Rheological behavior of water-clay suspensions under large amplitude oscillatory shear

Mixtures of solid particles and Newtonian fluids such as water-clay suspensions are prepared for industrial usage and have many engineering applications. Different methods, setups, and protocols are available to characterize rheological behavior of these aqueous suspensions. In this study, large amplitude oscillatory shear (LAOS) protocols are considered as the main goal for the first time to examine non-linear rheological behavior of sepiolite suspensions. Four types of sepiolite clays and a commercial bentonite clay as reference were used to prepare fresh water-clay suspensions. Viscoelastic non-linearities of suspensions were studied as a function of strain and strain-rate using Lissajous-Bowditch curves and non-linear quantitative parameters. Discovery Hybrid Rheometer (DHR-II) was used in oscillation sweep tests for measuring non-linear properties. Impact of frequency on the evolution of LAOS properties was also investigated by constructing Pipkin diagrams. Bentonite suspension an had ability of keeping its elastic characteristics at higher strains compared to sepiolite clays indicating that bentonite clay yielded more flexible and structurally stable suspension. Sepiolite suspensions presented higher elastic stiffness (gel-strength) compared to bentonite suspension at all frequencies. Strong correlation in viscous non-linear parameters indicated viscous dominant behavior for all clay suspensions in the non-linear regions. It was also demonstrated that there is some tendency of shear-thickening behavior, particularly more notable for bentonite suspension under viscous deformation. It is postulated that the reason is hidden behind the structural differences of bentonite (platelets like) and sepiolite (fiber like) clays. Although both clays are members of smectite group, their structures and viscosity build mechanisms are quite different.