Measurement Of Potential Distribution Research Articles

Charge nonuniformity light scattering

Classical models for colloidal forces assume that the particles are uniformly charged. However, charge nonuniformity can decrease suspension stability and reduce the accuracy of colloidal assemblies. Our lab group has previously seen that polystyrene latex particles are often nonuniformly charged, through the experimental technique of “rotational electrophoresis” [J.D. Feick, N. Chukwumah, A.E. Noel, D. Velegol, Langmuir 20 (2004) 3090]. Even though rotational electrophoresis is unique in finding zeta potential nonuniformity on individual particles, the technique is currently time-consuming and for practical reasons is limited to particles larger than 1 μm in size. We now introduce a modification of the rotational electrophoresis technique: “charge nonuniformity light scattering” (CNLS). CNLS takes advantage of two effects: (1) nonuniformly charged particles will rotate in an applied electric field and (2) light scattering from anisotropic particles changes when the particles align, an effect already used in the electric light scattering technique. By “visualizing” rotational electrophoresis with light scattering and interpreting the results with electrokinetic modeling, CNLS enables a measurement of zeta potential distribution for a colloidal suspension of particles with anisotropic geometry. In order to test the method, we synthesized model colloidal doublets composed of spheres with zeta potentials ζ 1 and ζ 2. Using translational electrophoretic mobility experiments, we found the difference ζ 2 − ζ 1 for our doublets. We then conducted experiments with CNLS, which gave the same value of ζ 2 − ζ 1, verifying the accuracy of the technique. Thus, CNLS allows for much more rapid measurements of charge nonuniformity and will soon be applied to more challenging systems.

Mechanical Properties of Sharpened Carbon Nanotube Tips

We investigate the mechanical properties of sharpened nanotube tips for use in scanning probe microscopy in terms of tip bending under a force acting on the side of the tip. The sharpened nanotube probe fabricated by means of a modified electrical breakdown process effectively acts as a probe with high lateral resolution not only in the topographic measurement but also in the potential distribution measurement. Based on molecular mechanics calculations for a sharpened triple-walled nanotube probe, although the interlayer van-der-Waals interaction weakens the probe stiffness expected on the basis of the continuum model, the stiffness of the tapered nanotube is confirmed to be 10 times higher than that for a single-walled nanotube with the same tip radius and the same length.

Interaction forces in bitumen extraction from oil sands

Water-based extraction process (WBEP) has been successfully applied to bitumen recovery from Athabasca oil sand ore deposits in Alberta. In this process, two essential steps are involved. The bitumen first needs to be “liberated” from sand grains, followed by “aeration” with air bubbles. Bitumen “liberation” from the sand grains is controlled by the interaction between the bitumen and sand grains. Bitumen “aeration” is dependent, among other mechanical and hydrodynamic variables, on the hydrophobicity of the bitumen surface, which is controlled by water chemistry and interactions between bitumen and fine solids. In this paper, the interaction force measured with an atomic force microscope (AFM) between bitumen–bitumen, bitumen–silica, bitumen–clays and bitumen–fines is summarized. The measured interaction force barrier coupled with the contacted adhesion force allows us to predict the coagulative state of colloidal systems. Zeta potential distribution measurements, in terms of heterocoagulation, confirmed the prediction of the measured force profiles using AFM. The results show that solution pH and calcium addition can significantly affect the colloidal interactions of various components in oil sand extraction systems. The strong attachment of fines from a poor processing ore on bitumen is responsible for the corresponding low bitumen flotation recovery. The identification of the dominant non-contact forces by fitting with the classical DLVO or extended DLVO theory provides guidance for controlling the interaction behavior of the oil sand components through monitoring the factors that could affect the non-contact forces. The findings provide insights into megascale industrial operations of oil sand extraction.

環状流路型電磁流量計の開発（２）ー鉛ビスマス流動中の電気ポテンシャル分布測定ー

環状流路型電磁流量計の開発（２）ー鉛ビスマス流動中の電気ポテンシャル分布測定ー

Indomethacin nanoparticles directly deposited on the fluidized particulate excipient by pulsed laser deposition

Nanoparticles of indomethacin (IM), a sparingly soluble drug in water, were prepared by pulsed laser deposition with Nd: YAG laser at 1064 nm. Variation of the deposition rate (DR) with various experimental conditions, such as species and pressure of the background gas, and laser fluence, was discussed. We obtained highest DR, 2.7 μg/cm2min, under He at 100 Pa with the laser fluence of 25 J/cm2. In the deposited solid product, no trace of drug decomposition was observed by HPLC. Deposition of IM nanoparticles was achieved on the fluidized excipient, potato starch particles of 20 μm regime. By TEM observation and zeta potential distribution measurement, we confirmed that surface of excipient particles was fully covered by nanoparticles of IM. Thus, the present method enables us a new method of one-step preparation of drug-excipient nanocomposites to eliminate tedious problems associated with nanoparticles handling.

