DETERMINATION OF PARTICLE SEDIMENTATION-RATE BY ULTRASONIC INTERFEROMETRY - ROLE OF PARTICLE-SIZE, DENSITY AND VOLUME FRACTION

The sedimentation rate (SR) of non-aggregated spherical particles in s uspension was determined using an ultrasonic interferometry technique (Echo-Cell); this method is based on A-mode echography and measures th e rate of formation of a sediment on a solid plate during settling. Th e particle accumulation rate, which is related to SR, is obtained from the interference of two waves reflected by two interfaces: one betwee n the plate and the sediment and the other between the sediment and th e suspension. Studies were carried out at 25 degrees C using latex sph eres of different diameters (7 to 20 mu m) and densities (1.062 to 1.1 90 g/cm(3)) suspended in distilled water at various volume fractions ( 1% to 5%). As anticipated by the Stokes model, linear relations were f ound between SR and both particle density and the square of particle r adius. Experimental SR values decreased with increasing suspension par ticle concentration; these concentration effects were in good agreemen t with those predicted by the Steinour model. Our results thus serve t o validate the theoretical aspects of the Echo-Cell method and suggest its usefulness as a tool for studies of RBC interaction and RBC aggre gation. (C) 1997 Elsevier Science Ltd.