Researchers have developed a remarkably simple way to convert ordinary graphite particles into very thin but superstrong sheets that are tougher than steel and as flexible as carbon fiber but can be made much more cheaply. The discovery could spawn entirely new types of materials for applications as diverse as protective coatings, electronic components, batteries, and fuel cells.
For tensile strength and stiffness, carbon is king. So it's no surprise that scientists have been working for years to develop ways to add Element 12 to composite materials for aircraft fuselages, military vehicles, and even racing bicycles and tennis rackets. Even bigger payoffs are possible by constructing carbon materials at microscopic scales, yielding the strongest materials of all. Researchers have made some progress building structures called carbon nanotubes--whose single-layer atomic structure is tightly bound and therefore super rigid--but the tubes are expensive to manufacture and so far can only be used in tiny amounts.
Now, a research team from Northwestern University in Evanston, Illinois, has assembled particles of graphene oxide, a form of graphite and a cousin of diamonds, into very thin sheets that are even stronger than those made of the nanotubes. The process works like this: the team disperses graphene oxide particles in specially treated water and then draws the mixture through a filter membrane. The water somehow causes the particles to bind into a paperlike layer on the filter's surface, the researcher reports in tomorrow's Nature. "We actually don't know all of the details of how the layering takes place," says physical chemist and co-author Rod Ruoff. Laboratory tests showed that the grapheme paper was as strong as that made from carbon nanotubes, yet unlike nanotubes, the material can be fabricated to any size. That makes graphene paper a prime candidate for a new generation of superstrong composite materials, Ruoff says.
The super paper does have its kryptonite, however. The sheets remain stable when exposed to air, says Ruoff, but immersing them in water slowly loosens the bonds. Also, says materials scientist Boris Yakobson of Rice University in Houston, Texas, because water is so common as either liquid as rain or vapor as humidity, it will likely affect graphene sheets exposed to the environment in the long run if the material can't be protected from water's effects. So, the next task is to find other molecules that can replace water in the fabrication process. That research challenge and others probably puts commercialization of the technology at least 5 or 10 years away, Ruoff says.