THE USE OF VISIBLE-LIGHT DIFFRACTION FOR MEASURING INTERPARTICLE SEPARATIONS IN CONCENTRATED SILICA DISPERSIONS

The diffraction of visible laser light has been used to measure the interparticle spacing for paucidispersed silica particle sediments. The diffractometer has improved resolution when compared to those commonly used in the past, and in particular, has the ability to measure over the depth of the sediment with a resolution of about 0.25 mm. This, combined with the substantial density difference between the silica particles and the suspension medium (ethanol) has allowed us to show clearly that there is a density gradient in the sediment, and that this gradient is related to the repulsive interparticle forces, which are electrostatic in origin. We also show how the flux of particles is expected to alter the kinetics of compaction of the sediment, and derive a theory for the maximum flux in the case of a hard sphere particulate system, as a function of the initial volume fraction.