General rheology

This section is a bit of a mixed bag! Rheology is everywhere with many subsets twists and turns.  Below are three presentations that concentrate on different  areas of rheology.

Shear Thinning is a very common feature of complex fluids where  the general trend for a wide range of fluids is rather similar; however the reason for the shear thinning can be very fluid specific. The presentation below puts the topic into perspective and it also introduces an initially surprising result that the apparent viscosity of a suspension can, in some casees fall below that of the matrix fluid.

The second presentation is about Extreme Rheology where one the one hand, linear viscoelastic measurements are made on very low viscosity fluids at very high frequency in order to detect short relaxation time viscoelastic behaviour. Whilst at the other end of the spectrum, extensional flow data is obtained for very high viscosity polymer melts.

Finally a presentation on “The Rheology of Swallowing” is given where the rheology of so called dysphagia fluids are presented, together with  a laboratory “human throat”!

Shear thinning

A very common feature of Non Newtonian Fluids is the characteristic of shear thinning, where the apparent viscosity of a fluid decreases with increasing shear rate. There can be a number of reasons for this shear thinning characteristic and the presentation below, given in 2005 at Sophia Antipolis (France) describes some mechanisms for three different case studies.

Extreme Rheology!

Exploring the boundaries of rheology can be fun and exciting! The presentation below describes some of the Cambridge Polymer Fluids Group work in measuring the viscoelasticity of low viscosity fluids and also the limiting extensional viscosity of very high viscosity, viscoelastic  fluids. Unfortunately not all of the graphs and photographs have come through in the presentation.

The rheology of swallowing!

The action of food and liquid swallowing is very complex! Some people have difficulty swallowing and sometimes this can be helped by using thickened fluids. The medical condition is known as dysphagia and there are specially formulated thickened drinks that usually contain starch marketed to assist overcoming liquid swallowing difficulties. It is believed that thickened fluids take longer to pass through the throat and give throat muscles more time to respond to the passage of the fluid in the throat. The presentation below shows experimental results on the rheology of certain dysphagia formulations and also describes a mechanical “Cambridge Throat” that was designed to mimic elements of the swallowing process.

Papers relevant to General Rheology