TABLE OF CONTENTS Differential centrifugal sedimentation (DCS), sometimes also called "two-layer" sedimentation, is a widely used analysis method that produces extremely high resolution size distributions of microscopic to sub-microscopic particles. The normal measurement range for the method is from ?0.01 ?m (10 nm) to ?50 ?m, although it is possible with some types of materials to extend the range to below 0.003 ?m (3 nm) or up to 120 ?m or more. This chapter provides some background information on particle size analysis by sedimentation, explains how the DCS method works and describes the advantages and limitations of the method. Several sample analyses are presented to help illustrate the capabilities of DCS.
Sedimentation of particles in a fluid has long been used to characterise particle size distribution. Stokes' law [1] is used to determine an unknown distribution of spherical particle sizes by measuring the time required for the particles to settle a known distance in a fluid of known viscosity and density. Sedimentation can be either gravitational (1 g force), or centrifugal (many g force).
Gravitational sedimentation is normally limited to particles of relatively large size, because the rate of sedimentation for small particles is too low to give a practical analysis time, and because Brownian motion of small particles becomes too large to allow effective settling. A very narrow distribution of small particles will be reported as a broad...
