Microdivers to study sedimentation in polydisperse, concentrated colloidalsuspensions

A small amount of polymer-particles with diameters in the 100 um range can be used as an ensemble of "microdivers" to study, sedimentation velocities of polydisperse submicron paiticles in concentrated opaque suspensions. Thi s tracer technique, based on Berg's (1941) diver method, is simple, measure s velocities directly, and does not require underlying theory, beyond conse rvation of momentum. It confirms that the polymer tracers reside at the pos ition in the suspension where the suspension density corresponds to their o wn density. Aqueous inorganic suspensions of 250 - 750 nm alpha -alumina pa rticles were studied, which is electrostatically, stabilized with nitric ac id in water, using - 100 mum polymethylmetacrylate and polystyrene particle s as tracers. Experiments were compared with predictions by, state-of-the-a rt continuum models for multicomponent sedimentation to underpin the validi ty, of the tracer technique.