Preparation of ultrathin polymer coatings adsorbed on iron via a covalent bond by multistep modification of a hydroxymethylbenzene SAM with ethoxysilanes and alkanediol for preventing iron corrosion in 0.5M NaCl

Abstract The film thickness, d of a p -hydroxymethylbenzene – C 6 H 4 CH 2 OH (HOMB) self-assembled monolayer (SAM) adsorbed on iron via a covalent bond was increased by multistep modification with tetraethoxysilane (C 2 H 5 O) 4 Si (TES) and 1,8-octanediol HO(CH 2 ) 8 OH (C 8 DO) and subsequently with 1,2-bis(triethoxysilyl)ethane (C 2 H 5 O) 3 Si(CH 2 ) 2 Si(OC 2 H 5 ) 3 (BTESE) and akyltriethoxysilane C n H 2 n +1 Si(OC 2 H 5 ) 3 (C n TES, n = 8 or 18). The protective ability of the film against iron corrosion was examined by polarization measurement of the iron electrode coated with the film in an oxygenated 0.5 M NaCl after immersion in the solution for many hours. The values of protective efficiency, P for the films, the HOMB SAM modified with TES and C 8 DO twice and subsequently with BTESE and C n TES were high, more than 81% at n = 8 and 85% at n = 18 in the range of the immersion time, t up to 240 h, respectively. The maximal P values of the respective films were 88.0% and 92.2%, of which approximate d values were 4.6 and 5.8 nm. The high protection of iron against corrosion was attributed to increases in the film thickness and interconnection between the adsorbed molecules with Si–O polymer linkages. The protective ability of the film was remarkably persistent during immersion in the solution for many hours. A slight enhancement of P was observed by additional modification of the modified HOMB SAM with C 8 TES due to increases in interconnection and close packed arrangement. The formation of strong adsorption bonds, σ -covalent bond and back-donating π-bond, between the carbon atom of HOMB moiety and iron atom was discussed.