27 research outputs found
Overscreening in 1D lattice Coulomb gas model of ionic liquids
Overscreening in the charge distribution of ionic liquids at electrified
interfaces is shown to proceed from purely electrostatic and steric
interactions in an exactly soluble one dimensional lattice Coulomb gas model.
Being not a mean-field effect, our results suggest that even in higher
dimensional systems the overscreening could be accounted for by a more accurate
treatment of the basic lattice Coulomb gas model, that goes beyond the mean
field level of approximation, without any additional interactions.Comment: 4 pages 5 .eps figure
Drag forces on inclusions in classical fields with dissipative dynamics
We study the drag force on uniformly moving inclusions which interact
linearly with dynamical free field theories commonly used to study soft
condensed matter systems. Drag forces are shown to be nonlinear functions of
the inclusion velocity and depend strongly on the field dynamics. The general
results obtained can be used to explain drag forces in Ising systems and also
predict the existence of drag forces on proteins in membranes due to couplings
to various physical parameters of the membrane such as composition, phase and
height fluctuations.Comment: 14 pages, 7 figure
Out of equilibrium thermal Casimir effect in a model polarizable material
Relaxation of the thermal Casimir or van der Waals force for a model
dielectric medium is investigated. We start with a model of interacting
polarization fields with a dynamics that leads to a frequency dependent
dielectric constant of the Debye form. In the static limit the usual zero
frequency Matsubara mode component of the Casimir force is recovered. We then
consider the out of equilibrium relaxation of the van der Waals force to its
equilibrium value when two initially uncorrelated dielectric bodies are brought
into sudden proximity. It is found that the spatial dependence of the out of
equilibrium force is the same as the equilibrium one but it has a time
dependent amplitude, or Hamaker coefficient, which increases in time to its
equilibrium value. The final relaxation to the equilibrium value is exponential
in systems with a single or finite number of polarization field relaxation
times. However, in systems, such as those described by the Havriliak-Negami
dielectric constant, with a broad distribution of relaxation times, we observe
a much slower power law decay to the equilibrium value.Comment: 15 pages RevTex, 4 figure
Mean first-passage times of non-Markovian random walkers in confinement
The first-passage time (FPT), defined as the time a random walker takes to
reach a target point in a confining domain, is a key quantity in the theory of
stochastic processes. Its importance comes from its crucial role to quantify
the efficiency of processes as varied as diffusion-limited reactions, target
search processes or spreading of diseases. Most methods to determine the FPT
properties in confined domains have been limited to Markovian (memoryless)
processes. However, as soon as the random walker interacts with its
environment, memory effects can not be neglected. Examples of non Markovian
dynamics include single-file diffusion in narrow channels or the motion of a
tracer particle either attached to a polymeric chain or diffusing in simple or
complex fluids such as nematics \cite{turiv2013effect}, dense soft colloids or
viscoelastic solution. Here, we introduce an analytical approach to calculate,
in the limit of a large confining volume, the mean FPT of a Gaussian
non-Markovian random walker to a target point. The non-Markovian features of
the dynamics are encompassed by determining the statistical properties of the
trajectory of the random walker in the future of the first-passage event, which
are shown to govern the FPT kinetics.This analysis is applicable to a broad
range of stochastic processes, possibly correlated at long-times. Our
theoretical predictions are confirmed by numerical simulations for several
examples of non-Markovian processes including the emblematic case of the
Fractional Brownian Motion in one or higher dimensions. These results show, on
the basis of Gaussian processes, the importance of memory effects in
first-passage statistics of non-Markovian random walkers in confinement.Comment: Submitted version. Supplementary Information can be found on the
Nature website :
http://www.nature.com/nature/journal/v534/n7607/full/nature18272.htm
Ionic liquids at electrified interfaces
Until recently, âroom-temperatureâ (<100â150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)â(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of âfirst-generationâ room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the âlater generationâ RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in âcocktailsâ of oneâs choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost âuniversalâ solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) âsister-systemsâ.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules
Phase diagram of a bulk 1d lattice Coulomb gas
The exact solution, via transfer matrix, of the simple one dimensional lattice Coulomb gas (1d LCG) model can reproduce peculiar features of ionic liquid capacitors, such as overscreening, layering, and camel- and bell-shaped capacitance curves. Using the same transfer matrix method, we now compute the bulk properties of the 1d LCG in the constant voltage ensemble. We unveil a phase diagram with rich structure exhibiting a low density disordered and high density ordered phases, separated by a first order phase transition at low temperature; the solid state at full packing can be ordered or not, depending on the temperature. This phase diagram, which is strikingly similar to its three dimensional counterpart, also sheds light on the behaviour of the confined system