The capacitance of a gold polycrystalline electrode has been measured in Na2SO4 electrolyte containing non-ionic surfactants, in which the hydrophobic chain was either perfluorinated (F1110) or hydrogenated (H1110). With both surfactants, the adsorption isotherms obtained with a rotating disc electrode reveal that the organic molecules are differently adsorbed in two potential domains located on either side of the potential of zero charge E0. The results are consistent with a flat orientation of adsorbed molecules for E < E0, and a partly upright or upright orientation for E >E0, this latter being sensitive to the hydrodynamic flow. Comparing F1110 with H1110 suggests that both the interactions metal-molecules and the intermolecular bondings depend on the hydrophobic chain.