A systematic study on the reaction mechanisms for the microencapsulation of a volatile phase change material (PCM) via one-step in situ polymerisation

Abstract

The microencapsulation of volatile phase change materials (PCMs) is very challenging to achieve high payload and excellent barrier properties. Our previous work indicates that the emulsifiers used in the process offer unique properties to the formulated microcapsules. In the present work, an assortment of hydrocolloid and synthetic emulsifiers were employed to tackle the reaction mechanisms of the encapsulation process. Microcapsules with exceptionally large payloads (up to ∼95.6 wt%) were produced with excellent core retention. The effects of emulsifiers were deliberated, in which it was found that the microcapsule quality is greatly affected by the functional groups located on the emulsifiers. Interfacial tension and interfacial dilatational rheology did not prove a significant correlation with the emulsifier type, although these factors still play a part in the stability of the O/W emulsion. It was conveyed that resorcinol is the most stable dihydroxybenzenes species in this process. Ammonium chloride alternatives were exploited, conveying that ammonium carbonate and ammonium nitrate can also be successfully used in this process. However, the chief finding of this work lies in the proof that carboxyl groups speed up the reaction rate to the extent that the UF particles become too large to maintain controlled and steady deposition onto the O/W interface, leading to porous microcapsules. The emulsifiers with hydroxyl groups created UF particles too small to do so. Intermediate reactions were displayed with amine/amide groups or a combination of groups. This work strongly broadens the understanding of how emulsifiers affect the one-step in situ polymerisation process, which, in turn, provides an array of available emulsifiers that can be used to encapsulate other volatile core material contents.