The use of cationic fluoroprobes to characterize ionic pathways in organic coatings

The spatial distribution of pathways by which ions enter and move through organic coatings was examined with the use of molecular fluoroprobes. A bis-phenol-A epoxy coating (10–15 μm thick) on titanium was anodically polarized in an electrolyte containing an activated fluoroprobe. Confocal scanning laser microscopy (CSLM) was used at an excitation/emission of 580/602 nm to characterize the penetration pattern of the Ca2+-X-Rhod-1 fluoroprobe. Both discrete fluorescence sites and regional fluoroprobe uptake were observed within a single epoxy coating. The chemical and/or physical reasons for the increased susceptibility of ionic species at these sites and regions are not yet known, but now provide focus to the local material sources for loss of barrier properties. This proof-of-concept experiment provides a means to attain unambiguous evidence for the mode of ion entry and passage through organic coatings. These experiments open a new avenue for the characterization of organic coatings.

► A molecular fluoroprobe was successfully used to identify ionic pathways in epoxy. ► Ions enter epoxy through both, discrete localized sites and regions. ► These methods provide unambiguous evidence for the mode of ion entry.