Colloid Detachment by a Moving Air-Water Interface: Effect of Particle Shapes.

Air-water interfaces interact strongly with colloidal particles through capillary forces. The magnitude of the interaction force depends, among other things, on the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface (AWI). We used hydrophilic polystyrene colloids with four different colloid shapes (spheres, barrels, rods, and elliptical disks), but otherwise identical surface properties. The non-spherical shapes were created by stretching spherical microspheres embedded in a film of polyvinyl alcohol. The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced and passed through the channel, thereby generating an advancing and receding AWI. The detachment of colloids by the AWI was visualized by confocal microscopy and quantified by image analysis. The advancing AWI was significantly more successful in detaching the deposited colloids than the receding AWI regardless of the colloid shape. Barrels were the most easily detached followed by spheres and spheroids.