Emergence of wrinkles during the curing of coatings

Wrinkles often emerge on a paint layer when a second coat of paint is applied on an already-coated substrate. Wrinkle formation occurs when the first layer absorbs organic solvent from the second layer. We set up experiments to mimic the double-coating process, focusing on the interaction between a paint layer and an organic solvent. In the experiments, we investigated the characteristic wavelengths of the wrinkles and the time of wrinkle emergence. We propose a simple model to explain (1) the buckling induced by swelling of the layer due to absorption of the organic solvent and (2) delamination of the layer from the substrate. A linear stability analysis of the model provides a relationship between the wavelengths and the characteristic timescale that agrees reasonably well with the data obtained from our experiments. Our results indicate that compression of the layer due to swelling and delamination are both important factors in the formation of wrinkles.