EVANSTON, ILL. (March 12, 12:15 p.m. ET) — Northwestern University scientists have turned to compressed polymers and the “free radical” chemical species they generate in a search for new energy sources.
Megan Fellman, the Evanston-based university's science and engineering editor, reports that the team found “incredible” promise but also grounds for caution.
The researchers led by Professor Bartosz Grzybowski demonstrated that radicals (charged atomic or molecular species containing unpaired electrons) from compressed polymers generate significant amounts of energy that can be used to power chemical reactions in water. Grzybowski notes that this energy has typically gone unused, but could be harnessed when polymers are under mechanical stress in ordinary circumstances – as in shoe soles, car tires or when compacting plastic bags.
The mesh of molecular chains in a polymer breaks down slowly over time due to the stress of ordinary wear and tear. When a polymer is squeezed, the pressure breaks chemical bonds and produces free radicals which are highly energetic. Radicals are responsible for normal human ageing, but also for DNA damage and cancer in the body.
The team discovered that a silicone polymer commonly used in implants for cosmetic procedures releases a large quantity of potentially harmful free radicals when the polymer is under only a moderate amount of pressure. The researchers suggest that the safety of certain polymer-based medical implants should be looked at more closely.
Grzybowski says: “We have established that polymers under stress create free radicals with overall thermodynamic efficiencies of up to 30 percent – approaching the energy efficiency of a car engine – and shoot the radicals out into the surrounding medium where they can drive chemical reactions. The radicals can be useful or they can be harmful, depending on the situation.”
The research team is the first to use this energy to drive chemical reactions merely by surrounding the compressed polymer with water containing suitable chemical reagents. The radicals created in the polymer migrate toward the polymer/water interface where they produce hydrogen peroxide, which then can drive chemical processes.
“You can get a surprisingly large amount of chemical energy from a polymer under compression,” says Grzybowski. “This energy is, in a sense, free for the taking. It is seldom retrieved from the deformed polymers, which then age unproductively. But you could recharge a battery from the energy produced by walking or driving a car. And you could capture even more energy when compacting millions of plastic bags.”
To illustrate the process, the team converted a Nike Air LeBron training shoe into a “lightning shoe,” where the air pockets in the polymeric sole are filled with a solution of a compound that lights up in the presence of radicals. After a person walked in the shoe for 30 minutes or more, enough radicals were created to generate a blue glow visible to the naked eye.
“One direction we are pursuing is to use this energy to sanitize water in developing countries. This is possible because hydrogen peroxide produced by squeezed polymers kills bacteria.”
The work is reported in a paper in the peer-reviewed journal Angewandte Chemie.