'Jammed Networks' may clear the way for better nanomaterials

December 2, 2005
Video sequences reveal how different additives affect the behavior of a plastic material (PMMA) when heated under fire-like cond

Jammed networks may cause upheaval in phone systems, but among wispy carbon nanotubes or nanofibers, a similar phenomenon may greatly improve flammability resistance and, perhaps, other properties in polymers, report researchers from the National Institute of Standards and Technology and the University of Pennsylvania.

Image: Video sequences reveal how different additives affect the behavior of a plastic material (PMMA) when heated under fire-like conditions. Top two rows show behavior during heating, and the bottom shows the final residue. Unmodified PMMA (left) behaves like a liquid, bubbling vigorously and leaving almost no residue. Adding a tiny dash (0.5 wt percent) of single-walled carbon nanotubes (center) nearly eliminated bubbling; the residue was slightly thinner than the original sample, and it had a smooth undulating surface. Numerous small “islands” formed during heating of the material with multi-walled carbon nanotubes (MWNTs) and vigorous bubbling was observed among islands. With continued heating, islands eventually coagulated, forming large islands separated by deep cracks. Image credit: NIST

Results achieved with two types of carbon nanotubes (single- and multi-walled) and with carbon nanofibers could help to eliminate trial-and-error in designing and producing nanocomposite materials with flame-retarding and other desired properties optimized for applications in areas ranging from packaging and electronics to construction and aerospace. The work appears in the December issue of Nature Materials.

Nanoparticle fillers--especially clays--have been shown to reduce the flammability of plastics and other polymers. Previous work on these nanoclay flame retardants, says NIST fire researcher Takashi Kashiwagi, indicates that the additives are most effective when they migrate to form a continuous surface layer, creating a "heat shield" on top of the more flammable polymer matrix. The shield, he explains, suppresses the "vigorous bubbling" that can occur as the matrix breaks down.

However, if the plate-like nanoclay particles cluster into islands, heat escapes through cracks between them, compromising their performance as flame retardants.

To get around this problem, Kashiwagi and colleagues chose to investigate carbon nanotubes and nanofibers, which tend to be narrower and longer than nanoclays. These structures also have been shown to enhance strength, electrical conductivity and other material properties. The researchers reasoned that the extended, sinuous geometry of the tiny tubes and fibers might lend itself to forming a "continuous, network-structured protective layer" that is free of cracks.

When the researchers heated polymethyl methacrylate (PMMA)--a clear plastic--dispersed with carbon nanotubes or nanofibers, the material behaved like a gel. In a process dictated by their type, concentration and other factors, the nano additives dispersed throughout the PMMA matrix and eventually achieved a "mechanically stable network structure." The researchers say the "jammed networks" formed as the nanocomposites underwent a change in identity, a transition from liquid to solid. The shift occurred at an optimal composition that the team called the "gel concentration."

For single-walled carbon nanotubes--sheets of carbon atoms rolled into cylinders--top fire retardant performance was achieved when the fillers made up only 0.5 percent of the total mass of the material. For multi-walled carbon nanotubes, which are nested sets of carbon cylinders, the gel concentration was 1 percent. Both types of nanotubes have the potential to surpass nanoclays as effective fire retardants, says NIST materials scientist Jack Douglas.

Results suggest that the gel concentration also may mark the point at which other nanotube-enabled improvements in material properties are maximized, Douglas adds.

Publication: T. Kashiwagi, F. Du, J.F. Douglas, K.I. Winey, R.H. Harris Jr., and J.R. Shields. Nanoparticle networks reduce the flammability of polymer nanocomposites. Nature Materials, December 2005, 928-933.

Source: NIST

Explore further: Why a new transparent conducting material is sorely needed for touch screens

Related Stories

Designing ice repellent materials

November 4, 2015

Materials that actively repel water and ice very strongly are sought after by the aviation industry and for many other technical applications. ETH researchers have now found out how to specifically design the rigid surfaces ...

Making green fuels, no fossils required

November 2, 2015

Using solar or wind power to produce carbon-based fuels, which are commonly called fossil fuels, might seem like a self-defeating approach to making a greener world. But when the starting material is carbon dioxide, which ...

Researchers design and patent graphene biosensors

November 13, 2015

The Moscow Institute of Physics and Technology (MIPT) is patenting biosensor chips based on graphene, graphene oxide and carbon nanotubes that will improve the analysis of biochemical reactions and accelerate the development ...

'Harmful' effects paradoxically enhance solar cell efficiency

November 12, 2015

(Phys.org)—Dissipation and decoherence are typically considered harmful to solar cell efficiency, but in a new paper scientists have shown that these effects paradoxically make the exciton lifetime in semiconducting carbon ...

Recommended for you

'Material universe' yields surprising new particle

November 25, 2015

An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act ...

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

New gene map reveals cancer's Achilles heel

November 25, 2015

Scientists have mapped out the genes that keep our cells alive, creating a long-awaited foothold for understanding how our genome works and which genes are crucial in disease like cancer.

A blue, neptune-size exoplanet around a red dwarf star

November 25, 2015

A team of astronomers have used the LCOGT network to detect light scattered by tiny particles (called Rayleigh scattering), through the atmosphere of a Neptune-size transiting exoplanet. This suggests a blue sky on this world ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.