Reinforcing polymers with carbon nanotubes; it's all on the surface.
Researchers who have successfully reinforced plastics with the addition of carbon nanotubes report the surprising discovery that the increased strength is not simply down to the strength of the nanotubes.
’We thought the stronger the material you throw into your polymer, the stronger the resulting composite, but we were wrong,’ said Martin Cadek, who worked on the project with Werner Blau’s group at Trinity College Dublin.
In fact, says Cadek, the degree of reinforcement depends on the interfacial shear strength between polymer and nanotube and especially on the surface area of the nanotube exposed to the polymer matrix 1. Think of it as a plate of noodles, he says. ’The smaller your noodle diameter in the same volume [the plate], the more sauce you need to wet them all.’ So it is with nanotubes; as their diameter decreases, the degree of interaction with the polymer matrix increases.
Cadek and colleagues made polymer-multiwall nanotube composite films using two types of polymer: either polyvinylalcohol or chlorinated polypropylene 2. They measured large increases in Young’s modulus (stiffness), which was increased by a factor of three; tensile strength, which was increased by a factor of four; and toughness, which was almost doubled. This was achieved at extremely low nanotube loading levels - about 1 per cent by weight. The reinforcement appears critically dependent on the interfacial polymer phase, they report.
Next, Cadek - who now works at German carbon and graphite production firm SGL Carbon Group in Bonn - plans to find out if this work can be extended to other polymers.
1. M Cadek et al, Nano Lett., 2004, 4, 353
2. M Cadek et al, Adv. Funct. Mater., 2004(in press)