Understanding the details of water in interfacial regions is a critical step toward advances in many fields including biomedicine, soil science, colloidal materials, and meteorology. In the surface science literature, there are abundant experimental and theoretical data on the water chemistry at solid surfaces in UHV; however, these studies do not allow extrapolation to the structure of interfacial water in contact with the bulk liquid phase. In studies focused on solid-liquid interfaces, information about interfacial water has been inferred from bulk measurements; direct molecular details from these studies are rarely available and results are often conflicting.
In order to close the gap between these two approaches and build a self-consistent base of fundamental knowledge about interfacial water, our group studies adsorption isotherm behaviors of water on well-characterized solid surfaces to attain thermodynamic (such as isosteric heat of adsorption) and structural information of the interfacial water and understand molecular fundamentals of interfacial water behaviors such as adhesion, capillary, mechano-chemical reactions, etc.∗ Our AFM system can also be used for scanning polarization force microscopy (SPFM), which allows imaging of adsorbed water layers and their dielectric responses. In collaboration with Dr. Alan Benesi in PSU Chemistry, we also study interfacial behavior of waters confined in nano-pores inside solid materials.∗∗
(a) Equilibrium thickness and structure of water layer adsorbed on silicon oxide. The insets are IR spectra of the OH stretch region.
(b) s- and p-polarized ATR-IR spectra of water layers adsorbed on a clean hydrophilic silicon oxide surface as a function of relative humidity at 270C.
- ∗ D. B. Asay and S. H. Kim, “Evolution of the Adsorbed Water Layer Structure on Silicon Oxide at Room Temperature” J. Phys. Chem. B 2005, 109, 16760-16763;
- ∗ A. L. Barnette, D. B. Asay, and S. H. Kim, “Average molecular orientations in the adsorbed water layers on silicon oxide in ambient conditions” Phys. Chem. Chem. Phys. 2008, 10, 4981 – 4986.
- ∗∗ B. O’Hare, M. W. Grutzeck, S. H. Kim, D. B. Asay, and A. J. Benesi, “Solid State Water Motions Revealed by Deuterium Relaxation in 2H2O-Synthesized Kanemite and 2H2O-Hydrated Na+-Zeolite A” J. Magn. Reson.2008, 195, 85 – 102.