Electric Conductance

1997 ◽  
Author(s):  
C. B. Li
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Colloidal Particles ◽  
Free Solution ◽  
Soil Particles ◽  
Electric Conductance ◽  
Variable Charge ◽  
Ac Electric Fields ◽  
The Difference ◽  
Variable Charge Soils

The migration of colloidal soil particles in an applied electric field has been discussed in Chapter 7. Soil particles carrying electric charges invariably adsorb equivalent amounts of ions of the opposite charge. Generally there is a certain amount of free ions present in soil solution. When an electric field is applied to a soil system, a phenomenon known as electric conductance occurs. As in the case for electrolyte solutions, soil particles and various ions interact with one another during their migration, and these interactions can affect the electric conductance of the system. Variable charge soils carry both positive and negative surface charges, and it can be expected that their interactions with various ions would be rather complicated during conductance. On the other hand, this makes the measurement of electric conductance an effective means in elucidating the mechanisms of interactions between variable charge soils and ions. Both direct-current (DC) electric fields and alternating-current (AC) electric fields can induce the migration of charged particles. In the latter case, the migration of these particles should be related to the frequency of the applied AC electric field. Therefore, in this chapter, after describing the principles of electric conductance of ions and colloids and the factors that affect the conductance of a soil, emphasis shall be placed on the interaction between variable charge soils and various ions as reflected by the frequency effect in electric conductance. For a colloidal suspension, the electric conductance may be regarded as the contribution of conductances of both charged colloidal particles and ions. These two parts may be called the electric conductance of colloidal panicles and the electric conductance of ions, respectively. However, in actual cases it is difficult to distinguish between these two parts. Therefore, it is a general practice to distinguish the electric conductance as that caused by colloidal particles plus their counterions from that caused by ions of the free solution. These may be called electric conductance of the colloid and electric conductance of the free solution. The former conductance is the difference between the electric conductance of the suspension and that of the free solution.

scholarly journals Tuning Single-Molecule Conductance by Controlled Electric Field-Induced trans-to-cis Isomerisation

2021 ◽  
Vol 11 (8) ◽  
pp. 3317
Author(s):  
C.S. Quintans ◽  
Denis Andrienko ◽  
Katrin F. Domke ◽  
Daniel Aravena ◽  
Sangho Koo ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Single Molecule ◽  
Quantum Interference ◽  
Single Molecule Level ◽  
Wet Chemical Synthesis ◽  
Single Molecule Junctions ◽  
Tunnelling Microscopy ◽  
The Difference

External electric fields (EEFs) have proven to be very efficient in catalysing chemical reactions, even those inaccessible via wet-chemical synthesis. At the single-molecule level, oriented EEFs have been successfully used to promote in situ single-molecule reactions in the absence of chemical catalysts. Here, we elucidate the effect of an EEFs on the structure and conductance of a molecular junction. Employing scanning tunnelling microscopy break junction (STM-BJ) experiments, we form and electrically characterize single-molecule junctions of two tetramethyl carotene isomers. Two discrete conductance signatures show up more prominently at low and high applied voltages which are univocally ascribed to the trans and cis isomers of the carotenoid, respectively. The difference in conductance between both cis-/trans- isomers is in concordance with previous predictions considering π-quantum interference due to the presence of a single gauche defect in the trans isomer. Electronic structure calculations suggest that the electric field polarizes the molecule and mixes the excited states. The mixed states have a (spectroscopically) allowed transition and, therefore, can both promote the cis-isomerization of the molecule and participate in electron transport. Our work opens new routes for the in situ control of isomerisation reactions in single-molecule contacts.

Reactions with Hydrogen Ions

1997 ◽  
Author(s):  
F. S. Zhang ◽  
T. R. Yu
Keyword(s):  
Ionization Energy ◽  
Alkali Metals ◽  
Chemical Properties ◽  
Hydrogen Ion ◽  
Hydrogen Ions ◽  
Soil Particles ◽  
Variable Charge ◽  
Hydrated Proton ◽  
Characteristic Features ◽  
Variable Charge Soils

Hydrogen ion is one kind of cation which possesses many properties common to all cations. Hydrogen ion also has its own characteristic features which are of particular significance for variable charge soils. The interactions between hydrogen ions and the surface of soil particles is the basic cause of the variability of both positive and negative surface charges of variable charge soils. The quantity of hydrogen ions in soils determines the acidity of the soil while the acidity of variable charge soils is among the strongest in all the soils. This strong acidity of variable charge soils affects many other chemical properties of the soil. In this chapter, the basic properties of hydrogen ions will be briefly discussed. Then, the products and the kinetics of the interaction between hydrogen ions and variable charge soils will be treated. The dissociation of hydrogen ions from the surface of soil particles has already been mentioned in Chapter 2. After the dissociation of an electron, a hydrogen atom becomes a proton (H+ ion). The ionization energy of hydrogen atoms is 1310 kj mol-1, whereas those of alkali metals, Li, Na, K, and Cs, are 519, 494, 419 and 377 kj mol-1, respectively. This difference in the ionization energy between hydrogen and alkali metals indicates that protons have a particularly strong affinity for electrons. Therefore, protons are apt to form a covalent bond with other atoms by sharing a pair of electrons, or to form a hydrogen bond. Because of the absence of an electronic shell, a proton has a diameter of the order of 10-13 cm, while other ions with electronic shells generally have a diameter of the order of 10-8 cm. Because a proton is so small, it is quite accessible to its neighboring ions and molecules. Therefore, there is very little steric hindrance when protons participate in chemical reactions. The above-mentioned features of proton are the basis for its particular properties. Free proton in solution is extremely unstable because it is very active. In an aqueous solution it will react with water molecules to form a hydrated proton, H3O+.

