Coacervation

Coacervation refers to a liquid–liquid phase separation in colloidal suspensions in which a polymer-rich coacervate phase forms within the continuous polymer solution. The process produces droplets of dense polymer that can be separated and used to form shells for encapsulation. Coacervation can be induced by changes in temperature, solvent quality, pH, or salt concentration.

There are two main forms: simple coacervation and complex coacervation. Simple coacervation involves a single polymer in solution when a nonsolvent or temperature change causes phase separation, resulting in coacervate droplets that can coat a dispersed core. Complex coacervation arises from interaction between two oppositely charged polyelectrolytes (e.g., gelatin and gum arabic) forming a dense polymer-rich phase due to electrostatic attraction.

Mechanism: Phase separation is driven by thermodynamic incompatibility between polymer-rich and polymer-poor phases, often described by Flory–Huggins theory; droplet formation, coalescence, and stabilization by surfactants or cross-linking to form solid shells.

Process: prepare polymer solution; induce coacervation by adding nonsolvent or adjusting pH/ionic strength; allow droplets to form and grow; separate and solidify the coacervate droplets by drying, cooling, or chemical cross-linking; final microcapsules can be obtained by removing core material or by drying.

Applications include microencapsulation of flavors, essential oils, fragrances, pharmaceuticals, and enzymes. Advantages include high encapsulation efficiency and mild processing; limitations include sensitivity to pH, ionic strength, and temperature, as well as challenges in reproducibility and scale-up.