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

Abstract

AbstractThe 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.