Preparation of a 16-hydroxyhexadecanoate ion self-assembled monolayer on a zinc electrode coated with hydrated cerium(III) oxide

A self-assembled monolayer (SAM) of 16-hydroxyhexadecanoate ion HO(CH2)15CO2-(HOC16A-) was prepared on a zinc electrode coated with a hydrated cerium(III) oxide Ce2O3 layer. The protective efficiency, P of the duplex film composed of the Ce2O3 layer and the SAM was examined by polarization measurement of the zinc electrode in aerated 0.5 M NaCl. The P value of the HOC16A− SAM on the Ce2O3-coated electrode was only a little higher than that of the Ce2O3-coated one. The contact angle of the surface covered with the film with a drop of water was far higher than the value of the HOC16A− SAM on passivated iron, suggesting that HOC16A− was partly adsorbed on the Ce2O3 surface via both CO2- and OH groups in a looped orientation. Because this orientation must be changed to an extended orientation during immersion in 0.5 M NaCl, some defects appeared within the SAM in places, resulting in a poor enhancement of P. The film structure was characterized by X-ray photoelectron and FTIR reflection spectroscopies.