Fluorescent probes based on chemically-stable core/shell microcapsules for visual microcrack detection

Core/shell microcapsule-based fluorescent probes are presented in this work for potential use as early visual detection tool of microcracks in structural materials. A new microcapsule-based system is developed consisting of a UV-screening polyurea shell containing a fluorescent liquid core. The UV-screening functionality allows to prevent unwanted fluorescence emission from intact microcapsules upon UV-light exposure and yields excellent visibility contrast of the locally damaged region where fluorescent liquid core released from ruptured microcapsules is present. In addition, by carefully tuning the chemical composition of the shell material, microcapsules with enhanced chemical stability can be formed, as demonstrated by their superior solvent resistance over dwell time originating from the highly crosslinked shell structure that prevents core extraction from the microcapsules. A thorough chemical, thermal, morphological and optical characterization combined with a functional demonstration of the damage visualization capabilities of this new microcapsule-based system highlights its potential as a highly chemically-stable damage sensor for microcrack detection in structural materials.