Rotational viscometry under presence of apparent wall slip

Abstract

A new way is suggested for treatment of the viscometric data, obtained in a rotational viscometer using several configurations of coaxial cylinders with different gap widths. Liquids are assumed to display both a general shear-thinning behavior and an apparent slip at solid boundaries. The body of primary data is at first smoothed using a conventional least-squares fitting. The subsequent procedure, called local filtering, gives a nonparametric representation of the both material functions γ̇=γ̇(τ) and u=u(τ). Several data sets for aqueous polymeric solutions with high content of electrolytes are treated to demonstrate the typical problems encountered in analyzing apparent wall-slip effects. When compared with the data found in literature, the slip velocities obtained are slightly higher, probably due to an enhanced coagulation caused by the presence of electrolytes.