Colloids causing coagulation

In the previous sections, we described the overall features of the heat-induced phase transition of neutral polymers in water and placed the phenomenon within the context of the general understanding of the temperature dependence of polymer solutions. We emphasised one of the characteristic features of thermally responsive polymers in water, namely their increased hydropho-bicity at elevated temperature, which can, in turn, cause coagulation and macroscopic phase separation. We noted also, that in order to circumvent this macroscopic event, polymer chemists have devised a number of routes to enhance the colloidal stability of neutral globules at elevated temperature by adjusting the properties of the particle-water interface. 

F. S. Brown and C. R. Bury 6 obtained colloidal solutions of phosphorus pentoxide in nitrobenzene by stirring the mixture in the presence of alcohols or organic acids. The hydroxy-compound is absorbed and peptizes the pentoxide. Traces of moisture cause coagulation. Cone. soln. set to gels on keeping. 

The potential is also closely connected with the stability of lyophobic colloids 3 if it is reduced below a critical value, the dispersed particles coagulate rapidly. Ions of opposite charge to the colloidal particles are easily adsorbed and cause coagulation. The effectiveness of the ions increases enormously with increase in valency according to the well-known... 

The mixing of seawater and freshwater in estuaries causes coagulation and flocculation of metal-organic rich colloidal material (Sholkovitz et al., 1978 Fox, 1990), and estuarine water... 

Organic ions are particularly effective in causing coagulation. This was well known in the older literature when organic salts such as quinine sulfate, etc. were used as coagulants [39]. More recently, attention has focused on the behaviour of surfactants both as stabilizers and as coagulants for polymer colloids. As is... 

A. Irreversible Colloids. — Some irreversible colloids are sensitive to electrolytes, while others remain unaffected. Some degree of r u-larity of behavior is manifested only by colloidal metals (free from contamination with other colloids), salts, and sulfides. Here the law obtains with a fair amount of certainty, that electrolytes cause precipitation. In general very small concentrations of salts, bases, and acids suffice to coagulate the colloid in question. The precipitate is not soluble in water. Nonelectrolytes, on the contrary, usually do not cause coagulation. The sensitiveness may be completely destroyed by the addition of often very small quantities of protective colloids. Even traces of these last-named substances may influence the reaction to a considerable degree. 

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