arXiv subjects

Nir Gavish

Publications and source records attributed to Nir Gavish.

24 records · Page 2Linked to original sources

arXiv2017

Mean field approach to first and second order phase transitions in ionic liquids

Ionic liquids are solvent-free electrolytes, some of which possess an intriguing self-assembly property. Using a mean-field framework (based on Onsager's relations) we show that bulk nano-structures arise via type-I and II phase transitions (PT), which directly affect the electrical double layer (EDL) structure. Ginzburg-Landau equation is derived and PT are related to temperature, potential and interactions. The type-I PT occurs for geometrically dissimilar anion/cation ratio and, surprisingly, is induced by perturbations on order of thermal fluctuations. Finally, we compare the insights with the decaying charge layers within the EDL, as widely observed in experiments.

cond-mat.soft↗

arXiv2016

Spatially localized self-assembly driven by electrically charged phase separation

Self-assembly driven by phase separation coupled to Coulombic interactions is fundamental to a wide range of applications, examples of which include soft matter lithography via di-block copolymers, membrane design using polyelectrolytes, and renewable energy applications based on complex nano-materials, such as ionic liquids. The most common mean field framework for these problems is the non-local Cahn-Hilliard (a.k.a. Ohta-Kawasaki) framework. In this work, we study the emergence of spatially localized states in both the classical and the extended Ohta-Kawasaki model. The latter also accounts for: (i) asymmetries in long-range Coulomb interactions that are manifested by differences in the dielectric response, and (ii) asymmetric short-range interactions that correspond to differences in the chemical potential between two materials phases. It is shown that in one space dimension (1D) there is a multiplicity of coexisting localized solutions, which organize in the homoclinic snaking structure, bearing similarity to dissipative systems. In addition, an analysis of 2D extension is performed and distinct instability mechanisms (related to extended and localized modes) of localized stripes are discussed with respect to model parameters and domain size. Finally, implications to localized hexagonal patterns are also made. The insights provide an efficient mechanistic framework to design and control localized self-assembly that might be a plausible strategy for low cost of nano electronic applications, i.e., a rather simple nano scale fabrication of isolated morphologies.

math.AP↗

arXiv2016

Dependence of the dielectric constant of electrolyte solutions on ionic concentration - a microfield approach

We present a novel microfield approach for studying the dependence of the orientational polarization of the water in aqueous electrolyte solutions upon the salt concentration and temperature. The model takes into account the orientation of the solvent dipoles due to the electric field created by ions, and the effect of thermal fluctuations. The model predicts a dielectric functional dependence of the form $\varepsilon(c)=\varepsilon_w-βL(3αc/β),\quadβ=\varepsilon_w-\varepsilon_{\rm ms}$, where $L$ is the Langevin function, $c$ is the salt concentration, $\varepsilon_w$ is the dielectric of pure water, $\varepsilon_{\rm ms}$ is the dielectric of the electrolyte solution at the molten salt limit, and $α$ is the total excess polarization of the ions. The functional form gives a remarkably accurate description of the dielectric constant for a variety of salts and a wide range of concentrations.

physics.chem-ph↗

arXiv2015

Theory of phase separation and polarization for dissociated ionic liquids

Room temperature ionic liquids are attractive to numerous applications and particularly, to renewable energy devices. As solvent free electrolytes, they demonstrate a paramount connection between the material morphology and Coulombic interactions: unlike dilute electrolytes, the electrode/RTIL interface is a product of both electrode polarization and spatiotemporal bulk properties. Yet, theoretical studies have dealt almost exclusively with independent models of morphology and electrokinetics. In this work, we develop a novel Cahn-Hilliard-Poisson type mean-field framework that couples morphological evolution with electrokinetic phenomena. Linear analysis of the model shows that spatially periodic patterns form via a finite wavenumber instability, a property that cannot arise in the currently used Fermi-Poisson-Nernst-Planck equations. Numerical simulations in above one-space dimension, demonstrate that while labyrinthine type patterns develop in the bulk, stripe patterns emerge near charged surfaces. The results qualitatively agree with empirical observations and thus, provide a physically consistent methodology to incorporate phase separation properties into an electrochemical framework.

physics.chem-ph↗

arXiv2009

Singular standing-ring solutions of nonlinear partial differential equations

We present a general framework for constructing singular solutions of nonlinear evolution equations that become singular on a d-dimensional sphere, where d>1. The asymptotic profile and blowup rate of these solutions are the same as those of solutions of the corresponding one-dimensional equation that become singular at a point. We provide a detailed numerical investigation of these new singular solutions for the following equations: The nonlinear Schrodinger equation, the biharmonic nonlinear Schrodinger equation, the nonlinear heat equation and the nonlinear biharmonic heat equation.

math.AP↗

arXiv2008

Critical power of collapsing vortices

We calculate the critical power for collapse of linearly-polarized phase vortices, and show that this expression is more accurate than previous results. Unlike the non-vortex case, deviations from radial symmetry do not increase the critical power for collapse, but rather lead to disintegration into collapsing non-vortex filaments. The cases of circular, radial and azimuthal polarizations are also considered.

physics.optics↗