Map of local mechanical properties of anticorrosive graphene-based coatings

An exciting challenge to face in the field of paints and protective coating is the design of materials characterized by high chemical and mechanical resistance able to avoid microscopic failure in the coating that can pave the way to oxygen, water and other pollutants, thus favoring corrosion reactions. In this context, the interest by researchers and industrialists around the world towards graphene as a material of the future for corrosion resistance is gaining momentum. In recent times, there has been much discussion about this material and its potential as an additive to paints and varnishes for the formulation of barrier effect coatings with exceptional anticorrosive properties. The structure of graphene nanoplatelets (GNPs) offers exceptional electrical and impermeability properties, low-density characteristics and a large surface area that guarantees perfect adhesion to different materials. Recently, the effectiveness of graphene nanoplatelets (GNPs), dispersed in low quantity in a waterborne epoxy resin, in enhancing the coating anticorrosive properties and strongly contrasting its photooxidative degradation has been demonstrated [1-2]. It is well known that epoxy-based coatings are vulnerable to ultraviolet (UV) damage and their durability can be greatly decreased in outdoor environments. In this work, we aim to focus on the exceptional ability of GNPs incorporated in the epoxy films, at different weight percentages, in increasing the photooxidative resistance of polymeric films, thus consequently determining a strong decrease of the mechanical damages caused by UV irradiation. The effects of UV light on the morphology and mechanical properties of the solidified nanofilled epoxy films are investigated by Atomic Force Microscopy (AFM), in the acquisition mode “HarmoniX”. This work highlights the possibility of extending traditional AFM imaging with a technique, which is sensitive to the punctual changing in the mechanical properties of the surface film, providing information on the heterogeneity of multiphase polymeric systems. The polyharmonic response varies with modifying local mechanical properties. It is worth noting that, by coupling the AFM phase maps with the AFM modulus maps, morphologies and distribution of crystalline aggregates (for both unfilled and GNP filled samples) can be simply identified. In this work, in order to supply pertinent information on the local changes caused by the photooxidative degradation, a comparison of the material properties on located regions, before and after UV irradiation, is shown. In particular, AFM microscopy, in the acquisition mode “HarmoniX”, has allowed studying both qualitative and quantitative nanometric-resolved maps of the mechanical properties, highlighting that the incorporation of low percentages, between 0.1 and 1.0 wt%, of graphene nanoplatelets (GNPs) in the polymeric film causes a significant increase in the mechanical stability of the irradiated films. The advantageous effect increases progressively as the GNP percentage increases. References [1] T. Monetta, A. Acquesta, A. Carangelo, C. Naddeo, L. Guadagno. Prog. Org. Coat., 135, 7-18, 2019. [2] L. Guadagno, C. Naddeo, M. Raimondo, V. Speranza, R. Pantani, A. Acquesta, A. Carangelo, T. Monetta. Materials, 12(6), 962, 2019.