## 4 Microencapsulation Techniques
### Physicochemical Process  
#### 4.3.1 Coacervation  
The coacervation involves a reaction between two or more oppositely charged polyelectrolytes (polycation and polyanion). The polycation is usually gelatin, while the polyanion is Arabic gum (acacia). There are two techniques of coacervation, the simple and the complex one.  
The complex coacervation involves three steps carried out under continuous agitation, i.e., (i) the preparation of emulsion by dispersing PCMs into an aqueous phase containing polycation; (ii) the formation of coating material by the addition of an aqueous solution containing oppositely charged polyanion (in this step the medium pH should be adjusted in a way to induce the separation phase and to ensure the deposition of coating materials on the oil interface), and; (iii) the stabilization of the microcapsules by crosslinking, desolvation or thermal treatment (Figure 10).  
Figure 10: Schematic representation of the different stages of the microencapsulation process by coacervation process.  
Microcapsules morphology and stability could be improved by adjusting pH and introducing an adequate amount of surfactants at higher stirring rates [147]. In addition, microencapsulation efficiency is affected by the operating parameters such as PCMs/polymers weight ratio, emulsion time and the chemical nature, and the amount of crosslinking agent [148].  
Complex coacervation is based on the interactions between two oppositely charged polyelectrolytes to undergo a liquid-liquid phase separation. Gelatin/gum Arabic, gelatin/sodium alginate [149], chitosan-co-poly(methacrylic acid) copolymer [150], or gum Arabic/chitosan [151] were selected to encapsulate PCMs.  
[PERSON] et al. reported developing with enhanced flame-retardant properties by coacervation technique [149]. They encapsulated \(n\)-eicosane as PCMs, and they used different shells such as aluminum oxide nanoparticle doped gelatin/gum Arabic and gelatin/sodium alginate. They observed a significant enhancement in their thermal stability and flame-retardant performance. Clay nanoparticles (clay NPs) doped gelatin/sodium alginate shells were also used as shell materials. They obtained a well-defined core-shell structure with a smooth surface. The presence of clay NPs improved the thermal stability of the microcapsules compared to microcapsules containing only gelatin/sodium alginate shell materials.  
[PERSON] et al. employed this process to encapsulate hexadecane-eicosane mixture using chitosan-co-poly(methacrylic acid) copolymer [150]. The acrylic copolymer was not only one of the polyelectrolytes but also acted as an emulsion stabilizer during the coacervation process to obtain an encapsulation efficiency of about 84% for loading PCMs content 66%. [PERSON] and [PERSON] prepared gum Arabic/chitosan microcapsules containing a commercial blend of triglycerides as core material [151]. They optimized the process parameters (phase volume ratio, stirring rate and time, pH, reaction time, biopolymer ratio, and crosslinking agent), affecting a stable emulsion and shell formation during the microencapsulation process. The optimal conditions, in this case, are pH = 3.6, a weight ratio of chitosan to acacia gum of 0.25, a volume ratio of the dispersed and continuous phases of 0.1, and an emulsion time of 15 min at 11,000 rpm.