On the behaviour of molecules of the quinoline group at the water-mercury interface: Part IV A. Electrocapillary study of 3-methyl-isoquinoline

Abstract

The adsorption of 3-methyl-isoquinoline at the mercury-water interface involves a number of rate-determining factors (local depletion uncompensated by mass transfer, influence of the diffuse-layer potential, slow kinetics) which has limited the present study to the most concentrated solutions. In that range, the major traits of the behaviour of 3-MeisoQ and isoQ are comparable at least qualitatively (rearrangement and desorption transitions, condensed layers, existence of a quasi-solid two-dimensional structure of invariant properties at negative potentials). Differences result from the steric hindrance of the methyl group on all adsorption modes, except that which involves the perpendicular-high orientation (with nitrogen and the methyl group facing the solution side of the interface). It appears that, as is the case for aliphatic alcohols or acids among others, meaningful comparison must be based on relative concentrations normalized with respect to the saturation value. The dependence of the rearrangement transition potential on surfactant concentration and ionic strength indicates that the inner potential difference is the most suitable independent variable.