Nancy Levinger
Colorado State University

Impact of a nanoscopic environment on the nature of water

A wide range of studies has revealed many subtle details about properties of water in bulk solutions.  However, nature presents many examples of water limited to nanoscopic proportions.  In these environments, many characteristics can differ from bulk properties.  Using a range of methods, we have explored the impact of nanoconfinenment on water in reverse micelles.  Experiments harnessing ultrafast time-resolved vibrational spectroscopy have revealed details about water relaxation and reorientation.  These studies also demonstrate the critical role of water in energy relaxation pathways for interfacial vibrations.  Additional studies utilizing multinuclear NMR spectroscopy provide measures of water bulk properties such as pH and ionic strength in minuscule water pools.  Results from 51V NMR spectroscopy studies suggest a pH gradient exists in the reverse micellar nanodroplets.  Spectra of the oxovanadate probes also show the propensity for CO₂ to acidify the interior of the reverse micelles.  Additional ultrafast time-resolved transient absorption studies indicate that a photoacid residing in the micelle core experiences a very different environment than it does at the interface corroborating the interpretation of a pH gradient in the micelle interior.  These results tie together to present a picture of the behavior of water in nanoscopic environments.