Why engineers want to control how nanotube forests grow

Forests of carbon nanotubes (CNTs) are held together by a adhesive force known as the van der Waals force. They're categorized based on their rigidity or how they are aligned. (Credit: iStockphoto)

Engineers grow carbon nanotube “forests” in high-temperature furnaces, but the forces involved are unpredictable and mostly left to chance.

A new study suggests there’s a way to predict how the structures, which are much smaller than the width of a human hair, form. Knowing this could make it possible to use them in a wide range of products—from baseball bats to body armor.

carbon nanotube forest
On the left, a scanning electron micrograph of a carbon nanotube forest. The figure on the right is a numerically simulated CNT forest. (Credit: Matt Maschmann)

Forests of carbon nanotubes (CNTs) are held together by an adhesive force known as the van der Waals force. They’re categorized based on their rigidity or how they are aligned.

For example, if CNTs are dense and well aligned, the material tends to be more rigid and can be useful for electrical and mechanical applications. If CNTs are disorganized, they tend to be softer and have entirely different sets of properties.

“Scientists are still learning how carbon nanotube arrays form,” says Matt Maschmann, assistant professor of mechanical and aerospace engineering at the University of Missouri. “As they grow in relatively dense populations, mechanical forces combine them into vertically oriented assemblies known as forests or arrays.

“The complex structures they form help dictate the properties the CNT forests possess. We’re working to identify the mechanisms behind how those forests form, how to control their formation, and thus dictate future uses for CNTs.”

Custom-made ‘forests’

Currently, most models that examine CNT forests analyze what happens when you compress them or test their thermal or conductivity properties after they’ve formed. However, these models do not take into account the process by which that particular forest was created and struggle to capture realistic CNT forest structure.

[related]

Experiments conducted in Maschmann’s lab will help scientists understand the process and ultimately help control it, allowing engineers to create nanotube forests with desired mechanical, thermal, and electrical properties. He uses modeling to map how nanotubes grow into particular types of forests before attempting to test their resulting properties.

“The advantage of this approach is that we can map how different synthesis parameters, such as temperature and catalyst particle size, influence how nanotubes form while simultaneously testing the resulting CNT forests for how they will behave in one comprehensive simulation,” Maschmann says.

“I am very encouraged that the model successfully predicts how they are formed and their mechanical behaviors. Knowing how nanotubes are organized and behave will help engineers better integrate CNTs in practical, everyday applications.”

The study will be published in the upcoming edition of the journal Carbon.

Source: University of Missouri