arXiv subjects

Yan Levin

Publications and source records attributed to Yan Levin.

At least 109 records · Page 6Linked to original sources

arXiv2005

Potential of mean force and the charge reversal of rodlike polyions

A simple model is presented to calculate the potential of mean force between a polyion and a multivalent counterion inside a polyelectrolite solution. We find that under certain conditions the electrostatic interactions can lead to a strong attraction between the polyions and the multivalent counterions, favoring formation of overcharged polyion-counterion complexes. It is found that small concentrations of salt enhance the overcharging, while an excessive amount of salt hinders the charge reversal. The kinetic limitations to overcharging are also examined.

cond-mat.stat-mech↗

arXiv2005

Electromagnetic instability of the Thomson Problem

The classical Thomson problem of $n$ charged particles confined to the surface of a sphere of radius $a$ is analyzed within the Darwin approximation of electrodynamics. For $n n_c(a)$ the Wigner lattice is unstable with respect to small perturbations and the ground state becomes spontaneously magnetized for finite $n$.

cond-mat.stat-mech↗

arXiv2004

Rupture of a liposomal vesicle

We discuss pore dynamics in osmotically stressed vesicles. A set of equations which govern the liposomal size, internal solute concentration, and pore diameter is solved numerically. We find that dependent on the internal solute concentration and vesicle size, liposomes can stay pore-free, nucleate a short lived pore, or nucleate a long-lived pore. The phase diagram of pore stability is constructed, and the different scaling regimes are deduced analytically.

cond-mat.soft↗

arXiv2004

To grow or to shrink: A tale of two rubber balloons

Two identical rubber balloons are partially inflated with air (to different extent) and connected by a hose with a valve. It is found that depending on balloon volumes, when the valve is opened the air will flow either from the larger (fuller) balloon to the smaller (emptier) balloon, or from the smaller balloon to the larger one. The phenomenon is explained in terms of the non-ideal rubber elasticity of balloons. The full phase diagram for the air flow dynamics is constructed.

cond-mat.soft↗

arXiv2004

On the fluid-fluid phase separation in charged-stabilized colloidal suspensions

We develop a thermodynamic description of particles held at a fixed surface potential. This system is of particular interest in view of the continuing controversy over the possibility of a fluid-fluid phase separation in aqueous colloidal suspensions with monovalent counterions. The condition of fixed surface potential allows in a natural way to account for the colloidal charge renormalization. In a first approach, we assess the importance of the so called ``volume terms'', and find that in the absence of salt, charge renormalization is sufficient to stabilize suspension against a fluid-fluid phase separation. Presence of salt, on the other hand, is found to lead to an instability. A very strong dependence on the approximations used, however, puts the reality of this phase transition in a serious doubt. To further understand the nature of the instability we next study a Jellium-like approximation, which does not lead to a phase separation and produces a relatively accurate analytical equation of state for a deionized suspensions of highly charged colloidal spheres. A critical analysis of various theories of strongly asymmetric electrolytes is presented to asses their reliability as compared to the Monte Carlo simulations.

cond-mat.soft↗

arXiv2003

Renormalized Jellium model for charge-stabilized colloidal suspensions

We introduce a renormalized Jellium model to calculate the equation of state for charged colloidal suspensions. An almost perfect agreement with Monte Carlo simulations is found. Our self-consistent approach naturally allows to define the effective charge of particles {\em at finite colloidal density}. Although this quantity may differ significantly from its counterpart obtained from the standard Poisson-Boltzmann cell approach, the osmotic pressures for both models are in good agreement. We argue that by construction, the effective charge obtained using the Jellium approximation is more appropriate to the study of colloidal interactions. We also discuss a possibility of a fluid-fluid critical point and show how the new equation of state can be used to shed light on the surprising results found in recent sedimentation experiments.

cond-mat.soft↗

arXiv2003

Pore dynamics of osmotically stressed vesicles

We present a theory for pore dynamics of osmotically stressed vesicles. When a liposome with an internal concentration of solute is placed inside a solute-depleted medium, an osmotic flow of solvent through the lipid bilayer leads to swelling of vesicle and to increase in membrane surface tension. This can result in membrane rupture and opening of thermal pores. Depending on the internal concentration of solute and the size of the vesicle, pores can close rapidly or be long-lived. We find that the life span of the long-lived pores scales non-trivially with the size of the liposome. Closure of the long-lived pore is followed by a rapid flicker-like opening and closing of short-lived pores. Our model is consistent with the observation of long-lived pores in red blood cell ghosts.

cond-mat.soft↗

arXiv2003

Why charges go to the surface: a generalized Thomson problem

We study a generalization of a Thomson problem of n particles confined to a sphere and interacting by a 1/r^g potential. It is found that for g \le 1 the electrostatic repulsion expels all the charges to the surface of the sphere. However for g>1 and n>n_c(g) occupation of the bulk becomes energetically favorable. It is curious to note that the Coulomb law lies exactly on the interface between these two regimes.

cond-mat.soft↗

arXiv2003

Slow dynamics under gravity: a nonlinear diffusion model

We present an analytical and numerical study of a nonlinear diffusion model which describes density relaxation of loosely packed particles under gravity and weak random (thermal) vibration, and compare the results with Monte Carlo simulations of a lattice gas under gravity. The dynamical equation can be thought of as a local density functional theory for a class of lattice gases used to model slow relaxation of glassy and granular materials. The theory predicts a jamming transition line between a low density fluid phase and a high density glassy regime, characterized by diverging relaxation time and logarithmic or power-law compaction according to the specific form of the diffusion coefficient. In particular, we show that the model exhibits history dependent properties, such as quasi reversible-irreversible cycle and memory effects -- as observed in recent experiments, and dynamical heterogeneities.

