Chalk up more remarkable skills for carbon nanotubes.

Researchers at MIT have discovered that carbon nanotubes can convert heat into electricity with surprisingly efficient results. The amount of power released in the experiments greatly exceeded the mathematical predictions.

Potentially, the discovery could lead to autonomous sensors the size of a grain of rice, smaller bodily implants or batteries that can pack more than 100 times power than today's lithium ion batteries, according to Michael Strano, MIT's Charles and Hilda Roddey Associate Professor of Chemical Engineering, one of the principal authors. The devices could also possibly generate either direct or alternating current.

The nanotube-powered car is likely years away, but the results add to the interesting collection of physical properties of these molecules that one day could transform quite a number of industries. Nanotubes are hollow tubes of carbon that are stronger than steel, can conduct electricity better than metals, and are flexible.

A key characteristic is their impossibly small diameter: they measure only five or so billionths of a meter wide. It's such a small space that electrons traveling down nanotubes are conducted ballistically. The electrons are never scattered or lost, a property that makes nanotubes zero-dimensional objects. Densely packed nanotubes could also lead to ultracapacitors capable of storing far more power than today's capacitors. (Blowing gases onto the outside surface of nanotubes can also generate current.)

The MIT researchers coated the nanotubes with a fuel and then ignited it. The heat penetrated to the inside of the nanotube and began to travel 10,000 times faster than the normal spread of the reaction. The traveling thermal wave in turn pushed electrons along the tube, creating a current.

Meanwhile, elsewhere on campus, another group of researchers has discovered a way to transform polyethylene, a common plastic, into an effective conductor of heat. If it can be brought to market, the plastic could be used to produce heat sinks for solar panels or computer chips. Additionally, you could see this material being exploited to draw heat to thermoelectric chips, which turn heat into electricity.

The plastic conducts heat as well as metal, but has several distinct advantages over metal. For one thing, the plastic could be produced in such a way as to conduct heat in a specific direction, whereas metals radiate heat in all directions. The plastic also serves as an electrical insulator.

The core of the discovery revolves around getting the polymer fibers to line up in an orderly direction by drawing them out of solution with the tip from an atomic force microscope, according to Gang Chen, the Carl Richard Soderberg Professor of Power Engineering and director of MIT's Pappalardo Micro and Nano Engineering Laboratories. (Side note: these microscopes are incredible. IBM let me move a few atoms with one once. Click link for pictures.)

Typically, polymer fibers get tangled like hairs in a hairball. Aligned, the polymer conducted heat 300 times better than regular plastic. Carbon nanotubes could also be added to the mix to improve conductivity.  

Last year, MIT researchers demonstrated how carbon nanotubes could boost the efficiency of fuel cells with carbon nanotubes.

Tags: batteries, carbon nanotubes, electrons, insulation, metals, mit, nanotubes, research, thermoelectrics, ultracapacitors, waste heat