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O: Fachverband Oberflächenphysik

O 61: Focus Session: Nanoscale Insights into Interfacial Electrochemistry I

O 61.2: Invited Talk

Wednesday, March 14, 2018, 11:00–11:30, HE 101

Optical imaging of surface chemistry and dynamics in confinement — •Sylvie Roke — Laboratory for fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland

Electrochemical processes, chemical surface reactions and transformations at interfaces depend strongly on the local electrostatic environment as well as on nanoscale structures. In addition, structural heterogeneities, confinement, and flow critically influence surface chemical processes. Here, we image the interfacial structure and dynamics of water in a microscopically confined geometry in three dimensions and on millisecond time scales with a 3D structurally illuminated wide-field second harmonic microscope. Image contrast reports on the orientational order of interfacial water, induced by charge-dipole interactions between water molecules and surface charges. The images are converted into surface potential maps. Spatially resolved surface acid dissociation constant pKa,s values are determined for the silica deprotonation reaction by following pH induced chemical changes on the curved and confined surfaces of a glass micro-capillary immersed in aqueous solutions. These values ranged from 2.3 to 10.7 along the wall of a single capillary, because of surface heterogeneities. Water molecules that rotate along an oscillating external electric field were also imaged.