Influence of hot phonons on wind forces in metallic single walled carbon nanotubes

The wind force exerted on the lattice by the flux of electrons under electric loading in single walled carbon nanotubes is studied using an ensemble Monte-Carlo simulation. The momentum transfer between electrons and the lattice is treated using Quantum Mechanics. The phonon distribution and the electron distribution of the carbon nanotubes are allowed to be populated away from thermal equilibrium to study the influence of hot phonons on the wind forces. While the presence of hot phonons creates a net increase in the phonon–electron scattering rates, it appears to have a very small influence on the amount of force exerted on the lattice.     

The prediction of the effective charge number in single-walled carbon nanotubes using Monte Carlo simulation

The ensemble Monte Carlo simulation is used to calculate the electron-wind forces per unit length of single-walled carbon nanotubes under an electric field applied through the nanotube axis. The electronic system and the ionic system are decoupled from each other. The rate of momentum transferred from the electronic system to the ionic system in the form of the emission or absorption of longitudinal acoustic and longitudinal optical phonons is calculated stochastically to determine the electron-wind forces. Complete unabridged energy and phonon dispersion relations are included in order to obtain more accurate results. The effect of the temperature and the electric field magnitude on the induced forces is also taken into account. Results are compared with a prediction based on quantum mechanical integral form that calculates the electron occupation probability based on a modified Fermi–Dirac distribution. Results show a quantitative agreement between the two methods, however, the method proposed in here we believe is more accurate, because it does not make simplifications for the electron occupation probability as in the modified Fermi–Dirac distribution.     

Enhanced Charge Transport in ZnO Nanocomposite Through Interface Control Using Multiwall Carbon Nanotubes

Hybrid strategy of ZnO with carbon nanotube (CNT) has been attempted, and synergistic effects have been demonstrated in ZnO‐CNT hybrid nanostructures owing to the advantageous effects of interface modification on the charge transport process. Here, we report the effects of interface control using multiwall CNTs (MWCNTs) on the charge transport properties in Al‐doped ZnO (AZO) nanocomposite. Although the AZO‐MWCNT nanocomposite is composed of numerous nanograins, it shows single crystalline charge transport behavior due to significantly weakened grain‐boundary scattering at room temperature. The dominant charge transport mechanism is converted from lattice vibration scattering to grain‐boundary scattering at 873 K due to the variation in the charge distribution at the grain boundary. The results demonstrate that interface control using carbon nanomaterials has a significant effect on the charge transport behavior in AZO nanocomposite.     

The effect of van der Waals and charge induced forces on bed modulus of elasticity in ac/dc electrofluidized beds of fine powders—a unified theory

Perturbation theory is applied to an ac electrofluidzed bed of fine powder (glass and FCC) using electric field bubble control to infer the relation between interparticle forces (microscale) and the bulk bed modulus of elasticity (macroscale). Electrostatically induced and permanent van der Waals forces are modeled in a unified theory with bulk fluidized bed behavior. The extrapolation of the electric field to zero strength gives the permanent bed force and bulk bed modulus of elasticity as limiting cases. The resulting equations involve atomic as well as macros-scale parameters. The charge induced forces are identified through the bed modulus of elasticity as a function of the applied electric field strength. The semi-empirical approach is based on the principle that the conservation equations for the perturbed fluidized bed become unstable at the onset of bubbling giving characteristic eigenvalues for the bed modulus, a condition that is readily identifiable experimentally. Eigenvalues from the one-dimensional linearized conservation equations for the fluidized state are examined for growth, neutrality, or decay from the perturbation, which together with bed data are evaluated at bubbling conditions to give the bed modulus of elasticity. Both Richardson-Zaki and Carman-Kozeny bed expansion models of fluidization are examined. The former approach is found to give self-consistent results in which the bed modulus varies linearly with the electric field strength. The results are extended to dc beds as a limiting case of zero field frequency.The modulus of elasticity (a macroscopic bed property) is finally related to particle charge separation at the particle level through an interparticle force model applicable to ac-dc electric fields.     

