Hindered settling of rod‐like particles measured with magnetic resonance imaging

Magnetic resonance imaging (MRI) is used to measure the time evolution of the volume fraction vs. height profile during batch sedimentation of rod‐like particle suspensions. At any instant during sedimentation, MRI clearly delineates the supernatant, suspension, and sediment regions. The rod‐like particles with a mean aspect ratio of 17.4 exhibit considerably larger hindered settling effects than spherical particles with increasing particle concentrations. This can be attributed in part to the larger increase in interparticle forces and relative viscosities with suspensions of rod‐like particles than with suspensions of spherical particles, as the particle concentration increases. The relative viscosity of the rod‐like particle suspensions is a function of the spin‐spin relaxation time, T2. Since T2 is a measurable MRI quantity, this suggests that MRI may be used as an instrument for rheological measurement.