cond-mat.soft↗

arXiv2002

Kinetics of charge inversion

Colloidal suspensions and polyelectrolyte solutions containing multivalent counterions can exhibit some very counter-intuitive behavior usually associated with the low temperature physics. There are two particularly striking phenomena resulting from strong electrostatic correlations. One is the like-charge attraction and the second is the polyion overcharging. In this contribution we will concentrate on the problem of overcharging. In particular we will explore the kinetic limitation to colloidal charge inversion in suspensions containing multivalent counterions.

cond-mat.soft↗

arXiv2002

Electrostatic correlations: from Plasma to Biology

Electrostatic correlations play an important role in physics, chemistry and biology. In plasmas they lead to thermodynamic instability similar to the liquid-gas phase transition of simple molecular fluids. For charged colloidal suspensions the electrostatic correlations are responsible for screening and colloidal charge renormalization. In aqueous solutions containing multivalent counterions they can lead to charge inversion and flocculation. In biological systems the correlations account for the organization of cytoskeleton and the compaction of genetic material. In spite of their ubiquity, the true importance of electrostatic correlations has become fully appreciated only quite recently. In this paper, I will review the thermodynamic consequences of electrostatic correlations in a variety of systems ranging from classical plasmas to molecular biology.

cond-mat.soft↗

arXiv2002

Thermodynamics of surface tension: application to electrolyte solution

In this contribution to the special issue of the Journal of Statistical Physics dedicated to Michael Fisher on his 70'th birthday, I shall review two thermodynamically distinct routes for obtaining the interfacial tension of liquid-vapor interfaces in mixtures. A specific application to the calculation of the excess surface tension of aqueous electrolyte solutions will be presented.

cond-mat.soft↗

arXiv2001

Criticality in strongly correlated fluids

In this brief review I will discuss criticality in strongly correlated fluids. Unlike simple fluids, molecules of which interact through short ranged isotropic potential, particles of strongly correlated fluids usually interact through long ranged forces of Coulomb or dipolar form. While for simple fluids mechanism of phase separation into liquid and gas was elucidated by van der Waals more than a century ago, the universality class of strongly correlated fluids, or in some cases even existence of liquid-gas phase separation remains uncertain.

cond-mat.soft↗

arXiv2001

Thermodynamic properties of a simple model of like-charged attracting rods

We study the thermodynamic properties of a simple model for the possible mechanism of attraction between like charged rodlike polyions inside a polyelectrolyte solution. We consider two polyions in parallel planes, with $Z$ charges each, in a solution containing multivalent counterions of valence $α$. The model is solved exactly for $Z \le 13$ for a general angle $θ$ between the rods and supposing that $n$ counterions are condensed on each polyion. The free energy has two minima, one at $θ=0$ (parallel rods) and another at $θ=π/2$ (perpendicular rods). In general, in situations where an attractive force develops at small distances between the centers of the polyions, the perpendicular configuration has the lowest free energy at large distances, while at small distances the parallel configuration minimizes the free energy of the model. However, at low temperatures, a reentrant behavior is observed, such that the perpendicular configuration is the global minimum for both large and small distances, while the parallel configuration minimizes the free energy at intermediate distances.

cond-mat.soft↗

arXiv2001

Micellization in the presence of polyelectrolyte

We present a simple model to study micellization of amphiphiles condensed on a rodlike polyion. Although the mean field theory leads to a first order micellization transition for sufficiently strong hydrophobic interactions, the simulations show that no such thermodynamic phase transition exists. Instead, the correlations between the condensed amphiphiles can result in a structure formation very similar to micelles.

cond-mat.soft↗

arXiv2001

Criticality in confined ionic fluids

A theory of a confined two dimensional electrolyte is presented. The positive and negative ions, interacting by a $1/r$ potential, are constrained to move on an interface separating two solvents with dielectric constants $ε_1$ and $ε_2$. It is shown that the Debye-Hückel type of theory predicts that the this 2d Coulomb fluid should undergo a phase separation into a coexisting liquid (high density) and gas (low density) phases. We argue, however, that the formation of polymer-like chains of alternating positive and negative ions can prevent this phase transition from taking place.

cond-mat.stat-mech↗

arXiv2001

Criticality in polar fluids

A model of polar fluid is studied theoretically. The interaction potential, in addition to dipole-dipole term, possesses a dispersion contribution of the van der Waals-London form. It is found that when the dispersion force is comparable to dipole-dipole interaction, the fluid separates into coexisting liquid and gas phases. The calculated critical parameters are in excellent agreement with Monte Carlo simulations. When the strength of dispersion attraction is bellow critical, no phase separation is found.

cond-mat.soft↗

arXiv2000

Counterion correlations and attraction between like-charged macromolecules

A simple model is presented for the appearance of attraction between two like charged polyions inside a polyelectrolyte solution. The polyions are modeled as rigid cylinders in a continuum dielectric solvent. The strong electrostatic interactions between the polyions and the counterions results in counterion condensation. If the two polyions are sufficiently close to each other their layers of condensed counterions can become correlated resulting in attraction between the macromolecules. To explore the counterion induced attraction we calculate the correlation functions for the condensed counterions. It is found that the correlations are of very short range. For the parameters specific to the double stranded DNA, the correlations and the attraction appear only when the surface-to-surface separation is less than 7 /AA.

cond-mat.soft↗