F-potential

The f potential of silver iodide can be varied over the range 75 mV, by varying the Ag or 1 concentration again demonstrating that varying the concentration of potential-determining ions can reverse the sign of the f potential. 

Fig. V-7. f potential of muscovite mica versus electrolyte concentration at pH 5.8 0.3. (From Ref. 76.)...

While the result should not have very exact physical meaning, as an exercise, calculating the f potential of lithium ion, knowing that its equivalent conductivity is 39 cm /(eq)(ohm) in water at 25°C. 

Stem layer adsorption was involved in the discussion of the effect of ions on f potentials (Section V-6), electrocapillary behavior (Section V-7), and electrode potentials (Section V-8) and enters into the effect of electrolytes on charged monolayers (Section XV-6). More speciflcally, this type of behavior occurs in the adsorption of electrolytes by ionic crystals. A large amount of wotk of this type has been done, partly because of the importance of such effects on the purity of precipitates of analytical interest and partly because of the role of such adsorption in coagulation and other colloid chemical processes. Early studies include those by Weiser [157], by Paneth, Hahn, and Fajans [158], and by Kolthoff and co-workers [159], A recent calorimetric study of proton adsorption by Lyklema and co-workers [160] supports a new thermodynamic analysis of double-layer formation. A recent example of this is found in a study... 

Fig. XI-14. Effect of hydrocarbon chain length on the f potential of quartz in solutions of alkylammonium acetates and in solutions of ammonium acetate. (From Ref. 183.)...

The adsorption appears to be into the Stem layer, as was illustrated in Fig. V-3. That is, the adsorption itself reduces the f potential of such minerals in fact, at higher surface coverages of surfactant, the potential can be reversed, indicating that chemical forces are at least comparable to electrostatic ones. The rather sudden drop in potential beyond a certain concentration suggested to... 

Fuerstenau and co-workers observed in the adsorption of a long-chain ammonium ion RNH3 on quartz that at a concentration of 10 Af there was six-tenths of a mono-layer adsorbed and the f potential was zero. At 10 M RNH3, however, the f potential was -60 mV. Calculate what fraction of a monolayer should be adsorbed in equilibrium with the 10 M solution. Assume a simple Stem model. 

In the asymptotic region, an electron approximately experiences a Z /f potential, where Z is the charge of the molecule-minus-one-electron ( Z = 1 in the case of a neutral molecule) and r the distance between the electron and the center of the charge repartition of the molecule-minus -one-electron. Thus the ip orbital describing the state of that electron must be close to the asymptotic form of the irregular solution of the Schrodinger equation for the hydrogen-like atom with atomic number Z. ... 

Figure 2.4 Components of the Li-F potential-energy curve E R) = E (R) + E(NL>(R), showing the localized natural-Lewis-structure model energy E(L> (circles, left-hand scale) and delocalized non-Lewis correction ,(NL) (squares, right-hand scale). The classical electrostatic estimate E (dotted line) is shown for comparison.

In [2] all the possible structures listed above were considered for each ternary fluoride. The potentials for A+-F- and M2+-F were exactly those derived for the binary systems AF and MF2, all of which were based on a single F -F potential. These potentials were assumed to be transferable unchanged to the ternary fluorides. 

Ciambelli, P Corbo, P Migliardini, F. Potentialities and limitations of lean de-NOx catalysts in reducing automotive exhaust emissions, Catal. Today, 2000, Volume 59, Issues 3-4. 279-286... 

Costan, G. Bermingham, N. Blaise, C. Ferard, J.F. Potential Ecotoxic Effects Probe (PEEP) a novel index to assess and compare the toxic potential of industrial effluents. Environ. Toxic. Water Quality 1993, 8 (1). 

In each case the electrokinetic measurements can be interpreted to yield a quantity known as the zeta (f) potential. It is important to note that this is an experimentally determined potential measured in the double layer near the charged surface. Therefore it is the empirical equivalent... 

Although the f potential is undoubtedly an important quantity in colloid chemistry, it is not totally free of ambiguity. The problem is this It is not clear at what location within the double layer the potential is measured. The derivations of this chapter show that the f potential is the double-layer potential close to the surface, but the precise quantitative meaning of close cannot be defined. We examine this briefly in Section 12.8. 

The objective of comparing values of f determined from electrophoresis with those determined by other electrokinetic methods was stated at the beginning of Section 12.6. Enough experiments have been conducted in which at least two of the electrokinetic methods we have discussed are compared to leave no doubt as to the self-consistency of f as determined by these different methods. There is no guarantee, however, that self-consistent f potentials are correct. Consistency means only that f has been extracted from experimental quantities by a self-consistent set of approximations. It should be emphasized, however, that the existence of a potential at the surface of shear —which is the common component in all the electrokinetic analyses we have discussed —is more than amply confirmed by these observations. 

In the quantitative sections of this chapter the primary emphasis has been on establishing the relationship between the electrophoretic properties of the system and the zeta potential. We saw in Chapter 11 that potential is a particularly useful quantity for the characterization of lyophobic colloids. In this context, then, the f potential is a valuable property to measure for a lyophobic colloid. For lyophilic colloids such as proteins, on the other hand, the charge of the particle is a more useful way to describe the molecule. In this section we consider briefly what information may be obtained about the charge of a particle from electrophoresis measurements. 

Throughout most of this chapter the emphasis has been on the evaluation of zeta potentials from electrokinetic measurements. This emphasis is entirely fitting in view of the important role played by the potential in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. From a theoretical point of view, a fairly complete picture of the stability of dilute dispersions can be built up from a knowledge of potential, electrolyte content, Hamaker constants, and particle geometry, as we discuss in Chapter 13. From this perspective the fundamental importance of the f potential is evident. Below we present a brief list of some of the applications of electrokinetic measurements. 

Numerous other applications could be listed in which electrokinetic characterization provides a convenient experimental way of judging the relative stability of a system to coagulation. Paints, printing inks, drilling muds, and soils are examples of additional systems with properties that are extensively studied and controlled by means of the f potential. 

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