Nanomechanical properties of hybrid nanocoatings

Abstract

This research focuses on the development of coatings and inorganic nanoparticles containing nanocoatings. Four different coatings were formulated based on specified chemical structures. The chemical formulations were varied systematically to achieve a polymer coating, a hybrid polymer-ceramer coating, a ceramer coating and a quasi-ceramic coating. Compositions containing epoxy polymer and/or silicone polymers were chosen for this study. Five different types of inorganic nanoparticles were chosen based on their nanostructures. Three different concentrations--0.1, 0.3 and 0.5 wt. %--of each type of nanoparticle were incorporated into coating formulations. Polished aluminum substrates were coated with 4 coatings and 60 nanocoatings. The coatings and nanocoatings were hardened and characterized using FTIR spectroscopy operating in reflectance mode. The surface topography and scratched coating morphology of the coatings were investigated with the help of atomic force microscopy. The pristine polymer coating showed smooth surface morphology, while the hybrid, ceramer and quasi-ceramic coatings showed surface roughness in the nanometer regime. The coatings and nanocoatings were tested for their nano-mechanical properties using the nanoindentation technique. The hardness modulus values were determined and correlated with the structure of the coatings and nanocoatings. The effect of nanoparticles on the hardness and modulus values of coatings was investigated. It was found that hardness increased with the addition of nanoparticles but inconsistent modulus values were seen in the nanocoatings. The coatings and nanocoatings were analyzed using the nanoscratch technique. The effect of nanoparticles on fracture and delamination was studied. The SEM analysis was conducted on the scratched coating to understand the failure mode in the material. It was discovered that scratch resistance increased with the increase in nanoparticle. However, the nanocoatings showed increased brittleness over the pristine coatings. The visco-elastic behavior of the coatings and nanocoatings was studied at five different test frequencies. The storage and loss modulus values were recorded for pristine coatings and nanocoatings. The variations in visco-elastic properties on the incorporation of the nanoparticles in coatings were investigated and correlated with the associated molecular structures. It was found that the storage modulus remained unaffected, while the loss modulus varied with test frequencies. Both the storage and loss modulus of the coatings varied marginally with the addition of nanoparticles.