Abstract
This study investigates dilute aqueous suspensions of bentonite particles using magnetic resonance imaging (MRI) velocimetry. Four different chemical conditions are tested to investigate the influence of pH and type of monovalent electrolyte on the local rheological behavior of bentonite suspensions. The results indicate the shear banding in a dilute suspension of 0.1 vol.% solid due to the formation of a continuous three-dimensional particle network under a certain chemical environment (i.e., pH 4 in 1 × 10−2 M KNO3). This network is responsible for the existence of the yield stress in that dilute suspension. Structural changes induced by modification of suspensions’ chemistry are examined via scanning electron microscopy. A previously established method based on processing the torques acquired via conventional rheometric measurement is also applied as an alternative way to recover local flow information. Within the shear rate range covered by our MRI velocimetry, the results of both methods show good agreement. This study suggests that the existence of a master curve (or global flow curve) for dilute suspensions is dependent on the bentonite particle organization, which is influenced by the suspension chemistry and the previous flow history.
Highlights
Suspension rheology is a broad domain of soft matter science that studies flow properties of liquid-solid dispersions
In all cases given below, the dimensionless velocity represents the ratio of the applied velocity to the velocity measured through magnetic resonance imaging (MRI)
The card house concept was used to explain the differences among the local flow behaviors of dilute bentonite suspensions prepared under different solution chemistry
Summary
Suspension rheology is a broad domain of soft matter science that studies flow properties of liquid-solid dispersions. Clay suspensions gained a lot of interest in the domain of granular and colloidal suspensions due to their unique properties, such as high aspect ratio, spatial chemical inhomogeneity, ion exchange capacity and swelling [1]. For example bentonite, have found their broad applications in multiple industries, including pelletization [2], filtration and purification [3], medicine [4], hydraulic barriers and radioactive waste disposal [5]. Bentonite (or montmorillonite) suspensions are often handled in mineral beneficiation [6], drilling [7], and mineral waste disposal [8] processes. The distance between the SiO2 -Al2 O3 -SiO2 sheets is the order of 10 Å [9] and can accommodate some water molecules and exchange cations such as K+ , Na+ , Ca2+ , Mg2+ [10].
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