Bk. Aral et Dm. Kalyon, EFFECTS OF TEMPERATURE AND SURFACE-ROUGHNESS ON TIME-DEPENDENT DEVELOPMENT OF WALL SLIP IN STEADY TORSIONAL FLOW OF CONCENTRATED SUSPENSIONS, Journal of rheology, 38(4), 1994, pp. 957-972
A flow visualization technique was applied to investigate the time and
temperature-dependent development of wall slip and the rheological be
havior of a concentrated suspension, containing 63% by volume solid gl
ass spheres and a poly (butadiene-acrylonitrile-acrylic acid) terpolym
er matrix, using steady torsional flow. Flow visualization allowed the
concomitant determination of the wall slip velocity and the shear vis
cosity of the concentrated suspension. The deformation rate, shear str
ess, and the wall slip velocity values during torsional flow were time
dependent and asymptotically reached steady-state values. The charact
eristic time necessary to reach steady state decreased with increasing
shear rate and temperature. Increasing temperature also increased the
wall slip velocity. The flow visualization technique was further util
ized to determine the yield stress of the suspension directly, which w
as found to decrease with increasing temperature. Increased surface ro
ughness prevented the wall slip of the concentrated suspension under c
ertain conditions; however, it frequently resulted in the fracture of
the suspension samples. Sample fracture became more pronounced with th
e preshearing of the samples.