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Yan Levin

Publications and source records attributed to Yan Levin.

At least 127 records · Page 7Linked to original sources
arXiv2000

Charge renormalization and phase separation in colloidal suspensions

We explore the effects of counterion condensation on fluid-fluid phase separation in charged colloidal suspensions. It is found that formation of double layers around the colloidal particles stabilizes suspensions against phase separation. Addition of salt, however, produces an instability which, in principle, can lead to a fluid-fluid separation. The instability, however, is so weak that it should be impossible to observe a fully equilibrated coexistence experimentally.

cond-mat.soft↗
arXiv2000

Interfacial Tension of Electrolyte Solutions

A theory is presented to account for the increase in surface tension of water in the presence of electrolyte. Unlike the original ``grand-canonical'' calculation of Onsager and Samaras, which relied on the Gibbs adsorption isotherm and lead to a result which could only be expressed as an infinite series, our approach is ``canonical'' and produces an analytic formula for the excess surface tension. For small concentrations of electrolyte, our result reduces to the Onsager-Samaras limiting law.

cond-mat.soft↗
arXiv2000

Crystallization of hard spheres under gravity

We present a simple argument to account for crystallization of hard spheres under the action of a gravitational field. The paper attempts to bridge the gap between two communities of scientists, one working on granular materials and the other on inhomogeneous liquid state theory.

cond-mat.soft↗
arXiv1999

The mean-field theory for attraction between like-charged macromolecules

A mean-field theory based on Gibbs-Bogoliubov inequality is constructed to study the interactions between two like-charged polyions. It is shown that contrary to the previously established paradigm, a properly constructed mean-field theory can quantitatively account for the attractive interactions between two like-charged rods.

cond-mat.soft↗
arXiv1999

The nature of attraction between like charged rods

Comment on the paper of Ha and Liu (Phys. Rev. Lett. {\bf 79}, 1289 (1997)) regarding the nature of attraction between like charged rods. We demostrate that their results do not produce the correct low temperature limit.

cond-mat.soft↗
arXiv1999

Density-functional theory for attraction between like-charged plates

We study the interactions between two negatively charged macroscopic surfaces confining positive counterions. A density-functional approach is introduced which, besides the usual mean-field interactions, takes into account the correlations in the positions of counterions. The excess free energy is derived in the framework of the Debye-H{ü}ckel theory of the one-component plasma, with the homogeneous density replaced by a weighted density. The minimization of the total free energy yields the density profile of the microions. The pressure is calculated and compared with the simulations and the results derived from integral equations theories. We find that the interaction between the two plates becomes attractive when their separation distance is sufficiently small and the surface charge density is larger than a threshold value.

cond-mat.soft↗
arXiv1999

The one-component plasma: a conceptual approach

The one-component plasma (OCP) represents the simplest statistical mechanical model of a Coulomb system. For this reason, it has been extensively studied over the last forty years. The advent of the integral equations has resulted in a dramatic improvement in our ability to carry out numerical calculations, but came at the expense of a physical insight gained in a simpler analytic theory. In this paper we present an extension of the Debye-Hueckel (DH) theory to the OCP. The theory allows for analytic calculations of all the thermodynamic functions, as well as the structure factor. The theory explicitly satisfies the Stillinger-Lovett and, for small couplings, the compressibility sum rules, implying its internal self consistency.

cond-mat.soft↗
arXiv1999

Simple Model for Attraction between Like-Charged Polyions

We present a simple model for the possible mechanism of appearance of attraction between like charged polyions inside a polyelectrolyte solution. The attraction is found to be short ranged, and exists only in presence of multivalent counterions. The attraction is produced by the correlations in the condensed layers of counterions surrounding each polyion, and appears only if the number of condensed counterions exceeds the threshold, $ n > Z/2 α$, where $α$ is the valence of counterions and $Z$ is the polyion charge.

cond-mat.soft↗
arXiv1998

Polyelectrolyte Solutions with Multivalent Salts

We investigate the thermodynamic properties of a polyelectrolyte solution in a presence of {\it multivalent} salts. The polyions are modeled as rigid cylinders with the charge distributed uniformly along the major axis. The solution, besides the polyions, contain monovalent and divalent counterions as well as monovalent coions. The strong electrostatic attraction existing between the polyions and the counterions results in formation of clusters consisting of one polyion and a number of associated monovalent and divalent counterions. The theory presented in the paper allows us to explicitly construct the Helmholtz free energy of a polyelectrolyte solution. The characteristic cluster size, as well as any other thermodynamic property can then be determined by an appropriate operation on the free energy.

