Polysaccharide assisted microencapsulation for volatile phase change materials with a fluorescent retention indicator

Abstract

Low freeze point paraffin-based phase change materials (PCMs) for thermal energy storage often have very high vapor pressure, rendering it extremely challenging to encapsulate. This work reports our success in fabricating amino resin microcapsules with low freeze point PCMs cargos. Our findings challenge the emulsifier selection criteria proposed a decade ago, and enable better understanding of the role of emulsifiers in the one-step encapsulation process without precondensate synthesis. A facile, low cost, efficient and efficacious screening method utilizing a fluorophore is reported here for fast examination of core retention without resorting to more complex or unnecessary quantification techniques. This method is transferable to other encapsulation methods or materials as a qualitative analysis tool. We report two new emulsifiers, i.e. xanthan gum and methylcellulose, which contribute to successful encapsulation of volatile cargos via the one-step in situ polymerization route. The concentration of xanthan gum affects not only the capsule size, but also shell thickness and surface roughness. Most importantly, we have demonstrated with methylcellulose that carboxyl or anhydride moieties in emulsifiers are not essential for the one-step process, contrary to the literature. Capsules produced with methylcellulose also demonstrate superior thermal cycling fatigue resistance.