Dynamic and Steady Shear Properties of Reversibly Cross-Linked Guar Solutions and Their Effects on Particle Settling Behavior

Abstract

Rheological properties of guar of molecular weight MW = 2.2×106 reversibly cross‐linked with borate ion at different cross‐linker concentrations were investigated using small amplitude oscillatory sweep (SAOS) and steady shear at 25 °C and atmospheric pressure. Polymer concentration was fixed at 0.003 g/ml above the overlap concentration (C* = 5×10−4 g/ml). Four borate ion concentrations of 31, 62, 93 and 125 ppm were used. A transparent Couette cell was used to study the settling behavior of particles under simple shear. Dynamic settling (i.e. under shear) results reveal that both shear thinning and elasticity of the suspending fluid affect settling rate. For a lightly cross‐linked sample, settling rate increases with increasing imposed shear rate; the settling rate decreases for a highly cross‐linked sample. Full‐field images of the Couette during settling show the development of a non‐homogeneous particulate structure during sedimentation in a highly cross‐linked sample. Extended particulate structures form in the direction of gravity for the zero‐imposed shear experiment (static settling), and in the shearing direction for the dynamic settling experiment.