Non-Newtonian Liquids

The resistance of a Newtonian liquid to flow is characterized by its viscosity, μ, defined as the ratio of shear stress to shear rate. While water has a very small viscosity (8.90 × 10−4 Pa·s), honey by contrast has a viscosity that is approximately 10,000 times higher (10 Pa·s). No matter how fast water or honey flow, these viscosities remain the same.

Non-Newtonian liquids have viscosities that change with the shear rate. A prototypical example is a suspension of colloidal particles, which can be either shear-thinning or shear-thickening. In a seminal paper published in Nature, I showed that in the quintessential shear-thickening mixture of cornstarch and water, the impact response is mediated by a non-equilibrium phase transition from a liquid-like to solid-like state mediated by the impacting object. This occurs through a dynamic jamming front that shoots out in front of the object, leaving everything behind its wake solid-like and rapidly siphoning momentum in the process. Such exotic behavior can be useful if harnessed. In liquid body armor (e.g. for ballistics or sports) it is being incorporated as a way to protect a wearer while remaining flexible. During the Deepwater Horizon oil spill, it was suggested as a means by which the leak could be stopped.

In our new work, we are going to take non-Newtonian liquids one step further and develop techniques to achieve local control of the viscosity of the fluid. One avenue toward this would be to tune the density/arrangement of the suspended colloidal particles. A second avenue would be to use active particles, which produce energy to ‘swim’ through the fluid and thus locally affect the effective viscosity through energy injection. Though far off, we hope to be able to use these capacities to build devices such as a ‘fluid flow cloak,’ which would allow us to ‘hide’ objects in the sense that their influence on a flow around them is imperceptible.

Publications

Dynamic Jamming Fronts
Scott Waitukaitis, Leah Roth, Vincenzo Vitelli, and Heinrich Jaeger
Europhysics Letters 102, 44001 (2013).

Solidificación de una suspensión de maicena y agua 
Scott Waitukaitis and Heinrich Jaeger
Revista Cubana de Física 29, (2012).

Impact-activated solidification of dense suspensions via dynamic jamming fronts     
Scott Waitukaitis and Heinrich Jaeger
 Nature 487, 205-209 (2012).