D3O: A REMARKABLE NON-NEWTONIAN FLUID
Soft, flexible foam that turns hard when subjected to force ideal for protective gear
It wasn’t hard to get the subjects’ permission for the experiment. That’s because they were dead. Scientists at the British company D3O (pronounced D -three-oh) wrapped the fingers of cadavers in their flagship product, a bright orange putty, and proceed to bang away with a hammer. The grisly experiment was designed to determine the force the bones in the finger could withstand without breaking. The intent was to have the dead help the living.
Oil rig workers often suffer injuries to the hand and as a consequence, there is a constant search for better protective gloves. The ones commonly used are bulky and lack flexibility. Enter “D3O,” the remarkable “intelligent material” that is soft and flexible until it is acted upon by a force. Then in a fraction of a second, it turns hard, offering protection to whatever it surrounds, only to return to its original flexible state once the force dissipates. Prototype gloves injected with D3O, based on the cadaver experiments, have received enthusiastic support from workers.
Let’s rewind to 1999, when British engineers Richard Palmer and Phil Green, both active snowboarders, bemoaned the uncomfortable bulkiness of the protective equipment available at the time. Palmer had worked for DuPont, where he had developed experience applying polymer chemistry to consumer products and thought he could come up with an improved material for protective pads. He joined forces with Green at the University of Hertfordshire, and the two hit pay dirt with “polyborodimethylsiloxane,” a substance that falls into the category of “non-Newtonian fluids.”
Mention laws of motion or gravity and the name of Isaac Newton immediately pops into mind. But the interests of the man regarded as one of the most influential scientists of all time went beyond formulating mathematical laws on paper. Newton was also interested in the behaviour of fluids, mostly because of his curiosity about alchemy. Fluids are substances that can be made to flow and that take on the shape of their container. That flow can be fast or slow, depending on the fluid’s thickness, or “viscosity.”
Water flows easily, oil with greater difficulty, and bitumen, the substance left when petroleum is refined, flows hardly at all. The flow of bitumen is actually the subject of what is said to be the world’s longest-running science experiment. In 1927 professor Thomas Parnell at the University of Queensland in Australia placed a sample of bitumen in a funnel with the aim of demonstrating to students that some substances may appear to be solid but in fact are high viscosity fluids. It would take a long time for the point to be made. A drop falls roughly once a decade!
Newton’s fluid experiments were not quite as dramatic, if one can call waiting for a drop to fall every 10 years dramatic. His contribution was the demonstration that viscosity was a function of temperature. An oil, for example, flows much more readily when it is heated. We experience this phenomenon while trying to start a car on a very cold day. Motor oil is a “Newtonian fluid” that at the low temperature is too viscous to circulate.
In contrast to Newtonian, the viscosity of “non-Newtonian” fluids is affected by factors other than temperature. Mechanical pressure, shaking, stirring or squeezing can alter the viscosity. A classic example is the slurry made by adding water to cornstarch. When handled, it feels like a liquid, but when quickly punched, the viscosity is suddenly increased to the extent that there is no splatter. This phenomenon is referred to as “shear thickening.” There have been impressive demonstrations of this phenomenon with people filling pools with the cornstarch mixture and running across the surface. The impact of the foot hardens the non-Newtonian fluid to the extent that it can support the weight of the body. Of course one must run quickly because as soon as the pressure is released, the fluid reverts to its less viscous phase.
Some non-Newtonian fluids instead of “shear thickening,” exhibit “shear thinning ” behaviour. In this case, pressure leads to reduced viscosity. A classic example is ketchup. Shaking the bottle, or giving it a whack on the bottom, exerts enough force to allow for easier pouring and random squirting.
Polyborodimethylsiloxane is a great example of a “shear thickening ” fluid, but for useful applications, it had to be converted into a material that instead of flowing would retain a desired shape.
Palmer and Green found a way to disperse the substance through a polyurethane foam matrix and came up with “D3O,” named after the lab where it was invented. Palmer knew he had made a potentially great discovery, but had no money to develop it commercially. In a bold move that eventually paid off, he sold his house and auctioned off his belongings to raise funds. Today, D3O is incorporated into cellphone cases and protective equipment for skiers, skaters, motorcyclists and the elderly who are prone to falling. In sports helmets it holds promise for reducing concussions. Newton would be amazed by this marvellous non-Newtonian fluid.