Mobile charges

When this equation is applied to a system composed of a macromolecule immersed in an aqueous medium containing a dissolved electrolyte, the fixed partial charges of each atom of the macromolecule result in a charge density described by p, and the mobile charges of the dissolved electrolyte are described by /O , which i derived from a Boltzmann distribution of the ions and coions. 

Fig. 1. Schematic diagram of semiconductor materials showing band gaps where CB and VB represent the conduction band and valence band, respectively and 0 and 0, mobile charge. The height of the curve represents the probabiUty of finding an electron with a given momentum bound to an N-isoelectronic impurity, (a) Direct band gap the conduction band minimum, F, is located where the electrons have 2ero momentum, ie, k = 0. The couples B—B, D—A, B—D, and B—A represent the various routes for radiative recombination. See text, (b) Indirect band gap the conduction band minimum, X, is located...

In perfect semiconductors, there are no mobile charges at low temperatures. Temperatures or photon energies high enough to excite electrons across the band gap, leaving mobile holes in the Fermi distribution, produce plasmas in semiconductors. Thermal or photoexcitation produces equal... 

At lower frequencies, orientational polarization may occur if the glass contains permanent ionic or molecular dipoles, such as H2O or an Si—OH group, that can rotate or oscillate in the presence of an appHed electric field. Another source of orientational polarization at even lower frequencies is the oscillatory movement of mobile ions such as Na". The higher the amount of alkaH oxide in the glass, the higher the dielectric constant. When the movement of mobile charge carriers is obstmcted by a barrier, the accumulation of carriers at the interface leads to interfacial polarization. Interfacial polarization can occur in phase-separated glasses if the phases have different dielectric constants. 

Thus when an electric field is appHed to a soHd material the mobile charge carriers are accelerated to an average drift velocity v, which, under steady-state conditions, is proportional to the field strength. The proportionality factor is defined as the mobility, = v/E. An absolute mobility defined as the velocity pet unit driving force acting on the particle, is given as ... 

There is a strong attraction between dye and fiber when oppositely charged. The mobile charged dyestuff chromogen "moves" from the external water phase to the stationary internal fiber phase. For like-charged entities repulsion occurs, and no movement of dyestuff from the water to the fiber takes place. 

A linear regression was performed on the data, giving a slope of 1.08, an intercept of 1.922, and = 0.94. The fit of the data to the linear relationship is surprisingly good when one considers the wide variety of ionic liquids and the unloiown errors in the literature data. This linear behavior in the Walden Plot clearly indicates that the number of mobile charge carriers in an ionic liquid and its viscosity are strongly coupled. 

Conjugated polymers are generally poor conductors unless they have been doped (oxidized or reduced) to generate mobile charge carriers. This can be explained by the schematic band diagrams shown in Fig. I.23 Polymerization causes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the monomer to split into n and n bands. In solid-state terminology these are the valence and conduction bands, respectively. In the neutral forms shown in Structures 1-4, the valence band is filled, the conduction band is empty, and the band gap (Eg) is typically 2-3 eV.24 There is therefore little intrinsic conductivity. 

FIG. 25 Titration theory vs mobility charge. (Reprinted from Ref. 98, Copyright 1995, with permission from Elsevier Science.)... 

An aqueous solution of a molecular substance such as sugar (C12 H22 Oi 1) or ethanol (C2 H5 OH) contains individual molecules in a sea of water molecules (Figure 3-181. We know that these solutes dissolve as neutral molecules from measurements of electrical conductivity. Figure 3-19 shows that pure water does not conduct electricity, and neither does a solution of sugar in water. This result shows that these solutions contain no mobile charged particles. Sugar and ethanol dissolve as neutral molecules. 

Saint-Martin H, Hernandez-Cobos J, Bernal-Uruchurtu MI, Ortega-Blake I, Berendsen HJC (2000) A mobile charge densities in harmonic oscillators (MCDHO) molecular model for numerical simulations the water-water interaction. J Chem Phys 113(24) 10899—10912... 

The continuity of the current inside the oxide requires that the concentration of mobile charge carriers varies with the variation of the field with distance from the interface, so that their product remains constant. 

When the two ends of a material containing mobile charge carriers, holes or electrons, are held at different temperatures, a voltage is produced, a phenomenon called the Seebeck effect (Fig. 1.11). The Seebeck coefficient of a material, a, is defined as the ratio of the electric potential produced when no current flows to the temperature... 

The Seebeck coefficient is frequently called the thermoelectric power or thermopower, and labeled Q or S. Neither of these alternatives is a good choice. The units of the Seebeck coefficient are not those of power. The symbol Q is most often used to signify heat transfer in materials. The designation S can easily be confused with the entropy of the mobile charge carriers, which is important because the Seebeck coefficient is equivalent to the entropy per mobile charge carrier (see Supplementary Material S3). 

The Seebeck coefficient for pure LaCo03 is +600 xVK-1. (a) What are the mobile charge carriers (b) Suppose these occur because the crystal contains a trace of an impurity, Co4+, calculate the defect concentration and the formula of the material (data from Robert et al., 2006). 

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