The Measurement of Low Yield Stress of Dilute Clay Suspensions using a Novel In-Line Microfluidic Rheometer*

The yield stress (τ_y) is a rheological parameter of great significance in particle suspensions as it depicts the inherent structural strength of the liquid-spanning network made up of particles. The τ_y is a function of the weight fraction of the solid particles, and hence, the former could be a surrogate measure of the latter, which is a useful process parameter in various applications such as the recovery of Athabasca bitumen oil from middlings in the Clark’s hot water extraction process, and the transportation of oil tailings and other minerals to the tailing ponds. These dilute particle suspensions possess a yield stress as low as a few mPa to a few Pa. The existing rheometers that possess the ability to detect low yield stress cannot be employed in-line, and the ones that can be, do not measure low yield stress. Thus, we propose using an inexpensive, easy-to-use, and easy-to-clean technique using an in-house microfluidic platform for in-line rapid measurement of low τ_y. The τ_y of the suspension of water and cloisite clay of various weight fractions ranging between 3 to 6% was measured to be between 0.065 to 8 Pa. The τ_y showed a cubic dependence on the weight fraction, and the relationship between them was used for the evaluation of the unknown weight fraction through the measurement of τ_y. We also evaluated a τ_y as low as 0.001 Pa and as high as 20 Pa using our technique for other examples such as whole blood, mucin suspensions, kaolinite suspensions, wastewater sludge, and carbopol gel.