Oriane Bonhomme
Institut Lumière Matière, UMR CNRS 5579, Université Lyon
website
Probing the molecular organization of liquids in bulk and at interface
Liquid molecular organization in the bulk or at interfaces, such as gas-liquid ones, is involved in many physical, chemical, or medically relevant processes. For interfaces, their specific chemical composition, molecular structure, dielectric and transport properties, compared with their bulk counterparts, drive important chemical reactions occurring in chemical and biological processes, such as liquid extraction, catalysis, membrane processes, or drug delivery, to name a few. In the bulk, this organization is also of utmost importance for understanding hydration and more generally solvation, ions dissolution and precipitation, protein folding and activity, all result from the interaction of ions with solvent molecules. In this context, we use optical methods, and notably Second Harmonic Generation (SHG), as tools to “see” the structure of liquids from interfaces to the bulk phase. Indeed, this non-linear optical process, in which two photons at a fundamental frequency are converted into one photon at the harmonic frequency, is intrinsically sensitive to symmetry at the molecular level or to electrostatic environment.
In this talk, I will first report our recent experimental studies on the molecular organization in the bulk of liquids from pure water to ionic liquids via concentrated aqueous electrolyte solutions. In the case of the pure water, I will also show how the combination of SHG experiments and Quantum Mechanical / Molecular Mechanics (QM/MM) calculations provides valuable information on the structure of the liquids on scales ranging from the very short distance (solvation shells) to the long distance (orientation correlations).
In the second part of the talk, I will present the studies performed at aqueous interfaces. I will first discuss the microscopic origin of the Surface-SHG intensity collected from air-water interfaces. I will finish by describing the perspectives of the optical techniques for the study of water/air interfaces and, in particular, how we can probe the intermolecular electronic interactions between adsorbed surfactants.
