Carbon-inorganic multilayered coatings from reactive precursors

The present master thesis focuses on the use of a novel bolaamphiphilic hexayne as a molecular precursor for the formation of hybrid carbon-inorganic nanocoating. The molecule, hexadeca-3,5,7,9,11,13-hexayne-1,16-diylbis(phosphonic acid), displays a central, highly reactive oligoyne segment able to carbonize when exposed to mild UV irradiation at room temperature, while the terminal phosphonic heads lead the molecular to form a self-assembled monolayer onto oxidic surfaces. By introducing of a metallic cation, which acts as a bridging element between different organic layers, a multilayered structure can be obtained, and eventually carbonized by UV irradiation. The target molecule was obtained from 4-bromo-1-butyne, protected at first by dethylphosphonate, followed by bromination of the terminal alkyne, Negishi coupling with 1,4-bis(trimethylsilyl)butadiyne to get the asymmetric triyne, a modified Eglinton-Galbraith homocoupling that furnishes the hexayne, and finally the deprotection of the terminal phosphonates by removal of the ethyl moieties, to furnish the diphosphonic acid. The self-assembly of the hexayne at the solid-liquid interface was investigated and optimized. Different multilayers were successfully produced by a layer-by-layer approach, which efficacy was proven by ellipsometry. As displayed by water contact angle and IRRA spectroscopy, the multilayers were characterized by a disordered layered architecture. UV-induced crosslinking turned the organic multilayered structure into a continuous, disordered amorphous carbon coating. TEM analysis proved its nanometric nature, as well as its structural stability and optimal adhesion onto the substrate. As highlighted by potentiodynamic polarization measurements, the metallic-carbon coating, when grown onto aluminum substrates, provided an effective barrier against corrosion, reducing the corrosion current density and the conductance up to one order of magnitude when compared to bare metal surfaces. Moreover, a shift to higher open circuit potential was recorded for the coated substrate, enforcing the effect of the multilayered coating as corrosion protection solution for aluminum surfaces.