LAS VEGAS —You know how in recipes, more doesn't mean better when it comes to an ingredient or a spice? The same thing goes for nanocomposites, according to Ica Manas-Zloczower, professor of advanced materials and energy at Case Western Reserve University.
More carbon nanotubes do not mean a better nanocompsite, she said in an April 28 keynote speech at Antec 2014 in Las Vegas. The key to success: finding the optimum recipe for nano-additives and proper mixing.
Manas-Zloczower gave a brief history of nanotechnology. “Nanocomposites have been present in nature for a very, very long time,” she said. Sponges are made of nano-materials. Seashells are good examples of stacked platelets. Egyptians used nanotechnology for inks used to decorate urns and bowls—it changes color from green to a brilliant red, depending on the lighting.
And clay as a nanofiller? Pottery has been around for centuries!
“So nanotechnology is not new. The question is, how do we apply nanotechnology to make composite materials with extraordinary properties?” Manas-Zloczower asked.
Nano-fillers can be carbon black, nano-rods, clay and graphene. Carbon nanotubes, she said, “have exceptional properties in terms of their mechanical properties, electrical properties and thermal properties.” They are used in a wide range of products, including wind turbines, adhesives and electronics.
“So if carbon nanotubes are such good fillers, why not use more?” she asked. The challenge is mixing them in so they disperse into the plastic composite. Too much and they clump up. “The hurdle is now to go from conglomerates of nanotubes to dispersed tubes, which have better properties,” she said.
Manas-Zloczower described research at CWRU in Cleveland. Adding a certain amount of carbon nanotubes into thermoplastic polyurethane — the sweet spot is 0.32 percent by weight — is ideal for dispersing the tubes into the polymer matrix. But adding extra tubes only contributed to more agglomerates, which ends up reducing the good properties that the tubes provide, such as tensile strength.
“It's like adding more detergent. It will not get clothes any cleaner,” Manas-Zloczower said.
The same principle applies to mixing, both in the type and duration of the process. “It's not always that mixing it more is better,” she said. Too much time spent mixing a sample by sonication (the use of sound energy), risks breaking of the tubes and changing their structure.
She also discussed surfactants, agents used to disperse the nanotubes, keeping them from agglomerating. She said which surfactants to use, and in what quantities, depends on the properties you want, so there are no easy answers.
The CWRU researchers also studied combining carbon nanotubes with graphene nano-platelets, to give good electrical and mechanical properties. And this “hybrid filler” method can work well, Manas-Zloczower said. The best ratio is a 4:1 tubes to graphene, to get the ideal dispersion.
Manas-Zloczower also is associate dean of faculty development CWRU. She is in the university's macromolecular science and engineering department.