Multilayer coating by plasma polymerization of TMDSO deposited on carbon steel: Synthesis and characterization

Polysiloxane films obtained from a cold remote nitrogen plasma polymerization of 1,1,3,3-tetramethyldisiloxane monomer mixed with oxygen show attractive properties and can be used for many applications. These films can also be modified in-situ by the (nitrogen + oxygen) remote plasma. An increase of the atomic oxygen concentration in the plasma leads to carbon removal and to an enhancement of the cross-linking of the Si-O-Si chains. The uppermost layer tends towards a silica structure while the core of the coating remained unchanged. By successive (deposition/plasma treatment) sequences, it was possible to obtain multilayer coatings which were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and contact angles measurements. The efficiency of such multilayer coatings to protect carbon steel against corrosion in NaCl 0.5 M was also investigated from polarization curves and Electrochemical Impedance Spectroscopy (EIS).