Polarization and interactions of colloidal particles in ac electric fields

2008 ◽  
Vol 129 (6) ◽  
pp. 064513 ◽  
Author(s):  
Manish Mittal ◽  
Pushkar P. Lele ◽  
Eric W. Kaler ◽  
Eric M. Furst
Keyword(s):  
Electric Fields ◽  
Colloidal Particles ◽  
Ac Electric Fields

Using Shear and DC Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

2014 ◽  
Author(s):  
Minami Yoda ◽  
Necmettin Cevheri
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Poiseuille Flow ◽  
Lift Force ◽  
Colloidal Particles ◽  
Solid Surfaces ◽  
Electric Field Magnitude ◽  
Field Magnitude ◽  
Combined Flow ◽  
Lift Forces

Manipulating suspended neutrally buoyant colloidal particles of radii a = O(0.1 μm–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the DLVO theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ̇ near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125 nm–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ̇, a scaling consistent with hydrodynamic, vs. electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field or in Poiseuille flow for the same γ̇. Initial results also imply that this force, when repulsive, scales as γ̇1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

Manipulation of Organic and Inorganic Colloidal Particles by Dielectrophoretic Forces

2007 ◽  
Author(s):  
Ramazan Asmatulu ◽  
Dennis Siginer
Keyword(s):  
Liquid Medium ◽  
Electric Fields ◽  
Colloidal Particles ◽  
Dielectrophoretic Force ◽  
Inorganic Particles ◽  
Ac Electric Fields ◽  
The Creation ◽  
Manipulation Process

Recently, manipulation of the micro and nanoscale objects has been of great interest in verity of engineering and scientific areas. Dielectrophoretic force (DEP) induced technique is predominantly used in the manipulation process in a liquid medium. The phenomenon behind DEP involves the creation of electric forces on particles to generate momentum in nonuniform electric fields, usually coming from AC electric fields. In the present study, we will discuss about the effects of DEP for the manipulation of organic and inorganic particles at micro and nanoscale in detail.

Using Shear and Direct Current Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

2014 ◽  
Vol 5 (3) ◽  
Author(s):  
Necmettin Cevheri ◽  
Minami Yoda
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Poiseuille Flow ◽  
Lift Force ◽  
Colloidal Particles ◽  
Solid Surfaces ◽  
Electric Field Magnitude ◽  
Field Magnitude ◽  
Combined Flow ◽  
Lift Forces

Manipulating suspended neutrally buoyant colloidal particles of radii a = O (0.1–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ· near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ·, a scaling consistent with hydrodynamic, versus electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field and in Poiseuille flow for the same γ·. Initial results also imply that this force, when repulsive, scales as γ·1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

Effect of Microstructure on Lifetime Performance of Barium Titanate Ceramics Under DC and AC Electric Fields

2010 ◽  
Author(s):  
Jay Shieh
Keyword(s):  
Fatigue Strength ◽  
Barium Titanate ◽  
Electric Field ◽  
Electric Fields ◽  
Time To Failure ◽  
Electrical Loading ◽  
Ac Electric Fields ◽  
Lifetime Performance ◽  
Weibull Statistical Analysis ◽  
Dc Electric Field

Bulk barium titanate (BaTiO3 ) ceramic specimens with bimodal microstructures are prepared and their dielectric and fatigue strengths are investigated under an alternating current (AC) electric field and a direct current (DC) electric field. It is found that under AC electrical loading, both the dielectric and fatigue strengths decrease with increasing amount of coarse abnormal grains. The scatter of the AC fatigue strength is characterized with the Weibull statistics. The extent of scatter of the AC fatigue strength data correlates strongly with the size distribution of the coarse grains. Such correlation is resulted from the presence of intrinsic defects within the microstructure. For DC electrical loading, the time to failure of the specimens with coarse abnormal grains is significantly shorter than the lifetimes of the specimens with only small normal grains. It is found that under a DC electric field of 6 MVm−1, the BaTiO3 specimens would fail within 200 h when abnormal grains are present in the microstructure. However, the lifetimes of the specimens containing abnormal grains vary significantly from one to another. The Weibull statistical analysis indicates that the amount of abnormal grains has little influence on the lifetime performance of bulk BaTiO3 ceramics under large DC electric fields. In most of the failed BaTiO3 specimens under DC electrical loading, regardless of their lifetimes, large through-thickness round holes with recrystallization features are present. A mixed failure mode consisting of avalanche and thermal breakdowns is proposed for the failed specimens.

