Probing Rapid Ion Transfer Across a Nanoscopic Liquid−Liquid Interface

Abstract

Rapid kinetics of tetraalkylammonium ion transfers (ITs) across the interface between water and 1,2-dichloroethane was measured by steady-state voltammetry at nanometer-sized pipet electrodes (with an orifice radius of 10−300 nm). Methodologies previously used for preparation and characterization of micrometer-sized pipets are shown to be suitable for experiments with nanopipets. The silanization of the outer pipet wall results in quantitative agreement between the experimentally measured and theoretically predicted values of the diffusion-limiting current to the pipet. An independent estimate of the orifice radius and the thickness of the glass wall were obtained by using a nanopipet as a scanning electrochemical microscopy (SECM) tip. The voltammograms of IT from the outer solution into the pipet and from the filling solution out of the pipet were analyzed to measure rates of both forward and reverse IT reactions (i.e., from water to organic and from organic to water). The measured standard rate constants are compared with the values predicted by the theory. The effects of the pipet geometry and silanization on the shape of voltammograms and the magnitude of the apparent IT rate constant are discussed.