Predicting microcapsules morphology and encapsulation efficiency by combining the spreading coefficient theory and polar surface energy component

Abstract

The morphology and encapsulation efficiency of thermoregulating microcapsules based on a spreading coefficient theory and polar surface energy component were evaluated. For this purpose the microencapsulation of phase change materials (PCMs) with different copolymer shells and using different suspending agents by the suspension-like polymerization technique has been carried out. Contact angles and interfacial tensions were measured, and results were discussed with respect to the internal structure as well as encapsulation efficiency of the microcapsules. A core/shell structure was expected as the equilibrium morphology, whereas the experimental structure exhibited a matrix morphology. A core-shell structure was favored by increasing the polarity of the polymer and decreasing the solubility between the core and shell. The type and amount of suspending agent do not have a significant influence on the final characteristic of the microcapsules. Shells with various polarities were synthesized from styrene (S), divinylbenzene (DVB) and hexa(methacryloylethylenedioxy)cyclotriphosphazene (PNC-HEMA), and it was found that a core-shell structure was only obtained for microcapsules with a high polar surface energy component.