Optical Imaging of Surface Chemistry and Dynamics in Confinement

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 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.

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• Unimpeded permeation of water through helium-leak-tight graphene-based membranes
• Commensurability Effects in Viscosity of Nanoconfined Water
• Elucidating the Bimodal Acid-base Behavior of the Water-silica Interface from First Principles
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Cited by in corpus (6)

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• Direct Quantification of Water Surface Charge by Phase-Sensitive Second Harmonic Spectroscopy
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• Flow-induced surface charge heterogeneity in electrokinetics due to Stern-layer conductance coupled to reaction kinetics
• Interfacial solvation explains attraction between like-charged objects in aqueous solution
• Energy Conversion via Metal Nanolayers