Correlation between Electrostatic and Hydration Forces on Silica and Gibbsite Surfaces: An Atomic Force Microscopy Study.

The balance between hydration and Derjaguin-Landau-Verwey-Overbeek (DLVO) forces at solid-liquid interfaces controls many processes, such as colloidal stability, wetting, electrochemistry, biomolecular self-assembly, and ion adsorption. Yet, the origin of molecular scale hydration forces and their relation to the surface charge density that controls the continuum scale electrostatic forces is poorly understood. We argue that these two types of forces are largely independent of each other.

Impact of surface defects on the surface charge of gibbsite nanoparticles.

We use high resolution Atomic Force Microscopy to study the surface charge of the basal plane of gibbsite nanoparticles, with a lateral resolution of approximately 5 nm, in ambient electrolyte of variable pH and salt content. Our measurements reveal surface charge variations on the basal planes that correlate with the presence of topographic defects such as atomic steps. This surface charge heterogeneity, which increases with increasing pH, suggests that for a pH between 6 and 9 the defect sites display a stronger chemical activity than adjacent, apparently atomically smooth regions of the basal plane.

Sorption-determined deposition of platinum on well-defined platelike WO3.

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.