A fast methodology to assess the quality of coatings on rough 3D surfaces

In industrial applications, it is crucial to characterise the quality of coatings during and after the manufacturing process. It is then relevant to elaborate a reliable procedure allowing for rapid inspection and easy-to-assess quality check. In this paper, we tested a qualitative methodology based on mechanical and visual analyses allowing for easily finding suitable parameters to generate resistant and uniform multi-layered coatings. This qualitative criterion was tested and refined against quantitative measurements. We focussed on carbon-based materials whose remarkable properties could be exploited in many applications, including multilayer coatings as a promising anticorrosion solution in the metal industry and as enhanced surfaces for heat exchange devices. Dip-coating was used to create multilayer coatings on rough 3D objects starting from water solutions of CNT and pure graphene. Visual uniformity and adhesion were chosen as criteria to analyse coatings qualitatively, while samples' roughness and the number of dips were the variable parameters. Different behaviours of the coatings were observed for graphene and CNT. For both, we found a critical number of dips after which the coating loses adhesion and stops to be uniform. The proposed colour maps, summarising the qualitative coatings' assessment, could be used as a methodological reference to issue technological recommendations when using multilayer coatings for specific purposes.