Viscosity Of Hard Sphere Suspensions Research Articles

Shear viscosity of hard sphere suspensions

Shear viscosity of hard sphere suspensions

Analytically predicting the viscosity of hard sphere suspensions from the particle size distribution

Suspension rheology is of widespread importance to industry and research. Hard spheres represent a benchmark by which to compare other particle suspensions, and there are a variety of analytical and numerical models available to describe their rheology. However, it is experimentally challenging to produce ideal hard spheres, where surface forces are negligible between particles, and where phase volume is precisely defined. Beyond the dilute regime, the model by Maron and Pierce [1] and Quemada [2], which we refer to as the MPQ model, is commonly used analytically to describe the relative viscosity of hard sphere suspensions as a function of phase volume and a maximum packing fraction (ϕm). We show that obtaining ϕm from empirical fits can lead to misinterpretation of experimental data. We reveal that reasonable prediction of the viscosity is obtained using the MPQ model when ϕm is set to the geometric random close packing fraction ϕrcp, which is independently defined from the particle size distribution using the packing model of Farr and Groot [3]. This ‘theoretical’ approach is tested using a wide variety of experimental data on colloidal and non-colloidal hard spheres without need for any fitting parameters or empiricisms. In addition, plotting the inverse of the square-root of viscosity as a function of phase volume, which linearises the MPQ model, provides a convenient means by which to clearly see where suspensions deviate from the model due to such effects as particle aggregation, particle softness and measurement errors. We also demonstrate the necessity of this approach by accurately predicting the viscosity of microgel suspensions up to ϕrcp; empirical fits across the full data set are erroneous because particle deformation and viscoelasticity lead to values of ϕ>ϕrcp. This approach provides a suitable unambiguous theoretical baseline for comparison to experimental studies on suspension rheology involving polydisperse size distributions.

Phenomenological Approach of the Effective Viscosity of Hard Sphere Suspensions in Shear-Thinning Media

Abstract In this work we investigate the rheological behaviour of macroscopic buoyant hard spheres dispersed in a shear-thinning suspending fluid. We focus on the phenomenological study of the influence of the shear-thinning behaviour of the suspending medium on the effective apparent suspension viscosity at different volume fractions. In the oil industry, the effective viscosity concept is widely used and very useful to quickly characterize a change of viscosity due to an increase of the solid content. Viscosity measurements are compared to the effective viscosity of a suspension of hard spheres in an Ostwald fluid. The power law index of the suspending fluid is shown, both experimentally and theoretically, to influence strongly the volume fraction dependence of the suspension effective viscosity. All experimental results are shown to be quite correctly plotted on a master curve, with only one adjustable parameter, the maximum packing fraction fm. The best fit is obtained for fm = 0.57, corresponding to the theoretical maximum random packing volume fraction.

Viscosity of Hard-Sphere Suspensions: Can We Go Lower?

To date, approaches seeking a definitive link between colloidal suspension microstructure and the corresponding viscosity predict that for dense suspensions, hard-sphere systems possess the lowest-...

Viscosity of Hard Sphere Suspensions

A simple functional representation of the concentration dependence of the low-shear viscosity η of hard sphere suspensions is proposed. The representation, which agrees with published literature at all volume fractions φ, has a hitherto-unremarked transition in its functional form at φ≈0.42≡φt. φt is definitely less than the volume fraction 0.49 of the hard sphere melting transition.

On the Viscosity of Concentrated Aggregated Suspensions

The Tsenoglou approach (J. Rheol.34,15 (1990)) to calculating the viscosity of concentratedaggregatedsuspensions has been shown to be flawed owing to a confusion between compact and fractal aggregates. The difference between these two regimes of particle aggregation has been clarified and appropriate formulas describing the viscosity of such suspensions have been derived. In addition, a generalized equation for describing the viscosity of hard sphere suspensions is also proposed.