LAUSR

Protective coatings systems (PCS) are a common and facile method to protect metal substrates from corrosion. The corrosion control performance of polymer-coated metal substrates is still predominantly evaluated by visual assessment. Unfortunately, for many decades, PCS material development and performance testing has basically been a complicated process of waiting to determine which coating, in relative terms, allows corrosion to occur first from an intentionally created breach through the coating. This type testing provides only relative ratings between PCSs performance. Electrochemical methods, like electrochemical impedance spectroscopy (EIS), each have caveats and pitfalls for qualifying or quantifying polymer coated metal substrates. When these data are studied carefully, these measurements result in many false positive and false negative results compared with real environmental testing and the paths to failure vary dramatically. The critical issue is that these methods don't result in a scientific basis for understanding either the pathway(s) or progressive milestones towards diminished PCS performance, failure, and the loss of substrate structural integrity for coated substrates. Data supports, that ultimately, all PCS fail to provide the necessary substrate protection. However, to make substantive gains scientist and engineers require a rational basis to design, engineer, test, quantify and/or estimate service life and remaining service life and repair future generations of PCS. Our research goal was to establish a quantifiable characterization protocol (CP) that directly detected, monitored, and ideally quantified the pathway(s) and important milestones of PCS corrosion (CP) spatially and temporally, with or without defects which related with testing and assessment variables regardless of environmental severity (real, laboratory, or accelerated). We report herein, the CP and the results from an embedded pH sensitive "turn-on" fluorescent probe blended with a simplified thermoplastic model PCS. The results support that the average localized macroscopic pH is detected and tracked and these "molecular titrations" result in values consistent with literature pH citations for pre-macroscopic corrosion processes, i.e., before delamination and a detectable breach. The results are in advance of visual corrosion detection and yet proportional to the steel substrate corrosion. The CP results deliver extreme early detection (within minutes), spatial and temporal tracking, and potentially quantifiable performance differences for the pathways and milestones towards failure of coated substrates with validated sensitivity to variables like defect versus defect free films, blending solvent type(s) influence, differences from varied degrees of annealing relative to Tg (thermoplastic films), substrate topography and preparation differences. The CP utilizes small sample areas (25 mm spheres) and gathers data in a manner designed to improve statistical relevancy, provide results within short timeframes using real time testing, diminish materials testing timelines and connect results with laboratory, accelerated, and real environmental severity differences. The results support that the CP directly measured the earliest possible in-situ corrosion processes using defect and defect-free simplified model PCSs.