While Evangelos Manias, a professor of materials science and engineering at Pennsylvania State University, says that the new material is impressive, he cautions that the process limits the ways the material can be used. If it is heated too much while being incorporated into a product, the clay particles might clump together, causing the enhanced properties to be lost.
Manias says that even more significant than the new material is the process used to make it. It’s been difficult to uniformly disperse nanoparticles such as the clays throughout polymers because they have incompatible chemical properties: the clay attracts water, while the polymers repel it. The problem is made more challenging in this case because the clay nanoparticles must connect only with the hard segments of the polyurethane and not with the soft, stretchy polymer mesh. Otherwise the material will lose its stretchiness.
To make it possible to locate the clay nanoparticles at just the right places, McKinley and his colleagues at MIT developed a system that uses two solvents, one to disperse the clay nanoparticles and the other to dissolve the polymer. These two solvents are then mixed until the suspended nanoparticles are spread evenly throughout the dissolved polymer. The solvent that dissolved the polymer is then evaporated, leaving behind a tangle of polymer that traps the clay particles. Because this method does not chemically alter the nanoparticles, as has been done in other approaches, the particles retain a chemical affinity to the rigid structures within the polyurethane, which causes them to connect to these and not to the soft parts of the structure.
Manias says that this process could apply to a wide variety of systems, using different nanoparticles, such as nanotubes, to make even more remarkable materials. “The most important thing is that this can be applied more broadly than just polyurethane,” he says. “There are whole fields of science where this can be applied.”