by Ruth Beran
Chemists don’t usually drop balls from helicopters flying at 1200 feet, but Prof Lyall Hanton and his team from the University of Otago wanted to test a new material they have created by throwing it out the window.
The material they were testing is a gel, made mostly of water. The balls, which could fit in the palm of your hand, not only survived the fall from the helicopter intact they also bounced when they hit the ground.
It’s a sign of how tough these gels are.
"From what we know…this will be the strongest gel reported,” says Lyall.
The gel is also incredibly stretchy, stretching at least 40 times, and will still bounce back to its original size after being compressed 99%.
There are advantages to having a strong, tough, stretchy gel. For example, it could be used to release a drug in the body. Unlike ordinary jelly which would just break up and be moved around the body, you could put it under the skin and “it’s going to stay there, and you know it’s going to stay there,” says Lyall.
The gel consists of 85% water, plus a monomer and a crosslinker. In the gel, the monomers form polymers, and the crosslinker binds the ends of these extremely long polymer chains in a three dimensional network. The gels are cross-linked in such a way that the long, linked polymer chains can be stretched much more than short chains, resulting in the strong, stretchable gel.
When asked what the monomer consists of, John McAdam says:
“That’s a secret. We’re not going to tell you what the secret ingredients are.” Shailesh Goswami adds: “Because we want to publish this work in some good journal and the chemistry world is a very, very cruel world.”
An initiator and a promoter is also needed to initiate the reaction and promote the cross linking process, and by weight only 15% of the gel is made up of the chemical ingredients, the rest is water.
This makes for a very cheap product. The monomer is $1 per kilo and the crosslinker is around $2 to $3 per kilo.
The gel then needs to be cured, either slowly at room temperature or in the oven at 30˚C for two hours.
The team are already thinking of possible applications such as soft bandages, a high-tech shoe pad for running shoes or for use in a gel actuator. The material is easily mouldable.
Listen to a previous story on gel actuators here.
However, given that the gel is mostly water, long term applications would require the gel to be in an environment away from air. “In time, the gel will dry out so the applications we would use this for would need to be ideally in closed ones” says Lyall.