“The new technique begins with a CNT array,” Zhu says, “which looks like a forest of CNTs growing up out of a flat substrate.” Because the aspect ratio of these CNTs is high, they are long and skinny – not rigid. That means the CNTs are leaning against each other in the array. “By grabbing the CNTs at one end of the array, we are able to pull them over onto their sides – and all of the other CNTs in the array topple in the same direction,” Zhu says. This results in CNTs with good alignment.
These aligned CNTs are then wound onto a rotating spool and sprayed with a polymer solution to bind the CNTs together. This creates a ribbon-like composite material that has a high percentage of CNTs by volume, which can in turn be used to make CNT composite structures for use in finished products like airplanes and bicycles. But that doesn’t address the need to straighten the CNTs.
To straighten the CNTs, Zhu and his team stretched the CNTs as the nanotubes are being pulled onto the rotating spool. This process improves the tensile strength of the CNT composite “ribbon” by approximately 90 percent (to an average of 3.5 gigapascals) and stiffness by more than 100 percent. By straightening the CNTs, the researchers were also able to almost triple the CNT composite’s thermal conductivity, to 40 watts per meter per kelvin. Electrical conductivity was increased by 50 percent to 1,230 siemens per meter.
NC State News :: NC State News and Information » New Techniques Stretch Carbon Nanotubes, Make Stronger Composites
Remember what the vice president quitly said at the signing of the health care bill, "This is a big f'in deal". Well, that's what this is for materials.