Time: Thursday 17 May 2018 at 14.15
Room: Å 4001
Title: “Mineral/water interfaces characterized by Ab Initio Molecular Dynamics: making the link between structure and SFG vibrational spectroscopy”
Speaker: Professor Marie-Pierre Gaigeot
LAMBE UMR 8587, Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, Université d’Evry val d’Essonne, Paris – Université Paris Saclay, France, firstname.lastname@example.org
In this presentation, we will review our recent theoretical works on the characterization of mineral/liquid water interfaces, i.e. silica/water (crystalline and amorphous) and alumina/water interfaces, making the link between structure and non-linear SFG (Sum Frequency Generation) experiments. Non-linear SFG spectroscopy in the 3000-4000 cm-1 spectral domain is indeed one method of choice to probe complex inhomogeneous solid/liquid and liquid/air interfaces. Although an extremely powerful technique, the detailed interpretation of the experimental signatures requires associated calculations. This is the challenge we have been tackling over the past 5 years, applying Ab Initio DFT-based molecular dynamics simulations (DFT-MD).
I will illustrate here some of our recent works showing how to separate vibrational signatures arising from the different layers of water at the interface, how to provide a direct interpretation of the H-Bond networks at play at interfaces (water-water vs solid-water networks), including our recent works unraveling 2-dimensional interfacial water networks, how to define the only three spatial regions of interest at any charged interfaces (BIL, Binding Interfacial Layer; DL, Diffuse Layer; Bulk) and how to universally interpret/assign SFG vibrational bands from these three regions, including χ2 and χ3 contributions into the theoretical signals. We will also show how our deconvolution schemes for SFG spectral interpretation provide direct knowledge of the isoelectric point at any aqueous surface and direct knowledge of the formation of an Electric Double Layer (EDL) when aqueous ionic solutions are considered at the interface. We will unravel trends in going from hydrophobic to hydrophilic surfaces at the interface with liquid water.
Acknowledgments: Collaborative works with Prof. Y. Ron Shen at the University of California at Berkeley, USA, Prof E. Borguet at Temple University, USA, Dr E. Backus, Max Planck Institute in Mainz, Germany. Works achieved with PhD/Post-Doc students S. Pezzotti, D. Galimberti, M. Pfeiffer-Laplaud, L. Potier, F. Siro Brigiano, A. Cimas.