1-D modeling of ion transport in rectangular nanofluidic channels

Based on the continuity hypothesis of fluid, 1-D mathematical models of ions’ transport in the rectangular nanofluidic channels are established by using the Poisson-Boltzmann (PB) equation and the modified Navier-Stokes (N-S) equations. The deduced equations are solved with MATLAB software. The results show that the distribution of the electric potential and the flow field could be predicted by the parameters, such as conductivity, surface charge density, solution concentration and channel height. The relationships between the parameters and the flow characteristics of the solution are also discussed. The research will help to the accurate manipulation of the solution in the nanofluidic channels.     

Surface-charge-governed electrolyte transport in carbon nanotubes

The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes(CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid–liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results,we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work.     

Self-energy-limited ion transport in subnanometer channels

The current-voltage characteristics of the alpha-Hemolysin protein pore during the passage of single-stranded DNA under varying ionic strength C are studied experimentally. We observe strong blockage of the current, weak superlinear growth of the current as a function of voltage, and a minimum of the current as a function of C. These observations are interpreted as the result of the ion electrostatic self-energy barrier originating from the large difference in the dielectric constants of water and the lipid bilayer. The dependence of DNA capture rate on C also agrees with our model.     

Conformation and dynamics of DNA confined in slitlike nanofluidic channels

Using laser fluorescence microscopy, we study the shape and dynamics of individual DNA molecules in slitlike nanochannels confined to a fraction of their bulk radius of gyration. With a confinement size spanning 2 orders of magnitude, we observe a transition from the de Gennes regime to the Odijk regime in the scaling of both the radius of gyration and the relaxation time. The radius of gyration and the relaxation time follow the predicted scaling in the de Gennes regime, while, unexpectedly, the relaxation time shows a sharp decrease in the Odijk regime. The radius of gyration remains constant in the Odijk regime. Additionally, we report the first measurements of the effect of confinement on the shape anisotropy.     

Visualization of conduction channels and the dynamics of ion transport in superionic conductors

A method for visualizing conduction channels is proposed. This method is based on graphical analysis of conduction channel fragments which belong to a Voronoi-Dirichlet elementary polyhedron and lie outside the rigid sphere centered at a fixed-sublattice ion that is located at the geometric center of the elementary polyhedron under consideration. Taking into account the weak nonrigidity of spheres and root-mean-square displacements of ions in the fixed sublattice makes it possible to construct a channel as the surface of the mobile ion density. The most probable regions of mobile ion motion are quantum-mechanically interpreted as channel walls, which is confirmed by constructing the equipotential surfaces of interionic potential for α-AgI. It is found that the Andersson mathematical dynamics and the dynamics of ion transport in AgI lead to the same pattern of the motion. The symmetry rules are used for predicting the directions of motion along the allowed vibrational coordinates of tetrahedral and octahedral α-CuI fragments.     

Diffusive transport in highly corrugated channels

Diffusion in waveguides with spatially modulated profiles is an important topic in modern electromagnetics and optics. Wave dynamics in the high-frequency asymptotics are governed by classical ray dynamics which can be characterised by looking at the diffusion of particles throughout the channel. We study the transport of particles (rays) in a channel with a sinusoidal profile at different values of the corrugation amplitude. We find that below a certain corrugation level the transport is ballistic, beyond this threshold, a diffusion-like behaviour emerges in the asymptotic limit of large times. In this regime particle transport slows down due to the trapping mechanism in the corrugated regions of the channel. We use the analogy with correlated random walks to discuss the observed transport regimes.     

Concerning contactless ion transmission in dielectric channels

The interaction between fast ions and the wall of a dielectric channel charged by randomly deposited ions of the flow was studied. It was shown that gradient forces repulsing ions from the wall caused by charge discreteness only arise when taking into consideration correlations in the relative position of the deposited charges.     

Fluoride ion transport in lead fluorothiocyanate

PbFCNS is found to be a F^? ion conducting solid of high room temperature conductivity (σ₃₀ ∽ 1.2 × 10^-4ω^-1cm^-1). The method of preparation and the conductivity properties of the material are described.     

Lithium ion transport in germanophosphate glasses

Glasses in the system Li₂O–GeO₂–P₂O₅ have been prepared using melt quenching route. Li⁺ ion transport has been investigated in these glasses using both d.c. and a.c. conductivity measurements. Arrhenius plots of d.c. conductivity exhibits two different slopes, which has been discussed in the light of cluster-tissue model. A.c. conductivity data has been fitted to single power law. Dielectric relaxation has been analyzed based on the behaviour of moduli. Good collapse on to master plots is observed for both a.c. conductivity and moduli. The behaviour of E_dc, s and β are found to be consistent when conductivity mechanism is considered as involving NBO–BO switching as the first step, which is followed by Li⁺ ion migration.     

Helium transport along lattice channels in crystalline quartz

The problem of He atom movement through channels of the quartz crystalline lattice is investigated. Providing the diameters of the atom and of the channel are of similar size the atom interacts with neighbor constituents of the wall. The conservation of momentum law in local form applied to the ‘helium-constituent’ interaction allows reduction of the problem to a one-dimensional one, which is similar to the movement of a dislocation in the Frenkel-Kontorova (FK) model. Within the framework of this model the activation energy for ‘helium+neighbor constituents’ is expressed by the shear modulus for the channel-forming material and the He polarizability. A metastable helium atom in the triplet state (2 ³S₁) is able to penetrate through the channel. In contrast, helium atoms in the singlet states, both ground state (1 ¹S₀) and metastable (2 ¹S₀), cannot penetrate.     

