The rheology of concentrated dispersions of weakly attracting colloidal particles with and without wall slip

TLDR: In this paper, it was demonstrated that weakly flocculated, concentrated colloidal dispersions show slip flow when sheared between smooth concentric cylinders, regardless of how small the stress and how long the flow is left to establish prior to measurement.

Abstract: It is demonstrated that weakly flocculated, concentrated colloidal dispersions show slip flow when sheared between smooth concentric cylinders. The precise pattern of behavior seen depends upon the stress and upon how long the flow is left to establish prior to measurement. With delay times of order hours, slip is not seen until a critical stress is exceeded (typically about 1 Pa) and, thus, the true low‐shear viscosity can be determined provided care is taken to ensure the stress does not exceed the critical level. With short delay times of order minutes, slip is seen irrespective of how small the stress is and the low‐shear viscosity can be underestimated by several orders of magnitude. Comparisons of flow curves obtained using smooth and roughened cylinders show that slip only occurs at the inner cylinder, and also that bulk flow is re‐established at higher stresses where the dispersions start to shear thin. The apparent low‐shear, relative viscosity measured in the presence of slip appears, to a first...