The exotic behaviour of non-Newtonian fluids
Solutions to big problems often come from small devices. This may look a bit surprising at first, but it is the mantra in the current research and technological landscape. For example, a significant part of our food, healthcare and manufacturing industries nowadays relies on fluids which are rather different from the ones we are familiar with. In fact, most of the fluids used in everyday life such as water are “purely viscous”, i.e. they instantaneously react to the rate of any shear forcing we apply to them.
However, if you try to squeeze ketchup from its bottle, you soon realize that its response depends on the history of forcing; once it starts coming out of the bottle squeezing it out even more becomes easier. Ketchup is a typical example of so-called “non-Newtonian fluid”, which may exhibit surprising behaviours and, even, respond as an elastic object instead of fluid under particular conditions. Inks for additive manufacturing (3D-printing), biological fluids (saliva, blood, etc) and fluids used in food processing are often non-Newtonian as well.
Being able to fully characterize, model and understand their behaviour is therefore of paramount importance nowadays, as it will allow us to optimize manufacturing processes, enhance the quality and safety of our food, and improve therapeutics while minimizing side-effects. However, we are still lacking the ability of characterizing non-Newtonian fluids reliably.
Linking the microscopic world to the macroscopic picture
The reason for such lack of reliable sensors is the interplay between interactions at the molecular level and the macroscopic response we can observe with our naked eyes. In fact, non-Newtonian fluids are often solutions composed of a purely viscous fluid and polymers or other molecules. The unusual macroscopic response of non-Newtonian fluids is a result of interactions happening at the microscale between the fluid and the molecules present in the solution. Therefore, any technique to characterize their behaviour must necessarily link the microscopic view with the macroscopic response, clearly a daunting task for any sensing technology. To make things worse, fluids of interest (e.g. saliva & blood) are often available in very small quantities.
Non-Newtonian fluids: a key opportunity for the UK?
The UK is at the forefront of research on such exotic fluids, with major initiatives aimed at developing descriptive models and experimental techniques to better understand non-Newtonian behaviours and to better exploit the potential of such materials. At the University of Liverpool, we have a substantial activity devoted to such task, and we are very grateful of the support EPSRC are providing us to pursue this research.
I am currently exploring the potential of using oscillating microstructures to characterise the response of both Newtonian and non-Newtonian fluids, as they operate at the perfect length and time scales, which are intermediate between the solute molecules and the bulk fluid. They represent a really promising technology whose full potential is yet to be discovered. Unlocking such potential will have a major impact on the UK economy, by enabling more efficient manufacturing processes, safer food handling and processing, and targeted therapeutics.