Search Results
Few-cycle laser driven reaction nanoscopy on aerosolized silica nanoparticles
2019, Rupp, Philipp, Burger, Christian, Kling, Nora G, Kübel, Matthias, Mitra, Sambit, Rosenberger, Philipp, Weatherby, Thomas, Saito, Nariyuki, Itatani, Jiro, Alnaser, Ali S., Raschke, Markus B., Rühl, Eckart, Schlander, Annika, Gallei, Markus, Seiffert, Lennart, Fennel, Thomas, Bergues, Boris, Kling, Matthias F.
Nanoparticles offer unique properties as photocatalysts with large surface areas. Under irradiation with light, the associated near-fields can induce, enhance, and control molecular adsorbate reactions on the nanoscale. So far, however, there is no simple method available to spatially resolve the near-field induced reaction yield on the surface of nanoparticles. Here we close this gap by introducing reaction nanoscopy based on three-dimensional momentum-resolved photoionization. The technique is demonstrated for the spatially selective proton generation in few-cycle laser-induced dissociative ionization of ethanol and water on SiO2 nanoparticles, resolving a pronounced variation across the particle surface. The results are modeled and reproduced qualitatively by electrostatic and quasi-classical mean-field Mie Monte-Carlo (M3C) calculations. Reaction nanoscopy is suited for a wide range of isolated nanosystems and can provide spatially resolved ultrafast reaction dynamics on nanoparticles, clusters, and droplets.
Universal emulsion stabilization from the arrested adsorption of rough particles at liquid-liquid interfaces
2017, Zanini, Michele, Marschelke, Claudia, Anachkov, Svetoslav E., Marini, Emanuele, Synytska, Alla, Isa, Lucio
Surface heterogeneities, including roughness, significantly affect the adsorption, motion and interactions of particles at fluid interfaces. However, a systematic experimental study, linking surface roughness to particle wettability at a microscopic level, is currently missing. Here we synthesize a library of all-silica microparticles with uniform surface chemistry, but tuneable surface roughness and study their spontaneous adsorption at oil-water interfaces. We demonstrate that surface roughness strongly pins the particles' contact lines and arrests their adsorption in long-lived metastable positions, and we directly measure the roughness-induced interface deformations around isolated particles. Pinning imparts tremendous contact angle hysteresis, which can practically invert the particle wettability for sufficient roughness, irrespective of their chemical nature. As a unique consequence, the same rough particles stabilize both water-in-oil and oil-in-water emulsions depending on the phase they are initially dispersed in. These results both shed light on fundamental phenomena concerning particle adsorption at fluid interfaces and indicate future design rules for particle-based emulsifiers.
Unravelling New Processes at Interfaces: Photochemical Isoprene Production at the Sea Surface
2015, Ciuraru, Raluca, Fine, Ludovic, van Pinxteren, Manuela, D’Anna, Barbara, Herrmann, Hartmut, George, Christian
Isoprene is an important reactive gas that is produced mainly in terrestrial ecosystems but is also produced in marine ecosystems. In the marine environment, isoprene is produced in the seawater by various biological processes. Here, we show that photosensitized reactions involving the sea-surface microlayer lead to the production of significant amounts of isoprene. It is suggested that H-abstraction processes are initiated by photochemically excited dissolved organic matter which will the degrade fatty acids acting as surfactants. This chemical interfacial processing may represent a significant abiotic source of isoprene in the marine boundary layer.