Scientists manipulate carbon nanotube growth

A team of scientists from the Massachusetts Institute of Technology (MIT) has created a new technique for manufacturing microstructured surfaces that possess three-dimensional textures, according to new research published in the journal Nature Communications.

The microstructured surfaces, made via the self-assembly of carbon nanotubes, could exhibit properties such as controllable mechanical stiffness and strength, or water repelling characteristics, the researchers suggest.

“It’s a new principle of using mechanics to control the growth of a nanostructured material

Senior research author John Hart

Senior research author John Hart said: “We have demonstrated that mechanical forces can be used to direct nanostructures to form complex three-dimensional microstructures, and that we can independently control … the mechanical properties of the microstructures.”

The technique developed by Hart and his team works by inducing carbon nanotubes to bend as they are grown - via the influence of chemical reaction.

To initiate the process, two patterns are printed onto a substrate. The first material is a catalyst of carbon nanotubes. The second material modifies the growth rate of the nanotubes.

By offsetting the two patterns, the nanotubes bend into predictable shapes as they extend, the researchers said.

“We can specify these simple two-dimensional instructions, and cause the nanotubes to form complex shapes in three dimensions,” said Hart.

“Where nanotubes growing at different rates are adjacent, they push and pull on each other, producing more complex forms. It’s a new principle of using mechanics to control the growth of a nanostructured material,” he said.

Aside from using the technique to create large expanses of the three-dimensional structures simultaneously, Hart claims it can also be used to manipulate other properties, such as electrical and thermal conductivity and chemical reactivity, by attaching various coatings to the carbon nanotubes after they grow.

“If you coat the structures after the growth process, you can exquisitely modify their properties,” Hart said.

“For example, coating the nanotubes with ceramic, using a method called atomic layer deposition, allows the mechanical properties of the structures to be controlled. When a thick coating is deposited, we have a surface with exceptional stiffness, strength, and toughness relative to [its] density,” he said.

“When a thin coating is deposited, the structures are very flexible and resilient.”

According to Hart, the microstructured surfaces have the durability of carbon nanotubes, which could allow them to survive in harsh environments, and could be connected to electronics and function as sensors of mechanical or chemical signals.