Published in Chemistry World, 2 Sep 2011
Researchers in the US claim to have uncovered the single-particle dynamics that leads to so-called non-Newtonian behaviour, which is exhibited in tomato ketchup, paints and many other liquids. The results of the study, which used a combination of confocal microscopy and force measurements, could help in the development of industrial machinery.
For normal, Newtonian fluids, the viscosity stays the same no matter how much shear stress is applied – water is a common example. But non-Newtonian fluids get thinner or thicker with shear stress. Tomato ketchup, for instance, stays almost solid in the bottom of a plastic bottle until it is squeezed, at which point it squirts out easily: it is ‘shear thinning’. Meanwhile, a mixture of cornstarch and water turns from being fluid-like to near-solid when shear is applied: it is ‘shear thickening’. […]
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