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

## TL;DR

This study uses real-time monitoring to track the formation of microcapsules for controlled release of reactive liquids, improving understanding of the process.

## Contribution

A dual-probe real-time monitoring method combining FBRM and PVM is introduced for microcapsule formation analysis.

## Key findings

- Probe insertion introduces localized shear affecting capsule size distribution.
- A power-law model converts FBRM data into true capsule diameters using log-normal fits.
- The method enhances understanding of process–structure relationships in microcapsule formation.

## Abstract

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.