Improvement of the film thickness by modification of the hydroxymethylbenzene SAM with tetraethoxysilane and octanediol for protection of iron from corrosion in 0.5 M NaCl

For enhancing the protective efficiency, P of a film prepared by modification of a p-hydroxymethylbenzene HOC6H4 (HOMB) self-assembled monolayer (SAM) adsorbed on iron by the formation of a covalent bond, an increase in the film thickness, d was attempted. The HOMB SAM was modified with tetraethoxysilane (C2H5O)4Si (TES), 1,8-octanediol HO(CH2)8OH (C8DO), 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 (BTESE) and alkyltriethoxysilane CnH2n+1Si(OC2H5)3 (CnTES, n = 8 or 18). The P value of the film was determined by polarization measurement of a covered iron electrode in an aerated 0.5 M NaCl solution after immersion in the solution for 1.5–72 h of the immersion time, t. High values of P, more than 82% were obtained for the films of HOMB SAM modified with TES, C8DO and CnTES and with TES, C8DO, BTESE and CnTES in the range of t up to 72 h. The highest value was 93.2%, for the film of HOMB SAM modified with TES, C8DO, BTESE and C18TES, of which d was 4.7 nm. The film of HOMB SAM modified with TES, C8DO and C8TES was characterized by contact angle measurement, X-ray photoelectron spectroscopy and FTIR reflection spectroscopy.