F. Soltani et U. Yilmazer, SLIP VELOCITY AND SLIP LAYER THICKNESS IN FLOW OF CONCENTRATED SUSPENSIONS, Journal of applied polymer science, 70(3), 1998, pp. 515-522
The rheological characterization of highly filled suspensions consisti
ng of a Newtonian matrix (hydroxyl-terminated polybutadiene), mixed wi
th two different sizes of aluminum powder (30% and above by volume) an
d two different sizes of glass beads (50% and above by volume), was pe
rformed using a parallel disk rheometer with emphasis on the wall slip
phenomenon. The effects of the solid content, particle size, type of
solid particle material, and temperature on slip velocity and slip lay
er thickness were investigated. Suspensions of small particles of alum
inum (mean diameter of 5.03 mu m) did not show slip at any concentrati
on up to the maximum packing fraction. However, suspensions of the oth
er particles exhibited slip at the wall, at concentrations close to th
eir maximum packing fraction. In these suspensions, the slip velocity
increased linearly with the shear stress, and at constant shear stress
, the slip velocity increased with increasing temperature. The slip la
yer thickness increased proportionally with increasing size of the par
ticles for the glass beads. Up to a certain value of (filler content/m
aximum packing fraction), phi/phi(m), the slip layer thickness divided
by the particle diameter, delta/D-P, was 0, but it suddenly increased
and reached a value that was independent of phi/phi(m) and the temper
ature. On average, the ratio of delta/D-P was 0.071 for aluminum and 0
.037 for glass beads. (C) 1998 John Wiley & Sons, Inc.