Non-destructive, subsurface analysis of self-stratifying coatings with optical coherence tomography

The detection and analysis of stratification is essential for the development, fundamental understanding, and quality control of self-stratifying coatings. However, commonly used methods are either destructive and time-consuming, or cannot reliably assess the extent of the layer formation or other resulting coating morphologies. In this study, optical coherence tomography (OCT) is explored as an effective technique for investigating self-stratifying coatings. First, the self-stratification pathways of an epoxy/silicone-based coating composition are imaged as a function of the binder phase mixing ratio. Subsequently, OCT is applied to evaluate parameter influences on self-stratification success, enabling differentiation between kinetic and thermodynamic limitations. Results show the feasibility of OCT for real-time monitoring self-stratification processes, assessment of parameter influences on stratification success, quantification of layer thicknesses, and detection of stratified structures with accuracy comparable to scanning electron microscopy.