Ionic electric field

Above 0.1m the values of aqueous salts flatten out and may become negative except where small ions are involved. In 90% acetonitrile, the 0l curve becomes steeper with increasing concentration. This is probably caused by depletion of the free water in the solvent, so that ion solvation by acetonitrile becomes significant. It is also possible that, because ionic electric fields are significant at greater distances in a solvent of lower dielectric constant, the overlapping of ionic co-spheres has a much more drastic effect on the enthalpy than it does in water for this salt. 

Another consequence of the ionic electric field is the large compressive pressure that it exerts on the solvent near the ion. Bockris and Saluja [62] calculated the effective pressure in the middle of the first hydration shell of aqueous ions, the numerical coefficient being valid at 25°C with the radii in nanometer ... 

A further quantity that is related to the pressure dependence of the permittivity, but also to its electric field dependence, is the mean molar electrostricted volume of a solvent in the presence of ions. The mean molar electrostriction of the solvent S in the presence of the ionic electric field was given by Marcus [21] as ... 

Hydration numbers at temperatures other than 25°C, up to 200°C, have been reported by Marcus [54, 83, 88] for some twenty common ions, obtained according to the electrostriction method and Equation 4.36. The values of increase appreciably as the temperature is raised and the compressive effect of the ionic electric field increases with the diminishing permittivity and structure of the water. 

Calculated free-ion hyperfine fields and ionic electric field gradients (without Sternheimer shielding) in the lanthanides and actinides of interest. 

High-pressure experiments up to 8.3 GPa at 4.2 K were carried out by Kratzer et al. (1986). The observed rise in Curie temperature dTc/dP = 3.5 0.3 K GPa is well within the range predicted by a calculation using a modified RKKY exchange (Jaakkola and Hanninen 1980). The pressure coefficient of is extremely small dB, [/dP= — 0.4 0.1 TGPa Similarly, the ionic electric field gradient decreases by 5% between ambient pressure and 8.3 GPa. Isomer shifts exhibit the linear pressure dependence expected from a compression of mainly s-like conduction electrons. 

Fig. 41. Comparison of measured ionic electric field gradient on Np monopnictides with calculated NpN values, [Taken from Dunlap and Kalvius (1985).]...

It is important to recognize the approximations made here the electric field is supposed to be sulficiently small so that the equilibrium distribution of velocities of the ions is essentially undisturbed. We are also assuming that the we can use the relaxation approximation, and that the relaxation time r is independent of the ionic concentration and velocity. We shall see below that these approximations break down at higher ionic concentrations a primary reason for this is that ion-ion interactions begin to affect both x and F, as we shall see in more detail below. However, in very dilute solutions, the ion scattering will be dominated by solvent molecules, and in this limiting region A2.4.31 will be an adequate description. 

One anomaly inmrediately obvious from table A2.4.2 is the much higher mobilities of the proton and hydroxide ions than expected from even the most approximate estimates of their ionic radii. The origin of this behaviour lies in the way hr which these ions can be acconmrodated into the water structure described above. Free protons cannot exist as such in aqueous solution the very small radius of the proton would lead to an enomrous electric field that would polarize any molecule, and in an aqueous solution the proton inmrediately... 

Migration is the movement of ions due to a potential gradient. In an electrochemical cell the external electric field at the electrode/solution interface due to the drop in electrical potential between the two phases exerts an electrostatic force on the charged species present in the interfacial region, thus inducing movement of ions to or from the electrode. The magnitude is proportional to the concentration of the ion, the electric field and the ionic mobility. 

Klapper 1, R Hagstrom, RFine, K Sharp and B Honig 1986. Focusing of Electric Fields in tire Actir e Sit of CuZn Superoxide Dismutase Effects of Ionic Strength and Amino-Acid Substitution. Proteins Structure, Function and Genetics 1 47-59. 

Ion kinetic energy spectrum. A spectrum obtained when a beam of ions is separated according to the translational energy-to-charge ratios of the ionic species contained within it. A radial electric field achieves separation of the various ionic species in this way. 

The 2eta potential (Fig. 8) is essentially the potential that can be measured at the surface of shear that forms if the sohd was to be moved relative to the surrounding ionic medium. Techniques for the measurement of the 2eta potentials of particles of various si2es are collectively known as electrokinetic potential measurement methods and include microelectrophoresis, streaming potential, sedimentation potential, and electro osmosis (19). A numerical value for 2eta potential from microelectrophoresis can be obtained to a first approximation from equation 2, where Tf = viscosity of the liquid, e = dielectric constant of the medium within the electrical double layer, = electrophoretic velocity, and E = electric field. 

An important characteristic of plasma is that the free charges move in response to an electric field or charge, so as to neutralize or decrease its effect. Reduced to its smaUest components, the plasma electrons shield positive ionic charges from the rest of the plasma. The Debye length, given by the foUowing ... 

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. 

Electrically assisted transdermal dmg deflvery, ie, electrotransport or iontophoresis, involves the three key transport processes of passive diffusion, electromigration, and electro osmosis. In passive diffusion, which plays a relatively small role in the transport of ionic compounds, the permeation rate of a compound is deterrnined by its diffusion coefficient and the concentration gradient. Electromigration is the transport of electrically charged ions in an electrical field, that is, the movement of anions and cations toward the anode and cathode, respectively. Electro osmosis is the volume flow of solvent through an electrically charged membrane or tissue in the presence of an appHed electrical field. As the solvent moves, it carries dissolved solutes. 

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