Microcapsules for Confining Fluids: Prediction of Shell Stability from Advanced SAXS Investigations

Polymeric microcapsules represent an effective tool to confine a broad range of materials for diverse applications. Melamine-formaldehyde capsules have been extensively used to encapsulate fragrances (or other substances) in order to control the perfume release and to extend its efficacy. Capsule properties can be controlled and tuned by varying synthesis conditions, such as batch composition, pH and temperature. Their stability is certainly related to structural features such as mechanical, thermal and morphological characteristics. Nevertheless, to the best of our knowledge, a quantitative correlation between capsules leakage profiles and structural features has never been attempted. We report on a model based on the small angle X-ray scattering (SAXS) to describe the relationship between the homogeneous wal structure and the leakage properties of melamine capsules. SAXS is a suitable technique to investigate the structure of capsule shell at the nanometer scale and has been employed here to disclose the wall structure and to "generate" a model-independent parameter that we called "fringe descriptor". We found that the fringe descriptor is able to quantitatively estimate both capsules' stability and performances.