Nonpolarizable

The O or S atoms in P=0 and P=S groups may act as electron donors although these groups form relatively weak complexes with electron acceptor compounds such as nonpolarizable, more electropositive (ie, hard) acids, including protons (14). Use is made of this property in the recovery of uranium from wet-process phosphoric acid by extractants such as trioctylphosphine oxide [78-50-2] and di(2-ethylhexyl) hydrogen phosphate [298-07-7]. 

Fig. 1-11 Nonpolarizable Zn/ZnSO electrode developed by Professor Haber in 1908.

Polarizability (Section 4.6) A measure of the ease of distortion of the electric field associated with an atom or a group. A fluorine atom in a molecule, for example, holds its electrons tightly and is very nonpolarizable. Iodine is very polarizable. 

Thermodynamically, all metal/solution interfaces are nonpolarizable, i.e., they can exchange electrical charges freely across the phase boundary. It is the extreme slowness of these exchanges that turns a nonpolarizable into a polarizable interface. Therefore polarizable interfaces are a limiting case of nonpolarizable interfaces.2... 

Nonpolarizable interfaces correspond to interfaces on which a reversible reaction takes place. An Ag wire in a solution containing Ag+ions is a classic example of a nonpolarizable interface. As the metal is immersed in solution, the following phenomena occur3 (1) solvent molecules at the metal surface are reoriented and polarized (2) the electron cloud of the metal surface is redistributed (retreats or spills over) (3) Ag+ ions cross the phase boundary (the net direction depends on the solution composition). At equilibrium, an electric potential drop occurs so that the following electrochemical equilibrium is established ... 

For an ideally polarizable electrode, q has a unique value for a given set of conditions.1 For a nonpolarizable electrode, q does not have a unique value. It depends on the choice of the set of chemical potentials as independent variables1 and does not coincide with the physical charge residing at the interface. This can be easily understood if one considers that q measures the electric charge that must be supplied to the electrode as its surface area is increased by a unit at a constant potential." Clearly, with a nonpolarizable interface, only part of the charge exchanged between the phases remains localized at the interface to form the electrical double layer. 

A nonpolarizable interface behaves as a capacitor C and a resistor R in parallel a polarizable interface responds as a pure capacitor. The higher the resistance R, the closer the behavior of the former to the latter. For R —> °o, a nonpolarizable interface becomes polarizable. The condition / — < corresponds to Am —> 0. This condition is met when the amount of M+ in the null solution is negligibly small. 

Equation (17) expresses the cell potential difference in a general way, irrespective of the nature of the electrodes. Therefore, it is in particular valid also for nonpolarizable electrodes. However, since

interfacial structure, only polarizable electrodes at their potential of zero charge will be discussed here. It was shown earlier that the structural details are not different for nonpolarizable electrodes, provided no specifically adsorbed species are present. 

Nonpolarizable interfaces, 2 Non-ideal solutions, Parsons-Zobel plot for, 55 Nucleation... 

Murphy and Waynewright, and change of upthrust on emersed metal, as a method of measuring, 34 Nikitas, at the air-solution interface, 30 in non-aqueous solutions, 71 for a nonpolarizable electrode, 4... 

The tip current depends on the rate of the interfacial IT reaction, which can be extracted from the tip current vs. distance curves. One should notice that the interface between the top and the bottom layers is nonpolarizable, and the potential drop is determined by the ratio of concentrations of the common ion (i.e., M ) in two phases. Probing kinetics of IT at a nonpolarized ITIES under steady-state conditions should minimize resistive potential drop and double-layer charging effects, which greatly complicate vol-tammetric studies of IT kinetics. 

In Ref. 30, the transfer of tetraethylammonium (TEA ) across nonpolarizable DCE-water interface was used as a model experimental system. No attempt to measure kinetics of the rapid TEA+ transfer was made because of the lack of suitable quantitative theory for IT feedback mode. Such theory must take into account both finite quasirever-sible IT kinetics at the ITIES and a small RG value for the pipette tip. The mass transfer rate for IT experiments by SECM is similar to that for heterogeneous ET measurements, and the standard rate constants of the order of 1 cm/s should be accessible. This technique should be most useful for probing IT rates in biological systems and polymer films. 

The generation and propagation of action potentials and electrical impulses between the tissues in higher plants can be measured by reversible nonpolarizable electrodes [1]. Since both Ag/AgCl electrodes are identical, we decided to call them reference and working electrodes as shown in Fig. 4. The reference electrode (—) was usually inserted in the stem or in a root of a soybean plant, and the upper (working) electrode (-I-) inserted in the stem or a leaf of the plant. 