Characterization of interactive force acting on colloidal particles near an electrode in presence of a high-frequency (>10 kHz) AC electric field using particle diffusometry

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Kshitiz Gupta ◽  
Dong Hoon Lee ◽  
Steven T. Wereley ◽  
Stuart J. Williams
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Particle Motion ◽  
Electrode Surface ◽  
High Frequency ◽  
Colloidal Particles ◽  
Low Frequency ◽  
Double Layers ◽  
Average Height ◽  
Ac Electric Field

Colloidal particles like polystyrene beads and metallic micro and nanoparticles are known to assemble in crystal-like structures near an electrode surface under both DC and AC electric fields. Various studies have shown that this self-assembly is governed by a balance between an attractive electrohydrodynamic (EHD) force and an induced dipole-dipole repulsion (Trau et al., 1997). The EHD force originates from electrolyte flow caused by interaction between the electric field and the polarized double layers of both the particles and the electrode surface. The particles are found to either aggregate or repel from each other on application of electric field depending on the mobility of the ions in the electrolyte (Woehl et al., 2014). The particle motion in the electrode plane is studied well under various conditions however, not as many references are available in the literature that discuss the effects of the AC electric field on their out-of-plane motion, especially at high frequencies (>10 kHz). Haughey and Earnshaw (1998), and Fagan et al. (2005) have studied the particle motion perpendicular to the electrode plane and their average height from the electrode mostly in presence of DC or low frequency AC (<1 kHz) electric field. However, these studies do not provide enough insight towards the effects of high frequency (>10 kHz) electric field on the particles’ motion perpendicular to the electrode plane.  

Electrostatic Adsorption of Cations

1997 ◽  
Author(s):  
G. L. Ji ◽  
H. Y. Li
Keyword(s):  
Surface Layer ◽  
Surface Charge ◽  
Electrostatic Interactions ◽  
Colloidal Particles ◽  
Bulk Solution ◽  
Potassium Ions ◽  
Electrostatic Adsorption ◽  
Variable Charge ◽  
Negative Adsorption ◽  
Variable Charge Soils

Adsorption of ions is a direct consequence of the carrying of surface charge for soils. Owing to the characteristics of variable charge soils in chemical and mineralogical compositions, these soils possess distinct amphoteric properties. Therefore, they can adsorb cations as well as anions. Under field conditions, most of the variable charge soils carry more negative surface charge than positive surface charge, hence they adsorb more cations than anions. Under certain conditions the quantities of adsorbed cations and anions are equal to each other. In this case the soil is said to be at its iso-ionic point. Generally, for most cations commonly found in soils, the interaction force between them and the surface of soil particles during adsorption is electrostatic in nature. However, owing to the characteristics of variable charge soils, a specific force may also be involved in the adsorption of some cations. This latter topic shall be discussed in Chapter 5. In this chapter, only electrostatic adsorption is dealt with. In the present chapter, the mechanism of electrostatic adsorption of cations by variable charge soils and the factors that may affect this type of adsorption are presented first. Then, the dissociation of adsorbed cations is discussed. Finally, the competitive adsorptions of potassium ions with sodium ions and of potassium ions with calcium ions are examined. According to the definition in physical chemistry, the concentration of solute in the surface layer of the solution is different from that in the interior of the bulk solution. If the concentration of solute in the surface layer is higher than that in the interior, the phenomenon is called adsorption. Conversely, it is called negative adsorption. In soil science, on the other hand, the heterogeneity in distribution of ions in soil colloidal systems is interpreted mainly in terms of electrostatic interactions occurring at the interface between soil colloidal particles and the liquid phase (Bear, 1964). Owing to adsorption or negative adsorption, the concentration of ions at the surface of soil colloidal particles or adjacent to the surface is higher or lower than that in the diffuse layer or the free solution.

Dynamic Electromechanical Response of Multilayered Piezoelectric Composites From Room to Cryogenic Temperatures for Fuel Injector Applications

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Yasuhide Shindo ◽  
Takayoshi Sasakura ◽  
Fumio Narita
Keyword(s):  
Domain Wall ◽  
Electric Field ◽  
Electric Fields ◽  
Wall Motion ◽  
Domain Wall Motion ◽  
Cryogenic Temperatures ◽  
Fuel Injector ◽  
Temperature Dependent ◽  
Piezoelectric Composites ◽  
Ac Electric Fields

This paper studies the dynamic electromechanical response of multilayered piezoelectric composites under ac electric fields from room to cryogenic temperatures for fuel injector applications. A shift in the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral/monoclinic phases with decreasing temperature was determined using a thermodynamic model, and the temperature dependent piezoelectric coefficients were obtained. Temperature dependent coercive electric field was also predicted based on the domain wall energy. A phenomenological model of domain wall motion was then used in a finite element computation, and the nonlinear electromechanical fields of the multilayered piezoelectric composites from room to cryogenic temperatures, due to the domain wall motion and shift in the MPB, were calculated. In addition, experimental results on the ac electric field induced strain were presented to validate the predictions.

Sign in / Sign up

Export Citation Format

Share Document