Composition of coacervate

Furthermore the composition of coacervate and equilibrium liquid is completely determined at a given total composition of the system. Coacervate layer and equilibrium liquid are in thermodynamic equilibrium the way by which one arrives at any particular final composition of the total system is of no influence on the composition of coacervate and equilibrium liquid. 

If one plots the composition of coacervates and equilibrium liquids on an isotherm (compare p. 257, Fig. 12b in Chapter VIII, where an equilateral triangle WGA... 

Fig. 18. Scheme for the composition of coacervate and equilibrium liquids in an isohydric scries of mixtures of 2% sols, if the coacervate had a constant composition (sec text). 

Fig. 20. Composition of coacervates and c-quilibrium liquids in some five isohydric series of mixtures of 2% gelatin and gum arabic sols. Top graph coacervates lie on the 5 branches of the curves top right in the graph. Equilibrium liquids lie on 5 branches of curves near the water comer. In order not to overload the figure only two of these latter curves arc drawn and further, apart from four, all tie lines, which connect coacervates to coexisting equilibrium liquids, are omitted.

In Fig. 22 the colloid compositions of coacervate (column 6) and equilibrium liquid (column 7) are plotted as a function of the mixing proportion of the two sols (column 1). Two separate curves result, C for the coacervate, E for the equilibrium liquid. These curves intersect at the equivalent mixing proportion. Here or at any rate nearly here lies the electrophoretic reversal of charge point of the coacervate. 

At other mixing proportions of the sols the colloid compositions of coacervate, equilibrium liquid and total mixture are no longer equal. 

Fig. 23. Composition of coacervates and equilibrium liquids at constant mixing proportion (1 1) of the 2% gelatin and gum arabic sols, but with the pH varying (see text).

Influence of an added salt on the composition of coacervate and equilibrium liquid... 

Fig. 25. Influence of CaClg on the composition of coacervate and equilibrium liquid produced in isohydric series of mixtures (pH 3.5) of 2% gelatin and arabinic acid sols, a the arrows on the coacervate curves give the position of the coacervate corresponding in each series of mixtures with the maximum degree of coacervation.

Classification and Nomenclature. Coacervates can be divided into simple ones and complex ones based on the complexity of their chemical composition. Simple coacervates form when a compound with a great affinity for water is added to a solution of a hydrophilic molecule, causing its dehydration and a decrease in its solubility. Molecules of the same chemical composition are thus involved in simple coacervation. Complex coacervates are obtained when solutions of positively charged molecules and negatively... 

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. 

The pH can also determine the type or composition of the coacervates formed from a three-component mixture, such as gum arabic, gelatin, and yeast nucleic acid, for example. In such a coacervate, at pH 3.36, the drops consist mainly of gum arabic and gelatin at pH 3.48, of gelatin, gum arabic, and nucleic acid at pH 3.8, of gelatin and nucleic acid. 

The volume occupied by the coacervate drops is generally 3 to 5% of the volume of the entire coacervate system. An increase in the concentration of the solutions from which the coacervate is formed leads to an increase of the total volume occupied by the coacervate layer. For example, when 1% solutions of protein and carbohydrate were used to form coacervates, the volume of the coacervate layer was 5.31% of the total volume of the coacervate system, whereas when 4% solutions of these substances were employed, 26.2% of the volume was occupied by the coacervate drops. A negative temperature coefficient is characteristic of coacervates whose composition includes fats and fatty acids the higher the temperature, the smaller the volume occupied by the coacervate layer. 

Practical Coacervate Formation. The composition of the various parts of the coacervate system was determined by using l c-labelled kappa-casein as one component of the coacervates, and then performing a mass balance on the system. The C-kappa-casein was prepared by reductive methylation of kappa-casein with l C-formaldehyde (15), This derivatization of kappa-casein was found not to materially affect its physical properties (16). 

To determine the composition of the coacervates, C-la-belled kappa-casein waS incorporated in the coacervates and a mass balance on the coacervate system was performed. The results of these studies are shown in Table III. Sixty percent of the kappa-casein in the gum arabic-kappa-casein coacervate system... 

The main advantage of coacervation by Polymer 2-Polymer 3 repulsion over polymer desolvation resides in the good control of the composition and viscosity of both the coacervate and dispersing phases. This, in turn, provides a means to control particle size and prevent undesired coalescence of the coacervate droplets. 

Lastly, we have determined that in addition to polymer structure, the addition order of materials, such as polymer, surfactant and salt, to a formulation affects the compositional range of coacervate formation and the coacervation mechanism. Depending on the flexibility of the polymer structure, the mechanisms of coacervation in the presence of added electrolyte can vary. Poly (4-vinyl pyridine)-LAS-NaCl systems show a polymer collapse mechanism with the formation of a super-salt when salt and polymer are pre-mbced. However, for the stiff cellulosic polymers, the pre-mixing of salt and polymer before surfactant addition enhances micelle-bridging without complete polymer collapse. Also, the addition... 

The dissociation state of a weak PE directly affects the complexation ability and the composition of the resultant PEC. - It was observed that a low pH may lead to suppression of polyelectrolyte dissociation, thereby leading to no complex formation. Increasing the pH increased the ionic strength, dissociation, and complex formation. Higher pH and ionic strength will lead to complete dissociation of polyion and an equimolar PEC coacervate will be obtained. 

Since now the problems, which are connected with this changed solubility, (properties and internal structure of the colloid-rich phase, its composition as a function of the composition of the colloid-poor phase) are amenable to experimental study in A and B, but only with difficulty or not at all in C and D on account of the high dispersed state, the study of crystallisation and coacervation is precisely the right way to obtain further information about the mechanism which leads to reduced solubility in macromolecular colloids. 

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