Interfacial Structure and Partitioning of Nitrate Ions in Reverse Micelles

The interfacial properties of NO₃^- were investigated using reverse micelles (RMs) in solution as proxies for sea spray aerosol (SSA) particles. By tuning the size of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) RMs doped with NO₃^- we are able to isolate the vibrational signature of interfacial NO₃^- using infrared spectroscopy. The infrared spectrum of interfacial NO₃^- along the asymmetric-stretch coordinate (υ₃) is blue-shifted and possesses smaller peak splitting relative to NO₃^- in aqueous solution. These observations are consistent with the reduced hydrogen-bonding availability of the interfacial region within the RM aqueous interior. We show that the partitioning of NO₃^- between the interfacial and core regions of the RM interior can be determined using a linear combination of interfacial and aqueous NO₃^- spectra. By fitting the interfacial partitioning curve of NO₃^- we demonstrate a method of determining quantitative interfacial affinity (χ_Interface) for ionic species doped within RMs.