Potassium ion transport in potassium ferrocyanide tri-hydrate

K₄Fe(CN)₆ ? 3H₂O is found to be a K⁺ ion conductor. It is suggested that K⁺ mobility originates from formation of hydrogen bonded aggregates of H₂O molecules in the vicinity of K⁺ ions.     

Pump-free transport of magnetic particles in microfluidic channels

The use of magnetic particles in microfluidic devices offers new possibilities and a new degree of freedom to sequential synthesis and preparative or analytical procedures in very small volumes. In contrast to most of the traditional approaches where the liquid phase is flushed or pumped along a solid phase, the transport of magnetic particles through a microfluidic channel has the advantage of reduced reagent consumption and simpler, smaller systems. By lining up different reservoirs along the transport direction, reactions with different agents can be accomplished. Here, we present a pump and valve-free microfluidic particle transport system. By creating a simple and very effective layout of soft magnetic structures, which concentrate an external homogeneous magnetic field, a passive, thus easy to operate structure was generated. Most importantly, this layout is based on a simple tube by which fluidic and magnetic parts are separated. The tube itself is disposable and can be replaced prior to vital reactions, thus helping reduce sample cross-contaminations without affecting the particle transport properties. The layout of the device was thoroughly examined by a computer simulation of the particle trajectories, and the results were confirmed by experiments on a micro-machined demonstrator, which revealed an effective transport speed of up to 5 mm/s in 30 mT magnetic fields. Thus, we present a microfluidic transport device that combines the advantages of magnetic particles in microfluidic systems with a simple single-use technology for, e.g., bioanalytical purposes.     

Numerical modelling of ion transport in flames

This paper presents a modelling framework to compute the diffusivity and mobility of ions in flames. The (n, 6, 4) interaction potential is adopted to model collisions between neutral and charged species. All required parameters in the potential are related to the polarizability of the species pair via semi-empirical formulas, which are derived using the most recently published data or best estimates. The resulting framework permits computation of the transport coefficients of any ion found in a hydrocarbon flame. The accuracy of the proposed method is evaluated by comparing its predictions with experimental data on the mobility of selected ions in single-component neutral gases. Based on this analysis, the value of a model constant available in the literature is modified in order to improve the model's predictions. The newly determined ion transport coefficients are used as part of a previously developed numerical approach to compute the distribution of charged species in a freely propagating premixed lean CH₄/O₂ flame. Since a significant scatter of polarizability data exists in the literature, the effects of changes in polarizability on ion transport properties and the spatial distribution of ions in flames are explored. Our analysis shows that changes in polarizability propagate with decreasing effect from binary transport coefficients to species number densities. We conclude that the chosen polarizability value has a limited effect on the ion distribution in freely propagating flames. We expect that the modelling framework proposed here will benefit future efforts in modelling the effect of external voltages on flames. Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/13647830.2015.1090018.     

Subunit modification and association in VR1 ion channels

Background  

The capsaicin (vanilloid) receptor, VR1, is an agonist-activated ion channel expressed by sensory neurons that serves as a detector of chemical and thermal noxious stimuli.     

Statistical model of current-coupled ion channels in nerve membranes

A statistical model of a driven system is developed. Its microscopic elements are the ion channels through a nerve membrane. Their conductances are stochastically switching under the competing influences of thermal noise and local membrane voltage. A current flow through the membrane induces a coupling between the channels via the electrolytes surrounding the membrane. The long range of the coupling permits a generalized mean field theory for the stationary membrane current as a function of the applied electrode voltage. We derive analytically the macroscopic conductance-voltage-temperature relation for the spatially uniform current state. It shows analogues of first and second order phase transitions. The critical temperature diverges at a finite coupling strength. The theory fits sodium conductance characteristics measured on nerve axon membranes from various species by a variation of only the coupling strength. This supports the hypothesis that this simplest possible model for sodium channels is universal for all species.The work of this author was partially supported by the Deutsche Forschungsgemeinschaft     

Streaming currents in a single nanofluidic channel

We report measurements of the streaming current, an electrical current generated by a pressure-driven liquid flow, in individual rectangular silica nanochannels down to 70 nm in height. The streaming current is observed to be proportional to the pressure gradient and increases with the channel height. As a function of salt concentration, it is approximately constant below approximately 10 mM, whereas it strongly decreases at higher salt. Changing the sign of the surface charge is found to reverse the streaming current. The data are best modeled using a nonlinear Poisson-Boltzmann theory that includes the salt-dependent hydration state of the silica surface.     

Maximum-entropy states for magnetized ion transport

For a plasma with fixed total energy, number of particles, and momentum, the distribution function that maximizes entropy is a Boltzmann distribution. If, in addition, the rearrangement of charge is constrained, as happens on ion-ion collisional timescales for cross-field multiple-species transport, the maximum-entropy state is instead given by the classic impurity pinch relation. The maximum-entropy derivation, unlike previous approaches, does not rely on the details of the collision operator or the dynamics of the system, only on the presence of certain conservation properties.