Preparation and characterisation of fragrance oil microcapsules: how does shell thickness influence mechanical strength?

This study aims to achieve long-term retention of the volatile, small molecular fragrance oil molecules by focusing on the preparation of silver shell fragrance oil core microcapsules. A three-step method of preparing such microcapsules was developed in this study. Firstly the polymer shell oil core microcapsules were prepared. Then the negatively charged Au NPs were adsorbed on the polymer capsule surface via electrostatic attraction as the catalyst. Finally, the silver shell was grown on the polymer capsule surface via the electroless plating method. The morphologies of the microcapsules and Au NPs were observed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), respectively. The retention/release of the oil core was analysed using Gas Chromatography (GC). The factors which influenced the morphology of the polymer capsules and the polymer shell thickness, including interfacial tensions between oil, polymer and aqueous phases and core/shell ratio, were discussed. The adsorption density of Au NPs on the polymer capsule surface was studied by looking into the surfactant concentration and Au NPs concentration. Variables that affected the silver shell thickness, such as Au NPs adsorption density and the silver salt concentration, were also investigated. The mechanical strength of the microcapsules was analysed using the micromanipulation technique. The relationship between the shell thickness and the capsules’ mechanical strength was explored.