Stability of colloidal solutions

Colloid solutions in the form of clays and paints have been used for more than 2000 years. Since then human beings have tried to understand how the stability of colloid solutions is affected by changes in the environment such as... 

The results obtained in studying colloidal forms of transport are less certain and not always reproducible. Therefore special experimental investigations of the stability of colloidal solutions of iron, silica, and mixtures of the two were conducted in conditions as close as possible to nature, in addition to summarizing and critically examining published data. 

In one and the same colloidal system, two opposite tendencies are embodied—a tendency toward a decrease in the total phase interface and enlargement of particles, and a tendency toward self-hardening due to adsorption of stabilizers—usually charged ions. Thus the stabilization of colloidal solutions is caused by the presence of electrolytes or hydration of ions, in particular of the counterions of the diffusional layer bound to the granule. All the factors that will raise the zeta-potential and increase the hydration of the micelles will enhance the stabihty of the sol. And con-... 

As has already been mentioned, the results of experiments on the stability of colloidal solutions are difficult to compare inasmuch as they were made with different concentrations of the sol, different pH, and with sols of different purity. Therefore we carried out several series of experiments with undialyzed colloidal solutions of FcjOj of various concentrations and strictly controlled pH values. The dependence of the stability of the colloidal solutions on time, the relationship of concentration of the sol and pH, the effect of electrolytes on sols of different concentration, and several other questions were studied. The results obtained are given in summary. 

Fig. 48. Stability of colloidal solutions of iron hydroxide of various concentrations (mg/1) as a function of pH.

The effect of electrolytes on the stability of colloidal solutions of silica remains insufficiently clear despite the substantial number of pubhshed works. 

Donnan has investigated the problem of stability of colloidal solutions from the thermodynamic standpoint, starting with the idea of an effective negative surface tension His investigation, which is an extension of that given in Vol I of this book, will be found m the Zeitsch phystk Chem, 46, 197, 1903... 

A study has been made of the aggregative stability of colloidal solutions of HDS as a function of concentration of a protein in the solution. It has been found that the presence of a protein at concentrations lower than 4 mg mL does not affect the stability of a colloidal solution of HDS because such a low amount of protein molecules is not sufficient for coalescence of silica particles into aggregates. At a high concentration of a protein (5 mg mL and more) the colloidal solution is stable owing to the colloid protection effect. The lower and upper limits of the dispersion stability make up an interval of concentrations (equivalence zone) suitable for flocculation of a colloidal solution of HDS to take place. In this case a colloidal solution of HDS possesses a higher proteinonektonic ability in comparison with an ordinary dispersion [5]. 

W. Heller and T. L. Pugh. Sleric stabilization of colloidal solutions by adsorption of flexible macromolccules. J, Polym. Sci., 47 203-217, 1960. 

The first question that presents itself is the cause of the stability of colloidal solutions. It is advisable to consider the two great classes separately the reversible, those that subdivide spontaneously and the irreversible, those that lack the property of spontaneous subdivision. 

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