Initial Charge Density Research Articles

First principle study of the origin of the large orbital magnetic moment in α − CoV2O6

The electronic structure of the CoV2O6 magnetic oxide is investigated using first principle density functional theory calculations with the full potential linearized augmented plane wave method. The spin–orbit coupling (SOC) and the GGA+U functional are included in order to determine the orbital magnetic moment (OMM) for the monoclinic C2/m (or α phase) structure where, experimentally, the ground state is found insulating with a large magnetic moment perpendicular to the chains direction in an antiferromagnetic configuration. It is exhibited, that the perturbation approach of the SOC gives only small OMM values but large ones can be obtained when special initial charge densities are used. An OMM as large as 1.5 μB in the direction of the octahedron axis perpendicular to the chains is obtained in agreement with the experiment. The electronic structure analysis shows that this large OMM results from the occurrence of a (zx,yz) hybridized state.

Charge of water droplets in non-polar oils

Recent advances in droplet manipulation methods by electric fields and signals require a deeper understanding of water droplet charge. In this paper, we have investigated the electrophoretic motion of individual water microdroplets injected into non-polar silicone and paraffin oil by video optical microscopy on an individual droplet basis to determine droplet charge. It was found that the initial surface charge density of surfactant free droplets directly after injection from a micropipette is positive and of the order of 10−6 C/m2, regardless of pH and ion concentration in the range from pH 4 to pH 10 and from 0.01 mmol/l to 1.5 mol/l, respectively. The experimental results together with molecular dynamics simulations show that the nature and polarity of the charge can be explained by anisotropic orientation of water molecules at the interface rather than selective adsorption of ions. Furthermore, we showed that slip at the liquid-liquid boundary must be taken into account when interpreting electrophoretic measurements of droplets.

Exact solution in the form of a shock wave for the Maxwell and gravitomagnetism equations

Over the last halfcentury , much attention in vari� ous fields of mathematical and theoretical physics (1-3) and in applied mathematics (4-7) has been given to approaches providing mathematically rigor� ous results, namely, to the search for exactly solvable models and to rigorous formulations of the original equations of such models as based on fundamental principles. In this work, the method of characteristics is used to construct exact solutions of model problems described by the Maxwell and gravitomagnetism equa� tions for the evolution of the charge or mass density function in spherical or infinite cylindrical domains. The initial charge or mass density distribution in such a domain is radially symmetric, i.e., depends only the radius . In the case of an inhomogeneous initial charge or mass density distribution, we show the existence of a shock wave solution ( Ψ�effect).

Encapsulation and surface charge manipulation of organic and inorganic colloidal substrates by multilayered polyelectrolyte films

Employing layer-by-layer (LbL) technique we could encapsulate both organic and inorganic nano- and microparticulate substrates by multilayer polyelectrolyte films of variable thicknesses. It has been observed that the uniformity of the polyelectrolyte multilayer does not depend severely on the chemical nature of particulate substrate; rather it depends on the initial surface charge density or ζ-potential of their bare surface. Higher ζ-potential of organic albumin nanoparticles helps to keep the polyelectrolyte chains unfolded. On the other hand, a lower ζ-potential of inorganic microparticles such as SiO2 induces a folding of dangling polyelectrolyte chains, forming domains of their aggregates or complexes at the particle surface, making the encapsulating multilayer inhomogeneous.

Coulomb explosion at low and high ion velocities

The ion-induced electric field is calculated for estimating the effect of the Coulomb explosion (CE) mechanism. The increase of the kinetic energy of lattice ions in the electric field of the track core is Δε∝(q(0))4, where q(r) is the induced initial charge density. Estimates are made for the irradiation of SiO2 by 2MeV/nucleon Kr beam: the mean energy of lattice ions reaches 8.1eV within 4fs in the track core. The Lorentzian and Gaussian charge density distributions lead to similar results. The type of solids affects Δε through the charge neutralization time. As a result of the decrease of q(0), Δε is reduced by about an order of magnitude in the range 2–8MeV/nucleon. The projectile velocity may affect the formation of ion-induced tracks by the CE mechanism.

Uranyl Adsorption at the Muscovite (Mica)/Water Interface Studied by Second Harmonic Generation

Uranyl adsorption at the muscovite (mica)/water interface was studied by second harmonic generation (SHG). Using the nonresonant χ(3) technique and the Gouy-Chapman model, the initial surface charge density of the mica surface was determined to be -0.022(1) C/m(2) at pH 6 and in the presence of dissolved carbonate. Under these same conditions, uranyl adsorption isotherms collected using nonresonant χ(3) experiments and resonantly enhanced SHG experiments that probe the ligand-to-metal charge transfer bands of the uranyl cation yielded a uranyl binding constant of 3(1) × 10(7) M(-1), corresponding to a Gibbs free energy of adsorption of -52.6(8) kJ/mol, and a maximum surface charge density at monolayer uranyl coverage of 0.028(3) C/m(2). These results suggest favorable adsorption of uranyl ions to the mica interface through strong ion-dipole or hydrogen interactions, with a 1:1 uranyl ion to surface site ratio that is indicative of monovalent cations ((UO(2))(3)(OH)(5)(+), (UO(2))(4)(OH)(7)(+), UO(2)OH(+), UO(2)Cl(+), UO(2)(CH(3)COO(-))(+)) binding at the interface, in addition to neutral uranyl species (UO(2)(OH)(2) and UO(2)CO(3)). This work provides benchmark measurements to be used in the improvement of contaminant transport modeling.

