Optical imaging of surface chemistry and dynamics in confinement

Abstract

Surface chemistry and dynamics are optically imaged label-free and non-invasively in a 3D confined geometry and on sub-second time scales AbstractThe 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 chargedipole interactions between water molecules and surface charges. The images constitute surface potential maps. Spatially resolved surface pK a,s values are determined for the silica deprotonation reaction.Values range from 2.3<pK a,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.Microscopic and nanoscopic structural heterogeneities, confinement, and flow critically influence surface chemical processes in electrochemical, geological, and catalytic reactions (1-5).Recent advances in micro-and nanotechnology are driven by these phenomena, often in combination with intrinsic surface or externally applied electrostatic field gradients. Micro-and nanocapillaries in combination with interfacial voltage gradients are used in the fabrication, manipulation, and characterization of droplets and interfaces (6-9) and highly amorphous materials (10). An electrostatic field gradient in a narrow channel can be used to separate (11) and identify analytes (12). Naturally occurring pores and interfaces employ extremely high electric field gradients to separate and transport chemicals from one aqueous phase to another (13). Artificial nanopores have recently been used to generate liquid jets (14) and electric power (15, 16). The increase in complexity of new materials and nano-and microtechnological developments (17) requires technology that can track, in real time, three dimensional spatial changes in the molecular structure of confined systems, such as curved interfaces and pores, as well as the response to electrostatic fields of these systems.

Energy conversion via metal nanolayers

“…4 offers the following phenomenological interpretation of our findings, followed by a detailed microscopic investigation below. At the pH values used here (5.8 for low and 8.0 for high-salinity water), the water:oxide interfaces we Page 10 investigate are charged (9,(12)(13)(14)(15)(16)(17). The electrostatic potential reaches not only into the aqueous solution but also into the oxide (18,19), depending on the local dielectric properties (20).…”

Flow-Induced Surface Charge Heterogeneity in Electrokinetics due to Stern-Layer Conductance Coupled to Reaction Kinetics

“…is shows that, in addition to the inherent heterogeneities of silica in equilibirum conditions [41], surfaces can exhibit dynamical heterogeneities. We note that the di usive and conductive contributions to j σ (see Eq.…”

“…e thin-EDL approximation [30] is therefore not possible here. In this Le er we choose parameters that represent silica at pH=6.5, such that − log 10 ρ C,b (M) = 6.5, Γ = 4.6 nm −2 , and pK = 6.75 (an average over the widely varying reported values [35][36][37]), with millimolar added salt concentrations ρ ±, b 1 mM such that λ D = 10 nm. e single reaction mechanism assumed here is actually too simple to capture the behaviour of silica quantitatively, but it serves our purposes here as a generic case.…”

Molecule‐Membrane Interactions in Biological Cells Studied with Second Harmonic Light Scattering

“…There hasb een an extensive body of work on the application of SHG as an imaging modality [56][57][58][59][60][61][62] following the first SH imaging study on the microstructure of polycrystalline ZnSe. [63] More recent applications include visualizing cell membranes stainedw ith SH-active dyes, [64] monitoring drug binding interactions at planar membrane surfaces, [65] mappingw ater surface potentials in glass micro-capillaries and on lipid membranes, [62,66] and development of super-resolution techniques for SH imaging. [67] Similar to our SHS ensemble studies, our application of SH imaging focused on the adsorption and transport of molecules acrossm embranes in living cells.…”