GAP SIZE AND SHEAR HISTORY DEPENDENCIES IN SHEAR THICKENING OF A SUSPENSION ORDERED AT REST

An investigation is made of the flow properties of a suspension of uniform 197 nra diameter spheres at a volume fraction of 0.50 dialyzed to equilibrium against 10–3M KC1 which displayed long-range orientational order at rest. In wide gap rheometers (i.e. tool gaps ≥ 0.5 mm) micro structures and flow properties are similar to those seen in many suspensions which are ordered at rest. Low shear rate response is found to be independent of rheometer tool gap down to 4.5 /xm. However the shear rate marking the onset of thickening is a decreasing function of rheometer tool gap for gaps smaller than 15 μm. These results are consistent with abrupt shear thickening seen in dense suspensions containing uniform particles arising from the formation of percolating clusters produced during shear melting. © 1986, American Institute of Physics. All rights reserved.