Micro cation

Colloid amphoion 4- micro cation 4- colloid anion... 

In the above given considerations an attempt has been made from modern points of view to explain the changes in the internal state of the coacervate for the case where both colloids are of the statistical clewed type. They will also be applicable though changed more or less if only one of the colloids is of this type, the other of the globular type (for example, serum albumin (positive) + gum arabic (negative), p. 233, Fig. 2). This will still be the case even for the variants to be discussed in the next section, colloid cation + micro anion or colloid anion -f micro cation ( 3, p. 384). The existence of the variant micro cation + micro anion (p. 407, 4) however raises new problems. We shall have to decide from the facts that considerations based on macromolecular structure, although they can be very useful, do not yet elucidate the essential point of the complex coacervation. See further p, 412, 4 c. 

DICOMPLEX SYSTEMS II. THE VARIANTS COLLOID CATION H- MICRO ANION AND MICRO CATION + COLLOID ANION... 

COLLOID CATION — MICRO ANION MICRO CATION — COLLOID ANION... 

Obviously an appropriately chosen micro cation — here the 6-valent hexol ion — can take the place of the colloid cation without changii] the nature of the typical complex relations characteristic of the first mentioned variant. 

This point of difference is not attributable to the fact that here we have an example of the variant colloid cation + micro anion, in the other case an example of the variant colloid anion f micro cation but to the choice of the micro ions. Roughly... 

Similar anomalies in the order of the terms of the double valency rule can naturally also occur in the variant micro cation + colloid anion but they then naturally manifest themselves in the rule of the cations. Even a glance at Fig. 37 shows that when we include the auto-suppression of the hexol nitrate in the valency rule of the cations we encounter similar features here 3 — 1 >2 — 1 >1 —1>.6 — 1. 

In general such displacements for a salt, which itself causes no dicomplex coacervation or flocculation, therefore indicate that the cation or anion in question already produces fairly powerful complex relations, although these are not yet powerful enough to cause dicomplex coacervation or flocculation. Therefore in this case dicomplex sols of the type colloid anion -f micro cation or colloid cation + micro anion are produced. 

The reader should reread in Chapter IX, Id and le (p. 269-273) bearing in mind that the term flocculability used there firstly makes no distinction between coacervation and flocculation, secondly that all the flocculations mentioned there belong to the dicomplex type colloid anion + micro cation. 

DICOMPLEX SYSTEMS, III. THE VARIANT MICRO CATION — MICRO ANION IN CONNECTION WITH THE THEORY OF COMPLEX COACERVATION... 

The problem of complex coacervation is considerably simplified by the existence of similar d emixing phenomena in micro ionic solutions. It follows then that specific colloid chemical considerations based, for example, on the macromolecular structure of the colloids are not really essential. The variants of dicomplex coacervation discussed in the previous paragraphs, together with the variant micro cation -h micro anion can all be formulated as a double decomposition... 

We need not again repeat the significance of point 1. for the theory of complex coacervation (the three variants treated in 2 and 3). As far as point 2. is concerned we note that the only apparently essential point of difference of complex coacervation with the demixing micro cation — micro anion (cited on p. 408 under 2). disappears. 

There is strong evidence in favour of the point of view 1. in the variants colloid anion + micro cation or colloid cation -f micro anion in the specific ion sequences for reversal of charge or for coacervation or flocculation. We remind the reader for example of the sequences Cs < Rb < K < Na < Li which occur with sulphate colloids and carboxyl colloids (p. 289). Here polarisation phenomena are still in the background and here the largest ion, that is to say, the least hydrated ion, is most suitable for reversal of charge or coacervation. This points strongly therefore to a direct contact between cation and ionised group of the colloid. 

Thus when one accepts point of view 1. for the variants colloid cation -h micro anion and colloid anion + micro cation there is, on account of the very great similarity, no reason for doubting that it also holds for the variant colloid cation + colloid anion (i. e. for the complex coacervation in the narrower sense). 

For the variant micro cation -h micro anion we can conceive the salt-rich layer in the same way. This layer can more or less be conceived as an ion lattice extremely strongly distorted by intruding water, whereby actually a molten salt containing water has been produced. The disturbances increase more and more in extent on rise of the temperature until finally the two layers become completely miscible. 

We arrive with this at the pronouncement that for the production of the flocculations discussed here the simultaneous presence of complex relations between a colloid amphoion a suitably chosen micro cation and a suitably chosen colloid anion is essential. 

In combinations with M07O24""", Fe(CN)6 ", Co(CN)e" and Hgl/ tricomplex flocculation occurs even with the micro cations which have a smaller affinity for the negative group of the amphoion than the above mentioned one. Thus this still takes place in the case of egg lecithin with Mg, Ca and Sr. Isoelectric gelatin also gives tricomplex flocculations with molybdate or with Hgl4" in the case of Mg, Ca, Sr and Ba but not with Fe(CN)6 " or Co(CN)6 ". 

In the preceeding subsection we have spoken without further comment of the greater or less intensity of complex relations between micro ions and colloid ions. Naturally what was meant was actually the comparison of the maximum intensities of these complex relations obtainable with the micro ions in question. Indeed, just as this is already the case in the dicomplex systems, colloid cation + micro anion or colloid anion + micro cation, the statement, that the intensity of the complex relations formed by a micro cation is still a function of the concentration, also holds for the tricomplex systems. 

Similar results in principle have been obtained in the combinations egg lecithin + carrageen + micro cation and isoelectric gelatin + carrageen + micro cation. 

Finally we may mention that composite coacervate drops are also known in which the complex coacervates belong to the type colloid anion -f micro cation (p. 384, Ch. X, 3). They are produced for example with hexol nitrate in a mixture of sols of ... 

Fig. 9. Composite coacervate drops consisting of two coexisting complex coacervates of the type colloid anion + micro cation (308 X linear).

---