Particle deposition onto solid surfaces with micropatterned charge heterogeneity: The "hydrodynamic bump" effect

A radial stagnation-point flow cell utilizing an optical microscope and an image-capturing device was used to directly observe the deposition kinetics of colloidal particles onto micropatterned glass surfaces with well-defined surface charge features. Surface charge heterogeneity was microfabricated onto glass surfaces by silanizing specified regions of the glass surface by a soft lithographic technique. At a certain combination of solution ionic strengths and particle Peclet numbers, the observed deposition rates deviated from predictions on the basis of a particle-deposition model for surfaces with macroscopic patchwise charge heterogeneity. The results are attributed to the interplay between hydrodynamic and electrostatic double-layer interactions and are explained by a phenomenon we term the "hydrodynamic bump" effect.