Deposition of Latex Colloidsat Rough Mineral Surfaces:An Analogue Study Using Nanopatterned Surfaces.

Deposition of latex colloids on a structured siliconsurface wasinvestigated. The surface with well-defined roughness and topographypattern served as an analogue for rough mineral surfaces with half-poresin the submicrometer size. The silicon topography consists of a regularpit pattern (pit diameter = 400 nm, pit spacing = 400 nm, pit depth= 100 nm). Effects of hydrodynamics and colloidal interactions intransport and deposition dynamics of a colloidal suspension were investigatedin a parallel plate flow chamber. The experiments were conducted atpH ∼ 5.5 under both favorable and unfavorable adsorption conditionsusing carboxylate functionalized colloids to study the impact of surfacetopography on particle retention. Vertical scanning interferometry(VSI) was applied for both surface topography characterization andthe quantification of colloidal retention over large fields of view.The influence of particle diameter variation (d=0.3–2 μm) on retention of monodisperse as well as polydispersesuspensions was studied as a function of flow velocity. Despite electrostaticallyunfavorable conditions, at all flow velocities, an increased retentionof colloids was observed at the rough surface compared to a smoothsurface without surface pattern. The impact of surface roughness onretention was found to be more significant for smaller colloids (d= 0.3, 0.43 vs. 1, 2 μm). From smooth to rough surfaces,the deposition rate of 0.3 and 0.43 μm colloids increased bya factor of ∼2.7 compared to a factor of 1.2 or 1.8 for 1 and2 μm colloids, respectively. For a substrate herein, with constantsurface topography, the ratio between substrate roughness and radiusof colloid, Rq/rc, determinedthe deposition efficiency. As Rq/rcincreased, particle–substrate overall DLVO interactionenergy decreased. Larger colloids (1 and 2 μm) beyond a criticalvelocity (7 × 10–5and 3 × 10–6m/s) (when drag force exceeds adhesion force) tend to detach fromthe surface irrespective of the impact of roughness. For polydispersesolutions, an increase in the polydispersity and flow velocity resultedin a reduction of colloid deposition efficiency due to the resultingenhanced double-layer repulsion. Quantification of surface topographyvariations of two endmembers of natural grain surfaces showed thathalf-pore depths and roughness of sedimentary quartz grains are mainlyin the micrometer range. Grains with diagenetically formed quartzovergrowths, however, show surface roughness mainly in the submicrometerrange. Thus, surface topography features applied in the here presentedanalogue study and resulting variation in particle retention can serveas quantitative analogue for particle reactions in diageneticallyaltered quartz sands and sandstones. The reported impact of particlepolydispersity can have an important application for quantitativeprediction of retention of varying types of minerals, such as differentclay minerals in the environment under prevailing unfavorable conditions. [ABSTRACT FROM AUTHOR]