Coacervate inclusions

The facts mentioned in 1 d brings us all the time up against the question whether the inclusion is really completely enclosed by the surrounding coacervate or indeed if a three-phase contact coacervate—inclusion—equilibrium liquid is present. This question cannot be solved by morphological observation alone. 

Spray drying, extrusion, coacervation and adsorption techniques are among the more widely used (1 ), A relatively new method is the molecular inclusion of flavor in beta-cyclodextrin (2, 3). 

On the process side, techniques like the fluid bed method, extrusion, coacervation, the submerged nozzle process and molecular inclusion have gained importance within the last 10-15 years [1-3, 7]. 

The schematic figure now indicates the fate of the lai e vacuoles. The latter are transported in the coacervate to the cathode in the case of positive coacervate drops, to the anode however in the case of negSLtive coacervate drops. This transport is probably anelectrophoresis, in fact not only vacuoles but also all inclusions (organic liquid drops, solid particles) move in the same sense (p. 445, Fig. 12). These inclusions behave as if... 

An inclusion may for example, with vertical observation give the impression of lyin centrally in a coacervate drop (Fig. 3A) while horizontal observations proves... 

Fig. 3. Different images of the position of inclusions in coacervate drops.

In the first case the inclusion, since it is specifically heavier or lighter than the coacervate, lies pressed against the unobservable thin coacervate lamella. 

Fig. 6. Position of inclusions (a) or of gelation vacuoles (b) in composite coacervate drops. The inclusions or vacuoles are situated at the boundary of the two coexisting coacervates.

Obviously these inclusions make a three phase contact with the two coacervates. 

If we assume that the position of the vacuoles in Fig. 6 b really represents an equilibrium position at an instant shortly before the gelation, at which therefore the two coacervates were still liquid, it then follows necessarily from this that the hypothesis tacitly assumed up to now, as regards the complete wetting of the enclosed G + N + a coacervate by the surrounding G -f- A + n coacervate, is in need of revision. This hypothesis was indeed based on the microscopic picture which these composite colloid bodies exhibit when observed vertically (p. 438, Fig. 5). We are here confronted with the same difficulty which we have mentioned already in the beginning of 1 e (p. 437) for inclusions with horizontal observation one observes the picture B of Fig. 3 (p. 437) for our composite coacervate drops. 

Morphologically there exists a fundamental difference between vacuoles and inclusions such as oil drops, carbon particles etc. These latter are absorbed spontaneously from the equilibrium liquid into the coacervate. ... 

Fig. 12. Behavour of liquid inclusions in complex coacervate drops in a d.c. electric field (schematic). A initial state, B final stage of the relative displacement, in which the organic liquid drop protrudes from the surface of the coacervate drop deformed by the, Buchner effect (see p. 347). Simultaneous vacuolation phenomena etc. in the complex coacervate drops (p. 347 and 452) are omitted from the scheme.

The G + N + a coacervate drops which are surrounded by a shell of G + A + n coacervate in composite coacervate drops (see p. 438), also behave like inclusions. If the G + A - - n coacervate is electrophoretically negative, then the enclosed coacervate drop is displaced inside the G 4- A + n coacervate shell in the direction of the anode if the surrounding coacervate is positively charged, then it is displaced towards the other side. If the surrounding coacervate is at its reversal of charge point then the enclosed coacervate is not displaced. 

In this method a small amount of a hydrosol, for example, a gum arabic solution, is coarsely emulsified in a solution of celloidin in a mixture of ether and amyl alcohol and this emulsion is applied in a thin layer on a glass plate. After allowing the ether to evaporate for some time, the film is placed in water. There are then round inclusions of the hydrosol in the membrane. If one makes a very dilute solution of a basic dye (for example toluidine blue) flow past this membrane, a considerable accumulation of the dye occurs in the enclosed gum arabic sol and coacervation after sometime. See Fig.35. 

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