Particle Size by Ultracentrifugal Sedimentation and Comparison to TEM

Particle Size by Ultracentrifugal Sedimentation and Comparison to TEM 21.7.4.1 Introduction 

Ultracentrifugal sedimentation can be used to measure particle size in the range of 10 nm to 40 pm. The particles in dispersed form are injected into a rotating disc spinning up to 2400 RPM. The sedimentation is stabilized by density gradient fluid through which the particles settle. The principle is based on Stokes law  

The rate of sedimentation inside the rotating disc is controlled by four factors the size of the particles, the difference in density between the particles and the fluid through which they pass, the viscosity of the fluid, and the rotational speed (centrifugal field). 

The main advantage of particle size analysis by ultracentrifugal sedimentation over other methods such as dynamic light scattering is the enhanced resolution precision (typically 0.25%) and accuracy. Particle bands differing by only 5% in size may be differentiated. 

The main disadvantage is the longer time required for analysis (10-30 min depending on the size of the particles). 

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