Particle deposition onto solid surfaces with microscopic charge heterogeneity: the "bump effect"

Abstract

Summary form only given. A stagnation point flow (SPF) setup was used to directly observe deposition kinetics of colloidal particles onto micropatterned glass surfaces with well-defined surface charge heterogeneity features. The SPF system consists of a microscope focused on a small collector surface area, with an automated computer controlled image-capturing device comprising a CCD camera. Surface charge heterogeneity was microfabricated onto glass surfaces by chemically modifying well-controlled fractions of glass surface with aminosilane using a soft lithographic technique. Particle deposition was observed for a wide range of flow rates (Peclet numbers) and solution ionic strengths. The observed experimental particle deposition rates at various physicochemical conditions were compared to predictions based on a patchwise charge-heterogeneity model. Comparisons revealed that (1) deviation from patch model occurs at high flow rates (or Peclet numbers), (2) patch model approximates deposition rate at lower Peclet numbers, and (3) deviation from patch model predictions occurs at a lower flow velocity for lower ionic strength runs. The particle deposition behavior and breakdown of patch model are attributed to coupling between hydrodynamic and electrostatic double layer interactions. A mechanistic model which we term the bump effect is used to describe deposition behavior on micropatterned glass surfaces.