Analysis of Low Density Particles Using Differential Centrifugal Sedimentation

Centrifugal sedimentation of particles suspended in a fluid is a well known method (1, 2) to measure the size distribution of particles in the range of about 0.02 micron to about 20 microns. The sedimentation velocity of any particle can be calculated if the particle density, fluid density, fluid viscosity, and centrifugal acceleration are known, using the well known Stokes' Equation (3). Stokes' Equation is modified slightly to account for how the centrifugal force inside a centrifuge changes as the radius of rotation increases, since during an analysis the radius of rotation changes as particles sediment. There are two conventional techniques for analysis: integral (sometimes called homogeneous) sedimentation and differential (sometimes called two-layer) sedimentation. These two techniques have inherent advantages and disadvantages.