Because this method avoids iterative calculations to attain the SCF condition, the extended Lagrangian method is a more efficient way of calculating the dipoles at every time step. However, polarizable point dipole methods are still more computationally intensive than nonpolarizable simulations. Evaluating the dipole-dipole interactions in Eqs. (9-7) and (9-20) is several times more expensive than evaluating the Coulombic interactions between point charges in Eq. (9-1). In addition, the requirement for a shorter integration timestep as compared to an additive model increases the computational cost. 

Most liquid phase molecular simulations with explicit atomic polarizabilities are performed with MD rather than MC techniques. This is due to the fact that, despite its general computational simplicity, MC with explicit polarization [173, 174] requires that Eq. (9-21) be solved every MC step, when even one molecule in the system is moved, and the number of configurations in an average Monte Carlo computation is orders of magnitude greater than in a MD simulation. For nonpolarizable, pairwise-additive models, MC methods can be efficient because only the... 

Warren GL, Patel S (2008) Comparison of the solvation structure of polarizable and nonpolarizable ions in bulk water and near the aqueous liquid-vapor interface. J Phys Chem C 112(19) 7455-7467... 

A high concentration of a strong, relatively nonpolarizable base, such alkoxide ion, is used to avoid El reaction. 

Cly-Ala Dipeptide in Aqueous Solution -Polarizable versus Nonpolarizable Force Fields... 

The evaluation of Gcicctrostatic has received a great deal of attention. It is clear that Eqs. (32) and (33), which are for nonpolarizable point charges and point dipoles, cannot reproduce the effect of the medium upon the solute molecule. A major contribution was made by Onsager, who took this molecule to be a polarizable point dipole located at the center of a spherical cavity 20 the resulting expression is,... 

In electrochemistry, the electrode at which no transfer of electrons and ions occurs is called the polarizable electrode, and the electrode at which the transfer of electrons and/or ions takes place is called the nonpolarizable electrode as shown in Fig. 4-4. The term of polarization in electrochemistry, different from dipole polarization in physics, indicates the deviation in the electrode potential from a specific potential this specific potential is usually the potential at which no electric current flows across the electrode interface. To polarize" means to shift the electrode potential from a specific potential in the anodic (anodic polarization) or in the cathodic (cathodic polarization) direction. 

With nonpolarizable electrodes the polarization (the shift of the electrode potential) does not occur, because the charge transfer reaction involves a large electric current without producing an appreciable change in the electrode potential. Nonpolarizable electrodes cannot be polarized to a significant extent as a result. 

The nonpolarizable electrode may also be defined as the electrode at which an electron or ion transfer reaction is essentiaUy in equilibrium i. e. the electron or ion level in the electrode is pinned at the electron level of hydrated redox particles or at the hydrated ion level in aqueous electrolyte. In order for the electrode reaction to be in equilibrium at the interface of nonpolarizable electrode, an appreciable concentration of redox particles or potential determining ions must exist in the electrolyte. 

In electrochemistry, the electrode current is conventionaUy classified into the faradaic current and the nonfaradaic current. The former is the electric current associated with charge transfer reactions at nonpolarizable electrodes and the latter is the current that is required to establish the electrostatic equilibrium at the interfacial double layer on both polarizable and nonpolarizable electrodes. The nonfaradaic ciurent, sometimes called a transient current, flows also in the course of establishing the adsorption of ions on electrodes. 

Next, we consider the interface M/S of a nonpolarizable electrode where electron or ion transfer is in equilibrium between a solid metal M and an aqueous solution S. Here, the interfadal potential is determined by the charge transfer equilibrium. As shown in Fig. 4-9, the electron transfer equilibrium equates the Fermi level, Enn) (= P (M)), of electrons in the metal with the Fermi level, erredox) (= P s)), of redox electrons in hydrated redox particles in the solution this gives rise to the inner and the outer potential differences, and respectively, as shown in Eqn. 4-10 ... 

The electrode potential defined in Sec. 4.3 applies to both nonpolarizable electrodes at which charge transfer reactions may take place and polarizable electrodes at which no charge transfer takes place. For nonpolarizable electrodes at which the charge transfer is in equilibrium, the interfacial potential is determined by the equilibrium of the charge transfer reaction. 

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