Assessment of Coating Adhesion Degradation by Atomic Force Microscopy Scratching

The effects of environmental exposure on polymer coating degradation were studied using atomic force microscopy (AFM) scratching. Adhesion was assessed by the coating removal rate during controlled-force contact mode scratching in the AFM. Low-carbon steel coupons were coated with an ultrahigh molecular weight epoxy resin and exposed to environments with high relative humidity and exposure to ultraviolet light. AFM scratching was performed both in air and in water to assess the effect of water on adhesion degradation. The average coating removal rate increased when samples were first degraded by environmental exposure and by scratching in water. AFM scratching is shown to be a quantitative method for the assessment of adhesion and adhesion degradation for coatings less than about 4 mu m in thickness.