Moisture induced crack filling in barrier coatings containing montmorillonite as an expandable phase

In order to explore the option of healing surface scratches in coatings using an expandable phase, the crack filling behavior of transparent, multi layer coating consisting of a polysiloxane film on top of a thin montmorillonite interlayer was studied. The filling process was monitored using confocal and SEM microscopy. Filling of cracks in the polymeric topcoat occurred primarily within the first two hours of exposure to moisture saturated air and resulted in a good restoration of the surface flatness. Beyond this 2 h healing period, further expansion of the clay layers resulted in a "pushing-up" effect of the swollen clay in proximity of the damaged coating. This paper attempts to quantify the crack closure of the clay-containing coating by monitoring changes in scratch width and area as a function of time.