Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Squeezing flow viscometry for nonelastic semiliquid foods--theory and applications.

Abstract: In most conventional rheometers, notably the coaxial cylinders and capillary viscometers, the food specimen is pressed into a narrow gap and its structure is altered by uncontrolled shear. Also, most semiliquid foods exhibit slip, and consequently the measurements do not always reflect their true rheological properties. A feasible solution to these two problems is squeezing flow viscometry where the specimen, practically intact and with or without suspended particles, is squeezed between parallel plates. The outward flow pattern mainly depends on the friction between the fluid and plates or its absence ("lubricated squeezing flow"). Among the possible test geometries, the one of constant area and changing volume is the most practical for foods. The test can be performed at a constant displacement rate using common Universal Testing Machines or under constant loads (creep array). The tests output is in the form of a force-height, force-time, or height-time relationship, from which several rheological parameters can be derived. With the current state of the art, the method can only be applied at small displacement rates. Despite the method's crudeness, its results are remarkably reproducible and sensitive to textural differences among semiliquid food products. The flow patterns observed in foods do not always follow the predictions of rheological models originally developed for polymer melts because of the foods' unique microstructures. The implications of these discrepancies and the role that artifacts may play are evaluated in light of theoretical and practical considerations. The use of squeezing flow viscometry to quantify rheological changes that occur during a product's handling and to determine whether they are perceived sensorily is suggested.

Rheological Properties of Disperse Systems of Spherical Particles in Polystyrene Solution at Long Time‐Scales

Abstract: The dynamic and steady flow properties of disperse systems of styrene–divinylbenzene copolymer particles in a polystyrene solution have been measured over wide ranges of frequency, shear rate, and strain amplitude by means of a cone‐and‐plate type rheometer. The main results may be summarized as follows. 1) These systems show Newtonian behavior at extremely low rates of shear, that is, the apparent viscosity is approximately constant. This fact indicates that the systems have no yield stress, although they appear to show one if only the behavior at high shear rates is considered. 2) They show linear viscoelastic behavior at strain amplitudes less than 0.5%, but striking nonlinearities at larger strains. However, at very long time‐scales, these systems are linearly viscoelastic and independent of the strain amplitude. 3) The nonlinear viscoelastic functions G1′ and G1″ decrease with increasing strain amplitude, but they are almost independent of strain for strains larger than 50%, over the entire frequency...

S-shaped flow curves of shear thickening suspensions: Direct observation of frictional rheology

Abstract: We study the rheological behavior of concentrated granular suspensions of simple spherical particles. Under controlled stress, the system exhibits an S-shaped flow curve (stress vs shear rate) with a negative slope in between the low-viscosity Newtonian regime and the shear thickened regime. Under controlled shear rate, a discontinuous transition between the two states is observed. Stress visualization experiments with a fluorescent probe suggest that friction is at the origin of shear thickening. Stress visualization shows that the stress in the system remains homogeneous (no shear banding) if a stress is imposed that is intermediate between the high- and low-stress branches. The S-shaped shear thickening is then due to the discontinuous formation of a frictional force network between particles upon increasing the stress.