Coatings characterization by AFM techniques

The aim of this work was the evaluation of the AFM characterization technique when applied to analyze the morphology and mechanical properties in coatings used in different industrial sectors, to highlight its advantages and limitations, and to propose improvements that should be taken into account when considering this technique. Three different manufacturing coatings were considered for analysis during this project. Several preparation methods were used according to the type of coating to be considered, such as: PVD process, sol-gel preparations and spin and bar coating deposition. Surface morphology analyses as well as measurements of surface mechanical properties were performed using Atomic Force Microscopy (AFM) characterization technique, including elastic modulus measurements through nanoindentation and hardness evaluation through nanoscratch resistance. Cantilevers with standard tips (ACT) and cantilevers with a diamond tip were selected for the tests according to the hardness value expected for each type of coating. By deposition of metallic coatings over polymeric substrates, very homogeneous surfaces can be obtained changing the processing parameters, and AFM allows the characterization of these surfaces to analyze the efficiency of the coating process. Considering ABS substrates, a silanization process using the same proportion (1:1) of silane (HMDSO) and oxygen offer higher homogeneity. Minlon substrates show an increase of the homogeneity using less amount of UV steps for crosslinking. Moreover, by using fluorinated sol-gel hybrid coatings with 77% and 60% of silica, an increase on homogeneity can be found compared with raw plastic materials. Higher mechanical properties can be reached by an increase of the amount of silica in the sol-gel formulation. Finally, when considering lignin-based coatings, the functionalization of soluble lignin fraction (SLF) with succinic anhydride is able to produce a product (SAL) able to be crosslinked with itself, that is able to produce similar performance to the one obtained using synthetic crosslinker (CYMEL-303).