Electrochemical characterization of micro-cracks in polyurethane resin films deposited on metallic surfaces

Abstract

Resin films based on polyurethane dispersions (PUDs) have recently gained substantial interest as surface protective coatings. However, defects in the resin films such as micro-cracks may induce high permeability to moisture, thereby compromising the coatings’ performance. In this contribution, we report on a simple electrochemical method for characterization of the micro-cracks in a resin film deposited on a copper surface. Electrochemical measurements are facilitated in a two-electrode cell where the resin-coated copper electrode serves as the anode. The ionic current flow due to electrolyte penetration within the micro-cracks of the resin film is measured and quantified. The ionic current (I) exhibits an inverse exponential dependence on the film thickness (x): I ∝ e−x . The physical basis for this dependence is discussed using a mathematical model that incorporates the surface fraction of micro-cracks in a layered resin film. While the analysis presented herein is for the specific case of PUD resins, the overall methodology is applicable to the characterization of many metallic and non-metallic surface coatings used in corrosion protection and surface functionalization applications.