Voltammetric study of adsorption layers of various 4-pyridyl terminated surfactants on a Au(1 1 1) electrode: Effects of electronic property of pyridyl group and intermolecular hydrogen bonding upon potential-driven phase changes

The major factors determining the potential-driven phase changes of the films of 4-pyridyl terminated water-insoluble neutral surfactants on a Au(1 1 1) electrode were described using the results of dc and ac voltammetric measurements. In total six surfactants were used to elucidate the effects of electronic property of the 4-pyridyl head group, hydrogen bonding ability between amide groups, direction of the amide bond, and bulkiness around the head group upon the potential dependent reorientation and adsorption–desorption processes. Comparison of the behavior of pentadecyl 4-pyridyl ether (C15–O–Py) and 1-pyridin-4-yl-hexadecan-1-one (C15–(CO)–Py), possessing respectively, the highest and lowest excess electronic charge on the pyridyl nitrogen among the six surfactants, revealed that the latter exhibits more distinct reorientation of pyridyl group corresponding to phase transition between condensed and loose-packed states and narrower potential region of the compact film formation. Introduction of amide group in the alkyl chains of the surfactants reduced the packing of the adsorbed film in the potential region of the compact film formation, as evidenced by an increase of the differential capacitance. It was found that the existence of amide group facilitates the potential-driven phase transition of closely packed film from a condensed state to a loosely packed state, whereas it suppresses the transition of loosely packed film. The concomitant steric effect was also discussed.