Mechanical Properties of Nanostructured Materials
Nanotubes are at least 10 times stronger than the strongest steels but only 20% as dense. While they have the potential to replace carbon fibers as fillers in advanced composites, results have been less exciting than expected. In order to act as efficient reinforcing agents, two conditions must be fulfilled: the nanotubes must be well dispersed and it must be possible to transfer stress from polymer to nanotubes. It is possible to address both these issues simultaneously by covalently attaching functional groups to the nanotubes. These act to disperse the nanotubes and by entangling with the polymer matrix enhance stress transfer. A large focus of our work is to use functionalized nanotubes, both commercial and home made, to improve the mechanical properties of a range of plastics at very low nanotube content (see papers 50,51,66,67,70).
Figure 6 Stress-strain curves for various volume fractions of MWNT in a polyvinyl matrix showing significant reinforcement. (see paper 51)
Figure 7 SEM image of a fracture surface of an MWNT-polymer composite showing nanotube pullout. (see paper 51)
In addition we employ a number of novel methods to produce reinforced composites. These range from fiber spinning (both coagulation and electro-spinning), infiltration of polymer into porous structures and vacuum filtration(see papers 38 and 59). In the case of both coagulation spinning and electrospinning we have made fibers as strong steel. Recently, in collaboration with the University of Texas we were able to demonstrate a method to coagulation spin composite fibers tougher than any other material known to man(see paper 41).