Techniques for measuring the yield stress of materials are numerous, but often plagued with diffculties and uncertainties in measurement. The... Show moreTechniques for measuring the yield stress of materials are numerous, but often plagued with diffculties and uncertainties in measurement. The primary methods include shear rheometry and, more recently, squeezing ow. Shear rheometry requires care on the part of the experimentalist to generate uniform flow fields and avoid shear banding or wall slip which may interfere with measurements. Squeezing fow tests are often performed with poorly controlled boundary conditions creating complicated flow fields. Further, the effects of the experimental modifications made to produce these boundary conditions in measurements are often not investigated and simply ignored. The main objective of this study was to develop a novel measuring technique to study the yield stress behavior of a model material, Carbopol. First attempts were made towards a novel lubricant injection squeezing (LIS) ow technique based on the continuous lubricated squeezing ow (CLSF) setup, as well as a novel lubricant film squeezing (LFS) technique which will allow measurement of the yield stress without the complicated treatment of either the sample or experimental setup required by currently favored methods. The novel techniques were developed and validated by direct comparison with shear measurements, the current gold standard for determining yield stress. Common squeezing techniques for characterizing yield stress fluids were also compared and found to be inadequate and inconsistent when compared to the shear measurements. The results from this study showed that the LIS and LFS methods are able to qualitatively determine a yield stress, but further investigation is required before they can be achieve their full potential as viable methods for determine yield stress. M.S. in Chemical Engineering, December 2015 Show less
