Silica nanocontainers with rhodamine B acylhydrazone for early fluorescent detection of steel corrosion.

Developing new materials for efficient fluorescent detection of metal corrosion is a highly relevant task. One challenge is that highly sensitive sensors might lose functionality after exposure to certain coating formulations. In this work, silica nanocontainers are used to encapsulate rhodamine B acylhydrazone, an efficient pH sensor. The resulting nanomaterial is then used in water-based epoxy and acrylic coatings for early-stage detection of steel corrosion. Coatings with as little as 0.01 wt% rhodamine B acylhydrazone show a marked increase in fluorescence intensity that correlates with the onset of steel corrosion. Coatings containing the dye encapsulated in silica nanocontainers demonstrate a significantly stronger response (4 times) compared to coatings containing the dye without an encapsulating agent. Furthermore, encapsulating rhodamine B acylhydrazone improves the dispersion of this hydrophobic dye in epoxy and acrylic coating formulations without requiring an organic solvent. The ability of the resulting coatings to detect corrosion by changes in fluorescence is validated by fluorescence spectroscopy and microscopy. Impedance spectroscopy investigations indicate that silica nanocontainers improve the barrier properties of the composite epoxy coatings on steel. The encapsulation of highly sensitive and hydrophobic molecules in silica nanocontainers can be an effective method for preparing smart coatings with desired characteristics.