$ and $η_{\rm cs}$, respectively, $α$ increases monotonically with inter-plate potential $V$ and average ion content, and is large if the ratio $η_{\rm cs}/η_w$ is large.

physics.flu-dyn↗

arXiv2024

Electrolubrication in flowing liquid mixtures

We describe the ``electrolubrication'' occurring in liquid mixtures confined between two charged surfaces. For a mixture of two liquids, the effective viscosity decreases markedly in the presence of a field. The origin of this reduction is field-induced phase separation, leading to the formation of two low-viscosity lubrication layers at the surfaces. These layers facilitate larger strain at a given stress. The effect is strong if the viscosities of the two liquids are sufficiently different, the volume fraction of the less viscous liquid is small, the gap between the surfaces is small, and the applied potential is large. The phase separation relies on the existence of dissociated ions in the solution. The effective viscosity is reduced by a factor $α$; its maximum value is the ratio between the viscosities of the two liquids. In most liquids, $α\sim1 $ -- $10$, and in mixtures of water and glycerol $α\sim 80$ -- $100$ under relatively small potentials.

physics.flu-dyn↗

arXiv2023

Phase lines in mean-field models with nonuniform external forces

We look at the influence of external fields on systems described by generic free energy functional of the order parameter. The external force may have arbitrary spatial dependence, and the order parameter coupling may be nonlinear. The treatment generalizes seemingly disparate works, such as pure fluids, liquid and polymer mixtures, lipid monolayers, and colloidal suspensions in electric fields, fluids and nematics in gravity, solutions in an ultracentrifuge, and liquid mixtures in laser radiation. The phase lines and thermodynamic behavior are calculated at the mean-field level. We find a ``surface'' critical point that can be shifted to higher or lower temperatures than the bulk critical point. Below this point, the transition from a ``gas'' phase to a ``liquid'' phase is first-order, while above it, the transition is second-order. The second-order line is affected by the spatial dependence of the force, while the first-order line is universal. Moreover, the susceptibility may diverge at a finite location ${\bf r}$. Several analytical expressions are given in the limit where a Landau expansion of the free energy is valid.

cond-mat.stat-mech↗

arXiv2022

Bistable colloidal orientation near a charged surface

Anisotropic particles oriented in a specific direction can act as artificial atoms and molecules, and their controlled assembly can result in a wide variety of ordered structures. Towards this, we demonstrate the orientation transitions of uncharged peanut-shaped polystyrene colloids, suspended in a non-ionic aprotic polar solvent, near a flat surface whose potential is static or time-varying. The charged surface is coated with an insulating dielectric layer to suppress electric currents. The transition between several orientation states such as random, normal or parallel orientation with respect to the surface, is examined for two different colloid sizes at low-frequency ($\sim 10-350$ kHz) or static fields, and at small electric potentials. In time-varying (AC) field, a detailed phase diagram in the potential-frequency plane indicating the transition between particles parallel or normal to the surface is reported. We next present the first study of orientation switching in static (DC) fields, where no electro-osmotic or other flow is present. A reversible change between the two colloidal states is explained by a theory showing that the sum of electrostatic and gravitational energies of the colloid is bistable. The number of colloids in each of the two states depends on the external potential, particle and solvent permittivities, particle aspect ratio, and distance from the electrode.

cond-mat.soft↗

arXiv2021

Electroprewetting near a flat charged surface

We look at the wetting of a pure fluid in contact with a charged flat surface. In the bulk, the fluid is a classical van der Waals fluid containing dissociated ions. The presence of wall and ions leads to strong dielectrophoretic and electrophoretic forces that increase the fluid's density at the wall. We calculate the fluid's profiles analytically and numerically and obtain the energy integrals. The critical surface potential for prewetting is obtained. In the phase diagrams, the line of first-order transition meets a second-order transition line at a critical point whose temperature can be higher or lower than the bulk critical temperature. The results are relevant to droplet nucleation around charged particles in the atmosphere and could possibly explain deviations from expected nucleation rates.