A hybrid approach to computing electrostatic forces in fluidized beds of charged particles

In particulate flow devices particles acquire electric charge through triboelectric charging, and resulting electrostatic forces can alter hydrodynamics. To capture this effect, the electrostatic force acting on individual particles in the device should be computed accurately. Electrostatic force is calculated using a hybrid approach consisting of: (1) long‐range contributions from an Eulerian electric field solved using the Poisson equation (2) short‐range contributions calculated using a truncated pairwise sum and (3) a correction to avoid double counting. Euler‐Lagrange simulation of flows incorporating this hybrid approach reveals that bed height oscillations in small fluidized beds of particles with monopolar charge decreases with increasing charge level, which is related to lateral segregation of particles. A ring‐like layer of particles, reported in experimental studies, forms at modestly high charge levels. Beds with equal amounts of positively and negatively charged particles are fluidized in a manner similar to uncharged particles. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2282–2295, 2016     

TAYLOR CONE ELECTROHYDRODYNAMICS. THE MINIMUM AND MAXIMUM FLOW RATES IN ELECTROSPRAYING

The surface charge at the liquid–gas interface in cone-jet electrospraying, almost relaxed from an electrochemical point of view, is driven by the radial electric field created to supply the current to the cone tip that the microjet withdraws. The electric stress applied on the liquid surface provokes a low or high Reynolds number motions in the electrified meniscus depending on a dimensionless parameter which relates the liquid viscosity and its electrical conductivity. The analysis of the surface motion is essential to quantify the surface current convected to the cone’s tip, which is shown to be negligible compared to the one driven by bulk conduction. In the case of high Reynolds number motions, we show mathematically, and also experimentally, the emergence of an interesting self-rotation phenomenon.In addition, an analysis of the equations governing the electrohydrodynamics of the charged liquid ligament issuing from the tip of an electrified meniscus in a steady cone-jet suggests the mechanisms which set the stability limits of this steady regime. It is shown that for low and moderate liquid polarities (less than 40 times the vacuum permittivity), the minimum liquid flow rate that can be electrosprayed in a steady cone-jet is reached when the surface tension stress at the cusp from which the jet issues, which provokes a resulting pressure gradient against the flow, overcomes the electrostatic “suction” effect. To show the role of the different forces involved, we have carried the calculation of the intervening ones in the momentum equation using the digitized shape of a cone-jet close to the minimum flow rate in the case of a permittivity 6.5 times larger than the vacuum one. For larger polarities, which impose large electrical conductivities as well, the role of viscous forces, polarization forces, and charge relaxation effects is discussed. In addition, we have carried out experimental measurements of the minimum flow rate using several different liquids. These results are discussed and compared with the experimental data from different authors, as well as with other previously given scaling laws and estimations of the minimum flow rate in cone-jet electrospraying.     

Electrophoretic,dynamic, and static light scattering on charged polymer emulsions

Light scattering studies on dispersions formed by phase separation of a polymer-solvent-non-solvent mixture show that the dispersions comprise charged droplets of the polymer-rich phase. The charge number is not large, and data on the electrophoretic-scattering and the dynamic scattering in the absence of an external electric field are both consistent with distribution of charge among the droplets. Data on the dependence of the static scattering on concentration and scattering angle show that the droplets are also disperse in radius. The data are discussed in terms of an interaction potential among the charged droplets relating the electrostatic interactions to the charge number and radius of the droplets, and the ionic strength of the solvent.     

