2 research outputs found
Optical Imaging of Surface Chemistry and Dynamics in Confinement
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 microscope 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 solution. 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 potential 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 molecules 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