cond-mat.stat-mech↗

arXiv2021

Liquid nucleation around charged particles in the vapor phase

We theoretically investigate the nucleation of liquid droplets from vapor in the presence of a charged spherical particle. Due to field gradients, sufficiently close to the critical point of the vapor--gas system, the charge destabilizes the vapor phase and initiates a phase transition. The fluid's free energy is described by the van der Waals expression augmented by electrostatic energy and a square-gradient term. We calculate the equilibrium density profile at arbitrary temperatures, particle charges, and vapor densities. In contrast to classical nucleation theory, here, both liquid and vapor phases are different from the bulk phases because they are spatially nonuniform. In addition, the theory applies to both sharp and diffuse interfaces and calculates the surface tension self-consistently. We find the composition profiles and integrate them to get the adsorption near the particle. We find that the adsorption changes discontinuously at a first-order phase transition line. This line becomes a second-order phase transition at high enough temperatures. We describe the transition point numerically and provide approximate analytical expressions for it. Similarly to prewetting, the adsorption diverges at the binodal phase boundary. We construct a phase diagram indicating changes in the binodal, spinodal, and critical temperature. It is shown that the field gradient enlarges the range of temperature and vapor density where liquid can nucleate.

physics.chem-ph↗

arXiv2019

Bistable colloidal orientation in polar liquid near a charged wall

We examine the translation and rotation of an uncharged spheroidal colloid in polar solvents (water) near a charged flat surface. We solve the nonlinear Poisson-Boltzmann equation outside of the colloid in two dimensions for all tilt angles $θ$ with respect to the surface normal. The colloid's size is assumed to be comparable to the Debye's length and hence field gradients are essential. The Maxwell stress tensor, including the ideal gas pressure of ions, is integrated over the colloid's surface to give the total force and torque on the colloid. From the torque we calculate the effective angular potential $U_{\rm eff}(θ)$. The classical behavior where the colloid tends to align in the direction perpendicular to the surface (parallel to the field, $θ=0$) is retrieved at large colloid-surface distances or small surface potentials. We find a surprising transition whereby at small separations or large potentials the colloid aligns parallel to the surface ($θ=90^\circ$). Moreover, this colloid orientation is amplified at a finite value of the aspect ratio. This transition may have important consequences to flow of colloidal suspensions or as a tool to switch layering of such suspensions near a surface.

cond-mat.soft↗

arXiv2017

Control of chemical reactions using electric field gradients

We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied the solvents separate and reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.

cond-mat.soft↗

arXiv2017

Recent advances in liquid mixtures in electric fields

When immiscible liquids are subject to electric fields interfacial forces arise due to a difference in the permittivity or the conductance of the liquids, and these forces lead to shape change in droplets or to interfacial instabilities. In this Topical Review we discuss recent advances in the theory and experiments of liquids in electric fields with an emphasis on liquids which are initially miscible and demix under the influence of an external field. In purely dielectric liquids demixing occurs if the electrode geometry leads to sufficiently large field gradients. In polar liquids field gradients are prevalent due to screening by dissociated ions irrespective of the electrode geometry. We examine the conditions for these "electro prewetting" transitions and highlight few possible systems where they might be important, such as in stabilization of colloids and in gating of pores in membranes.

cond-mat.soft↗

arXiv2016

Reversible Pore Gating in Aqueous Mixtures via External Potential

We examine theoretically porous membranes in aqueous mixtures. We show that large membrane pores can be reversibly gated from `off' (co-solvent-rich, poor conductor of ions and other solutes) to 'on' (water-rich, good conductor) states by an external potential. The transition voltage or charge for switching depends on the membrane hydrophilicity/hydrophobicity, the salt content, the preferential solvation of the salt ions, and the temperature. These parameters also determine whether the filling transition is abrupt or gradual.