cond-mat↗
arXiv1998

Complex Formation Between Polyelectrolytes and Ionic Surfactants

The interaction between polyelectrolyte and ionic surfactant is of great importance in different areas of chemistry and biology. In this paper we present a theory of polyelectrolyte ionic-surfactant solutions. The new theory successfully explains the cooperative transition observed experimentally, in which the condensed counterions are replaced by ionic-surfactants. The transition is found to occur at surfactant densities much lower than those for a similar transition in non-ionic polymer-surfactant solutions. Possible application of DNA surfactant complex formation to polynucleotide delivery systems is also mentioned.

cond-mat↗
arXiv1998

Rod-like Polyelectrolytes in Presence of Monovalent Salt

We investigate the properties of rigid polyelectrolyte solutions in presence of monovalent salt. The free energy within the Debye-Hückel-Bjerrum (DHBj) theory [M. E. Fisher and Y. Levin, {\it Phys. Rev. Lett.} 71, 3826 (1993)] is constructed. It is found that at thermodynamic equilibrium the polyelectrolyte solution consists of clusters composed of one polyion and various counterions. The distribution of the cluster densities is determined by finding the minimum of the Helmholtz free energy. The osmotic pressure and the average charge of the cluster are found and their dependence on Manning parameter $ξ$ is elucidated. A good agreement with the experimental results is obtained.

cond-mat↗
arXiv1998

Kosterlitz-Thouless and Manning Condensation

A comparison between the Kosterlitz-Thouless theory of metal insulator transition in a two dimensional plasma and a counterion condensation in a polyelectrolyte solution is made. It is demonstrated that, unlike some of the recent suggestions, the counterion condensation and the Kosterlitz-Thouless transition are distinct.

cond-mat.soft↗
arXiv1998

When Do Like Charges Attract?

We study the interaction potential between two polyions inside a colloidal suspension. It is shown that at large separation the interaction potential is purely repulsive, with the induced attractive interactions being doubly screened. For short separations the condensed counterions become correlated, what leads to an effective attraction between the two macromolecules.

cond-mat.soft↗
arXiv1998

Donnan equilibrium and the osmotic pressure of charged colloidal lattices

We consider a system composed of a monodisperse charge-stabilized colloidal suspension in the presence of monovalent salt, separated from the pure electrolyte by a semipermeable membrane, which allows the crossing of solvent, counterions, and salt particles, but prevents the passage of polyions. The colloidal suspension, that is in a crystalline phase, is considered using a spherical Wigner-Seitz cell. After the Donnan equilibrium is achieved, there will be a difference in pressure between the two sides of the membrane. Using the functional density theory, we obtained the expression for the osmotic pressure as a function of the concentration of added salt, the colloidal volume fraction, and the size and charge of the colloidal particles. The results are compared with the experimental measurements for ordered polystyrene lattices of two different particle sizes over a range of ionic strengths and colloidal volume fractions.

cond-mat.soft↗
arXiv1998

Debye-Hueckel-Bjerrum theory for charged colloids

We formulate an extension of the Debye-Hueckel-Bjerrum theory [M. E. Fisher and Y. Levin, Phys. Rev. Lett. 71, 3826 (1993)] to the fluid state of a highly asymmetric charged colloid. Allowing for the formation of clusters consisting of one polyion and n condensed counterions, the total Helmholtz free energy of the colloidal suspension is constructed. The thermodynamic properties, such as the cluster-density distribution and the pressure, are obtained by the minimization of the free energy under the constraints of fixed number of polyions and counterions. In agreement with the current experimental and Monte Carlo results, no evidence of any phase transition is encountered.

cond-mat.soft↗
arXiv1998

Liquid-state theory of charged colloids

A simple theory of the fluid state of a charged colloidal suspension is proposed. The full free energy of a polyelectrolyte solution is calculated. It is found that the counterions condense onto the polyions forming clusters composed of one polyion and n counterions. The distribution of cluster sizes is determined explicitly. In agreement with the current experimental and Monte Carlo results, no liquid-gas phase separation was encountered.

cond-mat.soft↗
arXiv1997

Sine-Gordon mean field theory of a Coulomb Gas

Sine-Gordon field theory is used to investigate the phase diagram of a neutral Coulomb gas. A variational mean field free energy is constructed and the corresponding phase diagrams in two (2d) and three dimensions (3d) are obtained. When analyzed in terms of chemical potential, the Sine-Gordon theory predicts the phase diagram topologically identical with the Monte Carlo simulations and a recently developed Debye-Hückel-Bjerrum (DHBj) theory. In 2d we find that the infinite order Kosterlitz-Thouless line terminates in a tricritical point, after which the metal-insulator transition becomes first order. However, when the transformation from chemical potential to the density is made the whole of the insulating phase is mapped onto zero density.

cond-mat↗