Coacervation: definition

In a critical and definitive review of this area (de Kruif et al.. 2004), the following general features of complex coacervation were asserted ... 

Coacervate drops may be converted into a layer or a flocculent precipitate on standing, but they may be reconverted into drops and solutions. This reversibility may have definite limits, because it is related to the conditions under which the coacervate was formed and its chemical composition. For instance, if the composition of a coacervate includes serum albumin, the number of conversions is usually limited to three or four, after which it is irreversibly denatured. 

For each coacervate system, a definite optimum concentration of the initial solutions exists at which the mean diameter of the drops is 5-8 p and their number is maximum and equal to 7 to 14 million per ml (11). An increase in the concentration of the initial solutions leads to the appearance of flocculates and reduction in the number of drops through sharp acceleration of their coalescence, while a decrease in the concentration as... 

Salts and Stabilizers Effects. Electrolytes, specifically mineral salts, have a definite effect on coacervates since they carry a charge and are therefore capable of changing the charge of the coacervate. If an added salt has a greater affinity for water than the coacervate, it dehydrates the coacervate drop, and thus breaks it down and converts it to a precipitate. The more hydrated the coacervate, the harder it is for it to hold water and the less salt is required for its precipitation. 

Some papers60-61 have been devoted to phase separation of polyionic complexes from partially furated (PVA-S) and aminoacetylated (PVA-AAC)poly(vinyl alcohol) in aqueous salt solutions. The separation liquid-liquid or complex coacervation occurs at a definite value of the charge density on the macromolecule. From the concentration dependence of the reduced viscosity of the initial components PVA-S, PVA-AAc and their equivalent mixture in water it follows that the viscosity of the components noticeably increases with dilution, and the curve of the equivalent mixture is concentration independent. This fact confirms the formation of the neutral polymer salt, due to electrostatic interactions of PVA-S (strong polyadd) and PVA-AAc (weak polybase). 

Coacervation is defined as the separation of colloid systems into two liquid phases, according to the lUPAC (International Union of Pure and Applied Chemistry) definition (Martins, 2012). 

As a coacervate fulfils the definition of Sol , given in 1 b (p. 2), we could also simply say that both layers are thus constituting an equilibrium between two ... 

Thus the above stated fact is exhibited clearly in this figure the water content is a minimum at the most favourable condition for complex coacervation (here a definite pH at the given mixing proportion). On decrease or increase of the pH the water content increases. 

A clear sol of purified egg lecithin (association colloid) does not flocculate immediately with La(N03)3 . Na-arabinate sol also gives no flocculation or coacervation with La(N03)g. The sol mixture of egg lecithin and Na arabinate similarly is clear. If however one adds a solution of La(N03)3 to a suitably chosen mixture of egg lecithin and Na arabinate sol, then flocculation immediately occurs in a definite range of concentrations. This flocculation completely bears the character of a complex flocculation. It becomes quickly suppressed on the addition of indifferent salts, (e.g. Co(NH3)6Cl3, CaClg, NaCl, K2SO4, K3CH(S03)3), in which the double vdency rule occurs ... 

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