Observed and simulated fluid drag effects on colloid deposition in the presence of an energy barrier in an impinging jet system.

The deposition and re-entrainment behaviors of carboxylate-modified latex microspheres (0.2-, 0.5-, 1.0-, and 2.0-microm diameter) were examined in an impinging jet system on both glass and quartz substrata under a variety of environmentally relevant fluid velocities (2.12 x 10(-4) to 1.06 x 10(-3) m sec(-1)) in both the absence and the presence of an energy barrier to deposition. In the absence of an energy barrierto deposition, deposition fluxes onto glass and quartz substrata increased with increasing fluid velocity for all four microsphere sizes, in accordance with expectations from theory. In contrast, in the presence of an energy barrier to deposition, deposition efficiencies onto glass and quartz substrata decreased with increasing fluid velocity for all four microsphere sizes. Lack of re-entrainment and observed strong attachment were consistent with the expectation that deposition occurs via the primary energy minima where nanoscale surface heterogeneity locally reduces or eliminates the energy barrier to deposition. Colloid deposition onto an overall opposite-charged surface was simulated using a particle transport model with randomly distributed hetero domains that were like-charged relative to the colloid. Varying the size and number of the hetero domains showed that simulated colloid deposition efficiencies decreased with increasing fluid velocity when the hetero domains were small relative to the colloid. The simulations thereby demonstrate that observed decreases in colloid deposition efficiencies with increasing fluid velocity are consistent with the hypothesis that colloid deposition onto overall like-charged surfaces occurs at nanoscale hetero domains where repulsion is locally reduced or eliminated.