Real-Time Dual-Probe Monitoring and Correlation of FBRM and PVM Measurements during PUF Microcapsule Formation

Microencapsulation enables the protection and controlled release of reactive liquids, however most characterization methods capture only endpoint properties. To address this gap, a real-time dual-probe approach using Focused Beam Reflectance Measurement (FBRM) and Particle Vision and Measurement (PVM) was employed to monitor the formation of poly-(urea-formaldehyde) (PUF) microcapsules containing dicyclopentadiene (DCPD) in this study. The four-stage synthesis was tracked in situ to evaluate emulsification, shell development and UF particle deposition under different stirring rates and poly-(ethylene-alt-maleic anhydride) (PEMA) concentrations. The method is applicable to capsule sizes measurable by both probes, i.e., > 10 μm for PVM and 1-1000 μm for FBRM. Within these ranges, the effective limitation in real-time monitoring arises from the PVM detection threshold. The results show that probe insertion introduces localized shear that influences capsule size distribution. A semiempirical power-law model was developed to reliably convert FBRM chord length data into true capsule diameters measured by PVM, using parameters derived from log-normal distribution fits. Overall, the integrated monitoring approach enhances understanding of process-structure relationships during microcapsule formation and provides a useful approach to improve microcapsule design in self-healing applications.