WALL SLIP EFFECTS ON DYNAMIC OSCILLATORY MEASUREMENTS

Concentrated emulsions, suspensions, foams, and polymer solutions often appear to slip along confining walls. This apparent slip is usually caused by large velocity gradients in a thin region adjacent to the wall, where the viscosity is low because of a reduced concentration of the suspended phase. Effects of wall slip on dynamic oscillatory shear measurements are less well understood. The stress waveforms obtained from dynamic oscillatory experiments on emulsions and dispersions, which one might suspect to slip at boundaries, are often quite complex. Authors initial goal in this work was to see whether it was possible to determine from the shape of the waveform whether slip was occurring. To understand what characteristics are required of a slipping layer to produce nonlinear waveforms, they propose a simple model of slip. The governing equations of motion are derived and three special cases are considered.