The many origins of charge inversion in electrolyte solutions: effects of discrete interfacial charges

We show that charge inversion, i.e. interfacial charges attracting counterions in excess of their own nominal charge, is a general effect that takes place in most charged systems next to aqueous solutions with multivalent ions and identify three different electrostatic origins for this effect 1) counterion-counterion correlations, 2) correlations between counterions and interfacial charges and 3) complexation. We briefly describe the first two regimes and provide a detailed characterization of the complexation regime from united atom molecular dynamics simulation of a phospholipid domain in contact with an aqueous solution. We examine the expected conditions where each regime should apply and describe a representative experimental example to illustrate each case. We point out that our results provide a characterization of ionic distributions irrespectively of whether charge inversion takes place and show that processes such as proton release and transfer are also linked to ionic correlations. We conclude with a discussion of further experimental and theoretical implications.Comment: 22 pages, 7 figure

Micellar Crystals in Solution from Molecular Dynamics Simulations

Polymers with both soluble and insoluble blocks typically self-assemble into micelles, aggregates of a finite number of polymers where the soluble blocks shield the insoluble ones from contact with the solvent. Upon increasing concentration, these micelles often form gels that exhibit crystalline order in many systems. In this paper, we present a study of both the dynamics and the equilibrium properties of micellar crystals of triblock polymers using molecular dynamics simulations. Our results show that equilibration of single micelle degrees of freedom and crystal formation occurs by polymer transfer between micelles, a process that is described by transition state theory. Near the disorder (or melting) transition, bcc lattices are favored for all triblocks studied. Lattices with fcc ordering are also found, but only at lower kinetic temperatures and for triblocks with short hydrophilic blocks. Our results lead to a number of theoretical considerations and suggest a range of implications to experimental systems with a particular emphasis on Pluronic polymers.Comment: 12 pages, 11 figures. Note that some figures are extremely low quality to meet arXiv's file size limit

Ground state structure and interactions between dimeric 2D Wigner crystals

We study the ground state ordering and interactions between two two-dimensional Wigner crystals on neutralizing charged plates by means of computer simulation. We consider crystals formed by (i) point-like charges and (ii) charged dimers, which mimic the screening of charged surfaces by elongated multivalent ions such as aspherical globular proteins, charged dendrimers or short stiff polyelectrolytes. Both systems, with point-like and dimeric ions, display five distinct crystalline phases on increasing the interlayer distance. In addition to alteration of translational ordering within the bilayer, the phase transitions in the dimeric system are characterized by alteration of orientational ordering of the ions.Comment: Revised versio

Properties of Quantum Hall Skyrmions from Anomalies

It is well known that the Fractional Quantum Hall Effect (FQHE) may be effectively represented by a Chern-Simons theory. In order to incorporate QH Skyrmions, we couple this theory to the topological spin current, and include the Hopf term. The cancellation of anomalies for chiral edge states, and the proviso that Skyrmions may be created and destroyed at the edge, fixes the coefficients of these new terms. Consequently, the charge and the spin of the Skyrmion are uniquely determined. For those two quantities we find the values $e\nu N_{Sky}$ and $\nu N_{Sky}/2$, respectively, where $e$ is electron charge, $\nu$ is the filling fraction and $N_{Sky}$ is the Skyrmion winding number. We also add terms to the action so that the classical spin fluctuations in the bulk satisfy the standard equations of a ferromagnet, with spin waves that propagate with the classical drift velocity of the electron.Comment: 8 pages, LaTeX file; Some remarks are included to clarify the physical results obtained, and the role of the Landau-Lifshitz equation is emphasized. Some references adde

The Phase Diagram of the U(2)×U(2)U(2)\times U(2) Sigma Model

We study the phase diagram of the $U(2) \times U(2)$ scalar model in $d=4$ dimensions. We find that the phase transition is of first order in most of the parameter space. The theory can still be relevant to continuum physics (as an effective theory) provided the transition is sufficiently weakly first order. This places restrictions on the allowed coupling constants.Comment: 3 pages (Latex), 2 eps figures, uses espcrc2.sty, epsf, talk given at LATTICE9