Two-dimensional x-ray scattering images of vertically oriented cylindrical nanoparticle stacks (left and right) in the polymer film, and a corresponding rendering of the particles. Image: Brookhaven National Laboratory |
Scientists working at NSLS are investigating a material that may
lead to greatly improved tires for cars and other vehicles. Their study is an
example of how incorporating nanoparticles into a regular substance can produce
a material with superior properties—in this case, increased durability and heat
resistance.
The research team, which includes scientists from Stony Brook
Univ. and Exxon Mobil,
focused on a material that could serve as the inner polymer lining of tires. At
NSLS, they used x-rays to investigate how incorporating nanoparticles of a
chemically modified clay material into a very thin layer of a polymer may
achieve tires that last longer than those currently on the market.
“By enhancing the properties of the polymer, there could be
significant improvements in tire performance and significant savings in
gasoline consumption, perhaps up to 30%,” said Stony Brook scientist Ben Hsiao,
who led the study.
In particular, the researchers wanted to find out how adding the
nanoparticles would affect the polymer film’s gas permeability—that is, how
well (or poorly, in this case) molecules can pass through it. Gas permeability
is one way to gauge how a material will hold up over time.
They learned that the combination of the particles’ shapes and
the varied ways they orient within the film create a “tortuous pathway” for
permeating molecules, causing them to zigzag through the film. As a result they
have to travel a longer distance over a longer period of time to cross it.
The group introduced different concentrations of clay
nanoparticles into several polymer film samples and studied each sample using
both x-ray scattering at NSLS beamline X27C and electron microscope imaging. In
combination, these techniques allowed them to see, in detail, how the particles
are distributed in the films.
They discovered that the particles take on two shapes,
cylindrical stacks and platelets, and position themselves in two ways. Some
particles settle horizontally within the polymer film, forming layers within
it, and others are oriented perpendicularly to the film.
Further, the group found that how the particles become
incorporated into the film is dependent on how the film is processed. When the
films are created using a process called melt pressing, the particles tend to
be cylindrical and orient themselves parallel to the layers of the film. This
effect was more pronounced when the researchers increased the density of
particles, which, they propose, seems to be because the particles do not have
the space to orient themselves in other ways.
The x-ray analysis also showed that the particles were evenly
distributed in the film. They did not tend to clump, even as the fraction of
particles by total weight was greatly increased.