Effect of electrode configuration and electronic conductivity on current density distribution measurements in PEM fuel cells

Abstract Current density and potential distribution measurements were conducted using a segmented current collector and flow field setup on membrane electrode assemblies prepared with segmented and unsegmented electrodes made from two different types of commercially available gas diffusion layers. Both galvanostatic and potentiostatic discharge modes were employed. Irrespective of the type of gas diffusion layer, when a common electrode was employed, significant performance variations were encountered between current collector segments in the constant voltage mode, while the segment to segment variations were minimal in the constant current mode. Both types of discharge modes showed negligible variations between segments in the case of segmented electrode. A simple mathematical model was developed to assist in the interpretation of the experimental results. The differences in contact resistances between the current collectors and the gas diffusion layer, especially on the cathode side have been identified as the primary reason for the experimentally observed behavior. Based on the results presented here, segmenting the electrode along with the current collector is recommended for current distribution studies. When using a common electrode, only the galvanostatic mode is preferred to minimize contact artifacts.

Local built-in potential on grain boundary of Cu(In,Ga)Se2 thin films

We report on a direct measurement of two-dimensional potential distribution on the surface of photovoltaic Cu(In,Ga)Se2 thin films using a nanoscale electrical characterization of scanning Kelvin probe microscopy. The potential measurement reveals a higher surface potential or a smaller work function on grain boundaries of the film than on the grain surfaces. This demonstrates the existence of a local built-in potential on grain boundaries, and the grain boundary is positively charged. The local built-in potential on the grain boundary is expected to increase the minority-carrier collection area from one to three dimensional. In addition, a work function decrease induced by Na on the film surface was observed.

自然電位法による石炭の自然発火の熱源検出に関する実験的研究

A corresponding distribution of electric potential is produced in a porous medium like sand and an aggregation of broken rocks, if a temperature distribution exists in the medium. The authors performed model experiments to investigate whether the measurement of the electric potential distribution can be used for locating the heat source. The main parameters measured are electric potential and temperature. The results of the experiments show that a distribution of electric potential is always created corresponding to the conditions of the heat source. It is concluded that there is a possibility that the measurement of potential distribution can be used for locating the heat source of spontaneous combustion of coal.

Floc morphology and cyclic shearing recovery: comparison of alum and polyaluminum chloride coagulants

This study investigated the floc formation and re-aggregation potential for alum, polyaluminum chloride (PACl) and a blend of these coagulants. Bench-scale testing included floc morphology characterization for well-developed floc, post-shear floc, and non-settleable (filter influent) floc. Different applications of coagulants were observed to produce non-settleable floc that was morphologically different. The alum treatment had a decrease in average floc size from coagulated to non-settleable conditions, whereas the PACl and PACl/alum treatments resulted in similar sized floc between these processes. Zeta potential distribution measurements showed that the alum treatment resulted in a negative shift from coagulated to non-settleable conditions whereas the PACl and PACl/alum treatments had no significant shift. A photometric dispersion analyzer (PDA) was employed to compare the differences between coagulant treatments with respect to shear induced aggregate breakup and recovery. The PDA allowed a dynamic monitoring of initial floc aggregation and measured the degree of recovery from cyclic shearing. The degree of recovery from shearing was greatest for the PACl/alum treatment likely as a result of increased collision efficiency due to more effective charge neutralization.

Experimental Measurements of Velocity, Potential, and Temperature Distributions in Liquid Aluminum During Electromagnetic Stirring

An experimental technique has been developed to measure both axial and transverse velocities and temperature distribution in molten aluminum. Couette flow of liquid aluminum, lead, tin, and low melting alloy in cylindrical container was chosen for calibration of the experimental technique and the magnetic probe. Velocity and temperature profiles for liquid aluminum rotating in cylindrical container at different angular velocities are obtained for two different values of the depth. We determined that the velocity values increase with magnetic induction.

Pockels surface potential probe and surface charge density measurement

A surface potential probe based on Pockels sensing technique is developed and applied to surface potential distribution measurement on insulating material. The probe consists of a super luminescent diode, a Pockels crystal, a polarized beam splitter, a 1 8 wave plate and optical fibers. As the detecting part of the probe is isolated from a grounded electrode, this probe can be placed closer to the measured object. The resolving power is 2 mm which is equivalent to the twice size of the detecting part. The modulation technique is introduced to this probe and the minimum sensitivity reaches 10 V . This probe is applied to the measurement of the potential distribution on an insulating material just after occurrence of a surface discharge. From this measured potential profile, the distribution of surface charge density is computed through a surface charge method.

