Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session D34: Environmental Interfaces III |
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Sponsoring Units: DCP Chair: William Schneider, Notre Dame Room: LACC 511A |
Monday, March 21, 2005 2:30PM - 3:06PM |
D34.00001: Going nonlinear in probing adsorption at aqueous surfaces of environmental importance Invited Speaker: Aqueous interfaces play a central role in the sustainability of our world and life on this planet. Making advances in understanding environmental, biological and technological issues that involve aqueous interfaces requires a fundamental knowledge of bonding and adsorption at these interfaces. In the studies to be presented in this symposium I will describe our most recent results in which we explore the structure and bonding that occurs at aqueous interfaces with a particular focus on issues that are relevant to environmental issues at both the aqueous/organic and air/water interfaces. Our studies involve a combination of nonlinear and linear spectroscopic techniques, thermodynamic measurements and molecular dynamics simulations. [Preview Abstract] |
Monday, March 21, 2005 3:06PM - 3:18PM |
D34.00002: Phase-Sensitive Sum-Frequency Vibrational Spectroscopy of Water on Hydrophilic and Hydrophobic Interfaces Victor Ostroverkhov, Glenn A. Waychunas, Yuen Ron Shen Water structures at hydrophilic and hydrophobic interfaces are relevant to many problems in various disciplines. Sum-frequency vibrational spectroscopy (SFVS) is a unique technique to study such interfaces at the molecular level. We have developed a phase-sensitive SFVS method that provides both magnitude and phase of the nonlinear spectral response from the interfaces, and allows more detailed understanding of the interfacial structure including water molecular orientations at different adsorption sites. We have studied water organization on hydrophilic quartz surfaces as well as surfactant-covered quartz surfaces. It is seen that the orientations of water molecules responsible for the ice-like and liquid-like peaks respond differently to variation of the bulk pH values. They are also different for hydrophilic and hydrophobic interfaces despite some similarities in the spectra. [Preview Abstract] |
Monday, March 21, 2005 3:18PM - 3:30PM |
D34.00003: Orientational structure of water molecules near the solid/water interface probed with Second Harmonic Generation Peng Wan, Harry Tom A new experimental method was developed especially to probe the Stern Layer effective capacitance and the interfacial depth of water allowing us to probe the accuracy of the Gouy-Chapman Stern model. This is done using Surface Second Harmonic Generation (SHG) performed at the silica/water interface. By varying the pH, salt concentration and temperature of the aqueous solutions, we gain insight into the molecular orientational structure in the interfacial region. [Preview Abstract] |
Monday, March 21, 2005 3:30PM - 4:06PM |
D34.00004: Atmospherically Relevant Interfaces and Reactions via {\it ab initio} Molecular Dynamics Invited Speaker: This abstract has not been submitted yet. [Preview Abstract] |
Monday, March 21, 2005 4:06PM - 4:18PM |
D34.00005: Determination of Thermodynamic Surface Properties of Carboxylic Acid Functionalized Silanes at Silica/Water Interfaces with Second Harmonic Generation Michael Musorrafiti, Christopher Konek, Hind Al-Albadleh, Paul Bertin, SonBinh Nguyen, Franz Geiger Using the $\chi ^{\left( 3 \right)}$ method of second harmonic generation, we report surface pK$_{a}$ values for a monoprotic carboxylic acid functionalized silica/water interface. We observe two pK$_{a}$ values at 9(1) and 5.6(2). The acidic pK$_{a}$ is similar to pK$_{a}$ values of organic acids in solution. The more basic pK$_{a}$ is consistent with lateral hydrogen-bonding stabilization among the interfacial carboxylic acid groups. From the measured data, we obtained relative surface potentials and surface charge densities. Using these values in the Lippmann equation, we can tracked the changes in interfacial energy relative to the neutral reference state over seven orders of magnitude, from 10$^{-7}$ mJ/m$^{2}$ to several mJ/m$^{2}$. [Preview Abstract] |
Monday, March 21, 2005 4:18PM - 4:30PM |
D34.00006: Watching Molecules Orient in the Stern Layer Jeff Turner, Zachary Schultz, Adele Poynor, Shan Jiang, Sung Chul Bae, Andrew Gewirth, Steve Granick The orientation of molecules near a surface is interesting not only from a fundamental viewpoint, but also for controlling chemical reactivity and surface engineering properties. Using a surface potential, we control the orientation of a zwitterionic benzene derivative, and follow this orientation with broadband IR/narrowband visible sum frequency spectroscopy. Another interesting system we study via SFG is the interface formed when water meets a methyl-terminated hydrophobic surface. For this system, SFG results are compared to our group's measurements using ellipsometry and neutron reflectivity techniques. [Preview Abstract] |
Monday, March 21, 2005 4:30PM - 5:06PM |
D34.00007: Oxide and Carbonate Surfaces as Environmental Interfaces: The Importance of Adsorbed Water in Surface Composition and Surface Reactivity Invited Speaker: Environmental molecular surface science is an important and expanding area of current research. This presentation focuses on advances in the molecular level understanding of the chemistry that occurs on the surface of oxide and carbonates in the atmosphere. In particular, the importance of water in the surface composition and surface reactivity of some representative oxide and carbonate surfaces including MgO, CaCO$_{3}$ and Fe$_{2}$O$_{3} $ will be discussed. [Preview Abstract] |
Monday, March 21, 2005 5:06PM - 5:18PM |
D34.00008: Instability of Water/Quartz Interfaces Weitao Liu, Yuen-Ron Shen Water/quartz interfaces play an important role in modern industry and environmental science, but as buried interfaces, they have not been well studied because of lack of experimental tools. Recently, second harmonic generation (SHG) and sum-frequency spectroscopy have been used to obtain valuable information about the interfaces. However, it was found that the results are often difficult to reproduce quantitatively even on the daily basis, suggesting that the interfacial structure may be continually varying in time. We used SHG to monitor the interface with different bulk pH in water, and observed the fluctuation of the signal over long periods of time, signifying that the interfacial structure could be unstable. After a sizable adjustment of the pH value, it took about 1hr for the SHG signal to reach some sort of equilibrium, but the fluctuations remain significant. Similar results on other water/oxide interfaces were obtained. SHG appears to be a valuable tool for monitoring interfacial instability. This work was supported by the National Science Foundation Science and Technology Center of Advanced Materials for Purification of Water with Systems (Water CAMPWS; {\#}CTS-0120978). [Preview Abstract] |
Monday, March 21, 2005 5:18PM - 5:30PM |
D34.00009: The structure of water on the (101bar0) surface of ZnO Olga Dulub, Bernd Meyer, Ulrike Diebold The room temperature adsorption of water on the ZnO(101bar0) surface has been investigated with scanning tunneling microscopy (STM), low energy electron diffraction (LEED), low energy He$^{+}$ ion scattering spectroscopy (LEIS), and DFT calculations. At low water coverage (0.5 - 1 Langmuir (L)), formation of 2D water clusters with a (2 x 1) periodicity was observed on the well-ordered surface. A mixed state with half the water molecules dissociated and the other half molecularly adsorbed was found to be the most favorable configuration of the water monolayer. At surface saturation, reached at exposures of $\sim $3 L, domains with (2x1) periodicity, as well as domains of (1x1) structure of the similar height, were observed. The (1x1) domain is a minority structure (about 10{\%} of the total water overlayer), localized in the vicinity of surface defects. The influence of defects on water adsorption was also examined on the slightly sputtered surface. In this case, no (2x1) superstructure was observed on the surface by LEED, although LEIS confirmed the presence of water species. [Preview Abstract] |
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