Planes, Trains and Automobiles …and Nanotubes?

Nanotubes coated with special chemicals break down brittle epoxy into stretchable, durable strings that hold cracks together and keep them from expanding. Photo Credit: RPI

Vehicle and airplane manufacturers have increasingly turned to epoxy composites for building new models. These plastic polymers are lightweight and durable, so help to increase fuel efficiency, but are often brittle and crack easily, which could compromise a vehicle’s structural integrity. Carbon nanotubes infused into the composites help to slow cracking by stretching across a gap and bridging the two sides together. But researchers at Rensselear Polytechnic Institute discovered that coating the nanotubes with a chemical called an amidoamine (sometimes found in soaps, shampoos and cosmetics) has an entirely different effect on the epoxy that results in a 5-fold reduction in crack growth over epoxies with untreated nanotubes.

At the points where the nanotubes and epoxy touch, the molecules in the epoxy have more freedom to move around. Under stress, this new characteristic allows the epoxy to deform into a more fluid structure, forming a network of connective fibers roughly 10 microns (1/100th of a millimeter) long and 100 nanometers in diamter. They span the width of a crack and help prevent it from getting bigger.

“This behavior, and the bridging fibers it produces, dramatically slows the growth rate of a crack,” [lead researcher Nikhil Koratkar said in a press release.] “In order for the crack to grow, those fibers have to first stretch, deform plastically, and then break. It takes a lot of energy to stretch and break those fibers, energy that would have otherwise gone toward enlarging the crack.”

As more aircraft, watercraft, and automobile manufacturers are turning to epoxy composites to make their vehicles lighter, further research into the effects of treated nanotubes on these materials will eventually lead to potentially stronger and safer vehicles as well.