Showing papers by "Friedrich Gunther Mugele published in 2014"

Sorption‐Determined Deposition of Platinum on Well‐Defined Platelike WO3

Abstract: The photodeposition of Pt nanoparticles from [PtCl6]2− on platelike WO3 crystals occurs preferentially on the small, subordinate facets. Rather than the often-used explanation of preferred light-induced charge migration, we propose that this phenomenon is due to differences in the intrinsic surface charges of WO3 facets exposed to water; thus, the dark sorption of [PtCl6]2− on positively charged facets/edges is preferred. This conclusion is based on 1) (dark) impregnation studies, which showed Pt deposition to also be facet-specific, and 2) aqueous-phase AFM studies, which suggest intrinsic surface charges to be in agreement with sorption-based Pt distributions

Charge Control and Wettability Alteration at Solid-Liquid Interfaces

Abstract: Most solid surfaces acquire a finite surface charge upon exposure to aqueous environments due to desorption and/or adsorption of ionic species. The resulting electrostatic forces play a crucial role in many fields of science, including colloidal stability, self-assembly, wetting, and biophysics as well as technology. Enhanced oil recovery is an example of a large scale industrial process that hinges in many respects on these phenomena. In this paper, we present a series of experiments illustrating fundamental aspects of low salinity water flooding in well-defined model systems. We show how pH and ion content of the water phase as well as the presence of model polar components (fatty acids) in the oil phase affect the wettability (i.e. contact angle distribution) of oil-water-rock systems. Specifically, we discuss high resolution atomic force microscopy (AFM) experiments demonstrating the preferential adsorption of multivalent cations to mineral surfaces such as mica and gibbsite. Cation adsorption leads to increased and in some cases reversed surface charge at thesolid-liquid interface. In the case of charge reversal, the adsorption process can trigger a wetting transition from complete water wetting in ambient oil (i.e. zero water contact angle) in the absence to partial wetting in the presence of divalent cations. While already dramatic for pure alkanes as base oil, adding fatty acids to the oil phase enhances the effect of divalent ions on the oil-water-rock wettability even more. In this case, contact angle variations of more than 70° can be observed as a function of the salt concentration. This enhancement is caused by the deposition of a thin film of fatty acid on the solid surface. AFM as well as surface plasmon resonance spectroscopy measurement in a microfluidic continuous flow cell directly demonstrate that adsorbed Ca ions promote secondary adsorption of acidic components from the oil phase. The combination of the effects discussed provides a rational scenario explaining many aspects of the success of low salinity water flooding.