Flow cell for real time observation of single particle adhesion and detachment

A flow cell was built for observing particle removal from test surfaces in real time. The removal force is the hydrodynamic force exerted on the particle by liquid flowing parallel to the test surface. Particle removal was detected visually either through a microscope or on a video monitor. All experimental results reported here are based on the removal of deposited 10 μm polystyrene (PSL) spheres from one of 3 surfaces: polished aluminum; polished bare silicon wafers (native oxide only); or thertnally oxidized silicon wafers. One of 3 cleaning liquids was used: dilute SC-1, dilute SC-2, or de-ionized water containing 0.01% Micro ® . The hydrodynamic removal force was controlled primarily by controlling the liquid flow rate. In all experiments, as the flow rate increased, single polystyrene latex (PSL) spheres detached first, then doublets, then triplets and finally larger agglomerates; that is, the adhesion force increased more rapidly with agglomeration than the hydrodynamic removal force. By applying theoretical calculations from the literature, this flow cell can be used to estimate the hydrodynamic forces necessary for removal of particles from surfaces.