Coexisting complex coacervates

Fig. 33. Complex coacerv-ation in mixtures of gelatin (G), Na arabinate A) and Na nucleate (iV) (pH 3.7) Inside the closed ellipseshaped region two coexisting complex coacervates noake their appearence. Outside this region but inside the region a b d c a only one complex coacervate appears. Dotted lines going from the side. 40 to the side GN give mixtures of constant electrophoretic velocity U (in arbitrary units). One of them, namely that for J7 == 0, is thus comparable with the dotted line in Fig. 32. The lines of constant U must, between their intersections with the ellipse, also represent tie-lines between coexisting G 4- A n and G iV 4- a coacervates.

Fig. 5. Composite coacervate drops consisting of two coexisting complex coacervates (124 x lin.). Enclosed drops belong to the G -f N a coacervate (weakly vacuolised), the surrounding coacervate shells to the G -f- A + n coacervate.

Fig. 8. Situation of the tielines in the region in which coexisting complex coacervates occur, (see text and compare fig. 33, p. 380, Ch. X, 2t)...

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

Figure 1 is a plot of total solids content versus pH for a 4.4 percent gelatin (275 bloom) - 0.48 percent polyphosphate mixture. The continous curve shown encloses the region in which complex coacervation occurs and two phases coexist. These two phases are a polymer-rich phase called the complex coacervate and a more dilute phase called the equilibrium liquid. The straight line that divides the curve into two parts is the total solids content of the mixture before coacervation (4.88 percent). Points that fall above this line (open circles) are total solids contents of the coacervate at various pH values. Points below this line (solid circles) are corresponding total solids contents for the equilibrium liquid. 

The point of difference with Fig. 32 is however that in the central part of the coacervate field abdca a new phenomenon occurs. Here lies a field of mixing proportions enclosed by a curve, in which two coexisting coacervates occur. Both coacervates are complex coacervates, which contain all three colloids, but the one is rich in A and poor in N, the other is on the contrary rich in N and poor in A,... 

Fig. 39. Topographical position of the three coexisting liquids (after complex coacervation of a gelatin 4- arabinate 4 nucleate sol mixture) in the cell compartments of an artifical tissue (schematic). The G 4- N -h a coacervate (grey) lies embedded in the G + A + n coacervate adjacent to the wall. This latter encloses a central vacuole (equilibrium liquid).

Spruijt E, Sprakel J, Cohen Stuart MA, van der Gucht J (2010) Interfacial tension between a complex coacervate phase and its coexisting aqueous phase. Soft Matter 6 172—178. doi 10. 1039/b911541b... 

As a result of this partial miscibility the two coexisting coacervates contain all three complex components. The one besides gelatin contains mainly A together with a little iV the other besides gelatin contains mainly N together with a little A, To distinguish them these coacervates can be denoted by the symbols G + -4 + n and G + iV + a respectively, whereby the components mainly present are therefore denoted by capital letters. In Chapter XI, If-h (p. 438) we discuss further the mutual wettir properties of these coexisting coacervates, as a result of which drops of G + + 72 and of G + AT + a unite to form composite coacervate drops. 

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