Sensing the onset of epoxy coating degradation with combined Raman spectroscopy/atomic force microscopy/electrochemical impedance spectroscopy

The paper presents the results of investigation on epoxy resin durability upon 12-week exposure to UV radiation. The aim was early determination of the onset of epoxy degradation and for this purpose an epoxy film on steel substrate systems were periodically inspected using Raman spectroscopy, atomic force microscopy and elec-trochemical impedance spectroscopy. The behaviour of examined polymer could be divided into three periods: immunity, degradation initiation and failure. Early degradation initiation could be sensed only with Raman spectroscopy and AFM topography imaging where decrease in intensity of particular Raman peaks and discrete changes in topography constituted the fingerprints of UV-induced changes. At this stage electrochemical impedance spectroscopy and local dc current mapping with AFM did not provide any signs of forthcoming degradation since the epoxy film still exhibited sufficient barrier properties. Obtained results can be helpful in proper selection of investigation techniques in the situations where precise evaluation of polymer degradation onset is of key importance.