Probing Interfacial Co‐Crystallisation using Simultaneous Potential and Current Measurements at Liquid‐Liquid Interfaces Polarised by Common Ion Approach

Abstract

The simultaneous measurement of potential and current variations at the interface between two immiscible electrolyte solutions, which was polarised using tetraalkylammonium cations as a common ion, is reported here. Various concentration ratios of tetramethyl‐, tetraethyl‐, or tetrapropylammonium were dissolved in each phase. Such biphasic systems were then used to verify that the measured interfacial potential difference agreed with theory. This experimental set‐up was then used to probe the interfacial cocrystallisation process of hydrophilic, cationic caffeine with lipophilic 1‐hydroxy‐2‐naphtoic acid (1H2N). The presence of caffeine in the aqueous phase led to higher current values, caused by interfacial charge transfer. Electrochemical noise analysis suggested that a two‐step process was occurring at the ITIES (i) a potential‐driven nucleation with the transfer of caffeine from the aqueous to the organic phase; (ii) a growth stage where the interfacial potential no longer plays a role.

Recent Developments in Single-Entity Electrochemistry

“…In pioneering micro-ITIES work by Kanoufi and co-workers, chronoamperometric detection of the stochastic collision of individual Pt nanoparticles was achieved at the water|1,2-dichloroethane (w|DCE) interface established when a capillary with an opening of 25 μm filled with aqueous H 2 SO 4 and Pt nanoparticles was placed in a bath solution of ferrocene (Fc) in DCE. Typically, spikes in current–time transients are recorded when an entity, such as a nanoparticle, straddles the polarized LLI, with the spike informing on oxidation/reduction processes involving the colliding entity. − In the case of Pt nanoparticles at the w|DCE, current spikes result from O 2 reduction in the aqueous phase, with the Fc-hydride complex oxidized in the organic phase. This approach offers distinct advantages over conventional electrode–solution interfaces, providing a defect-free, repeatable, and renewable interface .…”