Enhanced electret charge stability on polyethylene films treated with titanium-tetrachloride vapor

Low-density polyethylene (LDPE) films have been treated with titanium-tetrachloride vapor by means of the molecular-layer-deposition method. It is shown that such a treatment leads to a considerable improvement of the electret properties for both positively and negatively charged films. The temperature stability of the electret homo-charge has been increased by approximately 60°C. At the same time, the temporal stability of charge is also considerably improved. Modified low-density polyethylene films show no “cross-over phenomenon” when charged to higher voltages. Thus, it is now possible to produce electrets from polyethylene films with high initial charge densities, but without a strongly reduced charge stability. The influence of a chemical treatment with titanium-tetrachloride vapor on charge injection from aluminum electrodes into polyethylene films was also investigated. It is found that the interface between an aluminum electrode and a modified LDPE surface layer has different injection properties for positive and negative charges. Electrons can be injected across the modified interface, whereas injection of holes is either very limited or non-existent.

Semi-Analytical Model of Charge Image Formation in Electrophotography

High resolution latent image formation is an important step in electrophotography to achieve high quality prints. Presently, analytical models exist for the other important steps: photoconductor charging, development (both single and dual component), and transfer. We present here an analytical model of charge image generation on the surface of an organic photoconductor due to laser exposure. The inputs to the model include laser intensity profile as a function of time, quantum efficiency of the charge generation layer, hole mobility of the charge transport layer, and initial charge density on the surface of the PC. The output of the model is the PC surface charge map as it evolves in time, which is a key input to the toner development process in electrophotography.

Flocculation performance of a cationic biopolymer derived from a cellulosic source in mild aqueous solution

The flocculation behavior of cationic, quaternary ammonium groups containing cellulosic biopolymers, CDACs, synthesized by cationizing dialdehyde cellulose in mild aqueous solution was studied in a kaolin suspension. In particular, the role of CDAC dosage and solution pH, NaCl concentration, and temperature were clarified. In addition, the initial apparent charge densities (CDs), particle sizes, ζ-potential, and stability of CDs were determined. CDACs possessed a high flocculation activity in neutral and acidic solutions, but a significant decrease was observed in alkaline solutions (pH >9). This was also seen as a decline in the apparent CD and particle size of the CDACs in alkaline conditions. The measurements also indicated that the apparent CD decreased to a constant level of 3mmol/g in aqueous solutions. However, no notable decrease in flocculation performance was obtained after several days of storage. Moreover, the variation of NaCl concentration and temperature did not affect the flocculation activity.

COMPARISON OF ELECTRODE PROPERTIES OF BINARY, TERNARY AND QUATERNARY NANOCRYSTALLINE Mg2Ni-BASED POWDERS

The present investigation is focused on the electrode properties of various nanocrystalline Mg2Ni -based powders synthesized using high energy ball milling technique. The chemical composition was modified by the ternary (Nb) and quaternary ( Al and Nb ) additives. The process parameters were adjusted to achieve nanocrystalline based products. Characterization of the ternary and quaternary milled products using scanning and transmission electron microscopy and X-ray diffraction showed a composite microstructure of an amorphous core surrounded by nanocrystalline Mg2Ni . Electrode made from the quaternary milled product showed superior initial charge density and longer discharge duration.

Research on Polypropylene Electret Melt-Blown Nonwoven Doped with Nano-Tourmaline

Electret filter composed of permanently charged electret fibers is a good material for environmental protection. A novel kind of electret melt-blown nonwovens (EMNs) doped with nano-tourmaline was developed by corona charging in this paper. The structure of web, mechanical properties, surface charge density and filtration efficiency of samples were discussed. The results showed that the structure of EMNs became loose and the initial surface charge density was increased markedly. Furthermore, the EMNs exhibited higher filtration efficiency and lower pressure drop, especially the content of nano-tourmaline was about 6 wt. %.

