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Smashed fluids, broken eggs and a TV gameshow…???

13 October 2015 No Comment

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Last week, I was reviewing some content that my rheology colleagues had published on the Malvern website relating to the axial capabilities of our Kinexus rheometer. This was of interest since it complimented some published work I was sent by one of our Kinexus users, as well as a new BBC gameshow I happened to come across. I’ll explain a bit more!

In a recent blog, entitled “Kinexus, more than just a rheometer!” my colleague John Duffy talked about the advanced features of our Kinexus rheometers such as the ability to make measurements with non-standard measuring systems and capabilities which allow the simultaneous application of axial and shear deformations to simulate processes such as food mastication. Just last week Chuck Rohn continued this theme with an introductory webinar showing “How to make squeeze flow measurements on a rotational rheometer” and advantages of this approach over standard rotational testing for difficult samples such as pastes.

Coincidentally, in that same week I read an article from one of our users about how the axial capabilities of our Kinexus could also be used to help explain a unique feature of non-Newtonian fluids – shear thickening behaviour. The published article was from of one of our academic Kinexus users (Dr Mike Smith [i], School of Physics & Astronomy, University of Nottingham) and was entitled “Fracture of Jammed Colloidal Suspensions”.

Image taken from Smith, M.I. Fracture of Jammed Colloidal Suspensions. Sci. Rep. 5, 14175; doi: 10.1038/srep14175 (2015)

In this work Kinexus was used to apply an axial deformation to a concentrated colloidal suspension while measuring the resultant normal force in order to probe the process of granulation in these systems. A non-standard test for a rotational rheometer, but certainly achievable with the axial capabilities of the Kinexus and its flexible and programmable rSpace software. The results supported the idea that frictional contacts are created between jammed particles when shear thickening occurs and that there are two jamming regimes which contribute to the phenomenon. Furthermore, an external “vibration” device coupled to the rheometer could be used to control the extent of jamming and re-fluidise an induced solid structure. This is shown on the chart above – bottom image with vibration applied and the top image without.

So what’s this got to do with a BBC gameshow??

Well, when flicking through the BBC iPlayer one night I chanced upon a BBC program called “Six Degrees of Separation” [ii] presented by Professor Brian Cox. Not typically a program I would blog about, however, this certainly caught my attention as it talked about “viscosity” and “non-Newtonian” behaviour. As a rheologist, anything that raises the profile of “rheology” to a wider audience is certainly good by me! In fact, part of the remit for developing Kinexus was to help make rheology and rheometry more accessible with an SOP type approach to rheological testing, while at the same time providing enhanced instrument capabilities and programmable software for more advanced users like Dr Mike Smith.

In the program, the world famous “Pitch Drop Experiment” [iii] was discussed, talking about how apparent solids can flow like a liquid and how liquids, such as custard (i.e. a corn starch suspension), can behave like solids. The latter was demonstrated by dropping two eggs from a great height, one encased in a balloon full of custard and the other in a water balloon. The contestants had to predict which egg would break and they got it wrong by suggesting the water would provide greatest protection when in fact the custard did. Not a surprise to a rheologist!

The reason it did is that custard is a concentrated colloidal suspension which jams and shear thickens when rapidly deformed, as explained in Dr Smith’s paper. If only the contestants had read this paper first they may have got the answer right.  A slightly frustrating aspect of the program was that the word rheology wasn’t mentioned once, even though it is the branch of science that deals with the flow and deformation of non-Newtonian fluids and is so abundant and important in everyday life. Even Microsoft are still to recognise the importance of rheology, with spell-checked rheological texts likely to contain a reference to theology without careful checking as discussed in a previous blog “Rheology and Theology make a biblical connection” by Steve Carrington. So, all-in-all a good week for rheology and nice to see non-Newtonian fluids providing some light entertainment – but there is still work to be done!