Optical Imaging of Surface Chemistry and Dynamics in Confinement Carlos Macias-Romero, Igor Nahalka, Halil I. Okur, Sylvie Roke# Laboratory for fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Sci- ence (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytech- nique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland, #
[email protected]; Surface chemistry and dynamics are optically imaged label-free and non-invasively in a 3D confined geome- try and on sub-second time scales Abstract The interfacial structure and dynamics of water in a microscopically confined geometry is imaged in three dimensions and on millisecond time scales. We developed a 3D wide-field second harmonic mi- croscope that employs structured illumination. We image pH induced chemical changes on the curved and confined inner and outer surfaces of a cylindrical glass micro-capillary immersed in aqueous solu- tion. The image contrast reports on the orientational order of interfacial water, induced by charge- dipole interactions between water molecules and surface charges. The images constitute surface poten- tial maps. Spatially resolved surface pKa,s values are determined for the silica deprotonation reaction. Values range from 2.3<pKa,s<10.7, highlighting the importance of surface heterogeneities. Water mol- ecules that rotate along an oscillating external electric field are also imaged. With this approach, real time movies of surface processes that involve flow, heterogeneities and potentials can be made, which will further developments in electrochemistry, geology, catalysis, biology, and microtechnology. Microscopic and nanoscopic structural heterogeneities, confinement, and flow critically influ- ence surface chemical processes in electrochemical, geological, and catalytic reactions (1-5).