Specific Ion Effect

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

The behavior of a few typical electrolytes is illustrated in Figure 19.13. By definition, 7+ is one at zero molality for all electrolytes. Furthermore, in every case, 7+ decreases rapidly with increasing molality at low values of m2. However, the steepness of this initial drop varies with the valence type of the electrolyte. For a given valence type, 7 + is substantially independent of the chemical nature of the constituent ions, as long as m2 is below about 0.01. At higher concentrations, curves for 7 + begin to separate widely and to exhibit marked specific ion effects. 

De Cristofaro, R., and Di Cera, E. (1992). Modulation of thrombin-fibrinogen interaction by specific ion effects. Biochem. 31, 257-265. 

M. Mandu, E. Ruckenstein Specific Ion Effects in Common Black Films The Role of the Thermal Undulation of Surfaces, LANGMUIR 20 (2004) 1775-1780. 

When the ion is hydrated by all the adjacent molecules (it = r — 1), there is a strong lattice-site exclusion effect at high ionic concentrations, since the central site can be available to an ion only when both its first and second neighbors are free of ions (a total of 1 + w 4- w(w — 1) = ia2 + 1 sites). On the other hand, when the hydration number (r — 1) is low, almost any free site can be occupied by an ion, since in this case there is a high chance to find at least (r — 1) free water molecules around a selected site. In the next section it will be shown that there is a strong dependence of the site-exclusion effect on the hydration number and, hence, that specific ion effects can be important in the double layer interactions. 

It is clear that the DLVO theory is incomplete, a simple example being the stability of neutral lipid bilayers,9 or of the water films involving nonionic surfactants,10 where there is no double layer to provide the required repulsion. Another example is provided by the specific ion effects, namely, the different behaviors of systems immersed in different electrolytes of the same valence. Various electrolytes have been classified long ago by Hofmeister in an... 

Non-DLVO colloidal interactions specific ion effects explained by ion-hydration forces... 

M. Manciu, E. Ruckenstein Specific ion effects via ion hydration 1. Surface tension ADVANCES IN COLLOID AND INTERFACE SCIENCE 105 (2003) 63-101. 

Keywords Specific ion effect Ion hydration Structure-making ion Structure-breaking ion... 

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