New type of silicone exhibits both viscous and elastic properties
By Ben Coxworth
March 4, 2013
Looking for a more effective solution to the all-too-common wobbly table dilemma than a folded up bit of cardboard or piece of rubber under the leg, University of Virginia physicist Lou Bloomfield created a new type of silicone rubber called Vistik – it's malleable enough to take on any shape when pressed, but is still resilient enough to offer support, as it gradually starts to return to its original shape as the pressure is released. The material could have many applications ... beyond just steadying up wobbly tables.
Vistik is a viscoelastic material, meaning that it exhibits both viscous and elastic properties. As a result, when compared to something such as conventional silicone rubber, there’s a considerable time lag in its response to continuous pressure.
“It seems elastic in response to sudden forces or impacts, denting in proportion to the sudden, brief stress and then returning almost instantly to its earlier shape when that stress is removed,” Prof. Bloomfield explained to us. “But if you push on it for a long time (most of a second or more), it relaxes. It adapts to its new shape and begins to like it (temporarily). When you release the stress after the Vistik has adapted, it's slow to go back to its earlier shape. In fact, if you try to pull it back suddenly to that earlier shape, it will fight.”
The material is chemically inert, tolerates a wide range of temperatures, plus its malleability and elasticity can be adjusted by tweaking its formulation. It can become soft enough to take on the texture of a user’s fingerprint ridges, while remaining sufficiently elastic to bounce like a rubber ball.
Among its various potential applications, Bloomfield thinks Vistik might be particularly well-suited to things like shoe insoles. “When you step on such an insole, it will custom-fit to your foot by adapting out of the way of the various bumps that press especially hard on the un-adapted insole,” he said. “That adapting process will be complete after a few seconds, and then the insole will be firm and supportive as you walk or run. The short timescales of walking and running don't allow the insole time to re-adapt, so it acts as though it were forever form-fitted to your foot. When you take off your shoe, however, the insole will gradually return to its original as-manufactured shape.”
Vistik might also find use as a means of creating a firm yet temporary custom fit on the user contact points of canes, crutches, prostheses, or even golf club handles. Additionally, because strips of the material cling to one another like Velcro (yet can also be easily pulled apart), it could be used as a resealable adhesive for packaging, or as an alternative to the ziplock feature on plastic bags.
“The stuff is just different, it's like nothing else,” said Bloomfield. “Companies now studying it for commercial use are finding that they can't really use conventional tests and tools ... most of the conventional measures of rubber and similar elastic materials are time-independent tests and they aren't suited to Vistik.”
Prof. Bloomfield demonstrates the material in the video below.
Source: University of Virginia