Enhancement corrosion resistance of (3-methacryloxypropyl)silsesquioxane hybrid films and its validation by gas-molecule diffusion coefficients using MD simulation

In the first part of this work, based on silsesquioxanes (SSO) derived from hydrolytic condensation of (3-methacryloxypropyl)trimethoxysilane (MPMS) and tetraethoxysilane (TEOS), two hybrid films, f-MPMS-SSO (f-MS) and f-MPMS-TEOS-SSO (f-MTS) modified with 15 wt% TEOS, were prepared. The anticorrosion properties (corrosion potential, E _corr, and corrosion current density, I _corr) of the bare aluminum alloy (AA) and the two films on AA were tested by electrochemical measurements with typical potentiodynamic polarization curves. The I _corr values of three samples are significantly different with the order of f-MTS < f-MS < AA which implies that the TEOS addition in the f-MTS coating indeed enhances the electrochemical corrosion resistance. Correlations between the structures of two films and anticorrosion properties were discussed. In the second part of this work, two different 3D-amorphous cubic unit cells, cell(f-MS) and cell(f-MTS), as models were employed to investigate self-diffusion coefficients by molecular dynamics (MD) simulation for the NO₂, SO₂ and H ₂O molecules. All three self-diffusion coefficients of NO ₂, SO₂ and H₂O diffusing in cell(f-MTS) were less than the coefficients in cell(f-MS), which validates the corresponding anticorrosion-experiment results. Two reasons why the addition of TEOS in the system of f-MTS leads to a lowering of the gas self-diffusion coefficient compared to the f-MS system, were discussed.