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# 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 cases 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.

**Shear thinning-2005 (v2) (.pdf)**

**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.

**Extreme rheology 2009 (.pdf)**

**Stretching Rheology and Symmetry to the limits!**

**Stretching Rheology and Symmetry to the limits!**

Covid-19 resulted in a 2020 Institute for Non Newtonian Fluid Mechanics (INNFM) Port Merrion (Wales) meeting to be cancelled and so below I include the contribution that I would have given. The talk is a story that links my connections with * Wales* and highlights two areas of research one carried out in the

*and the other, forty years later in the*

**1970s***There are notes for each slide*

**2010s**.

**Port-merrion-2020-with-notes-2.pdf**

**The rheology of swallowing!**

**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.

**Dysphagia 2009 (v2) (.pdf)**

**Papers relevant to General Rheology**

- M.R.Mackley.
*Capillary rheometry. Chapter 1 in “The Physical Principles of Rheological*Measurement”. Ed. A.A. Collyer and D.W. Clegg, Elsevier. (1988) - V.Kamath and M.R. Mackley.
*The determination of polymer relaxation moduli and memory functions using integral transforms*Journal of Non-Newtonian Fluid Mechanics. 32, 119-144 (1989). - M.R.Mackley, R.T.J.Marshall, J.B.A.F.Smeulders and F.D.Zhao. The rheological characterization of polymeric and colloidal fluids. Chem Eng Sci. 49,16, 2551-2565 (1994).
- R. Liang and M.R. Mackley. Rheological characterisation of the time and strain dependence of polyisbutylene melts. Journal of Non-Newtonian Fluid Mech. 52, 387-405 (1994).
- L.Gervat., M.R.Mackley,T.M.Nicholson and A.H.Windle. The effect of shear on thermotropic liquid crystalline polymers. Phil Trans Roy Soc ( Lond).350, 1- 27 (1995).
- M.R.Mackley, R.T.J.Marshall and J.B.A.F. Smeulders. The multipass rheometer. Journal of Rheology. 39(6), 1293- 1309 (1995).
- M. H.Chisholm, M.R.Mackley, R.T.J.Marshall, and E.F.Putilina.
*A rheological study of the mesomorphic state of dimolybdenum and dicopper octanoates.*Chemistry of Materials. 7,10. 1938-1941 (1995). - J.M. Madiedo, C. Bower, M.R. Mackley and C. Gallegos.
*Reologia de Emulsiones estabilizadas por Biopolimeros*

Grasas Aceites. 48, (1997). - W K Wee & M.R.Mackley The rheology and processing of a concentrated Cellulose Acetate solution Chem Eng Sci. 53, 6. 1131-1144 (1998).
- C. Bower, M.R.Mackley, B.A.S.Smeulders, D.Barker and J.Hayes.
*The rheology, processing and microstructure of complex fluids.*In Modern aspects of Colloid Dispersions. - Ed R.H.Ottewill & A.R.Rennie. Kluwer pub 279-289 (1998).
- R.M de Roeck & M.R.Mackley.
*The rheology and microstructure of equine blood.*Dynamics of Complex Fluids. ed M.J.Adams, - R.A.Mashelkhar, J.R.A.Pearson &A.R.Rennie. Imperial College Press. 339-345 (1998).
- M.R.Mackley and R Rutgers.
*Capillary Rheometry.*Rheological Measurement, Ed 2, By A.A.Colyer and D.W.Clegg. Chapman Hall 167 – 188 (1999). - M Ranganthan, M.R.Mackley and P.H.J.Spittler. Experimental observations and modelling of time dependent capillary flow for a high density polyethylene using a multipass rheometer J Rheology ,43(2) 443-451 (1999).
- C. Bower, C Gallegos, M.R.Mackley & J.M.Madiedo The rheological and microstructural characterisation of the non linear flow behaviour of concentrated oil-in-water emulsions Rheol Acta 38 145-159 (1999).
- M.J. Thompson, M.R.Mackley and J.A.Nimmo.
*The high shear rheology of lithographic emulsions.*Surface Coatings International. Vol 83, 5 234-239 (2000) - K Lee and M.R.Mackley The application of the Multi-Pass rheometer for precise rheo-optic characterisation of polyethylene melts Chemical Engineering Science 56, 5653-5661 (2001)
- T.R. Tuladhar & M.R. Mackley Experimental observations and modelling relating to foaming and bubble growth from pentane loaded polystyrene melts. Chemical Engineering Science Vol 59/24 ,5997-6014 (2004)