Bitumen–Clay Interactions in Aqueous Media Studied by Zeta Potential Distribution Measurement

A novel technique to investigate the interactions between bitumen and clays in an aqueous solution from the measurement of zeta potential distributions is described. For a single component suspension (i.e., clay or bitumen), a single modal zeta potential distribution was obtained under a given solution condition. In the case of a two-component (i.e., bitumen and clay) mixture system, the measured zeta potential distribution showed either one or two distribution peaks, depending on the chemical condition of the suspension and the type/amount of clays present. In the absence of added calcium ions, a mixture of bitumen emulsion and clay suspension exhibited two distinct zeta potential distribution peaks, corresponding to the peaks measured individually for the bitumen and clays, respectively. With the addition of 1 mM calcium ions, however, only one zeta potential distribution peak was obtained for the mixture of bitumen emulsion and montmorillonite clay suspension. Depending on the montmorillonite clay to bitumen ratio, the peak position in this case shifted toward the value for montmorillonite clay suspension alone. For kaolinite, the addition of 1 mM calcium ions did not cause a substantial change in the bimodal zeta potential distribution. The results suggest qualitatively a stronger interaction of bitumen with montmorillonite clay than with kaolinite clay, when calcium ions were present. The slime coating of montmorillonite clay on bitumen droplets in the presence of 1 mM calcium was validated. The conclusions obtained from this study further justified our mechanistic hypothesis for the observed depression of bitumen flotation by montmorillonite but not by kaolinite clay addition when calcium ions were added. This study demonstrated that zeta potential distribution measurement could be a powerful tool to study slime coating phenomena in a complex colloidal system.

Electrokinetic study of clay interactions with coal in flotation

The effect of montmorillonite and kaolinite clays on fine coal flotation was investigated. A novel method based on zeta potential distribution measurement to study interactions of fine clay with coal was described. The zeta potential distribution measurement was performed with coal and clay suspensions, individually and collectively. The results were used to explain the observed depression of coal flotation by montmorillonite but not kaolinite clay addition. The settling tests confirmed that slime coating of montmorillonite clay on coal is detrimental to coal flotation.

Two-dimensional potential distribution measurement of surface discharge with subnanosecond resolution

The Pockels sensing system has been developed for directly measuring the potential and electric field distribution on a dielectric material. The system consists of an Ar ion laser, a Nd:YAG laser, a streak camera, and charge coupled device cameras. With this system, both the transient change in the potential distribution along a linear path of 50 mm in maximum length and the instantaneous two-dimensional potential distribution on a 25 mm square area can be measured simultaneously. The minimum resolution of this system reaches up to 0.2 ns. This article describes the transient change in potential distribution with a surface discharge in atmospheric air. The transient change of potential distribution with a propagating negative surface discharge in atmospheric air is measured with this system. The propagating direction component of the electric field Ex near the tip of the propagating streamer exceeds 3 MV/m.

負極性沿面放電の逆放電に伴う電位分布変化のナノ秒分解測定

負極性沿面放電の逆放電に伴う電位分布変化のナノ秒分解測定

Direct measurement of internal potential distribution in organic electroluminescent diodes during operation

Direct measurement of the internal potential distribution in an organic electroluminescent (EL) diode under operating conditions was carried out by inserting a third gold electrode in the bulk of the organic thin film to monitor the potential. This electrode was sandwiched between two driving metal electrodes. During the operation of the organic EL diode, consisting of hole transporting and emitter layers, the applied voltage was distributed mainly across the emitter layer. The present technique provides a useful method for elucidating the operating mechanism of various types of organic thin-film devices.

Potential distribution measurement in galvanic corrosion of Zn/Fe couple by means of Kelvin probe

Potential measurement with a Kelvin probe was developed to measure the electrode potential in the vicinity of an Fe/Zn couple boundary during galvanic corrosion of galvanized steel sheets under thin films of NaCl aqueous solutions of various concentrations. Using the Kelvin probe, the Zn surface potentials were measured for thin films of 0–0.5% NaCl solutions, and the obtained values were approximately −1.1 to −1.2 V (vs. Kelvin standard). The Kelvin potential of Fe showed a value close to that of the Zn surface in the vicinity of the Fe/Zn boundary, while at a sufficiently remote area it converged to −0.7 V. The transition zone existed only on the Fe side. The width of the transition zone decreased with increasing film thickness and salt concentration of water layer. The sacrificial effect of Zn reaches farther in NaCl solution films than in pure water because of low resistivity of salt solutions. The potential distribution in the boundary can be well explained by the transmission-line model. In thin film systems, the effective galvanic distance ( ξ) of Zn on Fe surface is proportional to δ f /ρ 1/2 , where ρ is the specific resistance and δ f is the thickness of water film covering the galvanic couple.

沿面コロナストリーマ中の電位•電界分布の2次元動的測定

沿面コロナストリーマ中の電位•電界分布の2次元動的測定

ポッケルス効果を用いた正極性沿面放電進展時の電位分布直接測定

ポッケルス効果を用いた正極性沿面放電進展時の電位分布直接測定

Developments in thermopiezoelasticity with relevance to smart composite structures

A review of theoretical developments in thermopiezoelasticity having relevance to smart composite structures is presented. The equations governing linear response of piezothermoelastic media are outlined, and a general solution procedure based on potential functions is described. Sensor applications aimed at predicting thermal loads and corresponding responses from measurements of electric potential distributions are described; studies on the control of composite structures (beams, plates and shells) via piezoelectric actuation are reviewed.