Cation, mobihty

Extending this to a system consisting of two kinds of cations (1 and 2) and one kind of anion, Klemm has derived equations for calculating internal cation mobihties. The internal mobility Map of an a ion with reference to a P ion is directly related to the velocity change in the relevant two ions caused by the perturbation field ... 

PEO is a hard polybasic molecule, so it is expected that ions will form strong complexes with the polymer, whereas Hg + should only interact weakly with the hard ethereal oxygen atoms. Complexes of PEO with both these cations are formed readily, but transference number measurements have demonstrated that, in this medium, Mg + ions are immobile and Hg ions are mobile, which suggests a possible inverse relationship between promoting complex formation and the consequential effects on cation mobihty. 

For example, Barlow and Margoliash [33] showed that phosphate, chloride, iodide, and sulfate, in decreasing order of effect, reduced the electrophoretic mobihty of human cytochrome c at pH 6.0 by up to a factor of 2. The cations lithium, sodium, potassium, and calcium had no effect. It is possible to account for the binding equilibria of these counterions so that the titration and electrophoresis results can be compared however, in many of the early electrophoresis experiments these data were not available and relevant conditions were not recorded or controlled. For general discussions on the extensive field of ligand binding to proteins, see Cantor and Schimmel [60] and van Holde [403]. 

Let us first concentrate on the potassium ion mobihty. A, in Eq. (4.72). As with any activated process, the potassium ions must overcome an activation energy barrier, which we will notate as a free energy AG, to move to the cation vacancy site, as illustrated in Figure 4.43. Recall from Section 3.0.2 that the fraction of ions with the required energy to overcome the barrier is given by the Boltzmann distribution and depends on exp(—AGVAT). It can be shown, then, that... 

Unlike the mobility of imsaturated hydrocarbons, the mobihty of saturated hydrocarbons in Na-X is, in fact, essentially unaffected by the presence of sodium cations. This has been confirmed by PFG NMR diffusion studies with benzene and -heptane in zeohte Na-X and La-X [103,151]. Since the triva-lent lanthanum ions are predominantly localized at positions in the hexagonal prisms and sodalite units, the molecules adsorbed in lanthanum-exchanged zeolites are essentially without contact to the cations. As a consequence of the specific interaction between the cations and the unsaturated hydrocarbon, the benzene mobility in Na-X was found to be two orders of magnitude smaller than in La-X, while the -heptane diffusivities were the same. 

The mobihties /t of the charge carriers in the materials from which OLEDs are fabricated are low in comparison to the mobilities in organic molecular crystals (see Chap. 8). Furthermore, they are very different in the different materials there are some materials in which predominantly electrons are transported (fig ft),), and some in which mainiy holes participate in the transport (/t), /tg). Hole-transport materials, e.g. the naphthyl-phenyldiamine-biphenyl derivative NPB, have a relatively low ionisahon energy and therefore form radical cations preferentially and reversibly. Electron transport materials, e.g. Alqs, have a relatively high electron affinity and thus form radical anions preferentially and reversibly. 

Computer simulation of struetures and interactions of molecular sieves with adsorbed moleeules has beeome a third powerful approach. Simulation methods are now available that have been shown to model aceurately structural details of framework geometry, cation location and the position and mobihty of molecules within the pores. These approaches can now be apphed to predict results for systems of interest (reducing expensive and time-consuming experimentation) and also where details cannot be determined by any other method. 

The excess mobihty-vs.-temperature curve was found to exhibit a max-immn at elevated temperatures near 150 °C, achievable at elevated pressure. The magnitude of the proton mobihty in pure water was not addressed in those studies, although attempts to determine it were made by Kohhausch at the end of the 19th centmy [78]. Focus was instead on the conductance of strong acids such as HCl in the Umit of infinite dilution. The difference of the measured conductance and the limiting conductance of a salt of a cation with size similar to that of was attributed to excess proton mobility, based on the assmnption that the hydrodynamic radius of both ions is similar. The excess mobility was taken to represent non-classical proton hops on top of the classical hydrodynamic motion of the HsO". ... 

The electrophoretic mobihties of cations (Pobs) can be related to the limiting ionic equivalent conductivity, Aekv, by the following equation ... 

The electric conduction of electrolytes is carried by ions. The ions migrate, each kind with its own individual velocity v+ or v as soon as an electric field with a field strength E is applied. The ratio of the velocity of an ion and the corresponding field strength is called the ion mobility m. Cations as well as anions contribute to the overall conductivity of an electrolyte, each contribution being based on the individual mobihty of the specified ion type. The conductivity of an electrolyte solution can be measured easily. Commonly, the specific conductance k (sometimes called SC) is determined. The latter is derived from the resistance of an electric conductor R and its dimensions length I and cross-sectional area A, as given by k = / A . The quantity k... 

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