Effect of charge carrier transport on sulfur dioxide monitoring performance of highly porous polyaniline nanofibres

Polyaniline nanofibres (NFs) with controlled diameters were synthesized using a template‐free method, with ammonium peroxidisulfate (APS) or ferric chloride (FeCl₃) as oxidants. Porosity studies reveal that NFs prepared with FeCl₃ possess higher effective surface area and larger pore volume compared to NFs prepared with APS. The FeCl₃‐assisted NFs show around twofold enhanced sensing response (ca 4.5%) towards 5 ppm of SO₂ at room temperature compared to APS‐assisted NFs (ca 2%). The enhancement can be attributed to the lower diameter, higher effective surface area and larger porosity of FeCl₃‐assisted NFs. To further explain this enhanced sensing response, the conduction mechanism was studied. NFs possessing a smaller diameter (ca 10 nm) are found to follow the one‐dimensional variable range hopping (VRH) model, whereas NFs with larger diameter (ca 100 nm) follow the conventional three‐dimensional VRH model. This can be due to the restriction of charge carrier transport into only one direction due to quantum size effects. Furthermore, the calculated Mott parameters suggest that the NFs prepared using FeCl₃ provide a better pathway for charge transport of charge carriers as compared to NFs prepared using APS in terms of shorter hopping distance, lower activation energy and lower hopping energy, and weaker localization of charge carriers. © 2016 Society of Chemical Industry     

Dimensional Analysis of Continuous High-capacity Electrodispersion of Aqueous Based Liquids in an Organic Continuous Phase

Abstract

High-intensity electric fields can be used to disperse aqueous-based solutions in a relatively nonconducting immiscible organic phase. Dimensional analysis of electrical dispersion performance from a single grounded nozzle between two charged electrodes can be characterised in terms of five dimensionless groups: an electrode height; nozzle-electrode distance; a nozzle Reynolds number; an electrical Bond number, which relates electrical to surface forces; and a Taylor number, which relates electrical to viscous forces. Experimental results on the electrodispersion of water in 2-ethyl-1-hexanol indicate that pulsed DC fields can accomplish electrodispersion utilizing a lower rms-voltage than steady DC fields. In addition, the pulsed-field-behavior varies with pulse frequency with 200 Hz fields being more effective for higher continuous-phase viscosities while 2000 Hz fields are more effective when the viscosity is lower. A steady DC field displays invariant behavior with changing viscosity. In the case of the 2000 Hz field, the Taylor number remains constant for all cases tested thus indicating that the dispersion behavior is controlled by the dynamic interactions of the forces induced by the transient field with the stability of the liquid stream emanating from the nozzle.     

Use of Electric Image Forces for Collection of Aerosols by Arrays of Drops

The use of electric image forces for collection of uncharged aerosols by two- and three-dimensional arrays of charged drops is considered. Trajectories of aerosols are simulated using an algorithm for transformation of electric image forces and flow field from spherical coordinate systems of the drops to the central system, where the equation of motion is solved. Radius and efficiency of collection of aerosols, as a function of the number of rows of drops, are presented for different geometries and charge levels. The nature of the weak image force dictates the need to use a charge level closer to the Rayleigh limit and optimized array geometries. Inertial effects that enhance dispersive modes, of otherwise convergent trajectories, become significant for aerosols as small as 20 w m. In this case, multiple values of radius of collection and collection efficiency can be obtained for the same number of rows. Geometries with no shifts between rows of drops are shown to be inferior to those involving a larger shift. The former geometries require a substantially larger number of rows for a prescribed level of collection and may not facilitate complete collection. Systems of uncharged drops and charged aerosols behave similarly to those with charged drops and uncharged aerosols. Three-dimensional arrays can be more efficient than two-dimensional ones, provided that weakness planes, where aerosols show deep penetration, are eliminated by appropriate shifts of rows. A decrease of the drop size at a fixed volume fraction with the charge set at its Rayleigh limit enhances the collection efficiency. Finally, the random model of collection, using the exponential distribution, is recast in order to accommodate for the effect of the order of the array and the deterministic nature of the aerosol trajectories.     

