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 (u(3)) 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 (chi(Interface)) for ionic species doped within RMs.