Electrolytes coagulation

The above explanation of acclimatisation is supported by the results obtained on adding mixtures of electrolytes to the hydrosol. Hydrolysis of the coagulating electrolyte has a pronounced influence and the presence of one electrolyte may diminish the coagulating power of another. More magnesium chloride is required to coagulate a sol containing lithium chloride than is required in the absence of lithium chloride. Also in the presence of sodium benzoate or sodium nitrite, more than the calculated quantity of potassium or barium chloride is required for precipitation. 

Figure 6. Log (c.c.c.) vs. pH for a PTFE latex using aluminum nitrate as the coagulating electrolyte (19)...

Coagulating electrolyte Coagulation threshold (precipitating capability, mmol/l) Coagulating electrolyte Coagulation threshold (precipitating capability, mmol/l)... 

Some results obtained by Storer (1968) using well-dialyzed polystyrene latices at pH 8.5 and mixtures of magnesium sulfate and sodium nitrate as the coagulating electrolytes are shown in Fig. 23. Distinct synergism was observed over the entire concentration range. The use of activities of the ions in the mixed system rather than concentrations, gave a reasonable explanation for the form of the data, bot it is also of interest that the discrete-ion treatment of Levine and Bell (1965) also predicts synergism for certain cases. 

Schulze first showed that inorganic colloids are especially sensitive to electrolytes of high charge, and Hardy pointed out that their stability is closely related to mobility in an electric field. The Schulze-Hardy rule states that the sensitivity of lyophobic colloids to coagulating electrolytes is governed by the charge of the ion opposite that of the colloid and that the sensitivity increases more rapidly than the charge of the ion. 

In the case when the depth of potential minimum is smaller than several kT, the coagulation (i.e., the combination of two particles) becomes thermodynamically unfavorable even at low height of the potential barrier (Chapter VII, 1), and the stability of colloidal system towards coagulation is of thermodynamic nature. This is confirmed by observed peptization of coagulated precipitates upon washing out the excess of coagulating electrolyte and by stabilization of sols by specifically adsorbed ions. 

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... 

The copolymer latex can be used "as is" for blending with other latexes, such as in the preparation of ABS, or the copolymer can be recovered by coagulation. The addition of electrolyte or free2ing will break the latex and allow the polymer to be recovered, washed, and dried. Process refinements have been made to avoid the difficulties of fine particles during recovery (65—67). 

Poly(ethylene oxide) associates in solution with certain electrolytes (48—52). For example, high molecular weight species of poly(ethylene oxide) readily dissolve in methanol that contains 0.5 wt % KI, although the resin does not remain in methanol solution at room temperature. This salting-in effect has been attributed to ion binding, which prevents coagulation in the nonsolvent. Complexes with electrolytes, in particular lithium salts, have received widespread attention on account of the potential for using these materials in a polymeric battery. The performance of soHd electrolytes based on poly(ethylene oxide) in terms of ion transport and conductivity has been discussed (53—58). The use of complexes of poly(ethylene oxide) in analytical chemistry has also been reviewed (59). 

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