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Abstract

The properties of lipid monolayers at the interface between two immiscible electrolyte solutions (ITIES) have attracted much attention over the last 30 years. This is mainly because of the biological relevance of lipids and the possibility of controlling ion and electron transfer across one leaflet of a cellular membrane. In the last decade, the electrochemical characterization of phosphatidylcholine (PC) adsorbed monolayers at ITIES suggested that the transfer of aqueous cations across the interface is facilitated by the complexation of aqueous cations with the PC zwitterionic head groups, followed by the depletion of lipids from the interface. In this work, we present a study on the effects of applied electric fields and electrolyte concentration on the interfacial structure of the ITIES by combining neutron reflectometry (NR) and electrochemical characterization techniques including the effects of an adsorbed lipid layer. Our results confirm that lipid depletion occurs as cations are transferred. However, we found that the presence of lipids favors the intermixing of the two-liquid phases on a length scale of a few tens of nanometers. To our knowledge, this has been the first NR-electrochemistry study of the ITIES. We believe that our findings could open new possibilities for coupling bioelectrochemical characterization and scattering based techniques at the liquid-liquid interface.