Flocculation hydrosols

Flocculation of Precipitated and Pyrogenic Silica Hydrosols by Polyethylene Glycols... 

Absorbance, relative, flocculation of silica hydrosols, 368-73 Acetyl groups, hydrophobic, PVA on PS latex particles, 89 Action-mass relationships, adsorption of soluble polymers, 29 Adsorbance... 

Transmission electron microscopy micrographs (Fig. 13.24) also indicate an important characteristic of the supported particles. As in the case of suspensions, they are either aggregated or isolated. Support surface properties may he an important factor governing this aggregation. After deposition on the support, we observed that samples prepared from acidic hydrosols are characterized by the presence of aggregated particles constituting flocculates ranging from 10 to 200 nm, whereas samples prepared via basic hydrosols contain only isolated particles. The opposite was observed when hydrosols were concerned. These final states of the supported particles may be controlled... 

W. Harrison 1 prepared unstable hydrosols of iodine by adding hydriodic acid to a dil. soln. of iodic acid and by adding alcohol to soln. of iodine in glycerol. The hydrosol is at first blue, but it quickly flocculates forming a grey aggregate which, if the cone, be small, can scarcely be recognized. J. Amann has prepared soln. in sulphuric acid and in propylamine. The relation between the colour and the nature of the solvent has already been discussed. 

Combinations of cationic starch and anionic microparticles are useful commercial systems. Shear-sensitive flocculation occurs, allowing microscale reflocculation in the formed paper sheet, which improves dewatering and retention.63,75,76 The microparticles can be colloidal silica, aluminum silicate, poly(silicic acid) or bentonite of specific size and surface area.77 79 Cationic, anionic or polymeric aluminum-containing compounds can be additional components. A three-part coacervate system uses a high molecular weight anionic polyacrylamide, cationic starch and silica.80 Cooking cationic starch in the presence of an anionic silica hydrosol was reported to improve drainage and retention.81... 

Churaev, Nikologorodskaya, and co-workers (33) investigated the Brownian and electrophoretic motion of silica hydrosol particles in aqueous solutions of an electrolyte at different concentrations of poly(ethylene oxide) (PEO) in the disperse medium. The adsorption isotherms of PEO on the surface of silica particles were obtained. The thickness of the adsorption layers of PEO was determined as a function of the electrolyte concentration and the pH of the dispersed medium. The results can be used in an analysis of the flocculation and stabilization conditions for colloidal dispersions of silica (with non-ionogenic water-soluble polymers of the PEO type). 

Sedimentation in emulsions may also be accompanied by the aggregation of emulsion droplets, referred to as flocculation. Flocculation leads to an increase in the effective size of settling aggregates, and as a result, leads to a higher sedimentation velocity. In dilute finely dispersed emulsions in which electrostatic stabilization is of primary importance, the major laws governing flocculation are close to those of coagulation of hydrosols, and are given by the DLVO theory (see Chapter VII, 4). In such systems flocculation may be reversible. 

Gold salts oxidize acetic acid solutions of benzidine to benzidine blue which is a quinoneimine type of dyestuff (compare page 283). Colored gold hydrosols are produced at the same time. Considerable quantities of heavy metals or alkali salts flocculate the reaction products and so prevent the formation of the sols and consequently impair the test. Platinum salts and oxidants which act on benzidine must be absent. 

The gel of stannic acid may be obtained either by evaporating the hydrosol or by precipitation with electrolytes. By the first method a transparent jelly is obtained that becomes glassy on drying and resembles the gel of silicic acid. In the second case flocculent masses are the result of the precipitation. 

An electrophoretic experiment with this hydrosol is designed so that a non-flocculated particle moves 100 pm in 10 s. The zeta potential is determined to be 20 mV. 

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