Charge transport in high mobility single crystal diamond

Time of Flight (TOF) measurements using conventional laser TOF and α-particle TOF setups have been carried out on high quality CVD diamond samples to study the electron and drift mobility and to compare them with the mobility data for IIA diamond. The measured mobilities for all samples investigated are in the range 2000–2250 cm²/Vs for holes and 2200–2750 cm²/Vs for electrons, thus close to the theoretical prediction as well as to IIa diamond mobility values. The charge transient profile measured in the laser TOF measurements is influenced by the electric field profile in the sample, which might be changed based on the charge trapping at low electric fields applied, depending on the surface atomic termination. The temperature dependence of the drift mobility indicates that at room temperature the scattering on acoustic phonons is the main dominant scattering mechanism and the contribution of other types of carrier scattering mechanism is negligible.     

Theoretical study of the scattering efficiency of rutile titanium dioxide pigments as a function of their spatial dispersion

We propose an original theoretical framework to model the scattering efficiency of white paint films as a function of the volume fraction and spatial state of dispersion of rutile titanium dioxide pigments, taking into account electromagnetic couplings. Numerical calculations are performed using a multiple T matrix formalism on an “elemental” volume extracted from the bulk of the paint and which we model as pigments and fillers in a polymer matrix. Qualitative studies show that, due to the dependent scattering phenomenon, the size of fillers can modulate the magnitude of loss in scattering efficiency by modifying the spatial state of dispersion of the pigments in the polymer matrix. In particular, fillers whose size is comparable to the dimension of the pigments improve the scattering efficiency by impeding crowding. It is also shown that the optical properties of the bulk material at arbitrary concentration can be approximated by extrapolating the optical properties calculated on a limited number of scatterers.     

A quantitative evalution of the photocatalytic performance of TiO2 slurries

This paper reports the results of a comparison between two TiO₂ photocatalysts that differ for particle size and absorption/scattering optical properties. The catalyst with larger particles and lower surface area performed better in the degradation of phenol than the specimen with smaller particles and larger surface area. Following carefully designed experiments, it is possible to assess the relative role of light absorption/scattering properties and catalyst-related efficiency by means of a basic kinetic model for the rate of photocatalytic reactions. Explicit relationships are derived in the framework of the steady-state approximation for the quantum yield as a function of one a-dimensional number collecting surface kinetic constants for charge carrier reactions at the interface, absorbed light and surface substrate concentrations. The dimensionality change to volume-defined quantities allows derivation of the explicit dependence of the quantum yield on substrate concentration and partition constants, catalyst concentration, and the rate of volumetric light absorption. Following this approach, the rate expression for slurry systems, valid in the absence of back reactions, is directly derived. Some further simplification of the rate equation for the case of low quantum yield regime leads to analytical relationships able to account for the dependence of the rate on catalyst concentration and absorbed light in the case of stirred and unstirred conditions. The reported properly designed experiments allow the estimation of catalyst-specific micro-kinetic constants.     

Correlations in the electron subsystem of a ferroelectric and the electron-phonon interaction

In a vibronic ferroelectric, besides the phonon order parameter also an electronic one is induced. The correlation properties of the latter are investigated, The density of the coupled electron-hole pairs in a condensate characterizing the ordered state is calculated to be proportional to the vibronic lattice distortion energy squared, The total momentum of the condensate equals to the momentum of the vibration driving the structural transition. The electronic correlation length is of the same order as for the phonon order parameter. Electronic contribution to the latent heat is possible.     

Molecular dynamics simulation of polymer nanoparticle collisions: orbital angular momentum effects

The collisional dynamics of polymer nanoparticles is investigated using molecular dynamics, with a particular focus on angular momentum effects. Unlike zero impact parameter collisions discussed elsewhere, which are greatly weighted toward sticking collisions, the outcome of collisions with non-zero angular momentum show much greater variability, showing both reactive (where polymer chains are exchanged between particles) and purely scattering trajectories. In the case of inelastic scattering trajectories, the profile for translation to vibration energy transfer is calculated.     

