(365j) The Squeeze Flow of Yield Stress Fluids

A systematic study of squeeze flow (SF) is performed on different concentrations of carbopol with varying yield stresses. A sample is placed between two parallel plates and a series of constant force steps applied, following the plate separation as a function of time. A thorough comparison is made between the experimental data and the SF theory. Precise rheological measurements of the simple yield stress fluids are performed in addition to the well controlled SF tests. These rheological measurements are used in conjunction with the SF equations to determine the dynamic height profile, allowing a direct comparison of theory and experiment throughout the entire test. The limiting height achieved during constant force SF reveals information as to the yield stress of the fluid as predicted by the theory. Additionally, the validity of the lubricational theory is tested; not only for the determination of the yield stress but throughout the flow as well. By carefully controlling the experimental conditions of the squeeze test the yield stress can be efficiently determined. We find that well controlled SF tests predict yield stress values that agree with the precise rheological tests with less than 15% error.