"It is a bit like trying to move through a street crowded with an enormous number of people. If you move slowly enough you can make progress and the crowd and you 'flow'. However, if you try and sprint down the street you will just knock into so many people that you'll never be able to move at the speed you want to and hence everything becomes grid locked."
The research was able to show that whilst many features of this kind of system were independent of the geometry of the flow examined, some effects due to the exposed fluid surface were much more important than had previously been thought. In particular an effect known as 'dilatancy' in which some of the particles poke through the surface of the liquid was found to play a crucial role in the jamming of the particles.
Dr Smith added: "The most incredible results were observed when the fluid was stretched at a velocity just below that required to form a jammed fluid. The fluid was found to form a thin filament which narrowed until it was about hundred particles in diameter. At this point the fluid was observed to recoil elastically, like a rubber band!
"This is particularly fascinating since the particles are specifically designed to behave like hard spheres with no attractive forces. Where does the elasticity come from? The liquid drains from the filament faster than the particles causing them to poke through the surface as before. The liquid surface forms a meniscus around the particles. It is this curved surface of the fluid which the researchers believe stores the energy and results in the unusual behaviour.
"We hope this research provides an important initial step in understanding how the physics in common industrial flows may differ from the carefully controlled set up found in conventional academic studies"
Hit it hard and it will fracture like a solid, but tilt it slowly and it will flow like a fluid. This is the intriguing property of a type of "complex fluid" which has revealed "new physics" in research by scientists at the University of Nottingham.
(Photo Credit: The University of Nottingham)
Hit it hard and it will fracture like a solid, but tilt it slowly and it will flow like a fluid. This is the intriguing property of a type of "complex fluid" which has revealed "new physics" in research by scientists at the University of Nottingham.
(Photo Credit: The University of Nottingham)
Source: University of Nottingham