Effects of Electrohydrodynamic Flow and Turbulent Diffusion on Collection Efficiency of an Electrostatic Precipitator with Cavity Walls

The effects of electrohydrodynamic (EHD) flow and turbulent diffusion on the collection efficiency of particles in a model ESP composed of the plates with a cavity were studied through numerical computation. Electric field and ion space charge density in the ESP were calculated by the Poisson equation of electric potential and the current continuity equation of ion space charge. The EHD flow field was solved by the continuity and momentum equations of gas phase, including the electrical body force induced by the movement of ions under the electric field. RNG k - l model was utilized to analyze turbulent flow. Particle concentration distribution was calculated from the convective diffusion equation of particle phase. As the ion space charge increased, the collection efficiency of charged particles increased because the electric potential increased over the entire domain in the ESP. The collection efficiency decreased as the EHD flow became stronger when the electrical migration velocity of charged particles was high. However, the collection efficiency could increase for the stronger EHD flow when the electrical migration velocity of charged particles was relatively lower. Also, the collection efficiency decreased as the turbulent diffusion of particles increased when the electrical migration velocity of particles was high. However, the collection efficiency could increase with the turbulent diffusion when the electrical migration velocity of particles was relatively lower.     

DC Electric Field‐Enhanced Grain‐Boundary Mobility in Magnesium Aluminate During Annealing

Magnesium aluminate spinel was sintered and annealed at 1300°C under an applied 1000 V/cm DC electric field. The experiment was designed such that current could be removed as a variable and just the effect of a noncontact electric field was studied. Enhanced grain growth was observed for both samples that were sintered or annealed after densification in the presence of an electric field. Grain‐boundary character distributions revealed that no microstructural changes were induced due to the field. However, the electric field was found to enhance the kinetic movement of cations within the lattice. Energy‐loss spectroscopy experiments revealed cation segregation resulting in regions of Mg‐rich and Al‐rich layers adjacent the grain‐boundary cores. The defects generated during segregation supported the generation of a space charge gradient radiating from the grain‐boundary core out into the bulk, which was significantly affected by the applied field. The interaction between the field and space charges effectively reduced the activation energy for cation movement across boundaries thereby enhanced grain‐boundary mobility and resultant grain growth.     

利用多重光散射法对纳米TiO2水分散体系稳定性研究

通过多重光散射法研究了纳米TiO2水分散体系稳定性的影响因素。文章探讨了分散剂类型、pH和NaCl质量浓度对水分散体系稳定性的影响规律以及分散剂对纳米TiO2颗粒在水分散液中粒径变化、沉降的微观作用特性。结果表明：纳米TiO2颗粒的粒径在100～200 nm时易相互吸附团聚沉降,分散剂会在纳米TiO2颗粒表面吸附形成双电层,产生更大Zeta电位负值,增强颗粒间的排斥作用,减缓粒径增长和发生沉降的作用,从而提升分散液稳定性;纳米TiO2颗粒的较佳分散条件为：w(六偏磷酸钠)=0.05%,pH=9～10且不加电解质NaCl;多重光散射法与传统的吸光度测试实验所得结果基本相符。     

First-principles prediction of charge mobility in carbon and organic nanomaterials

We summarize our recent progresses in developing first-principles methods for predicting the intrinsic charge mobility in carbon and organic nanomaterials, within the framework of Boltzmann transport theory and relaxation time approximation. The electron-phonon couplings are described by Bardeen and Shockley's deformation potential theory, namely delocalized electrons scattered by longitudinal acoustic phonons as modeled by uniform lattice dilation. We have applied such methodology to calculating the charge carrier mobilities of graphene and graphdiyne, both sheets and nanoribbons, as well as closely packed organic crystals. The intrinsic charge carrier mobilities for graphene sheet and naphthalene are calculated to be 3 × 10(5) and ～60 cm(2) V(-1) s(-1) respectively at room temperature, in reasonable agreement with previous studies. We also present some new theoretical results for the recently discovered organic electronic materials, diacene-fused thienothiophenes, for which the charge carrier mobilities are predicted to be around 100 cm(2) V(-1) s(-1).