Complex coacervates

The addition of electrolyte has a dissociating effect on coacervate complexes. 

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... 

In a study with a similar purpose, i.e., the better understanding of the mechanisms by which cationic retention aids operate in the presence of DCS, the formation of colloidal and coacervate complexes from CPAM and sulfonated Kraft lignin was studied [49]. Using a CPAM with lower molecular weight, the formation of colloidal complexes was promoted over coacervate formation. With CPAM of higher molecular weight, the re-conformation (into colloidal PECs) was too slow, and coacervate complexes were formed. 

Vanerek A, van de Ven TGM (2006) Coacervate complex formation between cationic polyacrylamide and anionic sulfonated kraft lignin. Colloids Surf A 273 55-62... 

This technique employs a conventional three-phase system the manufacturing vehicle (solvent), the flavor carriers (wall materials), and the flavor (core material). While there are several types of coacervation, complex coacervation is most commonly used in the food/flavor industry. 

Michaeli and Overbeek used the Debye-Huckel approach to estimate the enthalpy of the PE-PE and PE-solvent interaction [23]. In this model, the Flory entropy is used as the entropic term of the PE chain, and the electrostatic free enthalpy is calculated from the electrostatic energy of a strong PE [23]. By thermodynamic considerations, Michaeli and Overbeek showed that for small univalent counterions no coacervation (complex-formation between PE) occurs... 

Table 1 Hsts representative examples of capsule shell materials used to produce commercial microcapsules along with preferred appHcations. The gelatin—gum arabic complex coacervate treated with glutaraldehyde is specified as nonedible for the intended appHcation, ie, carbonless copy paper, but it has been approved for limited consumption as a shell material for the encapsulation of selected food flavors. Shell material costs vary greatly. The cheapest acceptable shell materials capable of providing desired performance are favored, however, defining the optimal shell material for a given appHcation is not an easy task.

Complex Coacervation. This process occurs ia aqueous media and is used primarily to encapsulate water-iminiscible Hquids or water-iasoluble soHds (7). In the complex coacervation of gelatin with gum arabic (Eig. 2), a water-iasoluble core material is dispersed to a desired drop size ia a warm gelatin solution. After gum arabic and water are added to this emulsion, pH of the aqueous phase is typically adjusted to pH 4.0—4.5. This causes a Hquid complex coacervate of gelatin, gum arabic, and water to form. When the coacervate adsorbs on the surface of the core material, a Hquid complex coacervate film surrounds the dispersed core material thereby forming embryo microcapsules. The system is cooled, often below 10°C, ia order to gel the Hquid coacervate sheU. Glutaraldehyde is added and allowed to chemically cross-link the capsule sheU. After treatment with glutaraldehyde, the capsules are either coated onto a substrate or dried to a free-flow powder. 

Eig. 2. Elow diagram of a typical encapsulation process based on the complex coacervation of gelatin with gum arabic. 

Any pair of oppositely charged polyelectrolytes capable of forming a Hquid complex coacervate can be used to form microcapsules by complex... 

A wide variety of capsules loaded with water-immiscible or water-iasoluble materials have been prepared by complex coacervation. Capsule size typically ranges from 20—1000 p.m, but capsules outside this range can be prepared. Core contents usually are 80—95 wt %. Complex coacervation processes are adversely affected by active agents that have finite water solubiUty, are surface-active, or are unstable at pH values of 4.0—5.0. The shell of dry complex coacervate capsules is sensitive to variations ia atmospheric moisture content and becomes plasticized at elevated humidities. 

Qv, X. Y., Zeng, Z. P. Jiang, J. G. (2011). Preparation of lutein microencapsulation by complex coacervation method and its physicochemical properties and stability. Food Hydrocolloids, Vol. 25, 6, (August 2011), pp. (1596-1603), ISSN 0268-005X... 

The typical microencapsulation process via complex coacervation is illustrated in Figure 6.7. 

Wilson, C. G. Tomlinson, E. Davis, S. S. Olejnik, O., Altered ocular absorption and disposition of sodium cromoglycate upon ion-pair and complex coacervate formation with dodecylbenzyldimethyl-ammonium chloride, J. Pharm. Pharmacol. 31, 749-753 (1981). 

Keywords Bio artificial pancreas, biomaterials, complex coacervation, immunoisolation, microencapsulation, polyelectrolytes, water soluble polymers. 

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