•Structural transition in the EDL of a model RTIL is revealed by MD simulation study.•Structure of the EDL in RTIL can vary between multiple layers and a single monolayer.•An ordered monolayer of ...counter-ions is formed at certain surface charge densities.•The monolayer coexists with apparently non-structured RTIL further in the electrode.
We have studied structural transitions in the electrical double layer of ionic liquids by molecular dynamics simulations. A model coarse grained room temperature ionic liquid (RTIL) with asymmetric sized ions confined between two oppositely charged walls has been used. The simulations have been performed at different temperatures and electrode charge density values. We found that for the studied charge densities the electrical double layer has a multilayered structure with multiple alternating layers of counter- and co-ions at the electrode–RTIL interface; however, at certain charge densities the alternating multilayer structure of the electrical double layer undergoes a structural transition to a surface-frozen monolayer of densely packed counter-ions (Moiré-like structure). At this point the dense ordered monolayer of counter-ions close to the electrode surface coexists with apparently non-structured RTIL further from the electrode. These findings might bring possible explanations to experimental observations of formation of Moiré-like structures in ionic liquids at electrified interfaces. Moreover, we report the formation of herring-bone interfacial structures at high surface charge densities, that appear as a result of superposition of two ordered monolayers of RTIL ions at the electrode–RTIL interface. Similar structures were observed experimentally; however, to the best of our knowledge they have not been modelled by simulations. We discuss the dependence of the electrical double layer structure in RTILs on the ion size and the surface charge density at the electrodes.
Monte Carlo simulations of a model ionic liquid show that if ions have charged heads and neutral counterparts, the latter give rise to the camel shape of the voltage dependence of the double layer ...capacitance. Neutral ‘tails’ of ions play the role of latent voids that can be replaced by charged groups via rotations and translations of ions. This provides extra degrees of freedom for the field-induced charge rearrangements in the double layer which results in the peculiar double-hump capacitance profile.
We investigate the basic mechanisms of the electrical double layer formation in ionic liquids near a flat charged wall, by performing Monte Carlo simulations of several model liquids with spherical ...and elongated ions that contain charged ‘heads’ and neutral ‘tails’. We analyze the structural transitions in response to the variation of the voltage across the double layer and their effects on the formation of the characteristic ‘camel shape’ capacitance recently observed in experiments
1,2. The camel shape was predicted earlier by the mean-field theory
3 for the case of an ionic liquid with large percentage of voids which allowed for substantial ‘electrostriction’ and thereby increase of the local charge density in the double layer. However, we show that in contrast to a liquid composed of spherical ions, in a liquid with anisotropic ions the double-hump ‘camel shape’ of the capacitance curve does not require high compressibility of the liquid. Many ionic liquids have elongated shape of ions, with charged ‘heads’ and neutral ‘tails’. We show that these neutral tails play a role of space fillers, or ‘latent voids’ that can be replaced by charged groups, following rotations and translations of ions. This feature allows an electric field-induced increase of the counter charge density without a substantial compression of the liquid. It causes rising branches of capacitance at
small positive and negative electrode polarizations. However, we show that at
large positive and negative voltages it has to be inevitably replaced by the ‘lattice saturation’, a universal effect, which does not depend on the model, in which the capacitance decreases inversely proportional to the square root of the voltage. This conclusion is supported by our analysis of the experimental results of Lockett et al. (2008)
1 that appear to follow this law staring from the potentials ∼±0.7–0.9
V. The competition between the two trends, one prevailing at low voltages and the other one at high voltages, results in the camel shape of capacitance, seen in our simulations.
In this paper we present a unified view on charge-driven structural transitions in the electrical double layer in ionic liquids and summarise molecular-scale mechanisms of the ionic liquid structural ...response to the surface charge.
•unified view on charge‐driven structural transitions in the electrical double layer in ionic liquids•molecular-scale mechanisms of the ionic liquid structural response to the surface charge•general classification of interfacial structures in ionic liquids
For interpretation of electroencephalography (EEG) and magnetoencephalography (MEG) data, multiple solutions of the respective forward problems are needed. In this paper, we assess performance of the ...mixed-hybrid finite element method (MHFEM) applied to EEG and MEG modeling. The method provides an approximate potential and induced currents and results in a system with a positive semi-definite matrix. The system thus can be solved with a variety of standard methods (e.g. the preconditioned conjugate gradient method). The induced currents satisfy discrete charge conservation law making the method conservative. We studied its performance on unstructured tetrahedral grids for a layered spherical head model as well as a realistic head model. We also compared its accuracy versus the conventional nodal finite element method (<inline-formula> <tex-math notation="LaTeX">{P}_{1} </tex-math></inline-formula> FEM). To avoid modeling singular sources, we completed our computations with a subtraction approach; the derived expression for the MEG response different from earlier published and involves integration of finite quantities only. We conclude that although the MHFEM is more computationally demanding than the <inline-formula> <tex-math notation="LaTeX">{P}_{1} </tex-math></inline-formula> FEM, its use is justified for EEG and MEG modeling on low-resolution head models where <inline-formula> <tex-math notation="LaTeX">{P}_{1} </tex-math></inline-formula> FEM loses accuracy.
The article analyses the challenges associated with the development of rural areas in the Kaliningrad region. The author analyses trends in the development of agriculture, population dynamics, and ...settlement patterns, while also exploring their interconnectedness and external impacts. The research draws upon comparative-geographical, economic-statistical, and cartographic analyses utilizing official statistical data. The study reveals that since the early 2000s, agricultural production in the Kaliningrad region has been outpacing the national average growth rate. This is primarily attributed to the advancement of larger organisations, while the growth rates of household and small-scale farms remain comparatively low. This development trend is underpinned by a surge in labour productivity accompanied by a substantial reduction in the workforce. Consequently, rural residents are increasingly seeking alternative employment opportunities, either moving to urban areas or engaging in a different type of economic activities. Contrary to the situation in most regions of the Russian Federation, the rural population of the Kaliningrad region is growing. This growth is facilitated by an influx of individuals from other parts of Russia and other countries. Following the polarisation theory, population growth is driven by municipalities in the western part of the oblast, while eastern rural territories are losing population due to both natural decline (common to the oblast as a whole) and migration. Eastern municipalities have the demographic potential to increase the working-age population, while the western part of the oblast does not. The region has been implementing a policy of support for rural territories, especially for the peripheral eastern municipalities. However, there is a need for the policy to be further reinforced, alongside the development of a comprehensive spatial development strategy for the region. The article outlines proposals in this regard.
We have investigated the screening of solute ion–electrode interactions in two ionic liquids (1-butyl 3-methylimidazolium tetrafluoroborate BMImBF4 and 1,3-dimethylimidazolium chloride MMImCl) by ...constructing free energy profiles for dissolved charged probes as a function of distance from a charged surface (graphene). The free energy profiles for three types of mutual interactions (surface and solute with opposite charges, solute and uncharged surface, and surface and solute with the same charges) differ from each other, but are remarkably similar in the two ionic liquids. They all show oscillations rather than the monotonic behavior predicted by Debye-type screening models. In both ionic liquids, there are high barriers impeding the motion of charged probes to the oppositely charged surface. We examined the local liquid structure around the probes and found that the free energy minima correspond to positions in which the solvation layers induced by the surface charge and the solvation shells around the probes enhance each other while barriers occur where they perturb each other.
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