The nanotechnology team from the University of Texas at Dallas, USA, and Brazilian collaborators have discovered that carbon nanotube films can produce bizarre mechanical properties when stretched or uniformly compressed. These unexpected but very useful properties can be used to make composites, artificial muscles, gaskets, or sensors. The research was published in the April 25 issue of the American Journal of Science.
When most materials are pulled in one direction, they will be thinner in the other direction, which is similar to how rubber bands are stretched. However, this specially designed carbon nanotube, known as "buckypaper", can increase in width when stretched, and can increase both in length and width in uniform compression.
Common materials shrink laterally when stretched. This phenomenon can be quantified by Poisson's ratio. Poisson's ratio refers to the expansion rate or shrinkage rate of a material when it is extruded or stretched. It is also called the transverse denaturation coefficient. For two thousand years, people have been using Poisson's ratio in the form of cork stoppers. Cork stoppers with near zero but positive Poisson's ratio are harder to insert but can be easily removed and vice versa.
By using an ancient method of manufacturing plain writing paper—drying fiber slurries—the researchers at the Institute of Nanotechnology at the University of Texas at Dallas produced nanotube films (bucky paper). This slurry is a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes. The researchers found that increasing the number of multi-walled carbon nanotubes in a base paper can dramatically change the Poisson's ratio from about 0.06 to about negative 0.20.
The researchers said that this change can be understood by comparing the deformation of carbon nanotubes with collapsible wine racks. If two adjacent carbon nanotubes are connected to form a pillar in a compressed wine frame, the Poisson's ratio is positive, and the stent will be narrowed when stretched; on the contrary, if the stent is locked so that it no longer collapses However, the pillars are extensible, and the increase in the length of the pillars produces a negative Poisson's ratio.
The researchers found that carbon nanotube films containing single-walled carbon nanotubes and multi-walled carbon nanotubes have strength-to-weight ratios and elastic moduli compared to single-walled carbon nanotubes or multi-walled carbon nanotubes. The weight-to-weight ratio and stiffness were increased by 1.6 times, 1.4 times, and 2.4 times, respectively.
This finding implies that the enhanced properties of the nanotubes by mixing different types of carbon nanotubes may also extend to nanotube membranes and other nanotube arrays, such as the nanoparticle tube crepe that researchers invented in 2005. Similarly, this Poisson's ratio adjustment capability can also be used to design nanotube-based membrane composites, artificial muscles, gaskets, stress and strain sensors, and chemical sensors.
When most materials are pulled in one direction, they will be thinner in the other direction, which is similar to how rubber bands are stretched. However, this specially designed carbon nanotube, known as "buckypaper", can increase in width when stretched, and can increase both in length and width in uniform compression.
Common materials shrink laterally when stretched. This phenomenon can be quantified by Poisson's ratio. Poisson's ratio refers to the expansion rate or shrinkage rate of a material when it is extruded or stretched. It is also called the transverse denaturation coefficient. For two thousand years, people have been using Poisson's ratio in the form of cork stoppers. Cork stoppers with near zero but positive Poisson's ratio are harder to insert but can be easily removed and vice versa.
By using an ancient method of manufacturing plain writing paper—drying fiber slurries—the researchers at the Institute of Nanotechnology at the University of Texas at Dallas produced nanotube films (bucky paper). This slurry is a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes. The researchers found that increasing the number of multi-walled carbon nanotubes in a base paper can dramatically change the Poisson's ratio from about 0.06 to about negative 0.20.
The researchers said that this change can be understood by comparing the deformation of carbon nanotubes with collapsible wine racks. If two adjacent carbon nanotubes are connected to form a pillar in a compressed wine frame, the Poisson's ratio is positive, and the stent will be narrowed when stretched; on the contrary, if the stent is locked so that it no longer collapses However, the pillars are extensible, and the increase in the length of the pillars produces a negative Poisson's ratio.
The researchers found that carbon nanotube films containing single-walled carbon nanotubes and multi-walled carbon nanotubes have strength-to-weight ratios and elastic moduli compared to single-walled carbon nanotubes or multi-walled carbon nanotubes. The weight-to-weight ratio and stiffness were increased by 1.6 times, 1.4 times, and 2.4 times, respectively.
This finding implies that the enhanced properties of the nanotubes by mixing different types of carbon nanotubes may also extend to nanotube membranes and other nanotube arrays, such as the nanoparticle tube crepe that researchers invented in 2005. Similarly, this Poisson's ratio adjustment capability can also be used to design nanotube-based membrane composites, artificial muscles, gaskets, stress and strain sensors, and chemical sensors.