An account is given of the development of the idea of a yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time. Originally, it was accepted that the yield stress of a solid was essentially the point at which, when the applied stress was increased, the deforming solid first began to show liquid-like behaviour, i.e. continual deformation. In the same way, the yield stress of a structured liquid was originally seen as the point at which, when decreasing the applied stress, solid-like behaviour was first noticed, i.e. no continual deformation. However as time went on, and experimental capabilities increased, it became clear, first for solids and lately for soft solids and structured liquids, that although there is usually a small range of stress over which the mechanical properties change dramatically (an apparent yield stress), these materials nevertheless show slow but continual steady deformation when stressed for a long time below this level, having shown an initial linear elastic response to the applied stress. At the lowest stresses, this creep behaviour for solids, soft solids and structured liquids can be described by a Newtonian-plateau viscosity. As the stress is increased the flow behaviour usually changes into a power-law dependence of steady-state shear rate on shear stress. For structured liquids and soft solids, this behaviour generally gives way to Newtonian behaviour at the highest stresses. For structured liquids this transition from very high (creep) viscosity (>106 Pa.s) to mobile liquid (

The yield stress—a review or ‘παντα ρει’—everything flows?

The use of rotating vane geometries for the measurement of the flow properties of very non-Newtonian liquids has become increasingly popular over the last 20 years. Originally, these geometries were used to measure the apparent yield stresses of inorganic dispersions, but have more recently been used to measure other rheological parameters also. These include the low-strain modulus and the steady-state flow-curves of structured liquids. The particular advantages of the vane geometry are its simplicity of fabrication, ease of cleaning and more than anything else, its elimination of serious wall-slip effects. The development of the vane technique and the theory to go with it, together with its use in various areas are described, where these areas include inorganic colloidal dispersions, foods, bioengineering fermentation broths, etc.

Rotating vane rheometry — a review

Rheological behavior and suspension structure of anatase titanium dioxide (TiO2) nanoparticles dispersed in pure water have been investigated over a range of volumetric solids concentrations (φ=0.05–0.12) and shear rates (γ=101–103 s−1). The nanoparticle suspensions generally exhibited a pseudoplastic flow behavior, indicating an existence of particle aggregations in the liquid medium. The suspensions became apparently thixotropic as φ was increased above 0.1. Relative viscosity (ηr) of the suspensions followed an exponential form with φ, i.e., ηr=13.47e35.98φ, revealing a pronounced increase in the degree of particle interactions as φ increased. Fractal dimension (Df) was estimated from the suspension yield-stress (τy) and φ dependence, and was determined as Df∼1.46–1.78 for the flocculated nanoparticle suspensions. This suggested that the suspension structure was probably dominated by the diffusion-limited cluster–cluster aggregation, due mostly to the strong attractions involved in the interparticle potentials. Maximum solids loading (φm) of the suspensions was determined as φm=0.146. This relatively low value of φm (compared with the random close packing of monosized particles, φm∼0.64) partially vindicated the existence of a porous, three-dimensional aggregate network of interconnected nanoparticles in the carrier liquid.

Rheology and colloidal structure of aqueous TiO2 nanoparticle suspensions

Optimal determination of rheological parameters for Herschel-Bulkley drilling fluids and impact on pressure drop, velocity profiles and penetration rates during drilling

F.L.G. Hsu

Papers

Characterization, Settling, and Rheology of Concentrated Fine Particulate Mineral Slurries

Estimation of the critical velocity in pipeline flow of slurries