cond-mat.soft↗

arXiv2014

Experimental Demonstration of the Stabilization of Colloids by Addition of Salt

We demonstrate a general non--Derjaguin-Landau-Verwey-Overbeek method to stabilize colloids in liquids. By this method, colloidal particles that initially form unstable suspension and sediment from the liquid are stabilized by the addition of salt to the suspending liquid. Yet, the salt is not expected to adsorb or directly interact with the surface of the colloids. For the method to work, the liquid should be a mixture, and the salt needs to be antagonistic such that each ion is preferentially solvated by a different component of the mixture. The stabilization may depend on the salt content, mixture composition, or distance from the mixture's coexistence line.

cond-mat.soft↗

arXiv2013

Stabilization of charged and neutral colloids in salty mixtures

We present a mechanism for the stabilization of colloids in liquid mixtures without use of surfactants or polymers. When a suitable salt is added to a solvent mixture, the coupling of the colloid's surface chemistry and the preferential solvation of ions leads to a repulsive force between colloids that can overcome van der Waals attraction. This repulsive force is substantial in a large range of temperatures, mixture composition and salt concentrations. The increased repulsion due to addition of salt occurs even for charged colloids. This mechanism may be useful in experimental situations where steric stabilization with surfactants or polymers is undesired.

cond-mat.soft↗

arXiv2013

Mixing-Demixing Phase Diagram for Simple Liquids in Non-Uniform Electric Fields

We deduce the mixing-demixing phase diagram for binary liquid mixtures in an electric field for various electrode geometries and arbitrary constitutive relation for the dielectric constant. By focusing on the behavior of the liquid-liquid interface, we produce simple analytic expressions for the dependence of the interface location on experimental parameters. We also show that the phase diagram contains regions where liquid separation cannot occur under any applied field. The analytic expression for the boundary "electrostatic binodal" line reveals that the regions' size and shape depend strongly on the dielectric relation between the liquids. Moreover, we predict the existence of an "electrostatic spinodal" line that identifies conditions where the liquids are in a metastable state. We finally construct the phase diagram for closed systems by mapping solutions onto those of an open system via an effective liquid composition. For closed systems at a fixed temperature and mixture composition, liquid separation occurs in a finite "window" of surface potential (or charge density). Larger potentials or charge densities counterintuitively destroy the interface, leading to liquid mixing. These results give valuable guides for experiments by providing easily testable predictions for how liquids behave in non-uniform electric fields.

cond-mat.soft↗

arXiv2013

Vapor-liquid coexistence of the Stockmayer fluid in nonuniform external fields

We investigate the structure and phase behavior of the Stockmayer fluid in the presence of nonuniform electric fields using molecular simulation. We find that an initially homogeneous vapor phase undergoes a local phase separation in a nonuniform field due to the combined effect of the field gradient and the fluid vapor--liquid equilibrium. This results in a high density fluid condensing in the strong field region. The system polarization exhibits a strong field dependence due to the fluid condensation.

cond-mat.soft↗

arXiv2012

Controlling the fluid-fluid mixing-demixing phase transition with electric fields

We review recent theoretical advances on controlling the fluid-fluid phase transition with electric fields. Using a mean-field approach, we compare the effects of uniform versus non-uniform electric fields, and show how non-uniform fields are better at altering the phase diagram. Focusing on non-uniform fields, we then discuss the behavior of the fluid concentration profile and the parameters (temperature, fluid concentration, etc.) that control the location of the fluid-fluid interface from both equilibrium and dynamic perspectives.

cond-mat.soft↗

arXiv2012

The interaction between colloids in polar mixtures above Tc

We calculate the interaction potential between two colloids immersed in an aqueous mixture containing salt near or above the critical temperature. We find an attractive interaction far from the coexistence curve due to the combination of preferential solvent adsorption at the colloids' surface and preferential ion solvation. We show that the ion-specific interaction strongly depends on the amount of salt added as well as on the mixture composition. Our results are in accord with recent experiments. For a highly antagonistic salt of hydrophilic anions and hydrophobic cations, a repulsive interaction at an intermediate inter-colloid distance is predicted even though both the electrostatic and adsorption forces alone are attractive.

cond-mat.soft↗