Rheology
[1] The term rheology was coined by Eugene C. Bingham, a professor at Lafayette College, in 1920 from a suggestion by a colleague, Markus Reiner.
[1][6][7][8] Rheology unites the seemingly unrelated fields of plasticity and non-Newtonian fluid dynamics by recognizing that materials undergoing these types of deformation are unable to support a stress (particularly a shear stress, since it is easier to analyze shear deformation) in static equilibrium.
In this sense, a solid undergoing plastic deformation is a fluid, although no viscosity coefficient is associated with this flow.
However, since rheology is concerned with fluids which do not have a fixed viscosity, but one which can vary with flow and time, calculation of the Reynolds number can be complicated.
Rheology has applications in materials science, engineering, geophysics, physiology, human biology and pharmaceutics.
Materials science is utilized in the production of many industrially important substances, such as cement, paint, and chocolate, which have complex flow characteristics.
Examples may be given to illustrate the potential applications of these principles to practical problems in the processing[11] and use of rubbers, plastics, and fibers.
The silicone toy 'Silly Putty' behaves quite differently depending on the time rate of applying a force.
Pull on it slowly and it exhibits continuous flow, similar to that evidenced in a highly viscous liquid.
The Space Shuttle Challenger disaster was caused by rubber O-rings that were being used well below their glass transition temperature on an unusually cold Florida morning, and thus could not flex adequately to form proper seals between sections of the two solid-fuel rocket boosters.
This disciplinary branch also deals with solid Earth materials which only exhibit flow over extended time-scales.
Long-term creep experiments (~10 years) indicate that the viscosity of granite and glass under ambient conditions are on the order of 1020 poises.
[12][13] Physiology includes the study of many bodily fluids that have complex structure and composition, and thus exhibit a wide range of viscoelastic flow characteristics.
[15] There are two current major hypotheses to explain blood flow predictions and shear thinning responses.
The two models also attempt to demonstrate the drive for reversible red blood cell aggregation, although the mechanism is still being debated.
[15] The bridging or "cross-bridging" hypothesis suggests that macromolecules physically crosslink adjacent red blood cells into rouleaux structures.
The surfaces of the red blood cells are bound together by an osmotic pressure gradient that is created by depletion layers overlapping.
[16] Changes to viscosity has been shown to be linked with diseases like hyperviscosity, hypertension, sickle cell anemia, and diabetes.
[21] An adequate rheology is important for the indulgence of many common foods, particularly in the case of sauces,[22] dressings,[23] yogurt,[24] or fondue.
They dissolve in the liquid phase as a colloid mixture that forms a weakly cohesive internal structure.
To avoid these undesired effects, superplasticizers are typically added to decrease the apparent yield stress and the viscosity of the fresh paste.
[28] The incorporation of various types of fillers into polymers is a common means of reducing cost and to impart certain desirable mechanical, thermal, electrical and magnetic properties to the resulting material.
[29] Usually when the use of fillers is considered, a compromise has to be made between the improved mechanical properties in the solid state on one side and the increased difficulty in melt processing, the problem of achieving uniform dispersion of the filler in the polymer matrix and the economics of the process due to the added step of compounding on the other.
The type and amount of surface treatment on the filler are thus additional parameters affecting the rheological and material properties of filled polymeric systems.
[30] A rheologist is an interdisciplinary scientist or engineer who studies the flow of complex liquids or the deformation of soft solids.