Influence of nitrogen dose on the charge density of nitrogen-implanted buried oxide in SOI wafers

To harden silicon-on-insulator (SOI) wafers fabricated using separation by implanted oxygen (SIMOX) to total-dose irradiation, the technique of nitrogen implantation into the buried oxide (BOX) layer of SIMOX wafers can be used. However, in this work, it has been found that all the nitrogen-implanted BOX layers reveal greater initial positive charge densities, which increased with increasing nitrogen implantation dose. Also, the results indicate that excessively large nitrogen implantation dose reduced the radiation tolerance of BOX for its high initial positive charge density. The bigger initial positive charge densities can be ascribed to the accumulation of implanted nitrogen near the Si-BOX interface after annealing. On the other hand, in our work, it has also been observed that, unlike nitrogen-implanted BOX, all the fluorine-implanted BOX layers show a negative charge density. To obtain the initial charge densities of the BOX layers, the tested samples were fabricated with a metal-BOX-silicon (MBS) structure based on SIMOX wafers for high-frequency capacitance–voltage (C–V) analysis.

Multiphysics Modeling of Electrochemomechanically Smart Microgels Responsive to Coupled pH/Electric Stimuli

A multiphysics model is developed to simulate the responsive behavior of smart pH-/electric-sensitive hydrogels when immersed into pH buffer solution and subjected to an externally applied electric field, which is termed the MECpHe model. Comparison with experimental data shows the MECpHe model to be accurate and stable. The influence of the externally applied electric voltage is discussed with respect to the distribution of diffusive ionic species and the displacement of the hydrogel strip. The influences of initial charge density and ionic strength on the swelling ratio and the bending deformation of the microgel strip are studied.

Charge trapping behavior of SiO 2-Anodic Al 2O 3–SiO 2 gate dielectrics for nonvolatile memory applications

In this study, Anodic Aluminum Oxide (AAO) is used as the storage layer instead of silicon nitride in a silicon–SiO 2–Si 3N 4–SiO 2–Silcon (SONOS) structure in flash memory devices and a double I– V method is utilized to investigate its charge trapping behavior on SiO 2–Al 2O 3–SiO 2 (OAO) triple stacks. The experimental results show that more initial charge density can be charged into the centroids of neutral charge trapping sites using post deposition annealing (PDA) treatment in OAO triple stacks. Under stress bias testing, OAO triple stacks exhibit a larger shift of threshold voltage than do ONO type devices. The trap energy levels of the bulk electron traps in high k AAO materials were determined. The initial trapping charges are produced during the fabrication process and are changed into centroids of neutral charge trapping sites after PDA treatment, which are responsible for charge trapping/de-trapping during programming/erasing. All devices show that the trapping centroid moves to the top oxide with an increase of stress time.

Computational analysis of the influence of initial fixed charge density on pH-sensitive hydrogels

In this paper, we conduct a computational analysis of the effects of initial fixed charge density on the responsive performance of pH-sensitive hydrogels to environmental change in solution pH. The analysis is based on a chemo-electro-mechanical formulation previously termed the multi-effect-coupling pH-stimulus (MECpH) model. In this work, we improve the MECpH model by incorporating the finite deformation formulation into the mechanical equilibrium equation. The present model consisting of coupled nonlinear partial differential equations is solved via a meshless numerical technique called the Hermite-cloud method with the modified Newton iteration methodology. After validation of the MECpH model by comparing the computational results with experimental data available in the literature, several computational case studies are carried out for analysis of the effects of initial fixed charge density on the distributive variations of the diffusive ion concentrations and electric potential and on the deformation of the pH-stimulus-responsive hydrogels, when they are immersed in different buffered solutions.

Metal Oxide Surface Charge Mediated Hemostasis

Blood coagulates faster upon contact with polar glasslike surfaces than on nonpolar plastic surfaces; this phenomenon is commonly termed the glass effect. However, the variable hemostatic response that we report here for contact-activated coagulation by different metal oxides, all of which are polar substrates, requires a refinement of this simple polarity model of how inorganic metal oxides activate the intrinsic pathway of blood coagulation. To our knowledge, the role of metal oxide surface charge as determined at the physiological pH and Ca2+ concentration of blood has not been previously investigated. We find that basic oxides with an isoelectric point above the pH of blood are anticoagulant while acidic oxides with an isoelectric point below the pH of blood are procoagulant. Using a thromboelastograph, we find that the onset time for coagulation and rate of coagulation post-initiation depend on both the sign and the magnitude of the initial surface charge density of the metal oxide. This work presents a useful strategy based on a quantifiable material parameter to select metal oxides to elicit a predictable and tunable biological response when they are in contact with blood.

