Electric charge separators

In some layered compounds, electric charge separation between the layers may destabilize the structures AurivilUus phases [Bi202] [B lM 03, l] " are examples. If oxygen vacancies are introduced into an Aurivillius phase, a stepped superstructure may form to release the charge separation and, probably, reduce the number of oxygen vacancies. For example, Bi2WO,5 is a well known n = I member of the family of Aurivillius phases. The unit cell consists of fluorite-like [Bi202] and... 

Like mitochondria, chloroplasts have an F-type ATPase which generates ATP from a proton gradient. Thylakoids are permeable to Mg2+ and Cl" so this is mostly a concentration effect (pH) rather than an electrical (charge separation) effect. In fact, the pH difference can be very marked typically the lumen is at pH 4 and the stroma at pH 8. 

The pyroelectric effect results from the electric charge separation resulting from the stress caused by the temperature change. A small potential difference, sometimes too small to measure, develops across... 

Coulomb forces result from the interaction between a charged surface and another charged or neutral surface. These forces can be attractive or repulsive, depending on the charge of each surface, and are relevant for particles with diameters larger than 5 pm [267]. For two-point electric charges separated by a distance h, Coulomb s Law gives ... 

Items 2 and 3 arise from the fact that both the "counterion" and the medium itself can markedly affect the nature of the growing chain end. Thus, the growing chain end may assume various forms that depend on the extent of electrical charge separation and range all the way from a polarized covalent (sigma) bond to a completely dissociated state of free ions. This characteristic presents the greatest distinction between the mechanisms of free-radical and ionic polymerization. 

Dipole (7.4) Two equal and opposite electric charges separated by a short distance. 

Derive the expression for the electric field around a point dipole, Eq. VI-5, by treating the dipole as two charges separated by a distance d, then moving to distances X d. 

An electric dipole consists of two equal and opposite charges separated by a distance. AH molecules contain atoms composed of positively charged nuclei and negatively charged electrons. When a molecule is placed in an electric field between two charged plates, the field attracts the positive nuclei toward the negative plate and the electrons toward the positive plate. This electrical distortion, or polarization of the molecule, creates an electric dipole. When the field is removed, the distortion disappears, and the molecule reverts to its original condition. This electrical distortion of the molecule is caHed induced polarization the dipole formed is an induced dipole. 

Two parallel plates of conducting material separated by an insulation material, called the dielectric, constitutes an electrical condenser. The two plates may be electrically charged by connecting them to a source of direct current potential. The amount of electrical energy that can be stored in this manner is called the capacitance of the condenser, and is a function of the voltage, area of the plates, thickness of the dielectric, and the characteristic property of the dielectric material called dielectric constant. 

When two conducting phases come into contact with each other, a redistribution of charge occurs as a result of any electron energy level difference between the phases. If the two phases are metals, electrons flow from one metal to the other until the electron levels equiUbrate. When an electrode, ie, electronic conductor, is immersed in an electrolyte, ie, ionic conductor, an electrical double layer forms at the electrode—solution interface resulting from the unequal tendency for distribution of electrical charges in the two phases. Because overall electrical neutrality must be maintained, this separation of charge between the electrode and solution gives rise to a potential difference between the two phases, equal to that needed to ensure equiUbrium. 

Electrically, the electrical double layer may be viewed as a capacitor with the charges separated by a distance of the order of molecular dimensions. The measured capacitance ranges from about two to several hundred microfarads per square centimeter depending on the stmcture of the double layer, the potential, and the composition of the electrode materials. Figure 4 illustrates the behavior of the capacitance and potential for a mercury electrode where the double layer capacitance is about 16 p.F/cm when cations occupy the OHP and about 38 p.F/cm when anions occupy the IHP. The behavior of other electrode materials is judged to be similar. 

Adsorption of bath components is a necessary and possibly the most important and fundamental detergency effect. Adsorption (qv) is the mechanism whereby the interfacial free energy values between the bath and the soHd components (sofld soil and substrate) of the system are lowered, thereby increasing the tendency of the bath to separate the soHd components from one another. Furthermore, the soHd components acquire electrical charges that tend to keep them separated, or acquire a layer of strongly solvated radicals that have the same effect. If it were possible to foUow the adsorption effects in a detersive system, in all their complex ramifications and interactions, the molecular picture of soil removal would be greatly clarified. 

Dielectric Constant The dielectric constant of material represents its ability to reduce the electric force between two charges separated in space. This propei ty is useful in process control for polymers, ceramic materials, and semiconduc tors. Dielectric constants are measured with respect to vacuum (1.0) typical values range from 2 (benzene) to 33 (methanol) to 80 (water). TEe value for water is higher than for most plastics. A measuring cell is made of glass or some other insulating material and is usually doughnut-shaped, with the cylinders coated with metal, which constitute the plates of the capacitor. 

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