Multivalent electrolytes

To maintain colloid stability over a long period of time (i.e. 2-3 years), one needs to ensure the following conditions High zeta potential by ensuring adequate coverage of the particles or droplets by ionic surfactant low electrolyte concentration low valency of the electrolyte (multivalent ions should be avoided). 

The flow can be radial, that is, in or out through a hole in the center of one of the plates [75] the relationship between E and f (Eq. V-46) is independent of geometry. As an example, a streaming potential of 8 mV was measured for 2-cm-radius mica disks (one with a 3-mm exit hole) under an applied pressure of 20 cm H2 on QT M KCl at 21°C [75]. The i potentials of mica measured from the streaming potential correspond well to those obtained from force balance measurements (see Section V-6 and Chapter VI) for some univalent electrolytes however, important discrepancies arise for some monovalent and all multivalent ions. The streaming potential results generally support a single-site dissociation model for mica with Oo, Uff, and at defined by the surface site equilibrium [76]. 

Though solid electrolytes for multivalent ions offer the advantage of a larger charge transfer, their conductivities are much lower than those of monovalent ions at ambient temperature because of a higher activation enthalpy for the ionic motion... 

Experience shows that solutions of other electrolytes behave in a manner similar to the examples we have used. The conclusion we reach is that the Debye-Hiickel equation, even in the extended form, can be applied only at very low concentrations, especially for multivalent electrolytes. However, the behavior of the Debye-Hiickel equation as we approach the limit of zero ionic strength appears to give the correct limiting law behavior. As we have said earlier, one of the most useful applications of Debye-Hiickel theory is to... 

Comparison of the concentrations of either the cation or the anion in the two phases thus has potential for evaluating the polyanion valence provided that estimates of the mean ion activity coefficient (y ) are available. Furthermore, as realized by Svensson [165], expression of the Donnan distribution of small ions in this manner has two advantages in that (i) Eq. 31 applies to each type of small ion in situations where the supporting electrolyte is not restricted to single cationic and anionic species and (ii) multivalence of a small ion is also accommodated. 

The retarding effect of electrolytes in the application of basic dyes to acrylic fibres increases with increasing concentration of salt up to a certain level. Increasing the concentration beyond this point has no further effect on exhaustion with certain univalent anions, whilst with multivalent types there is an increase in dye sorption (Figure 12.2)... 

These results have led to the conclusion that ionic mechanisms alone do not entirely explain the complex interactions that occur between basic dyes and acrylic fibres. Hydrophobic interaction also plays an important part and it has been demonstrated [55] that multivalent anions such as sulphate or phosphate can enhance the hydrophobic interaction, thereby also increasing dye sorption in some circumstances. Whilst such results are of interest in terms of dyeing theory, it is extremely doubtful whether there will ever be practical interest in exploiting the use of electrolytes at such high concentrations. 

J.L. Beckers, P. Gebauer and P. Bocek, Why robust electrolytes containing multivalent ionic species can fail in capillary zone electrophoresis../. Chromatogr.A 916 (2001) 41—49. 

Styrene-butadiene rubber (SBR) latexes which are compatible with cementitious compounds are copolymers. They show good stability in the presence of multivalent cations such as calcium (Ca++) and aluminum (A1+++) and are unaffected by the addition of relatively large amounts of electrolytes (e.g., CaCl2). Outdoor exposure to... 

From a pharmaceutical perspective, phospholipids-stabilized emulsions are remarkable. For example, they are relatively stable, with shelf lives of 18 months to 2 years being obtained after the initial heat sterilization. They resist the increased shear rates as the bottles are transported from producer to user and they can tolerate the addition of a wide variety of monovalent electrolytes for at least short periods prior to administration. However, they cannot resist freezing and changes in droplet size following exposure to freeze-thaw cycles can be used as a measure of the stability of the emulsion system. Most injectable emulsions are sensitive to multivalent cations such as calcium or magnesium salts, which rapidly flocculate the phospholipids-stabilized systems. 

Multivalent Electrolytes. For 2 1 electrolytes we assume n = 2 for the divalent ion and n = 1 for the monovalent ion. The latter is a necessary choice which supposes that a monovalent ion sees a singly charged ionic cloud represented by a reduced ionic atmosphere with one maximum. This model gives log 7 vs. a/7 plots which are remarkably like the experimental pictures. The... 

The two water desalination applications described above represent the majority of the market for electrodialysis separation systems. A small application exists in softening water, and recently a market has grown in the food industry to desalt whey and to remove tannic acid from wine and citric acid from fruit juice. A number of other applications exist in wastewater treatment, particularly regeneration of waste acids used in metal pickling operations and removal of heavy metals from electroplating rinse waters [11]. These applications rely on the ability of electrodialysis membranes to separate electrolytes from nonelectrolytes and to separate multivalent from univalent ions. 

The theory is extended to multivalent ions, in which case an inversion of the surface charge can occur with increasing electrolyte concentration. Depending on the sign of the surface charge, the adsorption of dipolar molecules on the surface can increase or decrease the repulsion [7.6]. When association equilibria are taken into account... 

In the framework of the traditional double layer theory, when there is a strong adsorption of a multivalent cation of the electrolyte, the stability ratio of a colloidal dispersion first decreases, passes through a minimum, followed by a maximum, after which it decreases as the concentration of the (multivalent) electrolyte increases. When the adsorption is weak, the stability ratio decreases mono-tonically with increasing electrolyte concentration. For a monovalent electrolyte, the stability ratio calculated in the framework of the classical double layer theory decreases monotonically with increasing electrolyte concentration. Consequently, in the traditional theory, the ion screening becomes dominant at high ionic strength, whereas experiment appears to show that the colloidal dispersion is restabilized. 

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