Mechanism of electromagnetic emission in plastically deformed ionic crystals

Experiments on the plastic deformation of LiF ionic monocrystals under uniaxial compression are performed with simultaneous recording of acoustic (AE) and electromagnetic (EME) emissions. A strong correlation between AE and EME events has been found, which clearly demonstrates that the observed EME is caused by a dynamical interaction between moving dislocations and charged vacancies in the ionic lattice during work hardening. The mechanism proposed to explain EME is based on the assumption that gliding edge dislocations sweep up the vacancies of a preferable sign. As a result, when a dislocation pileup is formed, a certain nonequilibrium charge density is accumulated at its head, resulting in electric polarization of the deformed crystal. As the external loading increases, a locked dislocation pileup bursts through the stoppers and quickly loses its bounded charge. The relaxation of this charge produces an intrinsic polarization current generating an electric pulse. It is assumed that the relaxation current can be described as an athermic viscous motion of vacancies under the kinetic friction force $\ensuremath{\sim}Bv$ ($B$ is the friction coefficient and $v$ is the vacancy velocity) in a self-consistent electric field determined by the distribution of the total charge density. A nonlinear integro-differential equation of motion for the nonequilibrium charge density is derived. For a special form of the initial charge density distribution, an automodel solution of this equation describing the polarization current has been built. The electrical signal generated by an acting slip system has been calculated. By comparing the calculated and experimentally measured electric signal patterns, the friction coefficient for the linear chain of vacancies (the analog of an edge dislocation extra plane) in LiF has been estimated to be $B\ensuremath{\simeq}0.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}\mathrm{g}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. This value is in accordance with the corresponding coefficient for dislocations in ionic lattices.

A double-front structure of detonation wave as the result of phase transitions

Using thermochemical code calculations, we show that the nanographite–nanodiamond phase transition, which may occur in the detonation products of a number of carbon containing explosives, can affect the detonation properties and can cause a specific detonation regime with some unusual peculiarities. Among them, we first note the failure of the Chapman–Jouguet condition and the presence of the sonic plane, where the Mach number is equal to unity, in a detonation product expansion wave at a lower pressure than that at the Chapman–Jouguet point. The peculiarities of this detonation regime are demonstrated by the example of TNT, HNS, and RDX. The computed detonation velocities are in excellent agreement with experiments over a wide range of initial charge densities for all of the investigated explosives. The results of this work allow one to explain, e.g., contradictory experimental data on the detonation pressure and on the length of the reaction zone for TNT. We believe that some other solid–solid, solid–liquid, and liquid–liquid phase transformations in the detonation products may also cause a detonation regime with the same features as shown here for the nanographite–nanodiamond transition. We suggest a computational study that should facilitate proposing detonation experiments strongly arguing in favor of the model presented.

Analysis and parametric sensitivity of the behavior of overshoots in the concentration of a charged adsorbate in the adsorbed phase of charged adsorbent particles: practical implications for separations of charged solutes

In this work, an analysis of the parametric sensitivity of the overshoot in the concentration of the adsorbate in the adsorbed phase, which occurs under certain conditions during an ion-exchange adsorption process, is presented and used to suggest practical implications of the concentration overshoot phenomenon on operational policies and configurations of chromatographic columns and finite bath adsorption systems. The results presented in this work demonstrate and explain how the development of an overshoot in the concentration of the adsorbate in the adsorbed phase could be enhanced or suppressed by (i) varying the diffusion coefficient, D 3, of the adsorbate relative to the diffusion coefficients, D 1 and D 2, of the cations and anions, respectively, of the background/buffer electrolyte, (ii) altering the initial surface charge density, δ 0, of the charged adsorbent particles, (iii) varying the Debye length, λ, and (iv) changing the initial concentration, C d3 0, of the adsorbate in the bulk liquid of the finite bath. The influence of the pH and ionic strength, I ∞, of the liquid solution on the development of an overshoot in the concentration of the adsorbate in the adsorbed phase is also presented and discussed through the relationships of these parameters to δ 0 and λ, respectively. Furthermore, a detailed explanation of the effects of each parameter on the interplay between the diffusive and electrophoretic molar fluxes, as well as on the structure and functioning of the electrical double layer, which are responsible for the concentration overshoot phenomenon, is presented.

Surface functionalisation for the self-assembly of nanoparticle/polymer multilayer films

The use of organosilanes as surface functionalising materials has been investigated as a precursor to the adsorption of ligand stabilised gold nanoparticles and the build-up of nanoparticle/polymer multilayer films. The purpose of surface functionalisation here is to produce a uniform surface with the maximum positive charge possible to enable the efficient adsorption of negatively charged gold nanoparticles. It is generally acknowledged that the characteristics of the first layer are important in determining the quality of the subsequent multilayer film and hence careful attention has been paid to its optimisation. Three aminosilanes have been investigated together with various methods for their deposition. The degree of nanoparticle adsorption in the resulting films was characterised using atomic force microscopy and X-ray photoelectron spectroscopy. The surface potential of the aminosilane films was also measured to provide information regarding the surface charge density. Our results show a strong correlation between the nanoparticle density and the initial surface charge density. Films of 3-aminopropyltriethoxysilane adsorbed from toluene yielded the highest level of nanoparticle adsorption.