AVS 45th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM9
Equilibrium Water Structures at Well-Defined Organic Surfaces

Friday, November 6, 1998, 11:00 am, Room 309

Session: Water and Ice Interfaces
Presenter: D.L. Allara, Pennsylvania State University
Authors: D.L. Allara, Pennsylvania State University
T.J. Boland, Pennsylvania State University
Correspondent: Click to Email
We report combined in-situ infrared vibrational spectroscopic and coverage measurements, from submonolayer to near condensation, of equilibrium water adsorption at well-defined organic surfaces synthesized by molecular self-assembly. The adsorption isotherm data were used to develop thermodyamic parameters of the adsorbed films while the IR data give information on the water structures. The IR spectra were interpreted quantitatively by using modeling based on electromagnetic theory and the known optical function spectra of various phases of water. The results reveal a range of water structures from ice-like to clathrate-like and liquid-like depending on the water chemical potential, the chemical functionality of the surface and on the presence of dilute inorganic salts dissolved in the near water films. In the case of hydrophobic methyl-terminated surfaces, the water adopts a liquid-like structure from submonolayer to near-condensation coverages in surprising contradiction to the traditional view of ordered water at hydrophobic surfaces. In contrast, for polar surfaces such as CO2H, the water adopts a strongly H-bonded structure up to the condensation point. The incorporation of dissolved salts at the interfaces serves to broaden the range of water structures observed.