Probing the structure of a water/nitrobenzene interface by scanning ion conductance microscopy

Abstract

A new experimental approach to probe the structure of a water/nitrobenzene (W/NB) interface by scanning ion conductance microscopy (SICM) is presented. A nanopipette filled with aqueous solution serves as a SICM tip. The tip current is produced by the transfer of chloride (Cl⁻) and tetraphenylarsonium (TPAs⁺) ions between the aqueous solution inside the pipette and outer organic solution. The tip current increases instantaneously as a sign of touching the interface when such a tip approaches the W/NB interface. The continuous change of tip current suggests ion penetrations into the interfacial region which is less than 1 nm, in accordance with the mixed solvent model. Ion distribution information can also be extracted from the current–distance (approach) curves obtained from solutions with a series of electrolyte concentrations. The experimental results show that the SICM approach curves are sensitive to the thickness of diffuse layers. This type of technique is actually a modified version of SICM, and is similar to the operation of ion transfer mode of scanning electrochemical microscopy (SECM) with a SICM instrumentation.