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Gas-phase modification of glassy carbon (GC) was investigated in an attempt to make a C−H-terminated surface that is resistant to oxidation. By using a hot filament technique, hydrogen radicals were generated from a flow of hydrogen gas, and then the radicals attacked glassy carbon electrode surfaces. The modified glassy carbon surfaces were characterized first by X-ray photoelectron spectroscopy, where the shape of the carbon 1s band shows a distribution of carbon oxidation states different from a fresh polished surface. The oxygen-to-carbon atomic ratio is low (<3%) and stays low in air for weeks. Hydrogen treatment had minor effects on Ru(NH3)6 3+/2+ cyclic voltammetry but increased ΔE p for Fe3+/2+ from 176 to 466 mV for a scan rate of 0.2 V/s. There is no significant difference in voltammetry at fresh polished glassy carbon surfaces or hydrogen-modified surfaces for dopamine, Fe(CN)6 3-/4-, and ascorbic acid. Raman spectroscopy of modified surfaces shows a small decrease in carbon disorder compared to the fresh polished glassy carbon with both microscopic and macroscopic observations. All these observations are consistent with the etching of the GC followed by formation of a hydrogen-terminated carbon surface. We attribute the major decrease in electron-transfer rate for aquated Fe3+/2+ to the absence of catalytic carbonyl sites on the hydrogen modified carbon.

Surface-active asphaltene molecules are naturally found in crude oil, causing serious problems in the petroleum industry by stabilizing emulsion drops, thus hindering the separation of water and oil. Asphaltenes can adsorb at water-oil interfaces to form viscoelastic interfacial films that retard or prevent coalescence. Here, we measure the evolving interfacial shear rheology of water-oil interfaces as asphaltenes adsorb. Generally, interfaces stiffen with time, and the response crosses over from viscous-dominated to elastic-dominated. However, significant variations in the stiffness evolution are observed in putatively identical experiments. Direct visualization of the interfacial strain field reveals significant heterogeneities within each evolving film, which appear to be an inherent feature of the asphaltene interfaces. Our results reveal the adsorption process and aged interfacial structure to be more complex than that previously described. The complexities likely impact the coalescence of asphaltene-stabilized droplets, and suggest new challenges in destabilizing crude oil emulsions.

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Synthetic crude oils derived from mined oil sands processed via the Clark hot water extraction process do not meet current specifications for pipeline transport and are corrosive to upgrader equipment by virtue of the high residual water content (2–5%) and salts. Formulated chemical additives used in this process can improve the oil quality by accelerating and enhancing the separation of water from oil. The identification and selection of these formulated additives is typically based on performance data collected in field testing for each component or blend. Herein, two methods are reported to study the effect of chemical additives on the phase separation behavior of water in diluted bitumen emulsions prepared in microfluidic devices. First, water droplets in diluted bitumen were created in the presence of chemical additives and the kinetics of droplet coalescence were compared for various additives and concentrations. Second, using a custom-made device geometry, water droplets in diluted bitumen were formed and aged prior to the addition of chemical additives. The treated droplets were observed to calculate the kinetics of droplet coalescence. The frequency of coalescence events was the same order of magnitude in both studies. The effectiveness of various additives can be determined by measuring the coalescence time, which is dominated by film drainage in the case of the best chemical additives.