Apparent single colloid systems

From 3 e 1 (see below) it will appear that the division "apparent single colloid systems does not not possess a sharp boundary between it and the next one called "gels . 

In the third main division will be found the apparent single colloid systems and in the fourth gels, containing an interpenetrating liquid system of micro-units. The last main division will deal with solid systems of a nature not further specified, consisting only of macromolecules. 

If, for example, the separated colloid-rich phase remains for some reason or other in a very highly dispersed state of division, then systems can be produced which are macroscopically and microscopically homogeneous. Two types of these systems are known, of which the one has throughout the nature of a liquid, the other that of a solid body. They can be called " apparent single colloid systems, (compare p. 7 Ch. I 3d). This nomenclature indicates that it is appropriate for various reasons to treat them as two-phase systems. In this respect they differ from the true ""single colloid systems (the original sols, the colloid crystals, the coacervates), in which the one-phase conception is the more appropriate. 

The difference between the two kinds of colloid systems resides in the equilibrium character of the true single colloid systems " and the non-equilibrium character of the "apparent single colloid systems . Considered from the two-phase standpoint, the mutual surface of contact between the colloid-rich and the colloid-poor phase is very great in these latter systems, so that they attempt to reduce this surface of contact. They will therefore chaise their properties with time while the true single systems do not change with time. 

From the above it follows that the conditions for the establishment of the liquid type of apparent single colloid systems in general consist of (a) a certain charge of the colloid, (b) a low sol concentration, (c) absence of electrolytic impurities and (d) the added substance which is used to reduce the solubility of the colloid must be a non-electrolyte... 

In still more dilute agar sols (0.02%) flocculation is no longer observed even after one day. We have here again obtained a liquid apparent single colloid system with the behaviour of a lyophobic sol , because if a small concentration of salt is present in this 0.02% sol then it flocculates right enough on cooling. 

D Formation of lyo-phobic sols high dispersion Liquid apparent single colloid system... 

E Gelation high dispersion Solid apparent single colloid system (Gels which are still preferably to be treated as two-phase systems)... 

At other pH values it can still remain in solution but if the pH is brought to the isoelectric point or if some salt is added, flocculation again follows. Under certain circumstances apparent single colloid systems can be formed. Such systems of the solid type (see p. 236, 1 d) are produced for example from the white of an egg on boiling, in which the concentrated sol is transformed into a gel. 

The loose connection between the contents of Volume I and II of this book, hitherto based only upon the presence of kinetic units of large mass (See definition Colloid Science on p. 2 1 b), is here reinforced by the apparent single systems of composite nature c. and presumably also by the two phase gels d. 

In the same way the large decrease of (rjs — Vo)nh V addition of alcohol is explained (Fig. 12, p. 200). In higher alcohol concentrations the macromolecular substance is not soluble, the opalescent systems obtained with small colloid concentrations really being systems of quite other nature than originally supposed (see Chapter VIII, Ic p. 234 Apparent single systems of composite nature ). 

Dispersed systems are said to be stable if, over a certain period of time, there is little detectable aggregation or settling of particles. In many colloidal systems, a stable thermodynamic state is reached only when all particles or droplets have become united in a single homogeneous lump of dispersed phase and, therefore, any apparent stability must be regarded as purely kinetic phenomenon. 

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