Adsorbed onto microcapsule surface

Colloidal surface-polymer interaction, 96 Complex fluids, definition, 1 Configuration of polyelectrolytes adsorbed onto microcapsule surface, 85-94 application in on-off control of enzyme reactions, 91,93/... 

Configuration of Polyelectrolytes Adsorbed onto the Surface of Microcapsules... 

Figure 1. Schematic representation of configurational change of polyions adsorbed onto outer surface of microcapsule (a) looped form (b) flat form.

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. 

Lee outlines three different physical methods that are commonly utilized for enzyme immobilization. Enzymes can be adsorbed physically onto a surface-active adsorbent, and adsorption is the simplest and easiest method. They can also be entrapped within a cross-linked polymer matrix. Even though the enzyme is not chemically modified during such entrapment, the enzyme can become deactivated during gel formation and enzyme leakage can be problematic. The microencapsulation technique immobilizes the enzyme within semipermeable membrane microcapsules by interfacial polymerization. All of these methods for immobilization facilitate the reuse of high-value enzymes, but they can also introduce external and internal mass-transfer resistances that must be accounted for in design and economic considerations. 

Results and Discussion. As shown in Table I, pH changes in P were affected by the amount of the polymer adsorbed onto the outer surface of the microcapsules. Thus, the amount of the adsorbed polymer was controlled by means of the initial concentrations of polyelectrolyte solution in the adsorption experiments the optimal condition was found by trial and error, as is usual for any chemical reaction. 

---