In-situ probing reactivity at buried interfaces: limits and challenges of iocai electrochemical impedance mapping and time lapse microscopy

摘要

The degradation of polymer coated metais is a combination of complex mechanisms involving local processes at buried interfaces.Classical monitoring of the degradation of such a system by electrochemical impedance spectroscopy does not allow to localize the phenomena while more detailed post-mortem morphological and chemical analysis does not provide real time information about the evolution of the interfaces.This explains the increasing interest to localized in-situ reactivity measurements.While Scanning Kelvin Probe(SKP)is used to monitor delamination of the polymer during exposure in humid air [1],Local Electrochemical Impedance Spectroscopy and Mapping(LEIS and LEIM)seems to be the most attractive tool to monitor the anodic reactivity at metal/polymer interface in immersion conditions and can be conducted in a quantitative way [2,3].LEIM seems however be less adopted for cathodic reactivity measurement because of diffusion and not charge transfer limited rate of cathodic oxygen or water reduction.However,the fact that cathodic reactivity generates hydroxide ions and/or gas formation offers a possibility to survey it using Time Lapse Microscopy(TLM).